effective length of elements in partial side-supported trusses
effective length of elements in partial side-supported trusses
(OP)
Hi
It seems in planar trusses that side bracing of compressed chord is provided at all joints but tension chord is not restrained completely against lateral movement (side-supported at some joints), the effective length of diagonal and vertical elements for out-of-plane buckling in non-restrained panels is greater than L (K>1)!
Though the "K" factor can be calculated by analytical or numerical modeling of this kind of elements, I'm looking for any recommendation of codes or previous researches for effective length of diagonal and vertical elements in above mentioned trusses.
Can anybody give more information?
It seems in planar trusses that side bracing of compressed chord is provided at all joints but tension chord is not restrained completely against lateral movement (side-supported at some joints), the effective length of diagonal and vertical elements for out-of-plane buckling in non-restrained panels is greater than L (K>1)!
Though the "K" factor can be calculated by analytical or numerical modeling of this kind of elements, I'm looking for any recommendation of codes or previous researches for effective length of diagonal and vertical elements in above mentioned trusses.
Can anybody give more information?






RE: effective length of elements in partial side-supported trusses
Many on this forum, and in my office, do not agree on this subject. I believe that this is more of a global buckling issue, and not a local buckling (buckling of a single diagonal) issue. Here is why - If the bottom chord displaces sideways and the digaonal goes along for the ride, its own buckling length is still its own actual length. You can think about this by imagining a vertical, slender pipe pin supported at its base with no lateral support at the top other than a cable that is slung over the top and attached to the ground on either side of the vertical pipe. If you tension the pipe, it may become unstable and flop down and rest horizontally on the ground, but its own buckling length (kl) is stil its actual length.
In my opinion, the bigger concern is the global stability (the pipe flopping over).
That being said, I've gone through a couple examples of energy calculations to check stability for such a case and have tentatively convinced myself that it's not a problem. See the attached paper for the energy method stability check I used.
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
Isn't covered somewhere in the code that truss members may be taken to have k=1.0 for all members?
I'm brain farting here pretty bad....
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
Mike McCann
MMC Engineering
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
The King post shown in Fig. 11 of the Nair paper posted by SEIT requires a brace at the bottom of the king post. Without it, the structure is unstable and will fail under load.
BA
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
1- Effective length of diagonals for this kinds of trusses is L(K=1).
2-Minimum stiffens of side supports are required for above assumption.
3-Diagonals can be designed as an ordinary column by formulas of AISC or other codes.
majmaz
RE: effective length of elements in partial side-supported trusses
BA
RE: effective length of elements in partial side-supported trusses
RE: effective length of elements in partial side-supported trusses
Dik