Nonlinear models are of paramount importance in the emerging field of performancebased 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.

Results from an experimental series of seven full-scale confined masonry walls with height-to-length aspect ratios ( H/L) from 0.3 up to 2.2 are summarized. Results show that neither the level of axial stress nor the aspect ratio had a significant effect on lateral stiffness. Inelastic behavior of the walls, characterized by normalized stiffness degradation with ductility demand, can be estimated with good accuracy with a bilinear function for a ductility demand up to 4.5. A substantial increase in normalized shear strength was observed for walls with decreasing aspect ratio. A correction factor to the nominal cracking strength was deduced based on differences of the flexural deformations for squat and square walls. The factor was then compared to the experimental normalized strength with good agreement. A new expression for inclined cracking shear that can be used for a wide range of wall aspect ratios is proposed.

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