Lintel Definition
A horizontal structural member which is fixed over the openings namely doors, windows etc. to support the structure or the openings is known as lintel. Lintels behave just like beam. They provide bearing for the masonry above the openings and transfers all the loads acting over the opening to the supporting walls.
Lintels are generally rectangular in shape. They can afford facilities for fixing the doors and window frames, wherever they are used. Lintels are made of several material such as wood, stone, brick, reinforced concrete, reinforced brickwork or rolled sections embedded in cement concrete.
Types of Lintels
Different types of lintels used in the construction industry are as follows :
- Stone Lintel
- Wooden Lintel
- Reinforced Concrete Lintel
- Brick Lintel
- Steel Lintel
- Reinforced Brick Lintel
1. Stone Lintel
Stone lintels are most commonly used in the areas where availability of stones is in abundant. Stone lintels are mostly preferred for stone masonry structures or buildings which are faced with stones.
The use of stone lintels is very rare due to its high cost and lack of capability to withstand the transverse stress. The thickness of stone lintel is generally 8 cm but as a thumb rule it is kept 4 cm per 30 cm span.
2. Wooden Lintel
Wooden lintels were used in old days when the technology was not that advanced. Wooden lintels are not totally extinct. Even today, in some construction works wooden lintels are used. The use of wooden lintels has been reduced in modern world due to unavailability of timber in the market. Moreover it is easily affected by white ants and other insects.
Timber catches fire easily, hence they are not recommended for use in fire proof constructions. The standard dept of wooden lintel should be 7.5 cm (min). They are generally manufactured in single piece or in parts which are assembled later on site. Wooden lintels are comparatively weak in nature and hence stone or brick arches should be used along with it. It should be designed using flexural formula to use over large spans.
3. Brick Lintels
These brick lintels are used to span small openings (less than one meter) with light loading. Brick lintels generally consist of bricks which are normally laid on end and occasionally on edge. The brick lintel is constructed over a temporary wood support (i.e. acting as centering) known as turning piece.
Bricks with frogs (i.e. depressions) are more suitable for construction of lintels as they are bounded and hence possess more shear resistance at the end joints (i.e. greater lintel strength). The lintel formed by using frog bricks is termed as joggled bricks lintel.
The following points regarding bricks lintels should be given due consideration :
- Bricks should be hard, well-burnt, free from defects such as lumps, cracks, flaws etc. and with sharp and square edges.
- The depth of the brick lintels, which varies with the size of opening and appearance of brickwork should be multiple of brick courses usually 10 cm, 20 cm etc.
- For bonding frog bricks, the cement mortar with mix proportion with 1:3 should be used.
- Brick lintels being weak in Strength cannot be used for heavy loads.
4. Steel Lintels
These lintels consist of steel angle or rolled steel joints. The former is used for small spans and light loading and the latter is used for large spans and heavy loading. A steel lintel becomes useful when there is no space available to accommodate the rise of an arch. Fig shows the various forms of steel lintels. The steel joints may be used singly or in combination of two or three units.
5. Reinforced Concrete Lintels.
Reinforced concrete lintels are common in use due to their durability, strength and fire resisting properties. Moreover they are cheap and easy in construction. They can be easily adopted for bigger span and heavy loading construction.
For the construction of R.C.C lintels 1:2:4 cement concrete reinforced along with steel bar is used. They can be of precast type or cast-in-situ. But for smaller spans (upto 1.2 meters), precast lintels are recommended.
Precast lintels are economical in nature as they are manufactured and cured in advance and the same mould can be used multiple times. While laying the precast lintels special care should be taken that the marked face should be kept at the top.
Generally for larger spans, these lintels are cast-in-situ type because additional reinforcement has to be placed in lintels due to heavy loading.
Depth of Lintel for Ordinary Loading
Generally for span of 1.2 meter, the depth of 15 cm is considered safe. As a thumb rule, addition of 25 mm for every additional 30 cm span is recommended.
6. Reinforced Brick Lintels (R.B Lintels)
The construction of brick lintels is very much similar to R.C.C lintels, but here good quality bricks are used instead of concrete. In case if brick lintels are supposed to be used for larger spans, they are reinforced with steel bars.
In case of reinforcing with bars the bricks are arranged in a pattern of parallel rows, such that 2-4 cm wide space is left length wise for inserting the street bars or rods. After placing the steel rods or bars the cement concrete or cement mortar is poured and the space is filled.
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