Mitigating higher mode effects in self-centering rocking frames by using a tuned mass damper

This paper proposes the application of tuned mass dampers (TMDs) for mitigating higher-mode effects in controlled rocking steel braced frames (CRBFs). The numerical study evaluates the effectiveness of using TMDs in rocking frames under different earthquake records. Furthermore, a connection detail is proposed to isolate the rocking frame from the diaphragm. The modified modal superposition (MMS) method is employed to design 12-, 16-, 20-, and 24-story CRBFs. Nonlinear response history analyses are performed to examine the influence of higher mode effects for the designed frames under twenty-two far-field ground motion records and fourteen near-field records without strong pulses (referred to as the FF and NF ground motion records, respectively). Furthermore, a particle swarm optimization algorithm is implemented to minimize higher mode effects in CRBFs with a TMD. Two optimization problems, Op1 and Op2, are considered for incorporating TMDs into the rocking frames. In Op1, the optimal TMD parameters, mass ratio, frequency, damping coefficient, and location are found. Subsequently, Op2 examines the specifications of the rocking joints, energy-dissipating fuse stiffness, fuse yield strength, number of cables, and the initial post-tensioning ratio of the PT cables, in addition to the TMD-related parameters and TMD placement. On average, the reductions in median story moments and shear demands in optimal designs are up to 18% and 24% under FF ground motion records and up to 22% and 29% under NF ground motion records, respectively. Finally, recommendations are presented for TMD and rocking joint parameters for the design of CRBFs equipped with TMD. • Proposed the use of a TMD in controlled rocking steel braced frames (CRBFs). • Evaluated the effectiveness of using TMDs in reducing higher mode effects. • Performed nonlinear response history analyses under far- and near-field records. • Proposed a connection detail to isolate the rocking frame from the diaphragm. • Performed optimization studies on rocking frames with a tuned mass damper (TMD).