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RE: wood screw design info (contractors substitution)

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My 2 cents would be this.....

If the allowable load of the Simpson hanger you used is governed by testing
then doing an A/B comparison screws to nails may not be appropriate.  If the
hanger is governed by a calculated value then an A/B comparison may be
appropriate.   

Also, did the contractor properly pre-drill his screw holes?  If not are
there splits?  

I hope the contractor is getting the bill for the extra time he caused you.


Chris
Haffner Consulting Engineering
541-478-3052
 

-----Original Message-----
From: Meyer, Albert [mailto:AMeyer(--nospam--at)CagleyHarman.com] 
Sent: Thursday, March 31, 2005 1:33 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: wood screw design info (contractors substitution)

Scott -

I realize that there are differences between screws and various nail types,
but for this particular case I looked at the common nail based on the
assumption that they used the type of hanger nails typical for hangers, i.e.
the N10 for simpson which has the diameter of a 10d common nail.  I was just
trying to give a ballpark idea of the differences in capacity understanding
that not all of the information was given.

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 3:45 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: wood screw design info (contractors substitution)


Albert,

You need to be a little careful as what type of nail will impact the
actual size and thus the single shear value.  Are they common wire nails,
box nails, or sinker nails?  Dave did not mention.  You actually get
values of 72 lbs for a 10d sinker nail, 81 lbs for a 10d box nail, and 102
lbs for a 10d common wire nail...all from table 11P of the 2001 NDS using
16 gage metal with Hem-Fir main member.  The comparable value for a #8
screw is 80 lbs.  So, depending on the type of nail, the screw could go
from slightly more capacity to about the same capacity of about 20% less
capacity.  In the end, a little more information is required.

And that does not even begin to address the adjustment factors such as the
group factor, geometry factors (i.e. spacing, end distance, edge
distance), etc.  Presumably, these factors would nominally be the same,
but the diameter of a #8 screw is at least a LITTLE different from the
nails, which could potentially affect the various factors.

Scott
Adrian, MI


On Thu, 31 Mar 2005, Meyer, Albert wrote:

> 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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