...
Transform
...
stiffness
...
involves
...
an
...
important
...
distinction
...
in
...
which
...
the
...
line
...
that
...
represents
...
the
...
position
...
of
...
a
...
...
object
...
may
...
be
...
different
...
from
...
the
...
line
...
that
...
represents
...
the
...
object
...
centroid
...
and
...
its
...
physical
...
attributes.
...
When
...
the
...
...
...
is
...
at
...
the
...
centroid,
...
these
...
lines
...
coincide.
...
In
...
this
...
case,
...
the
...
Do
...
not
...
Transform
...
Stiffness
...
for
...
Offsets
...
from
...
Centroid
...
option
...
generates
...
identical
...
results
...
regardless
...
of
...
whether
...
or
...
not
...
it
...
is
...
selected.
...
In
...
all
...
other
...
cases,
...
these
...
lines
...
are
...
different,
...
and
...
some
...
notable
...
points
...
include:
...
- Default
...
- settings
...
- .
...
- The
...
- default
...
- settings
...
- leave
...
- the
...
- Do
...
- not
...
- Transform
...
- Stiffness
...
- for
...
- Offsets
...
- from
...
- Centroid
...
- option
...
- unchecked.
...
- This
...
- does
...
- transform
...
- stiffness
...
- to
...
- account
...
- for
...
- the
...
- offset
...
- from
...
- the
...
- line
...
- drawn
...
- to
...
- represent
...
- that
...
- object
...
- in
...
- the
...
- model.
...
- Transformation
...
- .
...
- By
...
- selecting
...
- the
...
- Do
...
- not
...
- Transform
...
- Stiffness
...
- for
...
- Offsets
...
- from
...
- Centroid
...
- option,
...
- the
...
- centroid
...
- of
...
- the
...
- frame
...
- object
...
- is
...
- located
...
- along
...
- the
...
- line
...
- drawn
...
- to
...
- represent
...
- that
...
- object
...
- in
...
- the
...
- model.
...
It
...
may
...
be
...
best
...
to
...
implement
...
the
...
default
...
setting
...
by
...
leaving
...
the
...
Do
...
not
...
Transform
...
Stiffness
...
for
...
Offsets
...
from
...
Centroid
...
option
...
unchecked,
...
since
...
this
...
coordinates
...
stiffness
...
with
...
the
...
actual
...
physical
...
location
...
of
...
the
...
frame
...
object.
...
Transform-stiffness
...
example
...
Figure
...
1
...
illustrates
...
an
...
example
...
in
...
which
...
a
...
...
object
...
is
...
modeled
...
using
...
a
...
top-center
...
...
...
.
...
As
...
seen
...
in
...
the
...
first
...
image,
...
the
...
object
...
is
...
actually
...
located
...
entirely
...
beneath
...
the
...
line
...
which
...
represents
...
its
...
location
...
in
...
the
...
model.
...
By
...
following
...
the
...
default
...
setting,
...
stiffness
...
is
...
automatically
...
transformed
...
to
...
account
...
for
...
the
...
offset
...
location
...
of
...
the
...
object
...
centroid.
...
This
...
is
...
shown
...
in
...
the
...
second
...
image,
...
in
...
which
...
the
...
analytical
...
line
...
extends
...
downward
...
to
...
align
...
with
...
the
...
centroid.
...
Selecting
...
the
...
Do
...
not
...
Transform
...
Stiffness
...
for
...
Offsets
...
from
...
Centroid
...
option
...
has
...
the
...
effect
...
shown
...
in
...
the
...
third
...
image.
...
Here,
...
the
...
default
...
transformation
...
is
...
not
...
made,
...
and
...
the
...
analytical
...
model
...
aligns
...
object
...
attributes
...
with
...
the
...
projection
...
of
...
the
...
insertion
...
point
...
(top
...
center),
...
though
...
the
...
object
...
is
...
actually
...
entirely
...
beneath
...
this
...
line.
...
Different
...
stiffness
...
properties
...
will
...
result.
Bridge application
An instance in which this topic may be relevant is the modeling of a bridge superstructure. A line may be drawn to represent the location of a composite bridge deck. In relation to this line, girders may be specified with a top-center insertion point such that they are positioned below the line, which will then align with the plane of their top flanges. Then the deck may be specified with a bottom-center insertion point such that it is above the line, which will then align with its bottom surface. This would then form the basis of a composite bridge deck section.
Additional diagrams and a discussion on how insertion point affects horizontal reaction may be found in the Effect of insertion point on beam reactions test problem.
See Also
- SAP2000 Verification Problem 1-011
- Effect of insertion point on beam reactions test problem