Duplicating values from design report for sheet metal screws

[awa5114]

I have a question regarding calculating pull over capacities for TEKS screws. According to ESR-3223, Table 3 - Allowable Tensile Pull-Over Loads, the allowable tensile pull-over load for a #12-14 HWH screwed into an 0.048 inch thick steel sheet equals 619 lbf. However, according to AISI S100-07 Section E.4.4.2, the pull over load, Pnov/omega, is as follows:

Pnov = 1.5*t1*d’w*Fu1 where
t1 = 0.048 in.
d’w = dh = 0.4 in. Case (B)
Fu1 = 58 ksi (as indicated in footnote 3 of ESR 3223, table 3)
Omega = 3

Therefore,

Pnov/Omega = (1.5 )*(0.048 in.)*(0.4 in.)*(58 ksi.)*(1000 lbf/k)/3 = 578 lbf

This is not equal to 619 lbf. Now according to ESR-3223:
“ITW Buildex TEKS Select Structural Fasteners are recognized for use in engineered connections of cold-formed steel construction. Design of the connections must comply with Section E4 of AISI S100."
I therefore do not understand why the values are not matching. Please explain to me why. Thanks for your consideration.

 

[Guastavino]

As note "2" of the table on the ESR lists, "Nominal strengths are based on laboratory tests". The allowable loads are then multiplied by a safety factor of 3.

I would guess that AISI S100 has alternate methods for values based on testing that vary from the equations. I haven't read that in AISI, just my hunch.

So, in summary, you are using calculations, whereas they are using testing. Or so is my best guess.

 

[Ron]

ITW is but one manufacturer with its own Evaluation Report. AISI is intended to be universal and for any manufacturer. If you can assure yourself that ITW's products will used and the values relied upon, then use them; however, the standard of care would be to use the more conservative value which is the AISI value. They are not that different. I would use the AISI value.

...and as njlutzwe noted, you are comparing tested values to calculated values....there will almost always be a difference.

 

[awa5114]

I'm pretty sure I will be using ITW product. The problem with these evaluation reports is that for example, if I have a t1 = 0.0635" and t2 = 0.048", and need to calculate the allowable shear (bearing) capacity , which corresponds to Table 5 in ESR-3223, there is no appropriate column. So I cannot get the true tested value. Also there is no telling that AISI values will necessarily be more conservative.... is there?

 

[XR250]

In what situation are you needing pullover values this high? In my experience, plenty of other modes of failure will occur prior to pullover being an issue.