Base plates are usually used to distribute column loads over a large enough area of supporting concrete construction that the design bearing strength of the concrete is not exceeded.
The factored load, Pu, is considered to be uniformly distributed under a base plate.
The nominal bearing strength fpkip/in2or ksi (MPa) of the concrete is given by:
In most cases, the bearing strength, fpis 0.85Fc when the concrete support is slightly larger than the base plate or , 1.7Fc when the support is a spread footing, pile cap, or mat foundation. Therefore, the required area of a base plate for a factored load Puis:
is the strength reduction factor 0.6. For a wide flange column, A1should not be less than bf d, where bf is the flange width, in (mm), and d is the depth of column, in (mm).
The length N, in (mm), of a rectangular base plate for a wide-flange column may be taken in the direction of d as:
The width B, in (mm), parallel to the flanges, then, is:
The thickness of the base plate tp, in (mm), is the largest of the values given by the equations that follow:
m projection of base plate beyond the flange and parallel to the web, in (mm) (N =0.95d)/2