Implementation of advanced flag-shaped (AFS) systems for moment-resisting frame structures
A second generation of self-centering/dissipating systems, referred to as Advanced Flag-Shape (AFS) systems, has been recently proposed by the authors, consisting of combination of alternative forms of energy dissipation (yielding, friction or viscous damping) in series and/or in parallel with re-centering elements to achieve high seismic performance for both far-fault and near-fault motions. In particular, the unique properties of a system combining friction dampers in series with viscous dampers, then combined in parallel with re-centering and hysteretic dissipation elements, was found to lead to an enhanced, predictable and controllable performance of single-degree-of -freedom (SDOF) systems. In this contribution, after a brief introduction on the concept of the AFS systems, the extension of the concept from SDOF to MDOF frames systems is discussed and numerically investigated. Two critical issues of extending AFS for SDOF systems to MDOF frame systems are briefly discussed: a) the excitation velocities up the structure b) the global frame damping capacity within DDBD design. With reference to a set of frame systems, initially designed for self-centering un-bonded post-tensioned precast concrete frames using Direct Displacement-Based Design (DDBD), the seismic performance of AFS frames in comparison to conventional frames is investigated by means of non-linear time-history analyses using a suite of far field and near-fault earthquake excitations, where three key global response parameters are examined.