Closely correlating lower and upper bound plastic analysis of real slabs

Engineers assessing existing reinforced concrete slabs sometimes use plastic analysis to prove that the slabs are stronger than suggested by simple elastic methods. This approach allows engineers to avoid unnecessary strengthening and replacement work. The ‘yield line’ form of plastic analysis is particularly appealing because its results can be easily understood and checked. However, careless application of the method to complicated real slabs can produce ‘unsafe’ results. Many recent ‘safe’ alternatives are harder to interpret and check. This paper presents a new technique which eliminates the previous disadvantages of yield line analysis to ensure a safe and accurate result, but which remains easy to understand and check. When applied to real structures, the method allows engineers to apply powerful plastic theory whilst remaining confident in their results.