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Re: Bolting issues, generation II

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Majid:

I see from your trailer that you are at the University of Ottawa, which
probably means you have a testing facility available. If so and you have
the time and material available, install some high-strength bolts
(A325's or A490's) in lap joints. Make a few snug-tight (or even loose
if you want) and a few pretensioned. Then load them in shear and compare
the results.

See you in Toronto.

Charlie

P.S. There is a bolting short course scheduled for the Saturday (May 22)
after the AISC Conference in Toronto (May 19-21). You might be
interested.

Majid Sarraf wrote:
> 
> Dear Charlie,
> 
> I hopefully will meet you at AISC conference in Toronto. If you have time
> then, we will seat down together, have a cup of coffee, and find out a
> solution to this problem. Whoever who looses will have to pay for both of us!
> 
> You did not say if you agreed with the shear deformation and subsequent
> imposed elongation I showed in my simple sketch. However, I have my answer
> to your question.
> 
> >>Majid wrote:
> >>Assuming bolt axis is along a-a, shear deformation (exagereted here for
> >>the sake of argument) on the bolt can only develop as shown, because
> >>end rotation of the bolt head and nut is restrained by the plates in
> >>contact on both sides.
> >>
> >>Now, distance b-b is the bolt grip after inelsatic shear deformation
> >>takes place. Does not this mean additional elongation along the bolt
> >>length, i.e extera tension due to shear? So why tension be lost rather
> >>than increased?
> >>
> >>         _________________
> >>         |               |
> >>         |               |
> >>       a |               | a
> >>         |               |
> >>         |               |
> >>         -----------------
> >>
> >>
> >>         |\
> >>         | \
> >>       b |  \
> >>         |   \
> >>         |    \
> >>         \     \
> >>          \     \
> >>           \     \
> >>            \     \
> >>             \     \
> >>              \     \
> >>               \     \
> >>                \     \
> >>                 \     \
> >>                  \     \
> >>                   \    |
> >>                    \   |
> >>                     \  | b
> >>                      \ |
> >>                       \|
> >
> >Majid:
> >
> >A pretensioned bolt is normally stressed into the plastic range during
> >installation. That is, the bolt stretches a little bit (scientific term)
> >as the pretension induced is equilibrated as a clamping force on the
> >joint.
> 
> So far this is perfectly making sense to me. I never doubted this part.
> 
> >As an externally applied shear load is increased toward bolt shear
> >failure, inelastic deformations will occur in the bolt shank. These
> >inelastic deformations initiate when the combined stress due to the
> >pretension and the externally applied shear load is sufficient to cause
> >yielding.
> 
> Great!  Well this is exactly where that shear tension interaction comes to
> the picture. You are saying it right there: "combined stress due to the
> pretension and externally applied shear", and they are both high enough to
> cause yielding means to me they are both important enough to consider in
> strength consideration through an interactive relation.
> 
> > But as this yielding occurs, the bolt elongates and the
> >pretension is lost.
> 
> But pretension is still there when high shear and inelastic deformation was
> high enough to start yielding. How come all of a suden pretension reduces to
> zero and shear continues. This can be the case though, if we unload and then
> reload shear froce.
> 
> >Subsequently, the failure of the bolt occurs by
> >rupture just as it would for a bolt that initially had no pretension.
> >
> >Make any sense?
> 
> I hope you do not kill me for saying: "Sorry. Not yet".
> 
> Let us think about this some more before we meet in Toronto. I make sure I
> will bring enough change to buy you a coffee, just in case..!
> 
> With many thanks, and best regards,
> 
> Majid
> 
> >
> >Charlie
> >
> >
> >
> 
>               ~      ~           ~ ___
>                        [_________]-|__)
>               __________OO______O__O_O___________________________
>                   |==========================================|
>                   |                                          |
>                    \               Majid Sarraf             /
>                     \       Ph.D Candidate/Lecturer        /
>                      \   Department of Civil Engineering  /
>                       |        University of Ottawa      |
>                       |           Ottawa, Ontario        |
>                       |            Canada K1N 6N5        |
>                       |WEB SITE: www.uottawa.ca/~msarraf |
>                       |   Tel:(613) 562-5800 Ext. 6159   |
>                       |         Fax:(613) 562-5173       |
> |                                  |
>                        ~  ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
>