Physical and numerical investigation of integral bridge abutment stiffness due to seasonal thermal loading

Integral Abutment Bridges (IABs) are increasingly popular due to their reduced maintenance cost compared to traditional bridges with expansion joints. However, the widespread construction of IABs is currently limited by design code prescriptions resulting from the significant uncertainties associated with how the backfill interacts with the (integral) abutment and the deck. Under cycles of seasonal thermal loading, the backfill properties change, affecting the distribution of lateral earth pressures acting on the abutment walls. Moreover, the stiffness of the abutment can significantly influence the soil-structure interaction (SSI) in IABs. This research work investigates the effect of abutment stiffness (flexural rigidity) on soil-structure interaction in IABs under seasonal thermal loading through experimental analyses and numerical modelling. To better understand this mechanism and reliably assess the performance of IABs within their life cycle, a 1g small-scale instrumented physical model was built to simulate the backfill under accelerated seasonal expansion and contraction of the bridge deck. The experimental results were modelled numerically in PLAXIS and ABAQUS to assess the sensitivity to different flexural stiffnesses of the abutment and discuss suitable options for modelling such SSI systems through finite elements either using a geotechnical-oriented or a structural-oriented software package. It was found that flexible IABs can be more suitable for controlling earth pressure built-up within the early lifecycle of the soil-structure systems. The simplified numerical models can provide a first-order prediction of pressure distributions in the small-scale 1-g rig. This preliminary dataset informs necessary larger-scale experiments to assess the scaling and feasibility of 1-g tests.