CRACKING IN WALLS

Causes

Cracks are frequently found in brick masonry walls due to some of the reasons given below.

1. Brick masonry behave differently when constructed in conjunction with concrete foundations and concrete framing.
2. Combination of brick masonry with other members having greater deflections and strains.
3. Effect of deflection and shrinkage of concrete slabs resting on walls.
4. Due to introduction of new types of construction.
5. Restraint of stresses developed inside the brick masonry due to moisture absorption, temperature variation, etc.

17.12.2 Preventive Measures

Following are the preventive measures which could minimise the cracks in brick masonry.

1. Foundation Design

Depending on the type of foundation soil, the foundation has to be designed and the supporting masonry walls should be designed with adequate stiffness. Such a design will help to control excessive shear of flexural stresses in the masonry.

2. Expansion Joints

Providing horizontal and vertical expansion joints in walls helps to reduce the cracks to a considerable extent. Horizontal and vertical expansion joints absorb vertical and horizontal movement respectively. In general, expansion joints have to be provided for every 15 m. The sealant used for joints are natural or cellular rubber, bitumen, expanded plastics, coconut pith, etc. The depth of sealant should not be more than half the width of joint and should not be less than 4 mm. Figure 17.17 shows some typical locations for joints.

Figure 17.17 Plan of locations of expansion joint

Typical expansion joints in brick masonry provided at different locations to avoid cracks are shown in Fig. 17.18 to 17.20.

3. Isolation Joint

Isolation joint is similar to expansion joint but provided under the following conditions:

1. When it is desired to separate the foundation of machines from the rest of the structure.
2. When one portion of a building is higher than the other.
3. When one portion of a building rests on rock and the adjacent portion on com pressible clayey soil.

Figure 17.18 Expansion at corner of walls

Figure 17.19 Expansion joint at roof level

4. Sliding Joint

Sliding joint is provided when one part of a structure has a tendency to slide over the other due to variations in temperature and moisture content. Figure 17.21 shows the details of a sliding joint at floor level.

5. Slip Planes

Smooth slip planes are provided between the roof slabs and brick walls. Because of this arrangement, cracks will be developed only at the re-entrant corners. These cracks can be easily covered after the complete construction is over.

Figure 17.20 Expansion joint at foundation level

Figure 17.21 Sliding joint