KL/r Ratio for staggered bracing
KL/r Ratio for staggered bracing
(OP)
AS per ASCE 10-97 while calculating l/r for leg member which is continuously staggered as shown in fig 3.2 b and 3.2 c of ASCE 10-97 , we have to consider kl/r = 1.2 l/r.
Does this apply only to leg members or it will be applicable to lattice member also. (Lattice p7T as shown in attachement) ?
If only to leg members then why ? Your valuable comments on this will be highly appreciated.
Thanks
Nitin Patel





RE: KL/r Ratio for staggered bracing
If you use the latest version of PLS-CADD software, you can model all the redundants in the TOWER model and the nonlinear analysis will show where this bracing pattern will buckle. I would model this panel in PLS-TOWER with all members and use the 1.2 factor and apply a big compression load on leg P7 and a little wind perpendicular to the face using ASCE-74-2009M so you get wind on all the redundants and lacing members, then I would run a NL analysis and see if the panel is stable. Members P7T and P7L will be beam members.
I guess it depends if you want to gamble that the staggered bracing factors can be used and pick smaller members for P7T, or you can be conservative and assume P7T buckles out of plane where it is braced.
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I have been called "A storehouse of worthless information" many times.
RE: KL/r Ratio for staggered bracing
P7 is supported from both face. ( Not staggered ). Member P7T and P7L are not supported from two side at every point. We face problem during tower testing with this pattern during transverse load conditions ( No longitudinal load and very small vertical load on tower). Design of P7T and P7L members are considering KL/r = L/r.
Finally designer added few more members on transverse ,longitudinal and inclined face to support P7T and P7L at all points. With revised arrangement tower tested successfully recently.
Does it mean we have to consider KL/r = 1.2 L/r for bracing members also if we wanted to test tower without adding extra members ?
Nitin
RE: KL/r Ratio for staggered bracing
Are you designing in accordance with TIA-222-G? What tower analysis program are you using?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: KL/r Ratio for staggered bracing
Nitin;
The dashed members between P7T and P7L, do they connect the transverse and longitudinal faces of the tower? Is the tower square? If you use PLS-CADD software, I suggest you model all the joints and connect them as they are in the real world as beam members and run a nonlinear analysis to see how they behave. Your Lx or Ly are probably greater than 1.
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I have been called "A storehouse of worthless information" many times.
RE: KL/r Ratio for staggered bracing
My point is , Even if ASCE 10-97 clause is for leg member ( KL/r = 1.2L/r) , it should be applicable for lattice members if we are not connecting from two direction.
RE: KL/r Ratio for staggered bracing
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I have been called "A storehouse of worthless information" many times.