Stability of FRP Beams under Three-point Loading and LRFD Approach

Abstract

This article presents the results of an experimental and theoretical study of I-section fiber-reinforced plastic (FRP) beams subjected to a gradually increasing midspan load. The load is applied about the beam major axis from the compression flange side through a point below the shear center. The boundary conditions are flexurally and torsionally pinned. A 4 2 1/4 in. 3 pultruded I-section is adopted for the study and beam span lengths of 108, 96, 84, and 72 in. are used. The flexural-torsional response of the FRP beams is studied experimentally up to the maximum loadcarrying capacity. The experimental peak loads are compared with those arrived at theoretically using an equilibrium approach and are found to be in good agreement. To obtain a design expression for estimating the beam buckling load, an elastic buckling moment expression from the load and resistance factor design (LRFD) specification of the American Institute of Steel Construction is first modified. Next, a LRFD approach for the beam is outlined and its use demonstrated through analysis and design examples.