Sizing of the Design: Continuous Beam Strips.

The sizing of the rectangular beam is similar to the sizing of the upstand beam of the inverted T, i.e. based mainly upon bending moments and shear forces. However, the beam width must in this case satisfy that required for allowable bearing pressure criteria for the full contact area of the beam.

For inverted T beams the bearing stresses are reduced to an acceptable amount by the use of the ground strip forming the flange of the inverted T.

The main rib of the T beam is then determined from the design requirements for longitudinal bending and shear forces keeping a reasonably standard profile for shutter reuse to make the beam economic. The flange thickness and reinforcement is determined from the bending moments and shear forces acting on the cantilever slab/flange (see Fig. 11.35).

Casting of the beam is usually carried out in two lifts, the ground slab being cast up to the top of the flange leaving a roughened surface with the cage reinforcement projecting.

The main beam is then cast on the cleaned surface of the slab up to its top level (see Fig. 11.36).

Fig. 11.35 Inverted Tee beam – typical loads, moments and reinforcement.

Fig. 11.36 Typical casting stages for inverted
Tee beam.