Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Concrete Achor Bolts in Shear

[Subject Prev][Subject Next][Thread Prev][Thread Next]
2005 - We now have made the jump from the 1997 UBC to the 2003 IBC here in Oregon and I'm looking at one of the many mysteries that we are revisiting.
Question for those familiar with the current capacity of anchor bolts in concrete stem walls.  
IBC 2003 refers to ACI 318-02 (appendix D) for anchoring to concrete.     For a 3/4" diameter anchor bolt located in a 6" concrete stem wall, what is the capacity???     Assuming that an anchor bolt is located 2 1/2" away from the edge of the concrete stem wall (e.g. attaching a 2x6 wood sill plate), it appears that the shear capacity is controlled by the concrete breakout strength of the concrete (D.6.2 of ACI 318-02).    The allowable load is a function of the edge depth (2 1/2" in this case) even for in-plane shear for bolts loaded parallel to the free edge.   (The allowable load is limited to twice the calculated out-of-plane force and deeper embedment doesn't help.)  I have calculated 1.68 kips capacity for a 3/4" diameter bolt for ASD loads.
Using these new formulas (the values were reduced by 0.75 for Seismic Class "D"), the concrete breakout strength seems to control instead of the strength of the wood plate that used to be the concern.     The NDS-01 provides values and formulas for attaching the wood sill plates to concrete.   (with the new 1.6 seismic increase, a 3/4" diameter bolt in 2x Douglas Fir was good for 1.95 kips ASD)      I can't see the concrete failing before the wood plate.     If you bump the wood plates to 3x or 4x, you don't get any additional capacity because the concrete already controls the design.   2x4 plates make this even worse (780 lbs/bolt at 1 1/2" from edge)
Simpson Set 5/8" anchors, 1 3/4" edge distance loaded parallel to the stem wall is good for 2.2 kips ASD (ER-5279)
I am missing something here?
Portland, Oregon