UC San Diego

This study is aimed to acquire a better understanding of the seismic behavior of reinforced masonry (RM) structures at a system level, and to develop frame models for simulating the nonlinear flexural and shear behaviors of these wall systems. To capture the nonlinear, in-plane, cyclic behavior of flexure-dominated RM walls, a rational modeling method along with suitable material models, using a fiber-section beam-column element idealization is presented. The modeling method accounts for the buckling and low-cycle fatigue of vertical reinforcing bars as well as plastic strain localization, which may develop in RM walls under severe seismic actions. The model has been validated by experimental data on fully grouted planar walls and T-walls. In addition, a rational and simple method to construct lateral force-vs.-lateral displacement backbone curves is also presented. The proposed method produces backbone curves that show a good agreement with experimental data from the quasi-static, cyclic, loading tests of walls with rectangular and T sections.

There had been a lack of experimental data showing the ultimate displacement capacity of shear-dominated RM wall systems. To fill this data gap, a shake-table test program was carried out to investigate the displacement capacity of shear-dominated RM wall systems, and the influence of wall flanges and planar walls perpendicular to the direction of shaking (out-of-plane walls) on the seismic performance of a wall system. Two full-scale, single-story, fully grouted, RM wall specimens were tested to the verge of collapse. Each specimen had two T-walls as the seismic force resisting elements and a stiff roof diaphragm. The second specimen had six additional planar walls perpendicular to the direction of shaking. The two specimens reached maximum roof drift ratios of 17% and 13%, respectively, without collapsing. The high displacement capacities can be largely attributed to the presence of wall flanges and, for the second specimen, also the out-of-plane walls, which provided an alternative load path to carry the gravity load when the webs of the T-walls had been severely damaged.

A computationally efficient beam-column model is proposed to simulate the nonlinear flexural and shear behaviors of reinforced masonry shear walls for time-history analysis. A three-field mixed formulation based on the Hu-Washizu variational principle is adopted. This mixed element is free of shear locking, and allows a wall to be modeled with one element. To capture the nonlinear behavior of a reinforced masonry wall, the axial and flexural responses are evaluated at each integration point along the element with a fiber-section model, while the shear response in each loading direction is represented by a macro material model. The model accounts for the influence of the axial load, wall aspect ratio, and the flange on the shear response of a wall. To consider axial-flexure-shear interaction, the shear model accounts for the axial stress resultant from the fiber-section model, and the compressive strength of masonry in the fiber-section model decreases when severe shear damage developed. The model has been calibrated and validated with extensive test data. It has been demonstrated that the model is able to reproduce the experimental results from quasi-static cyclic loading tests of single walls as well as shake-table tests of wall systems with good accuracy.