The Spectral Matching module creates high-quality design ground motion time histories by taking actual earthquake accelerograms and adjusting them to match a target response spectrum. These time histories are used by structural engineers in non-linear analyses of the dynamic response of buildings and soil structures to earthquake ground shaking.

The ground motion time histories used in structural analyses need to accurately reflect a design level of safety and have realistic time-dependent characteristics. This requirement can be met by:

• Providing a target response spectrum that reflect the desired design level of safety,
• Carefully choosing accelerograms as input, and
• Using a powerful spectral matching algorithm.

EZ-FRISK™ gives you the tools to get this job done.

Target Response Spectrum

With EZ-FRISK™, you can provide a user-defined target spectrum or match to a uniform hazard spectrum from a probabilistic seismic hazard analysis.

By matching to uniform hazard spectrum, the design ground motion will consider the likelihood of earthquakes occurring at all surrounding faults, as well as the ground motion arising at a site from earthquakes of various magnitudes and distances. With EZ-FRISK™, you can directly enter the design return period.

Input Accelerogram Choice

Real earthquake ground motions have complex time-dependent behavior that is influenced by the magnitude of the earthquake and the distance between the earthquake epicenter and a site. With EZ-FRISK™, you can identify one or several combinations of magnitude and distance that characterize the seismic hazard of a site by using seismic hazard analysis to deaggregate the hazard by earthquake magnitude and distance.

EZ-FRISK™ provides a very useful tool that allows you to search through several thousand accelerograms in just a few minutes according to user-defined criteria. It displays all of the accelerograms, with thumbnail previews of the time histories and response spectra, sorted by the weighted criteria. The following criteria can be weighted by the user:

• RMS (target – scaled response)
• Scaling factor
• Arias duration (target – measured)

You can choose events with appropriate distance and magnitude from the highest-scoring accelerograms. This feature can save you hours in selecting good initial accelerograms.

Spectral Matching Algorithm

EZ-FRISK™ provides Norm Abrahamson’s time-dependent spectral matching method — RSPMATCH — with an integrated, interactive, visual user interface. RSPMATCH is widely considered to more reliably create realistic ground motions than methods that operate in the frequency domain.

Spectrally matched ground motion time histories for bedrock should be further processed to incorporate the site response, which is the modification of the time history caused by the unique layering of rock and soil at the site. EZ-FRISK™ now includes Site Response Analysis using SHAKE91. SHAKE91 propagates the bedrock time history through soil and rock layering to produce a site-specific outcropping ground motion. With EZ-FRISK™, you can quickly process a suite of matched accelerograms.