Diaphragm Cross-Ties

[WAstruc10]

For retrofit of an existing URM building with wood joist floors, my understanding from ASCE/SEI 31-03 is that the joists must form continuous cross-ties from one wall anchorage to the opposite side wall anchorage (in the absence of subdiaphragms). Pretty straight forward. But what about the perimeter URM walls that are parallel to the joist direction - I think common practice is to add a few bays of blocking and straps to develop the OOP wall anchor forces into the diaphragm, every 4 ft or so...but developing the load into the diaphragm seems to violate the principal of continuous cross-ties (since the diaphragm itself shouldn't be used in tension). And blocking/strapping all the way across the diaphragm every 4 ft seems like overkill. This situation is exacerbated in a current project of ours, where a long rectangular building has the floor joists running parallel with the long side, supported by beam lines perpendicular to the wall only every 20 ft or so. So my questions are: 1) Does the continuous cross-tie requirement apply only in one direction, or both? and 2) Do the diaphragm cross-ties have to engage every OOP wall anchorage, or could we just use the 20 ft o.c. beams as cross-ties even though the URM wall couldn't span horizontally between those points?