The correct answer is: C. Both forces of tension and compression as well as lever arm changes.
In prestressed concrete, high-strength steel cables are used to prestress the concrete. This means that the cables are tensioned before the concrete is poured, and the tension in the cables creates a compressive force in the concrete. This compressive force helps to resist the tensile forces that are created when the concrete is loaded.
The forces of tension and compression in prestressed concrete are not constant. The tension in the cables decreases over time due to relaxation, and the compressive force in the concrete decreases due to creep. The lever arm also changes over time due to creep and shrinkage.
The following is a brief explanation of each option:
- Option A: Forces of tension and compression change but lever arm remains unchanged. This is not correct because the lever arm also changes over time due to creep and shrinkage.
- Option B: Forces of tension and compression remains unchanged but lever arm changes with the moment. This is not correct because the forces of tension and compression are not constant.
- Option C: Both forces of tension and compression as well as lever arm changes. This is the correct answer because the forces of tension and compression are not constant, and the lever arm also changes over time due to creep and shrinkage.
- Option D: Both forces of tension and compression as well as lever arm remains unchanged. This is not correct because the forces of tension and compression are not constant, and the lever arm also changes over time due to creep and shrinkage.