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Simpson Titen Screws in Existing Concrete Stemwall

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I'm doing a residential addition and I 'm trying to connect a new girder to an existing stemwall footing.

 

Looking at the Simpson 2008 catalog, page 140, I see that there is a tabulated capacity of 3,950 lbs for a HU46 using (12)-1/4" diameter x 2-3/4" Titen Screws. This comes to a little over 300 lbs per screw. According to the tabulated values, the full capacity of the screw is 400 pounds each. However, in the literature on the website (http://www.simpsonanchors.com/catalog/mechanical/titen/loads_sheartension.html), there is a reduction in shear capacity if the anchors are spaced closer than 3" down to half the capacity at 1-1/2". I downloaded the HU46 hanger from the Simpson website and the spacing of the holes is 1", which is less than the minimum spacing for the screw.

 

Am I missing something?

 

Alternatively, I have considered using a LGUM46 with (4)-3/8" diameter x 4" long Titen HD screws. Using Simpson's ASD tables, I get a full capacity of 1,585 lbs per anchor. The reduction factor for spacing is 0.804. I looked at the reduction factor for edge distance using the minimum value of 1-3/4" and that factor is 0.24. The load is due to gravity, therefore the shear load is not towards the edge. I'm not sure if I should consider this reduction factor or not. I know that ACI 318 Appendix D would use 2x the capacity if the load is not towards the edge, but I don't know the basis of the ASD tables. I guess I should/could use the Simpson calculator, but I haven't yet.

 

Should I consider the 0.24 factor for edge distance? If so, this reduces the capacity to below my design load in a few cases.

 

Regards,

 

T. William (Bill) Allen, S.E.

ALLEN DESIGNS

Consulting Structural Engineers
 
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