Effects of Temperature Levels and Concrete Cover Thickness on Residual Strength Characteristics of Fire Exposed Reinforced Concrete Beams

Abstract

Reinforced concrete structures are often subjected to fire of various degrees. After fire if the structure does not collapse during the fire there is need for post-fire assessment of its structural integrity before the fate of the structure can be determined. With the knowledge of the temperature of the fire, thickness of concrete cover, residual strength of concrete and tensile strength of embedded reinforcement after fire exposure, we can predict the residual carrying capacity of the beams after fire. The experimental procedure involves some specimens of reinforcing steel bars (∅16mm) enclosed in varying concrete covers in concrete beams which were exposed to ISO 834 furnace temperatures for 2hrs. After fire, the steel bars were removed and tested for tensile strength characteristics and the reduction in strength trend compared with the current code predictions for stress strain relationship of hot-rolled reinforcing steels at elevated temperatures. The variation in the residual moment and shear capacities of the reinforced concrete beams with temperature were evaluated. The experimental residual strength index was found to be greater than the theoretical prediction in the code. The variation in cover thickness of concrete to embedded reinforcement in beams was also noticed to be of no significance to the post-fire tensile strength of the steel reinforcement if the fire temperature is below 700oC.

Keywords: Post-fire, flexure, residual strength, concrete cover, tensile strength, iso834 fire.