J. MORTON Brick Development Association

Traditional walls have been designed successfully using the guidance in B.S. Codes of Practice successive revisions of which have improved structural efficiency. The code is somewhat empirical in its approach with its origins in concrete wall design. A model, is proposed based on the behaviour of masonry materials which produces the general interaction curve for compression failure — namely material failure at low slenderness ratio values, instability at high levels of slenderness and the intention of both failure modes at slenderness values in between.
It is based on a pinned-pinned model, using a modified Rankine theory. Capacity reduction factors are derived which are similar in value, but not identical to, the B values in BS 5628: Part 1: they are therefore interchangeable with them.
The capacity reduction values can be written in terms of L/r slenderness ratios and Z/A eccentricity ratios. Thus the designer can determine, using one table of capacity reduction factors, the design load resistance of any solid wall or any other wall or column of irregular geometry. A limit is placed on the eccentricity of the applied load on walls of irregular plan form which lie within the kern of the section. The method can be applied to vertically loaded members carrying lateral loads and to columns in biaxial bending. By assuming a no tension material and by ignoring any cracked masonry in tension, a lower bound solution can be obtained for any non planar wall with a highly eccentric load.