Abstract Summary
An inerter is a mechanical two-terminal device that creates a force proportional to the relative acceleration between its terminals. A unique feature of this device is that it has the potential to produce high dynamic mass while its static mass remains at a fixed value. These devices, used as tuned inerter dampers (TIDs) at lower levels of multi-storeyed structures, have been noted in the existing literature to be superior alternatives to tuned mass dampers (TMDs), since they do not add high static mass on the top. The present study focuses on investigating the inelastic dynamic behavior of frames fitted with inerters. The study takes into account features such as various aspects of inelastic frame behavior (viz., strain hardening, pinching, and stiffness and strength degradation), bending-torsion coupling, irregularities in elevation (leading to weak and (or) strong ground floors), and transient nature of the ground motions. The focus of the study is on investigating the role of TIDs in (a) reducing the response and ductility demand, (b) enhancing load carrying capacity in linear regime by delaying the inception of yielding, (c) reducing the hysteretic energy absorbed and hence the damage to the system, and (d) modifying the magnitude of base shear transferred to the foundations. The question of optimal placement of TIDs, especially when the frames are prone to bending-torsion coupled oscillations, is also considered. We begin by validating the mathematical model for a frame with an inerter by comparing the model predictions with experimental observations made on a three-story shear frame tested on an electro-mechanical shake table. This is followed by two studies: Study-1: Here, we focus on the behavior of a five-storeyed inelastic building frame model fitted with a TID at the ground floor level and subject to transient earthquake support motions. The difference that the TID makes to ductility demand, hysteretic energy absorbed, and global damage indices is investigated. Study-2: Here, we consider a one-story frame asymmetric in plan, subjected to two-component earthquake support motions. The influence of location and number of TIDs on the bending-torsion coupled inelastic behavior of the frame is investigated. The presence of the inerter as TID in these studies is observed to be beneficial in terms of reducing response features such as the ductility demand, total hysteretic energy absorbed, and measures of global damage. On the other hand, the study notes that the magnitude of the base shear transferred to the foundation increases due to the presence of TID. The study points towards the need for investigating the behavior of large-scale realistic building frames fitted with inerter-based devices, developing strategies for choosing the optimal placement and number of inerters, and allowing for random nature of the earthquake ground motions in the models to take into account diversity of frequency content and duration.
