SUMMARY
In this study, we propose a new seismic control device, tuned viscous mass damper (TVMD), for building systems. We give a detailed description of an apparent mass amplifier using a ball-screw mechanism, which is one of the most important components for realizing the new device. We also derive a closed-form solution of an optimum seismic control design for a single-degree-of-freedom structure subjected to harmonic excitation. The performance of the new device is compared with those of the conventional viscous damper and viscous mass damper systems. The vibration control system using the TVMD is shown to be the most effective for linear structural systems with dampers having the same additional damping coefficient. The effectiveness of the TVMD for seismic excitation is verified by analyses and shake table tests with a small-scale TVMD. Copyright © 2011 John Wiley & Sons, Ltd.

Seismic control of single-degree-of-freedom structure using tuned viscous mass damper

One of the main shortcomings in current base isolation design/practice is lack of adaptability. As a result, a base isolation system that is effective for one type earthquake may become ineffective or may have adverse effect for other earthquakes. The vulnerability of traditional base isolation systems can be exaggerated by two types of earthquakes, i.e. near-field earthquakes and far-field earthquakes. This paper addresses the challenge facing current base isolation design/practice by proposing a new type of seismic isolator for the base isolation system, namely an adaptive seismic isolator. The novel adaptive seismic isolator utilizes magnetorheological elastomer (MRE) for its field-sensitive material property. Traditional seismic isolator design with a unique laminated structure of steel and MRE layers has been adopted in the novel MRE seismic isolator. To evaluate and characterize the behavior of the MRE seismic isolator, experimental testing was conducted on a shake table facility under harmonic cycling loading. Experimental results show that the proposed adaptive seismic isolator can successfully alter the lateral stiffness and damping force in real time up to 37% and 45% respectively. Based on the successful development of the novel adaptive seismic isolator, a discussion is also extended to the impact and potential applications of such a device in structural control applications in civil engineering.

https://iopscience.iop.org/article/10.1088/0964-1726/22/3/035005/pdf

Development and characterization of a magnetorheological elastomer based adaptive seismic isolator

Inspired by its controllable and field-dependent stiffness/damping properties, there has been increasing research and development of magnetorheological elastomer (MRE) for mitigation of unwanted structural or machinery vibrations using MRE isolators or absorbers. Recently, a breakthrough pilot research on the development of a highly innovative prototype adaptive MRE base isolator, with the ability for real-time adaptive control of base isolated structures against various types of earthquakes including near-?or far-fault earthquakes, has been reported by the authors. As a further effort to improve the proposed MRE adaptive base isolator and to address some of the shortcomings and challenges, this paper presents systematic investigations on the development of a new highly adjustable MRE base isolator, including experimental testing and characterization of the new isolator. A soft MR elastomer has been designed, fabricated and incorporated in the laminated structure of the new MRE base isolator, which aims to obtain a highly adjustable shear modulus under a medium level of magnetic field. Comprehensive static and dynamic testing was conducted on this new adaptive MRE base isolator to examine its characteristics and evaluate its performance. The experimental results show that this new MRE base isolator can remarkably change the lateral stiffness of the isolator up to 1630% under a medium level of magnetic field. Such highly adjustable MRE base isolator makes the design and implementation of truly real-time adaptive (e.g. semi-active or smart passive) seismic isolation systems become feasible.

https://iopscience.iop.org/article/10.1088/0964-1726/22/9/095020/pdf

A highly adjustable magnetorheological elastomer base isolator for applications of real-time adaptive control

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of concrete gravity dams

SUMMARY
Near-fault ground motions are characterized by long-period horizontal pulses and high values of the ratio between the peak value of the vertical acceleration, PGAV, and the analogous value of the horizontal acceleration, PGAH, which can become critical for base-isolated (BI) structures. The objective of the present work is to check the effectiveness of the base isolation of framed buildings when using High-Damping-Rubber Bearings (HDRBs), taking into consideration the combined effects of the horizontal and vertical components of near-fault ground motions. To this end, a numerical investigation is carried out with reference to BI reinforced concrete buildings designed according to the European seismic code (Eurocode 8). The design of the test structures is carried out in a high-risk region considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones and assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDRBs. The nonlinear seismic analysis is performed using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub-elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment–curvature law is adopted; the effect of the axial load on the ultimate bending moment (M-N interaction) of the columns is also taken into account. The response of an HDRB is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of near‐fault ground motions on the nonlinear dynamic response of base‐isolated r.c. framed buildings

