**APIS** - ATENA Parameter Identification Software - is an experimental parameter identification program used to determine input values of nonlinear simulations. A set of desired output values are compared to the simulation outputs and the selected optimization method is applied to provide a set of input parameters for the next iteration. Attempts to reach a solution which yields outputs closest to the desired values are carried out according to user preferences, namely the maximum number of iterations and the target error.

**APIS FRC** module offers an automated procedure to determine the multilinear function describing the tensile behavior of fiber reinforced concrete in ATENA models. A similar manual procedure is described in ATENA Science – GiD FRC Tutorial, including a detailed description of the ATENA material model CC3DNonLinCementitious2User used in the example.

**APIS SA** module provides a general inverse analysis procedure to determine values of ATENA model inputs. Given a set of desired outputs, a sensitivity analysis is performed for selected input variables, and a set of linear equations is defined and utilized in the iteration process. The sensitivities of each output to each input are calculated using FReET software and stored in a dedicated file named “SA.fre”. The error minimization function defined by the program is based on the obtained sensitivities and a Taylor expansion of outputs and inputs, which are translated to a locally linearized system. By solving the linear system, a new set of inputs is extracted and used in the next iteration.

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The results presented on this website were achieved within project FV30244 "IdeMaS" by MPO TRIO3 supported by Ministry of Industry and Trade of the Czech Republic.
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