UBC Theses and Dissertations
Investigation of effects of soil-structure interaction on the seismic response of bridges using a performance-based design approach Ashkani Zadeh, Kianosh
Soil-structure interaction (SSI) can have a significant impact on the response of structures subjected to strong earthquakes. Despite its major effects, SSI is not sufficiently addressed in current design code and practice. In this study, the effect of SSI on the seismic response of Reinforced Concrete (RC) bridges is studied within the framework of performance-based earthquake engineering. This thesis is organized in three phases that investigate three different aspects of SSI in relation to analysis, assessment and design. The Meloland Road Overcrossing (MRO) in California is chosen as the case study in this research. Phase one is focused on investigating the kinematic effect and variation of foundation motion from the free-field motion. To achieve this, detailed 3D continuum models are developed. Response time history analyses are performed on the models using ten unscaled ground motions to investigate variation of bridge foundation motions from free-field motions. The finite element simulation results show that an amplification of the free-field motions takes place in the low frequency regime that covers the first few natural frequencies of the system. The tau-averaging method and Elsabee and Morray Transfer function are unable to predict the amplification regime observed in the simulations. In phase two, a discrete simulation approach is adopted to carry out performance assessment of RC bridges considering soil-structure interaction. Four archetype models with various levels of SSI representation are developed. Incremental Dynamic Analysis (IDA) is performed using a set of 22 ground motions to derive collapse fragility curves for each archetype model. The role of SSI in the calculated collapse fragility curves and corresponding failure modes is investigated. A FEMA-based collapse assessment procedure is proposed to quantify the performance of RC bridges. In phase three, a comprehensive nonlinear continuum model of the MRO is developed. Seismic response of the continuum model in terms of drift, base shears, and spectral acceleration is compared to the discrete model developed in previous phase. It is shown that the responses predicted using the discrete and continuum approaches are significantly different mainly due to their differences in material constitutive models or representation of SSI effects, specifically the kinematic effect.
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