Question

When the building does not have closely-spaced modes of vibration, then _______ method has good accuracy in estimating the peak response quantities like member forces, storey forces, storey shears and base reactions.
1. Complete Quadratic Combination
2. Square Root of Sum of Squares
3. Absolute Sum
4. Double Sum Combination

Answer 1

Correct Answer - Option 2 : Square Root of Sum of Squares

Concept: -

1) As per IS 1893 (Part 1): 2016, cl. 3.1, closely spaced modes of a structure are those natural modes whose natural frequencies differ from each other by less than 10%.

2) As per IS 1893 (Part 1): 2016, cl. 7.7.5.3, If building does not have closely-spaced modes, then net peak response quantity can be calculated by Square Root of Sum of Squares method.

\(\lambda = \sqrt {\mathop \sum \limits_{k = 1}^{{N_m}} {{\left( {{\lambda _k}} \right)}^2}} \)

Here,

λ_k = peak response quantity in mode k,

N_m = Number of modes considered.