Effect of Externally Applied Loads on Bolt Preload 1

[Darkmann]

I'm new at joint design and have a question about bolt preload. The FEA model of the fastener is a simple 2-noded bar from which I extract axial loads and bending moments. I then apply these loads to a known fastener to characterize its strength. Here's my question: is the effective tension on the fastener the sum of the preload and the applied tension (the FEA tension) - the conservative way, I suppose. When the applied load becomes greater than the preload, does that mean that gapping will occur? If the externally applied load is compression, how does this affect effective tensile load on the bolt? Just ignore it? Or, are the tensile and compressive loads additive, resulting in an effective smaller load on the fastener.

 

[desertfox]

Hi Darkmann

Have a look at this site it should help:-

http://www.boltscience.com/pages/decomp1.htm

regards desertfox

 

[CoryPad]

The effective fastener tension is not a simple sum until gapping occurs. A joint is analogous to parallel springs, so the relative stiffnesses determine the effective tension. You are correct that if the applied load exceeds the preload, then gapping occurs. Normally joints do not have external forces acting to compress the actual joint (although thermal contraction can). You may be able to ignore compression forces.

Regards,

Cory

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