The global behaviour of reinforced concrete beams subjected to pure torsion is studied in this thesis. This study includes beams that have a rectangular cross section (plain or hollow), and made with normal and high strength concrete. Longitudinal and/or transversal prestress is also considered. The theoretical study is based on the space truss analogy with variable angle by considering nonlinear behavior of the materials. This model was initially applied in its original formulation to study the ultimate behavior of the beams. Afterwards, this model was modified in order to predict the overall behavior of the beams under torsion, from the beginning of loading up to failure.
Various constitutive laws proposed by several authors and found in the bibliography were tested in order to characterize the behavior of concrete in compression on the struts as well as the behavior of the reinforcement in tension (for both normal and prestress reinforcements). The softening and the stiffening effects were included in the analyses.
To support the study carried out throughout this work, two computer applications were developed by using the programming language DELPHI. The first application (TORQUE_MTEAV) was developed for the first phase of the work and was used to study the ultimate behavior of the beams under torsion. This application was based on the space truss model with variable angle by applying its original formulation with the consideration of various constitutive laws for the materials. The second application (TORQUE_MTEAVmod) was developed for the second phase of the work and was used to study the global behavior of the beams under torsion. This application was based on a modified space truss model with variable angle.
In order to evaluate the adequacy of the theoretical models and of the implemented modifications, the theoretical predictions were compared with experimental results from various studies found in the bibliography. After this analysis, the best theoretical predictions were also compared with the predictions from some codes of practice in order to evaluate the degree of optimization of the theoretical models when used for project. A simple computer application (TORQUE_DESIGN) was also developed for this purpose.