A. To check for inter-story drift

To instruct the program to check the drift between adjacent stories against a code-defined ratio, use the following procedure.

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.

Select the Post Analysis Commands tool in the Analysis Data group on the Analysis and Design ribbon tab.

The Analysis/Print Commands dialog for post-analysis commands opens.
Tip: If the dialog does not immediately open, click Define Commands on the Post Analysis Print - Whole Structure dialog.
Select the Story Drift tab in the Analysis/Print Commands dialog.
Enter an Allowable Drift Factor value. This is the drift ratio value as specified by the applicable building code.
Check the After Current option to insert the print command following the currently selected command within the Post Analysis Print - Whole Structure dialog. Otherwise, the print command will be added to the end of the STAAD input file.
Click Add. The command is added to the STAAD Input file.
Click Close.