Wood to concrete connections - 1997 NDS

[azcats]

When using the 1997 NDS to design wood to concrete connections, (ledgers, sill plates, etc.) it (Section 8.2.3) says to use the dowel bearing stress of concrete or masonry in place of the dowel bearing stress of the main member for the equations of section 8.2.1. Where does one get the dowel bearing stress of concrete or masonry? The values in Table 8.2E use a dowel bearing stress of 6000 psi, but they give no explanation of why or where that number comes from.

Any help is greatly appreciated.

 

[JAE]

Good question. I reviewed a few resources and couldn't find any reference to it. It possibly could be an older concept that the anchor shear force shouldn't exceed some prescribed bearing stress (i.e. 6000 psi). However, if you look at some other sources, a different concept can be used. The UBC 97, Section 1923 utilizes an ultimate load concept using a shear cone method of determining anchorage capacity both in terms of tension, shear, and combined. This would allow you to design with different concrete strengths, etc.

Nelson Stud Company also has some publications that deal with capacities of studs pulling out in a conical failure. While this wouldn't directly apply to your wood/bolt situation, their publications provide some good understanding of the concept.