I am currently modeling a 22 story steel building with braced frames. I keep getting the error "unstable structure detected. Instability found at rigid diaphragm defined at story XX and Diaphragm 1 for UX. Check the elements attached to this diaphragm or check PDelta effects." I checked the fixity of my braced frames and they are correct but I can not figure out the problem with my model. Attached is a picture of my floor plan if anyone has a suggestion.
