Composite Columns - Form of Construction.

Composite columns comprise steel sections with a concrete encasement or core.

Encased columns usually consist of standard I-beam or H-column sections with a rectangular or square concrete section encasement to form a solid composite section. Additional reinforcement is placed in the concrete cover around the steel section in order to prevent spalling under axial stress and in fire.

Concrete-filled columns consist of circular, square or rectangular hollow sections filled with concrete.

Additional reinforcement is not normally required, except in columns of large section. Examples of these different types of composite columns are shown in Fig. 22.1.

The steel structure is normally constructed in advance of the formation of the composite section.The minimum size of the steel element is therefore controlled by the construction condition. For practical reasons it is normally necessary to fill the tubular sections shortly after their erection but I-sections can be encased much later.

However, there are practical problems in concreting around a column with the floors in place. Alternatively, columns can be pre-encased in the factory and in situ concrete used to fill the zone around the beam–column connections.

Fig. 22.1 Examples of composite columns: (a) RHS and CHS concrete-filled section, (b) concrete-encased section
Fig. 22.1 Examples of composite columns: (a) RHS and CHS concrete-filled section, (b)
concrete-encased section

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