acceptance of stay cable - institution of structural engineers · time to review and improve these...

Acceptance of stay cable systems using

prestressing steels

Recommendation prepared by

Task Group 9.2

January 2005

Subject to priorities defined by the Steering Committee and the Presidium, the results of fib’s work in Commissions and Task Groups are published in a continuously numbered series of technical publications called 'Bulletins'. The following categories are used:

category minimum approval procedure required prior to publication Technical Report approved by a Task Group and the Chairpersons of the Commission State-of-Art Report approved by a Commission Manual or Guide (to good practice)

approved by the Steering Committee of fib or its Publication Board

Recommendation approved by the Council of fib Model Code approved by the General Assembly of fib

Any publication not having met the above requirements will be clearly identified as preliminary draft. This Bulletin N° 30 was approved as an fib recommendation in April 2004 by the fib Council.

This report was drafted by fib Task Group 9.2, Stay cable systems:

Dieter Jungwirth (Convenor) György L. Balázs (Budapest University of Technology and Economics, Hungary), Pierre Boitel (Freyssinet International, France), Yves Bournand (VSL Technical Centre Europe, France), Pietro Brenni (BBL Systems Ltd., Switzerland), Alain Chabert (Laboratoire Central des Ponts et Chaussées, France), Gordon Clark (Gifford and Partners Ltd., United Kingdom), André Demonté (Trefileurope Fontainunion, Belgium), Hans Rudolf Ganz (VSL International, Switzerland), Christian Gläser (Technical University München, Germany), Philippe Jacquet (Bouygues Travaux Publics, France), Jean-Francois Klein (Tremblet SA, Switzerland), Jacob Koster (Ballast Neerdam, The Netherlands), Benoit Lecinq (SETRA, France), Manfred Miehlbradt (EPF Lausanne, Switzerland), Theodore L. Neff (Post Tensioning Institute, USA), Toshihiko Niki (Sumitomo Electric Industries, Japan), Oswald Nützel (DSI Int. GmbH, Germany), Amar Rahman (BBR Systems, Switzerland), Reiner Saul (Leonhardt, Andrä und Partner, Germany), S. Sengupta (Span Consultants Pvt. Ltd., India), Khaled Shawwaf (DSI, USA), J.H.A. Van Beurden (Nedri-Spanstaal B.V., The Netherlands), Yash Paul Virmani (Federal Highway Administration, USA) Full address details of Task Group members may be found in the fib Directory or through the online services on fib's website, www.fib-international.org . Cover pictures: Sunshine Skyway Bridge (Florida, USA), Olympic Tent (Munich, Germany), Rosario-Victoria Bridge (Argentina), Millau Bridge (France), Ibi Bridge (Japan), Yiling Yangtze River Bridge (People’s Republic of China) © fédération internationale du béton (fib), 2005 Although the International Federation for Structural Concrete fib - féderation internationale du béton - created from CEB and FIP, does its best to ensure that any information given is accurate, no liability or responsibility of any kind (including liability for negligence) is accepted in this respect by the organisation, its members, servants or agents. All rights reserved. No part of this publication may be reproduced, modified, translated, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission. First published in 2005 by the International Federation for Structural Concrete (fib) Post address: Case Postale 88, CH-1015 Lausanne, Switzerland Street address: Federal Institute of Technology Lausanne - EPFL, Section Génie Civil Tel. +41 21 693 2747; Fax +41 21 693 6245; [email protected]; www.fib-international.org ISSN 1562-3610 ISBN 2-88394-070-3 Printed by Sprint-Digital-Druck Stuttgart

fib Bulletin 30: Acceptance of stay cable systems using prestressing steels iii

Foreword Cable-stayed structures have become increasingly popular over the last 10 to 20 years. Many long span stay cable bridges have been built for highway traffic with spans up to and now even beyond 1000 m main span. A significant number of cable-stayed railway bridges has also been constructed. More recently many very elegant pedestrian cable-stayed structures have been built and have become landmark structures. But also cable-supported roofs and other building structures have found increasing interest.

Surprisingly, there have been only a very limited number of specifications for the stay cable systems which form a key element of these structures. The best known are the recommendations published by the Post-Tensioning Institute in the USA, and more recently, the recommendations published by the French Highway Administration, SETRA.

These recommendations are the first specifications published by fib for stay cable systems. They introduce a significant number of new developments and specifications which have not been available in previous documents:

Corrosion protection philosophy with a multi-barrier approach for the prestressing

steel used for the stay cables and a rational design approach for structural steel components. A leak tightness test is also specified to verify the connection details between the free length and the anchorage zone of the stay cable

Design and testing of stay cables for the inevitable flexural effects which occur close to the anchorages and other deviation points of the stay cables. These recommendations specify testing that covers flexural effects up to a certain degree. Designers will not need to consider these flexural effects anymore in the design for stay cable systems tested in accordance with these recommendations

Selected information on stay cable vibrations and special damping devices to control such vibrations

Suitable details for lightning protection of cable-stayed structures Design considerations and testing procedures for stay cable saddles which are

increasingly popular for cable-stayed structures with very slender pylons State-of-the-art specifications for the main materials and components for stay cable

systems including quality control procedures Specific requirements for the common installation methods of stay cables are provided

including the strand by strand installation and stressing methods A comprehensive list of references, relevant standards, and extended literature.

I express my sincere thanks to Professor Jungwirth, the convenor of Task Group TG 9.2, and the members of TG 9.2. Professor Jungwirth has taken up the work with great initiative and has been able to motivate the Task Group members to produce a comprehensive and most valuable document, which will become a standard reference for stay cable systems specifications. I also express my thanks to the several experts who have dedicated significant time to review and improve these recommendations, in particular Michel Virlogeux and David Goodyear. I also extend my thanks to Gordon Clark for his editing of the report for English grammar. Hans Rudolf GANZ Chairman of Commission 9 Reinforcing and Prestressing Materials and Systems

Copyright fib, all rights reserved. This PDF copy of fib Bulletin 30 is intended for use and/or distribution only by National Member Groups of fib.

fib Bulletin 30: Acceptance of stay cable systems using prestressing steels iv

Contents Introduction 1

1 Scope 1

2 Definitions and symbols 2.1 Definitions 2 2.2 Symbols 4

3 Design and detailing 3.1 General 5

(3.1.1 Redundancy of cable-stayed structures – 3.1.2 Fire, impact, vandalism – 3.1.3 Replaceability of stay cables – 3.1.4 Transverse loads applied from stay cables to the structure – 3.1.5 Bending stresses in stay cables

3.2 Design / sizing of stay cables 8 (3.2.1 Service conditions (SLS) – 3.2.2 Fatigue limit state (FLS) – 3.2.3 Ultimate limit state (ULS) – 3.2.4 Earthquakes – 3.2.5 Construction and cable replacement

3.3 Detailing and lightning protection 12 (3.3.1 Detailing – 3.3.2 Lightning protection)

3.4 Saddles 17 (3.4.1 General – 3.4.2 Transfer of differential stay cable forces – 3.4.3 Minimum radius of curvature of saddle pipe)

3.5 Execution aspects 18 (3.5.1 Stage-by-stage analysis – 3.5.2 Length adjustment capability of stay cables – 3.5.3 Construction tolerances)

3.6 Cable vibrations 19 (3.6.1 General – 3.6.2 Special damping devices – 3.6.3 Cross ties)

3.7 Inspection and maintenance 21

4 Functional requirements for stay cables 4.1 Evolution of stay cable technology 22 4.2 General requirements 22

(4.2.1 General – 4.2.2 Durability design, corrosion protection)

4.3 Requirements for the free length 24 (4.3.1 Corrosion protection philosophy for tensile elements – 4.3.2 Protection philosophy for other materials – 4.3.3 Reference system for corrosion protection – 4.3.4 Equivalent systems for corrosion protection – 4.3.5 Systems with lower corrosion protection – 4.3.6 Additional requirements)

4.4 Requirements for the transition zones 28 (4.4.1 Corrosion protection – 4.4.2 Stay pipe dilation – 4.4.3 Guide deviators – 4.4.4 Damping of stay cables – 4.4.5 Anti-vandalism pipes)

4.5 Requirements for anchorages 32 (4.5.1 Types of stay cable anchorages – 4.5.2 Corrosion protection philosophy for mild steel anchorage components – 4.5.3 Additional requirements)

4.6 Requirements for saddles 35 (4.6.1 General – 4.6.2 Corrosion protection – 4.6.3 Saddle performance)


fib Bulletin 30: Acceptance of stay cable systems using prestressing steels v

5 Materials: properties, requirements, testing 5.1 General 36 5.2 High tensile steel for tensile elements (prestressing steel) 37

(5.2.1 General – 5.2.2 Hot dipped metallically coated prestressing steel)

5.3 Structural steel for anchorages, saddles, guide deviators and pipes 39 5.4 Stainless steel 39 5.5 Sheathing for prestressing strands 39 5.6 Filling materials 41

(5.6.1 Soft filling materials – 5.6.2 Hardening filling materials)

5.7 Stay pipes and other pipes 43 (5.7.1 General – 5.7.2 Thermoplastic stay pipes – 5.7.3 Steel stay pipes – 5.7.4 Other pipes)

5.8 Guide deviators 46 5.9 Damping devices 46

6 Testing of stay cable systems 6.1 General 46 6.2 Initial approval testing (qualification testing) 46

(6.2.1 Anchorage fatigue and tensile testing – 6.2.2 Saddle fatigue and tensile testing – 6.2.3 Leak tightness testing)

6.3 Suitability testing 55 6.4 Quality control testing 56

7 Installation 7.1 General 58

(7.1.1 Quality management system – 7.1.2 Qualification of personnel – 7.1.3 Execution documents)

7.2 Shipment and storage of components 59 7.3 Assembly and installation 59 7.4 Stressing and adjustment 61 7.5 Corrosion protection 63

8 Inspection and monitoring 8.1 General 64 8.2 Initial inspection 64 8.3 Routine inspection 64 8.4 Detailed inspection 65 8.5 Exceptional inspection 66 8.6 Monitoring 66

9 Maintenance, repair, replacement and strengthening 66

10 References and literature 10.1 References 67 10.2 Standards 68 10.3 Extended literature 71


fib Bulletin 30: Acceptance of stay cable systems using prestressing steels 1

Introduction Cable-stayed bridges are structurally optimised systems employing light stiffening beams, continuously supported by the stays, for large span cantilevers with an efficient transfer of forces to the pylons. Spans of up to 500 m with concrete decks and up to 1000 m with steel stiffening beams (either composite or pure steel decks) are economically practicable. The most important elements in these aesthetic structures are the stay cables. More than 20 years ago stay cables consisted of spiral strands and fully locked cables, as originally used in steel construction. Today special quality tensile elements similar to those used in prestressed concrete construction are setting new standards in these fields of application. Stay cables can be manufactured with prestressing steels within HDPE pipes or steel pipes with fillers for corrosion protection or with individually protected strands, which are either prefabricated or fabricated on site. Modular concept of the systems allows design using very large stays, the largest today with up to 205 strands (ultimate strength of 54 MN) per cable. While most of these stay cables are used for bridge construction, similar cables are also widely used in extradosed structures and building construction. Over the past years some national Stay Cable Recommendations have been issued, e.g. by PTI (USA), [1], and SETRA/CIP (France), [2]. Also a European specification is in preparation, see [S1]. These recommendations and specifications typically cover locally available materials and construction practices. These fib recommendations have been formulated by an international working group comprising more than 20 experts from administrative authorities, universities, laboratories, owners, structural designers, suppliers of prestressing steels and stay cable suppliers. This text has been written to cover best construction practices around the world, and to provide material specifications which are considered to be the most advanced available at the time of preparing this text. For ease of use (for client, designer and cable supplier), the complex content has been arranged thematically according to the system components into chapters focusing on performance characteristics, requirements and acceptance criteria. References are provided with a separate section on standards. An extensive list of literature on the subject of stay cables and cable-stayed structures is also provided. 1 Scope These recommendations are intended to give technical guidelines regarding design, testing, acceptance, installation, qualification, inspection and maintenance of stay cable systems using prestressing steels (strands, wires or bars) as tensile elements which can be applied internationally. These recommendations are meant to be applicable for cable-stayed bridges and other suspended structures such as roofs. They may also be used for hangers in arch structures and as suspension cables, as appropriate. Requirements and comments have been specified for all parties involved in design and construction in order to aim for a uniform and high quality and durability. The interfaces to the structural Designer are highlighted. The essential subjects are:

• Design and detailing of stay cables including saddles and damping devices • Durability requirements and corrosion protection systems • Requirements for the materials • Testing requirements for the stay cables • Installation, tolerances, qualification of companies and personnel • Inspection, maintenance and repair.


2 2 Definitions and symbols

The main subject of these recommendations are stay cables with tensile elements consisting of prestressing steel. Generally, these are strands and wires. Bars may be of practical use for short, single bar stays and are normally not used for typical highway bridge stays. In particular for architectural applications, stainless steel bars have been used. However, this type of bar is not specifically considered in these recommendations although the general philosophy given applies. These recommendations do not cover the technology of stay cables whose tensile elements are ropes, locked-coil cables, etc. or which consist of composite materials. Nevertheless, in many cases the specified performance criteria may also be applicable to these systems, although numerical values given for the acceptance criteria may need to be adjusted. For these systems it has been difficult to provide multiple protective layers similar to those specified for stay cables made from prestressing steel and therefore, the quality of corrosion protection may not be equivalent. While extradosed cables have similarities with stay cables, generally agreed design and system acceptance criteria are not yet available and therefore, this type of cable is not covered here. 2 Definitions and symbols 2.1 Definitions (see Fig. 2.1) Accessories Auxiliary components such as anchorage caps, anti-vandalism pipe, sleeves, boots, etc. Anchorage A mechanical device, usually comprising several components (anchor head or wedge plate, bearing plate, socket, ring nut, etc.), designed to retain the load in the stressed stay cable and to transmit the load to the cable-stayed structure. Anchorages can be as follows:

- Adjustable anchorage: Anchorage with a threaded nut or with shims, allowing an adjustment of the stay cable length without moving the prestressing steel relative to the anchorage

- Fixed anchorage: Anchorage which does not allow adjustment of the stay cable length. Anchorages may be further divided into:

- Stressing end anchorages which permit stressing of the stay cable - Dead end anchorages which are not provided for stressing of the stay cable.

Barrier / Corrosion barrier Envelopment of the tensile element of the stay cable protecting the element or cable from environmental influences and their consequences, in particular corrosion. Barriers can be of two types:

- External barrier: A barrier which is exposed to the outside environment - Internal barrier: A barrier which is directly applied to the tensile element.

Bearing See guide deviator.



Centralizer / Spacer A non-load bearing device between or around the tensile elements to fix the position of the stay pipe relative to the tensile elements. Cross tie Element connecting the stay cables between each other and/or to the structure (bridge deck) to modify the period of vibration of the stay cable. Damping device A device to control cable vibrations. Designer (consulting engineer) The engineer responsible for the design of the cable-stayed structure. His exact scope of works and role varies with local customs. Fatigue load Variable loads on the cable-stayed structure, in accordance with relevant standards for fatigue loading. Filler / Filling material An interface, filler, blocking agent or coating preventing the penetration of external contaminants to, or migration along, the tensile element. Free length The length of a stay cable beyond the cable anchorage or saddle and transition zones. Guide deviator A device (sometimes called elastic bearings) located at the end of the stay cable free length which provides two functions: (1) laterally guiding the stay cable to protect the anchorage from transverse forces and

bending stresses (Guide), and (2) deviating the tensile elements to form a compact bundle of parallel elements in the free

length (Deviator). These two functions may be combined into one single element or may be provided with two separate elements.

Guide pipe A pipe used as recess former in a cable-stayed structure (deck and/or pylon) for the installation and possible removal of the stay cable anchorage zone. The guide pipe is sometimes called formwork tube or recess pipe. Inspection A primarily visual examination, often at close range, of a structure or its components with the objective of gathering information about their form, current condition, service environment and general circumstances. National requirements are often specified. Lifetime / Service life / Design working life The planned period of use of the structure, or parts of it, for its intended purpose with the anticipated maintenance but without major repair. It must be specified by the owner.


4 2 Definitions and symbols

Maintenance A usually periodic activity intended to either prevent or correct the effects of minor deterioration, degradation or mechanical wear of the structure or its components in order to keep their future functionality at the level anticipated by the Designer/owner. Monitoring To keep watch over, recording progress and changes with time; possibly also controlling the functioning or working of an entity or process. Structural monitoring typically involves gathering information by a range of possible techniques and procedures to aid the management of an individual structure or class of structures. It is often taken to involve the automatic recording of performance data for the structure and possibly also some degree of associated data processing. Saddle A device to deviate a stay cable continuous from the deck through the pylon back to the deck or anchorage to transfer loads from the stay cable to the pylon. Sheathed strand Prestressing strand encapsulated by a factory-extruded polyethylene (PE) or polypropylene (PP) sheathing filled with a corrosion-protective soft filler. It is sometimes also called monostrand. Stay cable Complete cable system comprising one or several tensile elements fitted with anchorages, including saddles, if applicable, and the relevant corrosion protection and accessories. Stay pipe An enclosure encapsulating a bundle of tensile elements forming a stay cable in the free length. Transition zone The length of the stay cable where the tensile elements are supported by guide deviators and/or deviated from their arrangement in the free length to their arrangement in the stay cable anchorage. 2.2 Symbols AUTS Actual Ultimate Tensile Strength of steel GUTS Guaranteed Ultimate Tensile Strength of steel HDPE/PE Polyethylene (in the context of these recommendations, HDPE/PE stands for high-

quality, high-density polyethylene, now called PE 80/100 in Europe, and as specified in Chapter 5)

PP Polypropylene (in the context of these recommendations, PP stands for high-quality polypropylene, as specified in Chapter 5)

SLS Serviceability Limit States ULS Ultimate Limit States FLS Fatigue Limit States σ Stress Δσ Stress Range MPa Mega-Pascal, 1 MPa = 1 N/mm2 mrad Milliradian , 1mrad = 0.001 radian (1° = 17.4 mrad = 0.0174 radian)



ANCHORAGE

ANCHOR

RECESS/GUIDE

TRANSITION REGION

DEVIATOR SOCKET PIPE RING NUT WEDGE PLATE

CAP

ZONE

TRANSITION

ZONE

FREE

LENGTH

SUPERSTRUCTURE

GIRDER

PYLON

ANCHORAGE

ANCHORAGE

ZONE

TRANSITION

ZONE

FREE

LENGTH

DEFLECTION REGION

SADDLE

PYLON

GUIDE DEVIATOR

(BEARING)

A

ANCHOR

HEAD

GUIDE

DEVIATOR

A

Fig. 2.1: Definition of stay cable length / segments

3 Design and detailing 3.1 General This chapter addresses topics relevant for the stay cable system which must be considered and specified by the Designer. The owner specifies general requirements for the structure (building construction, bridge, etc.) including:

• Function (see also Chapter 4) • Importance (e.g. high or low damage tolerance)


6 3 Design and detailing

• Type of utilization • Lifetime.

For the design of cable-stayed structures the Designer should normally follow national codes. Design of the stay cables is not covered by these recommendations except as given below for some specific topics which are relevant for the sizing and detailing of stay cables, and for special protective features of the stay cable systems. 3.1.1 Redundancy of cable-stayed structures The failure of one single stay cable should not lead to immediate failure of the entire cable-stayed structure. The Designer should take into account in his design accidental breakage of any one stay cable in the structure including the dynamic effects caused by the breakage. Generally, redundant stay cable systems, i.e. systems consisting of multiple parallel tensile elements, are preferred to cables consisting of a single tensile element. 3.1.2 Fire, impact, vandalism Contrary to tunnels, bridges are well ventilated, and therefore relatively little exposed to high temperature rises in the event of a fire. However, a tank truck carrying hydrocarbons catching fire has in the past caused significant rise in temperature on a bridge deck. On a cable-stayed bridge, a truck could burn near a cable stay. This actually happened on the Second Severn Crossing in 1999. A fire such as this would normally be unlikely to affect more than one stay cable at a time, except in the case of a set of closely grouped stay cables (e.g. back stays). Structural stability is therefore not generally a problem if the structure is designed to allow for the failure of one stay cable, as is recommended above. However, some bridges are located in special environments, e.g. near fuel depots or oil refineries, where they will be crossed by large numbers of tank trucks carrying hydrocarbons. In such cases, improved fire resistance of stay cables may be justified to avoid loss of main tensile elements in the event of fire. Care should also be taken to:

• Facilitate removal of flammable materials from the deck (drainage) • Limit fuelling by flammable products on/in the structure (avoid the filling of stay

cables with hydrocarbon based products such as wax) • Retard temperature rise in the main tensile elements for the time needed to

extinguish the fire (usually not more than two hours). Special insulating materials may be added to the stay cable inside or around the guide pipe / anti-vandalism pipe.

The Designer should consider specifying the provision and performance of special protection pipes against impact, vandalism, fire, etc. near the anchorages, when required. 3.1.3 Replaceability of stay cables Particularly in bridges, stay cable systems should be replaceable. The Designer should specify whether the stay cables of the particular structure shall be replaceable, either one or several at a time. He should also specify whether replacement is feasible under full, reduced or no traffic load. He should then design the structure accordingly. Typically, for highway bridges, stay cable replacement should be allowed for by the design, one at a time, with reduced traffic load (closure of the nearest traffic lane).



