Serviceability conditions of friction dampers for seismic risk mitigations

Abstract

Friction dampers are widely used in structural vibration control to mitigate seismic risks. In literatures, many different friction damper designs have been proposed, tested and implemented, but most studies concerned the performance of newly fabricated dampers and very few considered their long-term behavior. Since most friction surfaces are made of metals, corrosion or grease contamination during the lives of dampers may occur, and subsequently their energy dissipating characteristics may be adversely affected. In this study, the effects due to different serviceability conditions of a linear motion friction damper are investigated. It begins with experimental investigations of damper specimens with four different serviceability conditions: (1) polished and dry, representing as-new condition, (2) polished and greased, representing a contaminated condition, (3) rust and dry, representing a long-term condition and (4) rust and greased, representing a long term and contaminated condition. Force-displacement hysteresis is obtained under cyclic loads. Coefficients of friction are calibrated from finite element models. It was found that the coefficient may reduce from 0.7 (as new, polished condition) to 0.16 (rust and greased condition). Energy dissipation is reduced by 56% in the experiments. In a following numerical investigation, such serviceability conditions are applied to a numerical building model subjected to earthquake ground motions. Results indicated that, corrosion and grease contamination diminish the effectiveness of dampers. In the worst scenario, the beneficial effects of added friction dampers is entirely removed if rust and grease is allowed to build up on friction surfaces.