A nonlinear static procedure for seismic assessment of unreinforced masonry buildings with rigid-diaphragms considering the effect of seismic incidence angle

The outcome of structural assessment of existing buildings can be influenced by the seismic incidence angle considered in seismic analysis, apart from other assumptions in numerical modelling. Since seismic excitation is a random process, the expected direction of ground motion is not known a priori. The current practice to obtain the structural responses in the nonlinear static analysis of three-dimensional building models is to apply load patterns along two mutually orthogonal directions, which are arbitrarily chosen. The responses so obtained would either be higher or lower if the seismic demand were to act along any other direction. This paper presents a nonlinear static procedure for unreinforced masonry buildings based on the popular N2 method to account for such effects. The procedure would not necessitate a tedious multi-directional static/dynamic analysis. The paper also presents polar plots showing how the seismic incidence angle significantly influences the resultant displacements at floor levels.