Column bases are usually assumed to be subject to axial compression and shear only. Uplift should be considered for column bases in braced bays.
Column bases typically consist of a square or rectangular plate welded to the column, with four holding down bolts provided outside the section profile. The first reason is the wide spacing of the bolts increases stability in the temporary condition. The second reason is that it makes plumbing (vertical) the column simpler. The last reason is the wider spacing of bolt location can ensure the holding down bolts have enough concrete to interact with.
The base plate should be a sufficient size, stiffness and strength to transmit the axial compressive force from the column to the foundation through the bedding material, without exceeding the local bearing capacity of the foundation.
Holding down system is intended to meet the following requirements:
Holding down bolts are usually placed in conical sleeves. An anchor plate is generally provided for each bolt, although a common plate. Holding down bolts should be moved as the concrete cures, to allow lateral movement when the steel is located. If not, bolts will be held so rigidly that they cannot be inclined to adjust the alignment of the steel base. Bolt holes through the base plate are made 6mm oversize to allow holding down bolts to be inclined. The best practice is to have all holding down bolts of the same grade because once the concrete has been cast, errors can be expensive to rectify.