design basis - vegvesen.no the safety level that is set for this design basis is to be maintained...

DESIGN BASIS

DESIGN BASIS

3/74

http://projects.cowiportal.com/ps/A058266/Documents/03 Prosjektdokumenter/03.6 Masterfiler/Prosjekteringsforutsetninger/RAP-GEN-001-Design basis Floating bridge.docx

DESIGN BASIS

ADRESSE COWI AS

Grensev. 88

Postboks 6412 Etterstad

0605 Oslo

TLF +47 02694

WWW cowi.no

OPPDRAGSNR. A058266

DOKUMENTNR. RAP-GEN-001

VERSJON 3.0

UTGIVELSESDATO 16.05.2016

UTARBEIDET Rolf Magne Larssen, Per Norum Larsen, Karl Strømsem og Bernt Sørby

KONTROLLERT Sverre Wiborg/Henrik Polk

GODKJENT Erik Sundet

DESIGN BASIS

4/74


Innhold

1 Introduction 7

2 INTRODUCTORY PROVISIONS 8

2.1 Area of application 8

2.2 Definitions 8

2.3 Purpose 9

2.4 Structural design 9

2.5 Documentation 10

2.6 Quality assurance 10

3 FUNDAMENTAL DESIGN PRINCIPALS 11

3.1 General 11

3.2 Design method 11

3.3 Service Life 11

3.4 Structural reliability 12

4 Functional Requirement 13

4.1 Water tightness 13

4.2 Design and Geometry 13

5 MATERIALS AND IMPLEMENTATION 16

5.1 Concrete structures 16

5.2 Steel structures 18

6 LOADS 20

6.1 General 20

6.2 Permanent actions 21

6.3 Variable actions 23

6.4 Accidental loads 32

6.5 Construction stage 35

7 DESIGN LOADS 36

7.1 Determination of load actions 36

7.2 Limit states 41

8 DESIGN CRITERIA 48

8.1 Restriction of movement of floating bridge 48

8.2 Concrete structures 49

8.3 Steel structures 50

DESIGN BASIS

5/74


9 EXPANSION JOINTS, BEARINGS AND EQUIPMENT 51

9.1 Bearings 51

9.2 Expansion joints 52

9.3 Equipment 52

9.4 Inspection and maintenance 53

9.5 Instrumentation 53

10 MOORING SYSTEM 54

10.1 General 54

10.2 Design procedure 54

10.3 Rules for construction 56

11 References 57

V-A 1 Wind environment and wind actions 60

1.1 Basic data 60

1.2 Wind environment based on NS-EN 1991-1-4:2005, 61

1.3 Power spectral density of wind turbulence and correlation between turbulence at two points 63

V-A 2 HYDROSTATIC AND HYDRODYNAMIC CLIMATE 64

V-A 3 OTHER ENVIRONMENTAL LOADS 74

DESIGN BASIS

6/74


DESIGN BASIS

7/74


1 Introduction

This document defines the basis of design and establishes the expected performance levels for the crossing

of Bjørnafjorden south of Bergen. The document covers the permanent bridge works. Special design criteria

for the temporary works shall be defined when the construction methods are known. Where no special design

criteria have been defined for the project, the design shall adhere to the applicable Norwegian codes,

standards and regulations.

DESIGN BASIS

8/74


2 INTRODUCTORY PROVISIONS

2.1 Area of application

These design rules apply to the feasibility study for crossing Bjørnafjord with a floating bridge.

In case of conflicting rules, the specific rules will govern over general rules.

2.2 Definitions

Terms used in the design premises have the following meaning:

Floating bridge

- A floating structure, designed for traffic loads directly applied on to the pontoons or on a separately constructed carriageway, which may have fixed or floating supports between the abutments.

Mooring system

- Arrangement of cables or similar structural elements that fix the floating bridge in the desired position. Mooring systems are split into the following parts: Bottom anchors (alternatively rock bolting), mooring lines and top connectors.

Buoyancy elements

- Pontoons or structural elements with similar characteristics that are connected to the bridge structure and mooring system. The buoyancy elements may or may not be completely submerged.

Abutment

- The adjacent structures to the bridge ending at shore and at "Flua". The abutment may be a part of the bridge mooring system.

Splash zone

- External surface that is periodically in contact with sea water

DESIGN BASIS

9/74


LAT

- Lowest astronomical tide

MSL

- Mean sea level

HAT

- Highest astronomical tide

Service Life

- The service life of the structure estimated from its completion date.

2.3 Purpose

The bridge structure and each separate element is to be designed such that the following criteria are met

during the required service life of the structure:

- The bridge is fit for purpose, and does not hinder traffic or other usage in its surroundings.

- Normal operation and maintenance is sufficient to keep the structure functional and operational

- Performs satisfactory under normal conditions in relation to amongst other displacements and dynamic responses.

- Secured watertight pontoons

- Capable of resisting all estimated loads and deformations with satisfactory resistance to withstand failure or conditions similar to a failure.

- Has necessary safety to withstand a none intended event.

2.4 Structural design

Floating bridges, both at the detail level and globally, will be designed to achieve a structure that:

- Will be built in a safe and secure manner.

- Will behave in a ductile manner in the Ultimate Limit State and local damages will not compromise the global integrity of the structure.

- A statically well-defined system with a simple stress development, where the calculation model corresponds to the actual structure.

- Local stress peaks is avoided.

- Is robust against changes in statical properties, variations in material parameters, corrosion and similar issues and constructural errors does not alter the stability and integrity of the bridge structure.

- Availability for inspections, maintenance and rehabilitation is satisfactory.

- Elements with shorter service life than the bridge service life are replaceable, eg. anchor cables, stay cables, bearings, expansion joints etc.

DESIGN BASIS

10/74


2.5 Documentation

Documentation requirements are defined in /1/.

2.6 Quality assurance

Requirements regarding quality assurance and internal control are defined in /1/

DESIGN BASIS

11/74


3 FUNDAMENTAL DESIGN PRINCIPALS

3.1 General

Floating bridges represent an area within engineering, where experience is limited and the design will show

signs of a pilot project. This implies that all involved parties must continuously evaluate both the design basis

and results.

The design assumptions should be in accordance with specified tolerance requirements for the construction

and installation of the bridge structure.

The safety level that is set for this design basis is to be maintained regardless of technical concepts or the

lack of written regulations for the given concept.

All design shall be in accordance with relevant Eurocodes as well as publication N400 and other rules and

regulations by the Norwegian roads administration.

3.2 Design method

The design is based on the limit state method. The purpose of the calculations is to prove satisfactory margin

for the dimensioning loads exceeding the resistance criteria for the range of limit states. The basis for the

design process is the partial factor method according to Eurocode NS-EN 1990.

3.3 Service Life

Floating bridges are designed on the basis of a 100 year service life (Design service life). The service life of

100 years should account for fatigue. Corrosion protection may have a shorter service life than 100 years, as

long as replacement of the corrosion protection system and its parts is possible.

Components and equipment with service life shorter than 100 years should be replaceable. The procedures of

replacing such components should be described.

DESIGN BASIS

12/74


3.4 Structural reliability

In general, the bridge is categorised as consequence class CC3 (High) and consequently reliability class RC3

in accordance with NS-EN 1990 Annex B. Inspection Level IL3 (extended inspection during execution,

requiring third party inspection) shall be applied.

Particular members of the structure may be categorised as consequence class CC2 (Medium) and

consequently reliability class RC2. For these members Inspection Level IL2 (normal inspection during

execution, inspection in accordance with the procedures of the organisation) shall be applied.

The level and methods of design supervision for the bridge will be deseeded by the Norwegian public roads

administration.

DESIGN BASIS

13/74


4 Functional Requirement

4.1 Water tightness

Buoyancy elements (pontoons) will be water tight, see chapter 8.2.2.

4.2 Design and Geometry

4.2.1 Road class

The road design should meet the requirements for design class H8 in /2/.

(Design class H8/H9 is to be revaluated by the NPRA)

Design traffic volume: 12000-14000 AADT (2040)

Speed limit: 110 km/h

4.2.2 Carriageway widths

The road is to be constructed with 4 lanes 3.5 m wide each, with 1, 5 m (3,0m for H9) wide outer shoulder.

Crossection design class H8

DESIGN BASIS

14/74


4.2.3 Guard rail

Strength class H2 with working width 1 m.

4.2.4 Protective Wind Screen

The documentation in this project in the present phase is based on a bridge without protective wind screen for

the traffic.

4.2.5 Alignment

The roads alignment must satisfy the requirements in /1/ and NA-Rundskriv 2015/2 from NPRA.

4.2.6 Freeboard

Freeboard is defined as the minimum vertical distance from the highest water level to the top of the floating

body's lateral surface, calculated in still water.

Freeboard for the construction is calculated with permanent loads; with unfavourable density of the

construction material including water absorption, permanent ballast, construction tolerances and reserve

ballast. For pontoons with moorings the permanent vertical force component from the mooring system should

be included in the calculation.

For construction parts that do not move with the tide, the freeboard should be measured from the highest

water level for a tide with a 100 year return period.

For an un-damaged construction the clearing to sea surface will be checked for environmental loads with 100

years return period, as well as 1 year environmental loads together with traffic load. The clearing should be

greater than or equal to zero for the mentioned load situations including dynamic effects.

For a damaged structure with unintended filling of the pontoon chamber the clearing to sea surface is checked

with a 100 year return period environmental load. The criteria for this situation will be decided in a later stage.

4.2.7 Structural weight contingency

A 4% structural weight contingency is included for all structural parts when calculating the freeboard. This is

included as permanent ballast in pontoons and can be taken out if the margins are exceeded. The structural

contingencies encompass the weight increase of pontoons and unintended weight increase of the

superstructure. An additional control of stability and dynamics must be carried out if the tolerances are

utilised.

DESIGN BASIS

15/74


4.2.8 Water ballast

Water ballast (sea water) is applied for ballasting in temporary phases.

Use of water as permanent ballast can be considered. If water is used its influence on the pontoons'

metacentre and dynamic behaviour (stability and sloshing) must be included in the calculation.

Compartments allocated for solid ballast shall not be used for filling of water ballast, neither in temporary

phases nor in permanent situation.

