Effects on Flexural Strength of Reinforced Concrete Beam Subjected to Fire

Abstract

Studies on reinforced concrete members have shown that there is loss of flexural strength of reinforced concrete beam when subjected to elevated temperatures. This is because; there are membrane forces and the redistribution of bending moment which considerably affects the behavior of the reinforced concrete beam. The aim of this study was to use non-linear analytical methods to determine the temperature reached at a given depth of concrete and hence determine the flexural strength at such elevated temperatures and hence give a way forward to develop a procedure in analyzing the reinforced concrete flexural member’s subjected to fire. This paper gives the way forward on the effects of fire on flexural strength of a beam at elevated temperature and at a given time. More so, it discusses effect of such beams cooled by quenching with cold water, a practical case which relates to the fire fighting process.It was found that, when reinforced concrete classes C20 is heated at 250°C there is a loss of up to 20.1% when heated for one hour and 24.88% when such member is heated for two hours. However, when heated at a temperature of 600°C for one hour, the loss of flexural strength ranges from 33.1% and 34.36% for members heated for two hours. For a member heated at a temperature of 750°C, the loss of strength ranges from 41.81% when heated for one hour 43.01% for members heated for two hours.When class C25 is heated at a temperature of 250°C and cooled by normal loading, for one hour, the loss of flexural strength is 18.22% and when heated for two hours, the flexural strength loss is 20.84%. For members heated at a temperature of 600°C the strength loss of such member is 24.37% and when heated for duration of two hours, it loses the flexural strength of 27.14%. For members heated and cooled by quenching with cold water, the flexural strength loss is very high compared to those cooled at room temperature.

Keywords: flexural strength, non-linear analytical methods, elevated temperatures, normal loading, quenching