STORY DRIFT DEFINITION IN ETABS 1

[IvG]

Hello, I would like to have some information about the exact way ETABS calculates the sory drifts. For example if a point is selected in deformed shape of reponse spectrum load case, ETABS displaces both displacements and drifts. What I can't understand is why the difference between the displacements in two adjacents floors divided by the floor height, is not equal to the value of the story drift calculated by ETABS.

 

[KenyaCragrat]

Hi IvG,

This may be due to the fact that ETABS reports absolute and total horizontal displacements at each floor (and deducts one from the floor above to report inter-storey drift), including the displacemnet caused by rotational deformation (this is only an issue in tall slender structures). In my opinion the lower values (excluding effects of whole-body rotation) are the correct inter-story drifts, as these are relevant to servicibility issues.