A lintel is a horizontal member which is placed across the openings like doors, windows etc. It takes the load coming from the structure above it and gives support. It is also a type beam, the width of which is equal to the width of wall, and the ends of which are built into the wall. These are very easy to construct as compared to arches.
Types of Lintels used in Building Construction
Lintels are classified based on the material of construction as:
- Timber lintel
- Stone lintel
- Brick lintel
- Steel lintel
- Reinforced concrete lintel
- Reinforced brick lintel
In olden days of construction, Timber lintels were mostly used. But now a days they are replaced by several modern techniques, however in hilly areas these are using. The main disadvantages with timber are more cost and less durable and vulnerable to fire.
If the length of opening is more, then lintel is provided by jointing multiple number of wooden pieces with the help of steel bolts which was shown in fig (a). In case of wider walls, lintel is composed of two wooden pieces kept at a distance with the help of packing pieces made of wood. Sometimes, timber lintels are strengthened by the provision of mild steel plates at their top and bottom, called as flitched lintels.
These are the most common types of lintels especially where stone is abundantly available. The thickness of these are most important factor of its design. These are also provided over the openings in brick walls. Stone lintels are provided in the form of either one single piece or more than one piece.
The depth of this type is kept equal to 10 cm / meter of span, with a minimum value of 15 cm. They are used up to spans of 2 meters. In the structure is subjected to vibratory loads, cracks are formed in the stone lintel because of its weak tensile nature. Hence caution is needed.
When the opening is less than 1m and lesser loads are acting, brick lintels are used. The depth of brick lintel varies from 10 cm to 20 cm, depending up on the span. Bricks with frogs are more suitable than normal bricks because frogs when filled with mortar gives more shear resistance of end joints. Such lintel is known as joggled brick lintel.
Reinforced Brick Lintels
If loads are heavy and span is greater than 1m, then reinforced brick lintels are useful. The depth of reinforced brick lintel should be equal to 10 cm or 15 cm or multiple of 10 cm. the bricks are so arranged that 2 to 3 cm wide space is left length wise between adjacent bricks for the insertion of mild steel bars as reinforcement. 1:3 cement mortar is used to fill up the gaps. Vertical stirrups of 6 mm diameter are provided in every 3rd vertical joint. Main reinforcement is provided at the bottom consists 8 to 10 mm diameter bars, which are cranked up at the ends.
If the superimposed loads are heavy and openings are large then we can go for steel lintels. These lintels consist of channel sections or rolled steel joists. We can use one single section or in combinations depending up on the requirement.
When used singly, the steel joist is either embedded in concrete or cladded with stone facing to keep the width same as width of wall. When more than one units are placed side by side, they are kept in position by tube separators.
Reinforced Cement Concrete Lintels
At present, the lintels of R.C.C are widely used to span the openings for doors, windows, etc. in a structure because of their strength, rigidity, fire resistance, economy and ease in construction. R.C.C lintels are suitable for all the loads and for any span. The width of lintel is equal to width of wall. Depth of lintel is dependent of length of span and magnitude of loading.
Main reinforcement is provided at the bottom and half of these bars are cranked at the ends. Shear stirrups are provided to resist transverse shear as shown in fig.
R.C.C lintel over a window, along with chhajja projection is displayed in below fig.
R.C.C boot lintels are provided over cavity walls. These will give good appearance and economical. A flexible D.P.C is provided above the lintel as shown in fig.