Determination of Irregularity Limits

Abstract eng:
Vertical and horizontal regularity provisions in the current New Zealand seismic design standard, NZS 1170.5 (SNZ 2004) are based on overseas codes. These regularity limits are based on engineering judgment rather than on rigorous analysis. This paper outlines a simple and efficient method of determining structural irregularity limits for structures designed using different analysis procedures. As an example, the methodology is applied to simple models of shear-type structures with different amounts of mass irregularity located at different locations within the structure, all designed in accordance with the Equivalent Static Method of NZS 1170.5, including P-Delta effects. These models were then analysed using inelastic dynamic time history analysis for the 20 SAC 10 in 50 earthquake records for Los Angeles. The additional median interstorey drift responses due to mass irregularity was computed which can be limited to an acceptable level. Irregularity limits for use in design can then be defined for a specified level of confidence.

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