Behaviour of beams supporting cantilever inclined slab with or without opening

Abstract

The simple span beams supporting inclined cantilever slabs in one or both sides of the beam are usually used for structures such as porch, entrance gate, passenger shed at bus stoppages or railway terminals. For aesthetic beauty and for effective disposal of rainwater, variable length of opening is provided in the middle part of the slab both in the parallel and perpendicular direction to the span length. The behaviour of beams supporting inclined cantilever slab without opening is similar to the behaviour of folded plates, which consist of a series of thin planar elements connected to one another along their edges. The analysis shows that the bending moment at mid span and shear force at any location of supporting beam decreases rapidly with increasing angle of inclination. When the slab is inclined 45° or more, it is even possible to avoid supporting beam. The behaviour of beam supporting inclined cantilever slab with full or partial opening at center span of the slab shows radically changed than that of beam connecting slab without opening. Inclusion of openings in cantilever slab results in complex distribution of bending moment, shear force, axial force and deflection of the supporting beam rather than a simple one. The presence of any opening in the inclined slab causes disturbance in the flow of internal forces which are the responsible factors to change the shapes and magnitudes of the internal forces. A limited parametric study is carried out for the idealization of columns, beams and their connecting slabs. The columns and supporting beams are idealized as one-dimensional beam element. The slab is idealized both as a plate element and as a one-dimensional beam element. Three-dimensinal analysis is carried out for different inclination of the connecting slab Le. 9=0°, 15°, 30°, 45°, 60° & 75° with the supporting beam without any opening in the slab. For each inclination, the bending moment, shear force, axial force, torsional moment and deflection of the beam are presented graphically in details. The analysis is repeated for various opening sizes in the slab both in parallel and perpendicular direction of the supporting beams. The analysis are done for butterfly shaped structures where slabs are projected in both sides of the beam and also for L-shaped structure where slab is projected in one side only.