Thanks steveh, it's part of an SMath program. I had used the approx values in the and the values are about 20% different than the values generated by a steel design program, and I was wondering if there is an easy more precise way. I had some time on my hands and was just putting some finishing touches on it. The output was from a module for calculating section properties for 'odd' sections using SSteel. I had used part of the info in the previoius thread to calculate the Cw coef, treating it as a rectangular HSS.
Another thing with SMath, I'm putting more and more stuff off the page, including partial calculations. They don't show up in the printed copy, but are there to use for writing and checking the program. Also reference material.
For the Torsional and Warping properties it's pretty much always a finite element solution (as far as I've been able to find in my research on the topic) Link Link
Thanks Celt... I was afraid that it was something like that, but was hoping for a 'solution'. I don't think that for most design that it makes much difference. I was just wanting my program to be more 'precise'.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
Yeah I always dead end there because my knowledge on the FEM side isn't up to snuff to move beyond knowing it's needed. I've slowly been trying to teach myself FEM, which I found lead me to realize I needed a full refresh on linear algebra as well as framed structure matrix methods before I could get into the "fun" plate elements.
I just like when I write a program that it is as 'correct' as possible, since I'm putting the effort into it, in the first place. Will have to leave the coef as approximate for now. Posted for anyone to use... I have about a dozen of the Properties programs.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
It's good to see the Northwoods logo on some new product dik. Have you had a chance to tinker with SMath's combobox extension? Or their option to save worksheets as exe files?
Thanks Koot... If I have a project where I'll likely have more than 2 or 3 of that type, I generally do an SMath program. I'm always developing new programs for it; I get bored when I don't have something tekkie to play with.
I've taken a quick peek at their combo box extension and it's OK. Not overly useful yet and I haven't looked at the *.exe generator at all, but I will. I wish SMath had a feature like Excel's VLookup function. I use it often for spreadsheet type data.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
Torsional warping will not be an issue for this type of section. There is probably a way to calculate it though. Maybe get ahold of Walter Pilkey's "Stress, Strain and Structural Matrices". That's the reference I used to use for weird things like this. Unfortunately, I don't have a copy of this book anymore.
When I took an aerospace engineering class there was a formula for the torsional constant of closed multi-celled beam sections. I don't have the notes from this class (taken 25+ years ago).
Thankfully, a quick google search came up with some references that look right to me:
The assumption is thin cells. But, I believe that's valid for your case. Even it it was a concrete box girder bridge, I think it would be appropriate. You'd have to get much thicker relative to the cell size for the assumption to no longer be valid.
I've provided some templates for section properties python package for various typical methods of strengthening if anyone's interested. Should get you started without needing to know python.
Note read the whole thing starting from part one as I make some insightful discoveries along the way like some aspects like intermittent welding of the plates means you don't actually have a closed box....!
I've revised the graphics file in the SMath program... just noticed that the second weld was a little tricky. Just updated the SMath file... It won't let me upload the new file.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
I make some insightful discoveries along the way like some aspects like intermittent welding of the plates means you don't actually have a closed box....!
I believe that statement, and its counterpart on your blog, to be fundamentally incorrect. See this thread around the location of the two sketches shown below (mine & Blodgetts).
I don't disagree the properties may be increased. But what's the real value, somewhere in between the two extremes but not the full theoretical value with intimate contact/connection.
I don't disagree the properties may be increased. But what's the real value, somewhere in between the two extremes but not the full theoretical value with intimate contact/connection.
I believe that the real value for any reasonable stitch welding pattern would be so close to the value for continuous welding as to make no practical difference. It's a bit like integrating an M/EI curve for deflection and having a 1/8" of your beam length somewhere along the way with with a reduced moment of inertia: it makes no real difference because the integration over that segment has a negligible impact on the total.
I feel that you're statement about "not actually having a box" when stitch welding is used is misleading without some manner of qualification. In all of the ways that would normally matter to a structural engineer, I believe that you would still have a box. Good engineers don't commonly fail to account for this (your blog) because they're ignorant of the impact. Rather, they don't account for it because they recognize that the impact doesn't warrant accounting for.
A great many welded, built up sections are assembled using stitch welding. If one truly cannot rely on those assemblies behaving compositely for torsion and lateral torsional buckling, the world has a lot of potential problems on it's hands.
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