Expansion Joints:

Concrete is subjected to volume change due to temperature variations, shrinkage, etc. Therefore, the provision must be made to cater for the volume change by way of joint to relieve the stresses produced. In little buildings, no expansion joint is required in the floor or in the roof because expansion is very small as it is a function of length. A long building undergoes huge expansion. It is estimated which for the worst conditions, a long building might undergo an expansion of as much as 2.5 cm. Thus, buildings longer than 45 m are commonly given with one or more expansion joints. Roof of a long building is affected through maximum temperature variations. A roof is subjected to expansion and contraction during day and night and causes pushing or pulling to the load bearing walls. Serious cracks have been found in the masonry wall supporting the slab. Hence, attempts have been made to create a condition for a slab to slide over the wall when it is under expansion or contraction. The details such as the length of structure where expansion joint is to be provided can be determined after taking into consideration many factors such as temperature, exposure to weather, time and season of the laying of the concrete, etc. Under no circumstances shall a structure of 45 m or more be without an expansion joint.

In the past, expansion joints were provided at closer intervals in the floors and pavements. These days from experience, it is seen that concrete does not actually expand to the extent indicated by the simple analytical calculations, since of the frictional resistance offered through the sub grade. It is, thus, possible to give expansion joint at a much farther interval than in the past. IS 456: 1978 recommends as under.

In view of the large number of factors involved in deciding the spacing, location and nature of expansion joints, a provision of expansion joint within reinforced cement concrete structures should be left to the discretion of the reinforced cement concrete designer. For reasons of general guidance, therefore, it is recommended that structures exceeding 45 m in length shall be divided by one or more expansion joints.