ABSTRACT
This chapter discusses the behaviour and design of torsion members. It looks at uniform torsion, non-uniform torsion and the design of torsion members for strength and serviceability. The resistance of a structural member to torsional loading may be considered to be the sum of two components. When the first component of the resistance to torsional loading completely dominates the second, the member is in a state of uniform torsion. In elastic uniform torsion, the twist rotation per unit length is constant along the length of the member. The uniform torsional behaviour of thin-walled closed section members is quite different from that of open section members, and there are dramatic increases in torsional stiffness and strength. In thin-walled open section members, longitudinal warping deflections w due to twist are much greater than those due to shear straining. The effects of distortion of cross-section are only significant in very thin-walled open sections, and in thin-walled closed sections with high distortional loadings.
