Improved bearing capacities of pultruded glass fibre reinforced polymer square hollow sections strengthened by thin-walled steel or CFRP

• Identification of reduced capacity of pultruded GFRP SHS under bearing load.
• Proposal of strengthening methods to improve the bearing capacity of GFRP SHS.
• Max 70% increase with CFRP strengthening; upto 380% after steel strengthening.
• Successful predictions of the improved bearing capacities of pultruded GFRP SHS.

Pultruded glass fibre reinforced polymer (GFRP) square hollow sections (SHS) are emerging as an alternative construction material in civil engineering. Different from thin-walled steel SHS, GFRP SHS is an orthotropic material and exhibits reduced capacity when concentrated bearing load is applied in the transverse to pultrusion direction. This paper examined two approaches to enhance the bearing capacity of the GFRP SHS, by using carbon fibre reinforced polymer (CFRP) sheets or thin-walled steel channel sections. Experimental studies were conducted on the strengthened pultruded GFRP SHS with two different dimensions. Two loading conditions, end-two-flange (ETF) and interior-two-flange (ITF), were applied to investigate the effect of loading position on the bearing capacity of the GFRP SHS. Experimental results were discussed with relation to the failure modes and load–displacement responses. It was found that the bearing capacity of pultruded GFRP SHS was effectively improved by up to 70% after CFRP sheets strengthening, and by over 380% after steel strengthening. Finally, equations were proposed for calculation of the improved bearing capacities of pultruded GFRP SHS with either CFRP sheets strengthening or steel strengthening. A reasonable agreement was achieved between predicted capacities and the experimental results.