Backbone Model for Confined Masonry Walls for Performance Based Seismic Design
Authors: Zahra Riahi, Kenneth J Elwood, S.M. Alcocer (Canada)
Reference: J. Structural Engg., ASCE, June 2009
Performance based model is proposed on the basis of both monotonic and reversed cyclic experiements assembled in an database and derived through iterative linerar regression analysis.Specimens with two tie columns, one on either edge of the wall; multiple longitudinal rebar per confining element; no bed joint reinforcement; no openings within confined panel; and a H/L ratio between 0.7-1.2 are considered. Effect of opening on strength characteriestics, capability of exisitng models to predict seismic behaviour for CM walls were studied and validity of predictive equations for specimens with bed joint reinforcement and high axial load were investigated. Models for cracking shear strength; effect of openings; max.shear strength; crakcing drift capacity; and Ultimate drift capacity were developed.
Conclusion & Future Scope:
The proposed models fails to match recorded response for aspect ratio above 1.2, tie column with one longi.bar, axial stress greater than 0.12fm. Future tests recommended for CM walls with openings; panel reinforcement; multiple confining elements, or high axial stress. Tie column transverse reinforcement is one of the design variable that proved insignificant to the ultimate deformation equaiton of this study, hence the factor needs to be studied. As the current CM codes criteria are mainly rely on conventional force-based equations developed for URM/RM walls, hence the effect of confining element is overlooked, hence incapable of predicting the recorded response with sufficient accuracy.