Spider DSA User’s Manual
359
Shock Response Spectrum Analysis
A Shock Response Spectrum (SRS) is a graphical presentation of a transient
acceleration pulse’s potential to damage a structure. It plots the peak acceleration
responses of a bank of single degree-of-freedom (SDOF) spring, mass damper
systems all experiencing the same base-excitation as if on a rigid massless base.
Each SDOF system has a different natural frequency; they all have the same
viscous damping factor. A spectrum results from plotting the peak accelerations
(vertically) against the natural frequencies (horizontally). An SRS is generated
from a shock waveform using the following process:
◼ Specify a damping ratio for the SRS (5% is most common)
◼ Use a digital filter to model an SDOF of frequency, f
n
and damping ξ.
◼ Apply the transient as an input and calculate the response acceleration
waveform.
◼ Retain the peak positive and negative responses occurring during the
pulse’s duration and afterward.
◼ Select one of these extreme values and plot it as the spectrum
amplitude at f
n
.
◼ Repeat these steps for each (logarithmically spaced) f
n
desired.
The resulting plot of peak acceleration vs. spring-mass-damper system natural
frequency is called a Shock Response Spectrum, or SRS.
Figure 219. Illustration of a multi-degree of freedom system model used to compute
SRS.
An SDOF mechanical system consists of the following components:
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