ension chord bracing 9built-up steel truss0

huangyhg

tension chord bracing (built-up steel truss)
hi all
i am engineering a welcome center and in the entrance room, there is a high curved roof that is being supported by built-up steel trusses that span 68 feet long and are generally 30 feet apart.  
i was wondering if there are any provisions on tension chord bracing for these long steel trusses?  any help would be greatly appreciated.
thank you.
struct engineer
there are no provisions in aisc for tension chord bracing (unless there is uplift and it is able to become a compression chord) and aisc is silent on the issue (they leave it up to engineering judgment.  
i personally believe that tension chord bracing is a good idea and always use it (if calcs show it necessary).  if you think about it, the only thing bracing the diagonals that are in compression are the top and bottom chords.  the top chord is usually sufficiently braced, but the bottom chord also needs to provide adequate strength/stiffness to act as a brace for those diagonal compression   
the only thing i have seen in regards to bracing is in appendix 6 of the aisc 13th edition.  however, there is nothing there in regards to tension bracing.
section d1 of the aisc does state that an "l/r preferably should not exceed 300" for tension members.  this could be achieved by increasing the   
strucphanatic34,
there is a very informative aisc engg. journal by james s. fisher ( 1983-q3) on tension chord bracing. you can buy it or if you are a   
this was discussed in some detail about 3-yrs ago with dissenting opinions - see
it could be that the stadium bottom chords have adequate out-of-plane strength/stiffness without the bracing.
i've certainly used it in certain situations... think standing on a suspended jump rope.
just out of curiosity, how is failing to brace the bottom flange at any location any different than failing to torsionally brace a beam at its ends?  
while i may agree that the buckling length of an individual web