Abstract

Among passive energy dissipation devices, friction dampers are used worldwide as means of increasing damping into structural building systems with the aim to reduce the seismic response. These devices, added either in-line with diagonal braces, or at the intersection zone of X- and chevron-bracing and installed in moment frame buildings, can reduce the demand of the primary frame system, the interstorey drift, and control the damage of non-structural components as building envelope. Regarding to their mechanical behavior, friction dampers dissipate energy through the relative sliding of plates clamped with post-tensioned bolts, while slipping occurs along the length of the slotted hole. This device reveals a rigid-plastic behavior defined by three phases such as: “stick-slip” before sliding occurs, “slipping”, and the “slip-lock” when the force in the device increases due to the bearing of the post-tensioned bolts.
Thus, the first part of this study is focused on establishing a computer model able to simulate the three-phase behavior of the friction damper installed in diagonal bracing by using OpenSees software framework. In light of this, the Bouc-Wen material characterized by smooth transition from elastic to plastic was calibrated through parametric study and employed to characterize the first two behavioural phases mainly controlled by the slip-force and available slip-distance. In addition, earlier experimental studies conducted by Pall (1979) were used to control the calibration. To simulate the slip-lock phase exhibited due to bearing of post-tensioned bolts, gap-elements were added in parallel to the Bouc-Wen model. In addition, to complete the friction-damped brace model, the action in series of the elastic brace and the friction damper model is considered.
The second part of this study illustrates the behavior of the 4, 8 and 12-storey building designed as moderately ductile (MD) moment resisting frame structure accordingly to NBCC 2010 and CSA/S16-2009. The studied buildings are located in Montreal and are subjected to 15 simulated and historical ground motions scaled to match the uniform hazard spectrum. Herein, beams and columns were defined as nonlinear force-based beam column element with fiber section and Steel02 material. From analyses, the mean values of the following parameters: maximum interstorey drift, maximum drift angle and maximum beam rotation are computed.
The third part is designated to analyze the seismic response of MD-MRF structures equipped with friction-damped brace devices through numerical simulations of 4-, 8- and 12-storey building, using OpenSees. It is showed that the proposed hysteresis model for friction-damped brace responds well under dynamic loading and it is able to tune the response within the prescribed limits. Driving devices into bearing shows transitional changes consisted of decreasing damping and increasing stiffness. When this phase is encountered, the MD-MRF might respond as a back-up system and as a re-centering system. It is revealed that the three-phase hysteresis model of friction damper developed in this study must be calibrated against experimental test results conducted under cyclic loading until failure is reached. Due to lack of experimental test results several assumptions were made.