Since the topics concerning quantifying dynamic behaviour of different mechanical systems are still of engineers’ concern, there is a significant need of developing new numerical approaches dealing with this research area. While discussing those issues, problems of effective modelling of uncertainties can not be neglected. One should know what is the influence of product variability and uncertainty of design parameters on natural frequencies and normal modes of considered systems. In the paper, dynamic behaviour of spot weld joints is studied. This way of metal linking is mostly used in automotive industry and it is very important to find out as much as possible about vibrations of car body in order to constantly improve comfort of travelling [
]. Finite element method is used for spot welds modelling. A several different variants of model displacements are considered. Different model meshes are used in order to quantify the convergences of the solutions. As far as modelling of uncertainties is concerned, a number of varying parameters are taken into account. Thicknesses of joined shell parts as well as material parameters are assumed to be uncertain. Positions of spot welds and their sizes are also not constant and can change their values randomly within specified ranges. There is a quite large set of existing methods which allow to solve dynamic problems and to introduce uncertainties into models. Some of them are being still developed like the transformation method and new approaches appear as combinations of existing ones. In the paper, genetic algorithms application is being tested as the main tool for mentioned research area. It is based on the optimization of global mass and stiffness matrices of mechanical system [
]. The first natural frequency is evaluated and its relationship with the ranges of uncertain parameters is discussed. The reference results are obtained with Monte Carlo Simulation approach, the vertex method, the transformation method and genetic algorithms used directly for optimizing the first natural frequency. Advantages and drawbacks of tested method are presented and conclusions about its applicability for different types of mechanical structures are described.