BISpec is a user-friendly program that computes Linear and Nonlinear spectra of earthquake records. Bispec makes it extremely easy to compute constant-ductility spectra and constant-strength spectra, for an Earthquake ground motion record, or to compute spectra and statistics (mean, standard deviation, etc.) for a suite of ground motions.

Bispec can also be used to analyze a single SDOF system under any ground acceleration record, and plot the displacement or force response over time. You can even watch an animation of the shaking in real time!

Since real earthquakes are not Unidirectional, each earthquake in Bispec can have either one or two components, which makes it easy to generate spectra for two directions (Bidirectional), as well as spectra for the 2D resultant of the two directions (Planar Spectra).

The program offers great flexibility for changing the dynamic properties of the SDOF system, such as Mass, Stiffness, Period and Damping.

In addition to elastic response, the nonlinear response of the structure can be specified by selecting one of several hysteretic models. The program currently has three nonlinear models. The current nonlinear models are:

  1. Bilinear model,
  2. Bilinear with Stiffness Degradation, and
  3. A Plasticity-Based Bilinear Coupled Element with Bi-directional interaction.

Linear spectral analysis can be performed by specifying multiple frequencies. Ranges of strengths could also be specified in nonlinear analysis which results in "Constant Strength Spectra". The program can also perform target searches for ductility resulting in "Constant Ductility Spectra".

The feature list does not stop here! Bispec is full of other features that make it an outstanding educational tool (such as the test-drive feature of the different hysteretic models and point-click feature of the spectra plot), and an essential utility for researchers and engineers working on seismic projects. An Engineer or researcher can obtain quick results by running a set of linear or nonlinear spectra in minutes or seconds! Additionally, multiple sets of nonlinear spectra can be plotted as a 3D surface plot, making it easier to visualize complex relationships.

Several ground motion formats can be easily imported and analyzed. Currently supported formats are the SAC, PEER, NGA, USC, SMC (USGS), and CSMIP (CDMG) ground motion formats. The program also supports a User-Defined option that can be used to fit a wide variety of other simple formats.