DESIGN GUIDE FOR STEEL BRIDGES*
Transcript of DESIGN GUIDE FOR STEEL BRIDGES*
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DESIGN GUIDE FOR STEEL BRIDGES*
Tavolo Plenario ANAS – FINCO
Roma, 27 Giugno 2017
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Outlook and summary 4
Experiences from 1st project 3
Design guide bauforumstahl 2
General introduction 1
Design guide for
steel bridges
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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
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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
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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
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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
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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
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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
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Outlook and summary 4
Experiences from 1st project 3
Design guide bauforumstahl 2
General introduction 1
Design guide for
steel bridges
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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?
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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
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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!)
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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!
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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
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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
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1. Alternative: Bolted site joints with
slip-resistant connections
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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
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● 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?
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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
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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?
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Proof of fatigue resistance
● New detail categories based on
EN 1993-1-9 (Eurocode 3)
112
112
140
125
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Detailing
Examples and recommendations
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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
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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
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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 !)
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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
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Outlook and summary 4
Experiences from 1st project 3
Design guide bauforumstahl 2
General introduction 1
Design guide for
steel bridges
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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
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Prototype bridge
first application after new research
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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
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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!
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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
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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
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Prototype bridge
welded site joints
● Butt weld after galvanization on site
● Spray metalizing with sealing RAL 9006
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Outlook and summary 4
Experiences from 1st project 3
Design guide bauforumstahl 2
General introduction 1
Design guide for
steel bridges
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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
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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
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Repair and strengthening (2014) by Eiffel Deutschland Stahltechnologie GmbH
Maintenance and repair
Severinsbridge in Cologne (DE)
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“Because the mankind builds
too many walls and
too few bridges…”
Isaac Newton
Eiweiler Viadukt, Saarland (DE)
www.promozioneacciaio.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.