Yield-Line Analysis - Is the 10% Rule Safe?

A short technical note has been prepared presenting results for the limit analysis of an 'L'-Shaped reinforced concrete slab. This slab has been analysed previously by yield line analysis and the predicted collapse load, which was published in a respected journal, has been found to be some 40% on the unsafe side of truth. This brings into question the validity of The Concrete Center's so-called 10% Rule. The results from various automated yield line methods are presented along with a lower-bound approach and the theoretically exact answer is provided to an accuracy of 1%.