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Field Behavior of an Integral Abutment Bridge Supported on Drilled Shafts

Field Behavior of an Integral Abutment Bridge

Supported on Drilled Shafts

Phillip S.K.Ooi,P .E.,M.ASCE 1;Xiaobin Lin 2;and Harold S.Hamada,P .E.,F.ASCE 3

Abstract:The abutments of integral bridges are traditionally supported on a single row of steel-H-piles that are flexible and that are able to accommodate lateral deflections well.In Hawaii,steel-H-piles have to be imported,corrosion tends to be severe in the middle of the Pacific Ocean,and the low buckling capacity of steel-H-piles in scour-susceptible soils has led to a preference for the use of drilled shaft foundations.A drilled shaft-supported integral abutment bridge was monitored from foundation installation to in-service behavior.Strain gauge data indicate that drilled shaft foundations worked well for this integral bridge.After 45months,the drilled shafts appear to remain uncracked.However,inclinometer readings provide a conflicting viewpoint.Full passive earth pressures never developed behind the abutments as a result of temperature loading because thermal movements were small and the long term movements were dominated by concrete creep and shrinkage of the superstructure that pulled the abutments towards the stream.In the stream,hydrodynamic loading during the wet season had a greater effect on the abutment movements than seasonal temperature cycling.After becoming integral,the upright members of the longitudinal bridge frame were not vertical because the excavation and backfilling process caused deep seated movements of the underlying clay resulting in the drilled shafts bellying out towards the stream.This indicates the importance and need for staged construction analysis in design of integral bridges in highly plastic clays.Also,the drilled shaft axial loads from strain gauges are larger than expected.

DOI:10.1061/͑ASCE ͒BE.1943-5592.0000036

CE Database subject headings:Bridge abutments;Drilled shafts;Strain gages;Earth pressure;Moment;Axial loads .Author keywords:Integral abutment bridge;Drilled shaft;Strain gage;Inclinometer;Earth pressure;Moment;Axial load .

Introduction

Integral abutment bridges ͑IABs ͒are jointless bridges that enjoy the following advantages over conventional bridges ͑Arockiasamy et al.2004;Hassiotis and Roman 2005;Kunin and Alampalli 2000;Mistry 2005;Wasserman and Walker 1996͒:1.Lower maintenance costs due to elimination of joints and

bearings.

2.Simpler and more economical construction ͑e.g.,only a

single row of vertical piles is needed at the abutment plus expansion joints and bearings are eliminated ͒.

3.Added redundancy and capacity during seismic events and

against buoyancy loads during flooding and wave loading during hurricanes or tsunamis.4.Improved ride quality.

5.Integral abutments and piles help resist uplift forces acting

on the beams at the end spans.In conventional bridges where the beam is not structurally connected to the abutment,uplift of beams at the end spans can occur during deck placement and during vehicular movement.

6.Integral abutments spread the lateral loads throughout the

structure/soil system so that all supports accommodate these loads.This reserve capacity is not available in conventional bridges since the lateral loads are not distributed to the abut-ments.

7.Bridge replacements can be accomplished easily with IABs

since they do not require large footings and they can be readily constructed behind existing buried foundations with-out the need for large excavations.

Despite the significant advantages,there are problems associ-ated with IABs,most of which arise from elimination of joints thereby forcing lateral movements to occur at the abutments.In both conventional bridges and IABs,lateral movements are caused by earth pressures,hydrostatic,traffic,impact,wind,and seismic loading.However,integral abutments are subject to the following additional superstructure-induced lateral loads not ex-istent in conventional bridges:͑a ͒thermal expansion and contrac-tion;͑b ͒concrete shrinkage ͑change in volume under zero stress ͒;and ͑c ͒concrete creep ͑change in volume under constant stress ͒.Excessive lateral movements may result in the following problems:

1.Piles that support integral abutments are subject to bending,

which can lead to formation of plastic hinges.To better ac-commodate lateral deflections,it is desirable to increase pile flexibility by supporting integral abutments on a single row of vertical steel-H-piles.

1Associate Professor,Dept.of Civil and Environmental Engineering,Univ.of Hawaii,Holmes Hall 383,2540Dole Street,Honolulu,HI 96822͑corresponding author ͒.E-mail:ooi@http://www.doczj.com/doc/77ec59d8cc175527072208f5.html 2

Former Research Assistant,Dept.of Civil and Environmental Engineering,Univ.of Hawaii,2540Dole Street,Honolulu,HI 96822.E-mail:xiaobin@http://www.doczj.com/doc/77ec59d8cc175527072208f5.html 3

Emeritus Professor,Dept.of Civil and Environmental Engineering,Univ.of Hawaii,Holmes Hall 383,2540Dole Street,Honolulu,HI 96822.E-mail:hamada@http://www.doczj.com/doc/77ec59d8cc175527072208f5.html

Note.This manuscript was submitted on June 5,2008;approved on February 16,2009;published online on April 14,2009.Discussion period open until June 1,2010;separate discussions must be submitted for indi-vidual papers.This paper is part of the Journal of Bridge Engineering ,V ol.15,No.1,January 1,2010.©ASCE,ISSN 1084-0702/2010/1-4–18/$25.00.

4/JOURNAL OF BRIDGE ENGINEERING ©ASCE /JANUARY/FEBRUARY 2010

J. Bridge Eng., 2010, 15(1): 4-18

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