Experimental investigation on the behaviour of FRP strengthened square hollow section steel members under monotonic and cyclic loading

Strengthening and rehabilitation of square hollow sections (SHS) are a major concern nowadays as SHS may fail due to higher service loads, fabrication and construction errors, degradation of material over time and adverse effects of the cyclic loading due to earthquakes. In this study, a detailed experimental investigation has been carried out for the implications of using carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) as a strengthening measure to mitigate the failure of SHS members under monotonic and cyclic loadings. Strengthened members displayed lower moment degradation and higher moment and energy dissipation capacities and higher stiffness and ductility compared to the bare steel members. Although the amount of CFRP and GFRP fibres were almost equal, CFRP strengthening can result in higher capacity sections due to having higher strength material properties compared to GFRP strengthening. The cyclic responses of the GFRP-strengthened member were close to that of the CFRP-strengthened member and can be more effective for strengthening steel SHS under cyclic flexural loading. The established theoretical model in the current paper can predict reliably the ultimate moment capacities of the strengthened SHS members. This study confirmed that strengthening SHS members with fibre composites will be effective for structures in seismically active regions.