Keywords: soil-structure interaction, seismic, incoherence, numerical model, soil response, bridge response.

Designing linear structures, such as bridges, overpasses or pipelines, requires evaluating the ground motion variability effects in order to quantify the relative displacements of the columns, in both longitudinal and transverse directions and to avoid collapse. Considering the damage extent of the recent 2010 Chile earthquake (M_w = 8.8), a similar seismic scenario was examined in the Mexican subduction zone. A deterministically-derived strong ground motion was developed for a seismic moment magnitude, M_w, of 8.7. This paper presents the results of a numerical study conducted using a two-dimensional finite difference model of a section of an overpass which is to be built in Mexico City, involving seven supports, using the program FLAC [1]. Initially, the response of the free field was calibrated comparing the results obtained with FLAC, with those obtained using a finite element model developed with the program QUAD4M [2], using equivalent linear properties. Cross-hole measurements were used to characterize shear wave velocity distributions with depth, and the depth to bedrock was defined throughout the geophysical investigation, along with SPT borings. The stress-strain behavior of the soil was described with a bilinear Mohr-Coulomb constitutive law. Massive raft foundation were considered as an elastic material and modeled with four node quadrilateral zones with equivalent volumetric weight and stiffness. The piles, columns and beams were modeled with two-dimensional beam elements. Good agreement was observed between the results computed with FLAC and QUAD4M for the free field. The presence of a soil layer under one support of the structure and a rock outcrop under the others, results in different amplification effects. These implications should be taken into account during the design process, thus the soil-structure interaction should not be overlooked. Longitudinal relative displacements were obtained in the mobile nodes of the structure. This numerical study and future instrumentation of this structure will help to gain insight into the importance of considering the soil-foundation-structure interaction and for this type of structures.

1

Itasca Consulting Group, "FLAC, Fast Lagrangian Analysis of Continua, User's Guide", Minneapolis, Minnesota, USA, 2005.

2

M. Hudson, I.M. Idriss, M. Beikae, "Quad4M User's manual. A computer program to evaluate the seismic response of soil structures using finite element procedures and incorporating a compliant base", 1994.

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