Seismic Design of Special Reinforced Masonry Shear Walls

The primary seismic force-resisting elements in buildings are horizontal diaphragms, vertical framing elements, and
foundations. Together, these elements, comprise the seismic force-resisting system (SFRS). In reinforced masonry structures, the vertical framing elements are generally structural walls. They resist out-of-plane loads from wind
or earthquake and transfer those loads to diaphragms and foundations. They also resist in-plane loads received from
diaphragms and convey them to foundations. Given the wide variety of masonry materials, forms, and local construction
practices, many kinds of reinforced masonry structural walls are possible. This Guide focuses on the design of one classification of walls for one loading case: special reinforced masonry shear walls subjected to in-plane seismic and gravity loads. From the least to the most stringent ductility requirements, three subcatagories are defined: ordinary,
intermediate, and special. Within the special classification, two fundamental types are distinguished:
flexure-dominated walls: walls whose behavior is dominated by flexure, with reliable ductility and inelastic displacement capacity
shear-dominated walls: walls whose behavior, often for reasons beyond the control of the structural designer, is dominated by shear, with limited ductility capacity.

Other materials usually allow the structural designer to locate and size structural elements to achieve the desired or
needed behavior, and the building is then constructed around these structural elements. Masonry, by contrast, serves
simultaneously as architecture (defining a building’s external or internal appearance as well as its internal functional program), enclosure (defining a building’s external envelope), and structure (resisting vertical and lateral loads). The
structural designer generally does not have the opportunity to choose the configuration of these wall elements; instead, the
other design factors dictate their locations and proportions. Thus, the structural designer must work with the elements that
configure the space. The designer must be able to anticipate the expected behavior of those elements so that he or she can adapt the design and detailing of each element appropriately to resist all required loading combinations to meet the intent of the code for stiffness, strength, and ductility. These requirements apply to structural walls in all Seismic Design Categories (SDC) as defined in ASCE 7, but can be particularly challenging for special walls because the expected level of ductility implied by the “special” designation may not be available.