Validation of seismic soil-foundation-structure interaction analysis procedures for instrumented bridges

Anoosh Shamsabadi, PhD., PE (Senior Bridge Engineer, California Dept of Transportation (CALTRANS)) Maziar Partovi, PhD (Senior Engineer, TNO DIANA BV)

Instrumented bridges in highly seismic regions are typically supported on complex pilefoundation systems consisting of vertical and battered piles supporting a pile-cap above the mud-line. These bridges provide vital transportation links to metropolitan areas, and their closure to traffic in the aftermath of a damaging earthquake can cause debilitating levels of hardship. Recognizing their importance, California Department of Transportation (Caltrans) and California Geological Survey (CGS) have instrumented a number of such bridges, and have been collecting their strong motion response measurements for more than two decades. The deployed instrument sets usually include down-hole sensor arrays, and accelerometers installed on piles, pile-caps, and decks.
Understanding the global Soil-Foundation-Structure Interaction of instrumented bridges is essential to capturing their performance during a major seismic event. In the present study, we model the pile-soil interaction by a series of discrete translational and vertical springs distributed along the pile length and so called “beam-spring” model and to simulate a real nonlinear impact of different soil layers and parameters in conjunction with development of confined stresses on foundation systems and superstructure’s behavior in seismic analysis, we need to simulate all these effects in a full scaled model, so called “continuum” model. To this end, we first develop a highly detailed three-dimensional nonlinear finite element model of instrumented bridges in California using both nonlinear beam spring as well as continuum models in DIANA. By applying system identification techniques over recorded motions, as well as recursive and heuristic modeling iterations, we then update theses finite element models, with the specific aim of calibrating the nonlinear continuum model parameters. We finally use the updated model and attempt to quantitatively assess the simplified modeling procedures viz., the beam-spring model and continuum model for seismic design and analysis of bridges

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