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Crank Beam End Load Calculation

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

 

RE: Crank Beam End Load Calculation

without meaning to sound like a "prick" ... can you draw a free body diagram ?

RE: Crank Beam End Load Calculation

Can't open the link without getting an ad, so I won't.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Crank Beam End Load Calculation

Dang it, I was dying to see this pic of a "cranked" beam. I bet a krunked beam is bent about four axes.

RE: Crank Beam End Load Calculation

There is nothing particularly unique about a cranked beam.  Using a frame program, you simply input your geometry, loads and end restraints and allow the computer to do the work.

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

(OP)
Hi BA and All,

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

The beam to sloping beam connection should have stiffener plates on the miter line, connecting the top and bottom flanges.  Use a full strength weld for the webs and flanges of the beam, then calculate the force in the stiffener plates by resolving the equilibrium condition at the node.

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

BA-
Please provide sketch :)  

RE: Crank Beam End Load Calculation

attmt opened fine for me.

it looked as though it was welded all round, no?

is this to be fabricated on site ??

RE: Crank Beam End Load Calculation

If you can't open this kind of file check the link below. Design Review is provided by Autodesk free of charge to be able to view, measure, redline etc. files such as this .dwf created (I assume) in AutoCad. It's pretty handy.

http://usa.autodesk.com/design-review/

RE: Crank Beam End Load Calculation

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?  

RE: Crank Beam End Load Calculation

Yup!

BA

RE: Crank Beam End Load Calculation

I drew it about 10 times and it still does not intuitively make sense to me....should I find another profession?  

RE: Crank Beam End Load Calculation

If the joint were just a full pen weld, what benefit does the stiffener add? Does the stiffener help with compression flange buckling?  

RE: Crank Beam End Load Calculation

If you think about the flanges of the beam as chords of a truss, then a tension member is needed between Nodes A and B.  

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

Well state BA- I like the truss analogy.
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

....cant even emoticon right.
I'm retiring.  

RE: Crank Beam End Load Calculation

one more thought....adding the "end plate" probably actually makes the welding easier.  

RE: Crank Beam End Load Calculation

Toad:

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

(OP)
Many many thanks BA. This has helped me alot. I appreciate that you have answered both my questions and were able to stay cool with my lack of knowledge in this area.

Thanks to everyone else who has put their input into this.

Best regards

Aaron

RE: Crank Beam End Load Calculation

i'd've thought that the web shear would have stayed in the web,
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

Just one amendment to the problem which BA has solved...the diagonal stiffener is in tension if the joint is opening, but in compression if the joint is closing.

RE: Crank Beam End Load Calculation

I am embarrassed to say that I was a bit confused until I sketched this out myself. And in 13 years of being a structural engineer doing plenty of steel design, I don't think I have ever heard of the term "cranked" beam. The last part I feel the weirdest about. Sounds so red-necky and made up.

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

I agree that when the moment is reversed, the stiffener plates are in compression.  It is usual to use a single stiffener each side of the web as seen in this link:

http://www.pacificcomputing.com/pdf/v14_CrankedBeam41.pdf

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

a2mfk-
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

a2mfk,
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

If you extend the thoughts in this thread to concrete, the difficulties of making efficient corner joints in reinforced concrete structures becomes apparent, but then we have discussed that a lot.

RE: Crank Beam End Load Calculation

Wow, just had a real "duh" moment after looking at that Tekla image. Since these types of connections are usually part of PEMB, and I have never worked for one of those companies, I never have given the end plates in those locations much thought. I had always assumed that was just part of the ease of shipping and erection, to do it all bolted with an end plate. But now I can see it also served the purpose of stiffening those out-of-plane surfaces.

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 am unilaterally taking credit for the FBD.
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

speaking of beer, IPA time?

RE: Crank Beam End Load Calculation

Gotta do the work, son! Did you break into BA's account to post that sketch?

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

A2mfk- sounds like you need a little practice...we talkin bout practice, its practice man, we talkin bout practice?  

RE: Crank Beam End Load Calculation

Hokie's terminology for the joints is a good way to describe this.  If the moments on the jnt. tend to increase the angle btwn. the two members (the jnt. is opening) and the web forces or stiffener forces will be in tension.  That's the top jnt. in BA's sketch from his post 29MAR11, 18:56.  And, that's a2mfk's sketch also, which was exactly what I was trying to describe, except I would use only one stiffener on each side, right at the miter line.  If the moments on the jnt. tend to decrease the angle btwn. the two members (the jnt. is closing) and the web forces or stiffener forces will be in compression.  They might cause web buckling which must be accounted for.  That's the lower jnt. in BA's sketch.  The flg. forces, basically (flg. area)(the avg. flg. stress) = T, in BA's sketch and are concentrated at that sharp transition and act akin to a point load, F, and cause a heck of a tensile stress concentration or causing web crippling just as a heavy, narrow point load on a top flg. of a beam must have stiffeners under it to prevent web crippling.

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

What is an ACC'er and how did I become one?  Is there a cure?

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

Free Diagram of the Body.  

RE: Crank Beam End Load Calculation

BA,
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

Now I'm feeling good and I'm looking for extra credit.
Anyone have any questions for me?
 

RE: Crank Beam End Load Calculation

Hell, on 29MAR11, 23:53, Toad was going to retire out of frustration, he said, "cant even emoticon right.
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. smile

BA....   I wouldn't have complained nearly as much if you had labeled those nodes D & H.

 

RE: Crank Beam End Load Calculation

BA-
The part that they left out is that the best conference is the Big Ten, Go Buckeyes!

RE: Crank Beam End Load Calculation

dhengr-
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

Just kidding Dhengr, don't get all pissy on me and post a 13,000 word ranting dissertation bigsmile  

RE: Crank Beam End Load Calculation

hokie,
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

IPA-
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

dhengr,

"D and H" would have seemed arbitrary.  I could have labelled them "1 and 2".

BA

RE: Crank Beam End Load Calculation

I wonder if the local liquor store carries India Pale Ale.  I shall inquire tomorrow.

BA

RE: Crank Beam End Load Calculation

Let the it be known to the court of dhengr that when Toad Jones, on the night of 29MAR11, at 23:53, said he was going to retire out of frustration, as he said, "cant even emoticon right.
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

Let the court know further that ToadJones has partaken of several IPA's and has retired for the night.  See y'all in the morning.

BA

RE: Crank Beam End Load Calculation

I have had extensive arguments on this with experienced engineers who simply just could not see it.

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

csd- Order all of the following:

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

Toad- I knew you were an OK guy, with that beer list you surely cannot be too bad...

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

a2mfk,

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

My buddy is a man's man for the most part, but loves vanilla vodka and coke. Tastes like candy. In general, my man code goes drinks should have no more than 3 ingredients, no slices of fruit or umbrellas on the edge of the glass, and nothing pink-colored. Don't order top shelf scotch or bourbon if you are going to mix it with anything but a splash of water or tonic to bring out the flavor, otherwise that is a waste of money.

RE: Crank Beam End Load Calculation

I think "man codes" are as fruity as the drinks they admonish.

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

BA...

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

Toad- beer is not a girl drink, I meant fru-fru mixed cocktails, you know the ones...

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

Personally, I think all of you guys need more to do.  I'm glad I'm not paying your salaries.

BA

RE: Crank Beam End Load Calculation

BA, rest easy, I type fast and don't bill for this crap...

RE: Crank Beam End Load Calculation

There are times I wish someone paid my salary

RE: Crank Beam End Load Calculation

We should pull a salary for our awesome contributions to this forum :)

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