M. BOGOSLAVOV (1) and N.G.SHRIVE (2)
(1) Department of Civil Engineering, University of Calgary, Calgary, Alberta, T2N 1N4, Canada
(2) Professor, Department of Civil Engineering, University of Calgary, Calgary, Alberta, T2N 1N4, Canada
The Canadian masonry design standard (code of practice) can be particularly conservative when it comes to the design of walls deemed slender. One of the major contributors to the conservatism is the definition of the effective flexural stiffness of the wall. The effective stiffness is a term which can be used in linear analysis to determine the flexural displacement of a wall accounting for the fact that the wall may be cracked in the zone of high moment and thus the stiffness is actually non-uniform over its height – the effective stiffness essentially averages the actual stiffness over the height. An experimental test program performed in the mid-1970s at the University of Alberta, in which the lateral displacement profiles of the walls tested were recorded at increasing loads up to failure, was used to evaluate the current provisions of the standard and to develop a better equation to define the stiffness. The equation derived involves the eccentricity of the applied axial load as well as the slenderness of the wall. The approach to determining the equation is described together with reasons why some walls showed higher effective stiffnesses than that calculated for an uncracked section. The proposed equation is applicable to the data set analysed and further work needs to be done to determine if it has wider applicability.
KEYWORDS: concrete blockwork, walls, slenderness, effective stiffness.