What is the SRS?
Originally designed to evaluate structural responses to an earthquake, the SRS is a valuable tool for testing environments with complex transient shocks. Engineers use an SRS test to evaluate a device’s response to a transient event likely to occur in the end environment.
An SRS vibration test generates more complex shock pulses than a classical shock test. To generate a specific SRS response, engineers often synthesize one of several standard synthetic waveforms such as burst random or WavSyn. Read more: Characteristics of SRS Waveforms.
The SRS can be used to:
- Describe a transient event in general terms
- Estimate the damage potential of an event
- Design structure resonances
- Define test specifications (particularly for seismic tests)
- Replicate failure modes
How Does SRS Work?
The SRS is a representation of time-domain data in the frequency domain. It models the original waveform’s response channels using a set of theoretical, single-degree-of-freedom (SDOF), mass-damper-spring oscillators. The SRS sequentially applies filters of increasing frequency to the time domain data and plots the characteristics of the filtered waveform.
The horizontal axis of the plot represents the natural frequency of each SDOF. The theoretical response of each SDOF is plotted on the vertical axis. It is important to note that the SRS is not the actual response of the device under test but a theoretical representation of the response.
What are the Shortfalls of SRS?
Unlike the fast Fourier transform (FFT), the SRS does not include time or phase information. Therefore, engineers cannot recreate the original pulse from an SRS. Additionally, acceleration pulses that differ in amplitude, frequency content, and duration can produce an equivalent shock spectrum, resulting in an extensive waveform selection process.
Still, SRS remains the most prominent tool for complex shock testing. The SRS technique straightforwardly characterizes a shock environment and can be defined with data from multiple shock events.
Webinar: Fundamentals of Shock Response Spectra (SRS)
SRS Test Generation in VibrationVIEW
- Easy test entry: Enter frequency/amplitude breakpoints of the background random acceleration spectrum in an easy-to-read tabular form using frequency and amplitude breakpoints. Two-hundred separate frequency/amplitude breakpoints can be entered, allowing for the entry of virtually any test.
- Test generation techniques: The SRS software supports many generation test techniques including linear and exponential chirp, WavSyn, burst random, linear and exponential chirp on burst random, enveloped random, and burst sine. Alternatively, iterate from a user waveform.
- Manual wavelet manipulation: Manually adjust the parameters of the underlying wavelets or allow VibrationVIEW to automatically create and run a test without intervention.
- Data plots: SRS pseudo velocity and SRS acceleration plots; acceleration for primary (+), primary (-), or maxi-maxi.
Common SRS Test Specifications
- IEEE-344: procedure for seismic qualification of electrical equipment in nuclear power plants
- AASME NQA-1: nuclear quality assurance requirements
- Bellcore (Telcordia) GR-63: procedure and test level for seismic qualification of telecommunications equipment. Defines five zones across the USA of varying seismic activity matching Uniform Building Code (UBC). Generally, not used for nuclear power plant equipment.
- QME-100: ASME standard; procedure for seismic qualification of mechanical equipment
- AC-156: requires structures and equipment to maintain integrity despite earthquakes
- ISO 4866.2010: measurement of vibration and evaluation of the effect on structures
- ISO/TS 10811-1:2000: vibration and shock in buildings with sensitive equipment
Developing an SRS with Recorded Data
In VibrationVIEW, the user can modify a recorded field environment to meet or exceed a specified SRS. The result is a time waveform similar to the field environment and with the same frequency response function.
A modified user waveform based on an enveloped set of recordings maintains real-world characteristics and creates an SRS waveform that accurately reflects recorded events. Read more: Using Recorded Data to Improve SRS Test Development.