1. Grade BeamIn construction. A grade beam is a type of foundation system used to distribute the weight of a building over unstable soil. The grade beam may sit directly on the loose soil, or be supported by pipe pilings that extend deep underground. Builders then position a series of piers or foundations wall on top of the beam to support specific building components. These foundation systems consist of heavy-duty concrete beams that are often reinforced with rebar or steel mesh for additional strength. Unlike standard spread footings, grade beams are designed to minimize deflection instead of simply transferring loads directly to the ground below. This allows the beam to span loose or unstable areas of soil, and redistribute building loads to areas where soil is more compact.

Figure 1.1: Grade Beams

2. Plinth BeamBasically plinth beam connects all pillars and serves as the base for construction of walls.

Figure 2.1: Plinth Beams

Coming to your question,Isnt we really required the Grade beam and plinth beam in a normal building?Ans: Its not about the type of building, its all about the soil we speak here for grade beam. Grade beam is a type of foundation system used to distribute the weight of a building over unstable soil. As shown in figure 1.1, Grade beams are casted and placed directly on the ground, in place of any footing or onto any pile.But, Plinth beams are the beams used to connect the pillars above ground to serve as base for walls etc. (See figure 2.1). You require a foundation for building a plinth; the foundation may be masonry or RCC. But Grade beam itself is a foundation and also acts as plinth because of its continuous nature.Grade beam acts as a foundation and also serves as plinth for construction walls but a plinth can only serve as base for walls but not as foundation.I hope your doubt has been cleared k. Subramanian Sir