Chapter 37: Movement in masonry

Dimensional changes in unreinforced masonry structures result from external influences such as settlement and from internal physical processes, which relate to the inherent properties and behaviour of the unit and mortar components of the masonry. This chapter concentrates on these inherent properties and discusses the four main causes of movement: changes in moisture content; reaction to load application; temperature changes; and chemical actions in relation to clay, concrete, calcium silicate, natural stone and reconstructed stone units. Where pertinent, reference is made to Eurocode 6 – Design of Masonry Structures. While each of these movements can occur in isolation, the chapter emphasises the fact that two or more of these movement types will at some stage in the life of the structure act cumulatively. It is when cumulative behaviour occurs that the performance of the structure is more likely to be affected and that movement failure, i.e. cracking, may occur. The effect of cracking on the durability of masonry structures is considered. However, it is also suggested that the onset of cracking may also be useful as it can indicate the potential presence of structural problems from external factors.