Confusion with bolted connection 1

[rofloligist]

See the attachment for loading scenario. The drawing is a simple beam with fixed supports via 2 bolts at each end. Am I correct in distributing the load, F, to each of the 4 bolts as a vertical reaction force of F/4? Is there an additional shear force caused by the moment about the center of the 2 bolts at A and at B as you would see in a cantilevered bolted connection? Or does the beam take up this moment and the bolts only see the vertical load? Thanks for the help!

 

[rb1957]

V/4 is good enough

yes, there'd be some sheardue to moment couples at the ends. The maximum end moment would be for the fully fixed case, VL/8, so the shear would be VL/8H.

Quando Omni Flunkus Moritati

 

[rofloligist]

Does this moment occur between bolts 1&2 and between 3&4? If I am correct, wouldn't this shear load from the moment would be FL/(8H/2) at each bolt as opposed to FL/8H? Thanks for all the help!

 

[rb1957]

moment VL/8 at each (both) end

Quando Omni Flunkus Moritati

 

[rofloligist]

I realize the moment is at both ends, but because the moment occurs between the bolts 1&2 wouldn't the moment arm be H/2 for each of the bolts. This is a much simpler version of the design I am analyzing and want to make sure I have the fundamentals down.

 

[rb1957]

the couple is between the bolts, a force acting over a distance.

take moments about one bolt ... M = P*H; or take moments about the middle ... M = P*H/2+(-P)*(-H/2) = P*H

Quando Omni Flunkus Moritati

 

[rofloligist]

Thanks rb, the second formula you posted was what I thought it was and it has clarified everything. The overall shear at each bolt would then be: Fshear = F/4 + M/H which could be combined using Pythagorean to find the resultant shear.

 

[rb1957]

"vector sum" is the expression i use

Quando Omni Flunkus Moritati

 

[rofloligist]

haha I was looking for a way to put it as I forgot the correct terminology

 

[kingnero]

In the expression M = VL/8 , does V equal to F or to F/2 ?

 

[rb1957]

V = F, the applied load

Quando Omni Flunkus Moritati

 

[kingnero]

OK, thanks

 

[boyze]

This could be further interesting if you get into the tight bolt versus loose bolt scenario, ie. does friction play into this, sometimes labeled slip critical joints. And/or hole size and tolerance to bolt diameter, ie, will one of the bolts "engage" before the other at each end. For some designs these scenarios should be considered. Not sure about your case.

Have Fun!

James A. Pike

http://www.xl4sim.com

http://www.erieztechnologies.com

 

[tbuelna]

That's a common question that comes up with this sort of analysis case. How do you account for the effects of fastener/hole fits and/or clamping friction?

With a fastener pattern loaded in shear you might assume the fasteners have proper shear fits, and you would probably ignore the effects of friction. But if the fasteners have clearance fits, then you might assume the fasteners initially do not equally share the loads. And sometimes in certain applications the fasteners are designed to transfer all of the shear force through clamped friction produced by fastener preload. If the fasteners have clearance fits and are loaded in single shear, then bearing stress at the hole edges might also be a concern.

The analysis can be as simple or complex as the situation dictates. But simplified analysis approaches usually require more conservative factors of safety. The person asking the question mentioned that the analysis case they are actually considering is more complicated than what is shown in the sketch. So it might be helpful if more details were provided of the analysis requirements.