Transient response analysis
A transient response analysis calculates the effect of time-dependent
load sources that act in any regular or arbitrary manner on a structure.
Typical transient load sources include wind gusts, seismic events, vibrating
machines, blast loads, pulse loads, footfall excitation, moving traffic,
- Supported transient load types are "Applied loads" (general
purpose time-dependent loads), "Initial displacements" (displacements
that are enforced at time zero and then removed), "Initial
velocities" (velocities that are enforced at time zero and then
removed), "Base acceleration (translation)" (support nodes
accelerating in-phase in any direction), "Base acceleration (rotation)"
(support nodes accelerating in-phase about any node), "Harmonic
loads" (masses vibrating in a regular sinusoidal motion) or "Periodic
loads" (arbitrary time-dependent loads that repeat periodically).
- A "Factor versus time table" can be defined for most
load types that defines the time-dependent properties of the load
- Load sources of different types and with different time-dependent
properties can be combined within a transient load case.
- Transient result load cases can be combined with static and other
load case types using combination load cases.
- Damping can be taken into account and applied as either "Modal"
or "Rayleigh" damping, or it can be disabled.
- You can choose the time range and the number of steps over that
range at which calculations are done.
- After a transient response analysis, the model can be animated
to show how it responds to the transient loads.
- Displacement, velocity, acceleration and phase diagrams can be
displayed for any nodes in the structure. These are time-history curves
that shows how the structure responds to the time-dependent load sources.
- Each time step (or just selected steps) can be converted to result
load cases that contain displacements, forces, moments, stresses and
reactions, just like you would get from a static analysis. You can
show diagrams or get reports for these load cases or use them in the
normal way in any of the design modules.
- Harmonic loads are supported in a transient response analysis,
however if you are interested in the structure's frequency response
(ie. displacement versus frequency) to harmonic loads then you should
run a harmonic
response analysis instead.
- A transient response analysis is linear only and therefore cannot
be performed if your model contains cable elements.
- Because it is linear, a transient response analysis treats tension-only
and compression-only members as normal members that can take tension
- P-D and
are not taken into account during a transient response analysis.
- A buckling analysis cannot be performed with transient load cases
and therefore compression effective lengths from a buckling analysis
are not available when doing a steel member design/check on transient
load cases. If you are performing a steel member design/check on combination
load cases that contain a mixture of static and transient load cases
then the transient load cases will not contribute to the calculation
of the compression effective lengths. This may not be correct and
so you should consider specifying your compression effective lengths
manually in those cases.
- A transient response analysis requires a dynamic frequency analysis
to be conducted first.
- The transient response analysis must be repeated after a dynamic
frequency analysis because its results will have been deleted.
- The accuracy of the transient response analysis depends on the
accuracy of the dynamic frequency analysis on which it is based. It
is therefore important that you set up your model correctly to achieve
accurate dynamic frequency analysis results. For example, if master-slave
constraints are used then positioning of the master nodes is particularly
important for correct mass distribution. For more information, refer
For a full step-by-step guide on how to prepare for and perform a transient
analysis, refer to "Step
by step guide to transient response analysis".