3.1.4 Transverse loads applied from stay cables to the structure Guide deviators installed near the stay cable anchorages laterally support the stay cable and limit the transverse displacements of stay cables at this location. As a consequence, they protect the stay cable anchorages from the effects of transverse loads. These transverse displacements and loads are mainly due to:

• Deformations of the structure and change of cable sag due to construction loads, wind and traffic loads, and due to temperature changes

• Cable vibrations. The transverse support provided by the guide deviator to the stay cable causes a kink in the stay cable geometry, see Fig. 3.1, and a corresponding transverse load applied from the cable to the guide deviator and to the structure supporting the guide deviator. The Designer has to design the structure supporting the guide deviator for the maximum transverse forces, F, applied from the stay cable. These transverse forces are the product of angular kink and axial stay cable force, usually the permanent stay force. As a guidance for preliminary design of the structure supporting the guide deviator, an angular kink of α=± 1.4 degrees (± 25mrad) is suggested as a reasonable assumption.

ANCHORAGE

!

!

F

F

Fig. 3.1: Angular deviations of stay cable at guide deviator 3.1.5 Bending stresses in stay cables

Depending on the actual cable force and cable weight, and in the absence of other loads, the stay cable will take a specific catenary cable profile. The cable will be subjected to pure axial tension only if the anchorages at either cable end are placed in the tangent to that specific catenary cable profile. Any deviation of the actual cable profile from the above, due to:

• transverse displacement of the cable under loads applied to the stay cable or structure

• rotation of the anchorages relative to the tangent because of applied loads, temperature changes or installation tolerances of anchorages, bearing plates and guide pipes

• stay cable vibrations

will introduce local bending stresses into the stay cable, in the region where the transverse displacement or rotation is applied. Devices such as cable anchorages installed with an inevitable placement tolerance, guide deviators, saddles, and clamping devices along the cable



length, e.g. for cross ties, introduce such deformations and corresponding bending stresses. The magnitude of these bending stresses can be calculated, see e.g. [2, 3], (3). When using stay cables designed and tested in accordance with these recommendations, rotations applied at the anchorage up to ± 0.6° (± 10 mrad) are covered by the system design and testing, and do not need to be considered in the design by the Designer, see Chapter 6. For structures with applied rotations which are larger, the Designer either has to consider the effects of the additional rotations beyond the above indicated value by design, or in extreme cases, he has to specify specific design and testing with the larger rotations. The Designer shall require from the stay cable supplier verification of the transition zones and stay cable anchorages for these rotations both for fatigue and strength. 3.2 Design / sizing of stay cables Load and design standards constitute an inseparable unit. The design of stay cables must comply with the respective national regulations. However, should there be no such information available the following may be taken as basis for the design of stay cables. 3.2.1 Service conditions (SLS) The cross section of stay cables is typically sized such that the maximum axial stresses in a stay cable under service conditions at SLS do not exceed specified limits. In the past, typically the maximum axial stress was limited to 45% GUTS. One reason for limiting the axial stress to such a low level was that secondary effects such as local bending stresses were usually not considered. With these recommendations, stay cable systems will be tested for axial and bending effects. Therefore, higher axial stresses of up to 50% GUTS are considered permissible. The permissible axial stresses are summarised in Table 3.1 and are based on and are compatible with the stay cable test performance specified in Chapter 6 for anchorages and saddles. This means that transverse bending due to an angular rotation of ± 0.6° (± 10 mrad) has already been taken into consideration. Only if these values are exceeded, the additional transverse bending must be considered separately by the Designer. But this is usually not the case. Permissible service stresses for stay cable systems tested in accordance with Chapter 6 of these recommendations (axial fatigue test with bending effect) 0.50 × GUTS 1)

Permissible service stresses for stay cable systems not tested in accordance with Chapter 6 (purely axial fatigue test without bending effect) 0.45 × GUTS 1)

1) Reference to the yield stress is not applicable for the prestressing steels specified in Tables 5.1 and 5.2. Table 3.1: Permissible tensile stresses in stay cables under SLS 3.2.2 Fatigue design (FLS) 3.2.2.1 Design philosophy The fatigue design of stay cables has to consider the relevant fatigue loads in accordance with national standards applied to the particular structure to determine actual stresses and fatigue relevant stress range in the stay cables (fatigue demand). In the simplest case, the relevant fatigue load is a specific truck (axle loads). Depending on the actual load definition used in the particular national standard, some allowance for span length, dynamic effects and others may have to be added.



The actual axial stresses and fatigue stress range demand of the stay cables resulting from the above loads are then compared with the design strength of the fatigue stress range of the actual stay cable system. The design strength of the stress range is based on the actual performance of the stay cable system in fatigue tests (applied stress range and number of cycles), suitably reduced in accordance with the safety philosophy of the national standard, taking e.g. into account the material factor for stay cables and the statistical effects of size/length of stay cable and the limited number of test results, to establish the design strength of the fatigue stress range, e.g. the 5% fractile value of the design fatigue strength of the actual stay cable system. In the simplest procedure of fatigue verification, the above fatigue stress range demand is compared with the endurance limit of the design strength of the fatigue stress range (the endurance limit is typically specified as the design fatigue strength (stress range) at a number of load cycles between 2 × 106 and 100 × 106), see e.g. [2]. In a refined procedure, the above fatigue stress range demand can be modified with some factors to account for the actual span of the member, mix of traffic loads, actual traffic volumes, actual service life, multiple lanes, etc. to obtain a “damage equivalent stress range” which then is compared with the design strength of the fatigue stress range at e.g. 2 × 106 load cycles. For special cases, the fatigue damage caused by different fatigue loads, each with a specific number of load cycles, can be accumulated with the Palmgreen-Miner’s rule for a given S-N curve of a specific stay cable system. 3.2.2.2 Fatigue strength of stay cable system PTI [1] has specified minimum fatigue test strengths/performance for stay cable systems depending on the type of prestressing steel used (wire = 200, strand = 160 and bar = 105 MPa) with 2 × 106 load cycles. These are historical values which have been chosen based on US domestic supply of strand and a 5% fractile strength limit design basis against computed design truck fatigue demand. These values have shown good results in the past. However, improved materials have become available since and more recent recommendations such as [2] and several project specifications have specified 200 MPa stress range for testing of strand stay cable systems. For these recommendations 200, 200, and 110 MPa minimum stay cable system test fatigue stress range performance have been specified for strand, wire, and bar stay cable systems, respectively. These minimum test performance requirements are applicable for 2 × 106 load cycles with an upper stress of 45% GUTS and in combination with an angular rotation of ± 0.6° (± 10 mrad) applied at the anchorage of the stay cable system, see Chapter 6. In an actual design situation, a fatigue verification may need to be done at another number of load cycles than 2 × 106. However, it would be most unpractical and expensive to perform stay cable system fatigue tests at various numbers of load cycles and stress ranges to establish “Wöhler-Curves” (S-N curves). Fortunately, a significant experience with fatigue tests is available both on tendons and individual anchored tensile elements which has demonstrated that the slope of the S-N curves (stress range – load cycle number) is reasonably well known for strand, wire and bar tendons. This knowledge of the slope of S-N curves provides sufficiently reliable “Wöhler-Curves” for stay cable systems which pass through the specified minimum test performance for 2 × 106 load cycles confirmed by tests. These “Wöhler-Curves” of the stay cable system performance are shown in Fig. 3.2 and are marked with the letter “C”. It should be noted that these curves do not represent actual performance of a stay cable system but minimum test performance requirements. Hence, the actual performance of an acceptable stay cable system must be above this Curve “C”, in general. If the material factor of the relevant national standard and the statistical effects as mentioned above are applied to the stay cable system test fatigue stress range performance,



the stay cable design strength of the fatigue stress range at 2 × 106 load cycles is obtained. Maintaining the same slope of the S-N curves, similar to above, “Wöhler-Curves” for the design strength of the fatigue stress range of the stay cable system can be obtained. These curves are marked with the letter “D” and are shown indicatively in Fig. 3.2. Presently, the actual level of Curve “D” can only be chosen with due consideration of the actual fatigue load definition in the particular national standard. 3.2.2.3 Fatigue strength of tensile elements For stay cable systems to achieve the specified minimum test performance requirements, the stay cable anchorage systems need to be carefully designed and detailed. In addition, the prestressing steels need to satisfy special characteristics which go beyond the performance of traditional materials used for pretensioning and post-tensioning, in particular for fatigue performance. These characteristics are specified in Chapter 5. Using the minimum fatigue performance specified for the prestressing steels specified in Chapter 5, and using the well known slopes of the S-N curves, one can also establish “Wöhler-Curves” for the minimum test performance of individual prestressing steel elements assuming the use of laboratory anchorages which ensure that the failure of the element will be away from the anchorage. These curves are marked with the letter “A” in Fig. 3.2. If the same individual prestressing steel elements, as represented by Curves “A”, are combined with the actual anchorage details of the stay cable system, e.g. wedge anchorage, one may expect some reduction of the fatigue performance from Curve “A” to somewhere in between Curves “A” and “C” depending on the selected design and detailing of the actual anchorage. This performance of an individual prestressing element, anchored with the actual anchorage details of the stay cable system, is represented in Fig. 3.2 by the Curve “B”. Since the performance depends on the proprietary anchorage design, no specific values can be given for Curve “B”, in general. Curve “B” may be used as an indication of the approximate performance of the stay cable system. It may be verified by testing of a series of single prestressing steel elements with the actual stay cable anchorage details to different fatigue stress ranges, and thus determine the number of cycles to failure. The slopes and minimum stress ranges at 2 × 106 load cycles used to establish the curves in Fig. 3.2 are summarised in Table 3.2. K1 K2 ∆σ (MPa) at 2 × 106 load cycles

upper stress of 0.45 GUTS A ≈ 6 2) 8 370

WIRE (Grade 1770 MPa) C 4 6 200

A ≈ 6 2) 8 300 STRAND (Grade 1860 MPa)

C 4 6 200

A ≈ 7 2) 8 180 THREADBAR1) (Grade 1050 MPa)

C 5 6 110 1) Smooth bar 20 % higher values 2) Exact slope is given by stress range values at 105, 5 × 105 and 2 × 106 cycles Table 3.2: Minimum performance requirements - S-N values for tensile elements and stay cable systems shown

in Fig. 3.2



5 5x10

10 6 10

5 10 7

6

50

100

200

300 400

500

1000

2000

n 2x10

n 2x10

6 2x10

6 n

1

k

A=SINGLE TENSILE ELEMENT

B=ANCHORED SINGLE TENSILE ELEMENT

C=STAY CABLE TEST

D=DESIGN VALUE FOR STAY CABLE

NUMBER OF CYCLES

a) WIRE STRESS RANGE

100

200

300 400 500

1000

2000

STRESS RANGE

b) STRAND

5 5x10

10 6

10 5

10 7

6 n

2x10

NUMBER OF CYCLES

100

200

300 400

500

1000

2000

! N/mm ?

STRESS RANGE

c) BAR

THREAD BAR, SMOOTH BAR 20% HIGHER

610 465

370

200

8

6

A

D

B

C

4

k k 1 2

k 1

k 1 k 2

A

500

300 380

200

D 6

4 8 B C

50 5

5x10 10

6 10

5 10

7 6

n 2x10

NUMBER OF CYCLES

k 1

k 2

A

6

8 B

C

180 220

280

110

5

D

GUTS

GUTS

GUTS

! N/mm ?

N/mm ? !

! !

10

Fig. 3.2: S-N diagrams for stay cable systems and individual tensile elements



3.2.3 Ultimate limit states (ULS) When verifying ULS, GUTS of the tensile elements can be considered as the characteristic tensile strength of the stay cable system. Safety factors in accordance with national standards shall then be applied to find the design strength. If such safety factors for stay cables are not provided in national codes, one may use a safety factor of γ=1.35 for stay cables tested with angular rotation as specified in Chapter 6, and of γ=1.50 for stay cables tested without angular rotation. 3.2.4 Earthquakes This design situation is often checked at ULS. Special ULS conditions may need to be considered for earthquakes, e.g. to avoid plastic deformations in the stay cable taking into account flexural effects under large deformations of the structure. 3.2.5 Construction and cable replacement These are design situations of relatively short duration with relatively little fatigue relevant loading. The main design objective is to avoid inelastic deformations in the stay cable system during construction or stay cable replacement. Therefore, verification of axial stresses against permissible stresses is often sufficient. The permissible axial stresses during construction and stay cable replacement under SLS load combinations are summarised in Table 3.3 and are based on and are compatible with the stay cable test performance specified in Chapter 6. This means that transverse bending due to an angular rotation of ± 0.6° (± 10 mrad) has already been taken into consideration. Only if these values are exceeded, the additional transverse bending must be considered separately by the Designer.

Maximum stresses during construction and stay cable replacement for stay cable systems tested in accordance with Chapter 6 of these recommendations (axial fatigue test with bending effect)

0.60 × GUTS

Maximum stresses during construction and stay cable replacement for stay cable systems not tested in accordance with Chapter 6 (purely axial fatigue test without bending effect)

0.55 × GUTS

Table 3.3: Maximum permissible tensile stresses in stay cables during construction and stay cable replacement 3.3 Detailing and lightning protection 3.3.1 Detailing 3.3.1.1 General The Designer has to design the structure such that:

• it is possible to inspect the stay cable at anchorages and saddles, and along the free length, e.g. by using cable cars

• it is also possible to fix clamps for lighting or to install vibration damping devices, if ever required.



3.3.1.2 Arrangement of stay cables The illustrations below show some important design and detailing features of cable-stayed bridges:

• Typical stay cable arrangements (Fig. 3.3): Fan, harp, and semi-fan • Typical cable arrangements at pylon heads and saddles for concrete and steel pylons

(Figs. 3.4a and 3.4b) • Cable attachments to the deck (Fig. 3.5).

FAN

HARP

SEMI-FAN Fig. 3.3: Typical stay cable arrangement

Fig. 3.4a: Concrete pylon heads

Fig. 3.4b: Steel pylon heads Fig. 3.4: Typical stay cable arrangements at pylon heads



CONCRETE SUPERSTRUCTURE

COMPOSITE OR STEEL SUPERSTRUCTURE

(a) Concepts

(b) Example for concrete deck

(c) Example for composite deck with pre-installed stay anchorages

(d) Example for composite deck

Fig. 3.5: Types of connections of stay cables to bridge superstructures 3.3.1.3 Dimensions of stay cables The dimensions of cable anchorages are specified by the cable producer, as are also the space requirements for the assembly and for stressing jacks. The interested reader is referred to the specific literature and brochures of the cable suppliers. However, in case no such information is available, average values are presented in Fig. 3.6 for preliminary design.



E mm

10 20 30 40 50 MN

4000

3000

2000

1000

10 20 30 40 50 MN

100

500

B, C mm

10 20 30 40 50 MN

100

200

300

400

A , D mm

1000

500

10 20 30 40 50 MN

A

*) MIN D, DEAD END LIFE END: MIN. D + ELONGATION

GUTS of cable

GUTS of cable

øH

øG

øF

C

B

*)

E

A ø F

E C

B

D

øH øG

ØF, G, H mm

D

Fig. 3.6: Dimensions of stay cables for preliminary design 3.3.2 Lightning protection The general concept of lightning protection consists of a collector, a transition line, and the earth (Fig. 3.7). The transition line connects the collector with the earth on the shortest distance possible. Lightning protection depends on the type of cable-stayed bridge, i.e. whether steel or concrete structure.



• Concrete cable-stayed structures: If the stay cables and / or the reinforcement of the pylon are not directly connected to the earth, a lightning strike into the pylon may cause significant spalling of concrete up to pieces of several 100 kg. Lightning protection of concrete pylons and stay cables of cable-stayed structures should generally consist of the following:

(1) Installation of collector lines from each stay cable anchorages in the pylon to the transition line. Installation of a collector line from the reinforcement near the top of the pylon to the transition line. Collector lines should be made of copper and have a cross section of at least 50 mm².

(2) Installation of a transition line in the pylon, in direct contact with the reinforcement cage, from the pylon tip down to the foundation. The transition line should have a cross section of at least 200 mm² and may consist of specifically designated reinforcing steel bars properly welded together to ensure adequate electrical conductivity. The transition line should be connected to the foundation earth which typically consists of a horizontal closed loop of reinforcing steel bars (min. 200 mm² cross section) placed low in the foundation, inside the concrete.

The concrete deck does not need any specific protection, in general. In case electrically isolated bearings are used, they need to be electrically connected to

the earth with cables (min. cross section of 50 mm², e.g. by copper bar ∅ 8 mm). Composite structures are suggested to be protected similarly to concrete structures. • Steel cable-stayed structures: Pure steel structures need no specific lightning protection systems. The same comment

for electrically isolated bearings applies as mentioned for concrete structures above.

CONCRETE TRANSITION LINE

200mm 2

LOOP EARTH

CONCRETE, COMPOSITE OR STEEL DECK

200mm 2

50mm 2

COLLECTOR LINES

FROM STAY CABLE

ANCHORAGES

DETAIL

STAY CABLE

DETAIL

Fig. 3.7: Lightning protection of concrete and composite cable-stayed structures



3.4 Saddles 3.4.1 General Saddles must be designed such as to ensure a safe transfer of vertical forces and of differential forces of stay cables from opposite sides of the pylon (main span and side span) in the erection and final state (friction, bond, shear keys, clamping) into the pylon structure. Load assumptions shall be in accordance with the relevant standards and the actual intended construction methods. If the stay cable has been specified to be removable, then the saddle needs to be designed such as to be removable also. This can e.g. be achieved with double steel-pipes, i.e. placing the saddle pipe, with a bundle of tensile elements grouted inside the saddle pipe, inside a guide pipe installed into the pylon structure. Transfer of differential forces from the saddle to the guide pipe may be achieved by shear keys or other mechanical connections. An alternative concept uses a battery of individual tubes, one for each tensile element, placed inside a guide pipe. The tensile element is not grouted inside the individual tube. However, the space between the individual tubes and the guide pipe is grouted. These two types of saddles are illustrated in Fig. 3.8.

CURVED RECESS PIPE WITH ANCHOR GROOVE

CURVED SADDLE PIPE WITH SHEAR KEY

GROUT

STAY PIPE

a) BUNDLE OF TENSILE ELEMENTS GROUTED INSIDE SADDLE PIPE

TENSILE ELEMENTS SHEAR KEY

CURVED SINGLE GUIDE PIPE / SADDLE PIPE

STAY PIPE

TENSILE ELEMENTS INSIDE

BATTERY OF INDIVIDUAL TUBES

b) INDIVIDUAL TENSILE ELEMENTS INSIDE INDIVIDUAL TUBES; NOT GROUTED

R

R

Fig. 3.8: Saddles for replaceable stay cables 3.4.2 Transfer of differential stay cable forces

Transfer of differential forces from the stay cable or individual tensile element into the pylon may be ensured by either one of the following three methods:



• Transfer of differential forces is ensured by friction. The friction coefficient between the tensile element and the individual tube (or the stay cable to the saddle pipe before grouting) depends on the technology which is used, and may vary in the range of 0.05 to 0.4. Whatever technology is used, the actual friction coefficient of the saddle system shall be confirmed by testing using realistic test set-up and surface conditions of all elements. The friction coefficient determined in the test shall then be reduced with a sufficient safety factor of not less than 1.5. This method allows the transfer of limited differential forces only

• Transfer of differential forces is ensured by bond (in fact, it is a combination of bond and Coulomb friction due to the curvature in the saddle). For this solution, the sheathing on the tensile elements needs to be removed, in general. Information on the actual bond strength of the uncoated tensile elements inside grout may be found in relevant standards. The actual surface conditions (cleanliness) shall be considered. However, typically the bond strength of clean uncoated tensile elements is not critical. If coated tensile elements are used and/or if no information is available, bond strength may need to be confirmed by testing. This method allows the transfer of significant differential forces

• Transfer of differential forces is provided with shear keys or other mechanical devices. 3.4.2 Minimum radius of curvature of saddle pipes The performance of the stay cable in the saddle depends mainly on the effect of fretting fatigue (small relative movements due to fatigue loading between individual tensile elements combined with transverse pressure). The transverse pressure is a function of the stay cable force, the saddle radius, and the bundle effect (number of layers of individual tensile elements sitting on top of each other). As a starting point for the detailing of saddles by the Designer, the following minimum radii of curvature may be assumed:

• For individual tensile elements inside individual tubes (no bundle effect): Min R ≥ 400 ∅

(∅: diameter of wire / individual wire of strand) • For bundle of tensile elements inside saddle pipe (with bundle effect):

Min R ≥ 30 D (D: diameter of stay pipe).

The actual performance of the actual saddle details should be confirmed by testing in accordance with Chapter 6, in particular if radii of curvature in the order of the above minima are used. 3.5 Execution aspects This section provides information on what the Designer should consider or provide for the erection of stay cables. Execution details relevant for installation on site are specified in Chapter 7. 3.5.1�� Stage-by-stage analysis The Designer has to perform a stage-by-stage analysis of the cable-stayed structure considering all stages including construction, service, and cable replacement. This analysis will provide amongst other results the force and elongation of each stay cable during each



stage of erection of the cable-stayed structure. This will form the basis for the installation of the stay cables by the specialist contractor, see Chapter 7. For stay cables assembled on site during installation, the stiffness of the structure (pylon and deck) as assumed in the above analysis, has to be known. For these cases, the Designer has to provide these stiffness values of pylon and deck for each construction stage to the specialist contractor responsible for the erection. An early exchange of the data between the Designer and the specialist contractor is recommended. 3.5.2 Length adjustment capability of stay cables Stay cables need some capability for length adjustment e.g. because of design and construction tolerances and possible future increase of service loads. The Designer shall specify the minimum length adjustment capability to be provided at the anchorages of stay cables both for:

• Re-stressing (increase of stay cable force); and for • De-tensioning (reduction of stay cable force).

