Storey Drift

Storey drift is the relative horizontal displacement between the top and bottom of a storey under lateral (seismic or wind) load, usually expressed as the inter-storey drift ratio = drift / storey height. It is the primary serviceability and damage-control check for lateral systems: excessive drift damages partitions, cladding, services and stairs, causes P-delta amplification and pounding with adjacent buildings, and is a key indicator of inadequate lateral stiffness even when member strength is adequate.

IS 1893 Part 1 Cl. 7.11.1 limits the storey drift under the design seismic force (with partial load factor 1.0) to 0.004 times the storey height for the un-factored case, and IS 16700 imposes wind/seismic drift limits for tall buildings. Drift typically controls the sizing of shear walls, moment frames and bracing in mid- and high-rise buildings far more than member strength does. The check must use the appropriate displacement (including the response-reduction-related amplification where applicable) and account for torsional amplification at the building's flexible edge.