An analytically obtained mathematical model of interaction between elements of cable-stayed bridges is developed. The influence of system's geometry, mechanical and physical parameters of main load-bearing elements (cables, pylons and stiffening girder) on the behaviour of all structure is observed. Some results and useful recommendations about optimal solution from economical and technical point of view are presented. A way to improve the fatigue conditions of the cable-stayed bridge is installation of active devices, which in an exact moment can decrease deformations and stresses from elements with poor load bearing capacity by giving them away to the others with higher capacity. Properties of such a system can be examined by the proposed method.