3.5.3 Construction tolerances The Designer should specify construction tolerances where relevant and where not already covered by relevant standards. In order to comply with the assumptions in these recommendations for flexural effects near anchorages, the Designer may need to specify a directional installation tolerance of the bearing plates and guide pipes of about ± 5 mrad (± 0.3 degrees) around the theoretical axis of the stay cable and a tolerance on the position of the reference point of the anchorage in x, y, z-direction of ± 10mm. 3.6 Cable vibrations 3.6.1 General Stay cables, through their inherent geometrical and mechanical properties, have proven to be relatively insensitive to vibration. However, under certain conditions stay cable vibrations have been observed on some projects. Stay cable vibration is a complex topic which goes beyond the scope of these recommendations. The interested reader is referred to specialist literature such as [4, 5, 6] and (21-23, 27, 28, 42-51, 54-58, 60, 61, 85, 88-89). Typical stay cables have a relatively small internal damping ratio with a logarithmic decrement in the order of δ ≈ 1 % for individually protected tensile elements and parallel wire stay cables and down to δ ≈ 0.05-0.10 % for cement grouted stay cables, where δ = ln(fn/fn+1) = 2πξ (ξ = damping ratio, f = amplitude of stay cable vibration at cycles n and n+1, see Fig. 3.9). The Designer has to verify whether the stay cables of the particular structure are stable against the different forms of vibration with the expected internal damping ratio. This verification shall include, but may not be limited to, the following:

• Rain-wind induced vibration (wind forces create an equilibrium of the water rivulets

moving on the cable which modify the cable aerodynamics): It is the most common cause of vibration observed on bridges. Large amplitudes may occur at moderate wind speeds in the order of 10-15 m/s when combined with light rain

• Parametric excitation: Due to periodic displacement of the anchorages caused by wind or traffic actions onthe deck or pylon. This action may be responsible for large amplitude vibration.



Risk of parametric excitation shall be assessed at the design stage of the structure. A risk of large amplitudes exists when A=2B/k, where A=frequency of excitation, B=frequency of stay cable, k=positive integer. Experience seems to indicate that the first stay cable mode and k=1, 2 are particularly critical.

Other types of cable vibrations such as galloping etc. are often not critical if the above types of vibrations are adequately considered. If the stay cables are not stable with internal damping only, the Designer has to specify additional measures to control stay cable vibrations. The provision of texture on the stay cable surface and the provision of special damping devices are particularly effective against rain-wind induced vibration. The provision of cross ties is particularly well adapted to avoid parametric excitation. These different measures are presented in Clause 4.4.4. Some basic design information is given below for special damping devices. For further details on special damping devices and cross ties please refer to Clause 4.4.4 and to specific literature from cable suppliers.

f

fn+2

TIME

STAY

fn

fn+1

! = In (fn / fn+1) = 2 " #

fn+1

STAY AMPLITUDE f

L

$ L

Fig. 3.9: Stay cable vibration – Definitions and measuring of damping 3.6.2 Special damping devices Special damping devices may include hydraulic, viscous and friction damping devices. These devices are typically installed near the stay cable anchorage(s), at a distance, ΔL, from the fixed point of the anchorage(s). All types of special damping devices have in common that the maximum theoretical damping ratio, δth, which one damping device installed near one stay cable anchorage can provide is:

δth = π (ΔL / L) (where L is the stay cable length).

If damping devices are provided near both stay cable anchorages, twice the above theoretical damping ratio can be achieved. The actual damping ratio of the special damping device installed in the structure is lower than the above theoretical value because of the actual efficiency of the damping device and because of the flexibility of the support of the damping



device. However, with a known or estimated actual efficiency of a damping device and a sufficiently rigid support, the Designer may estimate an appropriate distance ΔL of the damping device from the stay cable anchorage. This may assist the Designer in good detailing of the anchorages either above or below deck level, and proper design of the supporting structure for the damping device. When specifying special damping devices, the following information should be provided by the Designer as a minimum:

• Effective logarithmic decrement δ which the special damping device has to provide after consideration of the actual efficiency of the damping device and support stiffness. In practice, effective logarithmic decrements of δ = 3-4% have often been found to be sufficient to control wind-rain induced stay cable vibrations

• Any required special texture of the stay pipe such as helical ribs or dimples • For certain projects, a maximum stay cable amplitude under service wind loads has

been specified. Amplitudes in the range of “stay cable length / 1700” for the first and second mode of vibration have been specified. These are quite severe limits and are provided mainly for aesthetical reasons.

The designer may choose to specify measures for the installation of such special damping devices on the stay cables at the time of construction for actual installation only at a later time during the design life of the structure if the need is in fact confirmed by actual vibrations. 3.6.3 Cross ties The Designer may choose to specify cross ties to control stay cable vibrations. Cross ties serve mainly to change the frequency of the stay cable and may be of interest if there is a risk of parametric excitation. Cross-ties are effective in the plane of the cables only. Strength, stiffness, prestressing forces, and connection points of the cross ties need to be specified by the Designer. 3.7 Inspection and maintenance In the design of the structure, the Designer has to allow for the space to walk and climb inside the deck and pylon, if applicable, and the accessibility of components for the following operations on the stay cable: • Inspection and maintenance of the anchorages and special damping devices • Replaceability of the stay cables • Installation of the stay cable stressing equipment • Installation of the saddles.


22 4 Functional requirements for stay cables

4 Functional requirements for stay cables This chapter addresses mainly aspects which should be considered by the stay cable designer/supplier. 4.1 Evolution of stay cable technology

The stay cable technology as discussed in these recommendations has evolved gradually over the last about 25 years, from initial systems which were similar to normal post-tensioning tendons to today’s high performance stay cable systems, through the following main stages:

• Bare tensile elements (wire, strand and bar) encased inside cement grout (basic post-

tensioning technology) in either steel or HDPE stay pipe • Bare tensile elements (mainly wire) encased inside flexible tar epoxy grout in HDPE

stay pipe • Epoxy coated tensile elements (mainly 7-wire strands) encased inside cement grout in

either steel or HDPE stay pipe • Individually greased and sheathed monostrands encased inside cement grout in HDPE

stay pipe • Galvanised and individually waxed and sheathed monostrands without stay pipe and

filler. The most recent stay cable technology uses metallically coated tensile elements (mainly

galvanised), individually protected with wax and PE sheathing, encased inside a HDPE stay pipe without filler. Alternatively to the individual protection with wax and sheathing, a general injection of the stay pipe with wax around the galvanised tensile elements has been used. These two recent systems will be referred to in the following as “Reference systems”, and used as reference in terms of corrosion protection.

Parallel to the above evolution of the corrosion protection systems in the free length of the stay cables, anchorage systems have also evolved. 4.2 General requirements 4.2.1 General

• Each system component (Fig. 2.1), from the stressing end anchorage through the free length to an eventual saddle providing continuity to the next anchorage, should have the same safety and durability under SLS, FLS and ULS (no weak member in the system/chain)

• The fatigue and ultimate capacity of the stay cable system must be verified by testing (see Chapter 6)

• Transverse loads on the anchorages and/or bending stresses in the stay cable must be kept low by using appropriate system details and possible use of guide deviators (Fig. 3.1)

• The design lifetime, specified by the owner and/or the Designer, must be satisfied for the specified exposure class (see Clause 4.2.2) for each component. A maintenance program for the stay cable system should be prepared by the stay cable supplier which ensures meeting the design lifetime



• In addition to load and execution aspects, the durability of stay cables mainly depends upon the provided corrosion protection. A clearly defined corrosion protection concept must be submitted and verified by testing, as applicable (see Clause 4.3, 4.5.2 and Chapter 6)

• Stay pipes are used to keep wind forces on the stay cable low, and to protect the cable against environmental influences while also serving aesthetic purposes. They must be able to sustain forces from clamps used to fix the lighting or damping devices

• In structures with long design lifetime and significant risk of accidental damage, e.g. highway bridges, the stay cables must be exchangeable, either as the whole cable or as single tensile elements

• High quality materials must be provided (see Chapter 5) • Installation of the stay cables must be by qualified companies with experienced

personnel (see Chapter 7), including suitable working instructions and adequate quality control

• Stressing of stay cables with single strand jacks or multistrand jacks shall be done to the required force (with control of elongation) or to the required elongation (with control of force). Adjustment of stay cables for fine tuning of superstructure geometry may be provided with small stroke jacks (see Clause 7.4)

• Allowance for inspection and maintenance of stay cables shall be included in the system design (see Chapters 8 and 9)

• Possibility for additional damping to the stay cable with guide deviators, surface texture of the stay pipe, special damping devices, cross ties, or similar shall be provided in the stay cable design

• Stay cable design should include measures against impact, vandalism, fire and lightning.

4.2.2 Durability design, corrosion protection 4.2.2.1 Design working life The owner specifies the working life during which the system is expected to be durable and to perform within the specified performance levels provided it is subjected to regular maintenance. The design lifetime must not be confused with the execution guarantee covering construction defects which are discovered between 2 to 10 years after completion of construction. Single components of stay cables may have a shorter lifetime, e.g. guide deviators and damping devices or corrosion protection systems such as coatings. Such components will need regular maintenance or replacement for the stay cable system to achieve the design lifetime. The design target for the actually provided protection should be to minimise the overall life cycle costing. The design lifetime of stay cables may be defined as temporary, e.g. for construction:

• temporary use (≤ 2 years) • semi-permanent use (2 to 15 years). However, these temporary uses are not specifically considered in these recommendations.

If there is no specific information available for a particular project the authors of these recommendations suggest 50 years and 100 years design lifetime for building and bridge structures, respectively. Adequate maintenance is a necessity to achieve these design lifetimes.



4.2.2.2 Aggressiveness of environment, other aspects The aggressiveness of the environment is grouped into Exposure Classes (see [S2, S3]). A possible classification of Exposure Classes in accordance with [S2] is:

• "benign to low corrosion risk" (inside structures) C1, C2 • “medium to high” corrosion risk (outside structures, humidity) C3, C4 • "very high corrosion risk"

(e.g. bridges subject to de-icing salt or maritime climate) C5-1, C5-M Further environmental influences which must be taken into consideration for durability of some materials such as plastics (HDPE/PP) are UV-radiation, temperature, rain and wind. In addition to the above environmental influences, classified as "benign" to "very high corrosion risk", the following aspects have to be taken into consideration:

• Local exposure conditions of a particular component of the stay cable or the entire stay cable

• Accessibility for inspection: Access versus no access • Intervals of maintenance • Exchangeability of individual stay cable components. Fatigue is another important consideration for the durability of the stay cables.

4.2.2.3 Application of corrosion protection concept Any component of the stay cable system must be able to maintain its function during the specified design lifetime with the anticipated maintenance procedures. Below, the criteria for corrosion protection and durability are applied to stay cables for:

• The free length • The transition zone between free length and anchorage zone • The anchorages and the saddles. These criteria are also adapted to the most commonly used types of materials including: • Prestressing steel • Other materials • Mild steel.

4.3 Requirements for the free length 4.3.1 Corrosion protection philosophy for tensile elements

The free length of the stay cable consists mainly of the prestressing steels (strand, wire, bar) used as the main tensile elements of the stay cables and their protection layers. If not protected adequately, these types of steels may suffer from pitting corrosion and stress corrosion (see [7] to [9], (95)). There is presently no scientific model available to reliably predict these corrosion processes over time as a function of the exposure classes. Therefore, the design approach for these prestressing steels is to provide suitable permanent multi-layer corrosion protection which is adequate for the entire design life of the stay cable.



4.3.2 Protection philosophy for other materials This paragraph applies to other materials than those discussed above under Clause 4.3.1, and includes mainly non-metallic components such as HDPE/PP used for the stay pipe and sheathing. Based on present knowledge and experience, a 50 year design life may be justified based on accelerated testing for carefully selected virgin quality HDPE/PP materials such as specified in these recommendations in Chapter 5. Up to 100 year design life may be difficult to justify based on today’s knowledge. However, proper maintenance and, if necessary, replacement of the stay pipe, may achieve a 100 year design life of the system. This applies in particular for materials that contain a minimum of about 2 % well distributed carbon black. Presently, co-extruded or fully coloured HDPE is often used for the stay pipe. For these coloured stay pipes significant experience has been collected over the last 10-15 years. It should be checked that in particular the colour and the ductility of such pipes does not change significantly over time due to UV radiation and/or pollution. In cases where such change of colour cannot be excluded and is not acceptable, the design of the stay pipe and stay cable shall allow for either addition of new surface colour, e.g. by taping or equivalent, or for replacement of the stay pipe during the design life of the stay cable. As a general rule for all the other materials, either a durability equivalent to the entire design lifetime of the stay cable can be scientifically ensured or these materials/components shall be designed to be repairable or replaceable.

4.3.3 Reference system for corrosion protection The following permanent multi-layer corrosion protection system is, based on present knowledge and experience, believed to provide a 100 year design life of prestressing steels used in stay cables with high fatigue loading and in the most aggressive environment, exposure class C5 of ISO 12944-2, [S2]. It is called "Reference system” for the purpose of these recommendations and consists of the following independent layers (see Table 4.1). Material specifications and criteria for each layer of protection (1) to (3) are given in Chapter 5.

Layer Protection system (1) A layer of zinc coating applied to the prestressing steel surface: "internal barrier" (2) A filler of wax between the prestressing steel and the sheathing (if any) or the stay

pipe: "interface" (3) A PE or PP sheathing on the individual prestressing steel element, or alternatively a

general stay pipe encapsulating the entire bundle of prestressing steel elements: "external barrier"

Table 4.1: Reference system for multi-layer corrosion protection of prestressing steels in stay cables The “Reference system” for corrosion protection is schematically illustrated in Fig. 4.1. The cross section in Fig. 4.1 (a) shows the galvanized prestressing steel elements protected with individual layers of wax and sheathing. The tensile elements are strands. Fig. 4.1 (b) shows the bundle of galvanized prestressing steel elements protected with a general sheath (stay pipe) and the space between prestressing steel elements and stay pipe filled with wax. The tensile elements can either be strand or wire. In the latter case, the system is often called PWS. Even though not required for corrosion protection the system in Fig. 4.1(a) should be provided with a stay pipe also. The stay pipe is needed anyway because it provides in particular lower wind drag forces, and additional mechanical and weather protection.



7-WIRE STRAND

SHEATHING GALVANIZED STRANDS WAX / GREASE

AIR

SHEATHING WAX / GREASE

GALVANIZED STRANDS

OUTER SHEATH RECOMMENDED

a) Individually protected tensile elements (Stay pipe not filled)

b) Generally protected tensile elements (Stay pipe filled) Fig. 4.1: Reference systems for corrosion protection of prestressing steel The main purpose of each individual layer of protection is summarized in Table 4.2.

Layer Main purpose 1. Zinc • Temporary corrosion protection of the prestressing steel at exposed ends in

anchorages during construction, before the final protection is applied (e.g. before anchorage cap is installed)

• Temporary corrosion protection of the prestressing steel at locations where the sheathing is not closed or damaged during construction, and before the damage can be repaired

2. Wax • Avoid risk of condensation of water in voids in contact with the prestressing steel • Prevent the migration of water along the surface of the prestressing steel, if it ever

enters the system or barrier (system reserve, redundancy). N.B.: The effect of the thermal movement of the filler when cooling after the injection or under ambient temperature variations should be considered

• Corrosion protection 3. PE or PP

Sheathing or HDPE Stay Pipe

• Provide a permanently leak tight encapsulation of the prestressing steel against ingress of water, potentially laden with aggressive chemicals such as chlorides (maintenance necessary if used as “external barrier”, see Clause 4.3.2)

• Provide a barrier against diffusion of gas and vapour • Provide mechanical protection during handling and installation

Table 4.2: Main purpose of each layer of protection in the Reference system for corrosion protection

(specifications see Chapter 5) 4.3.4 Equivalent systems for corrosion protection The stay cable supplier has the choice to provide either of the following protection systems for the prestressing steel:



• The above “Reference system” with zinc coating, wax, and PE or PP sheathing or HDPE stay pipe

• An “Equivalent system” which provides three layers of protection with equivalent performance in terms of corrosion protection as the Reference system.

Demonstration of equivalency shall include but may not be limited to the aspects listed in Table 4.2 above, and shall be based on scientific investigations including comparative testing for each layer as follows (Note: Some layers of protection may complement favourably adjacent layers and provide sufficient protection even though they may not count as an independent layer):

• Internal barrier: Comparative testing of three at least 0.3m long samples of zinc coated prestressing steel (in accordance with the specifications in Chapter 5) and the proposed “Equivalent system” each in salt spray tests according to ASTM B117 over 300 hours (see [S4]) and stressed to 50% GUTS, or other testing as may be applicable to the proposed “Equivalent system”. The “Equivalent system” samples shall perform in the tests at least as well as the zinc coated samples (corrosion or blisters, etc).

• Interface: (1) Demonstration that the “Equivalent system” is capable of completely filling the space inside the prestressing steel, if applicable, and between prestressing steel and sheathing or stay pipe, as applicable. (2) Demonstration that the “Equivalent system” meets the “leak tightness / migration” test [S5] as specified in Table 5.5 or as may be applicable to the proposed “Equivalent system”. (3) Comparative testing of three samples of wax coated steel plates with steel plates coated with the proposed “Equivalent system” each in salt spray tests according to ASTM B117 over 300 hours (see [S4]), or other testing as may be applicable to the proposed “Equivalent system”. Steel plates shall be Grade 350 MPa or similar with a surface roughness comparable to prestressing steel. The coating thickness shall correspond to the actual mass per linear meter specified for the prestressing steel divided by the nominal surface (based on nominal diameter) of the prestressing steel. The “Equivalent system” samples shall perform in the tests at least as well as the wax coated samples.

• External barrier: (1) Demonstration of leak tightness of the proposed “Equivalent system”, e.g. by subjecting samples to 3m water head. (2) Demonstration of comparable performance for diffusion of oxygen and vapour either by testing or by calculation. (3) Demonstration testing of three samples of PE/PP coated sheathing and of the proposed “Equivalent system” each in the “impact resistance” test [S5] as specified in Table 5.5. The above testing may need to be adapted as may be applicable to the proposed “Equivalent system”. The “Equivalent system” samples shall perform in the tests at least as well as the PE/PP coated samples.

4.3.5 Systems with lower corrosion protection If the client/Designer specifies a design life of less than 100 years, e.g. for applications in buildings, a reduction of the performance of protection of the above layers or number of layers may be considered. Any reduction of protection shall be scientifically justified, and submitted to the Designer for approval. The same applies for less aggressive environments than exposure class C5 of ISO 12944-2, in particular for in-door applications. The same option for reduction of the protection system applies for the anchorage, transition zones and saddles.



