The elastic-plastic stress field method for structural concrete design: a complementary perspective to the use of rigid-plastic design approaches

Limit analysis is a widely-used approach providing a comprehensive and consistent frame for design of structural concrete elements. This approach has traditionally been applied by engineers following a rigid-plastic formulation, which allows to perform hand-made analyses. Yet, the rigid-plastic approach shows a number of shortcomings, namely to consistently account for the strain and cracking state of the element in the response of the member. Within this frame, the Elastic-Plastic Stress Field (EPSF) method has been proposed as an alternative and complementary tool to rigid-plastic approaches. The EPSF shares the same background and provides stress fields consistent to those of rigid-plastic analyses. In addition, since they account for the material compatibility, the EPSF provide information on the displacement and strain field at failure and can be generated in an automated manner. The information of the strain field can further be used to account for several issues related to the compression softening behaviour due to transverse cracking or to determining the strains in the reinforcement and concrete at failure. In this paper, the fundamentals of the EPSF method are briefly introduced and discussed in relationship with rigid-plastic design approaches by means of a number of examples. On that basis, some design recommendations for application of these tools are stated.