Effects of Seismic Directivity Within the Framework of the Lateral Force Procedure

Abstract eng:
In the present paper the influence of the seismic incident angle on the longitudinal steel reinforcement of R/C buildings within the context of the lateral force method of analysis is investigated. According to current seismic codes the horizontal static seismic forces are applied along the structural axes of the building, provided that can be clearly identified. In an extensive parametric study a wide range of buildings (symmetric, asymmetric, with or without orthogonal arrangement of their resisting elements) have been analysed and their response is computed due to the simultaneous action of the two horizontal seismic components for a series of different angles of seismic incidence. It is proved that, in general, different orientations of the seismic action may lead to differences of up to 29% concerning the required longitudinal steel reinforcement. The only case in which the structural response does not depend on the loading direction is that of structures which fulfill the criterion ΤB<Τα<ΤC for any value of α, where α is the angle of incidence, Τα is the uncoupled fundamental period of the structure along the α-direction and TB, ΤC are the lower and upper limits of the constant spectral acceleration branch.

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