4.2.9 Water absorption

Water absorption of concrete panels with wetted surface is assumed to increase the weight by 1%. Any

change beyond this is treated as a variable load.

4.2.10 Maintenance

The structure should be designed such that easy access for inspection and maintenance is achieved. Outer

surfaces should have a slight decline to make sure there is good water runoff. Details should be designed

such that pockets of water do not occur.

4.2.11 Navigation channel

The vertical navigation clearance is defined as the clear distance from the water surface at level HAT to the

bridge deck soffit in free spans, and should not be less than:

- In navigation channel: 45 m

The requirement for vertical navigation clearance should include the deflection from traffic in the serviceability

limit state "frequently occurring".

Horizontal navigation clearance is defined as free width for ship passage, and should not be less than:

- In navigation channel: 400 m

- Outside navigation channel: No requirements

DESIGN BASIS

16/74


5 MATERIALS AND IMPLEMENTATION

5.1 Concrete structures

5.1.1 General

Handbook N400, /1/, and current standards apply with the following additions in the clauses below.

5.1.2 Material factors

Material factors should be used in accordance to NS-EN 1992-1-1: 2004/NA:2008 table NA.2.1N.

5.1.3 Concrete

The concrete, its aggregates and workmanship should be in accordance to the requirements in Handbook

R762, /3/, with necessary adjustments according to NS-EN-1992.

The floating bridge structure shall not be built by concrete with characteristic strength less than B45.

Abutments shall consist of B45 concrete.

Low density concrete may be considered over normal concrete where advantageous.

5.1.4 Reinforcement quality

Rebar quality should be of B500NC according to NS 3576-3 and EN 10080.

5.1.5 Reinforcement placement

All cross sections shall have sufficient minimum reinforcement to ensure controlled cracking.

All panels will have double sided reinforcement.

DESIGN BASIS

17/74


5.1.6 Prestressing steel and systems

Prestressing steel, its components and workmanship is to satisfy the requirements of EN 10138.

All prestressing ducts are to be grouted.

Prestressing cable anchorages shall be cast in with normal concrete cover requirements.

Cables that are scheduled to be replaced during the service life of the bridge, shall not be grouted. Protective

measures for corrosion will in these cases be specified and approved.

5.1.7 Minimum thickness requirements

Sufficient wall thicknesses should be used to achieve proper casting of the rebar with tolerances.

Construction joints and the junction between walls and the bottom slab is of specific design importance to

ensure a uniform and waterproof construction.

5.1.8 Concrete cover

Concrete cover Exposure class Minimum cover

Pontoon in splash zone

(Panels and slabs above -3)

external surface XS3 130 mm(2)

internal surface XS1 85 mm(1)

Submerged panels and bottom slab

( cast under dry conditions)

external surface XS2 85 mm(1)

internal surface XS1

85 mm(1)

Concrete casted submerged XS2 120 mm(2)

(1) Including 15 mm negative tolerance

(2) Including 20 mm negative tolerance

DESIGN BASIS

18/74


5.2 Steel structures

5.2.1 General

Handbook R762, handbook N400 and current standards apply with the following additions in the clauses

below.

5.2.2 Material factors

Material factors should be used in accordance to relevant sections of NS-EN 1993.

For checks in the ultimate limit state see: NS-EN 1993-2: 2006/NA:2009 NA. 6.1.

For fatigue checks see: NS-EN 1993-2: 2006/NA:2009 NA. 9.3 and NS-EN 1993-1-9: 2005/NA:2010 NA.3.

For stay cables and tension bars see: NS-EN 1993-1-11: 2006/NA:2009 NA.6.

5.2.3 Construction steel

Steel type and maximum thicknesses shall comply with the requirements in Norwegian Standards NS-EN-

1993-1 and NS-EN-1993-2.

Steel strength to be according to S355, S420 or S460.

5.2.4 Corrosion protection

All steel surfaces shall have sufficient corrosion protection. The corrosion protection shall be designed for the

structure's expected service life.

Steel surfaces exposed to air shall be protected with coating according to Handbook R762, /3/, unless

specified otherwise. For inner surfaces of box girder corrosion protection is ensured using dehumidification

system and a light zinc-rich primer.

Permanently submerged steel surfaces shall have cathodic protection in the form of either sacrificial anodes

or induced voltage. All steel surfaces in tidal and splash zones shall be protected by special corrosion

protection systems, generally combined with a 10 mm rust allowance.

Enclosed surfaces unavailable for inspection and surface treatments, such as the inside of pipes, steel hollow

sections etc. shall be airtight and the airtightness ensured by pressure test.

Enclosed surfaces available for inspection and surface treatments, such as steel box girders, hollow steel

towers etc. shall be watertight. If internal corrosion protection is ensured by low internal humidity, the structure

shall be airtight. Doors, hatches and other openings shall be equipped with gaskets and closing devices that

ensure the airtightness. Valves (or something similar) must be utilized to even out differences in pressure

between the inside and outside of the airtight structure.

Railing fixes, embedded details and other minor steel parts shall in general be acid proof.

DESIGN BASIS

19/74


5.2.5 Stay cables

Cables with parallel strands or spiral strands (locked coil) can be used for the main bridges. The design of this

project is based on parallel strands. Properties of stay cables with parallel strands is detailed below.

Design Standards

The design of tension components shall comply with the requirements of NS-EN 1993-1-11:2006+NA:2009

General requirements

Adjustment and replacement

Stay cable and tie-down cable shall be adjustable and each strands replaceable.

Robustness and Structural Integrity

Stay rupture and loss of strength and stiffness of the stays due to a vehicle fuel spill fire is not considered in

the current phase of the project.

Material Properties

Stay cables shall be type Group C (NS-EN 1993-1-11: Table 1.1) comprising bundles of parallel seven wire

(prestressing) strands, anchored with wedges.

Properties (in accordance with EN 10138-3: Strands) shall be adopted:

Parameter Property

Nominal Diameter 15.7mm

Nominal Area 150mm2

Tensile Strength 1860MPa

Minimum Breaking Load Pn 279kN

Elastic Modulus of single strand 195kN/mm2

Coefficient of thermal expansion αT = 12 × 10-6 per ºC

Table: Stay cable properties

In the absence of more specific data, stay cables may be assumed to have a self-weight of 1.20 times the

bare steel weight to allow for the stay tube, strand coatings and fillers etc. Corrosion protection

The cable stays will be comprised of galvanised, greased, PE coated strands contained within a HDPE outer

pipe. The HDPE outer pipe is assumed to be of the standard type with respect to diameter.

DESIGN BASIS

20/74


6 LOADS

6.1 General

The loads are divided into categories based on their nature and the likelihood of their occurrence:

- Permanent loads (G)

- Variable loads (Q)

- Accidental loads (A)

The classification of individual loads is shown below. Load designations are given with a symbol for the main

group as well as a symbol for type of load. Deformation loads are treated as permanent loads in accordance

to the Eurocodes.

Permanent loads (G)

- Self-weight G-W

- Permanent equipment (surfacing, railings etc.) G-Add

- Permanent water head (buoyancy) G-B

- Permanent ballast G-S

- Stay cable forces G-Cable

- Anchorage cable pretension G-Mor

Deformation loads (G)

- Shrinkage, creep, relaxation (deformation loads) G-D

- Prestress in prestressing tendons G-P

- Forced deformations from erection G-Id

DESIGN BASIS

21/74


Variable loads (Q)

- Traffic loads Q-Trf

- Temperature Q-Temp

- Tidal loads Q-Tide

- Waves (hydrodynamic loads) Q-Wave

- Current Q-Cur

- Wind Q-Wind

- Marine Fouling Q-M

- Additional unintended variable loads Q-L

Accidental loads (A)

- Ship impact forces

- Anchor impacts and loads from falling objects

- Filling of floating body

- Failure in mooring system

- Abnormal nature loads

- Failure in stay cables

6.2 Permanent actions

6.2.1 General

Permanent effects are loads that are constant within the considered time frame, and include:

- Weight of the construction, surfacing and any non-removable equipment.

- Weight of permanent ballast

- External hydrostatic pressure from surrounding sea water up to the mean water level with mean density (mean buoyancy)

- Cable stay forces

- Mooring cable prestress

For floating bridges an equilibrium group is made of these permanent loads, denoted G-EQ, which is treated

as one load group when combined with other loads.

Permanent loads linked to permanent deformations are also classified as permanent effects, such as:

- Prestressing of tendons.

- Shrinkage, creep and relaxation.

- Deformations applied to the construction as a result of erection or installation method.

DESIGN BASIS

22/74


For permanent loads the expected mean value is defined as the characteristic value. Buoyancy shall be

calculated based on the outer dimension of the construction without additions from fouling.

6.2.2 Self-weight (G-W)

The structures self-weight shall be calculated from the weight density of the relevant construction material.

The effect of potential water absorption shall be evaluated (assumed to be 1%). The greatest occurring weight

density of the concrete including reinforcement is used. If the density turns out to be lower, permanent ballast

must be put in to account for this. Alternatively the draft will be changed and the super structure must be

corrected for this.

Weight of steel: 77kN/m3

Normal weight concrete (reinforced): 26 kN/m3

Light weight concrete (reinforced and density class 2.0): 22 kN/m3

6.2.3 Equipment (surfacing, railings etc.) (G-Add)

Design road surface weight shall always be included in the self-weight

- 100 mm thick wearing surface on concrete: 2.5 kN/m2

- 100 mm thick wearing surface on steel: 2.5 kN/m²

Weight of railings: 0.5 kN/m per railing

Weight of wind screens: 3 kN/m per screen. (Not included in the present stage of project.)

6.2.4 Permanent water head (buoyancy) (G-B)

The water density with variations is stated in Appendix 1. The unfavourable value for the load effect

considered shall be used. Variation of the water's density is treated as a variable load, see chapter 6.3.9.

6.2.5 Permanent ballast (G-S)

Permanent ballast is fixed ballast.

Rock (aggregate): 20 kN/m3

Olivine: 24 kN/m3

Iron ore: 38 kN/m3

Permanent ballast include construction tolerances of 4 % (ref. 4.2.8). Additionally the fixed ballast can be used

to correct draft if the concrete's weight density including absorbed water deviate from the expected variation.

