Keywords: precast frame structures, friction devices, energy dissipation, seismic retrofitting.

This paper describes a numerical study on a new type of friction damper proposed by Morgen and Kurama [1] with the aim of improving the seismic performance of precast concrete frame structures by using supplemental passive energy dissipation. The proposed friction damper is used locally at the beam-to-column joints of precast concrete frame structures without the need for braced members. To reduce the seismic displacement demands, the dampers dissipate energy through the relative rotation that occurs between the precast beam and column members. Post-earthquake inspections and repair of the beam-to-column joints can be easily completed since the dampers are placed externally to the joints. A simplified analytical model for the friction damper was developed and implemented in the computer code Ruaumoko. Parametric analyses were carried out in order to establish the optimum value of the slip force of the device and nonlinear dynamic analyses were conducted on different types of precast structures with and without dampers. A considerable reduction of the maximum top displacements was observed in the case of structures equipped with dissipating devices. The difference between the maximum top displacements of the structures was small for low-intensity level earthquakes, but it significantly increased in case of severe seismic actions. The application of the friction devices decreased the rotation demand at the column base of the structures. In case of severe seismic actions the rotation reduction was significant giving rise to a considerable decrease of the demand-to-capacity ratio. Moreover the numerical analyses showed a delay in the formation of the plastic hinges at the column base in the case of structures equipped with dissipative devices. The introduction of the friction devices decreased the damage at the column base, providing a considerable contribution to energy dissipation and to the reduction of the top displacement. The friction devices caused a moderate increase of the base shear, influenced by the values adopted for the slip force of the friction devices. The energy dissipated by the structural elements of the reference structures was reduced significantly by the insertion of the friction devices. The energy dissipation mostly concentrated in the device, decreasing the plastic demand in the structural elements of the reference structures. The energy dissipated by the protected structures, practically entirely due to the friction devices, showed a considerable decrease with respect to the original structures, consistent with the significant reduction of the top displacements.

1

B. Morgen, Y. Kurama, "A friction damper for post-tensioned precast concrete moment frames", PCI Journal, 49(4), 112-133, 2004.

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