Investigation on structural and thermal performance of reinforced concrete beams exposed to standard fire

Reinforced concrete (RC) structural members generally exhibit a fairly good fire resistance due to their low thermal conductivity and high thermal capacity. However, under prolonged duration of exposure, RC members experience loss of strength and stiffness. An experimental investigation is carried out to examine the influencing factors affecting the structural performance of the RC beams of different strength grades exposed to standard fire. Specimens were heated as per standard fire curve. Different grades of RC beams (i.e. M20, M30, M40 and M50) are tested under two-point loading. The effect of standard fire on the load-deflection response, first crack load, ultimate load, temperature in rebar, yield strength of rebar and moment of resistance are investigated in the RC beams. Temperature in steel at specified locations of a RC beam is also measured to determine the extent of damage. It is observed from the investigation that the mode of failure is dependent on many material parameters (w/c ratio, density, porosity) and structural factors (compressive strength of concrete, yield strength of rebar). Damage level of concrete with lower grade was higher up to 120min duration of heating and after that loss in strength of concrete with higher grade is significant. Water-to-cement ratio, compressive strength, temperature level in concrete or steel and rebar area are some of the key factors affecting the loss in strength of RC beams at elevated temperature.