Effect of pre-load on shear strehgth
Effect of pre-load on shear strehgth
(OP)
Hi all.
Typically, (Canadian) steel design codes state that a bolt will fail in shear at a stress of 0.6 * Ftu, over its nominal area.
Is this dependent on pre-load?
I am fully aware of the mechanics of pre-load on tension performance, but I've always wondered about shear.
I have also used the (Canadian) design code equations for combined tension and shear, but when these loads are external...
Any takers?
tg
Typically, (Canadian) steel design codes state that a bolt will fail in shear at a stress of 0.6 * Ftu, over its nominal area.
Is this dependent on pre-load?
I am fully aware of the mechanics of pre-load on tension performance, but I've always wondered about shear.
I have also used the (Canadian) design code equations for combined tension and shear, but when these loads are external...
Any takers?
tg





RE: Effect of pre-load on shear strehgth
Regards,
Cory
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RE: Effect of pre-load on shear strehgth
Let's say you're designing a bolted joint to support a simple gravity loaded beam. Consider, for example, a single angle beam connection. The bolts are torqued during installation, to some certain value, and are therefore in tension.
Assuming a bearing type connection, in sizing these bolts do you use the equations for shear only, or for combined shear and tension?
I have always done this using shear only, and this would suggest that the shear strength equations are independant of pre-load, or that pre-load has been considered in their derivation.
Is this correct?
tg
RE: Effect of pre-load on shear strehgth
RE: Effect of pre-load on shear strehgth
If the bolt is tightened down hard and is in tension, the joint is held in place by friction, right? Shear does not apply. The shear load works when the bolt is loose for whatever reason. The reason could be weird design, or sloppy installation. Conceivably, there could be some tension on a bolt that is loaded in shear.
Is this a question about code, or about mechanics of materials?
JHG
RE: Effect of pre-load on shear strehgth
If the bolt has a tensile preload plus a shear load, you will need to determine the allowable load combination using a combined-stress failure model, e.g. a Mohr's Circle, Tresca, or Von Mises theory. If you are designing a device to take a shear load (e.g. a pivot), consider using shear pins designed specifically for that purpose.
RE: Effect of pre-load on shear strehgth
In my third edition LRFD manual it is in the Specification, section J3.7.