Total Interaction Method for Torsion Design

The validity of Behera's total interaction theory for design of reinforced concrete beams (and a simplification thereof) is demonstrated by comparison with more than 200 test beams from various investigations. Numerical design examples and added test data show that a given combination of shear-torque-moment in a given beam size can be satisfied by quite different ratios of the longitudinal steel added for torsion to the total stirrup steel used. Although extra longitudinal steel is not significant factor in resisting pure torsion, it is a major (and possibly a decisive) factor under the combined loading. The optional designs offer possible economies over the ACI 318-71 Code method. Tests by Ma of six beams having unsymmetrical top and bottom longitudinal steel are also reported. The preliminary indication is that any strength loss with unsymmetrical longitudinal steel is largely overcome by extending bars a distance beyond the points of inflection.