Modal analysis and seismic response of steel frames with connection dampers

To reduce dynamic response of a steel frame of bolted connections, energy dissipation materials may be placed at a connection between the end plate and column flange or between the angle and member flange. By idealizing bolted connections and energy dissipation materials as rotational spring and damper respectively, this paper derives the mass matrix, stiffness matrix and damping matrix for the frame using a combination of the finite element method and the direct stiffness method. The complex modal analysis is then carried out to determine dynamic characteristics of the frame and to investigate the effects of connection stiffness and rotational damper on natural frequency and modal-damping ratio. By further introducing a generalized pseudo-excitation method, the vibration analysis of the frame subject to earthquake excitation is performed in the frequency domain to see how the connection stiffness and rotational damper affect the seismic performance of the frame. The parametric studies on the example frame with and without the connection dampers show that there is an optimal damper damping coefficient by which the modal-damping ratio of the frame can be considerably increased and the seismic responses, including both lateral displacements and internal forces, can be significantly reduced.