Preparation for future additional weight/ equipment may be done by using extra ballast until the extra weight is

installed. This must be included in the freeboard calculation. Stability calculations must take into account the

DESIGN BASIS

23/74


fact that all the fixed ballast could be "used up" by construction tolerances etc. The resulting change in GM for

the pontoon and bridge system shall be accounted for by running static and dynamic analysis.

6.2.6 Stay cable forces (G-Cable)

Applies to prestressing forces in cables of the main bridge that are included in the equilibrium group G-EQ.

6.2.7 Pretension in anchorage system (G-Mor)

Pretension in the mooring system is included in the equilibrium group G-EQ. For design of mooring lines ref

chapter 10.

6.2.8 Shrinkage, creep and relaxation (G-D)

Creep and shrinkage is applied in accordance with NS-EN 1992-1-1, 2.3.2.2, 3.1.4 and 5.8.4

Relaxation is applied in accordance with NS-EN 1992-1-1, 3.3.2 and 5.10.6.

6.2.9 Prestressing forces (G-P)

Applies to prestress tendons in concrete structures. Effects of friction and anchor losses at tendon as well as

the time dependent effects shrinkage, creep and relaxation shall be taken into account when determining the

prestress forces in tendons.

6.3 Variable actions

6.3.1 General Variable operational loads are loads linked to the expected use of the structure, and include:

- Traffic loads

Variable deformation loads are also regarded as variable actions, such as:

- Temperature

- Tides

Nature loads are usually regarded as variable actions, such as:

- Wind loads

- Wave loads

- Water current loads

Variable loads also include

- Marine Fouling (Including weight)

- Additional unintended variable loads

In the present stage effects of ice and snow is omitted.

DESIGN BASIS

24/74


6.3.2 Traffic loads (Q-Trf)

For traffic loads for influence lengths larger than 500 m the load model specified in “NA rundskriv 07/2015” will

be used. In this project we call this load model LMV. For load model LMV all traffic lanes are loaded with 9

kN/m and all pedestrian/cycle paths are loaded with 2 kN/m concurrently.

For traffic loads for influence length shorter than 500 m traffic loads according to EN 1991-2:2003 section 4

will be used. Both Load model LM1 and LM2 shall be considered. LM 1 is given below with reference to EN

1991-2 and NA to NS-EN 1991-2:2009 paragraph NA.4.3.2(3)

Qi = 1,0 for i = 1,2 and 3

q1 = 0,6

q2 = 1,0

q3 = 1,0

qr = 1,0

w = 10 m, i.e. n1=Int(10/3)=3.

DESIGN BASIS

25/74


Placement Axle loads [kN] Uniformly distributed

load [kN/m2]

Notional lane nr. 1 300 5,4



Remaining area 2,5

Load on pedestrian/cycle paths concurrent with other traffic loading: 2.5kN/m2

DESIGN BASIS

26/74


6.3.3 Temperature (Q-Temp)

Design for thermal loading is carried out in accordance to NS-EN 1991-1-5:2003+NA:2008 and NS-EN 1993-

2:2006+NA:2009.

Uniform distributed temperature variation

The girder is defined as “Type 1” structure (steel bridge, whit box section) after 6.1.1.

The isotherm chart in the national annex defines the lowest and highest air temperature whit a 50-year return

periode.

Figure 6-1 Left: Maximum air temperature, 50-year return period. Right: Minimum air temp, 50-year return period.

For Bjørnafjorden, the following air-temperatures will be:

1. Tmax= 32 ℃.

2. Tmin= -22℃.

For type 1 structures, the national annex NA.6.1.3.1 defines the uniformly maximum and minimum bridge

temperature as a function of max/min air temperature:

1. Te.max=Tmax+16℃= 48℃.

2. Te.min=Tmin-3℃= -25℃.

DESIGN BASIS

27/74


Assuming T0=11℃, which will be most favourable for the bridge during installation, the temperature variation

should be:

ΔTN.con/=T0-Te.min=11℃-(-25℃) = 36℃.

ΔTN.exp/=Te.max-T0=48℃-11℃=37℃.

ΔTk= +-37℃.

Bearings and expansions joints

The NS-EN1993-2 Bridges gives additional specifications for uncertainty of the temperature in A.4.2.

ΔTd=ΔTk+ΔTγ+ΔT0

Where ΔTγ is a safety addition to accounts for the uncertainty of the temperature difference in the bridge and

ΔT0 is a safety factors that accounts for the uncertainty of the bearings position at the reference temperature.

Since the uncertainly only is relevant for the expansion joint ΔT0=0.

ΔTk= 37℃.

ΔTγ= 5℃.

ΔTd=ΔTk+ΔTγ=37℃+5℃=+-42℃.

Temperature gradient over girder height

Values from the vertical temperature differences are found in the NS-EN 1993-2 national annex. For type 1

bridges; ΔTm.heat=18℃ and ΔTm.cool=13℃.

Assuming 100mm asphalt gives ksur=0.7/ksur=1.2.

DESIGN BASIS

28/74


Vertical linear variation temperature are then:

Top side hotter than bottom side: ΔTm.heat = 18℃ x 0.7=12.6℃.

Bottom side hotter than top side: ΔTm.cool = 13℃x1.2=15.6℃.

Combinations factors for uniform and gradient temperature:

ΔTm.heat (or ΔTm.cool)+ωN ΔTN.exp (or ΔTN.con)

ωM ΔTm.heat (or ΔTm.cool)+ ΔTN.exp (or ΔTN.con)

ωN=0.35

ωM=0.75

DESIGN BASIS

29/74


Temperature loads for concrete pontoons

For pontoons partly submerged, the following temperatures are considered:

Temperature gradient of the thickness of external walls/slabs: A B

External faces (sea/air) 10 -10

Inner faces (inside pontoon) 0 0

Temperature differences between structural parts of pontoons A B

Top slab 15 -15

Walls above MSL 10 -10

Walls/slabs below MSL 0 0

6.3.4 General information on environmental loads

The general basis in the Eurocodes is that the characteristic value of a variable environmental load on a

permanent structure is chosen as the least favourable load most likely to occur within a 50 year return period.

For a structures where the environmental loads are dominant it has been found to be more correct to define

characteristic environmental loads for different return periods directly and to use these loads directly into the

combination for relevant return periods, rather than to decide Ψ-values.,

Environmental loads include both wind, wave and sea current loads. It has been decided to treat these loads

as a characteristic load group (Environmental loads Q-Ek) in combination with other loads. Tidal variations is

at this stage treated as a separate variable load.

6.3.5 Hydrostatic and dynamic loads (Q-Wave and Q-Curr)

Hydrostatic and hydrodynamic loading shall be determined based on recognized theory in the field.

SINTEF has issued a report for this project providing some wave and current data, see ref. /4/. The project

group agrees that this data is not correct and therefore not a good basis for design. However, based on this

report, hand calculations for the wind and swell generated waves has been produced (documented in project

report NOT-HYDA-011). In combination with information from similar fjords a description of a design

environment for waves has been reached. It is presented in V-A 2 with suggestions for:

Description of the wave spectrum to be used

Description of directional spread

Description of the variation of the parameters mentioned above

Current parameters

DESIGN BASIS

30/74


Load effects from wind generated waves, swells and currents shall be determined. A double-peak spectrum

can also be used where this is considered appropriate. Analysis with waves will include first order effects,

effects of higher orders and sum-frequency effects.

The future analysis should include loads from vortex shedding.

A global dynamic analysis will be carried out to determine global dynamic load actions for hydrodynamic

loads. In the final stage of the project, such a dynamic analysis might be integrated with the static analysis to

produce reliable total loads. In the present stage of the project, the static and dynamic analysis are performed

with different calculation programs. Models used in these programs will be verified individually as well as

compared to each other in order to produce reliable total loads. Such an analysis must be detailed enough to

capture all the relevant natural periods of the structure.

Appendix V-A 2 contains more detailed information.

Slamming

Slamming shall in a later stage be analysed according to the methodology given in DNV-RP-C205.

Vertical slamming shall be considered for the pontoons if the draft is lower than the freeboard, calculated

according to the description given in chapter 4.2.6.

Horizontal slamming loads must be considered in relation to ship impact loads. If slamming loads are

assumed to be more severe with regards to the structural integrity of the pontoons than ship impact, a detailed

slamming analysis shall be performed.

6.3.6 Wind loads (Q-Wind)

Wind loads will be determined based on acknowledged theory in the field.

A basic description of the expected wind climate in the area has been developed in appendix V-A 1. The

description is based on the current codes, NS-EN 1991-1-4:2005, including national appendix NA:2009, as

well as supplementation from experiences obtained from similar projects carried out in Norway.

Load effects from wind is divided into static load effects from mean wind values and dynamic load effects from

dynamic wind response, and total load action is taken as the sum of these load effects. The standard

procedure used for calculation of wind loading response on dynamic sensitive bridges will be used. The

challenges to this procedure given by this special bridge structure is addressed in appendix V-A1

6.3.7 Tidal loads (Q-Tide)

Tidal loads are treated as a separate variable load and is not a part of the environmental load group. Tidal

variation is shown in V-A 2. Load case is defined relative to MSL (mean sea level). High water level load case

is HAT relative to MSL and low water level load case is LAT relative to MSL.

DESIGN BASIS

31/74


6.3.8 Combination of environmental loads (Q-E)

Environmental loads are comprised of wind loads, wave loads and current loads. These loads are treated as a

characteristic loads group (Nature loads Q-Ek) in combination with other loads. When establishing the

characteristic load with relevant return period the loads are combined as shown in the combination matrix

below.

We suggest to include a combination with the same return period on wind waves and swell for all return

periods. The rationale behind this is that swell is a result of a storm generating a near shore harsh condition

that is transferred to the bridge location through refraction and defraction. This means that the local wind

generated sea will be a result of the same storm hence the return period should be equal. The current is more

a result of tidal variation and it would probably not be correct to combine the same return period on current as

for the waves and wind as there is no clear statistical correlation.

However, at the present stage in the design it has been agreed to use the 100 year return period for all

environmental actions with the view that this is slightly conservative. At a later stage in the design it should be

discussed if a relaxation of this criteria should be done. The tidal loads will at this stage be treated as a

separate variable with the full characteristic values and not as a part of the environmental loads as explained

in last chapter. This is also conservative.

