Improvement of Fire resistance of Reinforced concrete colu mns by using diamond tie configuration

Abstract

As per the Indian codal guidelines, the ties in reinforced concrete columns are provided either as rectangular or circular depending on the shape of column. In addition to perimeter ties, single or multi-legged crossties are also provided for larger sections. At ambient temperatures, it has been observed that decrease in tie spacing is beneficial as it increases moment capacity of the section leading to better confinement. However, in case of fire the positive effects of decrease in tie spacing beyond 100 mm have not been observed. Considering that the transverse and circumferential cracks are observed in columns due to thermal gradients as known from literature review, the diamond tie configuration was adopted in reinforced concrete columns. Three reinforced concrete columns of full-scale size, 3.15 m each, (two control and other with diamond configuration) are loaded at service load with maximum expected load eccentricity. They are subjected to ISO-834 standard fire curve in a furnace. It is observed that there is an improvement in fire resistance by 150% for column with diamond configuration as compared to rectangular tie configuration with crossties. Further, it is observed that there was no appreciable variation in the amount of spalling for columns with diamond configuration. This indicated better confinement during fire for columns with diamond configuration. It also indicates that diamond configuration of ties reduces the effect of thermal gradient cracks in limiting the fire resistance of RC columns particularly at decreased tie spacing. © 2019 Associated Cement Companies Ltd.. All rights reserved.