connections between precast girders and cap beam...research objective • establishing reliable...
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Emerging ABC Connection Details for High Seismic Areas
Sri SritharanWilson Engineering ProfessorCCEE Department, Iowa State University
Connections between precast girders and cap beam
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Dr. Jay HolomboTY Lin International
Collaborator
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Research Objective• Establishing reliable moment resisting connections
between precast girders and the bent cap, especially for resisting positive moments so that ABC can be utilized in moderate-to-high seismic regions.• Negative moment resistance is not of a significant
concern
(Project Website: http://sri.cce.iastate.edu/ABC-Seismic/)
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Design Criteria
Fully develop the column plastic hinge capacity Elastic superstructure response under loads due to: Gravity + Column Overstrength Moment capacity (H) + 0.5g Vertical AccelerationExhibit sufficient ductility
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Inverted Tee/Rectangular Bent Cap
Columnplastic hinge
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As-built detail
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Precast ConstructionMonolithic
Construction
Holombo et al.
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System Test
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Negative Moment Resistance
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Positive Moment Resistance
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New Connections• Six different details were tested• Mechanisms – shear friction (dowel bars) or shear
friction and direction tension force transfer (unstressed strands)
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Precast I Girder to Precast Inverted-TeeBent Cap Connections• 1 - Grouted Unstressed Strand Connection (GUSC)
• Unstressed strands are placed through ducts in girder and cap and then grouted in place
• Dowel bars are placed transversely through the web of girder
• Diaphragm and deck are poured to secure girder to cap and encase dowel bars
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Precast I Girder to Precast Inverted-TeeBent Cap Connections• 2 - Looped Unstressed Strand Connection (LUSC)
• Looped unstressed strands are placed in bent cap and girder
• Bent cap looped strands extend from cap into diaphragm region
• Large-diameter dowel bars are placed through looped strands in girder and cap
• Diaphragm and deck are poured to secure girder to cap and encase looped strands and dowel bars
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Precast Bulb-Tee Girder to CIP Bent CapConnections• 3 - Extended Strand with a Lap Splice Connection
(ESLS)• Four girder prestressing
strands are extended and lapped with extended strands from opposite girder
• All extended strands are anchored with plates and anchor chucks.
• Dowel bars placed transversely through web of girder
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Precast Bulb-Tee Girder to CIP Bent CapConnections
• 4 - Extended Strand with Splice and End Plate Connection (ESSP) • Five girder prestressing
strands are extended from the end of the girder a short distance and then spliced with strand ties
• Extended strands and strand ties are anchored with plates and anchor chucks.
• Dowel bars are placed transversely through web of girder
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Precast Bulb-Tee Girder to CIP Bent CapConnections• 5 - Extended Strand Bent with Free End connection
(ESBF)
• Five of the girder prestressing strands are extended from the end of girder and bent at 90 degrees with no endanchorage
• Dowel bars placed transversely through the web of girder
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Precast Bulb-Tee Girder to CIP Bent CapConnections• 6 - Extended Strand with a Mechanical Splice
Connection (ESMS)• Four of girder
prestressing strands are extended and connected to extended strands from the opposite girder with mechanical splice chucks
• Dowel bars placed transversely through the web of girder
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Connection Test
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This video is also available at: http://sri.cce.iastate.edu/ABC-Seismic/experiments.htm
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This video is also available at: http://sri.cce.iastate.edu/ABC-Seismic/experiments.htm
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This video is also available at: http://sri.cce.iastate.edu/ABC-Seismic/experiments.htm
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Experimental Tests• Overall Performance (GUSC)
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Experimental Tests• Overall Performance (ESMS & ESLS)
-1400
-1200
-1000
-800
-600
-400
-200
0
200
400
600
-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11
Mom
ent @
Gird
er to
Ben
t Cap
in
terf
ace
(K-ft
)
Displacement (in.)
Moment vs. Black Actuator Displacement
G
G+H
G+H+0.5G
G+H+0.7G
G+H+1.0G
G+H+1.75G
ESMS
ESLS
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Positive Moment Resisting MechanismsTotal
Shear friction
Strand
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Conclusions
All connections exhibited sufficient moment resistance and remained elastic under the design loads that included 0.5g vertical acceleration effects.No structural damage was observed under loads corresponding to design demands.All connections showed considerable ductility under positive and negative moment demands.Precast inverted tee bent cap to provided some benefits over rectangular cast-in-place cap beam