REVISION OF CODE COMBINATION RULES FOR RESPONSE TO THREE COMPONENTS OF SEISMIC MOTION

摘要

Existing rules used in seismic codes for combining peak responses to three ground motion components are revised. The response values, r_e, estimated by three combination rules are compared with the critical response, r_(cr), for elastic systems. Assuming that a principal seismic component is along the vertical direction, the critical response is given by the CQC3-rule. The spectral intensity ratios for the two principal horizontal components are selected based on the properties of recorded motions, according to a recent study. The combination rules examined are the SRSS-, 30%- and the IBC-rules. The upper and lower bounds of the ratio r_e/r_(cr) for each combination rule are determined as a function of the spectral intensity ratio of the horizontal seismic components and the responses to one seismic component acting along the three structural axes. The relative influence of the inclination of a principal component with respect to the vertical axis is also examined; the estimated response using the 30% rule is compared with the critical response given by the GCQC3-rule that provides the largest value of response for all possible directions of the quasi-vertical and quasi-horizontal components.