Influence of Modelling on the Response of Asymmetric Buildings

In several earthquake-prone countries, many buildings have not been designed by seismic regulations and others have been constructed according to old seismic codes. Effective methods of analysis are expected to be available to evaluate the seismic performance of these buildings and to validate interventions of structural rehabilitation. The linear method of analysis, used for the design of new buildings, is however not suitable for this purpose because the plastic collapse mechanism of existing structures, and thus the behavior factor, is not known a priori. Consequently, this method of analysis does not provide a reliable prediction of the response of existing structures. Instead, the nonlinear dynamic analysis and the nonlinear static analysis consider the inelastic deformation of structural members and can predict the seismic response of existing buildings effectively. However, the response provided by these nonlinear methods of analysis can be strongly affected by the accuracy of modelling. Idealized beam and column models for nonlinear analysis vary greatly in terms of complexity and computational efficiency. Available finite element models for the nonlinear material response of beam–column members have fallen into two categories: concentrated plasticity and distributed plasticity. In this paper, the influence of modelling in the evaluation of the lateral torsional coupling of asymmetric buildings is investigated. In particular, four models are compared. In all the models, force Beam-Column elements are used to simulate the response of beams and columns. Further, in the first model considered, fiber cross-sections are assigned within the hinge region. This model is able to simulate the behavior of columns subjected to axial forces and biaxial bending. Instead, in the other models, two independent moment–curvature relationships are assigned within the hinge region to simulate the nonlinear behavior along two orthogonal axes of the cross-section. The adopted moment-curvature relationship is obtained starting from the moment-curvature analysis of the fiber cross-section subjected to the axial force produced by gravity loads. In particular, the moment-curvature relationship assumed in the nonlinear analysis is obtained by the previous curve by multi- or bi-linearization within the relevant range of curvatures. The four considered models are adopted to predict the nonlinear (dynamic and static) response of an asymmetric building designed in a previous research. All the analyses are performed by the OpenSees Computer program.