Analysis of the simultaneous influence of the horizontal seismic load components on buildings

Abstract

Earthquake records indicate that earthquake motion is an irregular oscillatory soil movement as a consequence of the heterogeneity of the soil material, as well as due to reflection, refraction, and interference of seismic waves. The trajectories of soil particle movement during an earthquake are proven to be chaotic, so the approximation of seismic effects by a simplified collinear model is very rough from an engineering point of view. The directions of the earthquake during the duration of the earthquake event affects the results of the seismic calculation. In this paper, the simultaneous influence of horizontal seismic load components on buildings has been analyzed. Actual seismic norms deal with this issue and define recommendations that should be applied in the design. This paper discussed how realistic and applicable these recommendations are in standard engineering design. A series of time history analyses of the horizontal stiffness of reinforced concrete regular and irregular structures were performed. Two earthquake events with a markedly changing direction of the ground acceleration vector were taken as the load. Significant differences in the influence values of the adopted representative parameters were determined for the two considered cases of collinear and simultaneous effects. In the conclusion, a critical review of the usual seismic calculation and the provisions of Eurocode 8, related to the effect of the horizontal components of the seismic load, is given. Finally, the paper comments on the introduction of corrective factors in cases where simultaneous action is not considered.