Why are prestressed concrete members preferred in many structural applications compared to ordinary reinforced concrete members?

Introduction / Context:
Prestressing introduces deliberate precompression to counteract tensile stresses from service loads. This approach enhances serviceability and often reduces structural depth, weight, and cracking compared to conventional reinforced concrete.

Given Data / Assumptions:

• Use of high tensile steel and high-strength concrete.
• Prestress suitably profiled to balance loads and control deflection.
• Focus on service-level performance (crack control and deflection) and shear behavior.

Concept / Approach:
Precompression offsets part or all of the tensile stress envelope that would otherwise crack concrete. With proper web reinforcement and tendon profiling (sag), shear capacity improves via clamping action and inclined tendon components, alleviating the need for oversized sections.

Step-by-Step Solution:
Introduce prestress to maintain compressive stresses across critical zones at service.Utilize tendon profiles to generate counter-moments and beneficial shear components.Detail to minimize losses and maintain long-term compression, controlling shrinkage and temperature cracking.

Verification / Alternative check:
Service stress checks show reduced or eliminated tensile stresses; deflection checks indicate improved stiffness. Shear verifications confirm enhanced capacity due to prestress and transverse reinforcement.

Why Other Options Are Wrong:
Each of options a, b, and c accurately states a recognized advantage. Hence the comprehensive choice “All the above” is correct, while “None of these” is false.

Common Pitfalls:
Overlooking relaxation and other losses, inadequate anchorage/fretting in post-tensioning ducts, and insufficient cover or grouting that compromise durability.

Final Answer:
All the above.