Web crippling behaviour of pultruded glass fibre reinforced polymer sections

We investigated the web crippling behaviour of pultruded GFRP sections under concentrated loading, employing four square hollow sections of different sizes. End-two-flange (ETF) and interior-two-flange (ITF) loading conditions were adopted, with specimens seated on a bearing plate. Specimens were also placed on the ground with end or interior bearing load to simulate the loading conditions of floor joist members. The observed failure initiated at web–flange junctions and was followed by buckling or crushing in the webs, and these modes were quite different from metallic sections. Correspondingly, two load limits were defined according to the progressive failure process. The effects of the loading positions (end loading or interior loading) as well as the supporting conditions (on a bearing plate or on the ground) on the web crippling behaviour are discussed. An effective web area in the pultrusion direction is identified to characterize the load transfer path within the web. Finally, a simple mechanism based design equation is proposed to estimate the strength of such pultruded GFRP sections subjected to web crippling.