Crank Beam End Load Calculation
Crank Beam End Load Calculation
(OP)
Hi All,
I need to calculate the forces for a Steel Cranked(Bent) Beam and was wondering if anyone knew of any good books that illustrate this well with example caluclations?
Even better; if anyone knows how I should go about doing this, would be very much appreciated. I've attached the CAD file for the drawing if this helps, and the connection in question is the top joint of the crank beam.
Many Thanks
I need to calculate the forces for a Steel Cranked(Bent) Beam and was wondering if anyone knew of any good books that illustrate this well with example caluclations?
Even better; if anyone knows how I should go about doing this, would be very much appreciated. I've attached the CAD file for the drawing if this helps, and the connection in question is the top joint of the crank beam.
Many Thanks






RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
Doing it by hand is not very difficult either. If the base of column is considered to be pinned and the left end of the beam is a roller, the structure is statically determinate, so all forces may be calculated from statics.
If support conditions are other than pin-roller, you should treat it as an indeterminate structure and solve in the usual way.
BA
RE: Crank Beam End Load Calculation
Thanks BA, what I really need is know how to design a connection for this joint, rather than its loads. Sorry, I didn't make this clear in my post.
Regards
Aaron
RE: Crank Beam End Load Calculation
Resolve the tensile force in the bottom flange each side of the splice into a tensile force in the stiffeners. It will precisely balance the tensile force resolved from the two compression forces from the top flange.
In other words, the stiffener provides a method of achieving equilibrium at the splice.
BA
RE: Crank Beam End Load Calculation
Please provide sketch :)
RE: Crank Beam End Load Calculation
it looked as though it was welded all round, no?
is this to be fabricated on site ??
RE: Crank Beam End Load Calculation
http://usa.autodesk.com/design-review/
RE: Crank Beam End Load Calculation
I attach a portion of the OP's drawing on which I have added a vector diagram showing how the forces react at Node A. T is the tension in the bottom flange and F is the force in the stiffener plates which run from Node A to Node B.
BA
RE: Crank Beam End Load Calculation
I guess I get a similar result.
If I draw a FDB at the joint with the forces in the compression and tension flanges at the joint along with the shears in the beams at he joint I wind up with what amounts to axial load in the stiffener plate. Make sense?
RE: Crank Beam End Load Calculation
BA
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
The beam web is capable of supplying some tension, but it is concentrated at the middle of the flanges. The outer regions of the flanges need stiffeners to hold them normal to the web.
BA
RE: Crank Beam End Load Calculation
I guess I at least had the FDB right [no smiley]
I can see how the plate has a tension resulting from the tension and compression flanges and I guess the shear at the node exacerbates this tension.
RE: Crank Beam End Load Calculation
I'm retiring.
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
I agree with what BA is suggesting, and will try to explain it a slightly different way. In a joint like the top joint which BA has so conveniently labeled in a flagrant self promotional way, the subliminal B & A didn't get by me..., the flange forces tend to try to cause the flanges to curl if the flgs. are wide enough, from web to flange tip, bf/2, and furthermore the total bot. flg. tension component "F" tends to pull the flanges way from the web and the total upper flg. compression component "F" tends to push the flgs. away from the web. The easiest way to counteract these forces and actions is with the diag. stiffeners BA suggests. These forces put the web in tension, so it's not a web buckling problem here, but rather a flange to web attachment problem over and above the std. shear flow calc. for the web to flg. fillet welds. Sometimes I'd partially bevel the webs for about 12" either side of the jnt. and fill that as a partial pen. weld at the joint, then just weld my std. fillets btwn. the web and the flg. right over that bevel weld. These corners usually involved some radius not a sharp direction change. The tension flg. would likely be welded full pen. and the web and comp. flg. might only be partial pen. welds.
The lower jnt. does have a web buckling potential because of exactly the opposite orientation of these same type flg. forces, thus the need for a several stiffeners there. At this jnt. these flg. forces tend to push (inner flg.) or pull (outer flg.) the flgs. into the web, putting the web in compression. So the web to flg. welds may still have this additional stress component over and above the std. shear flow which must be accounted for.
RE: Crank Beam End Load Calculation
Thanks to everyone else who has put their input into this.
Best regards
Aaron
RE: Crank Beam End Load Calculation
and that the bending loads would have stayed in the caps;
and that the big question is axial load along the cranked beam,
causing bending at the crank.
i'd still draw a full FBD to understand the internal loads.
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
Is this what we are all talking about (see sketch)?
I didn't follow all of dhengr's post, over my head I guess, so I may be missing some finer points.
As my fellow ACC'er BA has noted, the plate will be in compression when the moments are reversed. The bottom plates will push against each other forcing the flanges up, and the tension top flanges will pull each other down.
Great thread. Hardly ever have had to design one of these but now I know.
What about sizing the plates? 1/2" PL and call it done? Depending on the moment, angle between the beams, etc., the plate would be sized to resist the resultant perp. forces at the flanges?
