In my earlier articles, I have discussed major and minor causes of cracks. Studying these causes also help in the classification of cracks

Minor causes of Cracks

Major causes of Cracks

The classification of cracks is based on various factors

1. Direction of the cracks
2. Extent of the cracks
3. Width of the cracks (if tapers)
4. Width of the cracks
5. Depth of the cracks
6. Alignment of the cracks
7. Sharpness of the edges
8. Cleanliness
9. General

Direction of the cracks

1. Vertical
2. Horizontal
3. Diagonal
4. Straight
5. Toothed
6. Variable and irregular

The materials trough which crack passes should be recorded

Extent of the cracks

The cracks usually occur at starting and finishing points i.e. across the openings, passes round the edges of the materials or cracks close to the ground – passing through dpc (damp proof course) or confined above or below

Width of the cracks - if tapers

Mark the end of the crack

Direction of taper

(It is important to note the humidity of the day. Some cracks widen and close during the day due to thermal changes)

This is necessary for remedial work.

Width of the cracks

It can be measured through instruments and tell-tale signs. The changes in the length of the cracks should be noted

Depth of the cracks

Figuring out or measuring the actual depth of the crack is irrelevant, but how many of the materials of the wall have cracked is important to detect

For example, Just point film may have cracked which is not a very serious crack. A piece of very fine wire may be used to detect the fine crack.

Alignment of the cracks

A note should be taken of the levels of the materials on the two sides of the crack, one side sometimes being forward of the other can be done by feeling with the finger tip, passing it across the crack in both direction, when any direction in the level is readily apparent

Alignment indicated whether the crack has been produced by a straight pull, or with a tensile force or as with a diagonal pull as with a shear action

Sharpness of Edges

Most cracks have sharp edges but they may be rounded or roughened if the sides of the cracks have been brought together by compressive forces or by vibrations. Badly broken edges will often be indicative of initial compressive forces

Cleanliness

Examine the cracks with magnifying glass for the following reasons

• Brightness of the sides of the cracks
• The presence of dust, algae, insects etc
• The presence of decorative materials - example, Paint on the sides of the crack

General

Observe the crack over a period of time to know whether it is static or altering in size and if bows are there, measure the extent of bow

1. Movements of the ground
2. Over loading
3. Effect of gases, liquids and solids
4. Effect of changes of temperature
5. General causes such as vibrations etc

Unrestrained Movement of Building Materials

Movements of the ground

Mining subsidence, land slips, earthquakes, moisture changes due to clay shrinkable soils (for example, Black cotton soil).

Cracks occur because a part of the building is displaced from the rest without any change in the actual size of the material.

Overloading

• Overloading of the ground
• Overloading of the building itself
• Overloading of the building parts result in cracks

For example; Cracks under a floor due to overloading of slab.

Overloading forced may be due to

1. External (excessive wind/snow loads)
2. Internal (from heavy machinery etc.)

Effect of Gases, Liquids and Solids

Gases

• Only gas likely to produce cracks is carbon dioxide - CO2
• Causes carbonation of porous cement products
• Leads into an overall shrinkage showing crazing cracks

Liquids

• Water is the most commonly used liquid when not taken care of can prove hazardous for the structures.
• Construction water i.e., that is utilization of water during the construction process
• Water in the usage of the building

Effects of water

1. Physical (i.e. due to change in water content)
2. Chemical (directly or indirectly affecting other materials)

For example, Volumetric increase due to chemical changes or Steel corrosion, sulphate attack with water

Solids

Soluble sulphates are most common and are found in various materials and soil

They are a great cause of concern. They attack the cement products which in turn result in the deterioration of the structure

Effect of changes in Temperature

Various building materials are used for the construction of a building and all the materials have different coefficient of expansion. Due to changes in the temperature, the expansion and contraction of the building components takes place which result in the changes in the size and shape of the components

Smaller buildings are less affected

In larger buildings, the change in size of one part causes cracks although not in expanded part

For example; Crack below the slab/beam in RCC frame Brick pin buildings. These cracks can close up completely as a result of changes of temperature.

General Vibrations

Vibrations cause cracks in buildings only when their amplitude of vibrations is high

Apart from vibrations caused due to earthquakes, the vibrations caused due to heavy machinery, traffic, sonic booms are also responsible for the occurrence of cracks in buildings

Minor causes of Cracks

علل وقوع ترکهاي كوچك در ساختمان

Cracks in Buildings

Cracks result in applied forces greater than those which the building or its part can withstand. These forces may have emerged externally to the building or internally within the building or have been developed in the materials of the building as a result of Chemical changes. There may be a single force or a combination of forces having a single cause or several causes

This is a residential building at San Francisco. Major cracks have developed on the external facade of the building. The cracks running across the entire facade of the building are diagonally directed and diagonal cracks are generally structural cracks. They occur due to structural problems in the buildings. Structural cracks could be due to major or minor problem in the structural design. Intensity of structural problem is determined on the basis of the intensity of cracks developed

Most cracks occur due to drying of construction water

• These are generally superficial
• Do not affect the serviceability of the building
• Can be easily repaired

If cracks are more significant, repair work may be repeated periodically

Structural significance of the cracks tends to be exaggerated by a natural reaction of the owner

Many cracks do not have any effect on the stability of structure, because of “high factor of safety”

Cracking has adverse effects on appearance. Sometimes several cracks go unnoticed for years which affect the performance of the structure

Rain penetration through a crack depends on

1. Construction of a building
2. Degree of exposure
3. Capillarity of fine cracks
4. Wind driven rain penetration through wide cracks

Major Causes of Cracks occurring in Buildings

1. Movements of the ground
2. Overloading
3. Effect of gases, liquids and solids
4. Effect of changes in the temperature
5. General - e.g., Vibrations

In our next article, we will discuss in detail the major causes of cracks in Buildings