Buzzbromp
Civil/Environmental
- Jul 26, 2006
- 31
Hi,
I posted this thread a week ago and thank you for the responses.
I have a question regarding lateral torsional buckling. I have a plate that is stiffened with T-sections along its length, such that the web of the tee is welded to the plate. The plate is approximately 270 inches long and wide, with approximately 12 tees spaced 18 inches apart (approximate). The plate is about 5/8" thick, while the tee has a 5/8" thick web and a 1" thick flange. The loading is such that the plate is in tension and the flanges of the tees are in compression.
I'm analyzing this as a built up section with the plate having an effective width such that it is a compact shape. Since the web and flanges are all compact, should I consider lateral torsional buckling? Since I'm compact, local flange buckling is not an issue. I've been told that lateral torsional buckling is not an issue, because it is not an I-beam but more of a diaghram, and the diaghram will prevent the beam from having a rigid twisting deformation. I was hoping for any opinions on this.
Seemed the suggestions were to check the web as a torsional brace or treat the built up section as an independent beam and check for lateral bracing. I went with the latter, and came up with needing 2 braces. I used the compact section criteria in the 9th edition.
Now to my current question/comment.
I have been looking at another situation, rather than having a tee welded to the bulkhead, i have just plates. So essentially, there is not compression flange, and if i take an effective width of the plate, I have a built up Tee section with the stem in compression. I couldn't figure out how to apply this using the 9th edition, as comments on tee section with webs in compression is vague if not nonexistent. The 13th edition has a section on tees in flexural. These results showed that my effective tee is much stronger in LTB compared to yielding because of my very wide effective width causing relatively high weak axis moments of inertia and torsion constants. Also, treating the tee as a unstiffened compression element, like a flange of an I-section in weak axis bending, slenderness was checked to potentially reduce my yielding allowable from the Q factors of Chapter E (slender elements in compression).
Well, my comment/question is this. Results show that in general tee sections don't have issues with lateral-torsional buckling, because they typically have an Iy value greater than their Ix value, which i assume means yielding tends to control. Also, the 13th edition states that local buckling of the webs is not considered because the lateral-torsional equations also give the local buckling strength as Lb approaches zero. So I was surprised to see that this shows my plate with plate ribs only needs no lateral bracing, while using the 9th edition for my plate with tee ribs needed lateral bracing. I would think the tee ribs would be stiffer and less likely to need bracing. Either I am missing something, or I was very conservative on the tee lined plate.
Hope that made sense, thanks in advance for any comments.
This was
I posted this thread a week ago and thank you for the responses.
I have a question regarding lateral torsional buckling. I have a plate that is stiffened with T-sections along its length, such that the web of the tee is welded to the plate. The plate is approximately 270 inches long and wide, with approximately 12 tees spaced 18 inches apart (approximate). The plate is about 5/8" thick, while the tee has a 5/8" thick web and a 1" thick flange. The loading is such that the plate is in tension and the flanges of the tees are in compression.
I'm analyzing this as a built up section with the plate having an effective width such that it is a compact shape. Since the web and flanges are all compact, should I consider lateral torsional buckling? Since I'm compact, local flange buckling is not an issue. I've been told that lateral torsional buckling is not an issue, because it is not an I-beam but more of a diaghram, and the diaghram will prevent the beam from having a rigid twisting deformation. I was hoping for any opinions on this.
Seemed the suggestions were to check the web as a torsional brace or treat the built up section as an independent beam and check for lateral bracing. I went with the latter, and came up with needing 2 braces. I used the compact section criteria in the 9th edition.
Now to my current question/comment.
I have been looking at another situation, rather than having a tee welded to the bulkhead, i have just plates. So essentially, there is not compression flange, and if i take an effective width of the plate, I have a built up Tee section with the stem in compression. I couldn't figure out how to apply this using the 9th edition, as comments on tee section with webs in compression is vague if not nonexistent. The 13th edition has a section on tees in flexural. These results showed that my effective tee is much stronger in LTB compared to yielding because of my very wide effective width causing relatively high weak axis moments of inertia and torsion constants. Also, treating the tee as a unstiffened compression element, like a flange of an I-section in weak axis bending, slenderness was checked to potentially reduce my yielding allowable from the Q factors of Chapter E (slender elements in compression).
Well, my comment/question is this. Results show that in general tee sections don't have issues with lateral-torsional buckling, because they typically have an Iy value greater than their Ix value, which i assume means yielding tends to control. Also, the 13th edition states that local buckling of the webs is not considered because the lateral-torsional equations also give the local buckling strength as Lb approaches zero. So I was surprised to see that this shows my plate with plate ribs only needs no lateral bracing, while using the 9th edition for my plate with tee ribs needed lateral bracing. I would think the tee ribs would be stiffer and less likely to need bracing. Either I am missing something, or I was very conservative on the tee lined plate.
Hope that made sense, thanks in advance for any comments.
This was