RE: Crank Beam End Load Calculation
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It doesn't take a lot of time to design the plates for the forces calculated and that is what I would be inclined to do, but maybe 3/8" or 1/2" would be a reasonable minimum thickness.
BA
RE: Crank Beam End Load Calculation
I was a bit confused myself....the last time this thread came up, I was also confused.
I kept doubting myself as far as the FDB at the joint. Butm I basically had what you have...except I tossed in the shears also.
I have actually design a few cranked beams, but I never put the end-plate-stiffener in. I am not goign to lose sleep over it as they were years back and under the supervision of some good engineers.
The one large one I did design was bolted to the tops of two columns and cantilevered over one side up to a ridge and then back down to another column. The forces at the joint were so low I think I just called for a CJP weld and that was it.
Looking back, that was probably stupid as the end plate will (in my opinion) make fabricating the beam much easier and maybe make it possible to just use fillet welds. so, it is probably cheaper too.
RE: Crank Beam End Load Calculation
BA is probably trying to figure out what an "ACC'er" is, and how he came to be one.
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
Toad- I'm with you, I know I have designed one or two of them, and I cannot say I considered this. I also can rest easy at night because it was part of a moment frame that was mainly for wind and we used CJP welds all around. I think we may have considered end plates but the forces and architectural restraints would not have allowed that. It was also very much deflection and drift controlled design so I don't think the moment was all that bad.
Hokie- I was crediting you with pointing out the force reversal with a moment reversal. BA gets the credit for the original FBD. And we all get credit for learning something today, and for that, I am going to go get a beer and tip it to you guys.
On second thought, maybe Hokie and BA were just teaching and not learning.... :)
RE: Crank Beam End Load Calculation
I know BA gave me the confidence to do it, but I want full credit, Okay?
ToadJones (Structural)
29 Mar 11 22:12
BA-
I guess I get a similar result.
If I draw a FDB at the joint with the forces in the compression and tension flanges at the joint along with the shears in the beams at he joint I wind up with what amounts to axial load in the stiffener plate. Make sense?
BAretired (Structural)
29 Mar 11 22:26
Yup!
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
I love IPAs, but for some reason a little Irish Whisky on the rocks with a splash of water is what I selected for tonight's nightcap.
Been struggling with this project that has an L-shaped diaphragm with extra architectural funkiness added in to just give me a headache. Drag struts? Drag struts? We sittin here talkin 'bout drag struts?
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
My comment about a curve as opposed to the sharp transition had to do with the fact that I saw this problem often on curved members with a radius to the inner flange "r" and a radius to the outer flange of "r + member depth". And, the normal weld btwn. the flg. and the web which carries VQ/I shear flow, now also has a radial stress component perpendicular to the flg., and the weld must take both of these, or stiffeners must be used. This radial force component either pushes the flgs. into the web (BA's lower jnt.) or pulls the flgs. away from the web (BA's upper jnt.). This same phenomenon happens at the haunch in a laminated wood, three hinged arch, and shows itself as higher horiz. shear stress and a radial component perpendicular to the lams, and that radial stress must be limited or it'll pull the lams apart, in tension perpendicular to the grain.
RE: Crank Beam End Load Calculation
Toad...you get full credit for the FBD (and the FDB).
dhengr, it really was not flagrant self promotion...simply a standard way of referring to...oh, to heck with it, I think I'll join Toad in an IAP...API...AIP...whatever.
BA
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
a2mfk said it about you, but meant it for me. ACC is the Atlantic Coast Conference. His school, Florida State, and mine, Virginia Tech, are members of that conference and friendly (sometimes) rivals in sporting activities.
RE: Crank Beam End Load Calculation
Anyone have any questions for me?
RE: Crank Beam End Load Calculation
I'm retiring."
Now he wants the full patent rights on FBD's and FDB's too, and he thinks since BA said "Yup!," he must have invented them and has the right to them, we owe it to him. These whiz kids are gettin out of control.
BA.... I wouldn't have complained nearly as much if you had labeled those nodes D & H.
RE: Crank Beam End Load Calculation
The part that they left out is that the best conference is the Big Ten, Go Buckeyes!
RE: Crank Beam End Load Calculation
I would take exception to your last comment, but you made the comment, so I rejected it out-of-hand.
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
Thanks for clearing that up. I'm honored to be an ACC'er.
Toad,
I have a question for you. In fifty words or less, what is so great about IPA?
dhengr,
Please desist from referencing "BA's lower joint".
BA
RE: Crank Beam End Load Calculation
I like India Pale Ales because I like hops and beers that have a lot of hops. I find it a bit of an acquired taste. IPAs allows me to feel like I know as much as dhengr.
RE: Crank Beam End Load Calculation
"D and H" would have seemed arbitrary. I could have labelled them "1 and 2".
