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RE: Near future of Steel Moment Frames

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Title: RE: Near future of Steel Moment Frames

This will be an incomplete answer, since it will precede the availability of the Guidelines documents that SAC  finalized and FEMA is now printing. Once those documents are available, you'll be able to see a lot more of the specifics.

Regarding assemblies that utilize deeper column sections, SAC testing was very limited (3 specimens, I believe). Each tested specimen developed a tendency to twist, mostly due to the increased moment arm of the beam flange forces on the column, relatively smaller torsional restraint provided by the deeper column (with thinner cross-sectional elements) and lack of other sources of torsional restraint, like a slab or lateral framing members, in the test setup. The conclusion drawn out of this small set of specimens was that the twisting effect, if unrestrained, was dominant enough to change the basic performance of the assembly from that found with more typical W14 and W12 columns. I believe the resulting recommendations given do not prequalify deep columns, but do give guidance on the restraint that would need to be provided by a slab, bracing or other means to prevent the twist.

Regarding panel-zone contributions to frame deformations, it depends. Many SAC specimens were configured with very stiff panel zones. Many others had very weak panel zones. Still others were in between. For some connection types, panel-zone deformations were beneficial to connection performance. For others with different characteristics, stiffer panel zones were preferable. In the end, the prequalification information recommended by SAC addresses what panel zone characteristics should be pursued with each connection type.

Regarding costs, don't be alarmed when you see fluctuations in steel weight. Your owner or owner's representative needs to become a little more savy and understand that it is not 1930 anymore. Steel economy has almost nothing to do with the weight of the steel used to make the frame. It has everything to do with how well you select the members and connections to work together to reduce the labor involved in fabrication and erection. I've posted this link before, but look here to see where the real cost savings are (tell your owner/rep to do the same):

    http://www.engr.psu.edu/ae/steelstuff/economy.htm

The SAC work is coming to fruition, much to the credit of Ron Hamburger, Jim Malley, Steve Mahin and all of their supporting cast. AISC plans to carry the ball further too as this work continues to progress and be incorporated into the AISC Seismic Provisions for Structural Steel Buildings.

Charlie