Plinth Beam: Size & Dimension

In construction, a solid base is crucial, and that’s where the “plinth beam” comes in. This introduction covers the basics of a plinth beam, a horizontal support structure at the base of a building. Whether you’re a homeowner or just curious about construction, understanding the role of a plinth beam is key to ensuring stability and strength in a structure.

What Is a Plinth Beam?

A plinth beam is a reinforced concrete beam constructed at ground level, typically at the junction between a masonry wall and the foundation. It is designed to distribute the load of the wall over a larger area, reducing the pressure on the foundation and preventing soil erosion. Plinth beams are commonly used in areas with a high risk of soil erosion or in buildings constructed on soft soils.

They also provide additional support to the building in the event of an earthquake or other seismic activity. The size of a plinth beam depends on various factors such as the size and type of the building, the load-bearing capacity of the soil, and the local building codes and regulations.

However, the standard height of a plinth beam is usually kept between 225mm to 450mm, and the width is typically 150mm to 300mm.

Plinth Beam
Plinth Beam

Proper design and construction of a plinth beam are crucial to ensure the stability and longevity of a building. Inadequate or improper construction can result in settlement, cracking, or even collapse of the structure.

Read More: 8+ Foundation Construction Steps

What Is Plinth?

The plinth is one type of level or base that supports superstructure walls, columns, and structures. The function of the plinth is to pressure and load evenly across a column over a wider space.

The plinth is also used to elevate structures above the ground to ensure their protection from water and other surrounding elements.

Height of Plinth

The plinth height is between 300 – 450 mm above ground level, it is advisable to the kept peak of 150 mm above the onsite ground level be adopted.

What Is Plinth Level?

The plinth Level is a specific height from the ground level at which building superstructure construction starts. Generally, the plinth level height is kept between 300 mm to 450 mm.

Applications of Plinth Beam

The following are the reasons for providing the plinth beam,

  1. These beams in the structures prevent differential settlement and all the loads on the plinth beams are transferred equally due to the foundation.
  2. These beams prevent moisture from entering the building from the foundation.
  3. These beams bind all the columns.
  4. It prevents cracks from the foundation to the wall.
  5. This prevents the building to collapse during an earthquake.
  6. These beams distribute the load evenly.

Standard Dimensions of Plinth Beam

The width of the beam is usually 9 ″ or 225mm, as the wall width in India is 9 ″. So that the structure has a good look.

The minimum size of the RCC plinth beam should not be less than 9 “x 9” (225 mm x 225 mm), as a general rule of thumb.

The plinth beam size for a 1-story building is 9 “x 9″ (225 mm x 225) mm) and is 9″x 12” (225 mm x 300 mm) plinth beam sizes are used for 2 story (G + 1), 3 story (G + 2) and 4 story (G + 3) houses.

Applications of Plinth Beam

Following are the Applications of Plinth Beam,

  1. As per standards, it has been made mandatory in earthquake-prone areas to construct plinth Beam.
  2. It is applicable to construct a plinth beam Above Ground Level.
  3. Plinth Beam carries the load of the wall constructed above it.
  4. Water from the surface is prevented to get implicated into the soil using Plinth Beam.
  5. The best application of a plinth beam is to withstand outside actions such as water, tree roots, termites which could affect the life of the plinth.

Concrete Grade Suitable For Plinth

Concreting of Plinth Beam
Concrete Grade Suitable For Plinth
  • A minimum of 20Mpa Strength is required for Plinth in order to withstand outside actions.
  • Manual Mixing of concrete needs 20% extra cement to be added to the mixture, for compensation of losses.
  • Proper installation is mandatory in the case of Formwork prior to the concrete filling.
  • The strength of the plinth is well dependent on the adequacy of formwork secured while concrete filling.
  •  Concrete compaction is also one of the factors responsible for obtaining sufficient strength.

Read More: 25 Different Types of Beam In Construction & Their Use

Form Work and Steel Bars Used in Plinth

Formwork and Steel of Plinth Beam
Plinth Beam: Size & Dimension 6
  • Two Reinforcement Steel bars with a minimum of 12mm diameter are required to be provided at bottom of a beam.
  • However, at the top, 10mm diameter steel bars are recommended for the plinth beams.
  • Along with the 12mm diameter bars at the bottom and 10mm diameter steel bars at the bottom, it is compulsory to provide a 25mm concrete cover for protection.
  • A spacing of 15 cm along with 6mm stirrup diameter is recommended as per standards.
  • Formworks are installed prior to concrete filling in an adequate manner to ensure and obtain the required strength of concrete.
  • Another important factor responsible for gaining the required strength is the compaction of concrete.
  • Concrete compaction eliminates the void ratio within the concrete after placement.

What is Plinth Protection?

Plinth Protection
Plinth Protection

Plinth protection is provided to prevent water implication into the soil and reach the equal of the plinth wall and floor by capillary action resulting in moisture, acting as a barrier and water in the ground near the plinth wall blocks direct access to.

Plinth protection is supported by offering an additional shape or additional thickness/peak under the beam or under the foundation. In short, the plinth is the base of the structure that carries the weight of the structure to the soil.

Many times, the plinth has to deal with outside actions such as water, tree roots, termites as it affects the life of the plinth and fails it, so it is necessary to protect the plinth from such activities.

Read More: What is Lintel Beam? Propose, Size & Types

Purpose of Plinth Protection

  • Plinth protection is necessary to prevent water from leaking into the earth.
  • Plinth protection prevents water from entering the soil directly near the plinth wall, this is usually done by placing a plain precast slab width of 600 mm.
  • The purpose of a frame structure is to connect the plinth beam to all columns, reducing the efficient size and slope of the columns.
  • The welded beams commonly used in foundations are slightly deeper, acting as a reinforcement or mooring element.
  • Another reason for providing a plinth beam is to avoid different settlements in the building, due to the fact that the whole weight of the wall is below the skirting beam.
  • Fringed beams are typically used when the foundation is slightly deeper and thus serves as a reinforcement or mooring element.

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