4.3.6 Additional requirements In addition to the requirements listed under Clause 4.2 and 4.3 above, the detailed material properties as specified in Chapter 5 must be complied with. If bars are used as main tensile elements, couplings must be secured such as to avoid any loosening under load. HDPE pipe segments are typically welded by mirror welding to form a continuous stay pipe. These welds shall be able to develop the yield strength of the monolithic pipe section. Welded steel pipes shall meet the same requirement, in particular if they are bonded by a hardening filler to the main tensile elements. In that case, the welds need also to satisfy fatigue requirements comparable to those of the stay cable system. Connections and clamps fixed onto the stay cable shall be designed such as to avoid transverse forces or effects which may be harmful to the fatigue and tensile strength of the stay cable. If this cannot be ensured by design, such details shall be included into the stay cable system testing specified in Chapter 6. Special attention has to be paid to the design of plastic stay pipes, if injection of the free length with filling material is considered. Experience has shown that HDPE stay pipes, if inappropriately filled e.g. with too large pressure, may become brittle under changing environmental conditions (UV, temperature) and crack, thereby causing severe damage to the leak tightness of the stay cables. Consequently, corrosion protection, too, would be impaired. High temperatures reduce the rigidity of stay pipes and increase the risk of buckling. This can apply under service conditions but may also apply when injecting filling materials at elevated temperatures such as wax. In addition, filling materials injected at elevated temperatures will show significant thermal movements when cooling down, see Clause 4.4.2. This has to be adequately considered in the design and detailing of the system. The design of the wall thickness of the stay pipe shall consider whether it is suspended from the pylon above (acting in tension) or supported from the deck below (acting in compression). It shall also consider whether the stay pipe is injected with a filling material or not, see Clause 4.4.2. The design of the stay cable system free length shall include the provision of spacers only if a specified cover of the tensile elements by the anticipated filler is required for the system performance in terms of corrosion protection or other aspects, as applicable. Rattling of tensile elements inside non-injected stay pipes can be avoided by limiting the stay cable vibration amplitudes to values as proposed in Clause 3.6.2. Alternatively, spacers or clamps shall be specified by the supplier along the tensile element bundle at appropriate spacing. 4.4 Requirements for the transition zones 4.4.1 Corrosion protection Certain layers of protection specified above for the free length cannot be provided fully continuous from end to end of the stay cable. This applies in the transition zone in particular to the stay pipe which stops near the entrance of the guide pipe and to the sheathing of the prestressing steel which is removed inside the anchorage. Whenever one of the layers of protection is interrupted it must be replaced with an equivalent layer of protection (e.g. guide pipe instead of stay pipe, PE sleeve or anchorage casing instead of PE sheathing, etc.). Such transition zones occur particularly between the free length of the stay cable and the anchorage, and between the free length and any saddles. The transition of main to equivalent layer of protection has to be carefully detailed to ensure leak tightness. The adequate performance of



these transitions in terms of leak tightness is the subject of the leak tightness testing of the stay cable system as specified in Chapter 6. 4.4.2 Stay pipe dilation Consideration of the stay pipe dilation in the stay cable system design and detailing is essential to ensure satisfactory performance and sufficient leak tightness of the system. The transition zones must consider the effects of the dilation of the stay pipe due to temperature variations. The thermal coefficient of dilation of the stay pipe material has to be considered. This coefficient is particularly important for stay pipes made of HDPE or similar materials, and may be in the order of (10-20)10-5/°C, see Clause 5.7.2. Dilation requirements need also to consider whether the stay pipe is supported from the pylon (in tension) or from the deck (in compression). Alternatively to the above, the stay pipe dilation may be fully restrained. In that case, the connections in the transition zone have to be designed for the corresponding forces, and the stay pipe has to be checked for an eventual risk of buckling. In any case, the stay pipe connections in all transition zones to anchorages and/or eventual saddles have to be designed to avoid ingress of water into the anchorage or saddle zones. In addition, the low points in anchorages or saddles should have drainage. 4.4.3 Guide deviators The general requirements specified in Clause 4.2 apply. In the transition zones the single tensile elements coming from the anchorage are typically bundled by a deviator. Often guides are installed in order to minimise the transverse bending stresses resulting from changes in cable sag or deformations of the structure. If guides are not provided, the anchorage must be designed to cope with these bending affects. The guide deviators may be designed such as to provide some damping effect as well. The damping function may be verified according to Clause 4.4.4. The cable supplier shall provide the relevant material characteristics (spring stiffness of guide deviators) and specify the length of the transition zone. In accordance with Clause 3.1.4 these guide deviators shall be designed to resist the transverse forces generated by the maximum stay cable force during construction and during service life and the relevant angular rotations. Any longitudinal effects shall be considered also. Transverse forces in the transition zone must be absorbed such as to avoid fretting corrosion as far as possible. Any such possible effects on the fatigue strength are verified in the full-scale fatigue test specified in Clause 6.2. The guide deviators shall be installed such that unintentional longitudinal movement along the stay cable is prevented. 4.4.4 Damping of stay cables 4.4.4.1 Solutions to limit vibrations of stay cables Vibrations of stay cables are controlled to some limited extent by the internal damping ratio of the stay cable system and by elastomeric guide deviators. Where these damping ratios are not sufficient, additional measures need to be taken to control vibrations. There are three basic types of solutions to limit vibrations: • Cable surface (Fig. 4.2): The stay pipe may be manufactured with some geometrical ribs or dimples on



its external surface (see Clause 5.7.2). This solution is efficient mainly for rain-wind induced vibration • Cross ties (Fig. 4.3): Cross ties connected between stay cables or stay cables and deck modify the period of

vibration of the cables. They are principally efficient in the case of parametric excitation. This efficiency may be reduced for other types of excitation, and particularly in case of transverse vibrations. The connections of these cross ties to the stay cables need to be carefully designed. Aesthetic reasons and difficult accessibility for maintenance may lead to a preference for other solutions when possible

• Special damping devices (Figs. 4.4 and 4.5): The low internal damping capacity of the stay cable can be supplemented by either

hydraulic, viscous, or friction damping devices. For aesthetic reasons these devices are generally installed near the deck anchorage. The stiffness of the support of the damping devices shall be sufficiently high. A too flexible support will significantly reduce the efficiency of the damping devices. Dynamics experts advise to remove the guiding part of the guide deviator close to the damping device because it restrains the movement of the damping device. Characteristics of the damping devices should be relatively insensitive to the environmental conditions such as temperature. Damping devices are subject to wear and maintenance cost can be high. Accessibility, replaceability and adjustability are important parameters for the damping devices.

The stay cable system supplier may choose to offer one or several of the above means. He has to ensure that these means are compatible with his stay cable system and do not impose effects which may be harmful to the behaviour of the stay cable, or they have to be installed and verified during the stay cable testing in accordance with Chapter 6.

a) Helical ribs

b) Dimples

Fig. 4.2: Stay pipes with surface texture



AFTER COMPLETION STEEL ROPES

DURING CONSTRUCTION HEMP ROPES

A

B

C

B

C

A

(a) Concepts (b) Example of ropes during

construction Fig. 4.3: Cross ties (during working life) and hempropes (during construction) - Alternative installation schemes

CABLE

DAMPER

SUPERSTRUCTURE

(a) Concept (b) Example Fig. 4.4: External damping devices

(a) Friction damper (b) Viscous damper Fig. 4.5: Internal damping devices



4.4.4.2 Special damping devices The supplier has to design the damping devices he has chosen to offer such that they provide a total damping ratio (logarithmic decrement) which is equal to or larger than the effective damping ratio specified by the Designer, see Clause 3.6.2, for the expected range of temperatures and vibration modes of the stay cables. Any possible relative movement between the damping device and the stay cable shall be considered in the design of the damping device. The actual damping ratio of the damping device shall meet the specified value. By testing on site, selected stay cables may be excited to vibrate without and with the damping devices installed and the actual damping ratio may be verified from the observed vibration behaviour, see Fig. 3.9. The corrosion protection of the damping devices shall follow the same approach as presented in Clauses 4.3.2, 4.4.1 and 4.5.2 for other stay cable components, in general. The supplier shall provide to the Designer a maintenance program for the damping devices which is based on the above approach. Some special damping devices may permit installation after construction, at some time during the design life of the stay cables.

4.4.5 Anti-vandalism pipes The design of the transition zone must allow for installation of a special pipe protecting the stay cable against impact, vandalism and fire, if specified by the Designer. The details shall be designed such that these pipes do not impose forces or deformations to the stay cable which could be harmful for the stay cable performance, or these details will need to be provided for the stay cable testing in accordance with Chapter 6. Grouting of these pipes has been used to provide improved fire protection. 4.5 Requirements for anchorages 4.5.1 Types of stay cable anchorages Three different types of anchorages are used in construction (Fig. 4.6):

• Transfer of the permanent and fatigue loads in the prestressing steel by classical mechanical end anchorages, such as: - wedges for strands - button heads for wires and - nuts for bars

• Pure grout/bond anchorages including special cementitious grout or resin and cement grout (bond sockets)

• Mixed systems in which the permanent loads are generally transferred by classical anchorage systems and the fatigue loads (fully or partially) by bond.

The respective anchorage systems shall be specified by the supplier. The filling materials in the anchorage zones are considered to be proprietary materials which need to be specified by the system supplier, and which are not covered by the specifications in Chapter 5, in general.



WEDGE

BUTTON HEAD

MECHANICAL ANCHORAGES

NUT

GROUT / BOND ANCHORAGE

BOND SOCKET

MIXED SYSTEM

Fig. 4.6: Types of stay cable anchorages 4.5.2 Corrosion protection philosophy for mild steel anchorage components Corrosion protection of the tensile elements inside the anchorage, and of the anchorage components themselves shall be equivalent to that provided in the free length of the stay cable. This paragraph applies to low carbon steel components such as typically used as structural steels or for machined components of anchorages. For these types of steels the main durability concern is oxidation of the surface (surface corrosion, rust). The surface of mild steel components has to be coated with some corrosion protection system to avoid/limit corrosion. These coatings initially applied in the factory or on site, will be consumed over time depending on the aggressiveness of the environment (exposure class, ISO 12944-2, see [S2]). For anchorage components which are accessible for maintenance operations in-situ, the corrosion protection system may have a design life less than the design life of the stay cable. In this case, a maintenance program needs to be implemented to renew in-situ at regular intervals the protection system. The corresponding maintenance operations and periods between subsequent maintenance operations shall be specified by the stay cable system supplier. Anchorage components which are not accessible for maintenance operations in-situ after installation in the bridge, shall be designed with a corrosion protection system that shall remain effective during the entire stay cable design life without maintenance. If this cannot be achieved, these components shall be designed to be replaceable at specified intervals



corresponding to the actual design life of the component. The regular replacement of these components thus ensures meeting the design lifetime for the entire stay cable. These components need to be identified by the stay cable supplier in the maintenance program. For a particular coating applied to the steel component surface, ISO 12944-2 may be used to estimate the consumption rate of the coating as a function of the exposure class. The time required to consume the applied coating thickness defines the maintenance interval or the design life of the component. Coating materials not covered by ISO 12944-2 may be calibrated against those given in the standard by suitable experience and/or corrosion tests. Suggested maintenance intervals for the stay cables are considered to be in the range of 10 to 25 years. The durability of the corrosion protection systems of the anchorage (or saddle) is defined as the design life of the first component of the anchorage (or saddle) for which the corrosion protection system is consumed and cannot be renewed during a maintenance operation anymore. The main parameters of the corrosion protection approach for mild steel components such as used in anchorages (and saddles) are summarized in Table 4.3 [10]. The stay cable system supplier shall present the corrosion protection approach of his stay cable system in accordance with Table 4.3.

Aggressiveness of the environment: C5 1) (ISO 12944-2)

Design life of the stay cable system

Accessibility or replaceability of the components

Durability of the corrosion protection

system

Design life of the initially applied

corrosion protection system

Period between subsequent

maintenance operations

Replaceable 25 years 2) 25 years 2) 25 years 2)

Not replaceable Easy access

With maintenance ≥ 100 years 1)

25 years 2) 15 years 2) 100 years 1)

Not replaceable No access

100 years 1) No maintenance 1) Only indicative (to be specified by the Designer) 2) Only indicative (to be declared by the stay cable system supplier) Table 4.3: Corrosion protection philosophy for mild steel components Corrosion protection coatings shall be compatible with each other and with the galvanic corrosion protection, if any. The assembly of components shall be compatible with the overall durability of the stay cable. Particular attention shall be paid to the corrosion protection of threads, if there are any. The stay cable supplier shall define the type and thickness of coatings used on the mild steel stay components. He shall then demonstrate the durability of the mild steel components in accordance with ISO 12944-2, and declare in particular maintenance intervals and type of maintenance work anticipated such that the durability of the stay components is compatible with the design life of the stay cables specified by the Designer. He shall submit this information to the Designer for approval. 4.5.3 Additional requirements The performance of the anchorage system shall be verified by full-scale testing (see Chapter 6). Individual components may be dimensioned according to the approval guidelines for post-tensioning systems (see [11] and [12]) or the respective national regulations. The



bearing plates may be dimensioned according to standards for steel construction for SLS and ULS. In some cases anchorage sealing elements (stuffing boxes) are used. These separate the medium of the anchoring zone from the medium of the free length. Their properties may vary slightly, depending on the anchorage position (top or bottom). Details of these stuffing boxes need to be specified by the suppliers. Their adequate performance is the subject of the leak tightness test of the stay cable system as specified in Chapter 6. The anchorages must permit stressing of the tensile elements as intended. Sufficient space and access must be available for installation, stressing and inspection. The protective cap at the end of the cable must be removable for inspection of the anchorage. 4.6 Requirements for saddles 4.6.1 General Saddles are an option to replace the stay cable anchorages in the pylons of relatively small and slender structures mainly for reasons of space requirement. However, for large and significant structures, anchorages at the pylons are usually preferred for their proven performance in terms of tensile and fatigue strength, and because space requirements are typically not critical in such structures. Anchorages also offer advantages in terms of installation and possible future replacement of stay cables. The requirements specified in Clauses 4.2 must be met also for saddles. 4.6.2 Corrosion protection The corrosion protection of the tensile elements must either be continuous through the saddle or be replaced by another protection inside the saddle which is equivalent to the one provided in the free length, see also Clause 4.4.1. The corrosion protection of mild steel saddle components shall follow the same philosophy as presented for the stay anchorages, see Clause 4.5.2. 4.6.3 Saddle performance It is suggested that, whenever possible, the saddle should have the same performance in terms of tensile and fatigue strength as the stay cable anchorages. The bending of the stay cable at the entry into the saddle under permanent and variable loads shall be adequately considered (guide deviators, bending filters, etc.), see 4.4.3. The saddle systems should be confirmed by testing as specified in Chapter 6 during the initial approval process of the system, for the minimum radius of saddle curvature acceptable to the system, and declared by the system supplier. The differential forces, as specified by the Designer (see Clause 3.4), generated during construction and service life must be safely transferred to the pylon by friction, bond, mechanical connections or similar. Safe transfer of these differential forces shall either be verified by design or by testing, as required. Also the removability/replaceability of the saddle must be demonstrated as specified by the Designer, see Clause 3.1.3.


36 5 Materials: properties, requirements, testing

5 Materials: properties, requirements, testing 5.1 General High quality materials shall be used whose properties are generally regulated by national or international standards, including the respective test procedures. Minimum requirements are proposed below. Even higher quality standards may be specified by the Designer. The main materials for stay cables and their corrosion protection considered here are:

• High-tensile prestressing steels as main tensile elements. These are generally galvanized but may be epoxy-coated or other for “Equivalent systems”

• Standardized structural steels used for anchorage and saddle components • Zinc or other corrosion-protective coatings on the prestressing steel or structural steel

components • Stay pipes made of HDPE. In some cases they may be made of steel or stainless steel • PE/PP sheathing on prestressing strands (bars) • Filling materials such as wax and grease for the protection of the free length and

anchorage. Cementitious grout may be used for filling of proprietary anchorage components or for the filling of the free length of short/small stay cables proposed as “Equivalent systems”

• Rubber or poly-chloroprene rubber (e.g. neoprene) for guide deviators or damping devices.

The material requirements as well as the requirements for transport, storage and installation of materials must be complied with and specified in quality assurance and quality control manuals. The types of test certificates to be provided by the suppliers must be specified (e.g. EN 10204 [S6] or equivalent). In the approval and suitability tests (see Chapter 6) the properties of all materials used must be checked and recorded in the test reports. The test results must comply with the specifications. In addition, the cable supplier has to perform tests on samples of all important stay cable components upon delivery of the stay cable materials, see also Clause 6.4. Test results shall be recorded and checked for compliance. For the test frequency see Chapters 5 and 6. In addition to these tests on standardised components, QC testing on proprietary components shall be done and include:

• Geometry and surface hardness tests on anchor heads • Geometry and mechanical properties of anchorage components such as wedges and

nuts. It is necessary to take into consideration that all material properties are temperature-dependent. Although standard testing is performed at room temperature, the influence of high (e.g. up to 60° C) and of low temperatures (down to -30° C) particularly on organic materials has to be checked where relevant for a specific project. This may include such aspects as:

• Expansion of corrosion-protective compound at high temperatures or effectiveness at low temperatures

• Reduction of the stiffness and strength of HDPE at high temperatures including its effect on buckling

• Effect of varying thermal expansion behaviour.



5.2 High tensile steel for tensile elements (prestressing steel) 5.2.1 General Identification of steel is not limited to chemical and mechanical characteristics. The type of wire rod, production plant and the manufacturing process are essential parameters which may influence the performance and particularly the fatigue behaviour of the steel. A higher quality standard than for post-tensioning tendons is required. In addition to the standard production controls, test samples shall be taken and independent testing must be carried out (see Clauses 5.1 and 6.4). Furthermore, the process of production must be managed firmly and any change of process must be checked concerning the influence on the fatigue behaviour of the steel, such as:

• Wire rod and its origin (electric/blast and bloom/billet) • Drawing process (capacity of cooling, number of dies, drawing speed, surface of rod) • Process of applying the corrosion protection.

Quenched and tempered steel shall not be used in stay cables. More sensitive high-tensile strands with tensile strength in excess of 2000 MPa and bars with tensile strength of 1230 MPa are presently not recommended for use in stay cables. 5.2.2 Hot dipped metallically coated prestressing steel 5.2.2.1 Prestressing steel Strand, wire or bar used in cable stays shall conform to the applicable national or international technical standards for prestressing steel (see [S7] to [S15]) with very low relaxation (Note: "very low relaxation" is called" low relaxation" in ASTM standards) and be free of corrosion pits. Welding points present in rods before the drawing are acceptable. However, no welds are acceptable to be introduced in the final drawn wires. In addition, specific requirements for geometrical tolerances, resistance to tri-axial loading, fatigue and corrosion resistance shall be complied with. Recommended values for these properties are specified in Tables 5.1 and 5.2. Type of

steel Diameter Tensile

strength Cross section Recommended

tolerances on mass Characteristic ultimate force

mm MPa mm² % kN Strands 15.2 1860 140 ± 2 260

1770 265 Strands 15.7

1860

150 ± 2

279

1770 50.0 Wires 6 7 1670

28.27 38.5

± 2

64.3

Bars 26, 32, 36, 40, 50

1030 or

1050*)

531 to 1964 -2/+6 547 to 2022

*) Smooth or ribbed, Ø 50 only for Grade 1030 MPa Table 5.1: Classification of prestressing steels for stay cables



The dimensions and properties given in Tables 5.1 and 5.2 are based on draft prEN 10138:2004, [S8]. They may also be specified according to other standards with equivalent properties and quality, see [S9] to [S15]. Tolerances for cross section or mass vary between standards. Tight tolerances such as those given in Table 5.1 are recommended for stay cables.

Property Requirement Acceptance test method

Elongation at break Not less than 4.5 % ISO 15630-3 [S7]

Constriction at break Ductile break visible to naked eye, constriction

coefficient ≥ 25 % 1)

ISO 15630-3

Relaxation 1000 h at 0.70 GUTS, 20°C Not more than 2.5 % ISO 15630-3

Strands 300 MPa Wires 370 MPa

Fatigue stress range with an upper stress limit of 0.45 GUTS 3) Bars 2) 180 MPa

At least 2 106 cycles

ISO 15630-3

Strands 380 MPa

Wires 465 MPa

Fatigue stress range with an upper stress limit of 0.45 GUTS (alternatively to 2 106 cycles) 3) Bars 2) 220 MPa


ISO 15630-3

Strands 500 MPa Wires 610 MPa

Fatigue stress range with an upper stress limit of 0.45 GUTS (alternatively to 5 105 cycles) 3) Bars 2) 280 MPa


ISO 15630-3

Tensile test after the fatigue test At least 95 % of GUTS

or 92 % of AUTS

ISO 15630-3

minimum median Strands 2 h 5 h Wires 2 h 5 h

Stress corrosion with NH4SCN on uncoated material

Bars 25<d≤50 100 h 400 h

ISO 15630-3 Solution A

Deflected tensile test Strands Not more than 20 % ISO 15630-3 1) Except threadbar 2) Smooth bar 20 % higher 3) Values as given in Table 3.2 and Fig. 3.2 Table 5.2: Proposed mechanical characteristics for prestressing steels The above specified properties apply to the hot dipped metallically coated prestressing steel. However, they have to be satisfied also by the bare prestressing steel before coating. The high fatigue limits for prestressing steel are necessary to comply with the fatigue limits specified for the stay cable bundle (see also Clause 3.2.2 and (26)). 5.2.2.2 Metallic coating Metallic coatings of the steels as specified in Clause 5.2.2.1, may be hot dipped with either zinc or zinc/aluminium during the manufacturing process of the prestressing steel, and shall be in accordance with NF A 35-035, [S16] or similar standards. Important characteristics of these metallic coatings are summarized in Table 5.3. Electrolytic coating is not permitted.



Property Requirement Test method

- Continuity No defects

- Weight of coating 190 to 350 g/m² Zinc or zinc/aluminium coating

- Adherence No defects, cracks

EN 10244-1 and 2 [S17]

Table 5.3: Requirements for metallic coatings on prestressing steel [S16] 5.2.2.3 Other coatings For “Equivalent systems” other coatings than zinc or even no coating may be provided. For further information on other coatings see [8]. For some special applications the use of epoxy-coating on the prestressing steel, e.g. strands and bars, has been proposed. Epoxy-coating has as yet not provided convincing evidence of its effectiveness (it has been reported to be brittle at low temperatures and not diffusion-tight). Special attention must also be paid to the anchorage of epoxy-coated tensile elements. For further information see fib Bulletin 11, [8] and [S18]. The use of epoxy-coating on the prestressing steel can be considered as an internal barrier for an “Equivalent system”, if an external barrier and a suitable interface (see Clause 4.3.3) has been provided. 5.3 Structural steel for anchorages, saddles, guide deviators and pipes These are standard steels as typically used in steel construction. They shall be specified, e.g. according to national regulations or EN 10025 [S19] or other relevant standards. Special requirements for low temperatures may apply for certain applications. Delivery certificates should be provided in accordance with [S6] or similar. The regulations regarding weldability, minimum wall thickness, e.g. of pipes/tubes, have to be observed (see Clause 5.7.3). 5.4 Stainless steel For stay pipes consisting of stainless steel (e.g. when used as anti-vandalism pipes to protect cables against impact, vandalism or fire) the same requirements apply as for structural steel pipes. In addition, special care has to be taken in selecting appropriate materials and construction methods so as to avoid chloride induced pitting and crevice corrosion as it may occur in contact surfaces between components. Stainless steel with the following material numbers may be used, see e.g. Stahlschlüssel [13]: 1.4401, 1.4571, 1.4462 (increasing resistance to corrosion from No. 1.4401 to 1.4462). These materials have a high content of chrome, nickel and molybdenum. Care shall be taken to use appropriate welding electrodes. 5.5 Sheathing for prestressing strands Hot dipped metallically coated prestressing strands may be provided with extruded sheathing, in different colours, which is filled with filling material, e.g. wax. There are two main methods of applying the sheathing to the strand:

• A substantial quantity of grease filling is applied (with 15.2 or 15.7mm strands > 40 g/m) and the sheathing is circular around the outside contour of the strand so that the



strands are easily moveable against the PE/PP sheathing (< 60 N/m displacement resistance). This type of sheathing is used in unbonded prestressed concrete construction and has been used for grouted stay cables. However, it is not considered suitable for ungrouted stay cables as proposed in the “Reference system” because the sheathing may move too much under temperature changes and the substantial quantity of grease may build up excessive hydrostatic pressure.

