Seismic Analysis And Performance Evaluation Of Frame Structures Considering Directionality Of Bi-directional Earthquakes

Actual seismic ground motion consists of vertical and horizontal components. Asearthquake ground motion components can take place in any direction relative to theconcerned structure, directions in which ground motion produce larger structuralresponses than structure responses produced by ground motions applied along structureaxes may exist. Generally the angle in which produces the maximum structure responseis referred to as the critical incidence angle of structure under specific ground motions,and the maximum structure response is referred to as the maximum structure responseof the structure under specific ground motions. In actual design, seismic loads aregenerally applied only along the axis direction of the structure, which may lead to anunderestimation of the dynamic response of the structure. Thus in the design procedureof complex structures and important structures, multiple time history analyses areconducted changing the direction in which ground motions are applied to obtain themaximum structure response to guarantee the structure safety. Such procedures are ableto obtain the precise maximum structure response considering the directionality of theground motions, which may pay expensive prices in time and calculation.Based on linear time history analysis results, a method was proposed to determinethe critical incidence angle of bi-directional ground motions, and the accuracy of theproposed method was verified through applications to multiple buildings subjected tobi-directional ground motions. It is proved that the method can calculate the incidenceangle and the maximum structure response of structures with plastic material with lesstime history analyses and better results, which serves as a powerful tool to consider thedirectionality of the ground motion in the seismic design of frame structures.In this study, by calculating the limit state probability curve under varying degreesof earthquake ground motion, the directionality of ground motion is introduced into thebuilding structure seismic performance evaluation. A conclusion is drawn that onlyconsidering the structure responses under ground motion applied along structure axeswill lead to a notable underestimation of the deformation demand of structure underearthquakes. The influence of the interval of angle in conducting time history analyseswas also studied and the proposed method showed superiority in both precision andcalculation cost. Finally, a comparison was also made on a9-story and a20-story building on theprecision of30%rule and the SRSS rule of calculating shearing forces and moments.The results showed that the results processed by30%rule showed an inadequacy inseismic resistance safety reserve, at the same time the30%rule and the SRSS rulecalculations showed similar level of discretion.