The combination of increased live loads and a more conservative shear capacity in the recently implemented Eurocodes, resulted in a large number of existing solid slab bridges in the Netherlands being shear-critical upon assessment. However, an enhancement of the shear capacity can occur in slabs under concentrated wheel loads due to transverse load redistribution. To quantify this effect, a comprehensive series of experiments on slabs and slabs strips under a concentrated load near to the support and under a combination of a concentrated and a line load was carried out. The experiments show the difference in behaviour for slabs, carrying the load in a two-dimensional way, as compared to beams in shear. The results from the laboratory research are used to develop recommendations, that are easily used in combination with the codes. These recommendations are implemented in a spreadsheet-based first-level assessment tool, the Quick Scan method. The assessment with this tool of selected cases of existing solid slab bridges shows that applying the experimental results into the assessment practice leads to an improved selection ability of the Quick Scan method.

1. Challenge the future
Delft
University of
Technology
Applying Experimental Results
to the Shear Assessment Method for Solid Slab Bridges
Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer

2. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 2
Motivation (1)
Bridges from 60s and 70s
The Hague in 1959
Increased live loads
heavy and long truck
(600 kN > perm. max = 50 ton)
End of service life + larger loads

3. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 3
Motivation (2)

4. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 4
Motivation (3)
• First checks since mid-2000s
• 3715 structures to be studied
• 600 slab bridges shear-critical
• But: checks according to design
rules
• => Residual capacity & remaining
lifetime???
• Hidden reserves of the bearing
capacity
• Eg. Transverse load redistribution Highways in the Netherlands

5. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 5
Live Loads in NEN-EN 1991-2:2003

6. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 6
Shear Failure
Shear failure of the de la Concorde bridge, Laval, Canada
Shear failures of bridges: rare but brittle failures

7. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 7
Slabs under concentrated loads (2)
• Shear stress over effective width
• Fixed width, eg. 1 m
• Load spreading method

8. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 8
Slabs under concentrated loads (2)
• Shear stress over effective width
• Fixed width, eg. 1 m
• Load spreading method

9. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 9
Overview of Recommendations
• Evaluating existing solid slab bridges:
• NEN-EN 1992-1-1:2005
• 25% reduction of contribution concentrated load close to
support
• β =av/2d
• Combined: βnew =av/2.5d
• Effective width: French method and minimum 4d

10. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 10
Experiments (1)
Size: 5m x 2.5m (variable) x 0.3m = scale 1:2
Continuous support, Line supports
First series: concentrated load: vary a/d and position along
width

11. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 11
Experiments (2)
• 2nd series experimental work:
• Slabs under combined loading
• Line load
• Preloading
• 50% of strength from slab strips
• Concentrated load until failure
• Conclusions from 1st series valid
when combining loads?
• 26 experiments, 8 slabs
• Total: 156 experiments, 38 slabs

12. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 12
Experiments (3)

13. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 13
Slabs vs. Beams
• Transverse load
redistribution
• Geometry governing in slabs
• Location of load
• result of different load-
carrying paths
• Mid support vs end support
• influence of transverse
moment
• Wheel size
• more 3D action

14. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 14
Recommendations: Effective Width (1)
5000 1000 2500
b (mm)
20001500
0.5m
2.5m

15. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 15
Recommendations: Effective Width (2)
• Statistical analysis of Vexp/VEC
with beff1 and beff2
• NLFEA: shear stress
distribution at the support
• Lower bound: 4dl

16. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 16
Recommendations:
Transverse Load Redistribution
• 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

17. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 17
Recommendations:
Combining loads
• Experiments on slabs under line load + concentrated load
• Superposition is safe assumption
• Concentrated loads over effective width
• Distributed loads over full width

18. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 18
Application to Practice (1)
• Edge + 3 lanes
• First lane: av = 2.5dl
• Second and third lane:
effective width

19. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 19
Application to practice (3)
• Checks at indicated sections
• 9 existing Dutch solid slab bridges

20. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 20
Application to practice (4)
• Shear stresses: influence of recommendations
• QS-EC2: wheel loads at av = 2.5dl
• QS-DutchCode: wheel loads at av = dl
• QS-EC2 18% reduction in loads
• Shear capacity:
• QS-EC2: vRd,c ~ ρ, d
• low reinforcement + deep section = small shear capacity
• QS-DutchCode: τ1 ~ fck only
• QS-EC2 improved selection ability

21. Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 21
Summary & Conclusions
• Slabs under concentrated loads behave
differently in shear than beams
• Beneficial effect of transverse load
redistribution
• Recommendations:
• effective width from French method
• minimum 4dl
• reduction factor βnew = av /2.5dl
• superposition valid

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