Crank Beam End Load Calculation

[GradStructEng]

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

 

[rb1957]

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

 

[msquared48]

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

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

 

[a2mfk]

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

 

[BAretired]

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

 

[GradStructEng]

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

 

[BAretired]

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

 

[ToadJones]

BA-
Please provide sketch

 

[rb1957]

attmt opened fine for me.

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

is this to be fabricated on site ??

 

[4thorns]

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/

 

[BAretired]

Toad,

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

 

[ToadJones]

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]

Yup!

BA

 

[ToadJones]

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

 

[ToadJones]

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

 

[BAretired]

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

 

[ToadJones]

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.

 

[ToadJones]

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

 

[ToadJones]

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

 

[dhengr]

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.