What is a Lintel?
A Lintel is a horizontal structural member that is provided over the openings such as doors and windows in the buildings to support the load over the openings.
The lintel acts as a support, distributing the load across its length and transferring it to the vertical supports (typically the walls) on either side of the opening. It is an essential part of the building structure.
Merits of lintels over arches
Both lintels and arches perform the same function i.e. to transfer the weight of the structure above the opening to its sides.
If that is the case, then why do we use lintels instead of arches?
Even though lintels perform the same function as arches, they are preferred to arches due to the following reasons:
- The arches require more headroom space to span the openings.
- The arches require strong end walls (abutments) to withstand the arch thrust.
- The centering work to construct arches is much more complex and difficult when compared to the lintel construction.
Distribution of Loads over the lintel
British standard BS 5977-1:1981 explains the distribution of loads over the lintel. It defines two zones above the lintel. They are,
- Loading triangle
- Interaction zone
Let’s take a brief look at both of them.
1) Loading triangle – A 45° triangle above the lintel having 1.1 times the clear span of the lintel as its base.
2) Interaction zone – It is a zone outside the load triangle but within a 60° triangle having 1.1 times the clear span of the lintel as its base.
Clause 4.2 of BS 5977-1:1981 assumes that,
1. All the weight of the masonry within the load triangle is carried as a load on the lintel.
2. Any point or distributed loads applied to the masonry within the load triangle are dispersed at 45° and carried by the lintel.
3. The weight of masonry in the interaction zone is not carried by the lintel.
4. Any point or distributed loads applied to the masonry within the interaction zone are reduced by 50%, dispersed at 45°, and carried by the lintel.
Types of lintels used in construction
The lintels are classified based on their,
- Span and
- The Materials they are made of.
a) Based on the span
Based on the span, lintels are classified into two types namely, Cut lintel and Thorough lintel.
1) Cut Lintel
This type of lintel is provided only above the openings. These beams can be either precast or cast in place.
These types of lintels must have a necessary bearing to make sure the load is transferred properly to the sides of the openings.
Cut lintel is used,
- When the top level of the windows is not aligned at the same level.
- To reduce the cost of the construction.
2) Thorough Lintel / Continuos Lintel
This type of lintel runs throughout the span of the building. It is mostly made up of Reinforced Cement Concrete (RCC).
These types of lintels connect all the columns of the building thus improving the torsional rigidity of the whole building structure.
Thorough lintel is used,
- When the top level of all the windows of the building are aligned at the same level.
- Used in places that are prone to earthquakes to increase the rigidity of the building.
b) Based on the materials
Based on materials used in the construction, lintels are classified into the following types,
- Wooden lintels
- Stone lintels
- Brick lintels
- Steel lintels
- RCC lintels
Let’s take a brief look at each type of lintel mentioned above.
1. Wooden Lintels
This is one of the oldest types of lintels used in construction. Even nowadays, wooden lintels are used commonly in hilly areas where timber is cheaply available in abundance.
Wooden timber should be made of sound and hardwoods like timber, teak, rosewood, sal, etc. Otherwise, it is to be likely destroyed by fire and decay.
A single piece of timber can be usually used for small spans. For larger spans, two or more pieces of wood held together by bolts at suitable intervals can be used.
The wooden lintel must have an adequate bearing and it should rest on a mortar to have a firm and uniform base.
Advantages of using wooden lintels
- Easy to install
- Provide good aesthetic
- Easy to handle during construction
Disadvantages of using wooden lintels
- Relatively higher cost in plains where woods are not abundantly available.
- High susceptibility to catching fire
- Liable to decay by rot or termites
- Not suitable for larger openings
- Requires regular maintenance
2. Stone Lintels
Stone lintels are made of slabs of stones of sufficient length without any flaws. The use of stone lintel is recommended only in places where stone is available in abundance.
The minimum thickness of the stone lintel should be 15cm. Stone lintels can be used for openings up to 1m. If the span becomes greater than 1m, then it requires abnormally high stone thickness.
Advantages of using stone lintels
- Can be cost-effective when available in abundance in local areas
- Provide good aesthetic to the building
- Easier to install
- Provides good durability, and good fire resistance, and requires low maintenance
Disadvantages of using stone lintels
- Cost becomes high when not available in local areas
- Cannot be used for long spans
- Can cause challenges during transportation, handling, and installation.
- It cannot withstand transverse stresses and is weak in tension.
- Difficult to obtain slabs of stones of sufficient length and depth, free from any defects or flaws.
3. Brick Lintels
These lintels are constructed using hard, well-burnt bricks and are used to span only small openings (<1m) with light loading.
Bricks with frogs are most suitable for constructing lintels as they form juggles when bounded and possess greater resistance. The lintel formed by using frog bricks is termed as Joggled brick lintel.
The brick lintel is constructed over a temporary support known as a turning piece. For bonding bricks, cement mortar with a 1:3 mix proportion should be used.
Advantages of using brick lintels
- It is ideal and cost-effective for smaller openings (<1m)
- It can provide good traditional aesthetics to the structure
Disadvantages of using brick lintels
- Brick lintels cannot span larger openings without any additional support
- Brick lintels possess low strength, thus cannot be used for supporting heavy loads
- Construction can be time-consuming and involves complex processes like centering compared to other prefabricated materials.
4. Steel Lintels
These lintels are made up of rolled steel joists steel sections and are used to span larger openings. It is used particularly when they have to support heavy loads.
It can be used in two ways. For example, A separate I section can be used to span the openings but the problem is corrosion due to the exposure to environmental agents. So in order to keep the section safe from the environment, it is sometimes embedded in concrete and is used to span the openings.
Advantages of using steel lintel
- These lintels possess high strength and are capable of bearing high loads.
- It can be manufactured with precise measurements to span the openings.
- Resistant to decays, rots, and pests.
- Relatively lightweight when compared to other elements like stone.
- Easy to install
Disadvantages of using steel lintel
- Vulnerable to corrosion in areas with high humidity
- Steel is a conductor of heat, which means it can become hot in the event of a fire. While it does not contribute to the spread of flames, its high thermal conductivity can be a consideration in fire safety planning.
5. RCC Lintels
In recent times, Reinforced Cement Concrete (RCC) lintels have been extensively used all over the place and almost replaced all other materials in construction.
RCC lintels are constructed usually with M15 or M20 grade concrete with steel bars as reinforcement.
Plain concrete is not suitable for lintel construction because it is too weak in carrying tension, hence we use steel reinforcement to strengthen the lintels. The amount of reinforcement depends upon various factors such as the span of the lintel, width of opening, loading on the lintel, etc.
RCC lintels may be either pre-cast or cast in situ.
Pre-cast RCC lintels are preferred for small spans and ensure speedy construction as no time is needed for casting and curing. For larger spans, the lintel should be cast in site.
Advantages of using RCC lintel
- These lintels offer high compressive and tensile strength, thus increasing the overall performance of the lintel.
- These lintels are capable of supporting heavy loads over openings.
- It provides flexibility in design to accommodate various sizes and shapes.
- It is durable and resistant to fire, decay, pests, and weathering.
Disadvantages of using RCC lintel
- Prone to problems such as shrinkage, cracking, and spalling.
- The construction process for RCC lintels may take longer compared to using pre-fabricated materials. The need for formwork, curing time, and the setting process can impact project timelines.
Hope you understand everything you need to know about the lintels and types of lintels in detail. If you find this article helpful, let us know in the comment section.