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 nearfield 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.
Summary
Despite wide‐ranging studies on fragility analysis and collapse safety assessment of short to medium‐rise reinforced concrete (RC) structures, a new interest in the topic is still valuable and even necessary for tall RC buildings. This study aims at establishing fragility relationships as well as collapse probability of high‐rise RC core‐wall buildings under maximum considered earthquake ground motions. This study is carried out in a probabilistic framework on a case study of a fully 3‐dimensional numerical model developed to simulate seismic behavior of a 42‐story building having a RC core‐wall system. Proposing planar and vertical distributions of ductility and damage indices, the incremental dynamic analysis, and the multi‐direction nonlinear static (pushover) analyses were employed to reach the research goal. Median collapse‐level capacities were defined in terms of seismic responses (e.g., ductility/damage indices) as well as several intensity measures by employing statistical analyses and cumulative density functions. Available and acceptable collapse margin ratios were next estimated to quantify collapse safety at maximum considered earthquake shaking level. On an average basis, the statistics indicated 9%–10% and 5%–6% collapse probability of the building subjected to near‐ and far‐field ground motions, respectively.
Inelastic seismic responses of flexibly supported reinforced concrete (RC) moment-resisting frames representing short-to-tall structures stiffened with ductile RC structural walls were evaluated considering both far-field and near-field ground motions. A dual shear wall-frame resisting system with symmetric reference plan was created by adding shear walls into excitation direction of the three-dimensional frames developed by generic structure algorithm. The current study also aims to take into account soil–structure interaction effects in to damage assessment of multi-story RC buildings in terms of ductility demand, damage index, story shear force and overturning moment, as well as kinetic energy profile over the structure height. In doing so, the developed set of generic frames was considered accounting for different values of story strength, stiffness distribution and number of stories. A realistic modeling of nonlinear ductile behavior of RC elements was developed in combination with the sub-structuring method to consider the foundation flexibility in nonlinear seismic responses. Conducting a parametric study through nonlinear static analyses (pushover) as well as nonlinear response history analyses, the results indicated that the near-field ground motion presents much more damage than the far-field one. Inelastic dynamic responses to near-field records demonstrated that structures with a fundamental period greater than the pulse period respond differently from those that have shorter periods. The results were also presented as charts and tables that provide helpful information for engineering design purposes such as damage assessment of multi-story RC buildings with specific fundamental natural period and base shear strength.
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