design guide for steel bridges*
TRANSCRIPT
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
* 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.