Abstract
It is widely accepted that concrete columns confined with fiber-reinforced polymer (FRP) jackets exhibit significant increases in strength and ductility with reference to the unconfined case. Existing experimental studies have indicated that the hoop rupture strains measured in the FRP jackets are significantly lower than the material strain capacity determined by the flat coupon tensile tests. An FRP efficiency factor is then usually used to define the ratio of the average hoop rupture strain to the material strain capacity of the FRP jackets, which governs the lateral FRP confinement as well as the peak strength and ultimate strain of the FRP-confined concrete under axial compression. FRP jackets are also expected to be a promising solution to repair damaged RC columns after fire exposure. However, there is lacking research on the behavior of FRP-confined fire or heat-damaged concrete columns. In particular, the FRP efficiency factor of FRP-confined fire or heat-damaged concrete columns has not yet been established. The study presents the results of an experimental study aimed to investigate the effects of the historical high temperature and the layer of basalt FRP (BFRP) jackets on the efficiency factor of BFRP for the confined heat-damaged concrete cylinders. A sum of 51 standard concrete cylinders is prepared and tested under axial compression. The parameters varied between tests are the historical high temperature (200°C, 400°C, 600°C, or 800°C) that is used to produce the heat damage of concrete cylinders and the number of layers of BFRP jackets (2, 3, or 4). The test results have indicated that the efficiency factor of BFRP jackets increases with the historical high temperature but decreases slightly with the increase in the BFRP layers. A new temperature-dependent design equation for the BFRP efficiency factor of the confined heat-damaged concrete is proposed to consider the effects of the parameters mentioned above and can be used for practical design.
Highlights
Fiber-reinforced polymer (FRP) composites have been widely used for the repair and strengthening of concrete columns
The existing results have indicated that the fiber-reinforced polymer (FRP) jackets usually exhibit tensile rupture failure with a strain level lower than the maximum tensile strain of the material measured by the flat coupon tests (Rousakis and Tepfers, 2004; Berthet et al, 2005; Lam et al, 2006; Jiang and Teng, 2007; Wang and Wu, 2008; Smith et al, 2010; Lim and Ozbakkaloglu, 2014; Jian and Ozbakkaloglu, 2015)
To further investigate the basalt FRP (BFRP) efficiency factor of the BFRPconfined heat-damaged concrete cylinders, this study presents the results of the axial compressive tests aiming to examine the effects of the heat-induced damage level of concrete and the number of BFRP jacket layers on the efficiency of BFRP jackets in the BFRPconfined heat-damaged concrete cylinders
Summary
Fiber-reinforced polymer (FRP) composites have been widely used for the repair and strengthening of concrete columns. The existing results have indicated that the FRP jackets usually exhibit tensile rupture failure with a strain level lower than the maximum tensile strain of the material measured by the flat coupon tests (Rousakis and Tepfers, 2004; Berthet et al, 2005; Lam et al, 2006; Jiang and Teng, 2007; Wang and Wu, 2008; Smith et al, 2010; Lim and Ozbakkaloglu, 2014; Jian and Ozbakkaloglu, 2015). Some researchers have proposed FRP efficiency factors to describe the ratio of the hoop rupture strain of FRP jackets to the maximum tensile strain of the material.
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