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RE: Large Bay 'X' Bracing

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My rough calcs based on your info indicates roughly 1/2" elongation in the rods... (using 1-1/8" rods)... You will want to check what diameters you have available to you that are atleast that diameter.
 
As far as the decision between rods, single angles, and double angles the decision usually comes down to what is needed to handle the required forces and deflection limits.
 
Another worthwhile suggestion is to provide a simple wire tie where the two rods cross.  This will prevent the rods from 'slapping' together.
 
In some high seismic areas you may be restricted on your use of tension only bracing.  For those cases and possibly some rare cases where double angle bracing does not work we might consider HSS or Round HSS sections.  For me personally I would tend to use the HSS sections for case like chevron braces or the like where compression is also a part of the brace criteria, and the rods or angles for tension only bracing.
 
I don't have any suppliers currently in my head for clevises, etc. but I will see if I can find some info.
 
HTH,
Greg


From: Rich Lewis [mailto:seaint04(--nospam--at)lewisengineering.com]
Sent: Thursday, May 31, 2007 7:56 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Large Bay 'X' Bracing

Thank you all for your suggestions.

 

Your responses brought up another question in my mind.  What applications are best for using rod bracing and what applications are best for using double angles?  I didn’t run any numbers on the rod, but I was thinking that a bay that big would have more elongation of the rod than I would want.  The problem with double angles are the weight starts to add sag to the members.  Are there some ‘rules of thumb’ of when I would want to use rods over double angles or pipes?  I assume seismic design plays some role.  I am located in a low seismic region.

 

Can someone give me a web link to a hardware supplier for clevises, sleeve nuts, etc. for the larger diameter rods?

 

Thanks.

 

Rich

 

 


From: Effland, Greg [mailto:GEEffland(--nospam--at)butlermfg.com]
Sent: Wednesday, May 30, 2007 10:11 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Large Bay 'X' Bracing

 

Assuming the 21 kips is the brace tension load (and not the horizontal component) you should be able to handle that load with a 50 ksi 1-1/8" diameter or larger rod.  A rod that size should connect into the framing members with a clevis (note not every clevis is designed the same so check its capacity as well).

 

The L/r limit is very similar in both the 9th Edition and the 13th Edition (2005 spec).  For both specs the L/r limit is a "preferred" not "required" limit... the wording in the 9th edition is "For members whose design is based on tensile force, the slenderness ratio L/r *preferably* should not exceed 300.  The above limitation does not apply to rods in tension."  Emphasis on preferably added by myself... also per this note rods in tension are even excluded from the preference.  The 2005 spec has a very similarly worded user note in D1.

 

Hope this helps,

Greg


 


From: Rich Lewis [mailto:seaint04(--nospam--at)lewisengineering.com]
Sent: Tuesday, May 29, 2007 6:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Large Bay 'X' Bracing

I have a warehouse condition of a ‘X’ braced bay that is 31 feet high and 42 feet wide.  The diagonal length is over 51 feet.   I’m wondering if I should try to use the bracing as one large bay, or add a wind column in the middle and have two smaller bays.  The bracing is tension only for wind loads.  The load in the diagonal is about 21 kips.  What makes me most uneasy is the slenderness ratio of the brace.  If I try to limit the L/r ratio of the out of plane axis to 300 then I get extremely large angles.  If I ad a column I add almost 50% more bracing length, plus column and footing.

 

Thanks for your insight.

 

Rich