Sir, I'm a new user of stadd and I'm in learning process. Today I do a seismic analysis of a G+3 building . But I have some confusion at the output results as the area of steel at TOP FIBER is much more than the area of steel at BOTTOM FIBER (at mid section of a beam). So my confusion is Is it possible or my process of analyzing is wrong?? Thats all.
As you know the moments due to seismic will be minimal or zero close to the midspan. So midspan moments would usually come from gravity loads and so one would expect the bottom moments to be higher at midspan.
Here are a couple of things you may want to check
The top and bottom face are defined by the local Y axis of the beam member. The face in the direction of the positive local Y axis is considered as the top face and the other one is considered as the bottom face. In case your beam is oriented such that the local Y is pointing downwards, then the face which is actually the bottom face in your actual structure, will be considered as the top face by STAAD.Pro. So check for the beam local axis orientation.
Check if by mistake any of the gravity loads have been applied upwards as opposed to downward direction. Also watch out for the load combination factors for the gravity loads that you may have used in your load combinations or repeat loads. A negative factor would cause the loads to act upwards.
If these do not address your problem, upload your .std file and mention the details like which member you are looking at, which load case etc. and we will take a look.
Answer Verified By: Zhano
Seismic Analysis1.std
Sir, I upload one of my pre analysed buidings. Please check BEAM NO - 2, 5 etc. & Most importantly how can I check or change the beam local axis orientation?? I have no idea about it!!