Does bolt pre-tension come into play with AISC Eq J3-3a?
Does bolt pre-tension come into play with AISC Eq J3-3a?
(OP)
The specification J3.7 in AISC (I'm looking at the thirteenth edition) has a forumla for available tensile strength in a bolt when it is also subjected to shear.
The commentary uses this phrase "Tests have shown that the strength of bearing fasteners subject to combined shear and tension resulting from externally applied forces..."
We have a bolted connection where there is only shear. However, these bolts are to be pre-tensioned.
There is no other applied tensile force in the bolts or connection.
Does the pre-tensioning require use of section J3.7? Or is pre-tensioning not considered an externally applied force?
The commentary uses this phrase "Tests have shown that the strength of bearing fasteners subject to combined shear and tension resulting from externally applied forces..."
We have a bolted connection where there is only shear. However, these bolts are to be pre-tensioned.
There is no other applied tensile force in the bolts or connection.
Does the pre-tensioning require use of section J3.7? Or is pre-tensioning not considered an externally applied force?






RE: Does bolt pre-tension come into play with AISC Eq J3-3a?
Thus, I'd make it:
SLS = Total tension including pre-tensioning, plus shear (reducing applied shear by that transfered through friction)
ULS = Applied tension, applied shear (make no reduction for transfer of load through friction unless specifically designed as a slip-critical connection).
I don't know much of the AISC code, but it cannot get around basic mechanics.
RE: Does bolt pre-tension come into play with AISC Eq J3-3a?
I am not familiar with AISC but I am looking at some bolts on a product for the steel industry which have failed in service.
The failure appears to be from principle tensile stresses on the bolts, characterised by the crack in them growing at 45 degrees to the bolt axis.
Studying the loadings, it appears that we have only external shear loads on the bolts, so the only tensile stress the bolts can possibly see is that of the pretension loading.
I am attempting to show that the preloading coupled with the external shear loads result in the combined stress exceeding the yield stress of the fastener and thus causing them to fail.
RE: Does bolt pre-tension come into play with AISC Eq J3-3a?
In a similar fashion, you don't have to reduce bolt tension capacity because of pre-tensioning. This is because pre-tensioning results in a clamping force (compression in the plates) that must be overcome before you put any significant, additional tension in the bolts.
RE: Does bolt pre-tension come into play with AISC Eq J3-3a?
I don't have the thread link handy but it talked about the shear deformation essentially releasing the pre-tension stress which apparently nullified the tension.
If I can find the link I'll post it.
RE: Does bolt pre-tension come into play with AISC Eq J3-3a?
I found an article on the subject and it clearly states that preload does not effect the shear capacity.
See clause 2.4 in this link
http://preserve.lehigh.edu/cgi/viewcontent.cgi?art...