...
For
...
complex
...
or
...
irregular
...
structures
...
which
...
do
...
not
...
have
...
clearly
...
defined
...
orthogonal
...
directions,
...
it
...
may
...
be
...
unclear
...
as
...
to
...
how
...
the
...
orientation
...
of
...
...
...
analysis
...
should
...
be
...
applied.
...
In
...
the
...
paper
...
entitled
...
...
...
...
...
,
...
Dr.
...
Wilson
...
explains
...
that
...
combined
...
directional
...
effects
...
may
...
be
...
accounted
...
for
...
more
...
effectively
...
by
...
using
...
an
...
alternative
...
method
...
in
...
which
...
the
...
SRSS
...
combination
...
of
...
two
...
100-percent
...
spectra
...
analyses
...
is
...
applied
...
in
...
any
...
direction,
...
or
...
along
...
either
...
orthogonal
...
axis.
...
This
...
method
...
is
...
valid
...
because
...
design
...
forces
...
and
...
results
...
are
...
independent
...
of
...
the
...
reference
...
system
...
used.
...
Further,
...
this
...
method
...
also
...
accounts
...
for
...
independent
...
and
...
simultaneous
...
ground
...
motions
...
which
...
occur
...
normal
...
to
...
those
...
along
...
the
...
principal
...
direction.
...
References
- Wilson,
...
- E.
...
- (1995).
...
...
...
...
...
- Berkeley,
...
- CA:
...
- Computers
...
- and
...
- Structures,
...
- Inc.
...