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Re: DSA AND "OVERSIZE" HOLES IN SILLS AND LEDGERS

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Gaylord, the 1991 NDS covers your concerns in Chapter 8. Section 8.1.2.1 reads "Bolt holes shall be a minimum of 1/32" and a maximum of 1/16" larger than the bolt diameter". Section 8.2.3 reads "When a connection consists of one wood member attached to concrete or masonry (single shear) by bolts embedded in concrete or masonry, the allowable bolt design value, Z', for a single shear wood-to-wood connection shall apply with:
 
tm = 2ts = twice the thickness of wood member 
 
Fem = Fes = dowel bearing strength of wood member
 
The concrete or masonry shall be of ample strength to support the load."
 
The 1994 UBC in section 2311.2, paragraph 2 reads "Allowable shear values used to connect a wood member to concrete or masonry are permitted to be determined as one half the tabulated double shear values for a wood member twice the thickness of the member attached to the concrete or masonry." 
 
I find this to be a clearer definition of the increase allowed. This means that a 1/2" A.B. in a 2x sill would get 1/2 the value of a 1/2" bolt in double shear with members of 3" thick - 1430#/2=715# is the value I use. 
 
Ken Reed
kendeb(--nospam--at)maxinet.com