The main purpose of providing a sill band is to
- ASupport window frame
- BReduce wall height
- CControl cracking from window corners during shakingCorrect
- DCarry roof load
Solution
Concept
Crack control at window corners via sill bands
Formula
IS 4326 Clause 8.4 - Sill Band Detailing
Step-by-step solution
1. Window openings create geometric discontinuities that concentrate seismic shear stresses at their four corners. 2. During cyclic earthquake shaking, diagonal tensile shear cracks propagate outwards from the corners of window sills. 3. Continuous reinforced concrete sill bands tie the piers and masonry below openings, arresting crack propagation. 4. Therefore, the main purpose of a sill band is to control cracking from window corners during shaking. Answer: C
Explanation
In masonry buildings subjected to earthquake ground shaking, large stress concentrations develop around window openings. A reinforced concrete sill band is provided immediately below window sills to arrest and control diagonal cracking from opening corners.
Why the other options are wrong
A) The window frame is supported by the opening sill, which does not require a continuous RC band. B) Bands do not reduce wall height. D) Roof loads are supported by roof bands and lintel bands, not sill bands.
Shortcut
Sill band = Below windows to stop corner diagonal cracking during seismic shaking.
Common mistake
Believing the sill band is merely a support shelf for the window frame.
Correct answer: C) Control cracking from window corners during shaking