...
Translational
...
acceleration
...
loads
...
Acceleration
...
loads
...
are
...
used
...
to
...
simulate
...
the
...
ground
...
motion
...
of
...
a
...
...
...
acceleration
...
record
...
.
...
Software
...
assumes
...
complete
...
fixity
...
for
...
all
...
supports,
...
then
...
automatically
...
computes
...
acceleration
...
loads
...
at
...
each
...
node
...
and
...
structural
...
object.
...
Translational
...
acceleration
...
loads
...
are
...
taken
...
as
...
the
...
negative
...
of
...
the
...
product
...
of
...
assembled
...
...
mass
...
and
...
input
...
acceleration.
...
At
...
any
...
point
...
in
...
a
...
structure,
...
translational
...
acceleration
...
is
...
given
...
by
...
the
...
cross
...
product
...
of
...
the
...
position
...
vector
...
(relative
...
to
...
the
...
origin
...
of
...
rotation)
...
and
...
the
...
acceleration
...
vector.
...
Resultant
...
force
...
is
...
then
...
the
...
negative
...
of
...
the
...
product
...
of
...
this
...
translational-acceleration
...
value
...
and
...
the
...
translational
...
...
.
...
For
...
example,
...
RY
...
acceleration
...
would
...
generate
...
MY,
...
FX,
...
and
...
FZ
...
values.
...
For
...
additional
...
information,
...
please
...
see
...
the
...
...
...
...
(Acceleration
...
Loads,
...
page
...
304).
...
Rotational acceleration loads
Rotational acceleration is calculated independently from rotational inertia. This is done by applying, at the global origin, a unit rotation about the axis considered for rotational-acceleration computation.
While applying a rotational-acceleration load during time-history analysis, users may specify a coordinate system and an angle from the vertical Z-axis. Rotational acceleration is then applied at the origin of that coordinate system, about the designated axis.
- Rotational acceleration is constant through all points in a structure.
- Rotational inertia may induce negative moment values.