Shear strength of screws

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I've always taken a serendipity view of screw gauge when doing rough stuff as in "hey, I'd better use a bigger screw for this." I need to cobble together some two bys for a frame for a basement storage rack. I've got a box of number 9 2 1/2 inchers that ought to do the trick.
Question: Is there a formula for determining the minimum gauge for a screw if you know the load?
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On 4/6/2012 11:05 AM, Gramp's shop wrote:

My favorite screw for that application is a "Spax":
http://www.mcfeelys.com/spax-screws
I prefer them for attaching cabinets to walls these days because of the superior shear strength.
That said, most engineers will tell you that for many construction/structural projects nails will provide more shear strength than screws, so it really depends upon the application.
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I never thought about it. Just that so many screws today are absolute crap. If you shear off a screw while driving it into the wood, it is a bad sign. And it depends where you buy them too. I have had terrible luck with deck screws and lag screws from the local home depot. But the local ace hardware store gave me screws that were higher in quality, stronger and a few cents cheaper too.
If I got any kind of basic repair outside or in the garage these days, I just use their deck screws. It ain't art or furniture. But it is strong. They don't shear off and they don't rust outside.
The old standby rule about strength for fasteners is to estimate how many will do the job. Then put twice as many in there. I have always been accused of using too many screws anyway.
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On 4/6/2012 11:05 AM, Gramp's shop wrote:

What you also need to ask is if there is a way to determine the quality of the screw you are using. I know of #6 screws that are stronger than #10's.
All things be in equal, McFeeleys.com has the specifically information that you are asking and IIRC their catalog has a chart of this also.
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On Friday, April 6, 2012 12:05:36 PM UTC-4, Gramp&#39;s shop wrote:

Those will do. If you are concerned, smear a little construction adhesive in there too. Up here in the Northeast, if we are framing a house, we cannot use screws. Must use nails or you will not pass the framing inspection.
RP
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On Wed, 11 Apr 2012 14:26:06 -0700, RP wrote:

That seems a little strange - what's the rational given, if any?
I learned the hard way that any carpentry (as opposed to ww) work I do, someday I, or someone who comes after, will have to take it apart again. I use screws for all that now.
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On 4/11/2012 6:33 PM, Larry Blanchard wrote:

Nails generally have a greater shear strength than screws, thus the requirement in some areas are very specific as to the nails used, their size, makeup, and nailing patterns.

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Used to be that framing had to be toe nailed... Now I see nails used from top and bottom sil to studs. Not as strong. The toe nailing really locks it in from both sides. straight nailing will not withstand storm forces as much. But then again, most roofs will easily lift before the framing gives.
On 4/11/2012 7:37 PM, Swingman wrote:

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On 4/11/2012 7:05 PM, tiredofspam wrote:

Typically hurricane straps add tremendous strength if you are building for wind storm resistance.
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wrote:

If you google "strength of wood screws" you will find www.awc.org/pdf/.../Part11WoodScrewspp133to139.pdf.
Download the PDF and read it. You will find out all you ever wanted to know about wood screws, their strength and application. (and likely even MORE than you wanted to know). A good read.
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On Wed, 11 Apr 2012 20:57:15 -0400, snipped-for-privacy@snyder.on.ca wrote:

Um, remove the ... and give us the actual URL, please. Parsing error! Silly wabbit.
-- Happiness is not a station you arrive at, but a manner of traveling. -- Margaret Lee Runbeck
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On Wed, 11 Apr 2012 21:36:27 -0700, Larry Jaques

the post, Dumb bunny ;)
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On Thu, 12 Apr 2012 13:26:02 -0400, snipped-for-privacy@snyder.on.ca wrote:

_Not_ dumb, sir. Pureasslazy.
-- Happiness is not a station you arrive at, but a manner of traveling. -- Margaret Lee Runbeck
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wrote:

gives more information on screw strength and calculations. It is a LONG URL and may not work for you, but you can find it by googling as well. Google "wood mechanical fasteners".
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wrote:

on wood: mechanical fasteners. www.awc.org/pdf/ndscom97.pdf will find you my first reference to "Part XI: Wood Screws" in secion XI. All you ever wanted to know about wood screws (particularly in construction) from the American Forest and Paper Association.
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wrote:

Look up "fasten master" structural screws. They are approved for a LOT of general construction use - and their "timberlok" screw can be used in place of hurricane straps to fasten trusses to double top sills - as an example - replacing the tiedown strap and 12 nails with ONE fastener.
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And put on earth quake straps on the foundation and sil board. That will work in other cases of strong wind. A force trying to flatten a house.
Another thing we did in earth quake country was to put in shear walls. Often the outer boards are 1x tongue and grove but they silip and slide in wind. On the inside put sheet ply It doesn't have to be all walls, but some of the side on all sides. Keep that side from laying over.
Martin
On 4/11/2012 7:15 PM, Leon wrote:

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On Wed, 11 Apr 2012 20:05:15 -0400, tiredofspam <nospam.nospam.com> wrote:

(in tension) as yesterday's chewing gum.
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snipped-for-privacy@snyder.on.ca writes:

When it is nailed from the top plate or sill into stud endgrain, it suffices since the roof holds them together - the nail is to keep the stud aligned, any forces will be perpendicular to the nail.
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On 12 Apr 2012 01:17:25 GMT, snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote:

toe-nailing USED to be pretty well a requirement in the days of plain nails. Ardox nails help. TimberLok screws can be used in place of hurricane straps to connect trusses to sills. Fully code compliant, and you won't mistake them for a common screw or lag bolt - and you don't need to remove them or X-Ray to know how long the timberlok is (they are clearly marked on their black hex heads)
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