shear tests of reinforced concrete slabs and slab strips under concentrated loads
DESCRIPTION
Presentation from fib PhD symposium in KarslruheTRANSCRIPT
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23-07-2012
Challenge the future
DelftUniversity ofTechnology
Shear tests of RC slabs and slab stripsunder concentrated loads
Eva Lantsoght
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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
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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???
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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14Shear tests of reinforced concrete slabs and slab strips under concentrated loads
ResultsEffective width (2)
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15Shear tests of reinforced concrete slabs and slab strips under concentrated loads
ResultsEffective width (3)
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16Shear tests of reinforced concrete slabs and slab strips under concentrated loads
ResultsEffective width (4)
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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
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18Shear tests of reinforced concrete slabs and slab strips under concentrated loads
ResultsComparison to design models (2)
Best results: beff2 and Regan’s method
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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
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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!
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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
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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
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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
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24Shear tests of reinforced concrete slabs and slab strips under concentrated loads
Contact:
Eva Lantsoght
+31(0)152787449
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25Shear tests of reinforced concrete slabs and slab strips under concentrated loads
ExperimentsProperties of slabs (1)
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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