Failure of bolt vs pin in combined stress

[HungryDinosaur_imported]

Hi All,

Good day. Will a preloaded bolt only fail in shear or tensile stress, or combination of both? Or can it fail in bending as well?

In comparison, a pin can fail in shear, tensile or bending loads, or combination of all three loads.

Is there any literature or standard which states these differences or provides recommended practices to calculate these failures? I have a pin with 3 loads acting on it in all 3 axis. So what will be a good practice to calculate the failure? See attached. Any link to a reference standard or literature will be appreciated (ISO, AISC etc).

Regards,

HD

 

[human909]

This almost sounds like an abstract student homework problem, is it? This isn't really the forum for that, but at least own up to it if you are. If it isn't I apologise, either way you picture doesn't really explain anything and you should elaborate.

But given I'm posting I'll quickly answer. Pretty much anything can fail in any manner if you try hard enough. A bolt generally doesn't fail in bending as you generally won't be loading it in that manner. A pin generally wont have significant axial restraint so it hopefully won't be loaded or failing in tension. Again bending depends on the configuration, generally it will have some bending stress but shear will be the significant design parameter.

P.S. On a side note;

I'm currently looking into a pinned connection design for a modular truss. Think similar to a tower crane but smaller. Does anybody have any experience or references that I need to look at? Strength design isn't a challenge, I'm more after designing appropriate tolerances for firm fitting while still maintaining easy errection and dissasembly.

(Photo from a Seattle tower crane that collapsed, because they removed the pins. Surprisingly hard to find photos of these pinned connections online!)

 

[klaus.]

Eurocode tells you how to design pin connection

 

[HTURKAK]

Is the modular truss 3D ? In case of tubular structure, you can use the same concept like tower cranes.. You may use solid rectangular insert elements. In past, I designed Warren type roof truss with rectangular hollow sections and each truss was two pieces for easy transport. I used end plates with small brackets (similar to column base plates ). The connections was with preloaded high tension bolts.

 

[BAretired]

The OP's link indicates three forces acting on the pin. The X and Y forces can be combined into one lateral force. The Z force is axial. The supports for the pin are not shown, so it's hard to say. The X and Y combination will create shear in the pin and will cause bending if the faying surfaces are not tight together. Axial stress from the Z force will combine with bending stress, if they exist. Pins are normally in shear, not axial or bending. The shear resistance of pins is covered in the CISC code and I would think also in the AISC.

Bolts in pure shear are covered in the code. Bolts in combined shear and tension are covered in the code as well. Bolts in bending are not recommended. I don't believe they are covered in either CISC or AISC, but I could be mistaken.

BA

 

[drawoh]

Good day. Will a preloaded bolt only fail in shear or tensile stress, or combination of both? Or can it fail in bending as well?

That depends on what somebody does wrong, doesn't it?

The bolt will not fail in bending unless there is a mechanism present that bends the bolt. The bolt will fail in tension if it is over-torqued, or otherwise overloaded. It can fail in fatigue if it is under-torqued. If it is loose and overloaded, it can fail in shear. A pin cannot clamp your joint.

What happens if the bolt or pin is not made of the material you specified?

--
JHG

 

[r13]

Will a preloaded bolt only fail in shear or tensile stress, or combination of both? Or can it fail in bending as well?

Yes, yes. No.

 

[HungryDinosaur_imported]

Thanks all. Some good insights.

Regards

HD