A lintel is a beam that is used above the openings like doors, and windows to carry the load from the wall or partition above. The ends of the lintels usually placed in the wall which transfers the loads imposed from the above wall to the supporting sides of the wall. In some cases of load-bearing masonry structures, these are provided to the entire length of all the walls in the building. The width of the lintel is kept the same as the width of the wall. This helps to prevent the falling of masonry or bricks from above the openings and also prevents damage to the windows and doors.
The 7 types of lintels used in the building based on the type of material used are reinforced concrete lintel, brick lintel, reinforced brick lintel, steel lintel stone lintel, precast concrete lintel, and wooden lintel.
In a load-bearing masonry or stone building, there are 3 levels where beams are provided to resist the earthquake forces and they are the plinth level, the sill level – which is just below the window, and the lintel level – which is just above the doors and windows.
7 Types of Lintels
Following are the 7 types of lintels used in building construction:
1. Reinforced Concrete Lintel
Mostly, the reinforced concrete lintel is used over the openings of doors, and windows in the building due to its strength, rigidity, durability, economy, and ease of construction. Reinforced concrete lintel can be constructed for any length of the opening and it is suitable for all types of loads as it can be designed by the structural designed with suitable reinforcements. Reinforcement provides great strength and stability, and it can support any type of load over any span. The width of this is equal to the width of the wall while the depth depends on the length of opening and the magnitude of loads.
This is designed just like any other beam in the building or structural design. The 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.
2. Brick Lintel
Brick lintels are used when the opening in the building is less than 3 feet (1m) and there are fewer loads imposed from above. This is because brick can not handle much load and they will fail in shear, as they do not have the required tensile strength to support bending moments.
The depth of this type of lintel varies from 4 inches to 8 inches (10cm to 20cm), depending upon the length. Bricks with frogs are more suitable than normal bricks because frogs when filled with mortar give more shear resistance to end joints which is known as a joggled brick lintel.
3. Reinforced Brick Lintel
Reinforced brick lintels are used for heavy loads over the openings and /or span more than 3 feet (1m). The depth of this should be equal to 4 inches or 6 inches or a multiple of 4 inches (10 cm or 15 cm or multiple of 10 cm) or one brick thickness. The bricks are arranged so that a 1-inch (2 to 3cm) wide space is left length-wise between adjacent bricks for the insertion of steel reinforcement bars. This space is then filled with a cement mortar of mix ratio 1:3.
Vertical stirrups made of 6mm bars are used at every 3rd vertical joint. Primary reinforcements provided at the bottom are 8 to 10mm steel bars.
4. Stone Lintel
Stone lintels are most commonly provided over the openings in brick walls where stone is abundantly available. This is provided in the form of either one single piece or more than one piece kept one over another.
Thickness or the depth is the most important factor of its designwhich is kept equal to 4 inches / 3 ft length (10cm per meter span), with a minimum value of 6 inches (15 cm). It is used up to the length of 7 feet or 2 meters. This is not suitable for the structure which is subjected to vibratory loads, as it is weak in tensile strength due to which cracks are formed which can lead to failure.
5. Precast Concrete Lintels
Precast concrete lintels ready made and are available to be installed over the wall. These are made of reinforced concrete manufactured at different location and are transported to the construction site and installed over the openings over doors and windows. Since these are precast, it is available in different lengths and sizes.
6. Steel Lintel
Steel lintel is used when the length of opening is large and the loads from above the opening is very heavy. This is made using steel channel sections or rolled steel joists which provide great tensile strength, thus, it can carry heavy superimposed loads.
Steel sections are used as one single section or in a combination with other steel sections depending up on the requirement. When single sections are used, the steel joist is either embedded in concrete or cladded with stone facing to keep the width same as width of wall. When the sections are used as combination of two or more sections, then units are placed side by side which are kept in position by tube separators.
7. Wooden Lintel
Wooden or timber lintels were mostly used during olden days due to unavailability of modern construction materials. But these days timber is replaced by modern materials and techniques such as steel and reinforced concrete. However these are still being used in hilly areas but these are very costly and less durable and vulnerable to fire.
If the length of opening in the wall is large, then multiple number of wooden pieces are joined together to increase its depth which are joined with the help of steel bolts. For wider walls, two timber pieces are kept at a distance and the gaps are filled with packing wood pieces.
Sometimes, mild steel plates are used together with wooden linel which is placed at the top and bottom of wooden pieces. This arrangement of wood and mild steel plates have great tensile strength and can carry greater loads over a large length of openings which are called as flitched lintels.
