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Re: Wood: Using 2x ledger in

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In a message dated 97-12-24 22:11:03 EST, you write:

<< 
 >Dennis,
 >
 >While cross-grain tension is a valid concern, I don't think that the
 >thickness of a ledger should be any indication of its ability to resist
 >cross-grain tension.  In fact, Section 2310.2 (1994 UBC) requires
 >cross-grain tension be resisted by mechanical reinforcement.
 >
 >I think that if you check your Simpson catalog for nailing of face mounted
 >joist hangers, you will see that the minimum nailing into the ledger
 (header)
 >is 10d nails (3" long) and 16d (3.5" long) which would require a minimum 4"
 >(nom.) ledger.
 
 
 Most of the connections with 10d nails use Teco type nails which are 1-1/2"
 long. Simpson sells their N10 common nails which is equivalent to 10d common
 nails in shear (92 lbs per) . Even Simpsons N20A is only 1-3/4" long and has
 a shear value of 119 lbs per nail in shear. Each can be increased by code
 for short term loading 1.33 times. Each of their nails, however, is based
 upon a metal side plate increase (for hangers).
 The withdrawl value as noted in UBC table 23-I-H supports 16d nails at 42
 lbs per inch of embedment. To obtain the full shear value of a 16d common
 nail as noted in table 23-I-G you need 1-3/4" embedment into the stud.
 Therefore the allowable withdrawl value for the nails would be 1.75*42 or
 73.5 lbs per nail. With three nails in every other stud (32" o/c) the
 tensile resistance of the ledger at each connected stud would be 220.5 lbs.
 
 If we follow section 1611 of the UBC and take 30% of the wall weight we
 would get roughly (6'+4')*20psf*2.5'*0.3 or only 150 lbs. The diaphragm
 tributary to the ledger is only 4' therefore the lateral reaction from the
 diaphragm is 20psf*2.5'*4'*0.3 or 60 lbs more. Therefore, the 2x ledger
 should be adequate if we base it only on the capacity of the nailed
 connections alone.
 
 Finally, each Simpson face nailed hanger has a withdrawl value as well. With
 6 - 10d nails at 1-1/2" embedment, the withdrawl of the connection would be
 38lbs(for 10d)*1.5"*6 or 342 lbs - not the weak link here.
 
 BTW, I forgot to mention in my post to Dick Horning that the code values are
 per inch of embedment.
 
 >
 >Another concern with face mounted joist hangers on ledgers is the location
 of
 >the hanger nails in relation to the connection of the ledger to the wall.
 If
 >the ledger is bolted to a wall and the hangers are nailed to the ledger
 below
 >the level of the bolts, the ledger will be subject to cross-grain tension
 at
 >the bolt line.
 >
 >A. Roger Turk, P.E.(Structural)
 >Tucson, Arizona
 >
 
 I would agree that this might be a problem with a bolted or lagged
 connection and a high load diaphragm. Since the demand of the diaphragm is
 so small in my problem, the tension connection of the face nailed hanger
 would exceed the boundary nailed pull of the diaphragm from the top of the
 ledger. The load would be concentric to the joist connection rather than
 eccentrically loaded (based upon the distance from the center of the bolt or
 nail to the top of ledger).  The ledger connection to the stud would fail
 before cross-grain failure would occur.
 
 I am inclined to believe that a 2x ledger in this case is sufficient. I
 would only question its acceptablity if there was a specific code
 requirement or new data that would support the use of minimum 3x ledgers in
 wood framing.
 
 Thanks for your comments, they caused me to really think this one through.
 After running the numbers, it appears that the connection is adequate.

 
 Happy Holidays
 Dennis
  >>

Dennis

Would it still be a possible or perferable option to use a let-in ledger at
this stage.  I have used 2x ledgers to studs also, but generally only on
ceilings and roofs where possible.  If  it was a floor load that I had to
support, I would try and use a let-in ledger  (2x6 studs) and sit the joist on
top of the ledger and nail the floor joist to the sides of the studs if
possible. 
    
I know once the studs are up, its a pain to cut-in a ledger plus concerns on
overcuts by the framer. Also aligning joist and studs can be difficult.
Somehow  though I am more comfortrable putting the joist in bearing on the
wall, instead of hanging them off of a ledger on a stud wall.

Just a thought.

Michael Cochran
Brian L. Cochran Associates