The correct answer is B. 8d.
The anchorage value of a hook is the minimum length of the hook required to develop the full strength of the reinforcement bar. The anchorage value is typically specified in terms of the diameter of the reinforcement bar, d.
For a standard hook, the anchorage value is 8d. This means that the hook must be at least 8 times the diameter of the reinforcement bar in length.
The anchorage value of a hook is important to ensure that the reinforcement bar is able to resist the forces acting on it. If the hook is not long enough, the reinforcement bar may not be able to develop its full strength and may fail.
There are a number of factors that can affect the anchorage value of a hook, including the type of reinforcement bar, the type of concrete, and the method of anchorage. It is important to consult the relevant codes and standards when designing anchorages for reinforcement bars.
Here are some additional details about each option:
- Option A: 4d. This is the minimum anchorage length for a standard hook. However, it is not always sufficient to develop the full strength of the reinforcement bar.
- Option B: 8d. This is the most common anchorage length for a standard hook. It is sufficient to develop the full strength of most reinforcement bars.
- Option C: 12d. This is a longer anchorage length that may be required for some reinforcement bars.
- Option D: 16d. This is an even longer anchorage length that may be required for some reinforcement bars.