single equal angle bending with tip in tension - ASD
single equal angle bending with tip in tension - ASD
(OP)
Hi,
I need help understanding the specification for single angle bending in the ASD.
The ASD section 5.2.2 says that for an unbraced equal angle with the tip of the leg in tension, that "Fb is determined only by section 5.1.2".
5.1.2 indicates Fb=0.66Fy.
Does this mean that we do not need to check for lateral torsional buckling whenever the tip is in tension??
Is the reason for this the fact that the tip of the angle in tension will ALLWAYS reach 0.66Fy before buckling of the compression leg will occur??
I need help understanding the specification for single angle bending in the ASD.
The ASD section 5.2.2 says that for an unbraced equal angle with the tip of the leg in tension, that "Fb is determined only by section 5.1.2".
5.1.2 indicates Fb=0.66Fy.
Does this mean that we do not need to check for lateral torsional buckling whenever the tip is in tension??
Is the reason for this the fact that the tip of the angle in tension will ALLWAYS reach 0.66Fy before buckling of the compression leg will occur??






RE: single equal angle bending with tip in tension - ASD
From my interpretation of the code, and from my experience I would say that you can't have lateral torsional buckling when the tip is in tension IF you are braced to resist lateral torsional buckling of the section itself. Note that the member must have lateral torsional restraint to use the geometric axis procedure. If you do not have restraint to resist lateral torsional buckling then you should design the member using the principle axis procedure. This accounts for the tendacy of the member to translate out of plane. See section 5.2.2 and 5.3. Section 5.2.1 defines the limitations which must be met for the procedure of 5.2.2 to be used.
RE: single equal angle bending with tip in tension - ASD
Here's my logic:
1. I agree that 5.2.1 sets the conditions for two situations:
Paragraph a) is where the angle has LTB restraint along its length. If it does, then it permits you to use geometric axis method and you can then follow 5.1.1 and 5.1.2 to get the allowable stress.
Paragraph b) is where equal leg angles have a LTB restraint at the point of maximum moment. If this is true, then it also allows geometric axis design AND requires you to use 5.2.2b.
2. Now if you have equal or unequal legs - and you do not meet 5.2.1 a or b, then you still can use 5.2.2 - this is seen by the phrase "Equal leg angle members WITHOUT lateral-torsional restraint subjected to flexure...". Here you do not have continuous LTB restraint OR LTB restraint at the point of max. moment...yet it includes this condition in 5.2.2...
3. With 5.2.2, then, you must increase the fb by 25% (which is not required by 5.2.1) and you must use 5.2.2b.
RE: single equal angle bending with tip in tension - ASD
I think after reading the section again you are right although I have never designed an angle this way. I agree with what you are saying, but I have always felt that if the angle did not at least have resistance to lateral buckling at the maximum moment point that you are better off to design it using the principle axis method. While this is more involved, it is more accurate. I must say though, that 90% of the single angles I design are braced so it generally isn't as much of a problem for me. I do have to say that the code seems to be a little fuzzy in this section about when to do what, etc. Note that 5.2.3 states that unequal leg angles without lateral restraint must be designed using the principle axis procedure.
RE: single equal angle bending with tip in tension - ASD
RE: single equal angle bending with tip in tension - ASD
The end sentance in 5.2.2b states that "When the leg tips are in tension, Fb is determined ONLY by sect. 5.1.2" i.e. Fb=0.66Fy. This suggests that without LT restraint, and for the tip in tension, the allowable stress is 0.66Fy with no regard to LTB???
RE: single equal angle bending with tip in tension - ASD
RE: single equal angle bending with tip in tension - ASD
and I'd add that yes, it says that Fb is ONLY determined by 5.1.2. That is correct - but - that is dealing ONLY with the allowable stress Fb....not fb which is the actual stress.
The paragraph above in 5.2.2.a tells you what to do with the actual stress fb. Keep them separate in your mind.
RE: single equal angle bending with tip in tension - ASD
Read the whole 5.2 section. If you meet all the requirements then yes you use 0.66Fy as it states. It's not a matter of reading the one sentence that statement is in. You have to meet all the previously stated conditions in that paragraph as well.
RE: single equal angle bending with tip in tension - ASD
Tweedledee
RE: single equal angle bending with tip in tension - ASD
RE: single equal angle bending with tip in tension - ASD