Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges

Challenge the future

DelftUniversity ofTechnology

Applying Experimental Results

to the Shear Assessment Method for Solid Slab Bridges

Eva Lantsoght, Cor van der Veen, Joost Walraven, Ane de Boer

Applying Experimental Results to the Shear Asssessment Method for Solid Slab Bridges 2

Motivation (1)

Bridges from 60s and 70s

The Hague in 1959

Increased live loads

heavy and long truck (600 kN > perm. max = 50 ton)

End of service life + larger loads


Motivation (2)


Motivation (3)

• First checks since mid-2000s• 3715 structures to be studied

• 600 slab bridges shear-critical

• But: checks according to design rules

• => Residual capacity & remaining lifetime???

• Hidden reserves of the bearing capacity

• Eg. Transverse load redistribution Highways in the Netherlands


Live Loads in NEN-EN 1991-2:2003


Shear Failure

Shear failure of the de la Concorde bridge, Laval, Canada

Shear failures of bridges: rare but brittle failures


Slabs under concentrated loads (2)

• Shear stress over effective width• Fixed width, eg. 1 m• Load spreading method


Overview of Recommendations

• Evaluating existing solid slab bridges:• NEN-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


Experiments (1)

Size: 5m x 2.5m (variable) x 0.3m = scale 1:2 Continuous support, Line supportsFirst series: concentrated load: vary a/d and position along width


Experiments (2)

• 2nd series experimental work:• Slabs under combined loading

• Line load

• Preloading

• 50% of strength from slab strips

• Concentrated load until failure

• Conclusions from 1st series valid when combining loads?

• 26 experiments, 8 slabs• Total: 156 experiments, 38 slabs


Experiments (3)


Slabs vs. Beams

• Transverse load redistribution

• Geometry governing in slabs• Location of load

• result of different load-

carrying paths

• Mid support vs end support• influence of transverse

moment

• Wheel size• more 3D action


Recommendations: Effective Width (1)

5000 1000 2500

b (mm)

20001500

0.5m

2.5m


Recommendations: Effective Width (2)

• Statistical analysis of Vexp/VEC

with beff1 and beff2

• NLFEA: shear stress distribution at the support

• Lower bound: 4dl


Recommendations:

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 1.25βnew = av /2.5dl

for 0.5dl ≤ av ≤ 2.5dl


Recommendations:

Combining loads

• Experiments on slabs under line load + concentrated load• Superposition is safe assumption

• Concentrated loads over effective width

• Distributed loads over full width


Application to Practice (1)

• Edge + 3 lanes

• First lane: av = 2.5dl

• Second and third lane:

effective width


Application to practice (3)

• Checks at indicated sections

• 9 existing Dutch solid slab bridges


Application to practice (4)

• Shear stresses: influence of recommendations• QS-EC2: wheel loads at av = 2.5dl

• QS-DutchCode: 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 & Conclusions

• Slabs under concentrated loads behave differently in shear than beams

• Beneficial effect of transverse load redistribution

• Recommendations:• effective width from French method

• minimum 4dl

• reduction factor βnew = av /2.5dl

• superposition valid


Contact:

Eva Lantsoght

[email protected]

+31(0)152787449

Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges

Design

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