design guide for steel bridges*

DESIGN GUIDE FOR STEEL BRIDGES*

Tavolo Plenario ANAS – FINCO

Roma, 27 Giugno 2017

Outlook and summary 4

Experiences from 1st project 3

Design guide bauforumstahl 2

General introduction 1

Design guide for

steel bridges

Traffic

● Increase in traffic volume

Fatigue

Damages on bridges – the main

influence factors

Corrosion

● Increasing use of de-icing salt

corrosion at steel elements and

reinforcement of concrete

● Delayed or missing maintenance

of corrosion protection

Today

1950s

Conventional protection against

corrosion for bridges

● Bridges are long lasting constructions with an assumed life of 100 years

● Maintenance and repair are major issues for bridges

● In general: Steel bridge construction shows significant benefits compared to concrete bridge construction with regard to sustainability

● However, an organic coating must be renewed 2-3 times during lifetime

high effort in maintenance

Durable solutions are favorable due to economic reasons and to

minimize the traffic interference during maintenance actions

Hot-dip galvanization may provide major benefits!

0 25…30 50…60 75…90

How is the durability of

galvanized members?

● Compared to conventional corrosion

protection, hot-dip galvanizing is a very

long lasting and durable type of corrosion

protection

● Protection duration:

– Hot-dip galvanizing:

estimated protection duration several

decades (depending on environmental

conditions)

– Conventional coatings:

to be renewed every 25 to 33 years

● How long will the zinc coating/layer protect

the steel against corrosion under current

atmospheric conditions? 100 years?

– Corrosivity test according to ISO 9224 at

6 bridges in Germany

Source: Handbuch Feuerverzinken

Th

ickn

ess o

f zin

c la

ye

r in

µm

The intensity of corrosion depends

on the corrosivity

Duration of protection in years

Müglitzbrücke Dohna

Putlitz-Brücke, Berlin

Hochbrücke Rader Insel, A7

Brücke A93 Süd über Inn

Donaubrücke Deggenau, A3

A4 bei Korbußen

4 locations with

comparable data

from 1983

Source: IKS Dresden GmbH

Corrosion measurements at

bridges in Germany

How is the durability of

galvanized members?

80 to 100 years

life expectancy of hot-dip zinc coating (200µm), corrosivity C4: 80 to 100 years

A hot-dip zinc coating could last for the complete lifetime of a bridge

construction, verified by ISO 9223 and ISO 9224 at 6 different bridges in

Germany

lifetime of

construction

100 years

0

25…30 50…60 75…90

Organic coated lifetime of

construction

100 years

Hot-dip galvanized

Theoretical protective life period of an organic coating is 25-30 years

An organic coating needs to be renewed 2-3 times in a lifetime of a bridge

construction

0

Experience of HDG

Field measurement - validation

> 80 years

0

● Organic coating (repair needed during lifetime)

● Hot-dip galvanization (lifelong protection)

0

25…33 50…66 75…100 Service life of

bridges

= 100 years

Service life of

bridges

= 100 years

Periods of corrosion

protection:

Lier-bridge, Nete-Kanal (BE), 1993

Total length: 90,0 m

Spot check results (2014): measured zinc layer thickness > 300 µm

Ehzer-Bridge (NL), 1945

Spot check results (2007): measured zinc layer thickness = 69 – 219 µm

Höllmecke-Bridge, Werdohl, Sauerland (DE),1987

Total length: 30m

Spot check results (2014): measured zinc layer thickness: 150 -500 µm

Lydlinch-Bridge (UK), 1942, strengthenend in 1996

Spot check results (2014): m. zinc layer thickness = 126-167 µm (diagonals)

= 55-91 µm (bolt heads)

Source: Institut Feuerverzinken

Source: Institut Feuerverzinken Source: Institut Feuerverzinken

Source: Institut Feuerverzinken

Outlook and summary 4

Experiences from 1st project 3

Design guide bauforumstahl 2

General introduction 1

Design guide for

steel bridges

Design guide

General information

Research work summarized and fused into a guideline providing answers to

the following questions for steel and composite bridges:

● How is the durability of hot-dip galvanized members

(local environments)?

● Are there any special demands or restrictions for design and detailing?

● Are there any differences between coated and galvanized bridge

elements for static and/or fatigue design?

● Are there any special requirements to account for during erection?

● How to perform inspections, maintenance and repair of bridges with this

kind of corrosion protection?

