Hi
I have a strucrure that has modeled in staad pro and there are some double channels(front to front) for vertical bracing sections. When i want to design structure using AISC-360(ASD) there are some warning that tell me design of section for these members is not supported but when i use double channel(back to back) there is no problem. please someone tell me what's wrong with double channel(front to front) and is there anyway for designing this kind of sections using staad pro?