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Backbone model for confined masonry walls for performance-based seismic design Riahi, Zahra

Abstract

Nonlinear models are of paramount importance in the emerging field of performance-based earthquake engineering. In this study, an analytical model is developed capable of simulating the measured backbone of typical confined masonry (CM) walls whose response under lateral loads is mainly governed by shear deformations. Equations are developed for the cracking and maximum shear strength, and the cracking and ultimate deformation capacities. This model is based on the results of both monotonic and reversed cyclic experiments assembled in an extensive database, and developed through an iterative linear regression analysis. Owing to their anomalies, specimens with compression diagonal loading, height-to-length aspect ratio greater than 1.2, axial stress to masonry compressive strength ratio larger than 0.12, and those with column longitudinal reinforcement ratio below 1%, are not considered for the purpose of creating the, empirical equations. Several statistical and graphical tools are utilized to identify the most significant panel and tie column design variables; to set the functional forms that best relate them to model parameters; and to diagnose influential points that may exert undue impact on the analysis results. The effect of openings and panel aspect ratio on the strength characteristics of CM walls, the capability of existing equations to predict the observed backbone response, and the limitations of the proposed equations are discussed in detail. Model variability is also presented in lognormal fragility curves for different model parameters and at all limit states. The proposed backbone model is found to simulate reasonably well the seismic behaviour of CM walls whose properties conform to the assumptions of the model. However, it fails to track the observed backbone response of anomalous or atypical CM walls.

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