This document summarizes research on improving the assessment of shear capacity in reinforced concrete slab bridges. The research evaluated recommendations for effective slab width, a shear slab factor of 1.25, assuming superposition of loads, and a lower bound for minimum shear capacity. Testing of slab specimens and finite element analysis supported modifying the quick scan assessment method to use an effective width of 4dl, a shear reduction factor of av/2.5dl, and an expression for minimum shear based on original reinforcement yield strength. The improved quick scan method provided better selection of shear critical bridge sections.

1. Challenge the future
SHEAR ASSESSMENT OF
REINFORCED CONCRETE SLAB
BRIDGES
Eva O.L. Lantsoght*, Cor van der Veen*
Joost C. Walraven*, Ane de Boer^
*Delft University of Technology
^Ministry of Infrastructure and the Environment

2. 2
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
INTRODUCTION
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. 3
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
INTRODUCTION
CURRENT 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

4. 4
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
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

5. 5
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
RECOMMENDATIONS
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

6. 6
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
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

7. 7
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
RECOMMENDATIONS
LOWER BOUND FOR SHEAR
• Before 1962: QR24 type steel
• fyk = 240 MPa
• EC vmin based on fyk = 500 MPa
3/2 1/2 1/2
min 0,772 ck ykv k f f

8. 8
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
IMPROVED QUICK SCAN METHOD
LIVE LOADS
Detail of load spreading
Lane load of first lane

9. 9
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
IMPROVED QUICK SCAN METHOD
SECTIONS
• Checks required at indicated sections
• Selected cases: 9 existing Dutch solid slab bridges

10. 10
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
RESULTS
UNITY 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

11. 11
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
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

12. 12
Shear Assessment of Reinforced Concrete Slab Bridges
Eva Lantsoght, Delft University of Technology
Delft
University of
Technology
Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl
+31(0)152787449
14/06/2013 – 12h: PhD Defence at Aula TU Delft