R.C. de VEKEY Building Research Establishment

Since 1978 there has been a codified method for designing walls to resist lateral out-of-piane loads in BS5628:Part I[l) which is based substantially on empirical data for 28d old laboratory specimens. Usually when a gale occurs there are collapses of a few masonry structures resulting from wind induced lateral load. While many such failures are a result of under-design or ineffective support or connections, there is no doubt that weathering and deterioration is often a contributory factor and thus raises some questions about the long term safety of exposed slender masonry structures. A small durability programme was commenced in 1980 covering two clay bricks and two mortars. The results for up to 10 years exposure show that the flexural strength is maintained if the masonry is built and maintained in accordance with good practice, for example, BS5628:Part 3:1985[2], Table 13. The work also shows that any masonry which suffers from frost or sulphation damage to the mortar beds due to the use of inappropriate materials or bad detailing in relation to its exposure state is likely to decline in bond strength and eventually could become unsafe. Cantilever structures such as boundary walls, gable peaks, chimneys and parapets would be most at risk.