Probabilistic Performance-Based Seismic Design of Bridge Columns

Abstract eng:
Because earthquakes are random events it is reasonable to design structures taking into account the non-deterministic features of response. Performance-based design is intended to provide options to designers and bridge owners to manage the target performance of the structure. Probabilistic damage control approach (PDCA) is a new procedure for seismic design of bridges subjected to earthquakes. As part of a study funded by the California Department of Transportation (Caltrans), this innovative design methodology is developed by incorporating “Damage Index” (DI) and different earthquake return periods to provide flexibility to the designer. The damage level of the bridge is established for each earthquake level as a function of the degree of lateral displacement nonlinearity and is related to six apparent damage states (DS) defined in a previous study at the University of Nevada, Reno. The correlation between DI and DS was determined from a statistical analysis of measured data for 21 bridge column models subjected to seismic loads on shake tables. Extensive analytical modeling of seismic response of two-column bents was conducted. A wide range of variables was included in the study to address the effect of aspect ratio, transverse steel ratio, longitudinal steel ratio, material properties, site class, return period, target DI, and the number of columns in bents. Each column bents was analyzed under fifteen near-field and ten far-field ground motions. A statistical analysis of the demand DIs was performed to develop fragility curves and calculate the reliability index for each DS. The calculated reliability index and fragility curves show that the proposed method can be effectively used in seismic design of new bridges.

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