Precast Bent System for Bridges in Seismic Regions
Marc Eberhard, John Stanton Olafur Haraldsson, Todd Janes, Hung Viet Tran
University of Washington
NEES & PEER Annual MeetingSan Francisco, 8 -9 October 2010
Acknowledgments
WSDOTTRANSNOWValle FoundationFHWA, Highways for Life ProgramPEER
Background
Accelerate on-site bridge construction.Use precast concrete components.Connection details:
seismic-resistant construct
Construction Procedure
1) Excavate footing.
2) Position and brace precast column.
Construction Procedure
3) Place footing reinforcement and cast.
Construction Procedure
4) Set cap-beam, grout bars into ducts.
Construction Procedure
5) Place girders, diaphragms and deck.
Construction Procedure
Precast
Prestressed
CIP
RC (ref)
Precast
RC
Cap-Beam
to Column
Column to
Spread Footing
Column to
Drilled Shaft
Connections
Column-to-Cap-BeamConnection
Cap Beam Connection: Many small bars and ducts
Courtesy: BERGER/ABAM Engineers
Tight tolerances.
Precast columnPrecast cap beam6 # 18 rebar8.5” corrugated steel ductsHigh strength grout
Cap-Beam Connection: Large bars
Cap-Beam Connection: Conclusions
• Failure occurs in the column.
• Large-bar precast connection behaves the same as a cast-in-place connection.
Column-to-FootingConnection
Footing Connection: Construction
Headed bars
Footing Connection: Headed Bars
Strut and Tie Model.
Footing ConnectionHooked bars facing out(Conventional cip)
Load transfer is tangential to hook.
Ineffective!
Footing Connection: Construction
Spread Footing ConnectionVertical (gravity) load.
Lateral (seismic) load.
Spread Footing Connection: Test
After seismic testing. Foundation undamaged.
Spread Footing Connection – Gravity Load Test
Column crushed at: 3.5 * (1.25DL + 1.75LL).
No damage to footing. No sign of punching failure.
Spread Footing Connection
Constructability:- Column has no projecting bars.- No “form-savers”.- Easy to fabricate and transport.
Spread Footing Connection
Structural Performance:• Terminators provide better anchorage than
hooked bars facing outwards.• Failure in column. Footing undamaged in
lateral load and vertical load tests.• Seismic performance as good as, or better
than, conventional c.i.p. construction.
Implementation
Bid Opening:
October 14th
Pre-Tensioned System
Pre-Tensioned System PC cap-
beamSleeved strand
Bonded strandc.i.p.
footing
Bonded rebar
Cracking plane
Pre-Tensioned System
1.Pre-tensioning solves corrosion problems perceived to exist in post-tensioning.
2.Pre-tension in a plant.
• Good QC.
• Special equipment and extra site time for post-tensioning are not needed.
• Can add rebars for energy dissipation.
Thank You
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