A probabilistic risk analysis of steel building frames is presented using the hazard curve and the risk consistent response spectrum as inputs. The effect of soil amplification is duly considered for constructing the hazard curve and the response spectrum. The probability of failure of the frame is calculated by using the method of plastic analysis (mechanism method) and the first order second moment theory of reliability analysis. Plastic analysis is performed with equivalent (static) lateral load due to seismic effect, and the existing gravity load for probable mechanism of failure. Uncertainties considered in the study include those produced due to variations of the input motion, system parameters, modeling of the system and analysis procedure, energy absorption during the hysteretic loop and damage concentration effect. The method of analysis is illustrated by obtaining the annual frequency of failure of a twelve-storied steel building frame located at a hypothetical site, surrounded by three point sources of earthquake. The effect of important parameters on the probability of failure of the frame is also investigated by a parametric study.
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