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Re: cold formed braced frame

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I wouldn't use a K-braced frame under any circumstances in Seismic Zones 3
or 4.  See UBC Section 2213.8.4.2.  The concern is brace buckling leading
to column buckling leading to collapse.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

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



                                                                                                                    
                    "Mark Baker"                                                                                    
                    <shake4bake@eart      To:     <seaint(--nospam--at)seaint.org>                                               
                    hlink.net>                                                                                      
                    05/31/01 01:59        cc:                                                                       
                    PM                                                                                              
                    Please respond        Subject:     Re: cold formed braced frame                                 
                    to seaint                                                                                       
                                                                                                                  . 
                                                                                                                    




In other words, applying omega established for hot rolled sections would
still be mixing apples and oranges....

I'll let you know what bumping up my seismic forces by 2.2 results in. I
think I'll be o.k. but won't know for sure until I run the numbers.

Am I leaping to far to say you would not apply omega level force to a
k-braced frame of light gauge material?

Mark

----- Original Message -----
From: <Rick.Drake(--nospam--at)Fluor.com>
To: <seaint(--nospam--at)seaint.org>
Cc: <seaint(--nospam--at)seaint.org>
Sent: Thursday, May 31, 2001 12:14 PM
Subject: Re: cold formed braced frame


>
> Mark:
>
> A few additional thoughts before you go much further.
>
> Omega is a measure of the "pushover strength" of the structure as a
whole.
> In other words, how much load can it take beyond the prescribed base
shear
> force. I would expect that omega values for cold-formed steel to be very
> low, nowhere near those assigned to structural steel structures.
>
> Regards,
>
> Rick Drake, SE
> Fluor Daniel, Aliso Viejo, CA
>
> *****************************
>
>
>
>
>                     "Mark Baker"
>                     <shake4bake@eart      To:     <seaint(--nospam--at)seaint.org>
>                     hlink.net>
>                     05/31/01 09:56        cc:
>                     AM
>                     Please respond        Subject:     Re: cold formed
braced frame
>                     to seaint
>
.
>
>
>
>
>
> Thank you Rick, you have confirmed my reluctance to try applying special
> seismic provisions of chapter 22 to this structure.
>
> There seems to be no connection between any special seismic provisions
and
> the AISI specification for this type of structure. Section 2220 really is
> not applicable to this structure since 2220 deals with steel stud wall
> systems.
>
> The best thing I can see to do is apply omega to all member and
connection
> design.
>
> Thanks again,
>
> Mark
>
> ----- Original Message -----
> From: <Rick.Drake(--nospam--at)Fluor.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Wednesday, May 30, 2001 4:50 PM
> Subject: Re: cold formed braced frame
>
>
>
> Section 2213. 8 is part of Chapter 22, Division V, the seismic provisions
> for Structural Steel designed in accordance with the AISC ASD Manual.
Both
> the ASD Manual and this Division are not applicable for Cold-Formed
Steel.
>
> Try UBC Chapter 22, Divisions VI, VII, and VIII for Cold-Formed Steel
> requirements.  Section 2220 should be of great interest
>
> Rick Drake, SE
> Fluor Daniel, Aliso Viejo, CA
>
> ********************************
>
>
>
>
>                     "Mark Baker"
>                     <shake4bake@eart      To:     <seaint(--nospam--at)seaint.org>
>                     hlink.net>
>                     05/30/01 11:58        cc:
>                     AM
>                     Please respond        Subject:     cold formed braced
> frame
>                     to seaint
>
> .
>
>
>
>
>
>
> any thoughts on the following:
>
> Greenhouse structure.
> Framing of light gauge, cold formed  material.
> K-braced frames and x-braced frames taking  lateral.
> Zone4
>
> How can I comply with UBC 2213.8 seismic provisions  which were not
> intended for light gau. members?
>
> Won't I be mixing oranges and apples when  trying to apply adjustment
> factors to allowable axial stress which incorporate  Cc and Kl/r as in
> 2213.8.2.2.
>
> Section 2213.8.2.5 limits D/t ratio to 1300/Fy  which is far different
than
> the limt of .441E/Fy of AISI Spec. for Cold Formed  Steel Struct.
Members.
>
> I am inclined to design using AISI spec. for  allowable stresses and
apply
> omega to all connections and  members.
>
> Any thoughts?
>
> Thanks,
> Mark
>
>
>
>
>
>
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