Determination of the behaviour factor of steel moment-resisting (MR) frames by a damage accumulation approach

In most countries, seismic codes are changing, reflecting a new design philosophy based on multiple performance levels. A procedure that defines behaviour factors to reduce the elastic spectrum for different types of structures, considering all possible types of failure, is needed. The paper presents a method for the definition of the behaviour factor (qq-factor) for multi-storey steel frames, accounting for cumulative damage in structural components, by means of linear elastic time history analysis, of the Palmgren–Miner rule and of SS–NN (constant stress or strain range versus number of cycles to failure) curves extrapolated in the low-cycle fatigue range. This technique has been verified by a non-linear procedure that is different from the previous one, as a non-linear time history analysis with damage control has been performed instead of a linear one. The proposed approach can be useful in performance based design, since the linear procedure allows the definition of the qq-factor corresponding to different level of damage or collapse prevention.