A method, of design for shell concrete roofs using prestressed edge beams

Summary: In a beam provided with prestressing cables which follow a continuous curve between supports, the prestressing force resolves itself into two components: firstly, a horizontal compressive force, which remains very nearly constant throughout the span and secondly, a vertical distributed load, acting upwards and balanced by two downward reactions at the anchorages over the supports. By selecting a suitable curve for the cables, this vertical distributed load can be made uniform throughout the span: it can also be made to equal in value the uniformly distributed permanant loads acting on the beam, thereby cancelling all deflections caused by such loads. Prestressing forces are usually designed to counteract tensile stresses, the effect of such forces on the deflection being purely incidental. In the case however of thin concrete shells, the vertical prestressing forces provide an effective means of cancelling the edge disturbances caused by deflections in edge beams, thereby enabling the thin shells...