Fiber-Element Model for Cyclic Analysis of Concrete-Filled Fiber Reinforced Polymer Tubes

In recent years, concrete-filled fiber reinforced polymer (FRP) tube (CFFT) has been used as precast piles, girders, and pier columns in federally funded innovative bridge projects around the country. While the monotonic behavior of CFFT columns is studied rather extensively, their cyclic response is not yet fully understood. This paper presents a comprehensive composite beam-column fiber element for large displacement nonlinear inelastic analysis of CFFT beam columns. A two-dimensional three-node combined element is used with 13  degrees of freedom, including five for each end node and three for the middle node. The constitutive models for cyclic loading of FRP and concrete are described. The model is verified against the available cyclic test data of an earlier study on six CFFTs with and without internal steel reinforcement. A study is carried out to evaluate the effect of CFFT parameters on its hysteretic response, and to compare the response with reinforced concrete (RC) and concrete-filled steel tubes (CFSTs). The study shows the feasibility of designing CFFT columns with comparable hysteretic performance to RC columns. However, hysteretic response of CFFT columns cannot measure up to their CFST counterparts, unless their superior durability is considered in the selection process.