Pick up the assumption for the design of a pre-stressed concrete member from the following: A. A transverse plane section remains a plane after bending B. During deformation limits, Hook’s law is equally applicable to concrete as well as to steel C. Variation of stress in reinforcement due to changes in external loading is negligible D. All the above

The correct answer is D. All the above.

The assumptions for the design of a pre-stressed concrete member are:

• A transverse plane section remains a plane after bending. This is known as the Bernoulli hypothesis. It states that the plane sections of a beam before bending remain plane after bending. This assumption is valid for small deformations.
• During deformation limits, Hook’s law is equally applicable to concrete as well as to steel. Hooke’s law states that stress is proportional to strain within the elastic limit. This assumption is valid for concrete and steel within their elastic limits.
• Variation of stress in reinforcement due to changes in external loading is negligible. This assumption is valid for small deformations.

The assumptions are made to simplify the analysis and design of pre-stressed concrete members. The assumptions are valid for small deformations. However, for large deformations, the assumptions may not be valid.