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- To: <seaint(--nospam--at)seaint.org>
- Subject: steel connections, Fully Restrained vs Partially Restrained
- From: "Andrew Kester, P.E." <akester(--nospam--at)cfl.rr.com>
- Date: Thu, 17 Jan 2008 19:29:47 -0500
I am getting into more and more complicated steel moment frames. I work only in Florida in zero seismic zone, only wind and gravity frames. Per January Modern Steel Construction there was a question on PR vs FR. I have already studied and ran some numbers from AISC Section B3.6, p 16.1_218-222.
I need more info on determining if a connection is to be considered PR or FR. If it is designed and detailed per AISC as a PR or FR, I still have to do the analysis per the actual beam size to determine the Connection Stiffness? KL/EI correct, where K=Ms/Os. OK, I understand all that. Then I get this stiffness number and it puts me into 2<PR<20.... But my analysis assumes FIXED (I used RAM 2D for steel frame design). Now I see there is an area in the joints section where I can define a Z spring for rotation, which I think is the same as Ks=M/O (where O=rotation angle in radians and M= service moment in kips). So I plug in this K value for each joint and rerun the whole frame to see the effects?
What if I assumed a FR and am detailing it as FR? The connection is fully designed for service load (actual) moments, not to fully develop the moment capacity of the beam. Since the only variable I can readily manipulate in this equation without messing with the geometry of the building would be I of the beam, going bigger to push me into a stiff enough joint to get me into the FR.
But if I rerun the frame using the actual stiffness of the joint and I am OK with the results, then what? Can I still just design and detail the connection as FR for the actual service load moments? I have read through that section several times, and I guess because I am using this frame in wind and gravity loading, I do not see what the difference for me in it being PR or FR. In other words, so what? What do I do differently now that I know this? (Other than what I have stated above.) I know my drift, deflection, strength results all based on fixed connections with actual members chosen, they are all fine....
I would appreciate any additional documents you can point me to or advice on this. Also sent question to AISC and went through there website searching.
I was thinking to join AISC to download their guidelines. I found them useful at my old office, and it seems like there are quite a few more now. Looks like it opens me to access other downloads and info. Anyone out there doing a lot of steel design find this membership worth it?
THANKS! Sorry this is LONG...
Andrew Kester, P.E.
ADK Structural Engineering, PLLC
1510 E. Colonial Ave., Suite 301
Orlando, FL 32803
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