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Section 1
1-85
Time History Analysis for a Structure Subjected
to a Harmonic Loading
A Harmonic loading is one in which can be described using the
following equation
)t ( sinF)t( F
0
φ+ω
=
In the above equation,
F(t) = Value of the forcing function at any instant of time "t"
F
0
= Peak value of the forcing function
ω
= Frequency of the forcing function
φ = Phase Angle
A plot of the above equation is shown in the figure below.
Figure 1.38
The results are the maximums over the entire time period,
including start-up transients. So, they do not match steady-state
response.
Definition of Input in STAAD for the above Forcing
Function
As can be seen from its definition, a forcing function is a
continuous function. However, in STAAD, a set of discrete time-
force pairs is generated from the forcing function and an analysis
is performed using these discrete time-forcing pairs. What that
means is that based on the number of cycles that the user specifies
for the loading, STAAD will generate a table consisting of the
magnitude of the force at various points of time. The time values