Hook length for a straight bar in terms of the diameter of bar, d is:
- Ad
- B4.5d
- C9dCorrect
- D18d
Solution
Concept
In a bar bending schedule, each standard semicircular hook adds about 9d to the bar length.
Formula
Length of bar = clear length + 2 × 9d (for two hooks)
Step-by-step solution
1. A standard semicircular (U-type) hook is used at the end of a straight bar. 2. In estimation and bar bending schedules, the extra length taken for one such hook is 9d. 3. So hook length = 9d. Answer is (C).
Explanation
When a straight bar has hooks at its ends, extra steel is needed to form each hook. For a standard hook, this extra length is taken as 9d. For a bar with two hooks, add 18d in total.
Why the other options are wrong
A: d is far too small for a hook. B: 4.5d is about half of a hook. Do not confuse it with the 0.45d bend allowance. D: 18d is the total for two hooks, not one hook.
Shortcut
One hook = 9d. Two hooks = 18d.
Common mistake
Choosing 18d, which is the allowance for both ends together.
Correct answer: C) 9d