A simplified approach to modeling vertically irregular structures for dynamic assessment

The nonlinear dynamic analysis is the most sophisticated evaluation method for vertically irregular structures under the effect of the earthquake because the higher mode effects are significant. In particular, vertically irregular structure has a complex geometry, so errors can occur when inputting members as coordinates or when defining the properties of members. Therefore, a simplified modeling method is proposed in this paper. The proposed method was developed by converting vertically irregular structures to geometrically regular structures using a story stiffness equation. The results of modal analyses and nonlinear dynamic analyses obtained by both simplified and typical exact modeling methods were compared. As a result, the difference of fundamental period was about 11%, and the higher mode effects which were evaluated by ASCE 41 criterion governed in both models. In addition, the differences of story shear and story drift were about 15% and 24%, respectively. Therefore, the proposed simplified modeling method can be applied to initial structural design stages to save the project time by predicting approximate nonlinear dynamic results such as story shear, and story drift of vertically irregular structures.