Above, I expressed a lack of concern for the horizontal cold joints. I've changed my mind. Like a cold joint in a concrete beam, I now feel that the joint should be analyzed using shear friction principles and that the result of that should be vertical bars developed on either side of the cold joints. This would be similar to what FoxSE and Jayrod have proposed. Having multiple course grout pours at the top and bottom of the beam would be preferable for bar development purposes.
The only "out" that I can think of is if the mortar in the bed joints, acting on it's own without help from the grout, could supply the required horizontal shear capacity. In that regard, multiple lintel courses might actually help (more mortar). As Hokie mentioned, however, I think that the rational thing to do here is maximize grout volume.
This does have me wondering about the analagous situation with walls. With walls, we'll add in the shear strength of grouted cores and not worry about the cold/construction joints. Often there are vertical bars present that could be used for shear friction but not always.
Lastly, I have a research paper that concluded that horizontal shear transfer in unreinforced concrete beam cold joints is quite good. I know of no code based way to take advantage of that but it's reassuring none the less.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
