Yield Line Theory — Plastic Analysis of Reinforced Concrete Slabs

Yield Line Theory is a plastic limit-analysis method used in structural civil engineering to determine the ultimate load-carrying capacity of reinforced concrete slabs. Developed by K. W. Johansen in the 1940s, it assumes that at failure the slab subdivides into rigid regions separated by lines of intense plastic rotation — called yield lines — where the reinforcement has fully yielded. The approach gives the collapse load directly and is widely used in slab design and assessment.