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