مهندسی عمران شریف (Nov 2020)
SENSITIVITY ANALYSIS OF RC FRAME FAILURE TIME UNDER POST-EARTHQUAKE FIRE TOWARD DESIGN AND LOADING PARAMETER
Abstract
Several loads over the lifetime of buildings threaten the safety of structures. Earthquake, fire, explosion and ... hazards that jeopardize the safety of the structure.Post-earthquake fire (PEF) is one of the rare occurrences with high consequences.Resistance time of structures against fire in damaged structures caused by earthquake can be different from intact structures.In this research, the importance of designing and loading parameters on the resisting of reinforced concrete frames under post-earthquake fire loads has been investigated.For this purpose, the sensitivity of the parameters was investigated using the FOSM sensitivity analysis method based on random variables.The time of the first failure in the reinforced concrete frame is considered as the reinforcement frame resisting against the PEF load.The thermal load provided by ISO 834 is considered to thermal loading.The results show that, among the design parameters, the reinforcement yielding stresses are the most important parameter in the resistance of the reinforced concrete frame.Concreteresistance and dead load is also one of the most sensitive random variables.The modulus of the elasticity of the armature and the length of the span (if the armature cover is ignored) will produce the least sensitivity for the failure time.In the further analysis of PEF for ten earthquake records, the sensitivity of the failure time to seismic loads is investigated.The results show that seismic load in concrete frames (unlike steel frame) is the most sensitive to failure time.Among the loading parameters, the intensity of seismic load is most important in the resistance of reinforced concrete frames in post-earthquake fires loading.For example, in Sa = 0.7g, the response swing (mean plus minus two standard deviations) for a failure time of 145 minutes have been calculated.The highest swing for the reinforcement yield stress, concrete cover and concrete strength was calculated 60, 53 and 40 minutes, respectively.
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