x-bracing design considerations
x-bracing design considerations
(OP)
In designing x-braces, using angles with a bolted connection in the center, how does one determine the unbraced length? I want to use both members and not ignore the compression member. Does this move my Lu to the midpoint? I've read the answers posted in the RISA forum (unbraced length of X-brace design & V-brace segmenting).






RE: x-bracing design considerations
DaveAtkins
RE: x-bracing design considerations
The brace diagonal in compression has an unbraced length equal to half the total diagonal length.
RE: x-bracing design considerations
Correct me if I am wrong, but I believe I read somewhere regarding the bracing of the compression diagonal by the diagonal in tension and it was suggested to use a unbraced length of 0.65 L. I believe it was based on research done at the University of Michigan.
RE: x-bracing design considerations
Mike McCann
MMC Engineering
RE: x-bracing design considerations
RE: x-bracing design considerations
I don't understand reducing L, it should be the actual unbraced length under consideration. If you want to play around, do it with the "k" value, but be careful the codes often specify "k" by way of charts and nomographs.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: x-bracing design considerations
I don't see how the tension diagonal can brace the compression diagonal against out of plane buckling.
DaveAtkins
RE: x-bracing design considerations
Picard and Beaulieu in AISC Engineering Journal, 4th Quarter 1988, pp. 156-160.
Stoman, S. H., "Effective Length Spectra for Cross Bracings." ASCE Journal of Structural Engineering. December, 1989.
DeWolf, J. T., and Pelliccione, J. F., "Cross-Bracing Design." ASCE Journal of the Structural Division. July, 1979.
El-Tayem, A. A., and Goel, S. C., "Effective Length Factor for the Design of X-Bracing Systems." AISC Engineering Journal. First Quarter, 1986.
RE: x-bracing design considerations
Garth Dreger PE
AZ Phoenix area
RE: x-bracing design considerations
The tension diagonal definately does help the compression member due to the bowstring effect. It does not act as a full strength brace though due to the deflection. I would suggest you have a good read of the papers above.
Keep in mind that the restraint is only on one side of the member and therefore does not prevent twisting.
RE: x-bracing design considerations
"Tension/Compression system with members connected at the crossover point. If the member in tension
has a force of not less than 20% of the force in the compression member, the crossover point
provides support resisting out-of-plane buckling."
RE: x-bracing design considerations
RE: x-bracing design considerations