The correct answer is: A. 10%
Over-reinforcement is a condition in which the amount of reinforcement in a beam is greater than the minimum required to resist the applied loads. This can occur when the designer underestimates the loads or overestimates the strength of the concrete. Over-reinforcement can lead to a number of problems, including:
- A decrease in the ductility of the beam, which makes it more likely to fail catastrophically if it is overloaded.
- An increase in the cracking of the beam, which can lead to water infiltration and corrosion of the reinforcement.
- An increase in the cost of the beam, as more reinforcement is required.
The amount of over-reinforcement that is acceptable depends on a number of factors, including the type of beam, the loading conditions, and the desired level of safety. In general, it is recommended that the amount of over-reinforcement be limited to 10%. This will ensure that the beam has adequate ductility and will not be excessively cracked.
Option B is incorrect because it is too high. Option C is incorrect because it is too low. Option D is incorrect because it is not a valid option.