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RE: FEMA 350 continuity plates and panel zone thickness

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Scott –

 

I’m not an authority on FEMA 350, but off the top of my head, here’s my recollection:

 

  1. The flange weld is a F.P. weld and cannot deliver anything more than Af x Fy.
  2. For a SMRF, the panel zone must be designed for RyMp of the beam(s). This will certainly drive the column design, particularly when limited to the shallow depth sections tested in FEMA 350. Avoid web doubler plates! From what I’ve been told, bumping up the column by 50 PLF is still cheaper than adding web doubler plates. It just looks embarrassing; that’s all.
  3. If you have an IMF (or OMF in FEMA 350 terms), you can design the panel zone for the actual loads. To me, this is the biggest reason to try to get IMFs approved for projects I do, because the demand on the column drops off dramatically.
  4. The FEMA errata are available (free) on the AISC website. If you need help finding it, let me know.
  5. For design equations, use AISC LRFD equations, not the FEMA equations.
  6. Also, check out the opinion of the SEAOC Seismology committee on FEMA 350. That is available on the website (somewhere).

 

I’m sure the engineers who design steel for a living (unlike me who does it as a hobby) will certainly correct any mistakes I’ve made in the above statements, but that should get you started.

 

Regards,

 

T. William (Bill) Allen, S.E. (CA #2607)

ALLEN DESIGNS

Consulting Structural Engineers

http://www.AllenDesigns.com

V (949) 248-8588

F (949) 209-2509

 

-----Original Message-----
From: Haan, Scott M POA [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil]
Sent: Monday, May 16, 2005 11:26 AM
To: seaint(--nospam--at)seaint.org
Subject: FEMA 350 continuity plates and panel zone thickness

 

Anyone:

 

I don’t have an errata for FEMA 350.  FEMA 350 3.3.3.2 formula (3-7) appears to be for a beam framing into one side of a moment frame column.  AISC LRFD 2nd ed Figure C-K1.3 shows calculating panel zone shear by adding forces from moments on either side of the column and subtracting the story shear.  Formula 3-7 does not appear to cancel out the story shear or add the additional shear from a second beam on the other side of a column.  Are people using this formula (3-7) to check required panel zone thickness when there are beams framing into both sides of moment frame columns?

 

Also FEMA 350 3.3.3.1 tells you to use continuity plates that conform to K1.9 of the LRFD specification. My question is that if the full plastic moment goes through beam flanges then does the continuity plate need to be thicker than the beam flange?  It would seem if you were trying to transmit the full plastic moment through a beam flange with weld access holes the maximum force that could be transmitted would be the area of the beam flange times the yield stress. This is less then the plastic strength of the beam. Is this right?  I have a 97 UBC Seismic Design of Buildings and Bridges book that shows designing continuity plates for just the beam flange area times the yield stress. Should the continuity plates be designed for the beam flange area times the yield stress?

 

 

Scott M Haan