The plinth beam is meant to join all the columns reducing the effective length in a frame structure and plinth beam in a framed structure provided at or above ground level that takes the load of a wall that is built on it.
Between the wall and its foundation plinth beams are constructed and these are reinforced concrete beams, to prevent the extension or propagation of cracks from the foundation into the wall when the foundation suffers from settlement these beams are provided and these beams over the foundation distributes the load of a wall.
As we know that a superstructure lies above ground level that includes beams, columns, masonry walls and slabs, etc and the plinth beam in these types of structures separates the superstructure and the substructure which acts like a tie beam that keeps walls and columns connected.
Purposes Of Plinth Beam:
There are following purposes of these beams such as;
- In structures these beam prevents differential settlement and because to the foundation all the load on the plinth beam is uniformly transferred.
- These beams prevent dampness to enter the building from the foundation.
- These beams tie all the columns.
- From the foundation to reach the wall it prevents cracks.
- To collapse during an earthquake it prevents the building.
- These beams uniformly distribute the load.
Minimum Dimension and Concrete Strength For Plinth Beam:
As 20cm is a minimum depth of this beam and width should match the final foundation course.
The concrete strength for this beam shall not be smaller than 200Mpa and an extra of 20% cement need to be added to the mixture if the concrete is mixed manually.
Height Of A Plinth:
Above the permanent adjacent road level the ideal plinth height is 300mm to 600mm.
To prevent the water not to enter your house in the rainy season the plinth level has to be above the adjacent road level and adjacent properties may go below if the reconstruction of the road is constructed without removing the strata of the old road.
The plinth is constructed in such a way that the top of this is sufficiently above road level and this prevents drainage water to enter the house from outside, adjacent parking area will also increase causing difficulty for driving from the road if the plinth is too high above the road level.
To reach plinth level three to four stairs are required. So, due to these problems, the height should be kept very carefully and the height should not too high or too low.
Steel Bars And Formwork Used For Plinth Beam:
The two bars with a minimum diameter of 12mm at the bottom of the beam should be provided and at the top of these beams two bars with a minimum diameter of 10mm shall be provided. By 25mm concrete cover reinforcement bars should be protected and stirrups of 6mm and 15cm of spacing are connected.
The formwork for these beams construction should be properly installed and secured prior to concrete placement and to prevent steel bars from aggressive elements the concrete needs to be compacted sufficiently.
To prevent the infiltration of water in the soil that reaches the plinth wall and reaches the floor level by capillary action, the protection of plinth is necessary and beam protection reduces the direct entry of water into the ground. Plinth protection is an area around the building and by pouring a layer of approximately 100mm of common cement concrete the plinth protection is usually done.
To prevent water retention along the edge of the building, this is the main idea of this protection.
Importance Of Plinth Beam:
There are following importance of these beams such as;
To Carry Masonry Load At Ground Floor Level:
To carry the dead weight of the masonry wall on the ground floor level these beams are designed.
To Retain Backfilled Soil:
Usually houses are constructed 150-300mm above the level of adjacent road and as a retaining structure for the compacted soil used to fill the void from foundation level to the top of the plinth, these beams are used.
To Control & Avoid Different Settlement:
In case the soil is not compacted properly foundations may be subjected to differential settlement and in the masonry walls a differential settlement will cause cracks.
In reducing the differential settlement in the structure these beams helps in reducing.
To Act As A Tie Beam:
From the unsupported length of the column to the cross-section area of column slenderness ratio is delivered and the ratio of slenderness will be higher if the length of the column is higher which decreases the load-carrying capacity of building and tie beams are provided to decreases effective length of the column.
RCC plinth beam is must be provided if the foundation is very deep and this beam will also act as a tie beam for the foundation less than or equal to 6 feet.
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