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Re: ordinary braced frame - building frame system or bearing wall system

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If the braces are only designed for lateral, and the beams and such are not dependent on the bracing for support of vertical load, then the frame would be part of a building frame system.
The caveat is one braced frame "building frame system", in an otherwise bearing wall building does not a building frame system make.
Under the IBC, the transition appears to be stated as braced frames in light framed buildings.  I do not agree with the distinction, and believe the old UBC way of "bracing carrying vertical load" was closer to the true intent.  You can easily have brace frames in a predominantly wood shear wall building that do not carry vertical load, and the appropriate R factor for the entire structure would be for light frame shear walls.  It does not make sense to penalize an entire building for one or two brace frames, particularly when the brace frames will perform better than the wood shear walls.
----- Original Message -----
Sent: Wednesday, May 04, 2005 4:11 PM
Subject: RE: ordinary braced frame - building frame system or bearing wall system

I understand what you are saying.  My point is that if the columns carry gravity load and the braces are designed only for lateral forces then you can use a building frame system. Right? The code used to say ordinary braced frames where the braces carry gravity load.  


At the rate the codes are going, ordinary steel concentrically braced frames are going to be eliminated like half stresses, and timber heavy frames while most of the code change committee members are playing the slots in Las Vegas during the hearings.




From: Paul Feather [mailto:pfeather(--nospam--at)]
Sent: Wednesday, May 04, 2005 11:02 AM
To: seaint(--nospam--at)
Subject: Re: ordinary braced frame - building frame system or bearing wall system




The Blue Book states "A bearing wall system is characterized by shear wall or brace frame lateral force resisting elements that carry substantial vertical loads which, if they fail, eliminate the vertical load capacity of a substantial portion of the structure and/or lead to vertical instability.  The presence of minor load bearing walls in a building that would normally be classified as a building frame system does not necessarily mean that the building should be categorized as a bearing wall system.  The reasoning is the action of a multi-storied building is not significantly influenced by the presence of minor bearing walls around a stairwell, for example."


If you have a shearwall building with a couple of isolated brace frames where the braces are not required to carry gravity load, I would use the R value for the shear wall structure for the frame design.  The difference is only a couple of percent either way.  On the other hand if you have a predominantly building frame system with a couple isolated bearing walls, per the Blue Book example, I would use the R value for a braced frame structure.




----- Original Message -----

Sent: Wednesday, May 04, 2005 11:30 AM

Subject: ordinary braced frame - building frame system or bearing wall system


When do you have to use an R value for a bearing wall system instead of a building frame system for ordinary braced frames?  My understanding was that you have to use a bearing wall system R only if the braces normally carry gravity loads.  It is my understanding of the building frame system means there is steel frame that carries gravity loads by itself without the presence braces.