Assessment of the Shear Capacity of Existing Reinforced Concrete Solid Slab Bridges
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Challenge the future Delft University of Technology Assessment of the Shear Capacity of Existing RC Solid Slab Bridges Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer
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Presentation for Transportation Research Board, Annual Meeting 2013 Presented in the session "Topics in Concrete Bridges"
Transcript of Assessment of the Shear Capacity of Existing Reinforced Concrete Solid Slab Bridges
Challenge the future
DelftUniversity ofTechnology
Assessment of the Shear Capacityof Existing RC Solid Slab BridgesEva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer
2Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Problem
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
3Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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
4Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Assessment practice
Development of NEN 8700 series for existing structuresLoad 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
5Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Effective width in shear
45° load spreading - Dutch practice
45° load spreading – French practice
6Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Goals• Assess shear capacity of slabs
under concentrated loads• Determine effective width in
shear
7Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Experiments (1)
Size: 5m x 2.5m (variable) x 0.3m = scale 1:2
Continuous support, Line supportsConcentrated load: vary a/d and position along width
8Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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?
9Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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
10Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Explanation of recommendations (1)Choice of effective width
500
0 1000 1500 2000 2500b (mm)
11Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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%
12Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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
13Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Explanation of recommendations (4)Hypothesis of Superposition
14Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Explanation of recommendations (5)Hypothesis of Superposition
combination line conc
',
3',
c combi
c conc
f
f
15Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
ResultsMost unfavorable position (1)
Detail of load spreading
16Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
ResultsUnity checks AASHTO / EC2 (1)
•Checks required at indicated sections
•9 existing Dutch solid slab bridges + MBE example
17Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
ResultsUnity 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
•QS-EC2 more conservative for unity checks
S20T2
18Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
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
19Assessment of the Shear Capacity of Existing RC Solid Slab Bridges
Contact:
Eva Lantsoght
+31(0)152787449
