Columns

Precast rectangular columns are manufactured in a variety of lengths. The concrete surface is smooth and the edges are chamfered. Columns generally require a minimum cross-sectional dimension of 300 x 300 mm, not only for reasons of manipulation but also to accommodate the column-beam connections. The 300 mm dimension provides a two-hour fire resistance, making it suitable for a wide range of buildings. Columns with a maximum length of 20 m to 24 m can be manufactured and erected in one piece, i.e. without splicing, although a common practice is to work also with single-storey columns.

Precast rectangular columns may be provided with single or multiple corbels to support floor or roof beams, girders for overhead cranes, etc. The corbels are either completely under the beam or within the overall depth of it.

Characteristics of rectangular columns

The following figure gives the performance curves of rectangular columns under axial loading combined with bending moments. The calculations are made for modulated cross-sections from 3M x 3M (300 x 300 mm2) to 6M x 6M for rectangular columns. The indicated values for Nd and Md are design values at ultimate limit state, which means that the permanent and variable actions are multiplied by the appropriate safety margins.

Precast columns are fixed to the foundations with pockets, projecting reinforcing bars or holding down bolts. The first solution is mainly used for foundations on good soil; the second and third in the case of foundation piles.

 Column-to-column splices are made either by bolting mechanical connectors anchored in the separate precast components or by the continuity of the reinforcement through a grouted joint.

Round columns

Precast round columns are manufactured in a variety of lengths. The concrete surface is smooth and the edges are chamfered. Columns generally require a minimum cross-sectional dimension of 300 x 300 mm, not only for reasons of manipulation but also to accommodate the column-beam connections. The 300 mm dimension provides a two-hour fire resistance, making it suitable for a wide range of buildings. Columns with a maximum length of 20 m to 24 m can be manufactured and erected in one piece, i.e. without splicing, although a common practice is to work also with single-storey columns.