The cross-sections of a precast concrete beam will depend on its location within a structure, its purpose and how it is connected to other members. The simplest will be rectangular, probably with reinforcement links projecting out of the top around which in situ concrete can be cast.
Alternatively, beams may have projections, on one or both sides to support secondary members, such as floor slabs or staircases, or to carry brickwork or cladding. The beams will be provided with recesses at the ends, that fit over corbels or steel sections projecting from the columns.
For interior beam-column connections, continuity and moment transfer is provided by reinforcement laced through the projecting links and passing through the column. An in situ stitch is then cast. For edge and exterior columns connection of the reinforcement has to be via a cast-in socket or some form of welded connection.