Cracks in buildings are a common occurrence. Cracks can make the whole or a part of the structure unsafe. However, if a crack does not endanger the safety of a building, it may hamper aesthetic appearance or may create an impression of faulty work or may give a feeling of instability.
A component of a building develops cracks whenever stress in the component exceeds its strength. Cracks are caused by externally applied forces, such as dead, live, wind or seismic loads, or foundation settlement or it could be due internally induced stresses like due to thermal movements, moisture changes, chemical action, etc.
Type of Cracks:
Cracks can be broadly classified as structural or non-structural.
Structural cracks: These are caused due to incorrect design. Faulty construction or overloading may endanger the safety of a building. Cracking of an RCC beam is an instance of structural cracking.
Non-structural cracks: These are caused mostly due to internally induced stresses in building materials. These types of cracks generally do not directly result in structural weakening. But sometime non-structural cracks may make the building unsafe. For example, penetration of moisture through non-structural cracks may result in corrosion of reinforcement and thus may make the structure unsafe. Vertical cracks in a long compound wall due to shrinkage or thermal movement is an instance of nonstructural cracking.
Shape and size of cracks:
The size of cracks may vary in width from very thin hair cracks which are barely visible to naked eye (about 0.01 mm in width) to gaping cracks 5 mm or more in width. A commonly known classification of cracks, based on their width is:
(a) Thin – less than 1 mm in width
(b) Medium- 1 to 2mm in width
(c) Wide- more than 2 mm in width
As a general rule, thin cracks, even though closely spaced and greater in number, are less damaging to the structure and are not so objectionable from aesthetic and other considerations. Cracks may be of uniform width throughout or may be narrow at one end, gradually widening at the other. Cracks may be straight, toothed, stepped, map pattern or random and may be vertical, horizontal or diagonal. Cracks may be only at the surface or may extend to more than one layer of materials. Occurrence of closely spaced fine cracks at surface of a material is called ‘crazing’.
Reasons of cracks:
Principal reasons of occurrence of cracks in buildings are as follows:
a) Moisture changes
b) Thermal variations
c) Elastic deformation
e) Chemical reaction
f) Foundation movement and settlement of soil
Careful observation is to be done to ascertain the reasons of cracks in order to correctly diagnose it and apply appropriate remedial measures.