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,. control joint) of the floor.

Note: Additionally, the story stiffnesses used in calculating story drift or checking soft stories can be added to STAAD.Pro output by including the command PRINT STORY STIFFNESS in the post analysis print commands section.

Refer to TR.42 Print Specifications for additional information.

Note: For dynamic IS 1893: 2002 response spectrum, the story drift check is performed by adding a command line within the load case, rather than in the post-analysis print commands. Refer to TR.32.10.1.7 Response Spectrum Specification per IS: 1893 (Part 1)-2002 for additional information.