A lintel is a horizontal beam that distributes the load over openings in a structure. The weight that is above such openings is transferred to the surrounding vertical support. It spans openings such as windows, doors, fireplaces, etc., helping to maintain the stability of the building.
The beams are commonly made of reinforced concrete. However, other materials can also be used. The word lintel is derived from an old French word meaning “threshold.” The earliest lintels were found to be made of wood, which was replaced with stone for larger buildings. The first ever lintel was found around the first century BC.
The lintel beam’s primary purpose is to deliver stability and structural integrity to the building by supporting loads above openings. It can also add architectural value to a structure.
Types of Concrete Lintel Beams
- PCC Lintel Beam
- RCC Lintel Beam
- Cast in-situ Lintel Beam
- Precast Lintel Beam
- Prestressed Lintel Beam
PCC Lintel Beam
PCC lintel beams are horizontal structural elements composed of plain cement concrete. PPC lintels do not contain reinforcement. They are generally used for smaller spans and lighter loads.
The usual range of thickness of the PCC lintel is between 100 mm and 150 mm. In particular, PCC lintels are found to be suitable for non-load-bearing walls in framed structures, where the load to be borne by lintels is much lower.
Advantages
- In comparison to reinforced concrete lintels, PCC lintels are less expensive.
- It does not require skilled labor as the construction process is easy and simple.
- PCC lintels are durable and have a longer lifespan under proper maintenance.
RCC Lintel Beam
Reinforced concrete lintel beams are composed of concrete and reinforced with steel bars. They are a popular choice in modern construction for door and window openings. It has high tensile strength due to its reinforcement characteristics.
Reinforced lintel beams provide excellent resistance and create a balance for casting various shapes and sizes of openings, bringing flexibility. The design flexibility contributes to energy efficiency, allowing it to maintain sleek aesthetics matching its building design with a smooth finish. The reinforcement of this type enhances the corrosion resistance, bringing stability over time.
It is cost-effective and known for its highly durable and long-lasting nature, making it suitable for a maximum spanning of 2 m.
It has minimal thermal expansion, can be customized to meet regulatory standards, and offers safety applications to the building. They are a popular choice due to their high load-bearing capacity and low thermal expansion, and they perform well in seismic areas.
Cast in-situ Lintel Beam
Cast in-situ lintel beams are horizontal structural elements created by pouring concrete into the formwork on site. It is composed of cement, water, aggregate, and reinforcement, such as steel bars or mesh.
Advantages:
- Provides the necessary flexibility in designing. Also, it is customised according to specific project requirements.
- It can be seamlessly integrated with the surrounding structure, providing high strength and durability.
- Cast in-situ lintel beams are resistant to fire and weathering. Furthermore, it greatly helps in the weight distribution of the structure above the opening.
Precast Lintel Beam
Precast lintel beams are made from concrete, where the casting is done in a controlled environment off-site, transported and then installed in the construction location. Precast lintel beams are made from high-strength concrete. Also, it can be reinforced with steel bars.
M30 is typically used as a high-strength concrete in precast lintel beams. This type requires load-bearing length on both sides of the opening.
This lintel ranges from 4 inches to 12 inches in height. A minimum bearing length of 100 mm is recommended to ensure proper load distribution. Moreover, the precast lintel beam has a minimum comprehensive strength of 3000 PSI.
Additionally, they distribute loads to withstand seismic forces. They are considered highly durable by providing thermal insulation and improving energy efficiency.
Prestressed Lintel Beam
Prestressed lintel beams are pre-tensioned with steel tendons to enhance the load-bearing capacity. It is made from high-strength concrete and steel tendons.
. It offers superior strength compared to non-prestressed lintels.
As it is highly durable and resistant to cracking, it supports hefty loads. High-strength concrete such as M 40 grade is used. Prestressed concrete lintels can support weight between large piers. This is made possible by prestressing processes that help concrete resist the tensile force.
It is primarily of two types:
- Pretensioned: in this type the tendons are tensioned before the concrete is poured.
- Post-tensioned: the tendons are tensioned after the concrete is set.
Design and Construction of Concrete Lintels
Structural Requirement and Design
Load calculation majorly determines the load that needs to be supported by a lintel beam. With its self-weight, the weight of the masonry above and any additional weight, including the floors and the roofs, are calculated.
After a precise calculation, the next step is to identify the span length and the type of support required at every end. The size and reinforcement of the lintel are usually influenced by the span length.
The depth of a lintel is usually 1/10th of its height and thickness usually remains the same as the wall thickness. However, structural or civil engineers are required to accurately estimate the size.
The design reinforcement is then assessed based on the resistance to bending shear and compressive stress. The ideal material used for reinforcement is typically steel bars.
Formwork Preparation
A temporary structure, often called formwork, is constructed to support the concrete until it hardens. It generally matches up with the lintel dimension.
This precisely ensures that the lintel is well supported and helps in maintaining the shape during the concrete process.
Placement of Reinforcement
Placing the reinforcement bars provides the necessary tensile support and involves cutting, bending, and laying according to the design requirements.
With proper spacing and covering, the bars are positioned carefully within the formwork.
During the reinforcement placement, proper maintenance of distance for spacing is required both at the bottom and sides of the lintel. This is done by using tie wires or cover blocks.
Concrete Pouring
While pouring the concrete into the formwork, it is essential to ensure it is well compacted and avoid voids.
For achieving proper compaction, vibrators can be used. After the pouring process, the concrete is allowed to cure.
Allowing concrete to achieve full strength, the lintel should be kept moist and covered properly for a minimum of 7 days.
Formwork Removal and Finishing
Once the concrete gains sufficient strength, the formwork can be removed. This process duration depends on the curing conditions but generally takes around 7 days.
Conclusion
Concrete lintel beams are a vital component in providing structural support to openings like windows and doors. Careful consideration is required to facilitate lintels with adequate load distribution for specific requirements. This ensures durability with reliable long-term support, ensuring the necessary safety for building occupants.