Analysis and design of disturbed regions with strut-tie models

An interactive computer graphics program implementing the Strut-Tie model approach for analysis and design of reinforced and prestressed concrete members is presented. The program consists of three parts. The first and second parts are considered as a pre- and post-processor for a finite element code to analyze plane stress and plane strain problems as well as plane truss problems. The results of the first part (direction of compressive principal stresses) provide guidance in the development of strut-tie models. In the second part of the program a strut-tie model is developed and analyzed to determine the forces in the individual components of the model. The third part is a design routine for dimensioning and detailing of the proposed strut-tie model components (struts, nodes and ties). The use of computer graphics is shown to be an efficient way to develop and detail strut-tie models for the design of reinforced and prestressed concrete structures. Since it is unlikely that the full compressive strength of the concrete will be mobilized simultaneously over the entire section, a simplified and conservative approach is recommended, for design purposes, to dimension the struts and nodes for different values of concrete compressive strength. Different allowable limit values are determined by analyzing well documented full scale tests of reinforced concrete members with the strut-tie approach and non-linear finite element analysis. The behavior of eleven reinforced and prestressed concrete beams with shear span to depth ratio ranges between 1.06 and 2.65 is investigated. The application of the recommended design values of the effective concrete compressive strength is presented through three design examples. These examples include a rectangular dapped-end beam, a column corbel and a shear wall with opening. The strut-tie approach is found instrumental in understanding the function of both concrete and steel reinforcement in reinforced and prestressed members