Residual load carrying capacity of reinforced concrete cylinders after heating at elevated temperature

Abstract

The present research work is investigating the behavior of reinforced concrete (RC) cylinders after exposure to elevated temperatures. Reinforcement was done by using the longitudinal bars with closely spaced lateral ties (i.e. confinement). Experiments were carried out on the RC cylinders subjected to a single heating–cooling cycle of elevated temperature ranging from 200 to 800 °C with an interval of 200 °C for a holding time of 3 h. The crack patterns, color change, spalling and residual load carrying capacity of RC cylinders after exposure to elevated temperature have been observed. The residual load carrying capacity of RC cylinders has been compared with the load carrying capacity of control specimens at ambient temperature. The percent reduction in residual load carrying capacity after heating at 200 °C, 400 °C, 600 °C, and 800 °C temperature is 24.5%, 38.8%, 63.3%, and 83.7% respectively as compared with the load carrying capacity at ambient temperature. The finite element modeling (FEM) has been carried out to observe the thermal stresses and strains induced in the confined RC cylinders. Experimental observations of thermal strains and those obtained by the numerical model showed a good agreement. The scanning electron microscopy (SEM) has also been carried out to study the changes in the microstructure of confined high grade concrete and it was observed that the micro-cracks and pores increase and become more pervasive with increase in temperature.