X bracing buckling length
X bracing buckling length
(OP)
Hello,
(sorry for my english)
I have an X bracing system. the 2 braces are connected in the middle. the X bracing can work in compression and tension.
I attached a sketch
I would like to know the value of ky and kz for buckling length in both planes.
Lfy = ky L and Lfz = kz L.
Of course I will appreciate if you refer to a text whatever it is.
Many thanks
(sorry for my english)
I have an X bracing system. the 2 braces are connected in the middle. the X bracing can work in compression and tension.
I attached a sketch
I would like to know the value of ky and kz for buckling length in both planes.
Lfy = ky L and Lfz = kz L.
Of course I will appreciate if you refer to a text whatever it is.
Many thanks






RE: X bracing buckling length
The logic being that as one brace is in compression the other will be in tension and not allow the compression brace to buckle out of the plane of the page (in your sketch) or buckle in the weak direction. It wouldn't make sense either for the bracing to buckle in the strong direction.
RE: X bracing buckling length
If you still care to go through all the reading and reach this same conclusion, feel free!
"Design of Diagonal Cross Bracings" Part 1, 2, and Discussion. Picard and Beaulieu. Engineering Journal, AISC 3Q 1987, 4Q 1987, and 4Q 1989,
"Effective Length Factor for the Design of X-bracing Systems" El-Tayem and Goel. Engineering Journal, AISC 1Q 1986
Or if you care to go with energy methods:
"Practical Application of Energy Methods to Structural Stability Problems". Shankar Nair. Engineering Journal, AISC 4Q 1997
RE: X bracing buckling length
Actually the issue is the buckling out of plane. I did kz=0.7 instead of 0.5 just to keep some security.
The problem is the Control Office Socotec insists in puting kfz = 1.00 !! do you imagine so i was obliged to justifie many things....
I thank you so much for the references given, really thank you.
I will look for thoses books in google...
Cheers
RE: X bracing buckling length
Go here for the actual thread: thread507-293728: Tension Only X-Brace (Slendereness Ratio)
RE: X bracing buckling length
RE: X bracing buckling length
RE: X bracing buckling length
RE: X bracing buckling length
RE: X bracing buckling length
APP 6 maybe even easier if you use A-6-3....where Pbr = 0.01Pr.
This is only 1%.
RE: X bracing buckling length
I reasoned that although the tension brace might have the strength it probably didn't have sufficient stiffness, especially when the short members were in tension.
It is all very well to say it can resist 2% or 1% but how much does it deflect? What does that deflection do to the compression member?
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: X bracing buckling length
I did not say this before, but I would not use the tension member as a brace just for feel good reasons. Looking back again at the provided jpeg, the one brace is attached by a gusset running by the continuous brace. With that in mind, you would now have to take the gusset stiffness into consideration with the brace. Not to practical in my opinion.
As a matter of fact, i would not use the pictured set up as compression tension braces because of the gusset. A better solution would be to rotate the braces 90 degrees with the strong axis facing out of plane. Then it would be an easy matter to brace them in plane.
RE: X bracing buckling length
The Aluminum Design Manual published by ALCAN has a variety of bracing conditions and if there are two fasteners at the end of a X brace, then they use a value of 0.45 times the diagonal length.
Just looked at a recent project, and the engineer has used HSS round tube for x-bracing. The ends and the mid point have been flattened and bolts connecting the ends to the structure have been punched through the flattened part and a single bolt through the flattened mid point. I'm going to have to check that for my next project.
Dik
RE: X bracing buckling length
RE: X bracing buckling length
Really intersting to go through all your comments
Actually I did 2 calculations before I discover WillisV documents.
I took 2% Fancypants
I calculated the deflection out of plane and then I introduce a bending moment due to excentricity to calculate the brace regardeless the bukling length
But I checked the brace in compression and I found 0.7 L even conservative
By the way, you are lucky because the frensh code is not developped, they try. Actually Europe except UK are more concrete than Steel
Again many many thanks
One more question: I have AISC manual steel but I did not manage to find " APP 6 in AISC 360-05" any help to download it
RE: X bracing buckling length
Appendix 6 is in the specification portion of the book.
RE: X bracing buckling length
RE: X bracing buckling length