BA
RE: Crank Beam End Load Calculation
BA
RE: Crank Beam End Load Calculation
I'm retiring.", he was indeed referring to retiring to his quarters to rest after having worked nearly 16 hrs that day in the office, in the field and including some travel.
Let the court also know that ToadJones has a penchant for self deprecation and may not be as green as dhengr is wise.
RE: Crank Beam End Load Calculation
BA
RE: Crank Beam End Load Calculation
I think the reason why this is not normally a cause for failure is because most cranked beams are upsized for deflection and the web does restrain the inner portion of the flanges against this.
Anyway I am jealous that you guys over there have real hoppy IPA, over here in the country that invented them they have forgotten what one is and the IPAs are often the least hoppy of the lot.
Anyway have a Lagunitas Censored ale or IPA for me (but only for the brave!)
RE: Crank Beam End Load Calculation
Treogs- Nugget Nectar - maybe the best beer of all time IMO.
Sierra Nevada- Torpedo
Stone IPA
Stone Arrogant Bastard
Stone Double Bastard
Sam Adams Latitude 48 is actually a pretty damn good IPA
Of course, American IPA's are traditionally more hoppy than English and most of those listed above are Double IPAs
RE: Crank Beam End Load Calculation
BA- Aren't you Canadian, and you don't like beer, huh? Well, my one Canadian friend doesn't drink it either, and man do we bust his chops about it. Since he drinks girl drinks instead that is...
You mean besides being a little taste of heaven, what's so good about IPAs? Some would say the higher alcohol percentage, but those comments are usually made by amateurs and college kids. They awaken your taste buds, are very hoppy (some may say floral) in flavor, and have a crisp finish. Compared to most beer they are a splash of cold water in your face, and definitely may be bitter to some. They go well with certain foods, especially ones with some spice, and go well with any weather and can be refreshing on a hot Florida day. They are not for everyone, definitely not the faint of heart. IPAs are a love or hate thing for most people.
The "pale" comes from pale malts used to brew it, and "India" from the fact this kind of beer was widely exported to the British Indian Colony. Now I have read several times the extra alcohol and hops were originally intended to help the beer survive its long journey from England to India, but wikipedia (FWIW) says this is a myth.
All this at 10am while I drink my coffee, maybe looking to the weekend a little to early. And I will wrap up beer talk before big brother puts an end to this non-engineering discussion.
Steel connections, oh yeah, steel connections.. Love those things. Cranked beams and stiffener plates because of the out of plane forces, got it....
RE: Crank Beam End Load Calculation
I enjoy a cold beer on a hot day. Trouble is we don't get many hot days around here. What are girl drinks?
BA
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
I had a guy rip me a new one under the order of a "man code" for drinking Corona's w/ lime on the beach one day, telling me "no fruit in beer". The same guy was drinking a "Lite" beer. Ironic as hell I thought.
Miller Lite + Man Code = 3 dollar bill.
I will say that I agree that if you mix coke with a nice bourbon like Makers Mark or Beam Black Label, well, you're an idiot!
I also never understood mixing with water.
RE: Crank Beam End Load Calculation
I couldn't open the OP'ers. sketch so I didn't know what the picture was until you posted your sketch, which I didn't think was all that anatomical, a free diagram of the body (FDB), I think Toad called it. That lower joint is sometimes called a knee, and that's what I was referring to, it is not a cantilever, a wee-knee is a completely different member, not technically a joint. But, with your misunderstanding of my turn-of-phrase you certainly get a whole new meaning to the need for stiffeners and how to attach (weld?) them. I will probably never have occasion to use that exact phrase again, but I think you should maybe run a FEA on that member (I think that means female excitation & anticipation). Your von Mises stress level may be kinda high and confusing, but you will ultimately yield. Then if you are still hard up for something to do, Google "The Stress Analysis of a Strapless Evening Gown," it's a funny read, and some of the same principles might be applied to your current problem.
Now, I'm going back to working on my 13,000 word harangue about and for new patent holders.
RE: Crank Beam End Load Calculation
A lime in your corona, an orange with your Hoegaarden, etc. to me are quite acceptable, that is just garnish, and can bring out the flavor in belgium whites and wheat beers. Frankly, there is no way I can drink that crap Corona without one, go ahead, try it sometime. Anyone talking trash about beer, whilst drinking a mass produced American beer, needs a smack.
During the summer here in Florida its always in the 90s and very humid, so if I'm doing yardwork or on a kayak trip or chilling at the beach, I go very light and cheap (yep, head for the mountains of Busch) and have even put it on ice with a lime (its about hydration too). And I'm a beer snob for the most part. My wife does make fun of that concoction though, probably because I also will put a shot of tequila in there on occasion. My yardwork output starts to tail off as the day progresses I admit...
OK, seriously, I have to stop this whole discussion. Sorry structural engineering message board guys for being so off topic. Plus I have actual work to do, but its much more fun to day dream about beer on the beach...
RE: Crank Beam End Load Calculation
BA
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation
RE: Crank Beam End Load Calculation