Performance Of Base Isolation System Research Articles

Comprehensive Assessment of the Seismic Performance of an Innovative Hybrid Semiactive and Passive State Control System for a Low-Degree-of-Freedom Structure Using Real-Time Hybrid Simulation

The dynamic performance of base isolation systems provides an effective means to reduce the seismic vulnerability of buildings. However, large displacements in the base isolation during seismic events pose a major challenge for this control system. Recently, novel control systems have been implemented to control and reduce the excessive displacements. This study presents an evaluation of the seismic performance of unconnected-fiber-reinforced elastomeric isolators (U-FREI) and variable orifice damper (VOD) devices used together as a hybrid control system for a low-degree-of-freedom reference structure by employing real-time hybrid simulation (RTHS) testing technique. This physical cybernetic testing methodology allows a dynamic system of interest to be substructured into two components: numerical and experimental. In this study, the numerical substructure corresponds to a 2-degree of freedom model, representing a reference structure, and an experimental substructure was formed using the hybrid control system described. To develop an interface between the two substructures, a horizontal transfer system (HTS) was implemented and coupled with a vertical transfer system (VTS). Using RTHS, the performance of the reference structure and the hybrid control system was evaluated under six seismic events: CAM, CAT, El Centro, Loma Prieta, Pizarro, and Chihuahua, at a maximum acceleration of 0.10 g (0.981 m·s−2). The experimental behavior of the hybrid control system allows the reference structure to reduce its maximum drift by more than 24% compared to the fixed structure. Finally, the performance and accuracy of the RTHS tests were calculated.

Effects of Building Height and Seismic Load on the Optimal Performance of Base Isolation System

AbstractSeismic isolation has been widely accepted as one of the techniques that can be used to protect structures during earthquake ground motions. However, some challenges still exist such as the optimal control of excessive isolator shear strains imposed by some ground motions. The main purpose of this study was to assess the effects of building height variation and earthquake ground motion type on the optimal performance of the seismic isolation using lead core rubber bearing (LCRB). Nonlinear time history analysis for building models of various storeys isolated by LCRB and exposed to different real earthquakes was performed. To achieve this, the equations governing the motion of the isolated three different building models were presented, and an approach for solving the equations while taking into consideration of the optimized mechanical properties of the LCRB was developed. The LCRB performance was measured in terms of elastomer shear strains, derived after an optimal criterion leading to reliable substructure and superstructure responses was reached. The results showed that the combined effects of the earthquake type and building height significantly affect the substructure responses (maximum isolator displacement, energy dissipation capacity, maximum isolator force) and the superstructure responses (storey shear forces, storey drifts, floor displacements, and floor accelerations), which in some cases lead to a need for adding a fluid damper. In this regard, an attempt to couple the LCRB with nonlinear fluid viscous damper was made, and the performance of the hybrid was assessed. It was generally found that the hybrid can positively improve the substructure responses, thereby reducing the unwanted large elastomer shear strains without adversely affecting the superstructure responses.

Seismic vibration control of bridges with excessive isolator displacement

The effectiveness of base isolation (BI) systems for mitigation of seismic vibration of bridges have been extensively studied in the past. It is well established in those studies that the performance of BI system is largely dependent on the characteristics of isolator yield strength. For optimum design of such systems, normally a standard nonlinear optimization problem is formulated to minimize the maximum response of the structure, referred as Stochastic Structural Optimization (SSO). The SSO of BI system is usually performed with reference to a problem of unconstrained optimization without imposing any restriction on the maximum isolator displacement. In this regard it is important to note that the isolator displacement should not be arbitrarily large to fulfil the serviceability requirements and to avoid the possibility of pounding to the adjacent units. The present study is intended to incorporate the effect of excessive isolator displacement in optimizing BI system to control seismic vibration effect of bridges. In doing so, the necessary stochastic response of the isolated bridge needs to be optimized is obtained in the framework of statistical linearization of the related nonlinear random vibration problem. A simply supported bridge is taken up to elucidate the effect of constraint condition on optimum design and overall performance of the isolated bridge compared to that of obtained by the conventional unconstrained optimization approach.

