Seismic Response Evaluation of Posttensioned Precast Concrete Frames with Friction Dampers

Abstract

This paper presents a seismic response evaluation of unbonded posttensioned precast concrete moment frames that use friction dampers at selected beam ends. The dampers utilize the displacements that occur as a result of gap opening between the beam and column members during an earthquake. The parameters investigated include the number of stories, number and strength of the dampers, and amount of posttensioning. Nonlinear static and dynamic time history analyses of prototype structures show that the dampers provide a considerable amount of energy dissipation to a frame, while the posttensioning force provides a restoring effect resulting in self-centering capability (i.e., ability of the structure to return towards its undisplaced position upon unloading). The seismic design of the structures to achieve target displacement-based performance objectives is critically evaluated based on the analysis results. Comparisons with structures that use mild steel (e.g., Grade 60) reinforcement through the beam-column joints as well as structures that use only posttensioning steel (with no friction dampers) and structures that use combinations of mild steel and posttensioning steel are also provided.