In this project the behaviour of reinforced concrete beams loaded in combined torsion, bending and transverse shear has been examined Over one hundred beams were tested under known distribution of moment, shear and torsion to study their failure characteristics with particular reference to possible failure modes and the effect of reinforcement. It was found that for beams containing only longitudinal reinforcement, the effects of flexure tend to cancel each other and hence if a conservative value of the pure torsional strength is chosen torsion-flexure interaction can be ignored.

For beams containing both longitudinal and transverse reinforcement, two different types of torsion-flexure interaction were fo nd to be possible. For beams containing equal areas of top and bottom longitudinal steel the presence of flexure reduced the torsional capacity. On the other hand, for beams in which the area of tension steel exceeds that of the compression steel, the torsional capacity was considerably increased by the presence of moderate bending moments.

For beams containing only longitudinal reinforcement it was found to be satisfactory to assume linear interaction between the ultimate strengths in transverse shear and torsion. For beams containing both longitudinal and web steel the shear-torsion interaction behaviour was found to depend upon the section properties of the member.

Expressions for the failure loads of rectangular reinforced concrete beams loaded in combined bending, torsion and shear have been derived. These expressions were obtained in the main from a study of the equilibrium situation of the observed modes of failure. Good agreement between the predictions of these expressions and the experimental results was found, not only for beams of this investigation, but also for a large number of beams reported in the literature.

Simple, and fairly direct, ultimate strength design procedures were developed from the analysis equations. These procedures are presented in this thesis.