This paper provides an overview of cyclically loaded structures and experimental investigation techniques. The chemical composition and mechanical characteristics of the steels that crane secondary trusses and transporter cranes are made of are presented.Relative levels of the basic compressive and tensile stresses at truss chords and deck girder members are presented. The most heavily loaded pans of structures with possible fatigue crack formation have been revealed. It has been found that the indication of the presence of considerable fatigue deterioration is an elevated deformability of a structure or a change of its deformation diagram.