Experimental determination of the resistance of pultruded FRP beams failing by lateral torsional buckling

This paper presents experimental test results for Pultruded FRP (PFRP) beams failing by elastic Lateral- Torsional Buckling (LTB). Loading is three-point bending, with vertical load applied at the shear centre. Beams are simply supported at both ends for major axis flexure in a special fixture that can give either 'full' or 'free' fixity for flexure about the minor axis. Load is transferred into the specimen using a specifically-designed fixture that allows LTB deformation to be accommodated without restraint. Results are obtained for 38 tests using four different PFRP sections at four or five spans, and with or without fixity of the minor axis flexure at the ends. Buckling resistance is established from test measurements either by using the Southwell plot method when a specimen does not experience 4a sudden instability' or from the peak load when LTB failure gives a bifurcationlike response. Measured LTB resistances are compared with predictions obtained using a closed form equation to show that the latter may be suitable, after calibration and verification, for inclusion in a design standard.