Observed integral abutment bridge substructure response

Two integral abutment bridges in Vermont, USA were instrumented and monitored to report behavior under seasonal thermal load. This paper describes substructure response from 30 months of field data. The bridges are single span steel girder bridges of approximately 40 m on pile foundations. One bridge is straight while the other has a 15° skew. Variations in substructure displacements, backfill pressures and pile moments are reported under hot, cold and moderate ambient temperatures. Abutment and pile deformation plots highlight maximum displacements at the top of piles that are often only 1/3 to 1/2 of the values at the top of the abutment. Maximum pile moments correspond to concentrated curvature at the pile–abutment interface which did not correspond to peak temperatures. Substructure deformation response was predominantly elastic under bridge contraction, but highly non-linear under bridge expansion and varied from year to year. No indication of soil ratcheting was observed in the backfill materials and design for full passive pressure appears to be overly conservative for these single span structures. No indications of pile yielding were observed in the Grade 345 steel piles. Backfill pressures were consistent across the abutment in the straight bridge, but highly variable in the 15° skew bridge.