Nonlinear Soil-structure Interaction of Bridges : Practical Approach Considering Small Strain Behaviour

Abstract

The precise and functional simulation of soil-structure interaction problems requires an overall understanding of the nonlinear characteristics of both the soil and structure. A look at the literature reveals that a deep knowledge on solely one of the soil or structure usually ends up with complex solutions with practical limitations and lack of generality. Therefore, the current study aims to propose a nonlinear coupled soil-structure modelling strategy. To do this, first soil and structural nonlinearity are discussed separately in order to select the most feasible modelling framework. Furthermore, a large and rarely accessible database including shear modulus decaying curves, maximum shear modulus, and index properties is analysed thoroughly. It is observed that there is a strong correlation between plasticity index and soil nonlinearity in cohesive soils. Consequently, empirical relations are introduced for modelling soil nonlinearity which include a few parameters with clear physical meaning. In addition, it was shown that maximum shear modulus of plastic soils can be approximated with acceptable accuracy if the variability and overconsolidation ratio are low. With respect to the nonlinear structural modelling, fiber section and nonlinear shell approaches which are computationally faster and more practical compared to the complex continuum modelling platform are used in this study. All in all, straightforward yet precise nonlinear numerical models, including a reinforced concrete column, reinforced concrete wall, single pile-soil, pile group-soil, and wall-soil, are created and verified with respect to the large-scale tests in the literature. Finally, two fully coupled instrumented bridge-soil interaction cases in the literature are explicitly modelled and a good agreement is reached between the estimations and measured values. Also, sensitivity analysis is performed to identify the most crucial elements in a bridge-soil model. It is observed that backfill soil and wing walls are important elements, while the effect of soil resistance behind the pile caps is negligible on the overall response. In addition, simplified models which totally neglected the soil behaviour resulted in the most unrealistic estimations.