Wasn't the ABK method intended for determination of the performance of wood
diaphragms in Unreinforced Masonry Buildings? I believe the outcome was that
these diaphragms which were constructed typically of straight sheathing at
the roof and 1x diagonal sheathing at the floors were to be considered
I think the code bears this out as the performance of plywood sheathing is
more critical when used as a diaphragm supporting or supported by concrete or
masonry. I would certainly understand the distinction in this case.
For those unfamiliar with the ABK method was a methodology for treating shear
distribution through a typical wood diaphragm of a multi-story structure in a
manner different from traditional proportional distribution methods. It has
been a very long time since I have read the document which I obtained from
John Kariotis' office who happens to be the 'K' in the ABK.
If I recall, ABK was intended as a methodology to be used in the retrofit of
Unreinforced Masonry building which differed from the traditional
proportional distribution of shear by tributary area. The method considered
the diaphragm flexible in a URM building and distributed shear by the lessor
of the tributary shear from analysis or the diaphragms maximum capacity.
I may be wrong in this one as I thought the ABK was essentially the precursor
for what became the 1991 UCBC Appendix Chapter 1 and formerly the City of Los
Angeles RGA 1-91.
The difference between these and traditional distribution methods introduced
crosswalls which dampened the diaphrams deflection rather than shearwalls
which direct a tributary area of shear to the panels. Crosswalls were also
allowed to deflect in excess of the typical story drift, but limited by the
diaphrams maximum allowable deflection of I believe 1" per story.
It is not an easy method to understand, but I think the root of the issue
might be that it was intended for consideration with Masonry rather than wood
framed buildings. I think the use of wood diaphragms in wood framed
structures is an intirely different animal.
I look forward to your comments,