Presentation given at the International Bridge Conference 2013

1. Challenge the future
Delft
University of
Technology
Quick Scan Method
Dutch Approach for the Shear Assessment of Reinforced Concrete
Slabs Bridges
Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer

2. 2Quick Scan Method
Problem
Bridges from 60s and 70s
The Hague in 1959
Increased live loads
common heavy and long truck (600 kN)
End of service life + larger loads

3. 3Quick Scan Method
Highway network in the Netherlands
• NL: 60% of bridges built before 1976
• Assessment: shear critical in 600
slab bridges
• Residual capacity?
Highways in the Netherlands

4. 4Quick Scan Method
Live Loads in EN 1991-2:2003

5. 5Quick Scan Method
Assessment practice
Development of NEN 8700 series for existing structures
⇒Load Levels: New, Repair, Unfit for Use
Repair level: β < 3.8 (3.6 for bridges built before 2012) - EC
vs. design load at operating level, β = 2.5 - AASHTO

6. 6Quick Scan Method
Effective width in shear
45° load spreading - Dutch practice 45° load spreading – French practice

7. 7Quick Scan Method
Goals
• Assess shear capacity of slabs
under concentrated loads
• Determine effective width in
shear

8. 8Quick Scan Method
Experiments (1)
Size: 5m x 2.5m (variable) x 0.3m = scale 1:2
Continuous support, Line supports
Concentrated load: vary a/d and position along width

9. 9Quick Scan Method
Experiments (2)
• 2nd
series experimental work:
• Slabs under combined loading
• Line load
• Preloading
• 50% of strength from slab strips
• Concentrated load
• loading until failure
• Superposition hypothesis valid?

10. 10Quick Scan Method
Slabs vs. Beams
• Transverse load redistribution
• Geometry governing in slabs
• Smaller influence a/d
• result of different load-carrying paths
• Smaller influence of moment at continuous support:
• influence of transverse moment
• Larger influence size of loading plate
• more 3D action

11. 11Quick Scan Method
Explanation of recommendations (1)
Choice of effective width
5000 1000 1500 2000 2500
b (mm)

12. 12Quick Scan Method
Explanation of recommendations (2)
Choice of effective width
• Calculated from series vs. 45° load
spreading
• minimum 4d
• 4d average spreading of peak
• Comparison between database
(literature) + experiments and methods
• French load spreading method
underestimates less
• Lower COV for French load spreading
method
• Database: 63% vs 42%
• Delft experiments: 26% vs 22%

13. 13Quick Scan Method
Explanation of recommendations (3)
Slab factor 1.25
• Comparison between experiments
and EN 1992-1-1:2005
• based on normal distribution
• characteristic value at least 1.25
• Combination with β = av /2dl and
enhancement factor 1.25
⇒βnew = av /2.5dl
⇒for 0.5dl ≤ av ≤ 2.5dl

14. 14Quick Scan Method
Explanation of recommendations (4)
Hypothesis of Superposition

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Explanation of recommendations (5)
Hypothesis of Superposition
combination line concτ τ τ= +
'
,
3
'
,
c combi
c conc
f
f

16. 16Quick Scan Method
Results
Most unfavorable position (1)
Detail of load spreading

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Results
Unity checks AASHTO / EC2 (1)
• Checks required at indicated sections
• 9 existing Dutch solid slab bridges + MBE example

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Results
Unity checks AASHTO / EC2 (2)
• Shear stresses similar
• BUT: AASHTO resistance factor on shear force
• load factors ≈ different target reliability
• NEN 8700: γDL=1.15 & γLL=1.30
• AASHTO LRFR: γDL=1.25 & γDC=1.50 & γLL=1.35
• Shear capacity: Eurocode more conservative
• QS-EC2 more conservative for unity checks
• QS-EC2 vs QS-DutchCode: reduction in loads
by 18%
S20T2

19. 19Quick Scan Method
Summary & Conclusions
• Quick Scan: tool for first round of
assessments
• Recommendations:
• effective width from French method
• minimum 4d
• reduction factor βnew = av /2.5dl
• superposition valid

20. 20Quick Scan Method
Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl
+31(0)152787449