Shear tests of reinforced concrete slabs and slab strips under concentrated loads

23-07-2012

Challenge the future

DelftUniversity ofTechnology

Shear tests of RC slabs and slab stripsunder concentrated loads

Eva Lantsoght

2Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Overview

• Introduction• Project description

• Previous research• Experiments

• Setup

• Specimens

• Results• Results

• Overall width/Effective

width• Comparison to Code

methods• Comparison to NLFEA

• Conclusions

S9T6 at failure

3Shear tests of reinforced concrete slabs and slab strips under concentrated loads

BackgroundProject description (1)

Shear failure of the de la Concorde bridge, Laval

The Netherlands: 60% of bridges built before 1975

Traffic volume and loads have increased => Loads? Shear Capacity???

4Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Background Project description (2)

• Capacity of existing bridges in NL

• TU Delft• Concrete Structures• Structural Mechanics

• TNO• RWS

• 3715 relevant structures• 2020 built before 1976

• Study: bridge categories and specific details Highways in the

Netherlands

5Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Background Project description (3)

• Concrete Structures• Long-term tensile strength (C-1.4)• Beam shear – sustained loads (A-1.2)• Continuous girders – shear (A-1.2)• Prestressed slabs – CMA (A-1.5)• Slab bridges - shear/punching

Concrete bridges

6Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Background Shear and punching (1)

• Punching shear over perimeter around load

• Beam shear formulas over effective width at support• Effective width?

Beam shear, one-way shear Punching shear, two-way shear

7Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Background Shear and punching (2)

45° load spreading 45° load spreading – French practice

8Shear tests of reinforced concrete slabs and slab strips under concentrated loads

BackgroundPrevious research (1)

• Database: 207 tests slabs and wide beams in shear• a/d = 0,65 – 9,8• Different categories

• simply supported slab• continuous slab• real bridge• cantilever

• Failure mode based on pictures/ crack patterns: WB/P

9Shear tests of reinforced concrete slabs and slab strips under concentrated loads

BackgroundPrevious research (2)

• Recent research: slabs under line loads

• From database: 22 • Concentrated load• a/d < 2,5• Small: d < 15cm

• Comparison to EC2• Evidence for additional capacity• Experiments on larger specimens needed

10Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Goals• Assess shear capacity of slabs

under concentrated loads• Determine effective width in

shear

11Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ExperimentsExperimental setup

Size: 5m x 2,5m (variable) x 0,3mContinuous support, Line supportsLoad: vary a/d and position along width

12Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Experimental resultsExperimental setup (2)

• Distance between load and support (a/d = 1,51 and a/d = 2,26)• Simple or continuous support• Amount of transverse flexural

reinforcement• Reinforcement type: plane or ribbed

bars• Size of the loading plate• Type of support: line support or bearing• Concrete compressive strength• Loading in the middle of width or near

edge• Total width

BS2T1

First series: 30 specimens, 133 experiments

13Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsEffective width (1)

Specimens with different widths: threshold value observed

500

0 1000 1500 2000 2500b (mm)

14Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsEffective width (2)

15Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsEffective width (3)

16Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsEffective width (4)

17Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsComparison to design models (1)• EN 1992-1-1:2005

• Shear governing over punching• Two load spreading methods• CRd,c = 0,15

• French NA• Larger vmin for slabs• French load spreading method

• Regan’s method• Based on punching perimeter• # sides ~ width• Enhancement close to support• Enhancement for CS

18Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsComparison to design models (2)

Best results: beff2 and Regan’s method

19Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsComparison to design models (3)

beff2 better results than beff1

=> smaller range of AVG=> better COV

20Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsComparison to design models (4)

Ribbed bars vs. plain barsPlain bars: slightly smaller capacity≠ literature!

21Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ResultsComparison to NLFEA

• Sensitive to input parameters

• Compared to effective width

• beff2 compares best

22Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Recommendations

• Evaluating existing solid slab bridges:• EN 1992-1-1:2005• Effective width: French method, min 4d• 25% reduction of contribution concentrated load close

to support• β =av/2d• Combined: βnew =av/2,5d

23Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Conclusions

• Transverse load redistribution• Larger shear capacity in slabs• Enhancement factor 1,25

• French load spreading method for beff

• Literature• Experiments• NLFEA

• Loads close to support• Direct load transfer

24Shear tests of reinforced concrete slabs and slab strips under concentrated loads

Contact:

Eva Lantsoght

E.O.L.Lantsoght@tudelft.nl

+31(0)152787449

25Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ExperimentsProperties of slabs (1)

26Shear tests of reinforced concrete slabs and slab strips under concentrated loads

ExperimentsProperties of slabs (2)

Test SS/CS Pu (kN) Failure mode Fpres(kN)

Vmax(kN)

Vmax,EC(kN)

S11T1 SS 1194 WB + P 165 998 848S11T4 CS 958 WB + P 307 886 766S12T1 SS 931 WB + B + P 162 780 663S12T2 SS 1004 P 173 839 712S12T4 CS 773 WB + P + B 147 705 608S12T5 CS 806 WB + B 158 735 633S13T1 SS 1404 WB + P 157 1253 593S13T4 CS 1501 WB + P 240 1411 706S14T1 SS 1214 WB + P + B 133 1088 518S14T2 SS 1093 WB + P + B 162 975 462S14T4 CS 1282 WB + P + B 187 1207 605S14T5 CS 1234 WB + P + B 142 1157 578