The American Concrete Institute (ACI) has released a paper called Collapse Load Estimation of Rectangular Reinforced Concrete Beam-Slab Systems.
The paper, written by Bijily Balakrishnan and Devdas Menon, 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. Edge beams are generally made adequately stiff, whereby the slab can be analysed and designed for two-way bending, considering the edges to be simply support.
This study utilised yield line analysis and experimental studies. It found the final 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.
ACI says: the conventional yield line pattern (two-way slab-alone failure) will only happen 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 beam slab strength in all cases, regardless of whether the edge beams are stiff or shallow,” ACI adds.
According to ACI, the proposed yield theory has also been validated by experiments on square beam-slab systems reported in the literature. These insights can lead to more rational and economic strength design and detailing.
