Test: Torsion - Civil Engineering (CE) MCQ

In the case of structural concrete members subjected to torsion, shear stresses develop depending upon the type of cross section and magnitude of torque, the shear stresses in association with the flexural stresses may give rise to principal tensile stresses, the value of which when it exceeds tensile strength of the concrete results in the development of cracks on the surface of the member.

The distribution of torsion shear stress is uniform in circular sections where the magnitude of the shear stress is proportional to the distance from the center and in case of non circular sections involving warping of the cross section, approximate formula have been proposed based on elastic analysis.

An analysis of principal stresses in prestressed concrete members should include the combined effect of shear stresses due to transverse loads and torsion, together with direct stresses due to flexure and prestress and the maximum stress of circular section is given as:
16T/πD³, D = diameter, T = torsion.

The failure of a prestressed concrete member without additional un tensioned reinforcement, under pure torsion, is more or less similar to that of plain concrete where sudden failure is imminent almost simultaneously with the formation of first crack.

The research by Humphery and Zia has shown that by suitably adjusting the value of the prestressing force the torsional resistance can be increased by as much as 2.5 times that for the corresponding plain concrete member and for members subjected to pure torsion; concentric prestress is more advantageous than eccentric prestress.

The use of longitudinal steel or spirals independent of each other does not increase the ultimate torsional resistance but when both longitudinal steel and spirals are provided in prestressed members, the ultimate torsional resistance is enhanced and according can be expressed as T_tp + T_ts, where T_tp is the torsional resistance moment of the prestressed concrete section and T_ts is the additional torsional resistance moment of the non-prestressed reinforcement, which must consist of spirals and longitudinal steel.

The behavior of a prestressed concrete member is affected by the relative magnitude of the internal actions, such as torque, bending moment and shear force, in circular sections and if torsion is small, it has little effect on the overall behavior and the failure are controlled by either flexure or shear.

Members subjected to torque, bending and shear are generally reinforced with longitudinal and transverse reinforcements in order to study the contribution of the longitudinal and transverse reinforcement in resisting flexure, torsion and shear forces, it becomes necessary to analyze the system of forces acting on the warped cross sections of the structural element at the limit state of failure.

The skew bending theory is based on the plane deformation approach to plane sections subjected to bending and torsion, the skew bending theory was initially proposed by Lessing with subsequent contributions from Collins, Hsu, Zia, GEsund, Mattock and Elfgreen, of the several researches in this field, Hsu has made the most significant contribution based on the experimental investigations, his work forms the basis of the American, Australian(AS 1481) and Indian code (IS: 1343) provisions.

The space truss analogy theory, which is a modification of the planar truss analogy for shear and according to this theory the space truss, which is composed of longitudinal bars and diagonal concrete struts is subjected to twist in which the stirrups and longitudinal bars are considered the tension members and the diagonal concrete struts at an angle θ between the cracks and considered the compression members θ is idealized to 45 degrees.