The safety of masonry buttresses

The vault is the main element in most historical buildings. Masonry vaults exert an inclined thrust that must be resisted by a substantial mass of masonry: the buttress. The buttress system assures the safety of the whole construction. Most traditional structural design rules addressed the problem of buttress design. Today, an architect or engineer assessing the structural safety of a historical construction needs to estimate the safety of the buttress system with accuracy. This is not an easy matter. Among other possible failures, a buttress may fracture under certain conditions with a substantial loss of stability, it may show a certain leaning or it may be separated from the wall. Furthermore, buttress systems are complex structures – a combination of walls and counterforts, flying buttresses, etc. – made of different types of masonry, and their assessment cannot be handled in an abstract way. This paper outlines the development of buttress design since around 1700 to explain the main approaches used and to provide a historical context. The paper then goes on to summarise the state-of-the-art in modern masonry buttress analysis and to discuss estimations of safety.