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RE: Bolting issues, generation II

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Majid:

     I think what Charlie Parker is trying to say is that when you
pretension a bolt it shrinks.  As shear-induced deformations increase, it
elongates and thus it losts some pretensioning.  So, in order for a
pretensioned bolt to break in shear, it (the shear) has to overcome first
the pretensioning force.  And the forces (pretensioning and shear) act in
different planes.

    Just my 0.02 cents.

Rodrigo Lema


-----Mensaje original-----
De: Majid Sarraf <msarraf(--nospam--at)uottawa.ca>
Para: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
Fecha: martes, 26 de enero de 1999 21:17
Asunto: Re: Bolting issues, generation II


>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
>>
>>
>>
>
>              ~      ~           ~ ___
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>                  |==========================================|
>                  |                                          |
>                   \               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   |
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