Return period Wind Waves Current Sea level

(tidal loads)

Wind generated Swells

1 1 1 1 1 Mean

10

10 10 1 10 10

1 1 10 1 Mean

10 10 10 10 Mean

100 100 100 10 100 100

10 10 100 10 10

100 100 100 100 Mean

10000 10000 10000 100 10000 Mean*)

100 100 10000 100 Mean*)

10000 10000 10000 100 Mean*)

*)Storm tides should be included

Fig. 1, Combination of return periods.

DESIGN BASIS

32/74


6.3.9 Marine Fouling (Q-M)

Marine fouling is described in Vedlegg V-A 2

6.4 Accidental loads

6.4.1 General

Accidental loads are loads imposed to the structure due to incorrect operation or extraordinary situations such

as:

- Ship collisions

- Unintended filling of buoyancy bodies

- Failure of a single element in the bridge structure's mooring system

- Extraordinary environmental loads

- Rupture of cable stays

- Submarine landslides

Representative values for accidental loads are generally nominal values determined from engineering

judgement and cannot be linked to a specified probability level. The probability of incidents that can be

disregarded in the analysis should not be greater than 10-4 per year, to the extent the accidental load can be

determined based on probability calculations.

DESIGN BASIS

33/74


6.4.2 Ship impacts The capacity must be evaluated for impact and post-impact considerations, where the load and material factor is set to 1.0.

Impact events for the floating bridge: - Head-on-bow collisions with bridge pontoons - Deckhouse collision with bridge girder - Head-on-bow collisions with bridge girder - Sideway collisions

The impact energies must be determined by independent risk analyses, incorporating collision zone for the

bridge structure, meaning all bridge elements exposed for ship collision. To account for added mass of striking

ship, 10 % of the ship mass should be used.

Local damage may be acceptable, but in such case the bridge must be evaluated for post-impact

considerations (ref EN 1991-1-7-2006, 3.2).

Post-impact denotes a limit state for a damaged condition of the bridge, with load and material factors set to

1.0. The limit state must be according to N400, which states that the environmental return period must be 100

years if not documented otherwise. A damaged condition may involve the following and more: - Filling of compartments in the pontoons

- Mooring line failure

- Local plastic damage of bridge girder and columns

Elaboration on head-on-bow collisions with bridge pontoons: Bow impact should be considered for the main sailing direction with a maximum deviation of 30o. (ref EN 1991-1-7-2006, 4.6.3 ). Elaboration on deckhouse collision with bridge girder:

Unless other data is provided, the following indentation curve should be applied for the impact event:

Figure 2: Indentation curve of deckhouse from the Storebælt project.

DESIGN BASIS

34/74


6.4.3 Accidental filling of buoyancy elements

Unintended filling of buoyancy bodies includes filling of one or two neighbouring chambers close to the sea. If

this causes unacceptable heeling of the structure, then linking chambers together to reduce the heeling due to

simultaneous filling may be relevant.

All pontoon compartments shall be fitted with permanent water detectors, as well as automatic pumps to avoid

unintended water access.

6.4.4 Extraordinary environmental loads

Neglected at this stage in the project.

DESIGN BASIS

35/74


6.5 Construction stage

6.5.1 General

During construction of floating bridges it is assumed that buoyancy elements have constant draft in all

construction stages. Temporary water ballast is used to ballast buoyancy elements to final draft. Structure

self-weights, surfacing and permanent equipment is compensated for with adjustment of water ballast to

ensure constant draft is maintained during the erection phase.

Permanent equilibrium groups are established for the relevant construction stages, consisting of structural

weights, buoyancy, temporary water ballast and weight of temporary equipment.

DESIGN BASIS

36/74


7 DESIGN LOADS

The structure shall be checked for the following limit states:

- Ultimate limit state (ULS)

- Serviceability limit state (SLS)

- Accident limit state (ALS)

- Fatigue limit state (FLS)

Design load effects in the different limit states is determined by combining the effect of characteristic loads

multiplied by the load coefficients given in the following paragraphs.

Geometric deviations should be included in the calculations with their most unfavourable tolerance limits in

situations where it can have especially unfavourable effects on the structure's safety.

Alternatives to the partial factor method can be considered in relation to checks of stability, design of

anchorages, as well as in determining bridge movements where dynamic effects are relevant.

7.1 Determination of load actions

7.1.1 General

Load actions shall be determined by using recognized methods that take into account the variation of loads in

time and space, the response of the structure, the relevant environmental and soil conditions, as well as the

limit state that is being controlled. Simplified methods can be used if it is sufficiently documented that they

provide safe results.

DESIGN BASIS

37/74


7.1.2 Non-linear effects

Non-linear effects shall be evaluated, e.g. by using linearized models which give results on the safe side,

when it can be of relevance due to load and response characteristics. If such a simplification is impossible

then a non-linear analysis shall be used.

7.1.3 Hydrodynamic and wind dynamic response

Load effects of wind, waves and current are calculated separately. For combined effects see procedure

outlined in Section 0.

Hydro dynamical response is calculated using methods that give a good description of the actual water

kinematics, the hydro dynamical coefficients and the interaction between fluid and structure. Calculation

procedure should include possible non-linearity in the load definition, including any non-linear behaviour of

moorings; if used.

Characteristic values of wave loading are found by:

› Simulation of 10 no. of 3 hrs storm conditions for each of the dimensioning sea states

› Simulate wind generated waves and swell generated waves simultaneous

› Extreme values taken as mean of the 10 maxima found in the simulations

› Characteristic values taken as mean extreme multiplied by 1.25; approximating the 95%

percentile in the extreme value distribution

Bases for the hydrostatic and hydrodynamic loading are given in V-A 2 “Hydrostatic and Hydrodynamic

climate”.

Wind loadings are determined based on the procedures described in NS-EN 1991-1-4. The procedure should

be based on the following characteristics:

› Wind as a Gaussian process

› Structure linear elastic

› Response also a Gaussian process

› Maximum thus Rice distributed

› Extreme values Gumbel distributed

Characteristic values for wind loading is taken as expected maximum for the Gumbel distribution

› Calculated from the standard deviation of the response and the corresponding peak factor.

› Peak factor dependent upon duration (T) and zero-crossing frequency nv

› Calculations will be based on 10 min duration period

Bases for the wind loading are given in V-A 1 “Wind Environment and Wind Loading”.

DESIGN BASIS

38/74


7.1.4 Structural damping

The following values can be used for structural damping:

- steel: C = 0.005-0.008

- concrete, uncracked: C = 0.008

- concrete, cracked: C = 0.016

where C = / 2

= logarithmic decrement.

7.1.5 Correlation – combined environmental effects

Load effects of wind, waves and current are calculated separately. The combined effects are thus given by the

algebraic composition:

Q-Env = Q-Wind + Q-Wave + Q-Curr

The wind part consists of a static and a dynamic term:

Q-wind = Q-Wind_stat + Q-Wind_dyn

For the present location current is of marginal importance and is thus handled as a static loading term.

Summing this one have:

Q-Env = Q-Env_stat + Q-Env_dyn

where:

Q-Env_stat = Q-Wind_stat + Q-Curr

Q-Env_dyn = Q-Wind_dyn + Q-Wave

The procedure given in the separate sections for wind and wave describe the calculation of characteristic

values for each of these load effects. The remaining challenge is thus to find an appropriate rule for the

combination of these extreme values for the dynamic part of the environmental loading. The pure static part

will be present with full value always.

As the extreme dynamic values are found for different stochastic processes with different frequency content

and different response behaviour, it is unlikely that extreme values will occur simultaneous for all processes.

As different responses for the same processes (as e.g. bending moment about the two axes) also are found

as expected extreme values, one must in addition determine the probability that these occur at the same time.

This task requires an additional response characteristic to be determined, the correlation between the different

processes and responses. If the correlation is complete (i.e. the correlation is ±1) the maximum values occur

at the same time and the appropriate combination is a summation of extreme values. If the processes are

DESIGN BASIS

39/74


uncorrelated (i.e. the correlation is 0) the combined extreme value may be found by the “square-root-sum-of-

squares”-rule.

The remaining task is therefore to determine the correlation and perform an adequate summation based on

the found correlation value.

An evaluation of the correlation between load effects from dynamic wind and dynamic wave will be performed.

Based on the result of this evaluation a summation rule between these two dynamic processes are

determined.

Further an evaluation of the correlation between different responses for the load processes will be performed.

Based on the result of this evaluation, combination factors are determined (i.e. the αnm factors in the following

table).

Combination factors for one environmental load process responses

Combination matrix

Nx Qy Qz Mx My Mz

Dom Nx 1.00 α12 α13 α14 α15 α16

Dom Qy α21 1.0 α23 α24 α25 α26

Dom Qz α31 α32 1.0 α34 α35 α36

Dom Mx α41 α42 α43 1.0 α45 α46

Dom My α51 α52 α53 α54 1.0 α56

Dom Mz α61 α62 α63 α64 α65 1.00

Nomenclature in Global Analysis: Nx – axial force (for bridge girder) Qy – vertical shear force

Qz – horisontal shear force

Mx – torsional moment

My – bending moment about strong axis

Mz – bending moment about weak axis

Based on the above matrix for the correlation between different responses for one load processes, the

different dynamic load processes are combined. In general all combinations should be evaluated. At this stage

of the process, the governing load reactions are identified in the different parts of the structure and

combinations are focused on these load reactions.

DESIGN BASIS

40/74


A typical example could be for the bridge girder where only dominant moments about weak axis and strong

axis are considered as results show that dominant torsion or axial load is not governing for the bridge girder.

Further dynamic wave loads are dominant over dynamic wind loads giving a combination factor of 1.0 to be

used for wave response and 0.6 for dynamic wind to reflect that the events are not fully correlated. This thus

result in the following table:

Dynamic waves Static wind Dynamic wind

Dominant force N Mx My Mz N Mx My Mz N Mx My Mz

Axial force (N) 1.0 0.4 0.4 0.4 1.0 1.0 1.0 1.0 0.6 0.4 0.4 0.4

Torque (Mx) 0.4 1.0 0.4 0.4 1.0 1.0 1.0 1.0 0.4 0.6 0.4 0.4

M strong axis (My) 0.4 0.4 1.0 0.4 1.0 1.0 1.0 1.0 0.4 0.4 0.6 0.4

M weak axis (Mz) 0.4 0.4 0.4 1.0 1.0 1.0 1.0 1.0 0.4 0.4 0.4 0.6

For this example, shear forces follows the generating bending moment.

