Limit Design of Reinforced Concrete Frames

A limit design method is presented in which load factors against all possible modes of structural collapse and against yield of all critical sections are prescribed. The design plastic moments are some fractions of the elastic envelope moments under the specified ultimate load. The design problem consists of solving a system of linear equations or inequalities expressing the limit equilibrium conditions in terms of the scale factors of the elastic envelope moments. The principles of the simple plastic theory can be used for finding feasible limit design solutions. Optimal solutions can be obtained in relation to given criteria such as minimum moment area or maximum economy versus elastic design by using the techniques of mathematical programming. Two examples illustrate the application of the method to simple building frames.