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RE: FEMA 350 and SMRF's

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Title: RE: FEMA 350 and SMRF's

>... cyclic testing of ... special moment frame connections
>is required.  Does anyone know of any tests done on
>sections from W10 to W18? I know that these sizes are
>considered small for frames, but often in residential construction
>I now find myself designing moment frames. Am I limited to OMRF's?

There are a lot of tests out there that you can take advantage of if the details match up. The FEMA 350 recommendations provide the most complete summary available to date, but come with prescribed limitations. If you're outside those limitations, you're essentially on your own. When that is the case, you can do project specific testing or turn to a lower-ductility system that isn't so limited (assuming it is permitted in the building code. It may be a question of economics.

For the longer term, the information in the FEMA 350-355 series of publications is now working its way through the AISC consensus process. Much of it will wind up in the AISC Seismic Provisions (or another AISC publication if it is not appropriate for that). We're also identifying what is needed in terms of further research, such as for issues like deep columns, weak-axis connections, and others. We're also gearing up for the other design office tools needed to make seismic steel design easier (including more than just moment frames). Our priorities are still being identified. If you'd like to make constructive suggestions, please reply to me privately.

>a plan checker has insisted that it specifies only A572
>Grade 50 steel for all moment frame beam and column
>connections.  I design all of my steel frame connections
>with an increase in yield strength to grade 50 to compensate
>for the expected yield stresses for A36 steel, but still
>specify A36.

The plan checker is close, but not quite correct. For W-shapes, ASTM A992 is most common. Read all about it here:

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

Either way, though, you had the right idea that the expected yield strength for either material is essentially the same. The AISC Seismic Provisions requires that, when you are developing the strength of the steel, either material should be designed with an expected yield strength of 55 ksi (RyFy = 1.1*50 for A992; RyFy = 1.5*36 for A36). I know the latter is equal to 54 ksi, not 55 ksi, but you get the idea -- it's the same steel either way. Specifying ASTM A992 just ensures that you get better mechanical and chemistry controls.

Charlie