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Structural response module
To compute the nonlinear response of the single-degree-of-freedom (SDOF) oscillators, the VMTK was integrated with the open-source finite element model software OpenSees through its Python implementation. The nonlinear behaviour was introduced in numerical models though the uniaxial material Pinching4 and the capacity curves previously introduced by the user.
The numerical model allows for cyclic strength degradation that is implemented in three stages: (i) unloading stiffness degradation, (ii) reloading stiffness degradation and (iii) strength degradation. It should be noted the users can deactivate strength degradation by setting it to None on the GUI or False in the source code. Advanced users are welcomed to edit the degradation implementation to better suit their applications.
The toolkit allows modellers to include damping in their analyses. The default implementation is a mass proportional Rayleigh damping, but other damping options are available, as described in the OpenSees manual. When using the GUI, damping should be introduced through a comma delimited file containing two columns in which the first holds the building classes tags and the second their respective damping ratio. This format allows for batch computation of structural response across different building classes, only requiring the user to input the path to the directory containing the capacity curve files
Users can export either the maximum displacement (Max displ.) or the maximum acceleration (Max accel.) as the EDPs. These will be stored as csv files containing the results of the structural analysis as presented as a column array. For convenience when using the GUI the toolkit will also output a csv file containing the IML for each ground motion record for all the preloaded intensity measures. It was deemed necessary to provide the GUI with plotting capabilities that allows users to visually inspect their results, therefore the users are capable to plot the relationship between EDPs vs IML directly on the toolkit environment.