Concrete @ your Fingertips

In situ Beams

Many structures (e.g. buildings, bridges) require the construction of beams in situ. Generally these will be supported by walls or columns though sometimes they will be ground supported. Construction of a beam will require formwork (see also ‘Formwork’) for its sides and soffit. The latter will have to be supported temporarily (see also ‘Falsework’) until the completed beam has gained sufficient strength.

Once soffit formwork has been erected, the necessary reinforcing steel is fixed, making the necessary connection to the reinforcement in the supporting columns or other elements. The side formwork is then fixed. Spacers (see also ‘Reinforcement Accessories’) are required to make sure that there is adequate cover to the reinforcement.

The concrete is then cast and the top surface of the beam finished off to the required level. After finishing, the top surface must be covered to prevent moisture loss. Generally the side formwork may be removed the day after the concrete is cast, taking care not to damage the surface of the concrete, corners etc. All exposed surfaces must be covered with polythene or wet hessian to prevent moisture loss for about 5 days, so that the concrete is fully cured.

As indicated above, the soffit supports and the soffit formwork should not be removed until the beam had reached sufficient strength for it to carry its own weight and any additional imposed loads.

Acknowledgement: The Concrete Society