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SFRS Steel Frame Classification According to ASCE 7-10Helpful Member!(2) 

sasa2k (Structural) (OP)
9 Apr 12 18:14
I need help to classify SFRS frame (attached) according to ASCE 7-10 Table 12.2-1.

It is a typical frame for one bay crane building 24m wide, 20m high. Top element is a truss appx. 2m deep. The top and bottom chords of the truss are connected to the step column creating moment in the column.  Seismic design category is E, so there are some limitations what SFRS system to use.

Some suggested that this should be categorized as a moment frame, but I am not convinced as the moment frame assumes moments in the vertical and horizontal elements which is not the case here. Also, in this case, the plastic hinge zone will develop in the column instead in the beam.

Any suggestions?

Thanks

img http://files.engineering.com/getfile.aspx?folder=3a63eb52-2327-4454-abb5-02b14ff60900&file=image001.jpeg
Helpful Member!  ToadJones (Structural)
9 Apr 12 22:02
I haven't read this paper for a couple years and I know it is probably a code revision or two removed from the time it was written(2003) but it is chalk full of good information on seismic design of industrial buildings like you are dealing with.

I have to ask, why bring pain upon yourself by using step columns?  
ToadJones (Structural)
9 Apr 12 22:11
Actually, now that I have reread some of it, I think you will find your answers in the paper.

These buildings don't fit neatly into the code's box.  
Helpful Member!  ToadJones (Structural)
9 Apr 12 22:18
From page 12...

For one-story buildings with long-span
roof trusses incorporated into moment
frames, the authors suggest categorizing
the frame as an OMF with a strong
beam/weak column system. Therefore,
when this frame is subject to design-level
earthquake forces, flexural hinging
should occur in the column. IBC and
ANSI/AISC 341 do not prohibit this
behavior for OMF systems in one-story
buildings. The truss should be designed
for both gravity load and lateral load end
moments obtained from an appropriate
frame analysis. The roof truss should be
designed for end moments (due to earthquake
forces) consistent with developing
the maximum expected flexural capacity
of the supporting column (1.1 RyMp).
The top and bottom chord of the truss
must be connected to the column to
transfer the corresponding forces.
Research at Georgia Institute of
Technology (Georgia Tech) that was
sponsored by the Steel Joist Institute
(SJI) supports this design approach. This
design approach will be included in a
new release of SJI Technical Digest 11,
"Design of Joist-Girder Frames."
sasa2k (Structural) (OP)
10 Apr 12 20:55
Thanks ToadJones - the article covers my case exactly.

...and since you mentioned - step column may not work any more because of high seismic forces due to low R value for OMF. I may use separe crane column and save myself troubles.

Thanks again!

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