Seismic response analyses of an asymmetric base-isolated building during the 2011 Great East Japan (Tohoku) Earthquake

Analysis of strong motion recordings of a base-isolated building during the March 11, 2011, Great East Japan (Tohoku) Earthquake is reported in this paper. The building, located in Tokyo Bay area, is an asymmetric L-shaped structure consisting of seven-story and 14-story building with vertical opening. Vibration monitoring system was installed on the building in 2010, and seismic responses were recorded including the strongest shaking (peak ground acceleration 0.80–1.40 m/s2) experienced during the main shock of March 11, 2011, Great East Japan Earthquake. The building survived the earthquake without structural damage. The study in this paper includes response analysis, system identification, and seismic performance evaluation of the structure, especially performance of base-isolation system. The study shows that despite considerable shift in effective frequency of the building due to the increase in flexibility of isolation system during the main shock, large acceleration was recorded on the superstructure with the peak floor accelerations of nearly 300 cm/s2. Two factors contribute to this cause: one is the characteristics of the building where torsional modes dominate the seismic response of upper stories and the other is resonance, where dominant frequencies of ground motions coincide with the natural frequencies of torsional modes. Moreover, analysis shows that torsional modes were not significantly influenced by performance of base isolation, so that even though the base isolation has functioned properly, the upper stories still experienced large floor accelerations. The paper also discusses long-term observation of seismic responses during aftershocks and various levels of earthquakes between 2010 and 2012. Copyright © 2014 John Wiley & Sons, Ltd.

An external rotary friction device for displacement mitigation in base isolation systems

An analysis of the effect of recently observed near-fault and anticipated long-period ground motions indicates that conventional base isolation systems need an immediate retrofitting for improving their performance against earthquakes. In particular, the large displacement response of isolators, which might exceed the displacement limits, is of outmost importance. This study proposes a new external device for mitigating the displacement in conventional base isolation systems. The device consists of a rotary friction system with a wire wound on a shaft connected to a coil spring. The efficacy of the rotary friction is controlled by attaching a so-called ‘ratchet switch’ to the isolated object, which works in accordance with the changes in the direction of the movement at the end of the wire. Through computations, this study verifies the improvement in the performance of base isolation systems by using the rotary friction device. The results show that the proposed device markedly reduces the lateral displacement response of the systems against both near-fault and long-period ground motions. Furthermore, the robustness of the system with respect to the mechanical properties of the friction device is also verified for practical use. Copyright © 2013 John Wiley & Sons, Ltd.

Numerical assessment of seismic safety of liquid storage tanks and performance of base isolation system

Seismic isolation is a well-known method to mitigate the earthquake effects on structures by increasing their fundamental natural periods at the expense of larger displacements in the structural system. In this paper, the seismic response of isolated and fixed base vertical, cylindrical, liquid storage tanks is investigated using a Finite Element Model (FEM), taking into account fluid-structure interaction effects. Three vertical, cylindrical tanks with different ratios of height to radius (H/R

Performance of base isolation systems for asymmetric building subject to random excitation

The stochastic response of a one-storey model of a base isolated asymmetric building to random ground excitation is computed using the state space formulation. Three types of base isolation devices are considered: the laminated rubber bearing (LRB); the New Zealand system (NZ); and the resilient-friction base isolator (R-FBI). For the NZ and R-FBI systems, for which force-deformation behaviour is nonlinear, an equivalent linearization technique is applied to obtain an approximate response. The effect of linearization on the response is investigated by comparing the responses of the linearized solution with those obtained from simulation analysis. The RMS responses of the system are obtained under different parametric variations in order to investigate the effectiveness of different base isolation devices for stationary random ground motion. The study shows that the stochastic response of the asymmetric building isolated by an R-FBI system is less sensitive to the parametric variations.

A comparative study of performances of various base isolation systems, part II: Sensitivity analysis

AbstractA series of numerical experiments on the performance of different base isolation systems for a non‐uniform shear beam structure is carried out. Several base isolation systems are considered and the peak relative displacements and the maximum absolute accelerations of the base‐isolated structure and its base raft under a variety of conditions are evaluated. Several sensitivity analyses for variations in properties of the base isolator and the structure are carried out. A number of different earthquake excitations are also used in the study. The results show that performances of the base isolation systems are not sensitive to small variations in their natural period, damping or friction coefficient. The presence of a frictional element in the isolators reduces their sensitivity to severe variations in frequency content and amplitude of the ground acceleration. In particular, the resilient‐friction base isolators with or without sliding upper plate perform reasonably well under a variety of loading conditions. The rubber bearing type, however, leads to the lowest peak transmitted accelerations for moderate intensity earthquakes.