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Re: Steel Moment Frame Connections

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Hello Bruce:

Thank you for your reply on this subject.

> 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.  >

I once inquired about this and I got a reply from a SAC affilliate who lead
me to beleive that small frames should not have different connection
requirements than the bigger frames and that there were in fact some small
frame connection falures in Northridge. Maybe this has changed, but again it
would be reassuring to see more information on this subject. Your approach
seams very reasonable to me. I am unware of the Rw=2.67. for projects in San
Francisco. I did the same thing for the first post Northridge frame I worked
on based on an Rw=2. (Drift did not govern on that one)

Regards,

Jeff Smith

>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