• A low quantity of wax or grease is used as filling material (with 15.2 or 15.7mm strands ≥ 5 g/m). The PE/PP sheathing follows the contour of the strand.

Properties of the sheathing materials PE and PP are given in the Table 5.4 below. Only virgin PE or PP material shall be used for the sheathing. Recycled PE or PP shall not be accepted. For further information on sheathing materials see fib Bulletin 7 [14] or [1], [2], [12] or [S5]. Properties of the filling materials are specified in Section 5.6 below.

Property Requirement PE (PP) Test method Conformity1) Melt index ≥ 0.35 g and ≤ 1.4 g per

10 minutes under 5 kg ISO 1133 [S20] A, B

Specific weight, Density ≥ 0.94 g/cm³ (≥ 0.9 g/cm3) ISO 1183 [S21] A, B Carbon black 2.3 ± 0.3% ISO 6964 [S22] A Dispersion of the carbon black Index is max. 3 ISO 18553 [S23] A Distribution of the carbon black Index is max. C 2 ISO 18553 A Tensile strength ≥ 22 MPa on raw material

≥ 18 MPa on sheathing ISO 527-2 [S24] A, B

Elongation at break at 23° C ≥ 600 % on raw material ≥ 250 % on sheathing

ISO 527-2, 50 mm/minute (speed on test)

A, B

Elongation at break at –20° C ≥ 150 % on raw material ≥ 100 % on sheathing

ISO 527-2, 50 mm/minute

A

Thermal stability under O2 ≥ 20 minutes at 210 °C, without degradation

ISO/TR 10.837 [S25] A

1) A: Factory production control or guaranteed values by the manufacturer B: Control by independent body Table 5.4: Characteristics of PE sheathing (PP-characteristics in brackets if different from PE) and verification of conformity The manufactured sheathing shall satisfy the following requirements:

• The thickness of the sheathing for the “Reference system” shall be 1.5 mm (-0 + 0.5 mm). Another upper tolerance of the sheathing thickness may be specified by the stay cable supplier to suit the anchorage and sealing details.

• The sheathing shall have a minimum friction resistance against sliding on the prestressing steel of 3300 N/m (1000 N over a specimen length of 0.3m). This type of sheathing, usually with galvanised waxed strand, is preferred for use in stay cables.

• The filling material used for sheathed strands shall be in accordance with the specifications given in Clause 5.6. The filling material shall cover the outer surface of the strand and fill the interstices around the central wire and shall be applied in a sufficient quantity to ensure that water cannot migrate along the strand.

• The surface of the sheathing should have no defects or mechanical damage which may locally reduce the thickness of the sheathing by more than 20 %. No traces of the



filling material should be visible on the outside of the sheathing. The sheathing shall be watertight.

• The sheathing shall have sufficient impact resistance. Different standards are available, see Table 5.5.

The above requirements and the corresponding test procedures are summarised in Table 5.5.

Characteristics Test method Acceptance criteria Sheathing thickness Calibrated gauge ≥ 1.5 mm Friction resistance XP A 35-037.1, 3 [S5] ≥ 1000 N

Leak tightness / migration XP A 35-037.1, 3 No increase of mass due to absorption of water

Quantity of filling material Weighing ≥ 5 g/m

Impact resistance XP A 35-037.1, 3 ASTM G14 [S27] No perforation of the sheathing

Table 5.5: Characteristics of the sheathed and waxed stay cable strands 5.6 Filling materials Corrosion protection may be provided by means of a filling material in the sheathed strand as specified above, the anchorage zone and in the free length of the stay pipe. The filling material is typically a soft material but may be a hardening material for use in proprietary anchorage systems or for “Equivalent systems”. Filling materials may provide either active corrosion protection or only physical protection or may be used for filling of voids in order to prevent formation of condensation water and migration of water (interface). Alternatively to filling materials, circulation of a gas within the stay cable pipe (or part of it), with humidity and temperature control, may be considered (see Chapter 7). 5.6.1 Soft filling materials Soft filling materials have the following functions:

• They prevent the circulation of gases or liquids within the strand sheathing, the stay cable pipe and in the anchorage zone

• They may provide corrosion protection and an interface • They reduce friction between metallic components and avoid fretting corrosion.

The material shall ensure high chemical and physical stability. Soft filling materials may be subdivided into the following main categories:

• Wax • Grease • Soft resins.

Waxes, i.e. paraffins with low oil content, and greases, i.e. metallic soaps with fatty oils, exhibit different behaviour. Waxes are stiffer and need to be applied at elevated temperatures of about 100 °C. Greases can be applied at ambient temperature but de-oil more rapidly and tend to absorb water. The main requirements for grease and wax are specified in Tables 5.6 and 5.7, respectively.



Characteristics Test method /Standard Acceptance criteria Conformity3)

Cone penetration, 60 strokes at 25° C (1/10 mm)

ISO 2137 NFT 60-132 or ASTM D217 [S28]

220 – 320 A, B

Dropping point ISO 2176, NFT 60-102 or ASTM D566 [S29] ≥ 150° C A, B

at 40°C DIN 51 817, NFT 60-191 or ASTM D 6184 [S30]

At 72 hours: ≤ 2.5 % At 7 days: ≤ 4.5 % Oil separation

at 100° C At 50 hours: ≤ 4 % A

Oxidation stability DIN 51 808 [S31] or ASTM D942-02

100 hours at 100°C: ≤ 0.06 MPa 1000 hours at 100°C: ≤ 0.2 MPa

A

168 hours at 35°C NFX 41-002 (salt spray) 1) Pass Corrosion protection 168 hours at 35°C

NFX 41-002 (distilled water spray) 1) [S32] or ISO/DIS 9227 [S46]

No corrosion

A

Corrosion test DIN 51 802 [S33] Grade: 0 A Cl-, S2-, NO-

3: NFM 07-023 2) ≤ 50 ppm (0.005%) A Content of aggressive elements SO4

2- : NFM 07-023 2) [S34] ≤ 100 ppm (0.010%) A 1) Test sample consists of a structural steel plate Fe510 with a surface roughness comparable to prestressing

wire and strand. The plate is covered with a layer of grease of a maximum thickness corresponding to the declared mass of filling material per linear meter of monostrand divided by the nominal strand surface per linear meter (based on nominal strand diameter).

2) Applied accordingly to grease. 3) A: Factory production control or guaranteed values by the manufacturer B: Control by independent body

Requirements for grease pertaining to flowability, de-oiling, water absorption, saponification, micro-biological resistance, coefficient of expansion must be satisfied or declared, see also [2], [7] and [12].

Table 5.6: Grease specification

Characteristics Test method /Standard Acceptance criteria Conformity2)

Congealing point NFT 60-128 [S35] ≥ 65°C A, B Penetration (1/10 mm) at -20°C NFT 60-119 [S36] No cracking A

Bleeding at 40°C BS 2000:PT121 (1982) modified [S37] ≤ 0.5 % A

Resistance to oxidation 100 hours at 100°C ASTM D942.70 [S38] ≤ 0.03 MPa A

Copper-strip corrosion 100 hours at 100°C ISO 2160 [S39] Class 1a A

168 hours at 35°C NFX 41-002 (Salt spray) 1) Pass A Corrosion protection 168 hours at 35°C NFX 41-002 (Distilled water spray)1)

[S32] or ISO/DIS 9227 [S46] No corrosion A

Cl-, S2-, NO-3 : NFM 07-023 ≤ 50 ppm (0.005%) A Content of

aggressive elements SO4

2-: NFM 07-023 [S34] ≤ 100 ppm (0.010%) A 1) Test sample consists of a structural steel plate Fe 510 with a surface roughness comparable to prestressing

wire and strand. The plate is covered with a layer of wax of a maximum thickness corresponding to the declared mass of filling material per linear meter of monostrand divided by the nominal strand surface per linear meter (based on nominal strand diameter).

2) A: Factory production control or guaranteed values by the manufacturer B: Control by independent body Requirements for wax pertaining to flowability, water absorption, micro-biological resistance, coefficient of expansion must be satisfied or declared, see also [2], [7] and [12].

Table 5.7: Wax specification



Soft resins have been proposed for the filling of the free length for “Equivalent systems” and for anchorage zones. However, no generally accepted specification is available at this time. Filling of the anchorage zone or sometimes of the free length is done by heating the wax to a temperature appropriate for the stay cable components, followed by gravity injection or pumping, depending on the situation. At normal temperature the material hardens sufficiently to lose its fluidity. Depending on the rheological properties of the material, it will be more or less sensitive to external temperature variations (as stays are generally directly exposed to solar radiation, temperatures may rise close to melting point). Tendency to return easily to a liquid state may result in leaks wherever the tightness is not sufficient, and the consequent loss of filling material will decrease its protective function. Filling of anchorage zones is also possible with grease injected at ambient temperature. Grease will expand at elevated temperatures and sufficiently leak tight sealing details are essential to avoid loss of grease at such temperatures (see stuffing boxes, Clause 4.5.3). Whatever filling material is used, it must not be aggressive to the prestressing steel. 5.6.2 Hardening filling materials This chapter focuses on cementitious grout as it may be used in proprietary anchorage zones and sockets, in saddles, or in the free length of short stay cables with low fatigue stress range, designed as “Equivalent systems” or “Systems with lower corrosion protection”, see Clauses 4.3.4 and 4.3.5. As a minimum, cementitious grout when used in stay cable systems has to comply with the fib report, Bulletin 20, [15], or the PTI specification [16] or equivalent specifications. Cement grout may under certain conditions provoke fretting corrosion if it is in direct contact with uncoated prestressing steel. In order to avoid harmful corrosion by fretting specific measures such as limitation of fatigue stress range and transverse contact pressure on the prestressing steel are required. The effectiveness of such measures should be proven by fatigue testing of grouted stay cable systems, see Chapter 6. When fresh cementitious grout is in contact with zinc, hydrogen is produced which may penetrate the steel and induce hydrogen embrittlement. This may happen primarily during the short liquid phase of cementitious grout, lasting a few hours. Hydrogen may then penetrate the strands at defects of the zinc layer and in the areas of the wedge marks. However, up to now hydrogen embrittlement has not been observed. This is due to the fact that stresses in the stay cables are low (≤0.45 GUTS) and that the strands in accordance with the specifications given in Chapter 5 are not susceptible to hydrogen induced stress corrosion cracking, see also, [1, 17] and (25, 95). For the sake of completeness, it should be noted that there are other filling materials, such as polyurethane and plastic materials with delayed curing, see [8], or reaction resins with special fillers for the anchorage zone. These, however, are not subject of this section. Reference should be made to the relevant specifications of the suppliers. 5.7 Stay pipes and other pipes 5.7.1 General Stay pipes for initial construction are typically made of monolithic cross section. However, for repair stay pipes made of two-piece half shells may be used to install the HDPE pipe over existing stay cables. The half shells may be connected by lock or press joints,



pushing or pressing the individual halves against each other to form a closed pipe. The half shells may also be connected by longitudinal welding. The different options are illustrated in Fig. 5.1.

MONOLITHIC

LONGITUDINAL OVERLAPPING WELD MONOLITHIC PIPE

DOUBLE WALL PRESS JOINT Fig. 5.1: Three different options of stay pipes (with or without surface corrugations to limit wind-rain induced vibrations) Stay pipes may be used as a corrosion barrier (HDPE pipe with filler, see Fig. 4.1b). If not used as a corrosion barrier (such as for the system shown in Fig. 4.1a), they may serve other functions. In either case they may provide the following functions:

• Aesthetics by use of stabilised coloured pipes • Reduction of wind drag through the formation of a circular stay cable surface • Protection against vibrations induced by rain and wind with appropriate surface

corrugations. The effect of these corrugations on the drag coefficient of the pipe shall be verified

• Mechanical stability has to be checked for the external forces applied on the pipe.

If stay pipes serve as a barrier, they shall fulfil the following additional requirements:

• The pipe material has to be compatible with the filling material • The wall thickness has to be checked for the pressure of the filling material, if any is

used • The effects of thermal expansion have to be controlled • Depending on the material used, the corrosion or chemical stability have to be checked • Provision of encapsulation (leak tightness) and corrosion protection of the tensile

elements, if the pipe functions as a barrier (see Clause 4.3.3). For any stay pipe its mechanical properties and durability need to be specified. As stay pipes cannot be replaced easily, except as shown in Fig. 5.1, durability is an essential requirement. 5.7.2 Thermoplastic stay pipes Generally, thermoplastic stay pipes are made of HDPE. This material has sufficiently high mechanical properties and a good resistance to UV (test according to ASTM D3350 [S40] and ASTM D1693 [S41]). Such pipes show a high durability under ordinary conditions. Manufacturing methods allow either fabrication of the pipe in one colour or co-extrusion of a second colour on the external surface, and special treatment of the external layer for increased



UV resistance and also for aesthetic purposes. The pipes may be provided with helical ribs or dimples on the surface to control vibrations due to rain and wind, see Fig. 4.2. Material requirements for HDPE are specified in Table 5.8. The minimum wall thickness of stay pipes which are injected with fillers shall be Ø/17 (Ø = diameter of stay pipe in mm). The wall thickness of stay pipes which are not injected with fillers may be reduced to Ø/32 but should not be lower than 5 mm. Generally, stay pipes consist of straight segments, connected by mirror welding or by use of special sleeves. The connection shall be able to develop the yield strength of the monolithic stay pipe section. Only small diameter plastic pipes may be coiled in one piece, provided that only insignificant permanent deformations occur (coil diameter > 50∅). This requirement does apply to the stay pipe only. Requirements for prefabricated stay cables are provided in Chapter 7. 5.7.3 Steel stay pipes Materials for steel pipes shall be in accordance with Clause 5.3. For stainless steel see Clause 5.4. Minimum wall thickness of the stay pipe is ≥ ∅ / 50 (∅ = diameter) and ≥ 3 mm, if welding is anticipated. Other methods to form connections between individual pipe segments include sleeve couplers, threading, and spigot and socket (bell mouth). Property Requirement HDPE Test method Conformity 1) Melt index ≥ 0.35 g and ≤ 1.4 g per

10 minutes under 5 kg ISO 1133 [S20] A, B

Specific weight, Density ≥ 0.94 g/cm³ ISO 1183 [S21] A, B Carbon black 2.3 ± 0.3% ISO 6964 [S22] A Dispersion of the carbon black Index is max. 3 ISO 18553 [S23] A Distribution of the carbon black Index is max. C 2 ISO 18553 A Tensile strength ≥ 22 MPa on raw material

≥ 18 MPa on pipe ISO 527-2 [S24] A, B

Elongation at break at 23° C ≥ 600 % on raw material ≥ 350 % on pipe

ISO 527-2, 50 mm/minute (speed on test)

A, B

Elongation at break at –20° C ≥ 150 % on raw material ≥ 100 % on pipe

ISO 527-2, 50 mm/minute

A

Thermal stability under O2 ≥ 20 minutes at 210 °C, without degradation

ISO/TR 10.837 [S25] A

Thermal coefficient of dilatation Value to be declared by manufacturer

DIN 53752 [S26] A

Bending modulus ≥ 750 MPa at 23 °C ISO 178 [S42] A 1) A: Factory production control or guaranteed values by the manufacturer B: Control by independent body Table 5.8: Characteristics of HDPE stay pipe and verification of conformity 5.7.4 Other pipes The same requirements as specified above apply to other pipes such as recess/guide pipes and saddle pipes.


46 6 Testing of stay cable systems

5.8 Guide deviators Guide deviators are often made of a combination of steel (see Clause 5.3) and of elastomeric materials, such as rubber, natural rubber, synthetic material (poly-chloroprene, butyl rubber, etc.) or similar. Important properties of these latter materials are: Hardness of the material; stiffness of the component; and durability of the component. The supplier must specify, and warrant by inspections, the relevant material characteristics such as elasticity, hardness and durability. 5.9 Damping devices For special damping devices, the characteristics of the materials used need to be adapted to the following expected parameters of the stay cables:

• Temperature range • Displacement amplitude • Fatigue stress range • Frequencies and modes of vibration • Ageing and other environmental exposure conditions • And other relevant effects.

The relevant characteristics shall be declared by the supplier.

6 Testing of stay cable systems 6.1 General Three different levels of testing of stay cables are recommended:

(1) Initial approval (qualification) testing of the stay cable system (2) Suitability testing of the stay cable system for a particular project (3) Quality control testing of the stay cable components for a particular project.

The design and detailing aspects specified in Chapter 3 for SLS, FLS and ULS are only valid for stay cable systems which satisfy the stay cable testing specified in this Chapter. 6.2 Initial approval testing (qualification testing) The objective of initial approval testing of stay cable systems is to demonstrate the feasibility (practicability) and performance (reliability) of a proposed stay cable system design comprising a range of stay cable sizes and using the proposed materials. These tests are considered valid as long as there are no changes in relevant stay cable details. The different sizes of the stay cable system should be similar (anchorage or saddles), otherwise interpolation of sizes which are not tested may not be possible, see [12]. Initial approval testing of stay cable systems shall include:

• Three axial fatigue and tensile tests performed on typical cable sizes (one small, one medium, one large)

• One saddle test, if saddles are used, on a small to medium cable size



• One leak tightness test on a small cable size • Tests for the corrosion protection barriers, if necessary (see Clause 4.4.1).

For the above to apply, it is presumed that the stay cable system is made of a series of cable sizes which satisfy consistent design and performance criteria throughout the series. Once a particular stay cable system has successfully passed the initial approval tests specified above, it shall be deemed approved for general use in cable-stayed structures. Any change in material specification, structural details or leak tightness details will require re-testing of the fatigue and tensile tests or leak tightness test, respectively. If the supplier of a particular component is changed but the same material specification and structural details are used, only suitability testing in accordance with Section 6.3 will be required. 6.2.1 Anchorage fatigue and tensile testing A large number of stay cable tests were performed in the past as pure axial tests without flexural effects. However, installation tolerances, bridge deck deflections, and change of cable sag may introduce flexural effects into the stay cables near the anchorages. Flexural stresses due to some of these effects can be mitigated to some extent with the installation of adequate guide deviators near the anchorages. However, these guide deviators cannot eliminate all flexural stresses in stay cables. These guide deviators may also need to be removed if special damping devices to control cable vibrations are provided. Hence, recent recommendations such as [2] have tried to account for flexural effects in the approval testing of stay cables. fib recommends a fatigue test which includes flexural effects. As a simplification for practical reasons, the flexural effects are created with wedge-shaped shim plates beneath the anchorages which impose a rotation α=10mrad (≈0.6°) to the anchorage against the centre line of the stay cable assembly. This set-up allows testing in most existing laboratories without major modifications of the testing machine and is believed to be sufficiently representative of the real conditions in a cable-stayed structure. 6.2.1.1 Test specimen (Fig. 6.1) Two stay cable anchorages shall be assembled in accordance with the methods specified by the supplier, one a live end and one a dead end anchorage, if applicable, with the corresponding guide deviators to represent anchorage zones, transition zones and a minimum of 0.5m of the free length of the stay cable. The guide deviators shall be free to move longitudinally. Relevant accessories and corrosion protection details shall be included, if these may affect the fatigue and tensile strength of the stay cable system. Wedge blocking has to be considered, if applicable, see Clause 7.4. The main tensile elements (prestressing steel) shall be of the type intended for use in the stay cable system. The following data of the tensile elements shall be established:

• The main mechanical and geometrical properties of the tensile elements, including actual ultimate strength, to confirm compliance with the specified values in Table 5.1 and 5.2

• Fatigue testing of the individual tensile elements on one of the proposed three numbers of cycles and corresponding fatigue stress range to confirm the compliance with the specification in Table 5.2. However, at least 10 % of the samples shall be tested at the stress range specified for 2 × 106 cycles

• Calculated nominal (GUTS) and actual (AUTS) strength of the stay cable.



The length of the test specimen must fit the intended testing equipment but shall not be less than 3.5 m. If the stay cable system is to be used with different grades and types of prestressing steel, at least one test shall be done with a large cable size with the highest grade and/or load capacity. Cable sizes for the tests shall be chosen from the sizes shown by the system supplier in his brochure and shall represent a small, medium, and large size (but not necessarily the largest size) of the stay cable system. The largest cable size to be tested may be limited by the capacity of available test facilities. In Europe stay cables up to a capacity of about 73 15.7mm strands can be tested. In the USA a test facility with a capacity of up to 150 15.2mm strands is available. With stay cables with steel pipes, the stay pipe may function as an active load-carrying element, if the cable is injected with a hardening filler. In this case, filling of the test specimen shall be done while the cable is subjected to a stress of 75% of the fatigue range below the upper test stress. Injection shall be done at a lower stress as representative for the actual project, if the stay cables of the structure will be filled at a lower stress level. Injection of the filling material may be more representative of the conditions in the real structure if it is done while the test sample is inclined at about 30 degrees against horizontal. Components of the filling material shall be the same as those intended for use in the structure.

