Seismic Analysis of Integral Abutment Bridges Considering Soil-Structure Interaction

Abstract

Integral abutment bridges are single or multiple span bridges with the superstructure cast integrally with the substructure and designed without any expansion joints in the bridge deck. These bridges are usually designed to spread the stiffness and flexibility throughout the structure and the soil so that all supports accommodate the loads. These bridges usually include capped pile stub abutments. The piers are typically constructed in such a way that they may be cast either integrally with or independent of the superstructure. Semi-integral bridges are single or multiple span continuous bridges with rigid, non-integral foundations and movement systems primarily composed of integral end diaphragms, compressible backfill, and movable bearings in a horizontal joint at the superstructure abutment interface. The first integral bridge was built in 1938 at the Teens Run Bridge in Ohio in the United States. It consisted of five continuous reinforced concrete slab spans supported by capped pile piers and abutments. The construction of integral bridges has since spread throughout the United States and abroad. It is important to reduce or eliminate roadway expansion joints and associated expansion bearings to improve structure life and maintenance costs. Joint bearings are expensive to buy, install, maintain repair, and replace. Corrosion causes leaking expansion joints and seals which leads deicing salt from the roadway surface to attack the girder end bearings and concrete substructures. Therefore, many states have been eliminating joints and bearings where possible and trying to go with cost-effective alternative jointless bridges despite the uncertainty and complexity of integral bridge behavior. These integral bridges offer several advantages over conventional structures and are currently used in more than thirty different states, Canadian provinces, and Europe. However, engineers should have a good understanding of conventional bridges since integral bridges are subjected to the same secondary effects as conventional bridges, which include shrinkage, creep, thermal gradients, and differential settlement. In particular thermal movements need to be well understood because the movement must be accommodated by other means since deck joints are not provided.