Numerical verification is presented for modelling the magnetic effect of concrete structures reinforced with steel rebar. The model is based on the filling factor concept and takes into account magnetic anisotropy associated with the rebar pattern. Test problems are solved that prove applicability of the model in case of nonlinear properties of the reinforcement steel. A nonuniform field distribution is studied for a reinforced structure with an internal field source. Accuracy of simulated field maps with high gradients near ends of modelled structures has been assessed. The model has been verified in comparative computations with the use of other models. As an example, the proposed approach has been applied to a simplified magnetic model of the ITER tokamak complex. Then fields perturbations associated with the tokamak building structures have been evaluated for the gas breakdown at plasma initiation.