TOWARDS THE RECONCILIATION OF THE EMPIRICAL AND RATIONAL DESIGN PROVISIONS OF CSA S304-14

Abstract

Masonry structures in Canada are designed in accordance with CSA S304-14 which includes both empirical and rational design provisions. The two design methods result in inconsistent outcomes in certain cases. This thesis investigates one such case where the empirical design provisions for unreinforced, vertically spanning, non-loadbearing, exterior concrete block walls subject to wind load result in less conservative outcomes than the rational design provisions. This discrepancy of design outcomes can indicate either the inadequate levels of safety of the empirical design method or unnecessary conservatism of the rational design method. The goal of this study is to contribute to the reconciliation of the two design methods included in CSA S304-14 for the aforementioned case. A review of past experimental investigations suggests that parameters influencing the flexural tensile strength of walls include mortar type, support conditions, wall slenderness ratio, and the load application method. An experimental program was conducted to provide additional data in areas where test data was lacking: walls constructed using mortar cement mortar, walls with slenderness ratios equal and greater than 16, and walls with realistic support conditions. A database was compiled using test results from the past and the present experimental investigations, and was used to perform a reliability analysis for unreinforced concrete block walls subject to out-of-plane loading. The reliability analysis was conducted using a Monte Carlo simulation and the unfactored rational equation as the limit state function. Results were used to provide recommendations for the empirical provisions of CSA S304-14 assuming a minimum acceptable reliability index equal to 2.5 based on past investigations. Walls with slenderness ratios equal to or greater than 16 consistently resulted in reliability indices lower than 2.5. Walls with a slenderness ratio equal to 12 resulted in reliability indices lower than 2.5 when subjected to a 1 in 50 years wind pressures equal to 0.53 kPa and 0.29 kPa, respectively, for the minimum and maximum values of internal pressure. Potential correlation of the different included parameters may have influenced the results and, therefore, no changes to CSA S304-14 were proposed. It was, however, recommended that the standard include a commentary to inform users of the lack of quantitative evidence supporting the safety of unreinforced masonry walls subject to wind when designed according to the empirical provisions, in particular for increasing slenderness ratios and 1 in 50 years wind pressure.