...
What
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is
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center
...
of
...
rigidity?
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Answer:
...
Center
...
of
...
rigidity
...
is
...
the
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stiffness
...
centroid
...
within
...
a
...
floor-diaphragm
...
plan.
...
When
...
the
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center
...
of
...
rigidity
...
is
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subjected
...
to
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lateral
...
loading,
...
the
...
floor
...
diaphragm
...
will
...
experience
...
only
...
translational
...
displacement.
...
Other
...
levels
...
are
...
free
...
to
...
translate
...
and
...
rotate
...
since
...
behavior
...
is
...
coupled
...
both
...
in
...
plan
...
and
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along
...
height.
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As
...
a
...
function
...
of
...
structural
...
properties,
...
center
...
of
...
rigidity
...
is
...
independent
...
of
...
loading.
...
Certain
...
building
...
codes
...
require
...
center
...
of
...
rigidity
...
for
...
multistory-building
...
design-eccentricity
...
requirements.
...
For
...
a
...
given
...
floor
...
diaphragm,
...
center
...
of
...
rigidity
...
is
...
calculated
...
through
...
the
...
following
...
process:
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- Case
...
- 1
...
- applies
...
- a
...
- global-X
...
- unit
...
- load
...
- to
...
- an
...
- arbitrary
...
- point,
...
- perhaps
...
- the
...
- center
...
- of
...
...
- ,
...
- such
...
- that
...
- the
...
- diaphragm
...
- rotates
...
- R
...
- zx
...
- .
- Case 2 applies a global-Y
...
- unit
...
- load
...
- at
...
- the
...
- same
...
- point,
...
- causing
...
- rotation
...
- R
...
- zy
...
- .
- Case 3 applies a unit moment about global-Z,
...
- causing
...
- rotation
...
- R
...
- zz
...
- .
...
- These
...
- three
...
...
...
- are
...
- shown
...
- in
...
- Figure
...
- 1:
- Center of rigidity (X,Y)
...
- is
...
- then
...
- computed
...
- as
...
- X
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- =
...
- -R
...
- zy
...
- /
...
- R
...
- zz
...
- and
...
- Y
...
- =
...
- R
...
- zx
...
- /
...
- R
...
- zz
...
- .
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During
...
analysis,
...
...
automatically
...
calculates
...
this
...
coordinate
...
for
...
each
...
floor
...
diaphragm.
...
The
...
diaphragm
...
assignment
...
must
...
be
...
present
...
in
...
the
...
model.
...
Center
...
of
...
rigidity
...
and
...
center
...
of
...
mass
...
are
...
then
...
displayed
...
by
...
selecting
...
Display
...
>
...
Show
...
Tables
...
>
...
Building
...
Output
...
>
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OK.
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