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Re: Tube to Tube Moment Frames

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You have to look at every part of your load path to assure that the
prescribed design loads can be transmitted between the beam and the column
without exceeding any unacceptable limit states.  FEMA 350 is the result of
looking at the load paths of 9 types of moment connections.  Continuity
plates are not directly required by the code, but they may be required to
preclude unacceptable limit states in the load path, such as web buckling,
web yielding, column flange bending, etc.

Regarding the use of HSS columns, they are not covered by FEMA 350.  For
one reason, HSS sections tend to have low b/t ratios and perform very
poorly when subjected to cyclic loads.  They are not usually the first
choice in high seismic zones.

To assist you in the design of your connections, I suggest you look at the
AISC HSS Manual.  They have discussions and examples of w-shape beam to HSS
column moment connections.  Many of the limit states will be applicable to
your situation.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

******************************




                                                                                                                   
                    Eric Ober                                                                                      
                    <eric(--nospam--at)cagley.co      To:     seaint(--nospam--at)seaint.org                                                 
                    m>                                                                                             
                    06/28/01 09:40       cc:                                                                       
                    AM                                                                                             
                    Please respond       Subject:     Re: Tube to Tube Moment Frames                               
                    to seaint                                                                                      
                                                                                                                 . 
                                                                                                                   




I was aware of the strength requirements in AISC SPSSB Supp. 2.  I guess I
was thinking about connection
prequalification.  As I read the provisions again, it seems that prequal.
only applies to SMRF.  The other issue I was
looking at is the continuity plates.  I have all corner column conditions
with moment connections both ways.  Not sure
how to handle this requrement.

Eric Ober

Rick.Drake(--nospam--at)Fluor.com wrote:

> Before you go to far with your concept, you need to look at a copy of the
> AISC Seismic Provisions, including Supplement No. 2 (www.aisc.org).  You
> will have to design the connection for something greater than the plastic
> moment strength of the beam.
>
> Rick Drake, SE
> Fluor Daniel, Aliso Viejo, CA
>
> ***************************
>
>
>                     Eric Ober
>                     <eric(--nospam--at)cagley.co      To:     seaint(--nospam--at)seaint.org
>                     m>
>                     06/28/01 08:31       cc:
>                     AM
>                     Please respond       Subject:     Tube to Tube Moment
Frames
>                     to seaint
>
.
>
>
> I'm designing a porte cochere in Zone 4 in California near San
> Francisco.  It is intended to use steel OMF with tube columns and
> beams.  Has anyone done this in recent times?  Wondering about
> connection requirements mostly since FEMA 350 doesn't provide any direct
> guidance.  I was thinking about a connection similar to the Welded
> Flange Plate connection in FEMA 350.  Thanks.
>
> Eric Ober
> Cagley and Associates
> Rockville, MD
>
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