October 9, 2013
|
RISA-3D,
New,
Analysis
When
solving
a
RISA-3D
model
with
hot
rolled
steel
members
under
the
AISC
360-05
(13th
Edition)
or
AISC
360-10
(14th
Edition)
codes
you
may
find
references
to
a
factor
called
Tau_b.
To
understand
what
this
factor
is
you
should
first
be
familiar
with
the
Stiffness
Adjustment
in
RISA-3D,
then
see
the
AISC
360-10
Specification,
Section
C2.3.2:
“An
additional
factor,
Tau_b,
shall
be
applied
to
the
flexural
stiffnesses
of
all
members
whose
flexural
stiffnesses
are
considered
to
contribute
to
the
stability
of
the
structure”
Link:
Stiffness
Adjustment
in
RISA-3D
By
applying
this
factor
in
addition
to
the
0.80
factor
to
flexural
stiffness
(EI)
of
the
members
the
deflections
for
those
members
increase
significantly.
This
code
provision
is
only
intended
to
be
applied
to
members
whose
flexural
stiffness
contributes
to
the
stability
of
the
structure
though,
such
as
beams
and
columns
within
moment
frames.
The
calculation
of
Tau_b
is
a
function
of
the
ratio
of
axial
force
in
the
member
to
its
axial
yield
strength.
For
members
where
this
ratio
is
less
than
0.5
(members
which
are
less
than
50%
stressed
axially)
the
value
of
Tau_b
is
1.0,
which
means
that
is
has
no
impact
on
the
member
stiffness.
For
members
which…