Why is plinth beam provided??

Differnt practice is being followed by different people. Normally the peripherial plinth beams are provided 150mm below the NGL and the internal plinth beams at floor finish level.

The peripherial plinth beams are at such depth so that to avoid settlement of the internal floor in case we have to excavate for any drain to be provided near the building. also in case of the drain pipes being taken from the building the pipes can easily pass from the bottom of the peripherial plinth beams.

If the internal plinth beams are provided at lower level then the invert level of the drain pipes will become very low and the crossing of the pipes at the junction with internal plinth beams/peripherial plinth beams will create problem as we will be forced to take the pipes down and at places the final invert level may become too low. In case we are forced to provide the peripherial plinth beams at floor level than as a good engineering practice provide a nominal wall foundation all around to take care of the settlement of the floor in case of any diffing done near the building/peripherial plinth beams. This decision varies from engineer to engineer and from site to site. Plinth beams is always a helpful in respect of following: Plinth beams needs to be designed only for EQ/wind and the vertical loading will be carried throgh brick footings.

The brick masonry having footings act as shear walls for taking care of EQ forces (benefit in column design can be taken)

Load on columns and their footings is less as GF walls weight is directly on ground.

Footings requirements is bare minimum and also, foundation depth for brick footings can be shallower than main columns.

Footings help to take care of unequal settlements.