1. Assessment of the Shear Capacity
of Existing RC Solid Slab Bridges
Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer
Delft
University of
Technology
Challenge the future

2. Problem
Bridges from 60s and 70s
Increased live loads
common heavy and long truck (600 kN)
The Hague in 1959
End of service life + larger loads
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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
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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
cfr. design load at operating level, β = 2.5 - AASHTO
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5. Effective width in shear
45° load spreading - Dutch practice 45° load spreading – French practice
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6. Goals
• Assess shear capacity of slabs
under concentrated loads
• Determine effective width in
shear
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7. Experiments (1)
Size: 5m x 2.5m (variable) x 0.3m = scale 1:2
Continuous support, Line supports
Concentrated load: vary a/d and position along width
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8. Experiments (2)
• 2nd series experimental work:
• Slabs under combined loading
• Line load
• Preloading
• 50% of stress from slab strips
• Concentrated load
• loading until failure
• Superposition hypothesis valid?
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9. Slabs vs. Beams
• Transverse load redistribution
• Geometry governing in slabs
• Smaller influence a/d
• result of different load-carrying paths
• Smaller influence of moment at continuous support:
• influence of transverse moment
• Larger influence size of loading plate
• more 3D action
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10. Explanation of recommendations (1)
Choice of effective width
0 500 1000 1500 2000 2500
b (mm)
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11. Explanation of recommendations (2)
Choice of effective width
• Calculated from series vs. 45° load
spreading
• minimum 4d
• 4d average spreading of peak
• 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%
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12. Explanation of recommendations (3)
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
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13. Explanation of recommendations (4)
Hypothesis of Superposition
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14. Explanation of recommendations (5)
Hypothesis of Superposition
f c',combi
3
'
f c , conc
τ combination = τ line + τ conc
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15. Results
Most unfavorable position (1)
Detail of load spreading
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16. Results
Unity checks AASHTO / EC2 (1)
• Checks required at indicated sections
• 9 existing Dutch solid slab bridges + MBE example
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17. Results
Unity checks AASHTO / EC2 (2)
• Shear stresses similar
• BUT: AASHTO resistance factor on shear force
• load factors ≈ different target reliability
• NEN 8700: γDL=1.15 & γLL=1.30
• AASHTO LRFR: γDL=1.25 & γDC=1.50 & γLL=1.35
• Shear capacity: Eurocode more
conservative
S20T2
• QS-EC2 more conservative for unity checks
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18. Summary & Conclusions
• Different requirements for reliability
• 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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19. Contact:
Eva Lantsoght
E.O.L.Lantsoght@tudelft.nl
+31(0)152787449
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