Soil-Structure Interaction and Near Fault Pulse-like Earthquakes Effects on Seismic Responses of Isolated Bridges.

Seismic isolation technology is an effective tool for mitigating seismic risk and improving structural performance during strong earthquakes. However, some parameters, such as earthquake and soil characteristics, influence and may reduce isolation technology’s performance. This research aims to investigate the simultaneous effects of soil-structure interaction (SSI) and pulse-like earthquakes on the seismic responses of conventional and isolated bridges. Near-fault (NF) earthquakes with and without velocity pulses in their records are applied to the structure of a three-span bridge located in Vancouver (Canada), with and without considering the underlying soil. Using the direct method, three soil properties representing rock, stiff and medium soil are modeled by Abaqus software. Nonlinear time history analysis (NLTHA) is carried out, and structural responses regarding maximum deck acceleration, base shear, and displacement of the deck and the isolation systems are studied. Results demonstrate that pulse-type records cause higher seismic responses, and soil presence diminishes the negative effect of the pulse on the force demands. On average, and for the pulse-like records, the softer soil reduces the acceleration by up to 30% and base shear responses by up to 25% while increasing the displacement demand of conventional and isolated bridges by up to 80%. Therefore, careful attention should be paid to the isolation systems’ design to prevent underestimating the displacement demand for pulse-like records, especially on softer soils. Responses of the different isolation systems demonstrate that the optimum design could provide the displacement demand for pulse-type records even on softer soils.

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