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Re: Eccentric Shear on Screws

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> From: "Brad Cameron" <bsc(--nospam--at)>

> Given this, I wonder whether the equations as stated in the AISC manual
> for ultimate strength analysis are applicable to the dinky little screws
> I sometimes use. No way will I get 0.35 inches of movement out of a #10
> screw before it breaks or otherwise just gives up.=20

> strain)." Makes me wonder what the load deformation curve of a #10 screw
> looks like in cold formed steel.=20
> Anybody got any insights or suggestions - perhaps a way to derive
> coefficients appropriate for screws?

> Thank you in advance for your help!
> Brad Cameron
> Keymark Engineering

Are you designing a structure or writing software? Ultimately, you construct
an analytical model and conduct a confirming physical test. The cold form
steel design standard recommends and, in some cases, requires this.
Materials with high width/thickness ratios simply don't have nice linear
response in the same way as can be adequately assumed for materials covered
by AISC standards (e.g. small deformations, linear strain, etc.). The
effects of a 3/4" A325 plowing through plate is not the same as a fastener
that does not have a nut.

If I fasten 2 CF channels back to back and use fasteners at a common radius
for a moment connection (e.g. (4)#nn @ 4"x4"), I assume that I get decent
instantaneous centre of rotation response. Assume that hole deformation is
important. I also ensure that the members are suitably braced to minimize
effects due to member eccentricity. I would never put anything else into the
field without an appropriate test.

It would be nice to see Keymark software developed for Canadian code. The
basics are already written for the cold formed standard. Got any pull there?

Paul Ransom, P.Eng.
ph 905 639-9628
cell 905 802-3707
fax 905 639-3866

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