HELP IN BOLT CONNECTION CALCULATION

[integridadmecanica]

DEAR COLLEAGUES,

I am performing a beam stress calculation (that is used to dismount a motor wich weight is 1000 pounds).The beam is horizontally supported by 5/8" bolts in three points. I have performed calculation for the beams, i have got it the moments reaction and vertical reactions on supports.

My doubts is not in beam stress verifaction,my conceptual doubt is on Bolt stress verification, te worst case is on the cantilver part of the beam maximun span 31.5inch so the maximun moment is acting on support M=1000p*31.5inc. My question is, if the load is acting axially on the bolt but eccentric e=31.5 the stress on the bolt is always tension or the stress acting is from bending action so the S=M/W is right?
Or the bolt always is calculated as tensile stress S=Load/area?
I am attaching a ppt file to clarify my doubt
Kind regards

 

[desertfox]

Hi integridadmecanica

I have made the assumption your beam is rigid and calculated the bolt loads on that assumption, also I have taken the last bolt position to be the pivot as it appears from your drawing the beam is suspended from the bolts.
On this basis the bolt nearest to your 1000lb load is doing all the work, the second bolt will take some and your third bolt being the pivot will take none.


Personally this supporting arrangement doesn't look very safe to me, I would certainly want to see more bolts holding it up, however you give no detail of the beam etc so its difficult to comment further.
hope this helps

desertfox

 

[Lion06]

Do you have a single beam supported by three individual bolts from above?

To comment on that - the bolts
will not experimce bending. You probably want a nut above and below at the two bolts on the right since they will be in compression ( unless the beam can bear against something at the top.

The connection seems unrealistic at best. Are you going to bolt through the flange on one side of the web only? You'll have additional forces in that case.

 

[integridadmecanica]

Dear desertfox and StructuralEIT,

Thank you very much indeed. I was cleared the conceptfor meand it was how i suspected but i had some doubts regarding the beam behaviour.Yes the design is not very safe but it is the only way that there are to mount a beam inside a shelter machine. Personally i was calculated the bolt as if they were supporting the same bending moment that is calculated for the beam, but it is too much concervative.
Thanks again for your time and effort dedicate to this post.
I would like to know if you have or know some bibliografy to see this kind or bolt calculation

Regards
Fernando

 

[BAretired]

Interesting problem.

desertfox assumed the beam is rigid and rotates about a pivot point at the rightmost bolt. The strain (and stress) in each bolt is proportional to its distance from the pivot.

StructuralEIT assumed that the beam is supported on three unyielding supports.

The structure is indeterminate to the first degree, so you could remove the middle reaction, solve for the upward deflection at that point, then apply a downward load to give the same deflection. If you want to consider the bolt strain, you would need to use a vertical spring at each support.

The dashed red line in the attached sketch shows the approximate bending of the beam neglecting bolt strain. If the bolts are fixed against rotation, they will experience a combination of axial load and bending because the beam rotates at each support. If the bolts are free to rotate, they will experience only axial load. The arrows indicate the direction of the three reactions assuming unyielding supports.

BA

 

[desertfox]

Hi integridadmecanica

Have a look at this site its shows similar calculations to the one I posted earlier but scroll down till you see the title "bolts withstanding bending forces".

http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

desertfox

 

[desertfox]

Hi Again

This is a simple example of my calculation earlier it explains it better than I did.

http://www.ejsong.com/mdme/modules/7759G_Mechanical_Design/bolted_joints/bolted_joints.html

desertfox