rook1:
Are you asking how to calculate the tensionload or how the allowable tension load is calculated?
If its the allowable, here are some considerations. The bolt's allowable values will be based on several factors, probably some tested and some calculated. These different failure scenarios may be bolt failure in tension and pullout failure in concrete. That situation will be governed by embedment depth and edge distance, and will have lower numbers if the bolt is embedded in a masonry bond beam instead of a concrete footing. Also, flexure in the top plate will be a consideration and likely be the limiting value. Sometimes additional capacity is given to the top plate through the sheathing nailing in shear, so you have to watch how you consider that (i.e. if your nailing is used for uplift it is no longer available for shear). In addition, bearing failure at the connection to the top plate may govern if you are using a bolt solely for a large uplift load such as that from a girder truss. In that event you would need to specify a larger washer and check for bearing stress in the wood and bending in the washer. I have worked with a similar system to go-bolt and these are some of the things I consider and also that they use for determining their bolt allowable loads at a given spacing. I hope this helps you out.