Stiffness and strength behaviour of light weight components in the automotive industry are significantly affected by the properties of the joints. The applied joining process, the number and the location of the spot joints have thus a large technological and economic influence. The strength of spot welds can only marginally be increased by the strength of the applied plate material. By application of high strength steels the utilization of mechanical joining techniques like self piercing riveting is recommended which exhibit higher strengths. Because of light weight design and safety aspects the application of high strength steels in the development of car bodies becomes increasingly important. For an efficient design and optimization of these complex structures reliable CAE techniques are required. For spot welding suitable models for the evaluation of strength and life time of complex structures like car bodies have already been developed, but sufficient models for calculation of self piercing riveted joints are not existent up to the present, because the strength properties of mechanical joints are more difficult to integrate. For this reason, a substitution model has been created which accounts for a correct local stiffness and enables life time assessments. The model has been calibrated based on test data and by parameters like material properties, plate thickness, rivet diameter and their combinations into account. The result is a substitution model similar to that applied to spot welding, but by consideration of additional parameters to achieve a good agreement with the experiments. Summarizing, the substitution model covers all parameters (plate thickness, rivet diameter) which are relevant in the automotive and light truck industry.