No abstract

Estimating the residual strength of fire-exposed reinforced concrete (RC) structures is of great importance in determining whether the cooled structure is safely functional or immediate repair is needed. This paper describes the results of experimental and numerical investigations on fire and post-fire structural responses of a 2-story moment-resisting RC frame test specimen. The lower story of the test specimen, which was subjected to service loads, was heated for 60 minutes in accordance with the ISO-834 standard fire test. The test specimen exhibited a satisfactory structural performance during the fire course and considerably recovered much of its pre-fire deflection state when cooled. To investigate the re-serviceability and residual load bearing capacity of the cooled test specimen, a destructive cyclic vertical loading was conducted. A detailed 2D finite element model was developed as well. By comparing the test and analysis results, it was found that due to the fire damage the test specimen lost 30% of its load bearing capacity. The proposed numerical modelling approach in this study predicted considerably well the post-fire residual strength of the test specimen.

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.