A practical optimisation method for friction tuned mass dampers in multi-storey buildings subjected to earthquake excitations

To reduce lateral drifts, the parameters of friction tuned mass dampers (FTMDs) need to be "tuned up" during the design process, which can be a challenging task for multi-storey buildings subjected to real ground motions. To address this issue, this article proposes a practical particle swarm optimisation (PSO) algorithm to optimise simultaneously the parameters (frequency ratio and friction ratio) of FTMDs fitted on multi-degree of freedom (MDOF) systems and frames subjected to real seismic records. First, elastic MDOF systems with FTMDs were modelled in OpenSees software considering different number of storeys (5, 10 or 20), periods and stiffness distributions. Optimised frequency ratios and friction coefficients of FTMDs and the main structure response were then derived using an objective function that minimised the structures' maximum average roof displacement. FTMDs with optimised parameters proved very effective at reducing average roof displacements of the examined MDOF structures by up to 39 %, but the magnitude of the reduction depended on the period of the structure. Subsequently, the effectiveness of FTMDs at controlling the response of inelastic steel momentresisting frames (MRFs) was examined. For the examined structures and seismic records, the use of optimised TMDs led to marginally smaller (2%) roof displacements when compared to FTMDs. Therefore, FTMDs can be as effective as TMDs devices but with added advantages of less susceptibility to aging and temperature variations. It is also shown that higher mode effects experienced by real MRFs can be captured accurately by equivalent MDOF systems (difference in responses <4 %), which can therefore simplify the design.