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Challenge the future
SHEAR ASSESSMENT OF
REINFORCED CONCRETE SLAB
BRIDGESEva O.L. Lantsoght*, Cor van der Veen*
Joost C. Walraven*, Ane de Boer^
*Delft University of Technology^Ministry of Infrastructure and the Environment
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
INTRODUCTIONPROBLEM 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
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
INTRODUCTIONCURRENT SITUATION• NL: 60% of bridges built before 1976
• Assessment: shear critical in 600 slab bridges
• Quick Scan• spreadsheet-based• since mid-2000s• conservative, first-order method• result = unity check Highways in the
Netherlands
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
RECOMMENDATIONS EFFECTIVE WIDTH
• Experiments different specimen widths• Statistical analysis of Vexp/VEC with beff1 and beff2
• NLFEA: shear stress distribution at the support
• Lower bound: 4dl
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
RECOMMENDATIONSSLAB 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
Þβnew = av /2,5dl Þfor 0,5dl ≤ av ≤ 2,5dl
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
RECOMMENDATIONS HYPOTHESIS OF SUPERPOSITION
• Experiments on slabs under line load + concentrated load
• Superposition is safe assumption• Concentrated loads over effective width• Distributed loads over full width
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
RECOMMENDATIONSLOWER BOUND FOR SHEAR
• Before 1962: QR24 type steel• fyk = 240 MPa
• EC vmin based on fyk = 500 MPa
3/2 1/2 1/2min 0,772 ck ykv k f f
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
IMPROVED QUICK SCAN METHODLIVE LOADS
Detail of load spreading
Lane load of first lane
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
IMPROVED QUICK SCAN METHODSECTIONS
• Checks required at indicated sections
• Selected cases: 9 existing Dutch solid slab bridges
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
RESULTSUNITY CHECKS QS-EC2 VS QS-VBC• Shear stresses: influence of recommendations
• QS-EC2: wheel loads at av = 2,5dl
• QS-VBC: 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-VBC: τ1 ~ fck only
• QS-EC2 improved selection ability
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
SUMMARY & CONCLUSIONS
• Quick Scan: tool for first round of assessments
• Recommendations:• effective width from French
method• minimum 4dl
• reduction factor βnew = av /2,5dl
• superposition valid• vmin expression fyk
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Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of TechnologyDelftUniversity ofTechnology
Contact:
Eva Lantsoght
+31(0)152787449
14/06/2013 – 12h: PhD Defence at Aula TU Delft
