Seismic Performance of Circular Concrete Filled Steel Tube Columns for Accelerated Bridge Construction

Abstract

This study evaluates the seismic performance of circular concrete filled tube (CCFT) columns in accelerated bridge construction (ABC) projects. CCFT components are considered of interest for bridges subjected to seismic forces due to their efficient structural behavior under combined axial and bending loads: lateral stiffness of the steel tube is increased by the concrete and concrete confinement is provided by the steel tube. This paper addresses the ability of CCFT columns to perform adequately under gravitational and seismic loading before the concrete has reached its design strength. A reduced seismic hazard that accounts for this temporal condition is also implemented. The evaluation of performance is based on the probability of failure of the CCFT column. For this research, a Caltrans bridge used in previous PEER studies is adopted. The performance of a proposed CCFT column is compared to the original circular reinforced concrete (RC) column. Numerical analyses using concentrated plasticity models in OpenSees were used for this evaluation. Experimental data was used to calibrate the deteriorating response of CCFT columns in OpenSees. The analytical model predicts the CCFT column’s behavior under monotonic, static cyclic, and dynamic (seismic) loading. Then, the model was adapted to consider the effects of partial strength concrete to assess the column behavior under the temporary condition of the concrete not having reached full strength. The study accounts for temporary conditions, such as concrete compressive strength lower than the design value, and reduced seismic loads. The results indicate that CCFT columns with partial design concrete compressive strength can be used for ABC because the relatively low decrease in strength is offset by the reduced seismic loads for this temporal condition.