Static behavior of pultruded fiber-reinforced polymer thin-walled beams

Abstract

Pultruded profiles made of fiber-reinforced polymer (FRP) materials are increasingly used in the construction industry as primary and secondary load-bearing members, because of their low weight, high mechanical properties and good corrosion behavior. FRP structural members are usually pultruded with I, H, C, box or other thin-walled closed or open sections. The mechanical behavior of pultruded FRP members, having continuous unidirectional fibers embedded into a polymeric resin, can be described as transversely isotropic, where the plane of isotropy is perpendicular to the fibers. The static behavior of FRP pultruded profiles has been subject of numerous analytical and numerical investigations. Among the former, a common approach adopted in the past has been to extend to orthotropic materials the well-known theory for thin-walled beams developed by Vlasov and Timoshenko. In this paper, a different approach to the static analysis of FRP pultruded profiles is presented. The exact theory of thin-walled isotropic beams developed by Capurso in 1964 is generalized to the case of transversely isotropic materials and its predictions are analyzed. Such a theory eliminates the limitations related to St. Venant’s principle and thus allows determination of the state of stress in the proximity of restraints or concentrated loads, and the state of stress generated by arbitrary loads acting on the lateral surface of the beam. It is shown that, for transversely isotropic materials and within the range of mechanical properties of common FRP profiles, the discrepancy between exact and Vlasov formulations may be significantly larger than for isotropic materials. Hence, Vlasov theory may lead to significantly inaccurate predictions of the state of stress. A numerical example is presented for the I-profile.