Losses in prestressing after transfer: Which list correctly identifies common sources of prestress loss in practice (excluding friction/anchorage for simplicity)?

Introduction / Context:
Prestress in concrete reduces over time due to short-term and long-term mechanisms. Understanding these losses is crucial to ensure that the effective prestress at service remains adequate to control cracking and deflection.

Given Data / Assumptions:

• Losses considered after transfer to the concrete.
• Friction and anchorage slip are omitted here by the question.
• Material properties correspond to typical prestressed concrete practice.

Concept / Approach:
The main loss components are: (1) elastic shortening of concrete at transfer (especially significant in pretensioned members), (2) creep of concrete under sustained compression, (3) shrinkage of concrete as moisture is lost, and (4) relaxation of prestressing steel (reduction of steel stress under constant strain). Together, they can be a substantial percentage of the initial prestress.

Step-by-Step Solution:
Quantify immediate elastic loss using concrete elastic modulus and transformed-section relations.Estimate creep loss based on sustained stress and creep coefficients over time.Estimate shrinkage loss using shrinkage strain models and steel modulus.Account for steel relaxation per manufacturer or code curves (low-relaxation strands reduce this loss).

Verification / Alternative check:
Comparing code-based estimates (short-term plus long-term) against long-term monitoring validates that these four factors dominate loss predictions in practice.

Why Other Options Are Wrong:

• Options b and c: single-mechanism lists are incomplete.
• Option d: creep of steel is not a recognized dominant mechanism; relaxation is the appropriate steel-related loss.
• Option e: incorrect because real losses exist and must be considered.

Common Pitfalls:
Double-counting elastic losses in post-tensioned members, ignoring environmental humidity on shrinkage, and assuming zero relaxation for all steel types.

Final Answer:
Shrinkage of concrete, elastic shortening of concrete, creep of concrete, relaxation of prestressing steel.