Design guide for

hot-dip galvanized bridges

● General information for conception

● Batch galvanizing – durability,

repair, duplex systems

● Basics for design and construction

of galvanized bridges

● Design of joints (shop/site) and

proof against fatigue

● Detailing on the basis of examples

and recommendations for design,

suitable for hot-dip galvanizing

● Execution of site joints (bolted or

welded)

● Quality management

● Economic efficiency

● Sustainability

Characteristics of HDG coating

and general information

● Zinc layer is built up during dipping steel in

hot liquid zinc melt (450 ºC)

● HDG-process-specific aspects have to be

accounted for:

● Detailing has to respect good galvanizing

quality and possibility to dip it into bath

– Wetting of the entire steel surface by the

liquid zinc to be assured

– Draining and ventilations holes to be

provided in sufficient number and size

● Low-stress manufacturing needed to avoid

deformation of construction during

galvanization (heat treatment!)

Special demands for design and

detailing?

● HDG-process-specific aspects have to be taken into account and

constructional adjustments are necessary:

– Consider the thermal impact during dipping the structure in 450 ºC hot

zinc melt

– Elongation of structure by ~5mm/m in hot condition; complete relaxation

after cooling

– Temporary reduction of strength by 1/3 in hot condition

– Development of thermal induced residual stresses and overlapping

effects with other residual stresses

Avoid restraint effects due to hindered elongation!

Avoid/minimize constructive notches to reduce thermal induced stresses!

Prefer symmetric structures and low residual stresses arising from

fabrication to avoid distortion due to thermal impact!

Characteristics of HDG coating

and general information

● Layers of zinc coating:

– Iron-zinc alloying layers

– Pure zinc layer (not always)

– high resistance against mechanical

impact

● Choice of material

– Layer thickness is dependent on steel composition (Si-concentration)

● Quality of zinc: Active and passive corrosion protection

● Low-stress manufacturing needed to avoid deformation of construction

during galvanization (heat treatment!)

● Size and weight of segments to match to zinc bath size and crane capacity

– Currently, common dimensions of zinc kettles are ~ 17 x 1.8 x 3 m

– (Site) joints have to be foreseen

ca. 16-17 m

2. Welded joints after galvanization

Design of Joints

Welded/Bolted

1. Slip-resistant connections with

cover plates

Cp

M

sRdS F

nkF ,

3

,

Preload

Friction

Dispersal of

compressive stress

– Spray metalizing

(ZnAl15, EN ISO

2063) with

additional sealing

acc. to ZTV ING /

DIN EN 1090-2

– Expected

duration of

protection spray

metalizing ≥

organic coating

1. Alternative: Bolted site joints with

slip-resistant connections

2. Alternative: Welded site joints

with repair of corrosion protection

110 30

Weld

Spray zinc and sealant

Surface C, unprocessed and

intact hot-dip galvanizing

Surface B, sweep-blasted hot-dip galvanizing, average roughness depth up to Ry5 = 40 µm (G), thermal sprayed ≥ 200 µm and sealed

Surface A, blasted steel surface preparation grade: Sa 3, roughness level: coarse (G), roughness depth to Ry5 = 85 µm (G), thermal sprayed ≥ 200 µm and sealed

C B A A B C

Technology for equivalent retouching of

hot-dip galvanizing

● Proof of fatigue of steel and composite bridge constructions is reached

by classifying the bridge components into detail categories

Problem: These detail categories are only available for non-galvanized details and

elements (e.g. EN 1993-1-9)

125

125

S-N curves in accordance with EN 1993-1-9 (Eurocode 3)

Are there any differences in

design?

F

● About 500 small scale fatigue tests

by MPA/IfW Darmstadt:

Comparative experiments on hot-dip

galvanized and non-galvanized

specimens

● About 70 large scale/component

fatigue tests on hot-dip galvanized

specimens by TU Dortmund

Source: MPA Darmstadt

Are there any differences in

design?

New experimental tests on fatigue behavior (small scale/full scale)

Source:TU Dortmund

Test results

Reduction of fatigue resistance of hot-dip galvanized specimens

compared to non-galvanized specimens

F

N R =0,05

Example:

detail category

125

Non-galvanized

galvanized

Analysis according to Background-Document EC 3-1-9

Are there any differences in

design?

Proof of fatigue resistance

● New detail categories based on

EN 1993-1-9 (Eurocode 3)

112

112

140

125

Detailing

Examples and recommendations

Cost effectiveness and

sustainability – summary

Economy study: organic coating vs. galvanization

● Sum of costs is very project-specific (boundary conditions)

● Comparison demonstrates

– No design impact due to fatigue for most of single span bridges,

increase in section for multiple span bridge by one size

(of unfavorable combination of short (multiple) span and S460)

– Initial costs roughly the same

Cost effectiveness and

sustainability

Sourced: BASt-study Source: BASt-study

● Expenses for additional assembly joints are required

(the more joints, the more uneconomical)

● In high corrosiveness, zinc is usually slightly cheaper than organic coating

● Potential cost disadvantages for initial corrosion protection

● Additional costs at least balanced over the lifecycle by eliminating

maintenance measures

● Environmental impact and external costs (traffic jam) lower with HDG

Cost effectiveness and

sustainability

● Economy study: organic coating vs. galvanization

– Two repairs and/or renovations of the organic coating

(interval approx. 33 years)

– Including eventual repair of hot-dip galvanizing after 80 years

max. one maintenance measure for HDG bridges

Main issue now: concrete has to be renovated after 66 years at the

latest (Argument pro steel !)

