Hello All,
I recently created a model of an existing building with gravity only members. The intent of the model is to simply be able to perform load takedowns from the gravity column module, therefore the analysis is intended to be very rudimentary. To my surprise, after running gravity loads in the column module, I see that one of the columns is failing. After looking through the design report for the column, it appears the demand capacity ratio is well below zero at roughly 65%. The calculated parameters however states the following: "(C2.2) alpha*Pr > Pe1x and therefore results in a "failing" status of the column. C2.2 is within the stability chapter of the AISC specificaiton and considers initial imperfections of members that contribute to the stability of the structure.
I typically of course have a lateral resisting system in my building models :-) and expect to see such calculations within the "frame module" of RAM structural. Within the frame module I would then add notional loads to take into account imperfections/out of plumbness. Seeing as how I am only analyzing gravity columns in the column module, the program shouldn't quite yet know how notional loads will impact the stability of the structure until I run the frame module which considers lateral elements. Even if I do not have lateral members modeled in this rudimentary example, I do not believe that the column module should be able to anticipate the lack of a lateral resisting system. Can someone please explain how initial imperfections are taken into account in the gravity column module of Ram Structural and how the program is able to see the impact that initial imperfections has on a structure without considering the lateral resisting system?
Thank you for your time in advance!
-Daniel