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Re: L.A. City, Division 91

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As a plan check engineer, I see your point.  The problem is that Division 91
requires continuous ties at 24 feet max on center.  1631.2.9, item number 4
requires the ties between diaphragm chords which is often misinterpreted as to
mean the overall building chord.  A properly designed subdiaphragm system is
all that would appear to be needed as long as the sub diaphragm chords are
checked for vertical bending and axial seismic loads.  Also, struts and
continuity shall be provided in ever increasing subdiaphragms that meet the
ratios in table23-I-I until the load is delivered to the perpendicular
shearwalls or the tie continues to the other end of the building, whichever
occurs first.

With continuous ties across the entire building a diaphragm would almost be
unneccary.

If you would like to talk call me at (949)475-2901 or E-mail
TJB5424744(--nospam--at)aol.com

Ted Beckwith, RCE