Soil Structure Interaction of Integral Abutment Bridges

Abstract

Integral abutment bridges (IABs) are monolithically rigid structures distinguished by eliminating the use of expansion and bearing joints. This leads to enhanced structural performance and reduced maintenance costs. However, the complex soil-structure interactions (SSI) of IABs in response to seasonal variations in ambient temperatures are not yet fully understood. This research aims to use comprehensive numerical models to expand the understanding related to the intricate SSIs of these structures in response to various conditions. The Middlesex bridge in Vermont, USA, was selected as a case study for this research. The thermal response of the bridge was monitored over a period of two years, in which the acting pressures, internal forces, and deformations were measured. The numerical research conducted in this study first involved the development of two- and three-dimensional finite element (FE) models using the software PLAXIS, where the corresponding findings were verified against field acquired measurements for a single case-study bridge. Parametric studies were then conducted to investigate the effects of varying the constitutive soil model, thermal loading, backfill stiffness, abutment stiffness, pile size and orientation, and span length on the resultant earth pressure distributions and pile bending moments. It was found that using a linear constitutive soil model resulted in significant inaccuracies in the results. It was also found that theoretically approximated abutment displacements obtained using the measured temperatures yielded similar results to the field measured deformations. They hence can be used for future performance predictions for climate change studies. The study also revealed that increasing the backfill stiffness was found to increase backfill stresses and decrease pile bending moments. It also showed that varying the abutment stiffness had no impact on the earth pressures and pile bending moments. Smaller pile sections oriented for weak-axis bending yielded smaller pile bending moments and larger earth pressures. Increasing the span length increased backfill stresses and pile bending moments.