2016-2020 (Research Associate)

New Zealand design provisions regarding the out-of-plane instability of walls

The New Zealand code requirements addressing the out-of-plane instability of structural walls are based on the assumptions used in the literature and the analytical methods proposed for mathematical determination of the critical strain values, such as the height of the wall involved in development of the out-of-plane deformation. In this study, a parametric study is conducted using the numerical model verified during my PhD research for simulation of out-of-plane instability of rectangular walls. Sensitivity of the out-of-plane response of rectangular walls to variation of different parameters identified to be governing this failure mechanism is evaluated. For this purpose, several walls representative of the New Zealand construction practice are analyzed. The effects of wall slenderness (unsupported height-to-thickness) ratio, longitudinal reinforcement ratio of the boundary regions, length and axial load ratio on the out-of-plane response of these walls are evaluated. A clear trend has been observed regarding the influence of these parameters on the initiation of out-of-plane displacement. Based on this comprehensive parametric study, simple equations are proposed for prediction of the critical strain corresponding to development of out-of-plane instability in rectangular walls (Dashti et al. 2019e).

Research collaborations

• • NSF SAVI Wall Institute (https://apedneault4.wixsite.com/wall-institute):

Since 2014, I have been actively involved in the modeling group of the Virtual International Institute for Performance Assessment of Structural Wall (NSF SAVI Wall Institute), when the first workshop was held at the University of California, Los Angles. The objective of this institute is to provide a means for international collaborations on some major issues regarding concrete walls that have raised global concerns following the Chile and New Zealand earthquakes. The modeling group comprises more than 20 researchers from different universities including University of California-Los Angeles, California State University-Fullerton, Pontificia Universidad Católica de Chile, Universidad de Chile, University of Auckland, University of Ljubljana, University of Washington and University of Canterbury. A joint research program started in 2017, evaluating the applicability of different modeling approaches for prediction of the nonlinear response and failure modes of structural walls. Two categories of modeling techniques were investigated, namely macro models and micro (finite element) models. The scope and details of this joint research were discussed within several online meetings and group gatherings in international occasions including the 16^th WCEE (2017) and 11NCEE (2018). The response of several wall specimens that exhibited various failure mechanisms in the laboratory was simulated by various approaches included in both types of numerical modeling. During two years, different macro models and finite element model formulations were validated against these specimens that reflected a broad range of wall configurations and response characteristics. The outcome of this joint research is published in ACI Structural Journal (Kolozvari et al. 2018) and Engineering Structures (Kolozvari et al. 2019). The detailed evaluation of the investigated models is also published in separate journal papers that constitute a special issue in the Bulletin of Earthquake Engineering (SI: NONLINEAR MODELLING OF REINFORCED CONCRETE STRUCTURAL WALLS). A parametric investigation on applicability of the model proposed in my PhD research to nonlinear response prediction of planar RC walls is included in this special issue (Dashti et al. 2019a).