Advanced Flag-Shaped Systems for High Seismic Performance Including Near Fault Effects
Experience with recent earthquakes near urban centers (Northridge 1994, Kobe 1995, Chi-Chi 1999) highlighted two major challenges in seismic engineering: the hazard and peculiarity of near-fault earthquakes, characterised by low number of cycles and high velocity pulses in its motion and the urgent need for performance-based design and retrofit approaches for buildings in near-fault urban centers such as Wellington City. Meanwhile, the development of high-performance seismic resistant hybrid systems or flag-shape systems, incorporating combination of re-centering elements and hysteretic energy dissipation, have shown to significantly reduce the expected level of damage when compared with traditional (i.e. monolithic) ductile systems. However, traditional hysteretic dissipation is considered inherently inadequate to counteract the near-fault effects. In this paper, the innovative concept of Advanced Flag-shape Systems (AFS) is proposed as an alternative solution for high-seismic performance system in near-fault regions. AFS combines alternative forms of energy dissipation (yielding, friction or viscous damping) in series and/or in parallel together with re-centering elements to achieve high seismic performance for both far-fault and near-fault motions. The concept of AFS is first briefly discussed qualitatively and then numerically investigated using SDOF models subjected to push-pull and time-history analyses under a suit of far field and near fault events. Finally, the enhanced performance of AFS systems is compared and discussed with monolithic solutions or more traditional Flag-shape systems.