As a result of the heavier live load models and more conservative shear approaches prescribed by the recently implemented Eurocodes, a large number of existing reinforced concrete solid slab bridges in the Netherlands were found to be shear-critical. The beneficial effect of the transverse load redistribution in slabs under concentrated loads is not taken into account. To quantify this effect, a comprehensive number of experiments was carried out. These results are used to formulate recommendations for the assessment practice for the case of solid slab bridges. The recommendations focus on the effective width over which the axle load can be distributed and its lower bound, the beneficial effect of transverse load redistribution and the influence of the yield strength of the reinforcement on the lower bound of the shear capacity. These recommendations are implemented in the “Quick Scan” method, leading to a significant reduction of the shear stresses.

1. Recommendations for the Shear
Assessment of Reinforced Concrete Solid
Slab Bridges
Eva Lantsoght – Universidad San Francisco de Quito & Delft University of
Technology
Cor van der Veen - Delft University of Technology
Ane de Boer – Rijkswaterstaat
Joost Walraven – Delft University of Technology

2. Problem statement
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. 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. 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
• Level of Approximation approach in Model Code
– LoA I: Quick Scan => unity check

5. Explanation of recommendations (1)
Choice of effective width
5000 1000 1500 2000 2500
b (mm)

6. Explanation of recommendations (2)
Choice of effective width
• Calculated from series vs. 45° load
spreading
• minimum 4d
• 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%

7. Explanation of recommendations (3)
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

8. Explanation of recommendations (4)
Hypothesis of Superposition

9. Explanation of recommendations (5)
Hypothesis of Superposition
combination line conc   
'
,
3
'
,
c combi
c conc
f
f

10. Application to practice
• Evaluating existing solid
slab bridges:
– 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

11. Results
Most unfavorable position
Detail of load spreading

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

13. Results
Unity checks (2)
• Shear stresses: influence of recommendations
– QS-EC2: wheel loads at av = 2.5dl
– QS-Dutch Code: 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

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

15. Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl / elantsoght@usfq.edu.ec