As per IS 800:2007, in order to analyze a frame subjected to gravity loads, considering the sway stability of the frame, Notional Horizontal Forces should be applied. In reference to these notional horizontal forces, which of the following statement(s) is / are incorrect? i. These forces are to be combined with horizontal (lateral) loads as well as temperature effects ii. These forces account for practical imperfections and should be taken at each level as being equal to 0.5 percent of factored dead load plus vertical imposed loads applied at that level. iii. These forces should be applied on the whole structure, in both orthogonal directions, in one direction at a time, at roof and all floor levels or their equivalent; all of these acting simultaneously with factored gravity loads
- AOnly (i)Correct
- B(i) and (ii)
- C(ii) and (iii)
- D(i), (ii) and (iii)
Solution
Concept
Notional horizontal loads (IS 800 cl. 4.3.6)
Formula
NHF = 0.5% × (factored DL + IL at that level)
Step-by-step solution
1. NHF = 0.5% of factored dead plus imposed vertical load at each level (ii correct). 2. Applied in one direction at a time, with gravity loads (iii correct). 3. NHF are not combined with lateral loads or temperature effects, so (i) is incorrect.
Explanation
The code states that notional horizontal forces are not to be applied along with wind/earthquake or temperature effects.
Why the other options are wrong
Statements (ii) and (iii) are correct, so options containing them are wrong.
Shortcut
NHF ≠ combined with lateral loads.
Common mistake
Reading the question as 'which is correct'.
Correct answer: A) Only (i)