November 19, 2014
|
RISA-3D,
RISAFloor,
New,
Unbraced Lengths
Understanding
unbraced
lengths
and
how
RISA
software
accounts
for
them
is
essential
in
the
design
of
any
project.
In
RISA
there
are
three
main
types
of
unbraced
lengths:
Lb
values
(Lb,
Lu,
Le)
The
Lb
values
(Lbyy
and
Lbzz)
represent
the
distance
between
points
which
brace
the
member
against
flexural
(column-type)
Buckling
about
the
member’s
local
y
and
z
axes,
respectively.
Lb
bracing
prevents
the
entire
member
from
moving
laterally
(perpendicular
to
its
own
axis).
These
Lb
values
are
used
to
calculate
slenderness
ratios
(KL/r)
for
both
directions,
which
are
used
in
the
calculation
of
member
axial
compression
capacity.
Lcomp
Values
(Lcomp,
Le-bend)
The
Lcomp
values
(Lcomp-top
and
Lcomp-bot)
represent
the
distance
between
points
which
brace
the
top
or
bottom
flange
of
the
member
against
Lateral-Torsional
(beam-type)
Buckling.
These
Lcomp
values
are
used
to
calculate
the
member’s
flexural
(bending)
capacity.
Where
the
top
flange
of
the
member
is
in
compression
due
to
bending,
Lcomp-top
is
used.
Where
the
bottom
flange
of
the
member
is
in
compression
due
to
bending,
Lcompbot
is
used.
Lcomp
bracing
prevents
the
member’s
flange
from
moving
laterally
(perpendicular
to
the
member’s
axis).
The
top
flange
is
the
flange
on
the
positive
local
y-axis
side
of
the…