Spatial distribution of ductility demand and damage index in 3D RC frame structures considering directionality effects

Most of studies that examined the influence of incidence angles of bidirection ground excitations were focused on the estimation of engineering demand parameters (EDPs) only along two orthogonal axes varying ground motion orientations. However, variations of the EDPs have not been assessed in a desired horizontal angular distance from a reference direction that could be different than the incident angle. Furthermore, the structural demands along the height of structures were not also studied for different angles of the incident of ground motion. The current paper aims to assess these issues introducing spatial distribution of ductility demands and damage index induced to multi-storey reinforced concrete frames due to incidence-dependent bidirection ground excitations. Employing the concept of 3D archetypical frames, several pushover analyses and nonlinear response history analyses were conducted using two sets of ground motions classified as near-field and far-field records. The results of these comprehensive parametric analyses including the EDPs along different angular distances from a reference point were employed to perform regression analyses obtaining the critical EDPs. Several expressions for the critical EDPs (mostly oriented in non-principal planar directions) are suggested in terms of the orthogonal peak responses assumed to be assessed corresponding to the principal axes. Different expressions proposed in this study could be used to predict the critical ductility of structures by combining the structural ductility in two perpendicular directions when they are assessed due to the principal directions of excitations. Copyright (c) 2015 John Wiley & Sons, Ltd.