Seismic Response and Seismic Response and Capacity Evaluation of - - PowerPoint PPT Presentation

Seismic Response and Seismic Response and Capacity Evaluation of Exterior Capacity Evaluation of Exterior Sacrificial Shear Keys of Bridge Sacrificial Shear Keys of Bridge Abutments Abutments

Scott A. Ashford, PE, PhD Professor and School Head Oregon State University Corvallis, Oregon

2009 Caltrans-PEER Seismic Seminar Series

History of UCSD Work on Abutments

• Post-tensioned Abutments (2002)

– Megally, Silva, and Seible

• Sacrificial Shear Keys (2007)

– Bozorgzadeh, Bauer, Restrepo, and Ashford

• Abutment Backfill Models (2007)

– Bozorgzadeh, Ashford, and Restrepo – Initially considered diaphragm-type abutments – Worked with EMI on backfill soil types – Completed testing on seat-type abutment

Acknowledgments Acknowledgments

• The California Department of Transportation

(Caltrans) is gratefully acknowledged for the financially support of the experimental research on sacrificial exterior shear keys.

• This research was carried out at UC San
• Diego. The participation of the UCSD

faculty, staff, and students is also acknowledged.

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Schematic of Exterior Shear Key in Schematic of Exterior Shear Key in Bridge Abutments Bridge Abutments

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Wing-wall Back-wall Stem wall Footing Vertical pile Battered pile Exterior shear key Superstructure

1994 Northridge Earthquake 1994 Northridge Earthquake

Over half of damaged bridges Over half of damaged bridges suffered abutment damage suffered abutment damage

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Experimental Work Experimental Work

• Five test series, each including two test

units were built at a 40% scale.

• Main variables:

– Construction joint. – Amount and configuration of vertical reinforcement. – Amount and configuration of horizontal reinforcement.

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Elevation View of Reinforcement Elevation View of Reinforcement Layout of the Proposed Model Layout of the Proposed Model

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5A 5B Rough Construction Joint Headed Bars, 14#4 Foam (0.5” thick) Smooth Construction Joint Vertical Shear Key Reinforcement,4#4 Vertical Shear Key Reinforcement,4#4 24” 30 1/2” 16.75” 24” 48” 24”

Shear Key Test Specimens Shear Key Test Specimens Under Construction Under Construction

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Test Setup Test Setup

9 Hydraulic Actuator Guiding Frame Loading Arm

Failure of Exterior Shear Keys of Failure of Exterior Shear Keys of Two Test Series Two Test Series

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Failure occurred in a diagonal

strut in the stem wall. No sliding at the interface of shear key-abutment stem wall

• ccurred.

Performed as structural fuses

with sliding shear failure. Diagonal cracks formed in the stem wall but the maximum width of cracks were 0.012".

Current Model Proposed Model

Load Load-

• Displacement Curves

Displacement Curves

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100 200 300 1 2 3 4

Monolithic Construction Joint

60 120 180 0.5 1 1.5 2

using foam with bond breaker

Current Model Proposed Model

Displacement (in) Displacement (in) Load (kips) Load (kips)

V V

Conclusions Conclusions

• A model for evaluation of capacity of shear

keys under lateral force was developed based on Strut-and-Tie models.

• The proposed model showed better

agreement with test results than the current shear friction model.

• The current shear friction model

underestimates shear key capacity which may lead to damage of abutment wall or supporting piles.

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Conclusions Conclusions

• Based on results of experimental work,

several recommendations were proposed for construction details:

– Using smooth construction joint. – Shear key vertical reinforcement bars should be the only reinforcement connecting the shear key to the abutment stem wall. – Headed bars or hanger bars can be used in the stem wall to carry the force transmitted by the shear key.

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Research results Research results implemented along I implemented along I-

• 905 in San Diego in

905 in San Diego in September 2007 September 2007 Most testing carried out Most testing carried out in 2003/4, final report in 2003/4, final report dated October 2007 dated October 2007 Caltrans implements Caltrans implements good results quickly, in good results quickly, in this case before final this case before final report issued. report issued.

Shear Key Construction Shear Key Construction

Completed Keys Completed Keys

Results Available at UCSD Results Available at UCSD

• SSRP-2001/22, May 2002: “Seismic Response of

Sacrificial Shear Keys in Bridge Abutments,” S.H. Megally, P.F. Silva, F. Seible, 215p.

• SSRP-04/14, October 2007: "Seismic Response and

Capacity Evaluation of Exterior Sacrificial Shear Keys in Bridge Abutments,” A. Bozorgzadeh, H.L. Bauer, J.I. Restrepo, S.A. Ashford, 40p.

• SSRP-07/12, May 2007: “Experimental and Analytical

Investigation on the Stiffness and Ultimate Capacity of Bridge Abutments,” A. Bozorgzadeh, S. Ashford, and J. Restrepo, 196p.