Value of Historical Connectors 2

[bigmig]

I'm trying to determine the best way of giving
some capacity values to old style, square cut, tapered
nails in a building dating back to 1891. The connections are typically toe-nailed wood to wood.

Does anyone have references, tech articles etc that would point me in the right direction?

Could I send them to a lab to get material properties and then field test them, apply an adequate factor of safety and call it good?

I am just trying to avoid reinventing the wheel while salvaging as much of the historic nature of the structure as possible.

 

[a2mfk]

What type of connection specifically are you dealing with, a roof rafter to the top of a wall? Are you wanting shear and/or uplift out of this toe nail connection?

Personally, I would not rely on a toe nail connection, even one installed today in front of me, for much of anything... But I believe the wood will be the governing failure mode even for an older nail.

 

[bigmig]

The typical Z' value is what I am after. Per the NDS 05 Section 11.1.5 toe nails are totally legit.

"Add 4000 light guage metal hangers to the rafter ends on your 120 year old building because I feel toe nail connections aren't reliable" just doesn't have the ring to it that I would like to portray....

In otherwords, if the code says I can do it, I want to do it.

 

[SlideRuleEra]

bigmig - Late nineteenth century nails perform pretty much like modern nails since, as a2mfk stated, the wood is the limiting factor. Iron and steel from that time were typically good enough to carry loads that wood can withstand.

IMHO, the best place to get information from that time period is Google Books. For example, here is a nice 1883 summary of nail capacity (looks like the results given should be interpreted as the ultimate, not allowable load)

http://books.google.com/books?id=IH...EQ6AEwBA#v=onepage&q=construction nail&f=true

As long as the nails have reasonable dimensional proportions (length / crossectional area) and are in good condition, I would evaluate them the same way that modern nails are (with depth of embedment being a key factor). However, I would not completely rely on the old nails alone if the results of analysis are NOT conservative.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[bigmig]

SlideruleEra, Thanks for the interesting reference. I had never heard of google books. Quite fascinating.

 

[woodman88]

One problem with a tapered nail is what nail diameter to use in the Z equations.
I would calculation the diameter (if they vary per nail, get a typical and use .85 that value) at the interface of the main and side members for the side member Z value. And calculate the diameter at 1/3 the penetration into the main member for the main member Z value. The Fy I would use is 60,000 psi. Unless the Fy controls, then I would look at increasing the Fy.

Garth Dreger PE
AZ Phoenix area

 

[dhengr]

Bigmig:
A significant part of your study will involve putting some sort of stress grade rating on the existing lumber, since as others have said, that probably controls the design. There isn’t anything wrong with toenails in joints, they just aren’t worth much. Maybe some simple reinforcements, if needed, can be cleverly hidden or disguised. Part of my study would involve a load history study. That old building has likely seen some near historic wind, snow, whatever, loading events, in which case it has withstood the test of time, despite the lack of complexity of the building codes under which it was built. What did those old guys know, they got their Zee’s at night? They built building that lasted a few hundred years, and with reams of computer printouts and various Z’s we can’t get them to last 50 years.

 

[bigmig]

dhengr,

I would count on some historical data if I had some published values for wind and snow, but besides that I wouldn't count on the fact that it is still standing as a guarantee it will keep standing. Without data, I don't think that argument would get very far in court. Obviously failure in the eye of the common public is quite different than failure in my eye. Having an existing hip that is 20x overstress with a 6 inch wow in it is failure to me, but to the pedestrian on the street corner, it looks just fine since all he can see is that the roof is still standing.

Everyone is correct in stating that the wood will fail, and that failure is a function of the tapering nail diameter.
For less than $500 I can rig a spring guauge test in the wood species from the site, and yank 10 nails out, average the values and apply a appropriate factor of safety to run calcs with. I feel a lot better about defending this than assuming nail diameters on a tapered nail etc. Worst case scenario is I confirm the values from initial assumptions.

Based on the reference from Slideruleera, that is exactly how they did it back in 1883.