Fire resistance of reinforced concrete frames subjected to service load: Part 1. experimental study

Abstract

This paper describes the results of fire tests, which were carried out to study the behavior of moment-resisting reinforced concrete frame at elevated temperatures. The continuity of the beams with the columns generates considerable internal forces and rotation demands, which in turn could have detrimental (geometrical second order effect) and/or beneficial (increasing load bearing capacity) influences on the fire resistance of the global structure. In this paper, two 1/3 scale statically indeterminate RC frames, RCF1 and RCF2, under service loads were exposed to the ISO-834 fire. The target frame was a two-storey frame, in which the lower columns and middle beam were under fire attack. RCF1 was heated for 175 minutes until eventually its concrete beam failed from the excessive flexural cracks and deformations, whereas RCF2 was heated for 60 minutes until the temperature of the tensile reinforcements of its beam reached 550°C. The beam ends and the joints relatively attained lower internal temperatures owing to the unheated upper columns. The axial and moment restraints significantly increased the load bearing capacity of the fire-attacked beams without occurrence of any failure at the side columns and joints.