A lintel is one type of beam which used to support the above wall when openings like doors, windows etc. are necessary to provide a building structure. The main function of the lintel is to take loads coming from above wall and transfer its load to the side walls. The lintel beam generally ends into the masonry wall so as to convey the weight carried by them to the masonry walls and its width is same to the wall width. The lintel can also be used as decorative architecture element.
Types of Lintel
Lintels are classified into the following types according to the materials of their construction:
- Timber lintel
- Stone lintel
- Reinforced concrete lintel
- Brick lintel
- Reinforced brick lintel
- Steel lintel
Timber lintels are mainly used in the hilly areas where timbers are available. But in plain areas, uses of timber are limited because of the high cost. It also has other disadvantages.
- Without proper ventilation, timber is liable to decay.
- It is less durable.
- Timber being combustible it is vulnerable to fire.
This type of lintel is mainly used in this area where the stone is abundantly available. Its use is mainly confined to stone masonry structures. There are some disadvantages of using stone lintel. Firstly, its high cost and secondly its inability to withstand excessive transverse stress. The thickness of the stone lintel is a very important factor for its design. As a thumb rule, the thickness is taken as 4 cm. per 30cm length of span and the minimum thickness should be 8 cm.
Reinforced Concrete Lintel
At present, reinforced concrete lintels are very common in use because of their durability, rigidity, strength, and fire resisting properties. They are suitable for heavy loads and larger span. Also, they are economical and easy in construction. The main advantage of the RC lintels is being the adaptability to suit any size and shape. RCC lintels can be either pre-cast or cast-in-situ. Generally, pre-cast reinforced cement concrete lintels are used when the lintel span is smaller. Lintel width should be same as wall width. The depth of lintel depends on the length of span and the loading’s magnitude.
Concrete though strong in compression is very weak to tensile stress, so main reinforcement bars are used at the bottom to resist the tensile stress. Half of these bars are cranked at the ends. Shear stirrups are provided to resist shear stress. Normally, cement, sand, and aggregates are mixed in 1:2:4 ration to form cement concrete mortar.
Brick lintels are constructed with hard, well burnt first class brick. It can be formed as bricks on end, bricks on edge and coursed bricks laid horizontally over openings. This type of lintel is used when the opening is small (less than 1m) with light loadings condition. Their depth varies from 10 cm (depth of one brick) to 20 cm depending upon the span. Bricks with frogs filled with mortar give more shear resistance at end joints than the normal bricks.
Reinforced Brick Lintels
Heavy loadings and larger span length are the problems for brick lintels. These can be overcome by using the reinforcement bars. Reinforced brick lintels thus provide more support than the brick lintels. The depth of the reinforced brick lintels is equal to 10 cm. or multiple of 10 cm (or one brick thickness). The arrangement of the bricks should be such as that there is enough space in lengthwise between the adjacent bricks for the insertion of mild steel bars as reinforcement. After insertion bars, the remaining gap is filled with 1:3 cement mortar. 6 mm bars are used as vertical stirrups at every 3rd vertical joints. 8 to 10 mm bars placed at the bottom are used as main reinforcement.
Steel inlets can be suitable when the superimposed loads are heavy and the opening gaps are large. Steel lintels are more preferable when the depth of lintel plays an important role because the designer cannot ignore the depth of reinforced concrete lintels due to heavy loads. These lintels consist of channel sections or rolled steel joists. Depending upon the requirements, the lintel can be a single section or combinations of two or more. Single steel joist is either embedded in concrete or cladded with stone facing to keep the same width as the wall. Combination of two or more units are placed side by side and held in position by tube separator.