1 Structural Engineer, Parsons Brinckerhoff Halsall Inc., Toronto, ON, M4P 1E4, Canada, email dlaird@halsall.com
ABSTRACT
CSA S304.1-04 “Design of masonry structures” uses an engineered design method (limit states design), but also permits the use of an empirical design method. The empirical approach is only allowed for unreinforced masonry and only if the building and its location are within specified limits for building height, seismic hazard index and hourly wind pressure. Many locations in Canada are ruled out by the seismic and wind limitations. Those locations remaining are mainly in parts of the Prairies and Ontario. When unreinforced masonry walls are designed for wind and seismic loading in accordance with the engineered design method, the walls are often significantly stronger than required by the empirical design method. Should this be allowed to continue or should the two design methods be reconciled? That is the dilemma. This paper discusses the two design methods and gives example calculations to compare the two. The relevant changes to the two design methods, the design loadings, and masonry construction over the past 50 years are discussed. Some relevant differences with the current American masonry code are also mentioned. Possible reasons are examined as to why the empirical design method has had such a successful history and why the empirical design method continues to be permitted. Some recommendations are included.
KEYWORDS: empirical design, limit states design, flexural tensile strength, wind load, seismic load, reliability analysis
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