Determination of the Critical Angle of Seismic Forces for the Safety Assessment of 3D RC Buildings Using Lateral Force Analysis

Abstract eng:
In three-dimensional asymmetric buildings, the orientation of the applied forces with regard to the structural system as well as the vertical distribution of the lateral forces affect the structural response. The proposed study addresses the determination of the critical angle of incidence of the lateral static forces that are needed to carry out lateral force analysis within the context of procedures for the seismic safety assessment of existing structures. For this purpose, an analytical methodology is developed to obtain the critical angle of incidence that leads to the maximum demand in terms of storey displacements. The procedure is based on the properties of the centre of stiffness and the principal directions of single storey buildings and can be straightforwardly applied to single storey and multi-storey isotropic buildings with an arbitrary in-plan configuration. Isotropic are buildings that have proportional horizontal stiffness matrices and, as a consequence, possess principal directions. The proposed procedure is subsequently applied to general multi-storey buildings having any configuration in plan, as long as rigid diaphragms can be considered at the storey levels. Still, for the later type of buildings fictitious properties equivalent to the centre of stiffness and the principal directions have to be defined in advance. Finally, two case studies are presented and the applicability of the methodology is discussed.

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