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RE: wood screw design info (contractors substitution)

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Following up to Scott's post if you compare the values of a 10d common nail (Simpson hanger nails are most commonly N10 nails that have the diameter of a 10d  common nail but are 1 1/2" long) to that of a #8 wood screw, you get the following from the tables in the 2001 NDS:

Considering a 16 GA side plate and Hem-Fir species lumber member, the lateral capacity of the 10d nail (assuming minimum penetration of 10D where D is the nail diameter, here for a 10d nail equal to 0.148") the lateral capacity of the nail, Znail = 102 lb and the capacity of the #8 wood screw Zscrew = 80 lb.  The screws have about 80% of the capacity of the nail but if you don't need the full nail capacity you may be OK with the screws.

I haven't looked any further into the tables but I believe that when comparing the #8 screw to the 10d nail values would follow this same capacity difference regardless of the species or side plate thickness.


Albert J. Meyer, Jr., P.E.

Cagley Harman & Associates, Inc.
Structural Engineers & Parking Consultants
900 West Valley Forge Road, Suite 200
King of Prussia, PA 19406
610.337.3360 vc
610.337.3359 fx
www.cagleyharman.com


-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Thursday, March 31, 2005 2:55 PM
To: seaint newsgroup
Subject: Re: wood screw design info (contractors substitution)


Dave,

There are tables for screws into wood with a ASTM A653, Grade 33 steel
"side plate" (much like your Simpson hanger).  It is table 11M in the 1997
NDS.  If you tell me the "side member thickness" (i.e. gage of metal
hanger) and species of wood, then I should be able to tell you the single
shear value for a #8 screw from the table.

Scott
Adrian, MI


On Thu, 31 Mar 2005, David Handy wrote:

> Good afternoon all:
>
> I have a situation where I spec'd Simpson hangers and the appropriate nails. The contractor thought he was doing a good thing by substituting wood screws for the nails. The floors are now complete with many, many hangers. The project is a rather large expensive home. Simpsons line is that the hangers were designed and tested with wood nails because failure mode for nails is ductile whereas it is brittle for wood screws.  The Canadian code does not mention capacities for wood screws, however, lag screws and timber rivets are covered. I would have thought that lag screws would be made of a similar material as wood screws.
>
> I have a copy of the Wood Handbook from the USDA and it discusses the design methodology for screws and it does not say they cannot be used for structural connections. Simpson does use some screws but they are proprietary. In this document it mentions the NDS for Wood Construction published by the AFPA and LRFD for engineered wood published be ASCE.  I don't have either of these documents but it suggests that wood screws have design loads just like any other fastener.
>
> There is no doubt that I would have preferred the contractor to use the nails, however, as usual, the Engineer is the one to either approve or say rip it out. Ripping it out in this case is just not realistic. Removing screws and putting proper nails in is also problematic because nail capacity will not be as good as if no hole was already there.
>
> Any suggestions??
> Do the US codes allow for the use of wood screws in this situation??
>
> I was sure I read that a screws capacity would be at least as good as the same diameter nail. However, I have broken off wood screws before into maple and that is what makes me think that they are not as good.
>
> The comparison is for 10d and 16d nails with No. 8 wood screws.  I do have the AFPA technical report 12 for the general dowel equations for calculating lateral connection values. I think that someone out there must have some helpful technical knowledge so that I don't have to dive into those calculations.
>
> thanks
> Dave
>

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