Devdas Menon

The application of yield line analysis to carry out strength design of reinforced concrete (RC) slab systems is mostly limited to solid slabs without beams. In an earlier paper on isolated rectangular beam-slab systems, the authors had demonstrated that such analysis, considering plastic hinges in the beams along with yield lines in the slabs, can result in rational and economical designs. In this paper, it is shown that such yield line analysis can be further extended to beam-slab systems with secondary beams, and the predictions have been validated by tests carried out on four rectangular RC beam-slab systems (each comprising four symmetric grid units), supported at the four corners on pillars. Six possible collapse mechanisms have been investigated. It is established that the critical collapse mechanism is governed primarily by the beam-slab relative strength. It is shown how an economical and rational design can be achieved, making use of the proposed yield line analysis.

This paper attempts to take a fresh look at the behaviour of simple reinforced concrete beam–slab systems, subject to gravity loading. The simplest case of a square slab, integrally connected to edge beams and supported on pillars or columns at the four corners, is considered. It is shown that the usual design procedure of separating the slab analysis and design, from that of the edge beams (proportioned to be adequately stiff), is irrational in terms of expected behaviour at collapse. The expected diagonal yield line formation in the slab is kinematically incompatible with the expected plastic hinge formation in the edge beams. This paper attempts to resolve this dispute in design by showing how the mode of failure depends on a relative beam–slab strength parameter. The yield line theory, which considers the alternative possibility of combined beam–slab failure, is validated by experimental results reported in the literature. It is established that the prevailing design practice, assuming diagonal yield line formation in the slab, turns out to be not only irrational but also uneconomical. The combined beam–slab failure mechanism is more likely to occur in practice, and it would be rational and economical to aim for such a design.

This paper revisits the design of simple rectangular reinforced concrete (RC) slabs, integrally connected to edge beams, supported at the four corners, and subject to gravity loads. Typically, the edge beams are made adequately stiff, whereby the slab can be analyzed and designed separately for two-way bending, considering the edges to be simply supported. This paper establishes, through yield line analysis and experimental studies, that the fnal failure is more likely to occur by a combined beam-slab failure-typically by one-way bending along the long-span direction, with plastic hinges forming in the middle of the long-span beams. The conventional yield line pattern (two-way slab-alone failure) will occur only in exceptional cases where the long-span beams are heavily reinforced. It is clearly demonstrated that the actual mode of failure and the collapse load are governed primarily by the relative beamslab strength in all cases, regardless of whether the edge beams are stiff or shallow. The proposed yield theory has also been validated by experiments on square beam-slab systems reported in the literature. These new insights on collapse load estimation of rectangular beam-slab systems can lead to more rational and economic strength design and detailing.