Tension-only Bracing and AISC 341
Tension-only Bracing and AISC 341
(OP)
Hi,
I know AISC 341 defines width-to-thickness limits for compression members, but I was wondering if these apply to tension-only braces? Although you design these members as tension-only, compression and buckling will occur in these members upon load reversal, and it might be a good idea to avoid local buckling and plastic deformation of the section to maintain tensile capacity. So I was wondering if the width-to-thickness limitations should still apply to tension-only bracing members?
I know AISC 341 defines width-to-thickness limits for compression members, but I was wondering if these apply to tension-only braces? Although you design these members as tension-only, compression and buckling will occur in these members upon load reversal, and it might be a good idea to avoid local buckling and plastic deformation of the section to maintain tensile capacity. So I was wondering if the width-to-thickness limitations should still apply to tension-only bracing members?






RE: Tension-only Bracing and AISC 341
"Column and brace members shall meet the requirements of Section 8.2b."
It makes not distinction between compression and tension braces, so I think the answer to your question is that the braces are required to meet these requirements.
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Tension-only Bracing and AISC 341
This is in regards to a OCBF.
Requiring a minimum width thickness ratio for a tension member makes no sense to me. The system is designed to act in tension. When the the members inside of the system receive compression the will probably be slender (KL/r) an buckle globally allowing the opposite tension brace to pick up the load.
RE: Tension-only Bracing and AISC 341
"Bracing members shall meet the requirements of Section 8.2b"
in the grey commentary box immediately below it says:
User note: Bracing members that are designed as tension only (that is, neglecting their strength in compression) are not appropriate for K, V and inverted-V configurations. Such braces may be used in other configuration and are not required to satisfy this provision. Such members may include slender angles, plate or cable bracing, which are not excluded by section 6.1.
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Tension-only Bracing and AISC 341
Other than that, I would think it would be permitted to use tension only braces. And, I wouldn't think the element slenderness restrictions would apply because they are not designed to take compression.
Another way to look at is do these braces experience damage when subject to compression? And, does that damage them badly enough that their tension capacity could be compromised when load reversal occurs? If the answer is no, then you can use them. If you think the answer is yes, then you probably shouldn't use them.
RE: Tension-only Bracing and AISC 341
Look at what type of members you're using (are they HSS or pipes?) and look at the testing and see how many cycles you get out of non-compact members. While the code doesn't require it, you may want more cycles out of your system than the testing would indicate for non-compact elements.
I'm only familiar with the testing for HSS and pipes, but I personally wouldn't want to use slender members just because you may get less than 10 cycles with them. Wide flange sections and angles likely have better performance due to no cold rolling.
Something to think about.
RE: Tension-only Bracing and AISC 341
RE: Tension-only Bracing and AISC 341
If you are that concerned about it then just make the members in tension comply with the b/t ratio's of table D1.1.