DESIGN BASIS

41/74


7.2 Limit states

7.2.1 General The following has been taken into account when establishing the load coefficients:

- The possibility for loads to deviate from the characteristic values.

- The reduced probability for different loads contributing to the total evaluated load effect to achieve their characteristic values simultaneously.

- Deviations in the load effect calculation, to the extent that such deviations can be assumed to be independent of the construction material and design tolerance.

7.2.2 Ultimate limit state

The ultimate limit state shall be established for load combinations according to equation 6.10a and 6.10b in

Table NA.A2.4 (B) NS-EN 1990:2002/A1:2005/NA:2010.

The load descriptions are defined in section 6.1

An equilibrium group for characteristic permanent loads G-EQk containing self-weights, buoyancy, fixed

ballast, stay cable prestress and mooring pretension is established.

Wind, wave and current loads are treated as a characteristic load group (Environmental loads Q-Ek) in

combination with other loads. For internal combination of environmental loads see section 6.3.7.

Characteristic load for environmental loads on bridge without traffic loading is chosen to a return period of 100

years.

Characteristic load for environmental loads on bridge with traffic load is calculated as the largest loading with

a return of 1 year, 50% of loading with a 100 year return period, or an environmental load with a return period

which corresponds to wind gusts of 35 m/s at bridge deck elevation (this applies to bridges without wind

screens).

γ is load factor in accordance to table NA.A2.4(B) in NS-EN 1990:2002/A1:2005/NA:2010.

Ψ0 is combination factor in accordance to table NA.A2.1 in NS-EN 1990:2002/A1:2005/NA:2010.

For bridge without traffic loads the environmental loads are only evaluated as dominant loads (can also

evaluate permanent loads, temperature and other loads as dominant).

1) For permanent loads high or low factors are used. It can be beneficial to use 0.9 instead of 1.0 as the low

factor for permanent loads for certain checks. This is evaluated separately.

DESIGN BASIS

42/74


The purpose of this table is to show the principles for combining loads at the ultimate limit. Not all possible

combinations are shown and other possible combinations must be evaluated by the designer for the individual

projects. E.g. the case of dominant permanent load combined with 100 year nature load without traffic has not

been included.

Load combination in ULS (comb B)

Dominant loads G- EQK Q-TrfK Q-TempK Q-EK(1y) Q-EK(100y) QK

m/traffic u/traffic

γ x Ψ0 γ x Ψ0 γ x Ψ0 γ x Ψ0 γ x Ψ0 γ x Ψ0

Permanent load

Permanent load 1) G- EQK 1.35/1.0 1.2/1.0 1.2/1.0 1.2/1.0 1.2/1.0 1.2/1.0

Variable loads

Trafficloads Q-TrfK 0.95 1.35 0.95 0.95 - 0.95

Temperaturloads Q-TempK 0.84 0.84 1.2 0.84 0.84 0.84 Environmental loads with traffic Q-EK(1y) 1.12 1.12 1.12 1.6 - 1.12 Environmental loads without traffic Q-EK(100y) - - - - 1.6 - Other loads QK 1.05 1.05 1.05 1.05 1.05 1.5

DESIGN BASIS

43/74


7.2.3 Serviceability limit state - characteristic

Ψ0 is the combination factor according to table NA.A2.1 in NS-EN 1990:2002/A1:2005/NA:2010.

The characteristic serviceability limit state shall be combined for load combination in accordance to Table

NA.A2.6 in NS-EN 1990:2002/A1:2005/NA: 2010.

Load combinations in the characteristic serviceability limit state shall be used to determine bearing

displacements, etc.

The load definitions are defined in section 6.1.


ballast, stay cable pretension and mooring pretension is established.



Characteristic load for environmental loads on bridge without traffic loads is determined for a return period of

100 years.

Characteristic load for environmental loads on bridge with traffic loads is calculated as the largest load with a

return of 1 year, 50% of loading with a 100 year return period, or an environmental load with a return period

which corresponds to wind gusts of 35 m/s at bridge deck elevation (this applies to bridges without wind

screens).

Ψ0 is combination factor in accordance to table NA.A2.1 in NS-EN 1990:2002/A1:2005/NA:2010.

For bridge without traffic loading the environmental loads are only estimated as dominant loads (can also

evaluate permanent loads, temperature and other loads as dominant).

DESIGN BASIS

44/74


The purpose of this table is to show the principles for combining loads at the serviceability limit. Not all

possible combinations are shown and other possible combinations must be evaluated by the designer for the

individual projects.

7.2.4 Serviceability limit state – infrequent combination The in-frequent combination in serviceability limit state shall be in accordance to Table NA.A2.6 in NS-EN 1990:2002/A1:2005/NA:2010. Load combinations in in-frequent serviceability limit state with 1 year return periods can be used to check deflections, displacements and accelerations. The quasi-permanent or frequently occurring load combinations are the basis for controlling cracking and compression zone height in accordance to Eurocode NS-EN 1992-1-1 (ref table NA.7.1N). However, these load combinations do not include the contributions from traffic, environmental loads and temperature simultaneously. For negligible environmental loads the in-frequent occurring and frequent occurring combinations give approximately the same load effect. For high environmental loads the two combinations give very different results. It is therefore reasonable to use the in-frequent occurring combination for control of the compression zone height and cracking where environmental loads and traffic loads can occur simultaneously. The load factor for dominant temperature load is 1.0 when checking compression zone height.

The load notations are defined in section 6.1.



Load combinations in the characteristic serviceability limit state

Dominant loads G-EQK Q-TrfK Q-TempK Q-EK(1y) Q-EK(100y) QK

w/traffic w/traffic

Ψ0 Ψ0 Ψ0 Ψ0 Ψ0 Ψ0

Permanent loads

Permanent loads G-EQK 1.0 1.0 1.0 1.0 1.0 1.0

Variable loads

Traffic loads Q-TrfK 0.7 1.0 0.7 0.7 - 0.7

Temperatur loads Q-TempK 0.7 0.7 1.0 0.7 0.7 0.7 Environmental loads with traffic Q-EK(1år) 0.7 0.7 0.7 1.0 - 0.7 Environmental loads without traffic Q-EK(100år) - - - - 1.0 -

Other loads QK 0.7 0.7 0.7 0.7 0.7 1.0

DESIGN BASIS

45/74




Characteristic load for environmental loads for the in-frequent combination is calculated with a 1 year return

period, i.e. Ψ1, infq x Ek(50 year) is replaced with 1.0 x Ek (1 year).

Ψ1 / Ψ1,infq are combination factors in accordance to table NA.A2.1 in NS-EN 1990:2002/A1:2005/NA:2010.

Load combinations in the in-frequent occurring serviceability limit state.

Dominant loads Q-TrfK Q-TempK Q-EK(1year) QK

Ψ1 / Ψ1,infq Ψ1 / Ψ1,infq Ψ1 / Ψ1,infq Ψ1 / Ψ1,infq

Permanent loads

Permanent loads G-EQK 1.0 1.0 1.0 1.0

Variable loads

Traffic loads Q-TrfK 0.8 0.7 0.7 0.7

Temperature loads Q-TempK 0.6 0.8 0.6 0.6

Nature loads Q-EK(1year) 0.75** 0.75** 1.0 * 0.75**

Other loads QK 0.6 0.6 0.6 0.8

*1.0 replaces 0.8 x 50 years in table A2.1, which is assumed to equal 1 year.

** 0.75 = 0.6/0.8. Scaled from 50 years to 1 year.

DESIGN BASIS

46/74


7.2.5 Accidental limit state (ALS)

The accident limit state shall be checked in two stages, a and b, with load factors as given in the table below.

a: The structure in a permanent situation is subjected to an accident load. The purpose is to control the

magnitude of local damage for such an action.

b: The structure in damaged condition. A damaged condition can be local damage as stated in a, or any other

more explicitly defined local damage.

Design values for loads in the accident state are in accordance to Table NA.A2.5 i NS-EN

1990:2002/A1:2005/NA:2010. Ψ2 is a combination factor in accordance to Table NA.A2.1 in NS-EN

1990:2002/A1:2005/NA:2010.

The load definitions are defined in section 6.1.





Characteristic load for abnormal environmental loads are calculated with a 10 000 year return period.

Characteristic load for environmental loads for a damaged structure is calculated with a 100 year return

period.

Possible transient effects must be evaluated.

Stay cable failure in the high bridge is not considered at this stage.

DESIGN BASIS

47/74


Load combinations with accident loads

Stage a

Stage b (damaged condition)

Abnormal nature loads

Ship impact Pontoon filled with

water Lost

anchorage

Other damage

Ψ2 Ψ2 Ψ2 Ψ2 Ψ2

Permanent loads

Permanent loads G- EQK 1.0 1.0 1.0 1.0 1.0

Variable loads

Traffic loads Q_TrfK 0.2 0.2 0.2 0.2 0.2

Temperature loads Q-TempK 0 0 0 0 0

Other loads QK 0 0 0 0 0 Environmental loads in event of damage

Q-EK(100

year) 0 0 1.0 1.0 1.0

Accident loads

Abnormal nature loads Q-EK(*) 1.0

Ship impact A 1.0

Pontoon filled with water A 1.0

Lost anchorage A 1.0

Other damage A 1.0

*10.000 years

7.2.6 Fatigue limit state

A simplified evaluation based on the relevant Eurocodes is carried out at this stage.

At a later stage a thorough design check should be executed.

DESIGN BASIS

48/74


8 DESIGN CRITERIA

The assumptions and limit state values in the following are taken from relevant codes and projects design

basis. Where relevant codes or other design basis documents are not found, experience data is extracted

from similar types of projects.

8.1 Restriction of movement of floating bridge

General

The Eurocodes and Hb N400, /1/ do not specifically give requirement for the movement of floating bridges.

