J. MORTON Brick Development Association

In many codes, the reduction factors for plain masonry walls are derived from empirical equations which are considered to be the best fit to both the available experimental evidence and the various theoretical solutions. Many of these solutions are based on elaborate models which take secondary and tertiary effects into account – but which, because of this, are not themselves, easy to use in Practice and require simplification to facilitate codification.
A new approach has been suggested which offers a single set of capacity reduction factors for all sections. The reduction factors, called B* because they are interchangeable with, but not of the same value as, 0. defined in BS 5628, are written in terms of Lr/r stenderness ratio and e/(Z/A) eccentricity ratio. They can therefore be used for estimating the vertical load resistance of complex shaped masonry walls or columns. Its power as a design tool is due to it being derived from assumed elastic behaviour. Plastic behaviour complicates th e simple, straightforward approach which /3″ offers for the design of complex sections.
It can be argued, however, that the use of plastic behaviour provides a more realistic approach to the estimation of ultimate collapse load. If used for solid sections, as opposed to complex shaped sections, a plastic approach can still provide a simple design method.
This paper generates just such a method by developing the basic approach used for B* but basing the analysis on a plastic stress block. A simple set of reduction factors is derived for solid section walls. The factors, B** (which are interchangeable with, but not of the same value as, fi), are then compared with 0′ – its elastically derived equivalent, B from BS 5628 and * from Eurocode No. 6. Although not covered in this paper, B** reduction factors can be used to design biaxially loaded solid masonry columns of square or rectangular section.