Embed Size (px)
DESCRIPTION
As a result of the heavier live load models and more conservative shear approaches prescribed by the recently implemented Eurocodes, a large number of existing reinforced concrete solid slab bridges in the Netherlands were found to be shear-critical. The beneficial effect of the transverse load redistribution in slabs under concentrated loads is not taken into account. To quantify this effect, a comprehensive number of experiments was carried out. These results are used to formulate recommendations for the assessment practice for the case of solid slab bridges. The recommendations focus on the effective width over which the axle load can be distributed and its lower bound, the beneficial effect of transverse load redistribution and the influence of the yield strength of the reinforcement on the lower bound of the shear capacity. These recommendations are implemented in the “Quick Scan” method, leading to a significant reduction of the shear stresses.
Citation preview
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
