Welcome
to
a
high-level
walkthrough
of
dynamic
analysis
in
RISA-3D!
This
guide
introduces
essential
aspects
of
modeling
dynamics,
focusing
on
natural
frequencies,
mode
shapes,
and
the
impact
of
dynamic
behavior
on
structural
integrity.
The
Dynamics
Scenario
Imagine
we’re
tasked
with
evaluating
the
stability
of
a
cantilevered
pedestrian
bridge
that
spans
over
a
city
street.
The
bridge
is
connected
to
a
building
on
one
side
and
features
decorative
panels
and
a
lightweight
canopy.
The
concern?
Wind
gusts
and
foot
traffic
could
cause
the
bridge
to
vibrate.
Our
goal
is
to
understand
its
dynamic
properties—natural
frequencies
and
mode
shapes—and
assess
whether
it
can
handle
these
dynamic
forces
without
compromising
structural
stability.
We
start
by
setting
up
dynamic
mass
for
each
load
case:
Canopy
Load:
Applied
uniformly
along
the
length
of
the
bridge
to
account
for
wind
effects.
Pedestrian
Load:
Simulated
at
intervals
along
the
span
to
reflect
walking
traffic.
Decorative
Panels:
Modeled
with
specific
weights
on
each
side.
Once
mass
and
stiffness
are
set,
RISA-3D
enables
us
to
simulate
how
the
structure
behaves
dynamically,
revealing
which
parts
might
be
sensitive
to
specific
frequencies
or
forces.
Running
the
Eigensolution
Analysis
In
RISA-3D,
we
use
an
eigensolution
to
identify:
Natural
Frequencies
(intrinsic
vibration
rates…
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