I am modeling a steel moment frame. The columns in the moment frames are offset vertically from the roof level to the second floor level due to architectural constraints. This cannot be changed.
I have attached the framing plans in addition to the staad file of the model.
The loading for my roof is the following: Dead Load: 25 psf , Parapet Load: 110 plf , Snow Load: 30 psf
The loading for the second floor is the following: Dead Load: 65 psf , Live Load: 100 psf
This issue I am having with the model is that the vertical reactions (Fy) are very high compared to the loads applied. I have run my own numbers by hand and the reactions shown in this model appear to be incorrect. I am not sure what is wrong with the model. I have double checked almost all of my parameters. I am not a staad pro by any means. I am kind of an intermediate but I am not sure what is going on here. Help would be greatly appreciated.Also, the design is not final and I am working on all the other issues and warnings the model has output.
Again, help would be greatly appreciated. Please let me know if anything I have posted is not visible or if you have any questions as to why I did something.
Thanks,
-Warren.
PDFPDF
Frame 1.STD
as per your staad input file .,your default unit system is Kips (for force) and foot (for length) , which is considered also for the loading .
is your unit system correct. because in your post , you have mntioned the loadings in pounds per square foot
Best Regards,
Alex Immanuel Thainese
The structure is not stable due to Pinned supports. Change the supports into the Fixed, and the reactions will become reasonable.
Hello Alex,
You bring up a very good point. However, I made sure that when I input the loading in the model I converted the psf to kip per linear foot.
I appreciate your suggestion but that was not the issue. Maybe you should have looked at the model a little more closely.
-Warren
Modesta
I tried your solution, and although this works I do not wish to model the structure as fixed because I am not detailing it as fixed.
From my experience and understanding of structural engineering, Fixed base is a base which resists Moments along with Tension and Shear, which means detailing the base plate to take the moment and transfer it to my foundation. Whereas Pinned base resists only Tension and Shear that is transferred to the foundation and does not require the same level of detailing. In reality the action is always between the two, neither does a FIXED BASE nor PINNED BASE exists in reality.
Anywho, I digress. After some discussion with some of my co-workers I found that the solution to my problem was to keep the base pinned and add a custom support condition to act as a roller in the z-direction. So I added additional supports that was fixed but everything was released except that force in the z-direction. This solved my problem and gave me a closer correct approximation to my design scenario.
However, thank you for your suggestion Modesta,
Regards,