December 29, 2010
|
RISA-3D,
New,
Analysis,
P-Delta
When
a
model
is
loaded,
it
deflects.
The
deflections
in
the
members
of
the
model
may
induce
secondary
moments
due
to
the
fact
that
the
ends
of
the
member
may
no
longer
be
vertical
in
the
deflected
position.
These
secondary
effects
for
members
can
be
accurately
approximated
through
the
use
of
P-Delta
analysis.
This
type
of
analysis
is
called
“P-Delta”
because
the
magnitude
of
the
secondary
moment
is
equal
to
“P”,
the
axial
force
in
the
member,
times
“Delta”,
the
distance
one
end
of
the
member
is
offset
from
the
other
end.
Step
1:
The
model
is
loaded
with
the
Applied
loads
(P
shown
above)
Step
2:
The
model
deflects
Δ,
and
the
secondary
shear
force
(V)
is
calculated
for
every
member;
Step
3:
The
model
is
re-solved
(internally)
with
the
secondary
shear
forces
applied
(V
shown
above).
Step
4:
The
displacements
for
this
new
solution
are
compared
to
those
obtained
from
the
previous
solution.
If
they
fall
within
the
convergence
tolerance,
the
solution
has
converged.
If
not,
return
to
Step
2
and
repeat.
The
convergence
tolerance
is
found
in
the
Model
Settings
and
is
set
by
default
to
05%…
