] [Thread] [Date] [Author]

["Martin W. Johnson" <MWJ(--nospam--at)eqe.com>]

Section 1629.8.1 says that any structure MAY be, and certain structures SHALL
be, designed using the dynamic procedure.
Section 1629.8.2 Lists categories of structures which MAY be designed using the
static procedure.  This includes any irregular structure less than 5 stories or
65 feet in height.  The word MAY is used because, per section 1629.8.1, the
engineer has the choice of using either the static or dynamic method.
Section 1629.8.3 says that the dynamic procedure SHALL be used for all OTHER
structures.  This means all structures not meeting the limitations set forth in
Sectioon 1629.8.2 (irregular structures greater than 65 ft etc.).

My interpretation is that the static force method is permitted for a soft story
structure less than 65 ft in height, but a dynamic analysis is also permitted,
and is perhaps preferred.

I recently had the chore of looking at a 3 story building where this same thing
occurred - the engineer used a steel moment frame at the first floor to
accomodate a large open lobby, and then used extensive pywood shearwalls in
upper stories where residences were located.  I didn't like it but could only
spell out what the code says.  Because there were also lateral offsets between
the shearwalls and the moment frames I pointed out several code sections which
had been overlooked in the design, but the soft story was basically in
conformance with the code.

Martin