In this paper, the strength analysis of the material from two elements of a portal crane operated for about 33 years was carried out. The assessment was based on modelling and numerical simulation results using the finite element method of the load of three-point bending specimens. The constitutive relationships of the materials in the form of true stress-strain relationships were defined based on data from the uniaxial tensile test of the appropriate specimens. The iterative fitting method of the experimental and numerical relationship and the method that considers triaxiality and the Lode parameter were used. The accuracy of the defined stress-strain relationships was verified by comparing the load curves determined experimentally and numerically. Numerical modelling and simulation of the load of three-point bending specimens allowed obtaining stress distributions before the crack tip and the values of fracture toughness – J-integral. The results of the numerically calculated J-integral are similar to the experimental results. The trends in the stress component distributions indicate a high level of fracture toughness of the tested materials, ensuring a ductile nature of subcritical crack growth. The proposed methodology can be applied to other steels of operated structures.