Movement here is defined as deflection, rotations and accelerations. Fex. the deflection criteria L/350 given in

Hb N400 for traffic loads are not suitable for floating bridges. Thus, in this project the design group has

developed a set of limitations to control the movement of the bridge. The aim is to give adequate comfort and

safety for users. Regarding restriction of horizontal acceleration this is based on allowable tire friction and

vehicle speed of 110 km/h. The acceleration will also depend on the horizontal curvature of the bridge with

inclination of the deck. Thus a straight bridge will have a lower limit than a curved bridge with inclined deck. In

the next stage it is possible to reconsider this relative strict criterion based on improved knowledge of tire

friction or based on that vehicle speed can be regulated at severe storm condition. It is chosen not to have a

criterion of transverse movement of the bridge relative to the bridge length. If such a criterion is relevant it

must be linked to influence length of the girder or to lengths of dynamic mode shapes of the bridge girder. In

such a case it is suggested to limit the transverse deflection to L influence / 300 for a 1 year storm condition

(alternatively L infl /200).

The table below are based on information found on previous studies on floating bridges, motion criteria given

for pedestrian bridges and on tire friction as explained earlier. Below the table there are some footnotes to

explain the reason behind the criterion.

Motion Criteria Load Criterion

Vertical deflection due to traffic 0.7 x traffic Approx. 1 m

Rotation about bridge axis (roll) due to traffic 0.7 x traffic 1 deg

Rotation about bridge girder axis (roll) due to env. loads 1 year storm 1.5 deg

Vertical acceleration 1 year storm 0.5m/s2

Horizontal acceleration(curved/straight bridge) 1 year storm 0.5/0.3m/s2

Rotation about bridge axis (roll) due to static wind 1 year storm 0.5 deg.

DESIGN BASIS

49/74


The limit of vertical deflection due to traffic is chosen to maintain freeboard when traffic is combined

with one year storm. Thus, wave height + deflection due to wave loading + deflection due to traffic

shall be less than the chosen freeboard. As an example from the floating bridge the 1 year wave

height is approx.1.6 m, the vertical movement from environmental is approx. 0.25 m and the edge

deformation due to roll is approx. 0.5 m giving a total height of 2.35 m. If 4 m freeboard is chosen 1.65

m is left for deformation from traffic. Initially 1 m was decided since the freeboard was lower than 4 m.

Thus, a higher limit may be chosen in next stage, but it must be checked against available freeboard.

It must be noted that higher freeboard gives larger pontoons (especially for shallow pontoons).

Roll due to traffic and environmental loads is limited in order to keep the total inclination of deck to

7%. The inclination of unloaded bridge is 3 %. Thus, traffic combined with 1 year storm give a total

inclination of: 3% + tan( 1 deg + 1.5 deg) 100% = 7.4%.

Vertical acceleration is based on information from studies performed previous and from criterion for

pedestrian bridges.

Horizontal acceleration is based on tire friction and 110 kN/m, 0.5 m/s2 for curved bridge and 0.3m/s

for straight bridge.

8.2 Concrete structures

8.2.1 General

Concrete structures shall be designed in accordance to NS-EN-1992

8.2.2 Water tightness

The submerged boundaries of pontoons shall be water tight. This is ensured using criteria given in NS

3473:2003 in table A.9 column B “ Særlige strenge krav til tetthet”.

Thus, for bottom plate and external walls below MSL, zero membrane force in both directions are required.

The check is performed for in-frequent SLS combination which represent one year return period.

For construction elements above MSL crack criteria applies.

Where prestressing tendons are used, decompression criteria in table NA.7.1N should be used. It is

recommended to use in-frequent load combination in SLS in this check instead of frequent load combination

since the latter gives zero wave loading when other loads such as temperature is dominating and vice versa.

Interior walls are in intact condition not exposed to water pressure. In temporary phases some cells are used

for water ballast. In an accidental condition it is assumed that two adjoining chambers can be filled with water.

In this condition the penetration of water into adjoining chambers must be limited in order to avoid progressive

collapse. In order to ensure water tightness of internal walls, they will be designed to meet the serviceability

requirements of ACI 357 Guide for Design and Construction of Fixed Offshore Concrete Structure. This

standard limits reinforcement stress to 120 MPa. The hydrostatic pressure used evaluating serviceability shall

DESIGN BASIS

50/74


be those due to flooding to exterior sea level only. In addition shall the walls be checked for cracks criteria in

SLS in-frequent load combination.

8.2.3 Concrete joints

Joints subject to permanent water pressure or wave slamming shall have double seals.

8.2.4 Crack widths

The crack widths shall not exceed the values given in /1/ for load actions calculated in SLS – Infrequent

occurring combination. Water pressure in cracks should be accounted for where relevant.

8.2.5 Transverse shear

Water pressure in cracks will be accounted for regarding shear capacity checks of slabs subject to water

pressure.

Walls subject to water pressure should be considered for minimum shear reinforcement.

Shear reinforcement strain is limited to 0.9 x yield strain.

8.3 Steel structures

8.3.1 General

Steel structures shall be designed in accordance with NS-EN-1993.

The design as a whole shall as far as possible be based on the selected codes. Combining several codes and

recommended practices for the same structure shall be avoided.

DESIGN BASIS

51/74


9 EXPANSION JOINTS, BEARINGS AND EQUIPMENT

9.1 Bearings

General

The bearings shall be suitable for the type of loads, motions and environments for which the bearing structure

will be subjected. Parts of the bearing structure with an expected service life less than a 100 years should be

replaceable.

Design

Maximum forces are determined in the ultimate and serviceability limit states. Calculated values shall not

exceed the capacity guaranteed by the supplier.

The following effects shall be accounted for when checking bearing movements:

› Temperature

› Creep, shrinkage, prestressing and other potential loads

› Ambient temperature at installation of the bearing.

› Deformations (including elastic deformations) and movements due to construction method, foundation

settlements and other variables.

Maximum deflections shall be calculated in the characteristic serviceability limit state.

Design bearing displacements shall not exceed the upper deformations values given by the supplier.

It shall be ensured that the joint/bearing structure's displacement and rotational capacity is adequate for the

applied calculation model for checking of ultimate limit state.

DESIGN BASIS

52/74


9.2 Expansion joints

General

The expansion joint shall allow snow ploughing, and should be dampened to avoid unnecessary noise.

Expansion joints should not be placed at the bottom of sag-curves.

Extra water runoff systems should be included beneath the expansion joint, to make sure that water does not

run down on underlying structures.

Expansion joints shall be easily accessible. The expansion joint's wearing parts shall be possible to

disassemble for one driving lane at a time. Fasteners shall be resistant in contact with sea water and easy to

detach when being replaced.

Design

Expansion joint displacement and rotation shall not exceed the upper deformations values given by the

supplier.

In the SLS (characteristic) the distance between joint edges or slats that can be in contact with the wheels will

not exceed 80 mm.

9.3 Equipment

9.3.1 Drainage and bilge system

The study is based on using pumping system to be installed in all compartments of the buoyancy elements,

unless these are open to the sea, or filled with floating bodies that prevent water filling.

9.3.2 Hatches and ladders

Hatches, ladders, stairs and landings to provide clear access to closed compartments in the floating bridge

structure shall be included. Buoyancy elements shall have manholes with water tight hatches.

Walkways between rooms shall as far as possible lie above the water level.

9.3.3 Surfacing

The bridge structure and onboarding ramps shall have cover (wearing surfaces). The wearing surfaces shall

be designed as:

- Bituminous wearing layer on concrete or steel base courses, depending on the type of structure.

A 100 mm thick wearing surface will be taken into account in this stage of the design.

DESIGN BASIS

53/74


9.4 Inspection and maintenance

Access to all structural elements and equipment that requires regular inspection and maintenance during the

service life of the bridge structure shall be included.

9.5 Instrumentation

Detail design of instrumentation for continuous measurements of the structure's motions and other load

responses as well as monitoring of potential protection systems, reinforcement corrosion or other detoriation,

is assumed to be determined at a later stage.

Design and operation principles as well as scope will described at a later stage in the design process.

This also apply to installation of instruments and alarm devices for registration of un-expected large

accumulations of water in buoyancy elements.

DESIGN BASIS

54/74


10 MOORING SYSTEM

10.1 General

Parts of the mooring system will be designed for a shorter service life than the bridge. These will be designed

so that it is possible to replace single elements of the system, and a plan for replacement of components will

be developed.

10.2 Design procedure

Mooring design for the bridge will be performed based on the procedures as outlined in NS-EN ISO 19901-

7:2013 and DNV-OS-E301 Position Mooring. Safety factors are as requested based on NS-EN 1990.

Moorings should be checked for intact condition (ULS), for redundancy conditions having lost one or more

moorings (ALS) and for fatigue conditions. Further a check should also be done for the transient condition

between intact and redundancy condition.

10.2.1 ULS

The design for ULS will be based on the following design equation (from DNV-OS-E301) where the safety

factor is split into a partial separate safety factors for mean tension and partial safety factor for dynamic

tension:

where Sc is characteristic strength, Tc-mean is characteristic mean line tension and Tc-dyn is characteristic

dynamic line tension.

Sc is taken as dimensioning strength of the mooring line and based on NS-EN 1993-1-11 this is taken as

Suk/1.50 where Suk is characteristic value of breaking strength.

Main actions to be considered for mooring design are indirect actions from the bridge structure on the mooring

lines. Importance of eventual direct actions on mooring lines from current and vortex-induced vibrations

should be checked.

DESIGN BASIS

55/74


Indirect action originates from wave-induced actions, wind induced actions, current induced actions and from

pre-tensioning of the mooring system.

Wave induced actions are taken from the non-linear time domain simulations for the complete bridge model in

OrcaFlex as described in Chapter 6. The mooring system will be modelled fully in OrcaFlex using OrcaFlex

standard line modelling technique and the mooring will consist of chain, wire and potentially rope. Estimated

wave actions will be based on the same procedure as for the bridge structure itself; ten (10) 3-hour time

domain simulations.

Wind induced actions are taken from the NovaFrame wind analysis. In this analysis, the stiffness of the

mooring system is linearized based on information from the OrcaFlex model. Procedure will ensure that

appropriate linear stiffness is used.

Current induced actions are determined in the OrcaFlex model.

