STrength of BAR 2

[Hclrag123]

Hi ALL.
I am supposed to calculate the bending stresses on the A-36 STL Beam. Please refer the attachment for the loading conditions.
1.Can this scenario be considered as a Cantilever at clamp (A) and simply supported at the Wall (B)?
2.HOw to calculate the Maximum bending stresses induced in the Beam.(what formulas to use?)

3. In order to caculate the Reactions RA and RB at points A & B, CAN I USE THE EQNS,
F1=RB-RA
∑M=0 at A, RB*y +F1*(x+y)=0.
PLease advise.

Thanks in Advance.

 

[GregLocock]

1) sort of, often I would, sometimes I wouldn't.
2) the usual.

Is this for school?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[rb1957]

1) if you think the rigidity is there.
2) no, a propped cantilever is a redundant structure and you have to analyze it as such.
3) the reactions will be different (your's are for a simply supported beam), but other than that it's "straight forward"

 

[dhengr]

It’s a “straight forward” problem once you’ve had a few courses in Engineering Mechanics and Strength of Materials, or if you have a boss or local mentor who can guide you in your development as a designer or drafter. This elementary engineering education is best done face to face rather than long distance, and from people you don’t know. Otherwise, you should probably not be doing this problem if it can harm anyone other than just you, or if it isn’t for your own educational benefit. What is the clamp really intended to do, what is the clamp’s stiffness or fixity relative to the beam’s stiffness? Does the reaction at the clamp have to be fixed as relates to beam bending, or should the beam be free to deflect and rotate at that reaction? While it is good that you provided a sketch, the way the sketch is laid out and what is shown and doesn’t show, indicates a general lack of understanding of your own problem. There is much more to this problem than just the bending stress in the beam.

 

[MiketheEngineer]

Student posts are frowned upon??

 

[chicopee]

It is a strength of material redundant problem. Rotate the drawing 180 degrees and you get a typical S.o.M. problem. The clamp is a fixed support; the wall allows no deflection but will allow rotation of the beam; the end will deflect some amount. So get a book on the subject to solve the problem.

 

[rb1957]

the RH end can be clamped ... it doesn't Have to be the LH end !

 

[Walterke]

MiketheEngineer] Student posts are frowned upon??

As far as I know they usually get deleted. I think there's something about them in the forum rules.

NX 7.5
Teamcenter 8

 

[rb1957]

they'll get deleted if someone RF's it ...
possibly someone has, and Dave "the man" is looking into it.

maybe it is a student post ... it doesn't seem to be a real world problem, it does seem to be (IMHO) a dam'd fool way to support a beam ... as shown, as understood ...

 

[Hclrag123]

HI All,
First of All,I apologise for not putting a clear problem infront of you which gave way to all these discussions. Since i was not supposed to disclose the actual problem conditions i was trying to simulate it in a simpler way but never imagined it would sound stupid.

Here is the actual Problem.The beam is actually a pipe. The wall is a die and the CLamp is circular. The pipe passes through the clamp and extends a foot after clamp.The pipe is pressed against the die and bent to some angles.

Now out of your expertise i need to know what would be the best Free body diagram for this condition and how to resolve this. I am just a new budding designer with a lot of aspirations to be succesful in this area. Since i am a contractor i cannot share the equipment details here. Any help you can provide will be great. I hope this is not a simple classroom problem.Based the Reactions and forces on the clamp, die and pipe i need to design a stronger fixture to test the equiment itself later on.
I once again apologise for any inconvenence it might have caused.

 

[rb1957]

then, no, your sketch is reasonable, your description helps.

the clamp can be fully fixed. the wall reaction can be modelled as a single pt load ... where you place it is open for discussion ... form your description i'd place it at the LH edge, closer to the "manulipating" force.

this is a propped cantilever problem. Roark has canned solutions for this geometry. this is a standard problem dealt with as a "redundant structure" or "indeterminate structure".

 

[Hclrag123]

Thanks rb1957.
But my confusion is, as the pipe starts bending the exertion point of force at the wall (Die) keeps moving from may be center towards the LH end of the Pipe.Am i correct in interpreting this?
IF yes, then how do we calculate teh stresses in that case.

 

[rb1957]

yes, i think you're right. initially there'll be some distributed force at the "wall". As the pipe bends the "wall" force will peak at the LH side; reasonably as load increases the pipe will gap against the wall, so the "wall" reaction would be a point load at the LH edge.

when do you want to recover stresses ?
1) initial setup ... pretty boring zero everywhere,
2) towards the end of the deformation ... quite likely, wall is a pt force at the LH edge,
3) somewhere inbetween, like just as the pipe begins to yield ... try a couple "wall" reactions" ...
a) pt force at the LH edge,
b) triangular disributed for over the LH 1/2,
c) ...
i don't think you should see a significant difference.

