Grillage Foundation Design:
Figure 1 demonstrates a simple design of a one tier grillage foundation for a steel stanchion. The bending moment and shear force required for the grillage beam design can easily be arrived by the following simple method.
Let, W = Load supported by one beam in N.
L = The length of the beam in m.
l = The length of the base plate in m.
Figure 1 also shows the load distribution. It is apparent the highest bending moment in the beam
= (W/2 * L/4) – (W/2 * L/4)
= W/8(L-l) in Nm
In the beam maximum shear force develops at the edge of the base plate. The upward pressure of soil on the beam = W/L N/m
Cantilever projection of the beam beyond the edge of the base plate
Maximum shear force in the beam = W/L (L-l/2)