Matlab Codes for Computing FOSID

An appropriate seismic intensity measure (IM) for response prediction is central to reliable probabilistic seismic demand modeling of structures and subsequently, risk and resilience quantification. Fractional order IMs have shown the potential to yield improved demand models in recent studies. To further increase confidence in demand models, a novel Fractional Order Spectrum intensity measure considering Integral period and Damping ratio (named FOSID) is proposed. MATLAB/Simulink codes for computing FOSID are provided in this project as well as information about them in the Readme file. Given an input ground acceleration time series, users can easily obtain FOSID by executing the main file “FOSID_example.m” with the definition of the three key parameters in FOSID, including the fractional order, damping ratio, and upper bond of integral period. It is worth noting that FOSID has been found superior than Housner intensity (HI) – an optimal traditional IM, and the average spectral acceleration (Saavg) – a state-of-the-art non-fractional-order IM, for bridges under earthquake-induced liquefaction and lateral spreading hazard. It is expected that the benefits of FOSID can be most readily observed for long and/or tall structures with large fundamental periods or for structures in complex geotechnical conditions with significant nonlinear behavior and period elongation.