Analytical and Experimental Study of Lateral and Distortional Buckling of FRP Wide-Flange Beams

Abstract

A combined analytical and experimental evaluation of flexural-torsional and lateral-distortional buckling of fiber-reinforced plastic (FRP) composite wide-flange (WF) beams is presented. Based on energy principles, the total potential energy equations for instability of FRP WF sections are derived using the nonlinear elastic theory. For the analysis of lateral-distortional buckling, a fifth-order polynomial shape function is adopted to model the deformed shape of web panels. The models are validated by testing two geometrically identical FRP WF beams but with distinct material architectures produced by the pultrusion process. The beams are tested under midspan concentrated loads to evaluate their flexural-torsional and lateral-distortional buckling responses. To detect rotations of the midspan cross sections and onset of critical buckling loads, horizontal transverse bars are attached to the beam's flanges, and the bar ends are connected to linear variable differential transducers (LVDTs). For the same purpose, we use strain gauges bonded to the upper and lower surfaces near to the free edges of the top flange. A good agreement between the proposed analytical approach and experimental and finite-element analyses results is obtained, and simplified engineering equations for flexural-torsional buckling are formulated. The proposed analytical solutions can be used to predict flexural-torsional and lateral-distortional buckling loads for other FRP shapes and to formulate simplified design equations.