Effect of heating and cooling regimes on confined concrete in high strength concrete columns

Abstract

In this study, effect of various heating and cooling regimes on the residual compressive stress-strain behavior of confined high strength concrete is investigated. To this end, a total of 57 hoop confined and 21 unconfined high strength concrete cylindrical specimens of size 5.90 x 17.71 inch (150 mm x 450 mm) were tested. The specimens were exposed to seven different temperatures ranging from room temperature to1472°F (800°C). Two different heating rates (5°C/minute and 15°C/minute) and two cooling rates (natural air cooling and water quenching) were employed in the study. Measurements were taken for thermal gradient, spalling and residual axial load-displacement properties of confined high strength concrete. Test results indicate that the residual strength, strain corresponding to the peak stress and the post-peak strains of confined high strength concrete are affected only in the temperature range of 932°F to 1472°F (500 to 800°C). Experimental results show that faster rate of heating does not have any detrimental effects on the residual behavior of confined concrete. Lesser thermal induced effects were noticed in specimens exposed to faster rate of heating than in specimens subjected to slower rate of heating irrespective of the temperature of exposure. However, the results suggest that cooling with water quenching has adverse effect on the residual stress-strain properties of confined high strength concrete. Compared with natural cooling, thermal shock induced by water quenching caused more severe damage to confined high strength concrete, in terms of greater losses in confined concrete strength and increase in strains. The results of this study may be useful for designing the confining reinforcement of reinforced concrete columns against the multiple hazards of fire and earthquake.