The lengths of structural elements, and of superstructures in particular, change as a result of materials shrinkage, temperature fluctuations and loading variations – perhaps many times in the course of their lives. To avoid surface cracking and possibly more serious damage, the length of each individual structural element is often limited, with gaps between elements to allow movements. These gaps must be bridged over, and made trafficable if appropriate, in every state of expansion. Expansion joints of steel or aluminium offer well-proven solutions. These facilitate variations in length without constraints and cracking, protect the surfaces of adjacent structural elements, and, if necessary, prevent the ingress of water.
The watertightness of an expansion joint is determined not only by that of the joint itself but also by that of its connection to the waterproofing system of the supporting structure at each side. Details such as wall connections and T-joints present potential weak points and must be made just as watertight as the rest of the joint. Water is unforgiving of half-hearted solutions.
Cracking of a structure or its surfacing, or ingress of water, can lead to serious structural damage, and may result in consequential damages such as interruption of production and warehousing or water damage to goods.