We conducted a theoretical analysis of the peak factor, defined as the ratio of the response maximum to the response standard deviation of a single-degree-of-freedom system. We constructed a peak factor formula that uses the natural circular frequency, damping factor, and duration of ground motion, and thereby estimated the peak factor of each mode of a multi-degree-of-freedom system. Using these mode-dependent peak factors, we then modified the existing complex complete quadratic combination method to estimate the maximum acceleration of a non-classically damped model. The response of a mid-story isolated building model under white noise ground motion was analyzed, and it was confirmed that the reformed formula globally provides good estimates in most cases.
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