RE: Story stiffness calculation in staad?

Suvadeep Acharjee — Mon, 07 Jun 2021 12:17:37 GMT

There was an approximate methodology available in STAAD.Pro. The program used to compute story stiffness of a story by summing up the lateral stiffness of columns. The stiffness of a column was calculated as 12EI / L³ however this method is approximate one as it fails to capture actual story stiffness including the effect of bracings. Story stiffness should be computed using a displacement based approach. The story stiffness is calculated as the inverse of inter-story drift when a unit load is applied at the particular story. So in your case variation of story stiffness might be entirely justified. One may refer the following section for example calculation:

Home > What's New? > STAAD.Pro CONNECT Edition > CONNECT Edition Update 3 > RR 21.03.00-2 Features Affecting the Analysis and Design Engine > RR 21.03.00-3.5 Soft Story Checks per IS 1893

RE: Story stiffness calculation in staad?

Anirudh — Sat, 05 Jun 2021 04:36:33 GMT

There are no lateral resisting elements in my structures other than columns no shear walls retaining walls etc. It is purely R.c.c beam column structure

RE: Story stiffness calculation in staad?

Sye — Fri, 04 Jun 2021 23:02:01 GMT

There may be other lateral force resisting elements in your structure besides the columns that may be causing this variation.