 

[dhengr]

Granted, you shouldn’t divulge proprietary material when posting, but you must give enough info. so that we understand what you are trying to do, what problems you are having or trying to solve, and where you are going with it. Write your post, then reread it, step back and ask yourself, AS IF you had never seen your details and problem before, ‘if they can’t see my equipment, if they don’t know what I’m trying to do, will they understand what I’m asking, or am I leaving out some important details?’ Can they draw only one sketch from my description, or should I reword it, so this item or that couldn’t possible be located or oriented in the wrong way? What forces, sizes, dimensions, etc. should be included for clarity? Otherwise, you leave us wanting to help, but wasting our time by having to guess what you are doing, and then giving you half-ar$$ed answers, because we can’t see what you are doing from here. There are plenty of smart people here, willing to help and give of their time, but don’t you waste their time either. They will make assumptions based on your problem description so your description must lead them to the correct assumptions. Many of the more experienced people can make many very good assumptions, quickly, based on sketch proportions, material sizes or thicknesses, etc. so you must be careful in your description or sketch not to mislead them.

My take on your problem is as follows: (1) Your die must be shaped to cradle each pipe size, a half circle in shape to match the pipe O.D. For smaller pipe sizes the die is actually a wheel with a radius which produces a bend which prevents buckling or crimping of the pipe for that dia. and various wall thicknesses. The wheel’s outer surface or rim is shaped to that pipe O.D. (2) Your lever arm “x” is a changing length as you bend the pipe around the die and depending upon how and where force “F” is applied. “x” will start at the tangent point of the pipe and die at zero force, and then start decreasing as the pipe bends. At the same time, the force required to keep bending it will be increasing, but then “F” will start decrease as the pipe starts to yield. You must also support the pipe so that it doesn’t buckle or turn to an oval in the bending process. (3) Most small pipe and bar benders have the “F” force vector applied perpendicular to the pipe at the point of its application and actually moving radially around the die wheel. Thus, “F” will be pointing at your wall at a 90° pipe bend. Thus, “x” may not change much. The force applying mechanism looks similar to the die wheel so it cradles and supports the pipe too, and “x” is a fairly small dimension to improve the pipe support situation. You can calc. the force required to start causing the pipe to yield and have a permanent bend, at the max. “x,” this should basically be the max. force req’d. After that the force req’d. should actually start dropping (at least no longer increasing) unless your system does something to radically change “x” or the way the force is applied. But, when you’ve gone to all this trouble, adding 25 or 50% to the force application system and to the entire machine to sustain these forces is not real expensive.

Google pipe bending machines and pipe bending vendors and study their web sites. You should see some of the above.

 

[Hclrag123]

Thank you dhengr. I take your advise and make sure i follow it the next time.

I agree with your points of view on this problem.

Like rb1597 mentioned i think it is a overhanging Cantilever Beam situation. I am trying to find the Roarks eqns.

I basically need to calculate the Stresses in this pipe for a given force and the distance values, die stresses and clamp stresses.

I once again thank you dhengr and rb1597.

 

[rb1957]

if you don't mind, but that's a rather odd thing to want to know, if this is a pipe-bender. as a pip-bender the point is the bend the pipe, ie plastically deform it. i'd've thought that there were tables (machinists handbook ?) of the force required to bend a pipe.

so plastic stresses are another thing you're going to have to look into. and then there a whole bunch of real world issues, like preventing the pipe from crushing itself at the radius block which'll require either careful loading or temporary support (like filling the pipe with sand, which'll change your applied forces ...

 

[Hclrag123]

THanks rb1957.
I am still unable to find the Roark's eqns. Looks like i need to buy the book. Is it avalibale Anywhere on the web?

Any formulas on top of your head to try for me.

Well, as you mentioned the pipe crushing and egging etc are all taken care. Based on the things I mentioned earlier (Stresses in the pipe,Wall and Clamp) i need to design a test Fixture to test the equipment. This test fixture should never bend and be reused but the equipment will be operated at its full specs.

 

[rb1957]

so it's the raction on the "wall"/pipe radius block that you're interested in.

google "propped cantilever", plenty of hits.

solve it for yourself (if you can).

 

[Hclrag123]

Thank you all for your time and help.
I think i solved the problem. will get back if i need any further guidance.