Joints

Column splice joints usually occur at approximately mid-floor level permitting ease of access for connecting the pieces and avoiding clashing with the connections of beams at floor level.  Column lengths are usually made as long as practicable to minimise the number of splices and hence reduce costs.

The typical inner column of a multi-storey, multi-bay frame will have four beams connected to it at each floor level: usually two main beams and two tie beams. It would further complicate matters if there were also a joint in the column at the same point. It is usual, therefore, to:

• Make the column in one piece for the height of the building, where the height does not exceed about three storeys.

• Introduce column splices for taller columns, putting the joint not at mid-height of a storey - the theoretically optimum position, but at least 500-1000mm above the floor beams to afford easy access for the erectors. (The joint should be easily accessible to the erectors standing on the floor beam).

The lowest section of such a column normally carries the most load, and it needs to be stronger than higher sections. To provide for this, different sections with the same serial size are sometimes used, with the largest at the bottom. If this is done, it must be remembered that the serial size is only nominal: the overall dimensions in a serial size group may vary considerably, and shims will be needed to pack out at a splice joint. Countersunk bolts will help to reduce the bump effect of the splice at this point, but they are expensive.