Force- and Displacement-Based Seismic Performance Parameters for Reinforced Masonry Structural Walls with Boundary Elements

There is a need to evaluate existing, and introduce new, masonry construction techniques within a performance-based seismic design context to advance their adoption in the next generation of seismic design codes in North America. In this regard, a reinforced masonry (RM) structural wall system that incorporates confining boundary elements in the plastic hinge region presently lacks specific design requirements in the Masonry Standards Joint Committee and Canadian Standards Association S304.1 design codes. In addition, RM structural wall systems are omitted completely from the plan to develop a new performance-based seismic design methodology laid out by FEMA 445. This paper presents experimental results of four specially detailed RM structural walls subjected to fully reversed cycles of displacement-controlled loading as tested by the authors. In addition, the resulting analysis also includes one wall from a previous study for comparison purposes. All walls were detailed with lateral reinforcing ties confining a grouted core and four vertical reinforcement bars located at each of the wall ends. The design and detailing of the walls represented a range of parameters that would be anticipated to vary within low-to-medium-rise RM buildings. Each of the half-scale walls had overall dimensions of 1.8×4.0 m but varied by the level of applied axial load, the presence of interstory floor slabs, and the presence of confining boundary elements above the first-story height. The results of this experimental program indicate that boundary elements delayed the onset of buckling in the vertical reinforcement and reduced the impact of face-shell spalling on overall wall strength degradation. At 20% degradation from ultimate strength, the top drifts ranged from 1.82 to 3.73% and the displacement ductilities ranged from 6.6 to 15.2. This study is the first of a series of studies at McMaster University currently focused on introducing a broad set of experimental evidence aiming at establishing a new category of RM seismic force resisting systems in North American building codes.