FIRE RESISTANCE OF HPC COLUMNS AND THERMAL SPALLING

Abstract

Nowadays, high-performance concrete (l-IPC) is increasingly applied in various structures as it can satisfy the expectations for excellent mechanical properties and a long service life. 1-lowever, from the evidence of fire accidents that have happened in reality, it has been found that HPC is prone to explosive spalling under fire conditions. Spalling can occur in all concrete types when exposed to rapid heating (such as the one encountered in fires). The results from a number of previous studies have shown that 1-ugh strength concrete (HSC) is more susceptible to fire-induced spalling than Normal Strength Concrete (NSC). The explosive spalling can cause direct exposure of steel reinforcement to high temperatures, resulting in a lower fire resistance capacity of HPC structures compared with NSC structures. Calculation procedures provide a viable timesaving and cost saving means of determining a member's fire endurance without running full scale fire tests. Along with savings of time and money, the building official, architect, or engineer will have a much clearer concept of how certain variables affect fire endurance if analytical procedures are utilized but still the prediction of concrete spalling during heating-up has been largely an imprecise empirical exercise. It is still difficult to predict spalling by analytical methods owing to the complex microstructure and multiphase nature of concrete. An analytical procedure has been developed and presented in this dissertation which incorporates the effect of spalling and tie configuration in calculating the fire resistance of the reinforced concrete columns. The present approach uses the stress approach where in the spalling is supposed to take place when the stresses developed inside the concrete from the mechanical loading, thermal loading as well as the pore pressure exceed the tensile capacity of the concrete. This is believed to be a better approach than the conventional temperature approach where the spalling is supposed to occur when a particular temperature is exceeded. The procedure takes into account the fire induced pore pressures, thermal and mechanical strains. The fire resistance of all the columns investigated as per the procedure is lower than the fire resistance values calculated as per the Eurocode 2 method and the IS 1642:1989 code method which don't take the spalling effect into consideration