Strength model for heat-damaged reinforced concrete circular columns confined with carbon fibre reinforced polymer fabrics

The strength models for fibre reinforced polymer wrapped columns available in the research literature were developed at ambient temperatures. To date, no experimental or analytical data have been available on the behaviour of large-scale reinforced concrete circular columns loaded during heating and cooling and subsequently wrapped with carbon fibre reinforced polymer fabrics. This paper deals with the development of new design-oriented strength models to predict the compressive strength of unheated and heat-damaged reinforced concrete columns confined with carbon fibre reinforced polymer. In this paper, 18 O 204 mm x 750 mm identical reinforced concrete columns were fabricated and tested, of which 12 were subjected to elevated temperatures under stress and then subsequently confined with carbon fibre reinforced polymer sheets after air cooling. The variables considered in these tests included the level of heat exposure and the number of carbon fibre reinforced polymer sheet layers. The digital image correlation technique and conventional foil gauges were used to determine the axial strain of carbon fibre reinforced polymer coupons and axial and lateral strains over the surface of unheated and heat-damaged carbon fibre reinforced polymer-wrapped columns. It was found that it is possible to repair heat-damaged concrete even to the extent of achieving the original compressive strength prior to heating through the use of appropriate carbon fibre reinforced polymer materials. The developed models were compared with the strength of columns obtained from test results of both unheated and heat-damaged carbon fibre reinforced polymer-wrapped columns and also with the existing ambient temperature strength models.