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Re: "R" Value for Cross Bracing

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Tension only bracing is acceptable for one  and two-story buildings. (UBC
2213.8.5) so the 5.6 R value is correct in my opinion.
The value that you propose is not applicable since it is for a Bearing Wall
System.
I hope this will help.


Julio M. Guerra S.E.




                                                                                                              
                    FSRahbar@aol.                                                                             
                    com                  To:     seaint(--nospam--at)seaint.org                                            
                                         cc:                                                                  
                    02/04/2000           Subject:     "R" Value for Cross Bracing                             
                    12:29 PM                                                                                  
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                    seaint                                                                                    
                                                                                                              
                                                                                                              




I am checking a Metal-Structure building. It is similar to a Butler
Building
where there are no bearing walls and beams and columns support the entire
roof.

The building is long and narrow, therefore, the seismic loads in the narrow
direction is somewhat comparable with wind loads. The lateral resisting
elements in narrow direction are two sets of 3/4" diameter rod cross
bracing.
Obviously the rods only work in tension and not compression. The engineer
for
the building has used a "R" Value of 5.6 to determine the seismic loads.
This
"R" value is taken from Table 16-N, Building Frame System, Item 4, Ordinary
Braced Frames with Steel.

My questions are: Is "R" Value of 5.6 correct for this steel rod cross
bracing? Is the ordinary Brace Frame consist vertical truss and the members
can take both tension and compression?

It was my opinion that since the rod cross bracing system is not really
defined in Table 16-N, the closest system would be item 1-3 with tension
only
brace with "R" Value of 2.8.

I appreciate it someone can try to clear this.

F. S. Rahbar SE