I've wondered the same thing a number of times. I keep telling myself that I'm going to look this up, but have never had the time.
When I do find the time, I will probably start with AISC Design Guides 4 and 16 for end plate moment connections. These have a number of cases where multiply lines of bolts were used. Therefore, if you get ahold of some of the referenced papers, I imagine that one of them goes into more detail about how they arrived at the procedure. Part of this will get into yield-line theory for the plates (which you may or may not be interested in), but I would think that part of it has to cover the prying action on the bolts.
I would check prying on the first bolt line only. "Guide to Design Criteria for Bolted and Riveted Joints" by Kulak, Fisher, and Struik discusses this on page 271-272. Unless the flange is really thick or has stiffeners, the inner bolts take almost all of the tensile load.
First line of bolts only. It is easy to imagine that the first line of bolts must experience yielding before the prying forces are distributed to the outside gage lines. All bolts can share the shear loading.
But that would assume that the "prying" action was the "right direction" wouldn't it?
That is, if I have two members joined by a plate with two rows of bolts in each member; then if the bending moment being resisted is clockwise, the members "pivot" at the outside row of bolts and stretch the inner rows of bolts.
If my bending moment is counter-clockwise, then the outer row of bolts are being stretched, aren't they?
To me it's not really a question of whether the outer bolts will themselves be drammatically affected by prying action. Rather, it is a question about whether the presence of that outer line of bolts will affect the prying forces experienced at that inner line of bolts.
I don't have a real answer to that question, but I think it is a legitimate question....albeit an academic one. In practice though, I would think it woul be a better choice to do as Toad did and just consider the 1st line of bolts and maybe thicken the plate slightly.
