### Concrete Column Base Plate Design

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

*fp*kip/in2 or ksi (MPa) of the concrete is given by: In most cases, the bearing strength,

*fp*is 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*Pu*is:where

*is the strength reduction factor 0.6. For a wide flange column,*

*A*1 should 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:Where:

*m*projection of base plate beyond the flange and parallel to the web, in (mm)

(

*N =*0.95

*d*)/2

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