Columns
|
Betemi columns |
Pocket foundations |
Columns
Precast columns are manufactured in a variety of sizes, shapes and 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.
Сharacteristic of the rectangular columns:
|
Profile
|
h, mm
|
b, mm
|
Weight, kH/m
|
|
300/300
|
300
|
300
|
2,20
|
|
300/400
|
300
|
400
|
2,94
|
|
400/400
|
400
|
400
|
3,92
|
|
400/500
|
400
|
500
|
4,90
|
|
500/500
|
500
|
500
|
6,12
|
|
500/600
|
500
|
600
|
7,35
|
|
600/600
|
600
|
600
|
8,82
|
Сharacteristic of the round columns:
|
Profile round columns
|
Diameter, mm
|
Weight, kN/m
|
|
300
|
300
|
1.73
|
|
400
|
400
|
3.08
|
|
500
|
500
|
4.81
|
|
600
|
600
|
6.92
|
Corbels
Precast 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. This may occur, for example, where it is unacceptable for the connection to
project below ceilings or into service zones. Standard dimensions for normal corbels are given in the table. The indicated values for the allowable support load "N" are characteristic values without partial safety margins.
Hidden corbels
The BSF system consists of a hidden steel insert in the beam-to-column connection, enabling a beam support without underlying corbel. A sliding plate fits into a rectangular slot in the beam. A notch at the end of the plate fits over a lip at the bottom of a steel box cast into the column. The system can be used for both rectangular and round columns. The types of corbels and corresponding bearing capacities are given in the table.
Performance curves
The following figures give the performance curves of columns under axial loading combined with bending moments. The calculations are made for modulated cross-sections, from 3Mx3M (300x300mm2) to 6Mx6M for rectangular columns and 3M to 6M for round 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.
|
Plate type,
height/thickness
|
Allowable load, кH
|
Minimum beam dimension, mm
|
| |
|
height
|
width
|
| 150/20 |
200 |
200 |
400 |
| 200/20 |
300 |
200 |
500 |
| 200/30 |
450 |
300 |
500 |
| 200/40 |
600 |
400 |
600 |
| 200/50 |
700 |
400 |
700 |
| 250/50 |
950 |
400 |
900 |
Connections
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
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.
