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Re: Steel Moment Frame Connections

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In a message dated 98-08-21 21:41:04 EDT, you write:

<< On another front, I have noticed as recent as yesterday, observing
 residential projects under construction where steel moment  frames are going
 in with no apparent post northridge detailing. Same old full pen welds with
 backer bars and rats nest. There are wood framed, type V projects all over
 the bay area where I see this going on. Is FEMA 267 considered the current
 standard of care? I am sure some engineers have never heard of it.
 
 It would be very helpful if some of the testing of moment connections would
 address the concerns of us little guys using small frames for residential
 applications such as  W8 through W14 sections. >>
 
 
 We do lots of large residential construction, and almost all of our projects
have steel moment frames.  We do not rely on the fancy connections developed
for large building frames because I'm not convinced that the small frames (W8,
W10, W12) have the same weld problems with heat-effected zones, through-
thickness, etc.  Instead, we use the dumb and dumber approach.

We design all of our steel frames as Ordinary Frames.  Since the majority of
our buildings already have shear walls, the use of an Rw=6 is not a penalty
for the frame.  In order to satisfy the LA City requirement that the OMRF
connections resist a load based on Rw=2.67, we design the frame members for
stresses based on a multiplier of 2.25 (Rw=6 / Rw=2.67) in all load
combinations.  If the frame members satisfy this high load demand, then we
conclude that we can use standard pre-Northridge full-pen butt-welded flange
and bolted shear tab moment connections without cover plates, dogbones or the
like.  We do require that the backup bars be removed, even though the City
doesn't because we feel this is good practice.  It should be noted that we
check the drift requirements for the frame based on Rw=6 (the Code loads) not
the increased loads.

We have found that the large (2.25) increase in frame forces does not effect
the frame sizes too drastically since drift usually governs at Code load
levels.  Additionally, by using the higher forces we get stiffer frames which
are more compatible with the rest of the shear wall building and help minimize
nonstructural damage.  Lastly, the use of "typical" connections is much easier
to install for the smaller steel fabricators that we are using at the
residential level.

That's my 3 cents worth.

Bruce Resnick, SE
Parker Resnick Str. Eng.