BOLT DESIGN AND DIMENSIONING 1

[tiasimo]

CAN ANYONE GIVE ME A HINT WHER TO FIND A PROGRAM OR A FORMULA TO CALCULATE THE NUMBER OF BOLTS AND DIMENSIONS FOR AN EXAMPLE AS THE ONE ON THE PICTURE BELOW? (its a simplification of the problem)

Thanx

 

[Lutfi]

I think this is a good link for you to start with. I am assuming that you are an engineer or have engineering background.

Regards,


Lutfi

http://www.cdeco.com

 

[Lutfi]

oops! I forgot to paste the link. Here it is:

http://hcgl.eng.ohio-state.edu/~ceg532/chap8/ch8_2.htm

Lutfi

http://www.cdeco.com

 

[dozer]

I'm having a little trouble making out those arrows in your figure. Is that two forces both acting down or is it supposed to be representing torque? It looks like vertical load acting down to me. Every thing I'm going to say from this point is assuming this is the case. Note the assumptions presented on the page that Lutfi posted. First,the gusset plate is perfectly rigid. For the type of loading you seem to be showing here I don't think this would be a good assumption, unless the plate is very thick. What's very thick? Depends on the loads.

Also, this would cause a prying action which would put the bolts in tension. I just skimmed the Ohio State page but I'm very familiar with the concept. This is for a pattern of bolts that's eccentrically loaded and resisting the applied moment by shears only in the bolts. Yes, they talk about combining shears with tension and you will need this for your case but you need to understand where this is all coming from.

Boy, the more I try to explain the more I realize this is kinda complicated. Let me just cut right to the chase and tell you my thoughts. First, I don't think the bolts furthest away from the rod will be picking up much load. You may be saying, "But that's just the opposite of what the OH page is saying!". Remember though they are assuming a rigid plate. For forces acting in the plane of the plate this is not a bad assumption, but you have forces acting normal to the plate so now the bending stiffness (bent the weak way) becomes very important. To test my theory I would do an FEA on it.

There are things to watch out for with FEA also, but I fear I've already muddied the waters too much. If I had to do this by hand I would just assume that the two columns of bolts on either side of the rod acted. Share the vertical shear evenly between these six bolts in your case and compute the tension in the top two bolts by dividing the moment produced by the load at the end of the cantilever by the vertical distance between the top row and bottom row.

Yes, it crude and it begs the question, "Then why all the other bolts?" Bear in mind I'm analyzing this connection, not designing it.

I wish I could make it simpler for you, but there is really no easy answer. If this is an important connection you really need to have a qualifed structural engineer or mechanical engineer (with knowledge in machine design, stress analysis type stuff) look at it.

Oh, and if that was supposed to be a torque on the end of that shaft, forget everything I said and use the page that Lufti gave the link for . . . unless you want to start talking about instantaneous centers.

 

[desertfox]

Hi tiasimo

From your diagram you clearly show a torsional load on the end of the rod and therefore all your bolts are in shear and are not subject to bending or prying action.
You need to find the centroid of your fixing pattern and resolve forces on each bolt. The bolts furthest away from the load will carry a greater portion of the load. Lufti's link to that site of forces on fasteners is all you need.
One word of caution though use a good safety factor, I say this because unlike rivets which completely fill the hole there put into, bolts don't and therefore you may find in practice that not all bolts are taking the shear (ie bolts that don't come into contact with the side of the hole won't take shear, these bolts generate friction forces between the two plates only).

regards desertfox

 

[dozer]

How is that clear when both arrows appear to point down?

 

[desertfox]

Hi dozer

Fair point I thought that it was just round dot didn't realise it was an arrowhead, I assumed he was indicating a couple.
However if the rod was in bending one would expect the force to be shown on top of the rod not tangential at the mid point.


regards desertfox

 

[dozer]

Hi yourself desertfox

Maybe tiasimo will reappear and clear it up for us. At any rate, Lufti's link is a good one and should be very helpful.

 

[lordrailie]

Sorry for not answering fast, but I cannot login with my normal user, so I had to make a New one.

Thanx anyway

to clarify the problem...

I simplyfied the problem to a 1 downward load of 20 tons, assuming that my rod is completely rigid. See underneath the real problem so you can understand the problem.

 

[lordrailie]

?