# Shear values for deck screws and drywall screws.



## BayPointArchitect

After looking at other threads related to screws, I believe that there are those who believe that the performance of a screw is good resistance against pulling out but useless for shear capacity.  I admit that I have snapped off a few screw heads myself but I would think that a #8 screw would be worth a very conservative 100 lbs of shear strength regardless of where that screw came from and what it is made of.  I have hung more than a few wall cabinets with only two screws and watched people fill up those cabinets with their antique ceramic dishware.

My calculations and assumptions for a #8 screw:

Diameter with threads excluded from the shear plane = 0.164"

Radius = 0.082"

Area in shear plane = pi x radius ^ 2

= 0.0211 square inches

x 36,000 psi

= 760 psi ultimate strength

Fv = 0.22 Fu (coeficient used for bolts according to manual for steel construction - AISC 9th edition)

Fv = 167 lbs shear strength

Am I way off in my thinking?

Thanks


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## brudgers

BayPointArchitect said:
			
		

> Am I way off in my thinking?


  Yes. You need to use the document which is incorporated into the building code by reference instead of winging it.


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## pwood

take a 3"drywall screw and sink it halfway into a board and side hit it with a hammer , try same with 16 sinker. i would like nails ,thank you.


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## BayPointArchitect

In the Wood chapter 23 of the 2009 IBC, there is information regarding shear walls with nails and staples (not screws).

Altogether, the IBC doesn't say much about screws except when prescribed for use with fire resistive drywall assemblies in other chapters.

Considering that I do not have a copy of the NDS for Wood Construction, allow me to ask the question another way:

Is a #8 common wood screw equivalent in shear performance to a 16d nail if they are the same length?

Both have essentially the same diameter while comparing 0.162 inches (nail) with 0.164 inches (screw).

I might just build something out of three 2x4s using four 3-1/2" screws and slide this into a concrete test cylinder tester and see what the ultimate capacity of four screws would be.

Thanks


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## brudgers

BayPointArchitect said:
			
		

> Considering that I do not have a copy of the NDS for Wood Construction,


  you should not be designing connections until you have one.


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## globe trekker

> *Is a #8 common wood screw equivalent in shear performance to a 16d nail if they**are the same length? Both have essentially the same diameter while comparing 0.162 inches*
> 
> *(nail) with 0.164 inches (screw).*


In the best forum, electronic Forrest Gump voice imitation that I can present, "...I am not asmaht maay-an", but I would say "No", they are not equivalent in shear performance. IMO, I

am thinking that the screw has more surface area, that weakens the shear strength of it, while

the 16D has only the cylindrical area to resist shear forces.

When the shearing forces act on the screw, the threaded area would not be as strong as the

inner diameter area, thereby causing the screw to fail sooner than the compact cylinder

design of the 16D.

.


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## BayPointArchitect

... and that is exactly why I made it very clear ...

Diameter with threads excluded from the shear plane = 0.164"

The key word there is "excluded".

I am using the smallest of the smallest dimension while calculating the shear value... naturally.

Meanwhile, I am waiting for approval of my new membership application to the American Wood Council so that I can fill up my book shelf with the four volume set of NDS for Wood Construction.  I sure hope those two screws holding up the book shelf can handle the extra weight.

Now one of you is going to ask "why did you need to get a membership?".

For the 50% discount while purchasing a book that will tell me the shear value of a screw.

What an awesome system we live in.

Have a great weekend everyone.


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## pwood

the drywall screws are hard steel that snap,shear off with a tap. a vinyl sinker will bend back and forth many times before snapping. i would prefer the nail for a connection subject to shear,


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## Francis Vineyard

Instead of doing the calculations could examine the package or box of wood screws and find information such as follows: "The single-fastener load capacity of the sd9 exceeds the capacity of a 10d common nail, while the single-fastener load capacity of the sd10 exceeds that of the 16d common nail"

Technical reading for those who love calculations; http://www.awc.org/pdf/NDSCommentaryCompressed/Part11WoodScrewspp133to139.pdf

Hope this helps,

Francis


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## brudgers

globe trekker said:
			
		

> In the best forum, electronic Forrest Gump voice imitation that I can present, "...I am not a smaht maay-an", but I would say "No", they are not equivalent in shear performance. IMO, I am thinking that the screw has more surface area, that weakens the shear strength of it, while the 16D has only the cylindrical area to resist shear forces.  When the shearing forces act on the screw, the threaded area would not be as strong as the inner diameter area, thereby causing the screw to fail sooner than the compact cylinder design of the 16D.   .


  There's are reasons the building code incorporates the published tables by reference. This post is one of them.


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## TJacobs

There are differences between a #8 wood screw, a brittle drywall screw, and a cheap foreign decking screw.  There are deck screws with unthreaded shanks and are not brittle, but they are not cheap (Maze) http://www.mazenails.com/catalog/catalog.php?page=PAGE15&group=DZH.  Even these are case-hardened and you will spin off heads.  I have never used them except for decking and trim.

I bit the bullet and bought the NDS, the ASD and the WFCM.  Excellent reference material.


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## BayPointArchitect

A conservative 87 lbs per #8 screw according to the NDS commentary.

Although, a value of 148 lbs was considered acceptable once upon a time.

Now compare that with my calculated value of 167 lbs.

Books are good.

Thanks for the NDS recommendation.


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## GBrackins

sorry but I do not know how to insert a link ...

http://www.icc-es.org/reports/pdf_files/ICC-ES/esr-2236.pdf

for those wanting some thrilling reading material ...


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## GBrackins

oooopssss, guess I knew how without knowing how


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## mtlogcabin

You will notice they do not provide shear values for drywall screwshttp://www.scrooscoop.com/toppage1.htm''>http://www.scrooscoop.com/toppage1.htm' rel="external nofollow">

http://www.scrooscoop.com/toppage1.htm


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## ICE

Somebody should give him the answer straight from the NDS.  Then he will have buyers remorse.  :devil


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## brudgers

ICE said:
			
		

> Somebody should give him the answer straight from the NDS.  Then he will have buyers remorse.  :devil


  Unfortunately, there is no straight from the NDS answer...it's a table...or rather several tables.


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## gbhammer

It is simple get out in the field build a deck or three hundred and find out for your self that hardened screws cannot compare to a nail anytime ever when it comes to shear. If you don't want to do that then do what some others have said and sink a nail, a screw, and do an impact test.


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## GCtony

That "expert" on TV, Mike Homes.....but he udes screws for EVERYTHING.  I like the one where they screwed a built-up beam together that supports floor joist above.  (they looked like 3" Home Depot specials to me) But they used construction adhesive that I'm sure will never dry out and become brittle.

Thanks for the referance materials.


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