Soil-Structure Interaction of Spread-Base Integral Bridge Abutments

Abstract

ABSTRACT To reduce long-term maintenance costs arising from the deterioration of concrete bridges due to leaky expansion joints, integral bridges have been becoming increasingly popular in many countries. Abandoning expansion joints leads to complex soil-structure interaction problems including those caused by cyclic temperature changes in the deck. These have adverse effects on the performance of integral bridges in terms of deformation mechanisms, lateral earth pressures acting on the abutment wall, bending moment and axial stress in the deck. All these are of great concern to engineers. Centrifuge model tests were conducted on spread-base integral bridge abutments to simulate these temperature effects on the soil-structure interaction. Thermal expansion and contraction of the deck were modelled by imposing controlled cyclic displacements at the top of the abutment wall. Substantial horizontal sliding and the rocking of the abutment due to soil densification and “strain” ratchetting were observed. The measured lateral earth pressure increased with the amplitude of the displacements into the fill (in the passive sense) and the number of cycles, but at a decreasing rate. For the ultimate limit state and the 1 in 120 years return event, the measured lateral earth pressure coefficient was 3.7 and 4.2 for the abutment backfilled with dense and loose sand respectively. The measured bending moments varied fairly linearly with depth, rather than varying as a cubic function with depth as would be expected for a relatively flexible wall subjected to a triangular distribution of lateral pressure. The measured value appeared to reach the design bending capacity of the reinforced concrete wall and base for the 1 in 120 years return event.