The characteristic mean line tension, Tc-mean, is taken as:

pre-tensioning of the mooring system

The characteristic dynamic line tension, Tc-dyn, is taken as:

wind induced actions, both static and dynamic parts

wave induced actions, including waves from local wind driven sea, swell waves, wave drift force,

second order wave loading

current induced actions

Regarding load combinations, for the ULS load we will use a partial factor of 1.1 for the mean line tension and

a factor of 1.6 for the dynamic line tension. The partial factor 1.6 on dynamic line tension is in accordance with

load factors given for environmental loads in NS-EN 1990. The use of partial factor 1.1 on mean line tension is

in accordance with NS-EN ISO 19901-7:2013 and DNV-OS-E301 Position Mooring (Table D1, section 2.01).

10.2.2 ALS

For the ALS condition the following events are to be checked:

Transient failure of the most loaded line at peak loading during a 100 year storm

Survival of a 100 year storm after loss of two lines

For these events, we propose to use the same methodology as for ULS. Regarding load combinations, we will

use a partial factor of 1.0 for the mean load and a factor of 1.0 for the dynamic load. Basing the definition of Sc

on NS-EN 1993-1-11, one did agree that this should be given as Suk/1.35 where Suk is characteristic value of

breaking strength. This seems to be a rather conservative figure but is used as basis for the performed

checks.

DESIGN BASIS

56/74


10.3 Rules for construction

The design shall allow for measurements and later adjustments of the pretension in single elements of the

mooring

All elements in the mooring system shall have sufficient corrosion protection. Cables shall be protected by

coating, possibly combined with cathodic protection.

Bottom anchors for the bridge structure's mooring system may be gravity anchors, piles, bored or driven

anchorages or a combination. The type of anchoring system is decided based on the soil conditions at the

location and the relevant mooring system.

Bottom anchors shall be designed to allow replacement of other elements of the mooring system (Regulations

for potential anchors driven into solid rock must be clarified independently.)

DESIGN BASIS

57/74


11 References

A: Rules and regulations from NPRA:

/1/ Statens vegvesen: Håndbok N400, Bruprosjektering (2015) NB: HB 185 versjon 1 nov. 2013 var inkludert i konkuransegrunnlaget

/2/ Statens vegvesen: Håndbok N100: Veg- og gateutforming (2013).

/3/ Statens vegvesen, Håndbok R762: Prosesskode 2- Standard beskrivelse for bruer og kaier (2012)

B: Norwegian Standards:

Norwegian Standard NS-EN199X, X being a figure from 0 to 9.

Refered to in the text

C: Reports and publications

/4/ Bridge across Bjørnafjorden Metocean conditions, SINTEF, 2013-05-08

/5/ SSPA: Fergefri E 39 - Ship allision risk analysis for the Bjørnafjorden crossing (several preliminary versions, last 2015.02.20)

/6/ Multiconsult: Bjørnafjorden – Bunn og grunnundersøkelser (2012.06.25)

/7/ IPCC, «Fifth Assessment Report,» (2009).

DESIGN BASIS

58/74


D: Other rules and regulations/Basic documents :

/8/ PETROLEUMSTILSYNET, Forskrift om utforming og utrustning av innretningermed mer i petroleumsvirksomheten (Innretningsforskriften), April 2010

/9/ PETROLEUMSTILSYNET, Veiledning til Innretningsforskriften, April 2010

/10/ NORSOK standard N-001, Rev. 7, Juni 2010

/11/ PETROLEUMSTILSYNET, Veiledning til Innretningsforskriften, April 2010

DESIGN BASIS

59/74


A. VEDLEGG 1 Environmental loading

DESIGN BASIS

60/74


V-A 1 WIND ENVIRONMENT AND WIND ACTIONS

1.1 Basic data

The purpose of this Appendix to the Design Basis is to describe a design wind environment and the design

methods that should be used for calculation of wind actions on the floating bridge across Bjørnafjord.

The basic data for description of wind environment and wind loading are developed based on NS-EN 1991-1-

4:2005, inclusive tha national addendum NA:2009, which is the Eurocode that handles wind actions on

structures.

Figure V1-1 Map of bridge location and location of Slåtterøy Fyr including wind data for the period

1995-2004 taken from the Sintef report

DESIGN BASIS

61/74


For a bridge like this, the regulations of the Norwegian Public Roads Administration (NPRA) requires

measurement of the wind climate. As such data do not exist at this point in the project, a simulation of wind

environment for the bridge location has been performed. This simulation uses available data from metrological

stations in the area, see Figure V1-1, in order to achieve a long term description of the wind environment at

the bridge site. The result of these simulations is described in report NOT-KTEKA-007 «Wind simulations».

The performed simulations did give a better understanding of several parameters related to the wind

environment. Especially the information related to directional distribution of the wind at the bridge location

have given valuable information in connection with the determination of wind generated waves. For the actual

use related to wind loading some questions was raised to their given results and it is therefore decided to use

the defined environment in NS-EN 1991-1-4:2005 directly.

1.2 Wind environment based on NS-EN 1991-1-4:2005,

The wind environment described in NS-EN 1991-1-4 is based on a reference velocity as the basic parameter

for description of the wind environment. The basic wind velocity vb is defined as mean velocity over 10

minutes, 10 meter above flat terrain having roughness length of 0.05 m. The basic wind velocity vb is defined

as (ref. eq. NA.4.1 in NS-EN 1991-1-4):

vb = cdir • cseason • calt • cprob • vb,0

where cdir is a directional factor, chosen here as 1.0 for wind perpendicular to the bridge to be

conservative, not in accordance with the simulations

cseason is a seasonal factor, which should be 1.0 for a random point in time

calt is a height level factor which should be 1.0 below timber line level

cprob is a factor related to return period, deviates from 1 for yearly probability of occurrence that

deviates from 0.02

Based on the above reference velocity, the 10 min mean velocity vm(z), at height z above terrain, may be

determined using the roughness coefficient for this terrain by:

vm(z) = cr(z) • vb

The roughness coefficient cr(z) at height z above terrain may be given by:

cr(z) = kT • ln(z/z0) where kT is the terrain factor and z0 is the roughness length. Parameter kT is given by eq. (4.5) in the code

(but is also given explicitly in the NAD):

kT = 0.19 (zo/zo,II)0.07

Turbulence is described by the turbulence intensity defined as:

𝐼𝑖(𝑧) = 𝜎𝑖(𝑧)

𝑣𝑚(𝑧) 𝑤𝑖𝑡ℎ 𝑖 = 𝑢, 𝑣 𝑜𝑟 𝑤

where σi is the standard deviation of the turbulence components (i = u for along wind turbulence, i = v for

lateral turbulence and i = w for vertical turbulence) and vm is 10 minutes mean velocity.

Turbulence intensity for along wind component, Iu, is determined by:

𝐼𝑢(𝑧) = 𝑘𝑡𝑡(𝑧)

ln (𝑧/𝑧0)

where ktt is a factor chosen as 1.0 (but may be determined more exactly).

Turbulence intensity for lateral turbulence, Iv, and vertical turbulence, Iw, may be defined as:

Iv(z) = 0.75 • Iu(z) and Iw(z) = 0.50 • Iu(z)

DESIGN BASIS

62/74


Based on NS-EN 1991-1-4 the following parameters are selected:

Basic wind velocity: vb = 26.0 m/s (return period 50 year)

Roughness length z0 = 0.01 (costal area)

Parameter kT kT = 0.17 (ref. Table NA 4.1, NS-EN 1991-1-4)

This give for the actual location the velocities given in table below.

Return period Velocity at 10 m

[m/s]

Factor Velocity at 52 m

[m/s]

1 22.9 0.75 28.4

10 27.6 0.90 34.1

50 30.5 1.0 37.8

100 31.7 1.04 39.3

Turbulence

intensity; Iu

14.5% 11.7%

These parameters are given without any directional factor even though such a factor will be present, see

below. In essence these paramours will be used for wind from west which will be the dimensioning case and

the criteria that will be checked.

DESIGN BASIS

63/74


1.3 Power spectral density of wind turbulence and correlation between turbulence at two points

The frequency distribution of the turbulence is in NS-EN 1991-1-4:2005 described by the Kaimal spectrum for

the along wind component. The remaining components are not described in the code. Here the NPRAs

Handbook N400 do give some additional information.

This give in total the following description:

𝑅𝑖(𝑧, 𝑛) = 𝑛 𝑆𝑖(𝑧,𝑛)

𝜎𝑖2 =

𝑎𝑖 𝑓𝐿(𝑧,𝑛)

(1+1.5 𝑎𝑖 𝑓𝐿(𝑧,𝑛))5/3

where 𝑓𝐿(𝑧, 𝑛) =𝑛 𝐿𝑢

𝑥 (𝑧)

𝑣𝑚(𝑧) and i = u, v eller w

n: frequency in Hz

Lu(z) is the turbulence integral length scale given by

𝐿𝑥𝑢(𝑧) = {

𝐿𝑡 (𝑧

𝑧𝑡)

∝

; 𝑓𝑜𝑟 𝑧 ≥ 𝑧𝑚𝑖𝑛

𝐿𝑡(𝑧𝑚𝑖𝑛

𝑧𝑡⁄ )

∝; 𝑓𝑜𝑟 𝑧 < 𝑧𝑚𝑖𝑛

The factor α = 0.30, reference height zt is 10 m and the reference length scale Lt is 100 m, zmin is defined in

NS-EN 1991-1-4

The coefficient ai has the value:

Along wind turbulence u: au = 6.80

Transverse turbulence v: av = 2.35 (9.4*1/4)

Vertical turbulence w: aw = 0.79 (9.4*1/12)

The statistical dependence between the turbulence components at two points at a given frequency shall be

described by the following normalized co-spectrum:

𝑅𝑒[ 𝑆𝑖1,𝑖2( 𝑛, ∆𝑠𝑗)]

√ 𝑆𝑖1(𝑛) ∙ 𝑆𝑖2(𝑛)= 𝑒𝑥𝑝 (−𝐶𝑖𝑗

𝑛 ∆𝑠𝑗

𝑣𝑚(𝑧))

where Δsj is the distance between the two points

i1, i2 = u, v, w and j = y, z.

