Three-Dimensional Numerical Model for Seismic Analysis of Bridge Systems with Multiple Thin-Walled Partially Concrete-Filled Steel Tubular Columns

Thin-walled partially concrete-filled steel tubular (PCFT) columns have come to be used as the piers of elevated-girder bridges widely in Japan because of their excellent seismic performance: strength, ductility, and energy dissipation capacity. To consider this excellent seismic performance in design, it is essential to provide an analysis method to assess the ultimate behavior of the thin-walled PCFT columns by considering the cyclic local buckling of the steel tube, the behavior of the confined infilled concrete with cracks, and the interface action between the steel tube and infilled concrete. Up to the present, the shell–solid element model analysis has been the only numerical method that can be used to consider these complicated behaviors of PCFT columns in a direct manner. However, the use of this model requires unrealistically long computation time and often encounters numerical difficulty to obtain convergent solutions when applied to large structural systems such as the elevated-girder bridge systems with the multiple thin-walled PCFT piers. The objective of the present research is to propose a practical three-dimensional fiber-based model with a failure segment that is computationally efficient, yet accurate enough to assess the ultimate behavior of PCFT columns. This model was calibrated by an optimization technique, only referring to the in-plane hysteretic behavior of each single PCFT column calculated by the shell–solid element model analysis. The calibrated model is applicable to the seismic analysis of large structural systems with multiple PCFT piers under arbitrary multidirectional seismic accelerations. The accuracy and numerical efficiency of the proposed fiber-based model in the analysis of PCFT columns were confirmed extensively by the comparison to the shell–solid element model analysis results and the results of tests, such as cyclic loading tests and shake table tests.