The nonlinear seismic response of base-isolated framed buildings subjected to near-fault earthquakes is studied to analyze the effects of supplemental damping at the level of the isolation system, commonly adopted to avoid overly large isolators. A numerical investigation is carried out with reference to two- and multi-degree-of-freedom systems, representing medium-rise base-isolated framed buildings. Typical five-story reinforced concrete (RC) plane frames with full isolation are designed according to Eurocode 8 assuming ground types A (i.e., rock) and D (i.e., moderately soft soil) in a high-risk seismic region. The overall isolation system, made of in-parallel high-damping-laminated-rubber bearings (HDLRBs) and supplemental viscous dampers, is modeled by an equivalent viscoelastic linear model. A bilinear model idealizes the behavior of the frame members. Pulse-type artificial motions, artificially generated accelerograms (matching EC8 response spectrum for subsoil classes A or D) and real accelerogram...

Nonlinear response of rc framed buildings with isolation and supplemental damping at the base subjected to near-fault earthquakes

The insertion of steel braces equipped with viscoelastic dampers (VEDs) ('dissipative braces') is a very effective technique to improve the seismic or wind behaviour of framed buildings. The main purpose of this work is to compare the earthquake and wind dynamic response of steel-framed buildings with VEDs and achieve optimal properties of dampers and supporting braces. To this end, a numerical investigation is carried out with reference to the steel K-braced framed structure of a 15-storey office building, which is designed according to the provisions of Eurocodes 1 and 3, and to four structures derived from the first one by the insertion of additional diagonal braces and/or VEDs. With regard to the VEDs, the following cases are examined: absence of dampers; insertion of dampers supported by the existing K-braces in each of the structures with or without additional diagonal braces; insertion of dampers supported by additional diagonal braces. Dynamic analyses are carried out in the time domain using a step-by-step initial stress-like iterative procedure. For this purpose, the frame members and the VEDs are idealized, respectively, by a bilinear model, which allows the simulation of the nonlinear behaviour under seismic loads, and a six-element generalized model, which can be considered as an in-parallel-combination of two Maxwell models and one Kelvin model. Artificially generated accelerograms, whose response spectra match those adopted by Eurocode 8 for a medium subsoil class and for different levels of peak ground acceleration, are considered to simulate seismic loads. Along-wind loads are considered assuming, at each storey, time histories of the wind velocity for a return period T r =5 years, according to an equivalent spectrum technique.

Control of the earthquake and wind dynamic response of steel‐framed buildings by using additional braces and/or viscoelastic dampers

Displacement-based seismic design of hysteretic damped braces for retrofitting in-elevation irregular r.c. framed structures

The nonlinear dynamic response of reinforced concrete (r.c.) framed buildings subjected to near-fault ground motions is studied to check the effectiveness of current code provisions with reference to study cases. Three-, six- and twelve-storey r.c. plane frames, representative of symmetric framed buildings, are designed according to the European seismic code (EC8), assuming medium and high ductility classes and stratigraphic profiles A (rock) and D (soft soil) in a high-risk seismic region. The nonlinear seismic analysis is performed using a step-by-step procedure; a bilinear model idealizes the behaviour of the r.c. frame members. Artificially generated motions (matching EC8 response spectra for subsoil classes A and D) and horizontal motions (recorded on rock- and soft soil-site at near-fault areas) are considered. The results indicate that near-fault ground motions may require a special consideration in the code, in particular when designing r.c. framed structures placed on a soft soil-site; particular attention should be paid to the design of the frame members of the lower storeys.

Alfonso Vulcano

Papers

Effects of near‐fault ground motions on the nonlinear dynamic response of base‐isolated r.c. framed buildings

Nonlinear response of rc framed buildings with isolation and supplemental damping at the base subjected to near-fault earthquakes

Control of the earthquake and wind dynamic response of steel‐framed buildings by using additional braces and/or viscoelastic dampers

Displacement-based seismic design of hysteretic damped braces for retrofitting in-elevation irregular r.c. framed structures

Nonlinear dynamic response of r.c. framed structures subjected to near-fault ground motions