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RE: Nail connection factors

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See the last paragraph in NDS97 - 12.3.3.  Clinching is only useful in 
three member joints and it does not simply double the capacity.

Roger C. Davis
Architect
SDS Architects, Inc.

-----Original Message-----
From:	Alexander Sasha Itsekson [SMTP:sasha(--nospam--at)engstruc.com]
Sent:	Thursday, December 19, 2002 5:29 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Nail connection factors

 << File: ATT00003.htm >> Happy Holidays to everybody,

The architect in his wisdom decided to replace ceiling tie joists with the 
collar ties at the midheight of the pitched roof.  The pitch is 4:12 and 
the roof rafters and  collar ties are 2x8's.
Anybody who tried to design the rafter to tie connection knows that it is 
difficult to put enough fasteners in the joint to resist the tie tension. 
 In this case I have around 2500lbs of tension.

I have a few questions:

1.  The table 3.5 of the NDS'97 Structural Connections Supplement lists 
Construction loads and doesn't list roof live load as a typical 7 day 
duration load to be used with the C_sub_D=1.25. Can I still use a 25% 
increase in allowable shear values for my fasteners for the connection at 
roof framing design?

2.  I remember from way back when that if one specifies clinched nails, 
then one can use a 100% increase in allowable shear value.  I looked 
through NDS and the only reference that I could find is a 100% increase 
when used in a double shear application.  Don't we get an increase capacity 
due to the fact that the nail withdrawal is not an issue in lateral nail 
loading or is it just equivalent to a 12D embedment.

3. Using 16d nails connecting two 2x members the provided embedment is 1.5 
inch < 12*0.162=1.944.  Can I use Cd=1.0 if I specify that the nails are to 
be clinched.

4.  Any other thing that I should consider in designing this joint such as 
predrilling of nail holes, close attention to edge distances etc?

Thanks in advance,

Sasha Itsekson, SE


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