1 Ph.D., Department of Civil Engineering, McMaster University, Hamilton, ON, Canada, bantinbr@mcmaster.ca
2 Martini, Mascarin and George Chair in Masonry Design, Department of Civil Engineering, Hamilton, ON, Canada, eldak@mcmaster.ca
ABSTRACT
North American masonry design codes rely on a 45° cracked member assumption and truss analogy to estimate shear strength of members. Whereby shear strength is expressed as an algebraic summation of resistance offered by masonry, axial load and shear reinforcement. By contrast, the Modified Compression Field Theory (MCFT), which has gained a wide acceptance within the concrete design community, demonstrates that the 45° cracked member assumption can be overly conservative. Yet the MCFT or similar equilibrium-based approaches have often been thought of as incompatible with masonry due to the latter’s complex anisotropic behavior. A methodology is proposed to accurately estimate the angle of inclination of shear cracking and the shear resistance offered by the horizontal reinforcement and the masonry compression strut accounting for aggregate interlock effects within a masonry macro-element. A design equation is proposed and its ability to accurately estimate the shear strength of a structural wall is verified through a comprehensive review of applicable test results from available literature. The proposed Normal Strain-adjusted Shear Strength Expression (NSSSE) was found to predict the shear strength of 57 wall tests reported in literature with a mean ratio of experimental to theoretical strengths of VExperimental / VTheory = 1.16 (C.O.V. = 11.4%) and a 99% percentile of VExperimental / VTheory = 0.86 marking a significant improvement over existing design code expressions that is also firmly grounded in a sound theoretical formulation.
KEYWORDS: concrete block, design codes, shear wall, shear strength
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