Bennett Banting
Bennett Banting, Director of Technical Services, Canada Masonry Design Centre, 360 Superior Blvd., Mississauga, ON, Canada, Bbanting@canadamasonrycentre.com
ABSTRACT
Design for earthquake forces in Canada underwent major changes at both the national model building code and masonry design standard levels from 2004 to 2014. The most recent edition of
the CSA S304 Design of Masonry Structures published in 2014 introduced a new section: Clause 16 Special provisions for seismic design. One of the technical additions to the standard was a limit to the design level of axial load for Conventional Construction shear walls for buildings that possess with a moderate seismic hazard (IEFaSa(0.2) ≥ 0.35). A maximum axial compressive stress of not more than 0.1fʹm under seismic load cases is permitted. It is well understood that flexurally governed shear walls possess a greater level of inelastic energy dissipation when axial loads are low. In seismic design, it is generally preferable to have a small ratio of the depth of neutral axis, c, to the length of the wall, ℓw, to ensure inelastic yielding of flexural reinforcement. Although seismic response is likely enhanced by restricting axial loads to the required level, the proposed limit has shown itself to be difficult to meet within typical multi-storey loadbearing masonry raising concerns from the design community about its application. It can also be observed that the current limit is often more restrictive than what one could calculate using rational calculations or the limits for c/ℓw adopted by comparable walls systems in reinforced concrete and masonry design in the U.S. In lieu of the axial load limit of 0.1fʹm, a designer is permitted by CSA S304 to carryout a more comprehensive analysis, the basis of which is not defined by the standard. The following paper provides a rational means to meet the more comprehensive analysis requirements of the CSA S304 in order to design conventional construction shear walls with axial load levels that are over 0.1fʹm.
KEYWORDS: CSA S304, conventional construction, seismic design, shear walls