= 0,6° ! 10 mrad

"

DEVIATOR FREE TO MOVE

3,5m

# 0,5m "

(a) Actual test set-up (b) Principle of shimming to provide flexural effects Fig. 6.1: Stay cable fatigue and tensile test 6.2.1.2 Test procedure Testing has to be carried out by a qualified test laboratory. The stay cable specimen is mounted in the testing machine, observing the geometrical configuration intended to be used. The stay cable anchorages shall be supported on wedge-shaped shim plates with an angle α=10mrad and oriented such as to create an S-shaped cable profile, see Fig 6.1. The test specimen shall then be loaded to a maximum force of 45% GUTS. Subsequently, the specimen is subjected to a fatigue test with two million load cycles at an upper load of 45% GUTS, and an axial stress range as specified in Table 6.1. The test shall be done at ambient temperature with a test frequency of not more than 8 Hertz.

Upper stress 0.45 GUTS

Δσ (MPa) α(mrad) Strand stay cable Wire stay cable Bar stay cable

200 200 110

10 10 10

Table 6.1: Recommended stress range in MPa for stay cable fatigue testing



Alternative test procedures in which transverse displacements are applied to the stay cable such as to generate angular rotations of ± 10mrad at the anchorages may be considered acceptable instead of the above procedure. After completion of the fatigue test, the same specimen shall be subjected to an axial tensile test. The load shall be slowly and gradually increased until the maximum force resisted by the stay cable has been exceeded. 6.2.1.3 Measurements and observations The following measurements and observations shall be made and recorded:

• Description of test set-up and testing procedure • Compliance checking of the components with the specifications, hardness

measurement, a minimum of five ultimate tests on the single tensile elements • Complete record over the entire test period of the actual test parameters (cycles, stress

range, loads, etc.) • Relative displacement of the tensile elements with respect to the anchorage on at least

two elements • Relative displacements between anchorage components (e.g. wedge to anchor head) on

at least two components • Automatic detection of failures of tensile elements during the fatigue test (e.g.

acoustic) • Complete force-elongation diagram, continuously recorded during the tensile test • Measured maximum force • Elongation of the tensile elements on entire length of the specimen between bearing

plates at measured maximum force • After completion of the tensile test, the specimen shall be dissected and its

components shall be carefully examined. All failures of tensile elements or other components and their locations shall be identified. Examination of the specimen shall include any presence of moisture or corrosion on the tensile elements

• Photographic documentation of observations. 6.2.1.4 Acceptance criteria The following acceptance criteria shall apply:

• During fatigue testing, not more than the following number of individual wires may fail: - 2 wires if the total number of wires is less than 100 - 2% of the actual number of wires, rounded to the next whole number, if the total number of wires is 100 or more - Any failure of bars shall result in rejection of the stay cable system

• No failure shall occur in the anchorage materials, or in any component of the anchorage during the fatigue test. This includes cracks of welds and bolts in the anchorage and at connections to the anchorage pipe

• The stay cable specimen shall develop a minimum tensile force equal to 92% AUTS or 95% GUTS, whichever is greater, and an elongation at maximum force of not less than 1.5% of the specimen length between bearing plates

• No failure shall occur in the anchorage material or in anchorage components up to 95% GUTS or 92% AUTS. This requirement does not apply to cracking of wedges



• Presence of corrosion on the tensile elements found during the dissection of the specimen shall be submitted to the Designer for evaluation. In order to be acceptable, the signs of corrosion on the tensile elements shall be fully removable by wiping with a soft untreated cotton cloth. Any pitting corrosion shall be cause for rejection.

6.2.2 Saddle fatigue and tensile testing Saddles of stay cables shall satisfy the same fatigue and tensile performance as the stay cable anchorages, see Clause 6.2.1. Testing of a particular saddle design shall be done with one representative stay cable size as suggested in Clause 6.2.2.1 below. Saddles of smaller or larger stay cable sizes, but with similar design, may be confirmed based on geometrical similarity between the radius of curvature, RT, and the number of layers of tensile elements in the saddle pipe, nT, used in the test and those values intended to be used on a project, RP and nP, as follows:

RP / nP ≥ RT / nT.

The objective of the saddle fatigue and tensile test is to confirm the performance of the saddle in terms of fretting fatigue at the entrance into the saddle. The anchorages are not the subject of interest in this test. 6.2.2.1 Test specimen (Fig. 6.2) One stay cable saddle and two stay cable anchorages shall be assembled in accordance with the methods specified by the supplier. The test specimen shall include the anchorage zones with the guide deviators as applicable, and a minimum of 2m free length between the anchorage zones and the entrance into the saddle, with an inclination of about 30 degrees against horizontal. Relevant accessories and corrosion protection details shall be included, if these may affect the fatigue and tensile strength of the stay cable system. The main tensile elements (prestressing steel) shall be of the type intended for use in the stay cable system. The same data of the tensile elements shall be established as given in Clause 6.2.1.1. If the stay cable system is to be used with different grades and types of prestressing steel, the test shall be done with the highest grade and/or load capacity. The saddle test shall be carried out with a representative small to medium size stay cable with an ultimate capacity of at least 15 MN corresponding to approximately 55 15.7mm strands, or as may be limited by the capacity of available test facilities. With stay cables with steel pipe in which the stay pipe functions as a load-carrying element, the same grouting procedures apply as given in Clause 6.2.1.1. Similar to the anchorage testing in Clause 6.2.1 also the saddles shall be tested such as to include flexural effects at the entrance into the saddle. The flexural effects shall be created with a rotation α = 10mrad of the saddle assembly in the plane of the test specimen, see Fig. 6.2. and subsequent cyclic movements of the saddle in the vertical plane to create the specified stress range Δσ.



GUIDE

DEVIATOR

> 2m

STRESSING JACKS,

0,45 GUTS +

ULTIMATE

! -

!

2

STEP 1: Test set-up

=10 mrad (0.6°) CABLE

NOMINAL ALIGNMENT

VERTICAL MOVEMENT

"

~

!

!

! o

! u

SADDLE JACKS

! = 0,45GUTS

! = 0,45GUTS - !

STEP 2: Fatigue loading ! -

!

2

(MEDIUM)

"

u

o

o

o

30º

f

f

f

Fig. 6.2: Saddle fatigue and tensile test 6.2.2.2 Test procedure Testing has to be carried out by a qualified test laboratory. The stay cable specimen is mounted in the testing machine, observing the geometrical configuration intended to be used, i.e. usually with the free length tangential to the saddle and anchorages. The saddle assembly is then lifted by such a distance as to generate an angular rotation α = 0.6° (10 mrad) in the plane of the test specimen at the exit from the saddle, and the actual position of the saddle assembly recorded. The test specimen shall then be simultaneously loaded by stressing jacks at either end of the specimen to a maximum force corresponding to a stress of 45% GUTS - Δσ/2. The saddle shall be lifted in an upper position until the force in the stay reaches 45% GUTS, and the position of the saddle recorded. The saddle assembly shall then be lowered into a lower position by such a distance as to reduce the stay cable axial force measured at the anchorages to a stress of 45% GUTS minus the specified stay cable stress range Δσ in accordance with Table 6.1, and the actual position of the saddle assembly recorded. The fatigue test can then start by moving the saddle with the jacks for two million displacement cycles between the upper and lower position of the saddle assembly as recorded above. Every 500,000 cycles the forces at the upper and lower positions shall be checked and the positions corrected to create the specified forces, if necessary. The test shall be done at ambient temperature with a test frequency of not more than 8 Hertz. After completion of the fatigue test, the same specimen shall be subjected to a tensile test, loaded symmetrically by the stressing jacks at the anchorages, at the position with an angular rotation of α = 0.6° (10 mrad).



6.2.2.3 Measurements and observations The following measurements and observations shall be made and recorded:

• Description of test set-up and testing procedure • Compliance checking of the components with the specifications, hardness

measurement, a minimum of five ultimate tests on the single tensile elements • Complete record over the entire test period of the actual test parameters (cycles, stress

range, loads, movements, etc.) • Relative displacement of the tensile elements with respect to the anchorage on at least

two elements • Relative displacements between anchorage components (e.g. wedge to anchor head) on

at least two components • Movement of saddle during fatigue test • Automatic detection of failures of tensile elements during the fatigue test (e.g. acoustic) • Measured maximum force • After completion of the test, the specimen shall be dissected and its components shall

be carefully examined. All failures of tensile elements or other components and their locations shall be identified. Examination of the specimen shall include any presence of moisture or corrosion on the tensile elements

• Photographic documentation of observations. 6.2.2.4 Acceptance criteria The following acceptance criteria shall apply:

• During fatigue testing, not more than the following number of individual wires may fail: - 2 wires if the total number of wires is less than 100 - 2% of the actual number of wires, rounded to the next whole number, if the total number of wires is 100 or more.

• No failure shall occur in the anchorage and saddle materials, or in any component of the anchorage and saddle during the fatigue test. This includes cracks of welds and bolts in the anchorage and saddle, and at connections to the anchorage pipe

• The stay cable specimen shall develop a minimum tensile force equal to 92 % AUTS or 95 % GUTS, whichever is greater

• No failure shall occur in the anchorage material or in anchorage components up to 95 % GUTS or 92 % AUTS. This requirement does not apply to cracking of wedges

• Presence of corrosion on the tensile elements found during the dissection of the specimen shall be submitted to the Designer for evaluation. In order to be acceptable, the signs of corrosion on the tensile elements shall be fully removable by wiping with a soft untreated cotton cloth. Any pitting corrosion shall be cause for rejection.

6.2.3 Leak tightness testing The purpose of the leak tightness test is to verify the adequate sealing of the stay cable system between the free length and the anchorage to avoid the ingress of water into the anchorage zone. There may be other weak points in a particular anchorage design for the ingress of water into the anchorage zone, e.g. at bolted connections. If such details exist, they should be included in the testing or the detail alone may be subjected to water at a pressure of not less than the one specified for the leak tightness test.



The test procedure proposed below is based on the procedure specified by the SETRA Recommendations [2]. However, the test duration has been reduced. The procedure specified in the PTI Recommendations [1] was also considered but was felt to insufficiently represent the relevant effects of movements and temperature and therefore, was not retained here. 6.2.3.1 Test specimen (Fig. 6.3) One fully assembled stay cable anchorage, including transition zone, a minimum of 1 m of free length, tensile elements, and all sealing details (anchorage cap), coatings and sheathings, stay pipe and filler as applicable, as specified by the system supplier, shall be subjected to a leak tightness test. The following data of tensile elements shall be established:

• The main geometrical properties of the tensile elements, including the filler and sheathing, if any

• Mass of filler, if any • Thickness and outside diameter of sheathing, if any, over three diameters at 0°, 60°,

and 120°. One representative size of stay cable anchorage shall be tested. The specified ultimate strength of the tensile elements shall not be smaller than 7.0 MN, corresponding to approximately 27 15.7mm strands. 6.2.3.2 Test procedure Testing shall be carried out by a qualified test laboratory. Tests done in the supplier’s laboratory shall be accepted if all essential test stages are supervised by an independent witness. The leak tightness test specimen is mounted in the testing machine in a vertical position, observing the geometrical configuration intended to be used. The test specimen shall be loaded axially to a stress of 30% GUTS, at ambient temperature. The test specimen shall then be immersed into dyed water of a minimum of 3m head above the bearing plate, see Fig. 6.3. Subsequently, the specimen is subjected to 10 load cycles between the stress levels of 45% and 20% GUTS, and finally left under a load corresponding to 30% GUTS. Subsequently, the test specimen is subjected to a series of 8 cycles of temperature variations in the range of ΔT and imposed stay cable rotations Δα, in a sequence as specified in Fig. 6.4. The test parameters Δα and ΔT are specified in Table 6.2. The rotations Δα shall be applied at a frequency of not more than 1 Hertz. Guide deviators may be installed in the test specimen if they are intended to be permanently installed in all applications. The transverse movement amplitude shall be adapted to create the same angular deviation of ± 25mrad (± 75/3000). Stay cable stress: 30% GUTS

Rotation Δα Temperature Range ΔT

± 1.4° (± 25mrad) 40°C

Table 6.2: Leak tightness test parameters



STEELTUBE

DYED WATER

ANCHOR BLOCK

3,0m

MULTISTRAND JACK

FOR AXIAL LOADING

ANCHOR BLOCK ON SLIDING PLATE

SLIDING PLATE

ANCHOR BLOCK

PTFE INTERFACE

FOR ANGULAR DEVIATION

ANCHOR CAP

LEAK TIGHTNESS

e.g. SEALING

WITH GUIDE DEVIATOR

TRANSVERSE JACK

WITH TRANSVERSE JACK

= +75mm

= +75mm

CRITICAL POINT FOR

WITH

GUIDE DEVIATOR

CENTRAL

HEATING

SUPPORT

FRAME

= +75mm

3,0m

ALTERNATIVE WITHOUT GUIDE DEVIATOR

IF NECESSARY TEST CAP

DETAIL:

Note: Dyed water level to be 3m above critical point for leak tightness (see also Clause 4.4.1) Fig. 6.3: Leak tightness test set-up The rotation Δα shall be applied by lateral movement of the stay anchorage at the top of the specimen. The lateral movement shall be determined such as to create the rotation Δα at the location where the sealing of the individual tensile elements or the entire bundle of tensile elements between anchorage and transition zone / free length is achieved. Fig. 6.3 illustrates the dependence of Δα and lateral movement. For stay cable systems which do not have such well defined sealing details, the stay cable supplier shall propose where the rotation Δα shall be applied in the test, e.g. at the critical connection and / or transition between the free length and the anchorage zone such as the entrance into a socket anchorage. The proposal shall be reviewed by the Designer for acceptance for a particular project.



TIME

0,45

0,1

0,2

0,3

0,4

0,5

60

40

50

20

30

10

25

25

20

10

10

20

30

30 COLD HOT

>9h

>3h

>9h

CONSTANT LOAD

250 CYLES

10 L.C.

SOME

HOURS

LONGITUDINAL FORCE, GUTS TEMPERATURE

LOAD HISTORY

CYCLES °

ANGULAR

DEVIATION

!"

C

mrad

#9h

Fig. 6.4: Leak tightness test procedure 6.2.3.3 Measurements and observations The following measurements and observations shall be made and recorded:

• Compliance checking of the components with the specifications • Complete record over the entire test period of the actual test parameters (cycles,

temperature, movements, loads etc.) • After completion of the test, the specimen shall be dissected and its components shall

be carefully examined. Any presence of moisture and dyed water inside the anchorage and in particular on the surface of the prestressing steel shall be recorded

• Photographic documentation of observations.

6.2.3.4 Acceptance criteria The following acceptance criteria shall apply:

• The test specimen is considered acceptable if, after completion of the test and dismantling of the specimen, visual inspection shows that the dyed water has not entered the anchorage.

6.3 Suitability testing Basic materials and components of the stay cable system such as strands, pipe, and anchorage components shall satisfy the same specifications as the components used for the approval testing. However, they may be fabricated by different suppliers or processes than those used during approval testing.



The objective of suitability testing is to demonstrate the satisfactory performance of these materials and components of a stay cable system fabricated from a specific supplier and/or a process and intended for use on a particular project. Suitability testing of a stay cable system shall be done for each project (i.e. one test per project) and shall include:

• One anchorage fatigue and tensile test on one nominal cable size. The assembly of the test specimen shall be identical to the one for initial approval testing, see Clause 6.2.1.1. The specimen shall be tested with the actual type and source of tensile element intended to be used on the particular project. The specified ultimate tensile strength of the tensile elements installed in the test specimen shall not be less than 5.0 MN, corresponding to 19 Ø 15.7mm strands. Alternatively, several smaller test specimens may be tested with the same test procedure. However, the total number and total length of the tensile elements with these smaller test specimens shall not be less than those in the proposed test set-up with one specimen. The proposed test set-up and test procedure shall be submitted to the Designer for approval before testing. The test procedure, measurements and observations, and acceptance criteria shall be identical to those specified for initial approval testing, see Clauses 6.2.1.2 to 6.2.1.4. If the suitability test does not satisfy the acceptance criteria, the stay cable supplier has the choice between the following two options:

• If no change is made to the materials of the stay cable system, perform two more identical suitability tests. Both tests need to pass to make the stay cable system acceptable

• Change the materials (tensile elements) and repeat the suitability test. 6.4 Quality control testing The objective of quality control testing is to demonstrate that the properties of materials and components installed in the cable-stayed structure are equivalent to the properties of the materials which were used for initial approval and suitability testing. For the main stay cable materials, the tests listed in Table 6.3 shall be performed with the proposed test frequency. The corresponding test reports shall be submitted to the Designer for approval. Cementitious grout shall be tested on site as proposed by fib [15]. Other materials and components used on the project may be accepted based on QC certificates provided by the supplier. Additional quality control tests on the anchored tensile elements are sometimes performed by the stay cable system supplier at his own discretion. If such tests include fatigue testing, it is recommended to perform the fatigue tests at different stress amplitudes to obtain information on the Wöhler-Curve, see Fig. 3.2.



Material Type of test Test frequency Tensile element (strand, wire, bar)

Bare element: - Tensile strength with

elongation at break

- Fatigue test acc. to Table 5.2 at one of the three proposed cycle numbers but not less than 10% of the samples at 2 106 cycles (min. one)

- Deflected tensile test acc. to Table 5.2

- Weight of zinc coating acc. to Table 5.3

- Leak tightness test, acc. to Table 5.5

- Geometry of bare or coated tensile element as applicable

- Mass of filler, for sheathed tensile elements only, see Table 5.5

1 tests for every 20 tonnes of tensile element supplied for the structure 1)

2 tests for every 100 tonnes of tensile element supplied for the structure 1) 1 test series for every 100 tonnes 1 test for every 20 tonnes 1) 2 tests for every 100 tonnes 1) 1 test for every 20 tonnes 1) 1 test for every 20 tonnes of tensile element supplied for the structure 1)

PE/PP sheathing - Tensile strength, elongation, density and melt index after manufacturing, see Table 5.4

- Thickness of sheathing, table 5.5

- Friction resistance of sheathing on strand, see Table 5.5

- Impact resistance, see Table 5.5

3 tests for every 10 tonnes of sheathing supplied for the structure 3 tests for every 10 tonnes of sheathing supplied for the structure 3 tests every 100 tonnes 1) of prestressing steel 1 test for every 100 tonnes 1) of prestressing steel

Soft filling material Congealing point (wax), Dropping point (grease) and Cone penetration

3 tests for every 10 tonnes of filler supplied for the structure

HDPE stay pipe - Tensile strength, elongation, density and melt index after manufacturing, see Table 5.8

- Thickness of stay pipe

3 tests for every 10 tonnes of pipe supplied for the structure but at least one test for each stay pipe size including butt welds 3 tests for every 10 tonnes of pipe supplied for the structure but at least one test for each stay pipe size

1) But minimum of 3 tests per project Table 6.3: Quality control testing of stay cable systems


58 7 Installation

7 Installation 7.1 General 7.1.1 Quality management system The specialist contractor responsible for the installation of the stay cables shall have a quality management system in compliance with ISO 9000 standards [S43], or equivalent, covering all aspects of quality control, supply and installation of the stay cable system. Comprehensive literature on the subject exists; see [S43, 18 to 21]. 7.1.2 Qualification of personnel Generally, the cable manufacturer or supplier installs the stay cables, i.e. is the stay cable specialist contractor, or is responsible for providing site specialists. Key technical staff shall have adequate experience in the installation of stay cable systems. Personnel shall be suitably trained in the activities to be performed on site. Reference [21] includes specific requirements for the personnel of post-tensioning companies, its training and experience, and may similarly be applied to stay cable installation. 7.1.3 Execution documents The following documents shall be present on site:

• Assembly drawings of the stay cable system, with connections to the deck and pylon and with the vibration damping devices (if any)

• Certificates of the quality control testing of the stay cable components (traceability) • Deck construction programme • Tolerances on the structural parts of the deck and pylon (particularly for the stay cable

anchorage orientation) • Definition of the cable forces and elongations (from the Designer).

The following method statements for stay cables shall be present on site:

• Site preparation: Definition of the storage areas, access and platforms for the cable installation, space requirements for the stay cable installation

• Procedures for transport, storage and handling of the individual components • Procedures for prefabrication of the stay cables, if applicable • Procedures for site assembly before installation (anchorages, stay pipe, connections

including e.g. butt welding of HDPE stay pipes etc.) • Procedures for the stay cable components installation and stay cable erection • Procedures for temporary corrosion protection (if any) • Procedures for the temporary installation of vibration damping devices (if any) • Procedures for stressing, including measures to be taken in case of deviations from

specified force or elongation values • Procedures for filling of anchorages and stay pipe, as applicable • Procedures for final protection of anchorages, connections, etc. • Procedures for inspection at the end of construction for hand-over.

The relevant installation operations are considered below.



