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Re: Stair Ledger

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Thor's approach seems reasonable.  Yield strengths of lag screws are given in Table 9.3A of the 1997 NDS, based on ANSI/ASME Standard B18.2.1-1981.  I've not specified that lag screw quality be documented by the supplier, so I don't know whether or not it's a big deal to require certification of lag screw quality -- my guess is that it is going to be more complicated for the contractor than buying them in bulk from Home Depot.  Also, standard lag screw dimensions are tabulated in Appendix L of the NDS {important for analyzing and detailing the connections if Thor's approach is used}, but my experience is that available lag screws commonly deviate from those dimensions.
 
Nels Roselund
Structural Engineer
-----Original Message-----
From: Mattesons <matteson(--nospam--at)yosemite.net>
To: seaint <seaint(--nospam--at)seaint.org>
Date: Friday, December 29, 2000 6:41 PM
Subject: Re: Stair Ledger

I'm not an architect, but last time I was wandering around in UBC Chapter 3 or 5 looking at stair construction requirements I recall that YOU  CAN  NOT  HAVE COMBUSTIBLE  STAIR  CONSTRUCTION  in this type of occupancy.   Check with your  very diligent inspector.
 
Lags into the studs COULD work for wood or steel ledger.  You would need to design the lags as cantilevering the thickness of the gypsum plus 1/2 the ledger thickness, plus do other unpleasant checks for Mode III or whatever failure in main member.  I recall that even approaching UBC side member  perp. to grain table values, the lags are overstressed in bending at a cantilever length of LESS than their diameter....
 
Good luck,
 
Thor
 
 

>For a 4-story, wood-framed, senior housing facility, the building official
>requires that the stairways be sheathed with gypboard on the outside, one
>layer of 5/8", and the gypboard cannot be interrupted by ledgers.  Neither
>will he allow the floor joists to bear on the stairway walls.