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Concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) have in the last decade been used as girders, beam columns, and piles. The focus of research, however, has been exclusively on their monotonic behavior, with little or no attention to the implications of using CFFT in seismic regions. A total of six CFFT specimens were tested as simple span beam columns under constant axial loading and quasi-static reverse lateral loading in four point flexure. Three of the tubes were made using centrifuge (spin) casting with 12.7 mm thickness with the majority of the fibers in the longitudinal direction, whereas the other three were filament wound with 5 mm thickness and ±55° fiber orientation. One specimen for each type of tube had no internal reinforcement, whereas the other two incorporated approximately 1.7 and 2.5% steel reinforcement ratios, respectively. The two types of tubes represented two different failure modes; a brittle compression failure for the thick tubes with the majority of the fibers in the longitudinal direction, and a ductile tension failure for the thin tubes with off-axis fibers. The study showed that CFFT can be designed with ductility behavior comparable to reinforced concrete members. Significant ductility can stem from the fiber architecture and interlaminar shear in the FRP tube. Moderate amounts of internal steel reinforcement in the range of 1–2% may further improve the cyclic behavior of CFFT. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer (FRP) materials are generally known for their linear elastic response to failure. The present study evaluated the implications of using FRP as primary and sole reinforcement for concrete structures in seismic regions through an experimental and analytical investigation on the cyclic response of two different types of laminated glass FRP tubes filled with concrete. The study showed that concrete-filled tubes can be designed with an appropriate laminate structure for a ductility level comparable to that of conventional reinforced concrete columns. The nonlinearity and ductility in these types of structures stem from the off-axis response of the FRP tube. A hysteretic model was developed for the tube, and was cast into a two-dimensional three-node combined fiber element for the concrete-filled FRP tube. Good agreement was shown between the analytical models and the experimental results. [Copyright &y& Elsevier]