The research which is reported upon in this Paper was evidently very carefully carried out and, as with most research, was subject to a limited budget. There are certain matters which would require investigation before I would feel I could adopt the form of construction described.62. Fig. 14 shows friction forces acting downwards on the web of the beam, and, therefore, contributing significantly to the shear strength of the slab. The Paper does not describe the surface condition of the beam webs in the tests, but if they were in a slightly rusty condition the frictional resistance would be greater than if, say, the surface was shot-blasted or painted. In practice it would be necessary to paint the part of the beam below the slab and even if the specification required the upper part not to be painted this would be very difficult to ensure. It would, therefore, appear desirable for further tests to be carried out to investigate the effect of painting or shot-blasting the web.63. The friction forces shown in Fig. 14 could develop only if a horizontal compression existed between the slab and the web. Where slabs of equal spans were continuous over such beams, or cantilevered beyond the beam, such compression forces could normally be ensured. In certain cases of unequal spans, however, and in the case of beams at the end of a slab, the compressions would not arise. In these cases, it might be sufficient to weld reinforcement to the web and lap this with the bottom slab reinforcement, but tests of this would be desirable.64. In practice it is likely to be difficult to compact the concrete of the slab under the flange, and poorly compacted concrete in this zone would be a serious source of weakness. Compaction would be easier if a series of holes were drilled through the flange on each side of the web, t o allow the escape of air, but even this might not guarantee compaction and it would, of course, cause a larger beam section to be required to provide the necessary flange area.65. I would be glad to hear from the Authors that further research on these matters was envisaged and I hope that it will enable practising engineers to adopt this form of construction with confidence.One aspect of this subject requiring some investigation is the effect of concrete shrinkage on the strength and deformations of the slabs at beam-slab junctions.67. In a rectangular framed floor system each slab panel would be enclosed by four beams. Concrete shrinkage in such a panel would result in a tendency for the slab to shear along the supporting beams, and move away from the supporting beams (i.e. develop tensile stresses between the slab and surrounding beam webs, with possible loss of the vertical friction force on the web).68. It is noted that the type of specimen used in the investigation was short in length along the beam (305 mm) thus minimizing the effects of shrinkage along the beam, and a cantilever on each side of the supporting beam virtually eliminated effects of shrinkage transversely to the beam.69. Another related problem in ...