7.2 Shipment and storage of components Stay cable components shall be suitably packed for shipment and storage on site to protect them against mechanical damage, and corrosion. Storage conditions shall ensure that they are kept within an acceptable range of temperature and humidity. This applies in particular to:

• Main tensile elements packaging to avoid damage to steel and sheathing during transportation and storage, as applicable

• Anchorage components to avoid damage to corrosion protection and sealing, as applicable

• Stay pipes to avoid excessive and / or permanent deformations such as longitudinal curvature and / or deformations of the cross section (do not exceed the elasticity limit of the materials), see Clause 5.7.2

• Prefabricated stay cables shall be shipped to site on coils with sufficiently large diameter which do not cause harmful deformations to the stay pipes. At about 20°C a minimum coil diameter of 17 times the pipe diameter is typically required.

Metallic surfaces of components shall be protected against corrosion during shipment and storage. This may be achieved by applying the permanent protection in the factory or, if this is not the case, by applying a suitable temporary corrosion protection to the surfaces. Storage on site shall protect stay cable components from direct exposure to wind and rain. 7.3 Assembly and installation Generally, the following assembly and installation procedures are used for stay cables:

• Installation of stay cables completely prefabricated in a factory (Fig. 7.1) • Installation of stay cables pre-assembled on the site, e.g. on the deck, by crane with

spreader beams (Fig. 7.2) • Installation of stay cables assembled on site during installation (Fig. 7.3).

Assembly and installation procedures shall be adequately documented in method statements prepared by the specialist contractor responsible for the installation. The actual assembly and installation methods shall ensure that the tensile elements are installed parallel to each other. Installation of the stay cable anchorage supports (bearing plates and guide pipes) and the stay cable anchorages and saddles shall be within the specified tolerance. The actual installation tolerances of anchorages achieved on site shall be recorded and shall be verified by the Designer to satisfy the specified tolerances, see Clause 3.5.3. Prefabricated stay cables, and HDPE pipes in general, shall be installed such that they are not excessively bent. Adequate minimum radii of curvature of prefabricated stay cables and HDPE pipes shall be satisfied depending on actual temperature during the installation and on the equipment used to avoid damage to the HDPE pipe. At about 20°C a minimum bending diameter of 25 times the pipe diameter is typically required. Fig. 7.4 shows saddle details to avoid sharp bends of stay cables at the entry into the anchorages at the deck. Similar details can be used at the entry to the anchorages at the pylon. The stay pipe wall thickness must be sufficiently strong so as to prevent the formation of bulges at high outside temperatures, see clause 5.7.2. The length of prefabricated stay cables shall be within the specified tolerance. The stay cable supplier shall demonstrate the feasibility of the proposed welding procedures of the stay pipe with a series of test samples before the start of the installation of the stay pipe. The proposed procedures shall be approved by the Designer.


60 7 Installation

During the manufacturing process structural welds in steel pipes must be tested to 100%, e.g. by X-rays. For corrosion protection Clause 4.5.2 applies. During assembly care has to be taken not to overload or damage the stay pipes. The pressure during injection of filling material has to be limited (see Clauses 4.3.6 and 7.5). If the stay pipe is filled with grout or wax, its thickness shall be adequate, see Clause 5.7, and spacers shall be placed inside the pipe if a specific cover is required. Stay pipes shall be installed with sufficient allowance for thermal expansion, as required for the particular project. Stay cable anchorages and other exposed parts shall be suitably protected against ingress of rain and other water during construction. Installation of specific damping devices, cross ties, monitoring sensors, and alike shall be done such that the stay cable components and the stay cable encapsulation are not compromised nor damaged.

Fig. 7.1: Transport of prefabricated cables Fig.7.2: Installation with spreader beams

Fig. 7.3: Assembly of stay cable on site Fig. 7.4: Saddle detail to avoid sharp bents of stay pipe during installation into the anchorage at pylon and deck Installed anchorage components, tensile elements, and stay pipe shall be inspected for damage. Any damage which is judged unacceptable shall be repaired to the satisfaction of the Designer, or the component shall be replaced.



In the course of installation, damage to the HDPE stay pipes must not extend deeper than 2 mm or exceed 20 % of the wall thickness. Damage and cracks shall be repaired by welding or by using rehabilitation tapes, see Chapter 9. Another alternative would be to exchange or replace damaged pipe sections e.g. with half-shells or slotted tubes with longitudinal weld seams (Fig. 5.1). 7.4 Stressing and adjustment The stressing sequence and stressing forces and corresponding elongations are specified by the Designer for each installation and stressing stage of the stay cables. One value is used as target, the other as the control. The stressing operation can be achieved either by adjustment of the force in the stay cable or by adjustment of the geometry of the structure. The latter procedure is particularly suitable for flexible structures. If the stay elongations are specified the corresponding stressing forces shall be given by the Designer and be recorded on site for checking, and vice versa. The stay cable specialist installing the cables may need to convert the data provided by the Designer to suit his specific installation and stressing procedure. This comment applies in particular to the single strand installation and stressing procedures with monojacks. With these procedures one tensile element is installed at the time and immediately stressed to a predetermined force. When the next tensile element is installed and stressed, the force in the previously installed elements will change because of the deformations of the structure. This effect needs to be properly accounted for. Therefore, the stay cable specialist must determine the force in each tensile element of a stay cable by calculation such as to provide the specified total cable force once all the tensile elements have been installed and stressed. For this calculation the stay cable specialist needs from the Designer information on the stiffness of the cable-stayed structure (deck and pylon), see Clause 3.5.1. He also needs information on the actual construction loads on the deck during the stressing from the Contractor. Hence, a close cooperation of all parties involved is essential. For the actual stressing operation on site the stay cable specialist has to ensure that the overall total force in the stay cable is within acceptable tolerance of the specified value, and that the forces in the individual tensile elements are equal within acceptable tolerance. To consider temperature influences during the stressing operation (e.g. deflections of pylons due to differential temperature) and/or the influence of the variations of the stiffness of the structure (deck and pylon) and/or the tolerances of material properties of the tensile elements, on the total stay cable force, the specialist contractor may choose the following procedure for stressing:

• Stress the stay cable initially to a target of about 80% of the final stressing value • Measure actual force and elongation and compare the actual values with the

theoretical values • Extrapolate the actual values at 80% to the target value • Finalise the stressing to the modified target values.

The objective of achieving forces in individual tensile elements which are equal within acceptable tolerance may be assisted by load cell measurements or coupling of single strand jacks on a reference tensile element and the actually stressed element. Alternatively, or in addition to the above, the specialist contractor may apply an equalising procedure of the individual tensile elements at the end of the particular stressing stage. During this procedure, either a part or all of the tensile elements are lifted-off the anchorage, the force checked and adjusted, if necessary, to the specified force, and the tensile element seated again.


62 7 Installation

Stay cables shall be stressed using procedures and equipment which assure that the individual tensile elements of one stay cable have equal forces within a tolerance of +/- 2.5% of the final stressing force at the end of construction. The stay cable shall be stressed to the target value (force or elongation) and the control value (elongation or force) shall be within a tolerance of ± 5%. Stressing jacks shall be suitably calibrated with an accuracy of ≤ 1.0%. Calibration certificates shall be not older than 6 months. Either one of the following stressing equipment may be used:

• Multi-strand jacks (Fig. 7.5), stressing all tensile elements of the entire stay cable at the same time

• Single strand jacks (monojacks), stressing individual tensile elements of a stay cable one after the other (Fig. 7.6)

• Compact multi-strand jacks with a limited stroke (say about 50mm) may be used for final adjustment of the vertical alignment in particular if detensioning of the stay cable is required.

Any of the above equipment and procedures shall ensure that:

• Wedge bites on an individual tensile element do not overlap by more than 50% of the wedge length and allow the wedge to bite into a least 20mm of virgin strand surface

• No wedge bites remain inside the final length of the stay cable between anchorages. The above requirements mean that usually fine adjustment of the stay cable length shall be accommodated by ring nuts on the anchorages or equivalent. In particular any detensioning of the stay cable during final adjustment of the vertical alignment of the structure must be accommodated with the ring nut. The travel of the ring nut shall be sufficient to assure at least the above requirements, or as specified by the Designer, see Clause 3.5.2. Stay cable forces are often quite low at installation, and may increase significantly during construction and service life. Such significant changes of forces need to be addressed, e.g. by wedge blocking (power-seating), lubrication of components, etc. Blocking of wedges is particularly recommended if zinc or other coatings are applied on the tensile elements. Detailed procedures for power-seating or wedge blocking shall be available on site as applicable.

Fig. 7.5: Large multi-strand jack Fig. 7.6: Stressing of stay cable with monojack



If guide deviators are provided they shall be installed and adjusted such that the actual angular deviations of the stay cable in the transition zone and at the anchorage are within the specified acceptable values, see Clauses 3.1.4 and 3.1.5. 7.5 Corrosion protection Any exposed metallic surface on anchorage components, see e.g. Fig. 7.7, shall be protected against corrosion as specified in Chapter 4. If the permanent protection is only applied at the end of construction, or needs to be locally removed for installation, these exposed surfaces shall receive suitable temporary protection. With the recommended layers of protection as given in Chapter 4, temporary protection of the exposed surfaces of the tensile elements is provided by the zinc coating. For other protection systems, equivalent temporary corrosion protection is required, e.g. by corrosion-protective oils, nitrogen, dried air, or equivalent. Generally, anchorage components are factory-provided with corrosion protection, e.g. zinc or other protective coatings. Special care shall be taken when applying permanent corrosion protection by injection of the stay pipe with a filling material. During filling with wax as soft corrosion-protective compound special attention has to be paid, among other things, to providing and maintaining a suitable temperature (range of 50° to 100°C depending on the actual material) so as to attain a void-free filling of pipes. The thermal volume change during cooling of the wax is to be considered. In case of cement grouting of the free length, the relevant material specifications and procedures of the fib Recommendations for Grouting [15] shall be applied. Suitability tests for the grout are absolutely necessary, and grouting pressures need to be carefully controlled. Anchorage zones and caps shall be injected with the filler specified in the system documentation. This filler, if different, shall be compatible with the filler used on the tensile elements.

Fig. 7.7: Corrosion protection coating on anchorage bearing plate and cap


64 8 Inspection and monitoring

8 Inspection and monitoring 8.1 General All cable-stayed structures shall be designed and detailed to permit adequate inspection of the relevant stay cable components. At the end of construction, an initial inspection shall be performed to comprehensively document the as-built quality of the cable-stayed structure and the stay cables, see also [1], [22] and [S44]. During the design life of the structure the stay cables shall be inspected at regular intervals (included in general site surveillance) to either confirm the good performance or to detect any relevant damage early. If any damage is detected, this may be reason for an exceptional inspection, and the relevant component(s) should be subjected to maintenance, repair and / or replacement as applicable. Five different types of inspection are typically applied:

• Initial inspection • Routine inspection • Detailed inspection • Exceptional inspection • Monitoring.

Documentation of inspections of a structure may include, but may not be limited to, the following information:

• Date of inspection, name of inspectors • Programme of inspection • Data collected during the inspection and / or monitoring • Observation of defects, photographic documentation etc.

While inspection applies to the entire structure, this Chapter considers mainly the stay cables. 8.2 Initial inspection The initial inspection shall be performed at the end of construction, at the time of hand-over of the structure to the owner. This initial inspection shall establish a proper reference (“birth certificate”) of the structure and the stay cables for future inspections, and shall include at least the following:

• Survey of the superstructure alignment • Record of the actual stay cable forces • Record of temperatures (ambient, structure and stay cable components at the time of

the survey) • Periods of critical modes of vibrations of the stay cables.

8.3 Routine inspection Routine inspection is achieved as “walk-through” inspection on the structure typically performed once a year. Routine inspection may include, but may not be limited to, the following observations, made usually visually without the use of auxiliary instruments:



• Proper condition and position of stay pipes, welds, wrappings, guide deviators,

clamps, damping devices, etc. • Condition of anti-vandalism protection • Qualitative control of cable sag • Signs of stains, leaks and deformations in anchorage caps and plates • Checking of installed monitoring system • Unusual cable vibrations.

8.4 Detailed inspection Detailed inspection is suggested to be performed every three to six years on about 25% to 50% of the components. This should assure complete inspection of all components within 12 years. The amount / frequency of inspection should be such that all components are inspected at least once within their specified period between subsequent maintenance operations, see Table 4.3. For detailed inspections special measuring tools and adequate access means such as trolleys, scaffolding, etc. should be used. In addition to the controls for routine inspection, detailed inspection may include, but may not be limited to, the following examinations:

• Condition of the stay cable anchorages, rust formations • Uniformity of stay pipe surface • Damage in stay pipe • Defects at welded joints • Defects in filling materials • Opening of anchorage caps and check for presence of water, degradation of filling

material, etc. • Corrosion of tensile elements at exposed surfaces after removal of anchorage caps • Leak tightness of sleeves / boots • Conditions of:

- elastomeric guide deviators (tight fit, bolts) - damping devices (leakage, tight fit) - clamps, as applicable (e.g. tight fit)

• Corrosion protection of guide pipes and components of anchorage and transition zones • Condition of installed drains in the anchorage and transition zones • Condition of load carrying elements

- sag of stay cables - geometrical deviation between cable anchorage and structure

• A topographic control of the structure is recommended. In addition to the examinations listed under Clauses 8.3 and 8.4 above, the following special investigations may be performed as they may be specified in the inspection plan of the project:

• Non-destructive inspections of cables - as are usual with steel cables – may be carried out by means of the magnetic induction method [22] or other appropriate NDT (non-destructive testing) methods. If fractures are detected in the tensile elements (in accessible areas other than anchorage zones or guide deviators) visual inspections may be performed by cutting a window into the stay pipe

• Measuring of cable load by load cells, lift-off of anchorage with a suitable jack, or measuring of critical modes of vibrations with accelerometers on selected stay cables


66 9 Maintenance, repair, replacement and strengthening

• Careful opening of the stay pipe at relevant locations and investigation of the tensile elements and/or the filling material (only suggested if there is a reasonable doubt to find a problem)

• Removal and replacement of individual tensile elements for detailed investigation, if applicable (see Clause 4.2).

8.5 Exceptional inspection Exceptional inspections shall be carried out in case of damage due to accidents, vandalism or catastrophes. They may also be performed in case unexpected damage is detected during either a routine or detailed inspection. Finally they may be performed before hand-over of the structure to a new owner. The program of the exceptional inspection shall be adapted to the specific event for which it is called for. 8.6 Monitoring Continuous monitoring of stay cables with suitable equipment is still relatively rarely applied. However, suitable monitoring equipment and tools for transmittal of the data to the owner, Designer, or specialist companies are becoming more easily available and may offer additional important data on the performance of the stay cables and the structure. The following monitoring methods may be considered for stay cables:

• Load monitoring on some stay cables either with load cells for the entire stay cable or load cells on one individual tensile element of the stay

• Vibration monitoring on selected stay cables or groups of stay cables • Acoustic monitoring of stay cables may be applied on cable-stayed structures with

confirmed problems to monitor the development of breakages of wires and individual tensile elements. This may provide information on when appropriate action must latest be taken to avoid safety hazards.

9 Maintenance, repair, replacement and strengthening Stay cables shall be maintained in accordance with the maintenance program specified by the stay cable supplier to achieve the specified design life, see Chapter 4. Damaged stay cables must be repaired as soon as possible in order to prevent further damage to tensile elements, filling materials, HDPE pipe and anchorage components (FIP Recommendations [23]). Maintenance, repair, replacement and strengthening comprise:

• Maintenance (e.g. painting of steel parts, see Clause 4.5.2) • Special repairs (e.g. repair of stay pipe: Polyvinylidene fluoride tapes in accordance

with ASTM D1000, [S45], may be used in case of damage and for application of paint coats)

• Replacement of cables (e.g. after accidental damage) • Strengthening if necessary e.g. due to increased traffic loads.

In any case, all works carried out on the structure shall be recorded in the bridge record, including the following information:



• Date, location and type of repair work • Date of cable replacement, list and certificates of materials used for replacement, list

of contractors, stressing records • Details of structural modifications • Name of the responsible person in charge of the maintenance, repair and replacement.

10 References and literature 10.1 References [1] “Recommendations for stay cable design, testing and installation”, Post-Tensioning

Institute (PTI), Phoenix, Arizona, 2000 [2] “Cable Stays - Recommendations of the French interministerial commission on

Prestressing“, SETRA, Bagneux, France, June 2002 [3] Fürst, A., Marti, P., Ganz, H-R.: “Bending of stay cables“, Structural Engineering

International, IABSE, Zurich, February 2001, pp. 42-46 [4] Kovács, J.: “Zur Frage der Seilschwingungen und der Seildämpfung”, Die Bautechnik

(59), 1982, Heft 10, pp. 325 – 331 (On the question of cable vibrations and cable damping)

[5] Starossek, U.: “Bridge dynamic”, Vieweg, Wiesbaden, 1991 [6] Virlogeux M.: “Cable Vibration in Cable Stayed Bridges”, Bridge Aerodynamics,

Larsen Esdahl Editors, Rotterdam, 1998 [7] FIP Recommendation “Corrosion protection of prestressing steel”, London, 1996 [8] fib Bulletin 11, State-of-art report: “Factory applied corrosion protection of

prestressing steel”, Lausanne, 2001 [9] FIP Recommendation “Corrosion protection of unbonded tendons”, London, 1986 [10] Bournand, Y.: “Enhancing the durability of stay cables”, fib Congress, Proceedings,

Osaka, 2002 [11] FIP Recommendation “Recommendations for the acceptance of post-tensioning

systems”, London, 1993 [12] ETAG 013: “European Technical Approval of post-tensioning kits for prestressing of

structures”, EOTA, Brussels, June 2002 [13] “Stahlschlüssel”, Verlag Stahlschlüssel Wegst GmbH, Marbach, Germany [14] fib Bulletin 7, Technical report: “Corrugated plastic ducts for internal bonded post-

tensioning”, Lausanne, 2000


68 10 References and literature

[15] fib Bulletin 20, Guide to good practice: “Grouting of tendons in prestressed concrete”, Lausanne, 2002

[16] “Specifications for grouting of post-tensioned structures”, Post-Tensioning Institute

(PTI), Phoenix, Arizona, 2000 [17] FIP-Notes 1991/4 “Galvanisation of prestressing steels” [18] FIP Guide to Good Practice “Quality management systems for post-tensioned concrete

structures according to ISO 9001”, London, 1998 [19] FIP Guide to Good Practice “Quality assurance and quality control for post-tensioned

concrete structures”, London, 1986 [20] FIP Recommendation “Qualification and approval of prestressing contractors and

system suppliers”, London, 1998 [21] CEN Workshop Agreement CWA 14646 “Requirements for the installation of post-

tensioning kits for prestressing of structures and qualification of the specialist company and its personnel”, CEN, Brussels, January 2003

[22] FIP Guide to Good Practice “Inspection and maintenance of concrete structures”,

London, 1998 [23] FIP Guide to Good Practice “Repair and strengthening”, London, 1990 10.2 Standards [S1] prEN 1993-1-11: “Design of structures with high strength tensile elements” (in

preparation), Draft February 2002 [S2] ISO 12944 - Parts 1 and 2, “Paints and varnishes - Corrosion protection on steel

structures by protective paint systems”, 1998 [S3] EN 206-1 “Concrete: Specification, performance, production and conformity”, 2000 [S4] ASTM B117 “Standard practice for operating salt spray (fog) apparatus” [S5] XP A 35-037.1-3 “Torons en acier à haute résistance protégés gainés” [S6] EN 10204 “Metallic products; type of inspection documents” [S7] ISO 15630-3 “Testing of prestressing steel”, 2001 [S8] prEN 10138 “Prestressing steels”, Parts 1-4, Draft 2004 [S9] BS 5896 “Specifications for high tensile steel wire and strand for the prestressing of

concrete” [S10] NF XP A35-045 “Produits en acier - Armatures de précontrainte”



[S11] ASTM 416M “Standard specification for steel strand, uncoated seven-wire for

prestressed concrete” [S12] ASTM 421M “Standard specification for uncoated stress-relieved steel wire for

prestressed concrete” [S13] ASTM 722M “Standard specification for uncoated high-strength steel bar for

prestressed concrete” [S14] PC Wires and Strands: JIS G 3536 (1999) “Uncoated stress-relieved steel wires and

strands for prestressed concrete” [S15] PC Bars: JIS G 3109 (1994) “Steel bars for prestressed concrete” [S16] NF A 35-035 “Hot-dip galvanized smooth wires and strands for prestressing”,

AFNOR Paris, April 1993, new revision, July 2001 (only in French) or ECISS/TC 19/SC 2 N224: 2002-10 or zinc and zinc alloy coated prestressing steel wires and strands; Draft pr EN 10337:2003

[S17] EN 10244-1,2 “Steel wire and wire products, non-ferrous metallic coatings on steel

wire”, Parts 1 and 2 [S18] ASTM 882M “Standard specification for epoxy-coated seven-wire prestressing steel

strand” [S19] EN 10025 “ Hot rolled products for non-alloyed structural steels – Technical delivery

conditions ”, 1994 [S20] ISO 1133 “Plastics - Determination of the melt flow rate (MFR) and the melt volume

rate (MVR) of thermoplastics”, 1999 [S21] ISO 1183 “Plastics – Methods for determining the density and relative density of non-

cellular plastics”, 1987 [S22] ISO 6964 “Polyolefin pipes and fittings – Determination of carbon black content by

calcinations and pyrolysis – Test method and basic specification”, 1986 [S23] ISO 18553 “Method for the assessment of the degree of pigment or carbon black

dispersion in polyolfefins pipes, fittings and compounds”, 2002 [S24] ISO 527-2 “Plastics – Determination of tensile properties – Part 2: Test conditions for

moulding and extrusion plastics” [S25] ISO/TR 10837 “Determination of the thermal stability of polyethylene (PE) for use in

gas pipes and fittings” [S26] DIN 53752 “Prüfung von Kunststoffen – Bestimmung des thermischen

