Blodgett's vs. AISC Steel Manual
Blodgett's vs. AISC Steel Manual
(OP)
I was wondering if someone could take a look at these simple calcs and offer advice regarding my approach on weld sizing. I use Blodgett's handbook and use the weld line method and then I use AISC fillet weld capacity and get different answers. I suppose that's due to the way I couple the moment and only count on top weld for the tension.
Thoughts?
Thoughts?
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
edit: is the cantilever plate 4" thick or 1/2" thick?
I'm making a thing: www.thestructuraltoolbox.com
(It's no Kootware and it will probably break but it's alive!)
RE: Blodgett's vs. AISC Steel Manual
I'll take the recommendations and go about this another way.
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
Two problems I see otherwise: you're not considering shear and you're acting like you'll have a full 4" of fillet weld top and bottom. You won't. There's a curvature at the corners of those tubes and you lose quite a bit. Especially something as thick as 1/2" wall HSS. You actually can't count on much of anything for that - you'll essentially have a pipe. (Check out the dimensions in the Square HSS table in the steel manual - workable flat.)
You can use Blodgett's analysis equations - once you fix your 2" and 4" mixup, you'll see that it gives you the same demand on the weld. And once you get the demand on the weld, you can use the current AISC equations to size it. Just be mindful of the actual shape and the combined shear stress from bending, tension, direct shear, and compression if the weld is transferring the compression (usually best to assume it is unless you're detailing it otherwise).
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
So let's assume you do have a 4" fillet weld and ignore shear for the sake of this calculation... why would the moment be divided by 4"? I suppose I assume the moment would act in the center of the weld group which would cause a 2" moment arm (fillet's on top/bottom of 4" hss). Or is this the long way of doing this?
RE: Blodgett's vs. AISC Steel Manual
I think I saw in another post you're only a couple years out of school. Do not underestimate the power of a free body diagram. Our work is fundamentally simple if you can break down the more complex stuff into those basic "easy" tasks. Statics is as important in this as it was your first semester of engineering courses. More so when you consider this could keep something from crushing somebody.
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
I got ahead of myself on that. Thanks for everyone's help...
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
No worries. It's easy to do. There's certainly a temptation to take shortcuts after a while...but it's amazing how many of my own errors I've caught that were nothing more than not doing a proper FBD, not writing out units in my calcs, etc.
RE: Blodgett's vs. AISC Steel Manual
Allowable Weld Stress:
fall = 0.6 Fexx / Ω = 0.6 * (70,000 psi) / 2 = 21,000 psi
Allowable Weld Stress w/ Throat Thickness Adjustment:
fall * 0.707 = (21,000 psi) * 0.707 = 14,847 psi
Blodgett:
w = (3,562 lb/in) / (14,847 psi) = 0.24 in
AISC:
(57 in-kip) / 4 in = (0.928 kip/in) D (4 in)
D = 3.84 sixteenths = 0.24 in
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RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
I get it. You had a welder (or, more likely, a bad contractor's friend who picked up a welding machine at a yard sale) botch a job. But could you paint with a wider brush? Yikes.
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
RE: Blodgett's vs. AISC Steel Manual
I agree, the problem with the picture above is the supervision, not the so-called welder. Whoever let that guy perform structural welds without assessing his capabilities upfront, should be fired. The "welder" simply shouldn't have been hired for this job.
RE: Blodgett's vs. AISC Steel Manual
When you load fillet welds transversely like the OP's sketch you lose ductility, which makes the connection even more critical. I would personally modify the detail to have some more redundancy or ductility.
RE: Blodgett's vs. AISC Steel Manual
"...a certain percentage which is 100% true".
Boy howdy, that is some serious obfuscation/double speak. This is what happens when hasty generalizations are called out and someone isn't willing to own up to it.
"Ya'll need to hang out more with the people who build the structures, I was one of them."
Translation: his anecdotes are bigger than everyone else's combined, so here is an ad hominem to get everyone to go away.
"It's a real problem which must be accounted for with realistic expectations."
"Of course drug and alcohol addiction are high amongst construction workers (there is mental health data that supports it), and it would be nice to reduce it. However, you were making a weird claim about the likeness of a welder to be a meth addict. Oddly specific that encourages people to think "likely a meth addict" when they come across a welder rather than just assess the situation at hand and give people you don't know a charitable starting point. Back in the office... when designing a welded joint, there are reasonable ways to evaluate the risk of the joint that can certainly include the difficulty of field conditions, redundancy/plastic redistribution, % sustained loading, ductility, etc. Oversizing a joint to some degree from theoretical vectors/magnitudes is a normal practice when determined with care. Randomly increasing weld sizes and lengths while dreaming the imagery of a stereotypical movie/tv show meth addict is not one of them.
"I have nothing against welders, however you must be prepared for when the bad ones show up, which happens to everyone at some point."
First, if you have nothing against welders, you would own up to the generalization and implication of your words. Second, when I am called out to the field to address poor welding, there is literally ZERO value in maintaining the presumption of the welder, who I don't know, quite possibly being a meth addict. And, "must be prepared", is an absurd retort to no one in this thread downplaying the need to be prepared to fix improper weld joints.
-Mac