Comparison of Stress Field and Strut-and-Tie Analyses

Strut-and-Tie and Stress Field Methods can be used for the design of discontinuity regions of reinforced concrete members such as deep beams, diaphragms, walls, brackets, areas around opening, anchorage zones, etc. Strut-and-Tie Method is widely used in today’s practice for hand calculations or it is frequently implemented in single-purpose programs or Excel design sheets. It is simple to use with clear link-up with contemporary national standards, but it is limited to the verification of Ultimate Limit State. Above that, the author’s experience is that even professionals have inadequate knowledge of the main principles for the creation of the models in cases of atypical details. Simplified assumptions of Stress Field Method are similar to the ones used in hand calculations, but the method is improved to allow ductility and Serviceability Limit State verifications. Stress Field Method can be seen as a generalized Strut-and-Tie Method, in which 2D members with stresses instead of force resultants are considered. The method is based on clear material properties and strength criteria corresponding with the ones used in national codes and regulations. Despite the obvious benefits, the method is not as widely used in common practice as Strut-and-Tie Method. To demonstrate the potential of Stress Field Method, the assessment of well-known example of deep beam with a large opening was performed using both methods in Eurocode context. The results of both analyses were compared. The influence of (i) detailing and (ii) model parameters was investigated with respect to ultimate load and mode of failure. The study has shown (i) wider possibilities to proof structural safety and reliability than the Strut-and-Tie Method would allow, and (ii) an excellent agreement of the results in the checks viable by both methods.