The basic principles for the analysis of prestressed concrete sections at the ultimate limit state of flexural strength described in previous pages are also applicable to composite sections. For the section shown in Fig. 10.5(a), it may be assumed initially that, at the ultimate limit state, the neutral axis lies within the slab and the section may then be treated effectively as a rectangular beam. The position of the neutral axis should later be checked to see whether it does, indeed, fall within the slab. For the section shown in Fig. 10.5(b), the position of the neutral axis may be determined on the assumption that the section is rectangular, but the different strengths of the concrete in the slab and beam regions of the compression zone should be taken into account.