Längenausdehnungskoeffizienten“ (Testing of Plastics – Determination of the coefficient of linear thermal expansion)



[S27] ASTM G14 “Standard test method for impact resistance of pipeline coatings (Falling weight test)”

[S28] ISO 2137 “Petroleum products – Lubricating grease and petroleum – Determination of

cone penetration“ (NFT 60-132, ASTM D217 are considered equivalent) [S29] ISO 2176 “Petroleum products – Lubricating grease – Determination of dropping

point“ (NFT 60-102, ASTM D566 are considered equivalent) [S30] DIN 51817 “Determination of oil separation from lubricating grease under static

conditions” (NFT 60-191, ASTM D6184 are considered equivalent) [S31] DIN 51808 “Testing of lubricants; determination of oxidation stability of greases;

oxygen method“ (ASTM D942-02 is considered equivalent) [S32] NFX 41-002 “Protection against physical, chemical and biological agents – Salt spray

test” [S33] DIN 51802 “Testing lubricating greases for their corrosion inhibiting properties by

SKF EMCOR method“ [S34] NFM 07-023 “Liquid fuels – Determination of chlorides in crude petroleum and

petroleum products“ [S35] NFT 60-128 “Produits pétroliers – Détermination du point de figeage des parafines,

des cires, des vaselines et des pétrolata“ [S36] NFT 60-119 “Produits pétroliers – Détermination de la pénétrabilité au cône des

produits parafinaux“ [S37] BS 2000:PT121 “Methods of test for petroleum and ist products – Oil separation on

storage of grease” [S38] ASTM D942.70 “Standard test method for oxidation stability of lubricating greases

and the oxygen bomb method” [S39] ISO 2160 “Petroleum products – Corrosiveness to copper – copper strip test” [S40] ASTM D3350 “Standard specification for polyethylene plastics pipe and fitting

materials” [S41] ASTM D1693 “Standard test method for environmental stress-cracking of ethylene

plastics“ [S42] ISO 178 “Plastics, Determination of bending modulus“ [S43] ISO 9001 – ISO 9003 “Quality Systems” and EN ISO 9000 Series “Quality

Management Systems”, 2000



[S44] DIN 1076 “Ingenieurbauwerke im Zuge von Straßen und Brücken: Überwachung und Prüfung”, 1999 (Civil engineering structures for roads and bridges: Supervision and testing)

[S45] ASTM D1000 “Standard test methods for pressure-sensitive adhesive-coated tapes

used for electrical and electronic applications“ [S46] ISO/DIS 9227 “Corrosion tests in artificial atmospheres - Salt spray test”, 2004 10.3 Extended literature (1) “Cable-stayed and suspension bridges”, FIP/IABSE Proceedings, Deauville, France,

1994, Vol. 1 and 2

(2) Kanok-Nukulchai, W.: “Cable-stayed bridges, experiences & practice”, Proceedings of the International Conference on Cable-stayed Bridges, Bangkok, Thailand, November, 1987

(3) Gimsing, N. J.: “Cable supported bridges”, John Wiley & Sons, Chichester, 1993

(4) Menn, C.: “Prestressed concrete bridges”, Birkhäuser, Basel, Boston, Berlin, 1990

(5) Roik, K. et.al.: “Schrägseilbrücken”, Ernst & Sohn, Berlin, 1986 (Cable-stayed bridges)

(6) Walther, R.: “Ponts haubanés”, Presses Polytechniques Romandes, Lausanne, 1985 (Cable-stayed bridges)

(7) Girmscheid, G.: “Entwicklungstendenzen und Konstruktionselemente von Schrägseilbrücken”, Die Bautechnik (64), 1987, Heft 8, Seiten 256 - 267 (Tendencies of development and construction elements of cable-stayed bridges)

(8) Leonhardt, F., Andrä W. and Zellner, W.: “Entwicklung von weitgespannten Schrägseilbrücken”, in Beyer, Lange: “Verkehrsbauten”, Betonverlag, Düsseldorf, 1974 (Development of long-span cable-stayed bridges)

(9) Leonhardt, F. and Zellner W.: “Cable-stayed bridge”, IABSE Surveys, Periodica, 2/1980, p. 13

(10) Man-Chun Tang: “Die Schrägseilbrücken - eine Form der externen Vorspannung”, in Spannweite der Gedanken, Springer-Verlag, Berlin, 1987 (Cable-stayed bridges – A form of external prestressing)

(11) Matt, P., Müller H. R. and Morf, U.: “Cables for cable-stayed structures”, FIP-Notes, 1985/1

(12) Weitz, F. R.: “Schrägseilbrückensystems”, Thyssen Techn. Berichte, Heft 1/83 (Cable-stayed bridge systems)

(13) Dillmann, U., Gabriel, K., Schlaich, J.: “Seiltragwerke: Entwurf, Konstruktion und Bauausführung”, Institutsmitteilung, TU Stuttgart (“Cable-stayed structures: Design, construction and execution”, Institute informations, Technical University Stuttgart)



(14) Schlaich, J. and Bergermann, R.: “Fußgängerbrücken”, Institut für Baustatik, TH Stuttgart, Schwäbische Druckerei GmbH, Stuttgart, 1994 (“Pedestrian bridges”, Institute for Construction Analysis)

(15) Saul, R., Svensson, H. and others: “The Sunshine Skyway Bridge in Florida”, Die Bautechnik, 9/1984

(16) Jungwirth, D.: “Hochleistungsfähige Schrägseile aus der Sicht des Betonbauers”, Beton- und Stahlbetonbau, 11/12, 1988 (High-strength stay cables used in concrete construction)

(17) Saul, R. Svensson, H.S.: “On the corrosion protection of stay cables”, Stahlbau, 59/1990

(18) König, G. and Gerhardt, H. C.: “Nachweis der Betriebsfestigkeit gemäß DIN 4212 - Kranbahnen aus Stahlbeton und Spannbeton, Berechnung und Ausführung”, Beton- und Stahlbetonbau (76), 1982, Heft 1, Seiten 12 - 19 (Proof of fatigue limit state according to DIN 4212 - Crane supports made of reinforced concrete and prestressed concrete, design and execution)

(19) Andrä, W. and Saul, R.: “Versuche mit Bündeln aus parallelen Drähten und Litzen”, Die Bautechnik (51), 1974, Heft 9, Seiten 289 - 298 (Tests with bundles made of parallel wires and strands)

(20) Hirsch: “Kontrolle der wind- und erdbebenerregten Schwingungen weitgespannter Schrägseilbrücken”, VDI-Berichte, Nr. 419, 1981 (Control of the wind and earthquake-generated vibrations of wide-spanned cable-stayed bridges)

(21) Herzog, M.: “Vereinfachter Nachweis der aeroelastischen Stabilität von Hängebrücken”, Bauingenieur, 68, 1993 (Simplified proof of the aeroelastic stability of suspension bridges)

(22) Klöppel, K., Thiele, F.: “Modellversuche im Windkanal zur Bemessung von Brücken gegen die Gefahr winderregter Schwingungen”, Der Stahlbau, 12, 1967, sowie 7, 1975 (Model tests in the wind tunnel for the dimensioning of bridges against the danger of wind-generated vibrations)

(23) Eibl, J., et al.: “Baudynamik”, Beton-Kalender, Teil II, Ernst & Sohn, Berlin, 1988 (Structural dynamics)

(24) Schambeck, H. and Kroppen, H.: “Die Zügelgurtbrücke aus Spannbeton über die Donau bei Metten”, Beton- und Stahlbetonbau (77), 1982, Heft 5, Seiten 131 - 136, Heft 6, Seiten 156 - 161 (The Zügelgurt Bridge made of prestressed concrete over the Danube at Metten)

(25) Jungwirth, D.: “Durability of stay cables and improvements”, FIP/IABSE Congress in Lisbon, 1997, and FIP Congress in Amsterdam, 1998

(26) Andrä, W., Saul R.: “Die Festigkeit, insbesondere die Dauerschwingfestigkeit langer Paralleldrahtbündel”, Die Bautechnik (56), 1979, Seiten 128 - 136 (The strength, especially the fatigue strength, of long parallel wire cables)



(27) AIM “Fifth International Symposium on Cable Dynamics”, Santa Margherita Ligure/ Italy, September 15-18, 2001

(28) C. Petersen: “Schwingungsdämpfer im Ingenieurbau“, Maurer Söhne GmbH, München, 2001

(29) Birkenmaier, M.: “Fatigue Resistance of Tendons for Cable-Stayed Con-struction” IABSE Proceedings P-30/80, IABSE Periodica 2/1980

(30) Birkenmaier, M. and Narayanan, R.: “Fatigue Resistance of Large High Tensile Steel Stay Tendons,” IABSE Colloquium of Steel and Concrete Structures, Lausanne, 1982

(31) CEB Bulletin No. 189, 1989: “Durable concrete structures: Design guide” and CEB Bulletin No. 858, 1997: “New approach to durability design”

(32) “Guides to Good Practice – Grouting of Vertical Ducts,” Federation Internationale de la Précontrainte, 1978

(33) Hamilton III, H.R., Breen, J.E., and Frank, K.H.: “Bridge Stay Cable Corrosion Protection, I: Grout Injection and Load Testing, “, ASCE Journal of Bridge Engineering, May 1998, p. 64

(34) Augusto S.: “Evaluation of Degree of Rusting on Prestressed Concrete Strand”, PCI Journal, Vol. 37, No. 3, May-June, 1992

(35) Stallings, J.M., and Frank, K.H.: “Stay Cable Fatigue Behavior,” Journal of Structural Engineering, ASCE, Vol. 117, No. 3, March 1991, pp 936-950

(36) Tabatabai, H., Ciolko, A.T., and Dickson, T.J.: “Implications of Test Results from Full-Scale Fatigue Tests of Stay Cables Composed of Seven-Wire Prestressing Strand,” Proceedings of the 4th International Bridge Engineering Conference, Vol. 1, Transportation Research Board, Washington, D.C., August 1995, pp. 266-277

(37) “PTI Guide Specification – Acceptance Standards for Post-Tensioning Systems,” Post-Tensioning Institute, Phoenix, AZ, September 1998

(38) Grassl, M., and Kruppe J.: “Investigation on the Fatigue Stresses of the Stay Cables for the Rhinebridge Neuwied” (in German), Forschung Strassenbau und Strassen- verkehrstechnik, Vol. 367, 1982. Published by the German Federal Ministry of Transportation

(39) Circulaire n° 99-54 du 20 août 1999 instituant un avis technique des coulis d’injection pour conduits de précontrainte, délivré par la commission interministérielle de la précontrainte

(40) “VSL Stay Cables for Cable-Stayed Bridges”, VSL International, Losinger Ltd., Berne, Switzerland, January 1984.

(41) Goodyear, W.D.: “Stay Cable Fatigue Design Loading”, PCI Journal, Vol 32, No. 3, May-June, 1987



(42) Irwin, P.A.: “Wind Vibrations of Cables on Cable-stayed Bridges,” Proceedings, ASCE Structures Congress XV, Portland, Oregon, April 14-16, 1997

(43) Starossek, U.: “Cable Dynamics – A Review,” Structural Engineering International IABSE, Vol. 4, No. 3, 1994

(44) Davenport, A. G.: “The Dynamics of Cables in Wind,” Proceedings, International Symposium on Cable Dynamics, Liege, Belgium, October 19-21, 1995

(45) Hikami, Y., and Shiraishi, N.: “Rain-Wind Induced Vibrations of Cables in Cable- stayed Bridges,” Seventh International Conference on Wind Engineering, Aachen, Germany, 1987, Journal of Wind Engineering and Industrial Aerodynamics, Vol. 29, 1988, pp. 409-418

(46) Simiu, E., and Scanlan, R.H.: “Wind Effects on Structures,” Third Edition, John Wiley & Sons, New York, 1996

(47) Yamada, Y., Shiraishi, N., Toki, K., Matsumoto, M., Matsuhashi, K., Kitakawa, M., and Ishizaki, H.: “Earthquake and Wind-Resistant Design of the Higashi-Kobe Bridge”, Cable-Stayed Bridges: Recent Developments and their Future, Elsevier, 1991

(48) Matsumoto, M., Hikami, Y., and Kitazawa, M..: “Cable Vibration and its Aero-dynamic/Mechanical Control,” Proceedings, Vol. 2, IABSE/FIP Conference; Cable- stayed and Suspension Bridges, Deauville, France, October 1994, pp. 439-452

(49) Saito, T., Matsumoto, M., and Kitazawa, M.: “Rain-Wind Excitation of Cables on Cables-stayed Higashi-Kobe Bridge and Cable Vibration Control,” Proceedings, Vol. 2, IABSE/FIP Conference; Cable-Stayed and Suspension Bridges, Deauville, France, October 1994, pp. 507-514

(50) Miyata, T., Yamada, H., and Hojo, T.: “Aerodynamic Response of PE Stay Cables with Pattern-Indented Surface,” Proceedings, Vol. 2, IABSE/FIP Conference, Cable-Stayed and Suspension Bridges, Deauville, France, October 1994, pp. 515-522

(51) Kobayashi, H., Minami, Y., and Miki, M.: “Prevention of Rain-Wind Induced Vibration of an Inclined Cable by Surface Processing,” Proceedings, Ninth Inter- national Conference on Wind Engineering, New Delhi, India, 1995

(52) Virlogeux, M.: “Design of Cables for Cable-Stayed Bridges: The Example of the Normandie Bridge,” Proceedings, International Symposium on Cable Dynamics, Liege, Belgium, October 19-21, 1995

(53) Carne, T.G.: “Guy Cable Design and Damping for Vertical Axis Wind Turbines,” Sandia National Laboratories, Report SAND80-2669, 1980

(54) Pacheco, B.M., Fujino, Yi and Sulekh, A.: “Estimation Curves for Model Damping in Stay Cables with Viscous Damper, “ASCE Journal of Structural Engineering, Vol. 119, No. 6, June 1993, pp. 1961-1979

(55) Xu, Y.L., and Yu, Z.: “Vibration of Inclined Sag Cables with Oil Dampers in Cable- Stayed Bridges,” Journal of Bridge Engineering, ASCE, Vol., No. 4, Nov. 1988, pp. 194-203



(56) Tabatabai, H., and Mehrabi, A.: “Design of Mechanical Viscous Dampers for Stay Cable,” Journal of Bridge Engineering, ASCE, Vol. 5, No. 2, May 2000, pp. 114-123

(57) Larsen, A.: “Computer Simulation of Wind-Structure Interaction in Bridge Aero- dynamics,” Structural Engineering International (SEI), IABSE, Vol. 8, No. 2, May 1998, pp. 105-111

(58) Verwiebe, C.: “Exciting Mechanisms of Rain-Wind-Induced Vibrations” Structural Engineering International (SEI), IABSE, Vol. 8, No. 2, May 1998, pp. 112-117

(59) Tanaka, H.: “Aeroelastic Stability of Suspension Bridges during Erection,” Structural Engineering International (SEI), IABSE, Vol. 8, No. 2, May 1998, pp. 118-123

(60) Mendes, P. A., and Branco, F. A.: “Numerical Wind Studies for the Vasco da Gama Bridge, Portugal,” Structural Engineering International (SEI), IABSE, Vol. 8, No. 2, May 1998, pp. 124-128

(61) Geurts, C., Vrouwenvelder, T., van Staalduinen, P., and Reusink, J.: “Numerical Modelling of Rain-Wind-Induced Vibration: Erasmus Bridge, Rotterdam”, Struc- tural Engineering International (SEI), IABSE, Vol. 8, No. 2, May 1998, pp. 129-135

(62) Paulson, C., Jr., Frank, K. H., and Breen, J. E.: “A Fatigue Study of Pre- stressing Strand”, Research Report 300-1, Center for Transportation Research, The University of Texas at Austin, TX, April 1983

(63) “Fretting Fatigue in Post Tensioned Concrete”, Center for Transportation Research, University of Texas at Austin, Report # 465-2F

(64) Tabatabai, H., and Mehrabi, A.B.: “Bridge Stay Cable Condition Assessment Using Vibration Measurement Techniques,” Proc. of NDE98, Structural Materials Tech- nology III, SPIE Vol. 3400, San Antonio, TX, March 31 to April 3, 1998

(65) Teller, C.M., Suhler, S.A., and Matzkanin, G.A.: “Nondestructive Inspection of Fatigue Damage in a Stay-Cable Specimen Using the MPC System,” Final Report, DTFH61-89-P-00874, November 7, 1989, Federal Highway Administration, Washington, D.C.

(66) Teller, C.M., Suhler, S.A. and Matzkanin, G.A.: “Nondestructive Inspection of Fatigue Damage in a Second Stay Cable Specimen Using the MPC System”, Final Report, DTFH-1-90-P-00505, September 13, 1990, Federal Highway Ad- ministration, Washington, D.C.

(67) Barton, J. R., Teller, C. M., and Suhler, S. A.: “Design, Develop and Fabricate a Prototype Nondestructive Inspection and Monitoring System for Structural Cables and Strands of Suspension Bridges, Volume 1: Final Report,” Report No. FHWA/RD-89/158. U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., May 1990

(68) Teller, C.M., Suhler, S.A., and Matzkanin, G.A.: “Nondestructive Inspection of Stay Cables on the Pasco-Kennewick Bridge Using the MPC System”, Final Report, P10-00-208-89, February 20, 1990, Federal Highway Administration, Washington, D.C.



(69) Burkett, W.R., and Frank, K.H.: “Fatigue and Static Tests of 55-Strand Stay Cable Specimen for the Baytown Bridge,” Ferguson Structural Engineering Laboratory, The University of Texas at Austin, August 1989

(70) Suzuki, N., Takamatsu, H., Kawashima, S., Sugii, K., Iwasaki, M.: “Ultrasonic Detection Method for Wire Breakage”, Kobelco Technology Review (Japan), No. 4, August 1988, pp. 23-26

(71) “Test Report on Weather Resistance of Wrapping Tapes for Cable Stayed Bridges”, Shinko Wire Company, Ltd., Amagasaki, Japan, April 1984

(72) Berthier Y.: “Maurice Godet’s Third Body Approach”, Proceedings of the 22nd Leeds-Lyons symposium, 1996

(73) Dowson D.: “The Third Body Concept: Introduction of Tribological Phenomena”, Tribology Series 31 pp., 21-30 September 1996, Elsevier Publisher

(74) Berthier Y., Vincent L., Godet M.: “L’Usure et la fissuration induite en petits débattements: génèse, formalisme et remèdes”, Mécanique, Matériaux, Electricité, Vol. 428, October 1988

(75) Calgaro J.-A., and Lacroix R.: “Maintenance et réparation des ponts”, Presses de l’ENPC, 1997 (refer in particular to the chapter: Pathologie des câbles de suspension by Gourmelon J.-P.)

(76) Chauvin A.: “La construction du pont à haubans de Coatzacoalcos II – Annexe: Haubans à gaine métallique injectée”, Annales de l’ITBTP, January 1986

(77) Chauvin A.: “Developments in the Technology of Bridge Stays”, 10th International Congress of the FIP, New Delhi, February 1986

(78) Clements H., Cremona C.: “Etude mathématique du phénomène d’excitation paramétrique appliqué aux haubans de ponts”, Etudes et Recherches des Laboratoires des Ponts et Chaussées, Série OA18, LCPC Paris, January 1996

(79) Combault J., Conversy F., Thivans P.: “Structures haubanées, contraintes de flexion locale dans les haubans”, FIP Conference, 1982

(80) J. Combault: “Retensioning the Cable Stays of the Brotonne Bridge”, Bangkok Congress, Vol. 2, 1987

(81) Combault J., Conversy F., Thivans P.: “Structures haubanées, contraintes de flexion locale dans les haubans”, La Technique Francaise du Béton Précontraint, 11th FIP Congress in Hamburg, 1990

(82) Conti E. and Tardy R.: “External Prestressing in Structures, Non-linear Calculation Tests of Prestressed Beams”, AFPC Workshop on Behaviour of External Prestressing in Structures, Saint-Rémy lès Chevreuse, France, June 1993

(83) Cremona C.: “Courbe universelle pour le dimensionement d’amortisseurs en pied de haubans”, Revue Francaise de Génie Civil, Vol. 1, n°1/1977, pp. 137 to 159



(84) Dowel E.H., Curtis H.C., Scanlan R.H., Sisto R.: “A Modern Course in Aeroelasticity”, Kluwver Academic Publishers, 1989

(85) Foucriat J.-C.: “Effets du vent sur les grands ponts suspendus et à haubans ; évaluation des risques d’excitation des vibrations des haubans du Pont de Normandie”, Annales AFPC – ITBTP, October 1988

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(87) Irvine M.: “Cable Structures”, MIT Press Boston MA, 1981

(88) Kubo Y., Kato K., Maeda H., Oikawa K., Takeda T.: “New Concept on Mechanism and Suppression of Wake-Galloping of Cable-Stayed Bridges”, AFPC Conference on suspension and cable-stayed bridges, Deauville, France, October 1994, Volume II, pp. 491-498

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