As per IS 1893-2002 Part-I, the approximate fundamental natural period of vibration for Moment-resisting frame building without brick infill panels for RC frame building is taken as (with h and d as height and base width of building in m)
- ATa = 0.075h0.75Correct
- BTa = 0.075h0.95
- CTa = 0.085h0.70
- DNone of the above
Solution
Concept
Fundamental period of RC frame building
Formula
Ta = 0.075 × h0.75
Step-by-step solution
1. IS 1893-2002 Part-I gives empirical formulas to calculate the fundamental natural period Ta of buildings. 2. For a moment-resisting RC frame building without infill panels, the formula is Ta = 0.075 h0.75. 3. In this expression, h represents the total height of the building in meters. Answer: A
Explanation
According to IS 1893-2002 Part-I, the empirical formula for estimating the fundamental natural period of a bare RC moment-resisting frame building without infill walls is Ta = 0.075h0.75, where h is the building height in meters. For steel frame buildings, the constant coefficient changes to 0.085. This parameter helps determine design lateral seismic forces acting on the structure.
Why the other options are wrong
B) The formula exponent specified in IS 1893 is 0.75, not 0.95. C) The expression 0.085h0.75 applies to steel frame buildings, not RC frames. D) Option A is correct according to IS 1893-2002 Part-I.
Shortcut
Natural period Ta for RC frame without infill = 0.075h0.75.
Common mistake
Confusing the formula constants for RC frame buildings with steel frames or buildings with infill walls.
Correct answer: A) Ta = 0.075h^0.75