Cij is given as: Cuy = Cuz = 10, Cvy = Cvz= Cwy = 6.5 og Cwz = 3.0

DESIGN BASIS

64/74


V-A 2 HYDROSTATIC AND HYDRODYNAMIC CLIMATE

Wave conditions

Various sources exists for wave conditions at the bridge location. SINTEF has issued a report for this project

providing some wave and current data, see ref. /4/. Based on the performed wind simulations (ref. NOT-

KTEKA-007 Windsimulations) a fetch analysis and diffraction analysis, based on US Army Shore Protection

Manual 1984, have been performed in order to establish probable data for wind and swell generated waves,

documented in project report NOT-HYDA-011.

Based on the fetch analysis and diffraction analysis, the following wind generated directional wave conditions

have been derived at the midpoint of the bridge with basis of 10 year and 100 year wind estimates. The

estimates are calibrated against simulations from NorConsult and checked against measured wave data.

1 year condition

1 year conditions

24.5 m/s Hs Tp

Heading (m) (s)

N 1.2 4.1

NNE 1.2 3.1

ENE 1.2 3.1

E 1.2 3.9

ESE 1.2 4.8

SSE 1.6 4.7

S 0.9 3.3

SSW 1.3 4.3

WSW 1.5 4.4

W 1.5 4.6

WNW 1.5 4.7

NNW 1.5 4.6

DESIGN BASIS

65/74


10 year conditions

10 year conditions

27 m/s Hs Tp

Heading (m) (s)

N 1.3 5.2

NNE 1.3 4.9

ENE 1.3 5.9

E 1.3 6.3

ESE 1.3 6.2

SSE 1.7 5.4

S 1.0 4.0

SSW 1.4 5.2

WSW 1.9 5.4

W 1.9 5.6

WNW 1.9 6.0

NNW 1.6 5.8

100 year conditions

100 year conditions

33 m/s wind Hs Tp

Heading (m) (s)

N 2.0 5.2

NNE 2.0 4.9

ENE 2.0 5.9

E 2.0 6.3

ESE 2.0 6.2

SSE 1.8 5.4

S 1.5 4.0

SSW 2.3 5.2

WSW 3.0 5.4

W 3.0 5.6

WNW 3.0 6.0

NNW 2.5 5.8

It should be noted that the wave conditions are based on 1-hour average wind as this is considered to be the

averaging period that fits best with fully developed wind seas given the fetch length in the fjord. The sea states

are slightly conservative as the 1 hour wind used in the analysis is 33 m/s while the updated design wind is

31.7 m/s.

DESIGN BASIS

66/74


For the design analysis carried out the wave height directly from North (N) has been reduced to Hs = 1.6 m as

the fetch analysis could not give Hs higher than this.

To investigate if the structure is sensitive to periods not defined above a variation of Tp based on formulas in

DNV-RP-C205 should be checked.

The wind generated sea states will be run with the JONSWAP with a γ=3.3. A variation of γ in the range of 2 –

4 should be checked. A directional spread for cosn(Θ –Θm) with n = 2- 5 will be used.

The 100-year design wind waves will be combined with swell as defined in the table below.

100 year swell conditions

Hs Tp

(m) (s)

0.4 12

0.4 13

0.4 14

0.4 15

0.4 16

0.2 17

0.2 18

0.2 19

0.2 20

DESIGN BASIS

67/74


For further investigations in the next phase an updated table will be used for swell waves, based on updated

and more extensive analysis performed during the late spring of 2015 as specified in a memo from SVV 8

May 2015 after a joint meeting to discuss metocean data. The resulting table is shown below:

100 year swell

conditions

Hs (m) Tp (s)

0.1 6

0.1 7

0.15 8

0.2 9

0.25 10

0.3 11

0.3 12

0.3 13

0.3 14

0.3 15

0.3 16

0.25 17

0.2 18

0.15 19

0.1 20

0.1 30

Swell will be entering the bridge area both through the north channel and the south channel and is caused by

the offshore extreme 100 year wave conditions diffracted into the fjord

Due consideration to this fact should be given when assessing the effect of potentially two swell directions

entering the bridge.

Swell will be modelled using the Jonswap spectrum with a γ=7 and a directional spread for cosn(Θ –Θm) with n

= 10-20 will be used.

The wave conditions derived using fetch and simplified diffraction analysis is believed to be conservative. SVV

is updating the design waves and in a next revision of this section the updated wave conditions should be

included. I

For fatigue analysis and fatigue life estimation and updated scatter diagram based on the updated wave

climate analysis by SVV April 2016 (overleaf).

DESIGN BASIS

68/74


FREQ

UEN

CYTABLEofHm0vs.Tp

Hs

dataat

A3

01jan1979

31des2015

TpMarg.

Cum.

Hm0

<11-1.5

1.5-2

2-2.5

2.5-3

3-3.5

3.5-4

4-4.5

4.5-5

5-5.5

5.5-6

6-6.5

6.5-7

7-7.5

7.5-8

8-8.5

8.59

9-9.5

9.5-10

>10

Sum

distr.

distr.

0.15

8080

15931

21019

6722

51752

47.7%

47.7%

0.20

3172

9229

661

13062

12.0%

59.8%

0.25

1133

5941

3986

11060

10.2%

70.0%

0.30

2717

5798

8515

7.9%

77.8%

0.35

1252

4955

597

6804

6.3%

84.1%

0.40

547

1886

1731

4164

3.8%

88.0%

0.45

307

1673

2004

3984

3.7%

91.6%

0.50

254

791

1691

2736

2.5%

94.2%

0.55

434

1431

182

2047

1.9%

96.0%

0.60

262

681

655

1598

1.5%

97.5%

0.65

126

307

440

873

0.8%

98.3%

0.70

86

203

301

590

0.5%

98.9%

0.75

44

122

211

377

0.3%

99.2%

0.80

33

76

154

10

273

0.3%

99.5%

0.85

17

20

131

19

187

0.2%

99.6%

0.90

32

47

38

117

0.1%

99.7%

0.95

18

26

27

71

0.1%

99.8%

1.00

10

26

25

61

0.1%

99.9%

1.05

713

28

48

0.0%

99.9%

1.10

25

11

18

0.0%

99.9%

1.15

46

10

121

0.0%

99.95%

1.20

12

81

12

0.0%

99.96%

1.25

15

17

0.0%

99.97%

1.30

14

38

0.0%

99.98%

1.35

21

710

0.0%

99.98%

1.40

22

40.0%

99.99%

1.45

14

50.0%

99.99%

1.50

22

0.0%

99.99%

1.55

11

0.0%

99.995%

1.60

00.0%

99.995%

1.65

11

0.0%

99.996%

1.70

22

0.0%

99.998%

1.75

11

0.0%

99.999%

1.80

11

0.0%

100%

1.85

00.0%

100%

1.90

00.0%

100%

1.95

00.0%

100%

2.00

00.0%

100%

2.05

00.0%

100%

2.10

00.0%

100%

108412

Sum

8080

15931

25324

26969

20752

8941

2199

189

25

20

00

00

00

00

0108412

Marg.distr.

7.5%

14.7%

23.4%

24.9%

19.1%

8.2%

2.0%

0.2%

0.0%

0%

0%

0%

0%

0%

0%

0%

0%

0%

0%

0%

Cum.d

istr.

7.5%

22.1%

45.5%

70.4%

89.5%

97.8%

99.8%

#####

#####

100%

100%

100%

100%

100%

100%

100%

100%

100%

100%

100%

DESIGN BASIS

69/74


CURRENT

In the SINTEF report /4/. estimates for the current conditions and velocities are

given based on simulations. As a basis of design these results are used without

further analysis. The data will be updated when further information is available

either as an updated report or as measurements.

Loads from current are based on two current profiles across the fjord.

1. Constant current, u, across the fjord.

2. Cross current constant current but in two direction 180

degrees. i.e. half the fjord width in one direction and

half the fjord width in the other direction

Figure 0-1 Current profiles across the fjord

For cross current it may be assumed that Vc = 2/3V0.

Until new data is received it is assumed that the current velocity is equal to the

maximum velocity for the cross current case. We consider it to be probable that

large scale vortices occur in the area of the bridge.

DESIGN BASIS

70/74


The current velocity, u, for different depths is assumed to vary as given in the table

below. Linear interpolation may be used between the depths given in the table.

Depth

(m)

Current velocity related to return period

u[m/s]

1 year 10 year 100 year

0-5 0.50 0.60 0.70

10 0.30 0.35 0.40

20 0,23 0.25 0.27

30 0.23 0.25 0.27

50 0.17 0.21 0.25

100 0,13 0.14 0.16

150 0.13 0.14 0.16

10 000

TBD

TBD

TBD

It may be assumed that current force acts normal to the axis of the structure at any

given position.

It is assumed that the same current profile is valid both for current going in and out

of the fjord. This will be updated when the final SINTEF report is available.

DESIGN BASIS

71/74


TIDAL VARIATION

To estimate tidal variation the Kystverkets measurement point in Bergen is used as

reference. Then the standard tables to transfer to secondary harbours has been

used. We are using the harbour Osøyro which is close to the bridge crossing. The

correction factor (multiplication factor from Bergen to Osøyro is 0.81.

Tidal amplitudes

Lowest Astronomical Tide (LAT) 0.0 m

Mean Low Water (MLW) 0,36 m

Mean Sea Level (MSL) 0,73 m

Mean High Water (MHW) 1,09 m

Highest Astronomical Tide (HAT) 1,46 m

DESIGN BASIS

72/74


Water levels for given return periods

Return period (years) HAT (m)

LAT (m)

1 1,62 -0,08

10 1,76 -0,18

50 1,85 -0,23

100 1,88 -0,26

10000

Not Defined Not Defined

The mean water level shall be increased with 0,8 m due to climate change where

this is unfavourable.

WATER DENSITY

The following density of the sea water may be assumed

Mean value 1025-1027 kg/m3

DESIGN BASIS

73/74


MARINE FOULING

Marine Fouling is assumed to occur on structural surfaces against the sea and up

to 0.5 m above the still water level.

Dist. from water level Thickness Mass per m^2. Submerged

weight per m^2.

+0.5 to -12 m 150 mm 200kg/m2 468 N/m2

> 12 m 75 mm 100kg/m2 234 N/m2

DESIGN BASIS

74/74


V-A 3 OTHER ENVIRONMENTAL LOADS

EARHTQUAKE

This environmental load condition is not included in the present design calculations

ICE LOADING

This environmental load condition is not included in the present design calculations