Experiments on the strength of reinforced and prestressed concrete beams and of concrete-encased steel joists in combined bending and torsion†

Summary A series of reinforced and prestressed concrete beams and concrete-encased steel joists was tested in combined bending and torsion, with ratios of bending moment to twisting moment varying from pure bending to pure torsion. In all, 33 full-size beams were tested. Measurements of defiexions and strains due to bending and to torsion were made at selected points. The agreement between theory and experiment was generally good. The torsional strength of concrete can be augmented by suitable shear reinforcement. The resistance of the reinforced concrete beams to torsion, however, still depends on the tensile strength of the concrete; it is not therefore possible to gain an increase in strength comparable with that resulting from the addition of tension reinforcement to a plain concrete beam subject to bending. On the other hand the insertion of even a small quamity of shear reinforcement turns the abrupt torsion failure of plain concrete into a gradualfailure accompanied by considerable cracking and def...