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In this paper the stiffness matrix for a straight two-node crackedTimoshenko beam element is derived. The equation of motion of the complete systemincludes translational and rotational mass matrices. The vibration characteristics ofplane frame structures with a single edge crack are investigated using a modified line-spring model. The natural frequencies and the corresponding mode shapes aredetermined for edge cracks of different depths. By using an extension of the Pariscrack propagation law, the fatigue evolution of cracked frame-structures and thedetermination of the bending moment redistribution is analysed and graphicallyillustrated. The retarding effect on the crack growth rate in the case of redundantstructures subjected to repeated loading is pointed out.