Determination of Acceptable Structural Irregularity Limits for the Use of Simplified Seismic Design Methods

Current NZ code regularity limits for structures are based on engineering judgement rather than on quantitative analysis. This paper describes a quantitative method to determine limits for structural irregularity for structures designed using different analysis procedures. In this method, a parameter such as the change in median response, or the increased probability of greater demand, may be computed and then limited to an acceptable level. Irregularity limits based on a specified level of confidence are selected and these are then proposed for use in design. The method is illustrated by an example considering mass irregularity.