Recommendation for zinc layer

thickness – quality management

● Recommended zinc layer thickness of

> 200µm to reach highest durability

– To consider: influence of Si-content in

steel on zinc layer thickness

steel grade choice

– Contact to galvanizer; provision of

samples/test galvanizing, if necessary

● Corrosion loss depends on corrosivity

Steel

Zinc layer

Duration of protection

0,14% ≤ Si ≤ 0,35%

Corr

osio

n loss

Outlook and summary 4

Experiences from 1st project 3

Design guide bauforumstahl 2

General introduction 1

Design guide for

steel bridges

Prototype bridge

first application after new research

● New composite bridge over

motorway A44 (Germany)

● Owner: State of Hessen

● Implementation: DEGES

● Project under construction

Galvanized bridges acc. to current

state of knowledge are possible !

ca. 36 m

Quelle: HIG, DEGES

Prototype bridge

first application after new research

Prototype bridge: samples for

galvanizing and spray metalizing

● Ensuring the minimum thickness of 200 µm

● To carry out with designated construction material (layer thickness

depends on the material)

● Here also to test the procedure of repairing the corosion protection (spray

metalizing) at welded site joints, not mandatory for every bridge!

● Choice of sealing:

– RAL- or DB-colors or

– Transparent

● Note:

Changing the visual

appearance of hot dip

galvanizing in the lifecycle

of bridge

Prototype bridge:

samples for galvanizing

● Welds (even if grinded) become visible after galvanization !

(higher Si-content of filler metal)

Use filler metal with low Si-content!

Long products don‘t need butt welds before galvanization !

● Higher layer thickness has more negative influence on fatigue behavior

and should therefore be avoided!

Prototype bridge:

Different plates – different appearance

● Blasting of the surface provides increased layer thickness, but also

alternating appearance of the zinc coating

● Different materials on the upper and lower limit of the required silicon

content provide widely varying layer thickness? (200-700μm)

– Bottom flange: Si = 0.17%, Web & Top flange: Si = 0.28%

650µm

matt gray

Prototype bridge:

Preparation before galvanization

● Covering paint must be thickly

applied and sharply demarcated

● Cut surfaces of plates must be

reworked elaborately (grinding,

milling …)

● Despite finishing, defects can not

be avoided

much care is required!

● Zinc adoption at edges and side

surfaces of rolled sections is the

same as at the rest of the profile!

No surface preparation P3 required

advantage for rolled sections!

● For welded sections P3 is not

sufficient, additional actions

required increased expenses

Prototype bridge

welded site joints

● Butt weld after galvanization on site

● Spray metalizing with sealing RAL 9006

Outlook and summary 4

Experiences from 1st project 3

Design guide bauforumstahl 2

General introduction 1

Design guide for

steel bridges

Conclusion and summary

● Hot-dip galvanizing provides benefits for bridges in terms of corrosion

protection

– Extreme long maintenance-free service life (under current

atmospheric conditions a lifelong corrosion protection is possible).

– Damage to corrosion protection system due to transportation or during

erection/assembly or peeling off coating does not occur

– Proof against fatigue can be performed on the basis of EC3 by

scientifically proven detail category definitions

● Special advantages, when using rolled sections:

– No welded butt joints before galvanizing

– Fatigue often not relevant, thus galvanizing leads only to moderate

adjustments of the design and rarely to increased sections

– No faulty development of zinc layer at surfaces

– Uniform appearance of the surfaces over whole section

Steel bridges get more economical and sustainable

Other possibility for application:

WiB for DB

● Filler beam bridges

– Span mostly below 20 m

– Simple cross sections

– Suspension points available (holes)

– Optionally Duplex-System

Repair and strengthening (2014) by Eiffel Deutschland Stahltechnologie GmbH

Maintenance and repair

Severinsbridge in Cologne (DE)

“Because the mankind builds

too many walls and

too few bridges…”

Isaac Newton

Eiweiler Viadukt, Saarland (DE)

www.promozioneacciaio.it

ufficiotecnico@fpacciaio.it

* The present document is derived from a study conducted in june 2016 by BAUFORUMSTAHL

(Fondazione Promozione Acciaio’s corresponding association in Germany) with the technical

contribution of ArcelorMittal.