AD.2007-09.2.4 Check Story Drift
The PRINT STORY DRIFT command can now be used to check the story drift against a code-specified maximum drift ratio.
Story drift is calculated as the relative horizontal displacement of two adjacent floors in a building. Inter-story drift can also be expressed as some factor times the story height. The allowable factor generally varies from one country code to another and may also vary depending on the type of loading. For example, in IS 1893: 2002 for seismic loading the allowable limit for inter-story drift is 0.004 times the story height whereas in IS 875 for wind loading it is 0.002 times the story height.
The drift at a particular story level in either lateral direction is calculated as the average of all the joint displacements present in that floor level. However if floor diaphragm is present, the drift is calculated at the center of mass (i.e,. master joint) of the floor.