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Re: Foundation A.B. Capacity

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Jake, here is some comments:

1. Typically, the concrete will fail before the steel does. I am not sure 
what type of foundation you have, but the deeper the embedment, the larger 
the cone (concrete cone failure). If you are considering a stem wall for a 
raised foundation, your capacity should not (in my opinion) consider the stem 
as helping to resist the tension. I would develop the capacity in the footing.

2. This generally means designing the footing of the all to resist bending so 
as to distribute enough load into a rectangular foundations to allow for 
sufficient concrete to act as a "deadman" before failing as a beam.  Although 
this is starting to get a bit beyond my talents (since I would have created a 
deeper deadman type resistance for the anchor) I would assume that you can 
use the stem of the foundation wall and model the foundation as a "T" section 
in bending. 

3. Of course, the one thing that may help the foundation in bending is the 
bearing on the stemwall to compensate for the uplfit (tension) on the panel. 
In my experience, I have designed the foundation as a simple rectangular 
footing with sufficient mass to compensate for the tension. I tend to 
disregard more elaborate design at the edge of a bearing wall where the 
foundation is continuous and enlarge foundations at corners or extend them 
far past the walls at each end where they occur within the interior of the 

Sorry I could not be more specfic as to design considerations.


In a message dated 7/20/99 5:26:09 PM Pacific Daylight Time, 
jwatson(--nospam--at) writes:

<< I am trying to find the capacity of an anchor bolt in a residential
 foundation wall.  The case has a large uplift do to a "Simpson" holdown
 (about 15k service loading). It is a traditional 8" foundation wall with
 a simpson HD15 anchor that requires a 1.25" dia anchor bolt.  Simpson
 doesn't make a corresponding SSTB.  I tried to design an anchor bolt
 using the provisions of ch19, div III but am very confused.  According
 to the provisions, I first calculate the projected area area at the top
 of the wall (Ap) then reduce according to edge distance.  The reduction
 amounts to edge distance divided by embedment length.  I have two close
 edges (4") so I squared the reduction.  After doing all this, the UBC is
 trying to tell me that a 30" long A.B. is weaker than a 12" long A.B. 
 If someone could clarify these provisions, I would be very grateful.
 P.S. Here's the fun part, if I design it at as a rebar, then I have more
 than 10x the capacity of an A.B.
 Thanks in advance, 
         Jake Watson, E.I.T
         Salt Lake City, UT >>