In a two-hinged parabolic arch, (i) if support yields, then horizontal thrust increases (ii) if ribshortening is considered, then horizontal thrust reduces Which is the CORRECT option?
- ABoth (i) and (ii) are true
- B(i) is true but (ii) is false
- C(i) is false but (ii) is trueCorrect
- DBoth (i) and (ii) are false
Solution
Concept
Horizontal thrust in a two-hinged arch
Step-by-step solution
1. Spreading (yielding) of supports reduces the thrust (i is false). 2. Rib shortening reduces the thrust (ii is true).
Explanation
Thrust is the redundant force. Any extra horizontal movement of the springings or axial shortening of the rib relieves it, so it reduces.
Why the other options are wrong
Option B says the opposite for support yield.
Shortcut
Yield and rib shortening both reduce H.
Common mistake
Assuming the thrust increases with yield.
Correct answer: C) (i) is false but (ii) is true