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Recommendations for the Shear Assessment of Reinforced Concrete Solid
Slab Bridges Eva Lantsoght – Universidad San Francisco de Quito & Delft University of
TechnologyCor van der Veen - Delft University of Technology
Ane de Boer – RijkswaterstaatJoost Walraven – Delft University of Technology
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
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
Assessment practice
• Development of NEN 8700 series for existing structuresÞ 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
Explanation of recommendations (1)Choice of effective width
500
0 1000 1500 2000 2500b (mm)
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%
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
Þβnew = av /2.5dl Þ for 0.5dl ≤ av ≤ 2.5dl
Explanation of recommendations (4)Hypothesis of Superposition
Explanation of recommendations (5)Hypothesis of Superposition
combination line conc
',
3',
c combi
c conc
f
f
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
ResultsMost unfavorable position
Detail of load spreading
ResultsUnity checks (1)
• Checks required at indicated sections
• 9 existing Dutch solid slab bridges + MBE example
ResultsUnity 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
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
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