As I understand from SEAOC seminar on 2/27, the deflections of unblocked
diaphragms with respect to blocked diaphragms approximate the ratio of the
strength of unblocked vs. blocked.
You can figure delta for a blocked diaphragm based on equations in APA
literature or UBC Standards. You would then multiply this delta by the
ratio of (UNblocked strength from UBC diaphragm table/BLOCKED strength from
UBC diaphragm table).
For example, if your diaphragm has1/2-inch sheathing in the "Case 1" panel
layout with 6/6/12 nailing, then the numbers from the table are 285 for
unblocked and 320 for blocked, so you multiply delta for the blocked
diaphragm by 285/320.
I can hardly wait to try this myself....