I should add some very important information....
1). I am referring to short slots that are 90º to one another
2). The direction of the applied load can be at nearly any angle.
3). Slip or movement of the members has no effect on the structure;
to ask another way, can it be assumed that the connection goes into bearing or does having slots 90º from on another make this assumption invalid/impossible?
Never read that part in AISC so I can't tell you for sure, but it's not allowed in the Canadian code as per 22.3.5.2 (b)
"Short slotted holes may be used in any or all plies of slip=critical or bearing type connectionsand without regard to direction of loading in slip-critical connections, but shall be normal to the direction of the load in bearing-type connections."
If you have slots in both directions, they won't both be normal to the direction of load. Even if it were allowed, it seems like a bad idea.
AISI tested this type of connection in cold-formed steel and I believe the results will be in the next version of the NASPEC. The reduction factors changed slightly from the ones that are used with round holes.
I have never seen orthogonal slots used, without slip-critical connection to maintain member elevation or horizontal adjustment. The holes must slip completely in the vertical direction to achieve bearing. This would negate the reason for using a vertical slot.
The only time I've personally used a pair of slots at right angles is for things like tie down bolts in a beam seat connection where I have no loads in either slotted direction and want fitup tolerance on the connection.
Sorry for the delay in getting back to you. Note that the attached document is from AISI but it has not been officially published. You will probably see this in the 2013 NASPEC.
