Steel column base plate is used to spread the compression load from column to a sufficient area of the footing to avoid overstressing.
They serve several purposes:
- To provide column bearing – To aid in the transfer of column axial stresses to the concrete pier or footing
- To aid in the prevention of concrete crushing beneath the column.
- To give temporary support to the column during steel installation by allowing the column to behave as a vertical cantilever (in conjunction with anchor bolts).
Dimensions of steel column base plate
The base plate is usually larger than the column size (depending on the shape of the column) by as much as 2” to 4”, in order to provide a drill hole for the anchor bolt holes outside of the column outline. It is usually connected to the column with fillet weld (up to 3/4” in size) on both side of the web and flange and usually shop welded.
How steel column base plates are fabricated?
Steel Base plate can be welded to the columns cross section or bolted using lug angle. High-strength, non-shrink grout is placed between the column base plate and the supporting foundation. To keep the base plate in proper elevation in order avoid any error in positioning of columns, following three techniques are employed
- Levelling plates (for base plates up to 20 or 22 inches). The leveling plate should meet the flatness tolerances specified in ASTM A6. It may be larger than the base plate to accommodate anchor rod placement tolerances. It can be used as a setting template for the anchor rods
- Levelling nuts (for base plates up to 36 inches) also called as shim stacks
- Preset base plates (for base plates larder than 36 inches).
Minimum number of bolts required to connect steel column base plates
At least four anchor bolts should be placed at the four corners of column base plate as per the OSHA regulations
Finishing requirements of steel column base plates
Following is the excerpt taken from ANSI/AISC 360-16 Specification for Structural Steel Buildings Section M2.8 and M2.9.
Design of steel column base plate connections
The ANSI/AISC 360-16 Specification for Structural Steel Buildings does not provide any specific procedure to design column base plate. However, the design process of steel column base plates is discussed here based on the design examples given in the AISC Steel steel construction manual.
