Eight reinforced concrete beams with two different concrete strengths and four different schemes of reinforcing were tested to failure in pure torsion. SR⁻⁴ strain gages were used to measure the concrete strains at the surface of the test beams.

A review of analytical and experimental studies in the literature is presented and briefly discussed. The test results were then compared with the theoretical predictions developed by Cowan, Ernst and Gesund.

In general the failure surface of the test beams agreed with those previously predicted. The test ultimate torque varied considerably from the predicted ultimate torque of Cowan and Gesund. Ernst’s basic equation was modified to compensate for less than the minimum longitudinal reinforcement in four of the beams. With this modification Ernst’s theoretical predictions were very close to the test results.

A study of the test results also shows that one of the presented theories is valid for one particular case, but that none of the theories is valid for every case. Consequently, there is a need for further research in this subject in order to develop a more exact theory for use in design.