Resilient-friction Base Isolator Research Articles

Seismic Fragility Assessment of RC Building Using HAZUS Methodology and Incremental Dynamic Analysis

The technique of coupled building strategy is more viable to protect the adjacent buildings of dissimilar in characteristics against seismic hazards. The philosophy of coupled building control in which adjacent buildings are allowed to exerts counter-acting forces one upon another. This study includes the seismic performance of various Coupled Buildings with respect to Uncoupled Buildings for which two models of Coupled Building are considered that is, first one is the two-shear type adjacent buildings connected in-line with MR dampers and second one is same as first with taller building is isolated by Resilient-Friction Base Isolator at its foundation. The seismic response analysis of RC coupled buildings are studied in terms of peak responses subjected to unidirectional excitation due to Kobe 1995 earthquake. The governing equation of motion of various coupled buildings is solved numerically by Newmark’s step-by-step method. The dynamic behaviour of semiactive MR damper and R-FBI base isolation system has been predicted by modified Bouc-Wen model and Wen’s model respectively. This study employed the Lyapunov direct approach as a control algorithm for the stability analysis and design of semiactive MR controller. The responses of various coupled buildings and uncoupled buildings are simulated through MATLABâ computing software. This study outlined that model of Coupled Building-2 performs more effective in controlling the seismic responses whereas model of Coupled Building-1 performs well not only in reducing the responses but also avoid pounding from the adjacent buildings. Further, there is significant reduction in responses of taller building isolated by base isolation system whereas marginal reduction takes place in shorter building which is not isolated.

Multi-hazard stochastic response assessment of base-isolated buildings

The stochastic response of multi-story buildings isolated by laminated rubber bearing (LRB), lead-rubber bearing (N-Z system), friction pendulum system (FPS), and resilient-friction base isolator (R-FBI) is investigated under the independent multi-hazard scenario of earthquake ground motion (EQGM), wind load (WL), and blast-induced ground motion (BIGM), which are considered as uncertain inputs. A polynomial regression-based Monte Carlo simulation (PRBMCS) is proposed to enable computationally efficient fragility assessment of base-isolated buildings. The suitability of the PRBMCS for stochastic assessment of the base-isolated buildings is compared with the conventional Monte Carlo simulation (MCS), response surface method (RSM) and Cloud analysis. The fragility curves obtained using the PRBMCS are in good agreement with that of the MCS relatively. The study includes: the effects of the characteristic parameters of the four base isolators on the fragility of the base-isolated buildings under the three hazards; influence of the extent of uncertainty in the excitations; and comparison of fragilities of the base-isolated and fixed-base buildings. Notably, the influences of characteristic parameters of the isolators on the fragility of the base-isolated buildings are different under the three hazards. The differences in the stochastic behaviour under the different hazards could have contradictory influences on the selection of isolation parameters.

Multihazard Response Control of Base-Isolated Buildings under Bidirectional Dynamic Excitation

The issues of safety and posthazard functionality of structures under multihazard scenarios are some of the significant challenges in the current dynamic and rapidly growing urban environment. In this paper, multistory base-isolated buildings are investigated under the independent multihazard scenario of earthquake and blast-induced ground motion (BIGM). Multistory building models equipped with five different types of isolation systems, namely, the laminated rubber bearing (LRB), lead-rubber bearing (N-Z system), pure friction (PF) system, friction pendulum system (FPS), and resilient-friction base isolator (R-FBI) are assessed under bidirectional multihazard excitations. The suitability of the isolation systems and their key parameters in protecting multistory buildings is evaluated. Furthermore, the influence of the superstructure characteristics, such as the superstructure damping and the number of stories, is also assessed. The effect of bidirectional hazards on fixed-base buildings is also presented for comparison. The key response quantities of base-isolated buildings are presented and compared for different isolation systems. Parametric investigations are also conducted, and the trends of the response quantities are presented to study the influence of important parameters of isolation systems in protecting the buildings under the multihazard scenario of earthquake and BIGM. The results of the investigation show that the behaviors of the buildings equipped with various isolation systems are different for the two hazards. Moreover, the influences of the key parameters of the isolation systems are found to be different for various hazards. Therefore, the selection of design parameters of isolation systems shall be made with due consideration of the influence of multiple hazards. Additionally, the influence of the properties of the superstructure, such as the number of stories and the damping of the superstructure, on the behavior of the base-isolated buildings under the multihazard loading, is presented.

Improvement of the Performance Based Seismic Design Method of Cable Supported Bridges with Resilient-Friction Base Isolation Systems (II-Proposal for the Seismic Design Procedure)

In a previous paper, ambient vibration tests were conducted on a cable stayed bridge with resilient-friction base isolation systems (R-FBI) to extract the dynamic characteristics of the bridge and compare the results with a seismic analysis model. In this paper, a nonlinear seismic analysis model was established for analysis of the bridge to compare the difference in seismic responses between nonlinear time history analysis and multi-mode spectral analysis methods in the seismic design phase of cable supported bridges. Through these studies, it was confirmed that the seismic design procedures of the “Korean Highway Bridge Design Code (Limit State Design) for Cable Supported Bridges” is not suitable for cable supported bridges installed with R-FBI. Therefore, to reflect the actual dynamic characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure is proposed that applies the seismic analysis method differently depending on the seismic isolation effect of the R-FBI for each seismic performance level.

Improvement of the Performance Based Seismic Design Method of Cable Supported Bridges with Resilient-Friction Base Isolation Systems (I- Analysis of Field Testing of Cable Supported Bridge)

In this study, a field bridge test was conducted to find the dynamic properties of cable supported bridges with resilient-friction base isolation systems (R-FBI). Various ambient vibration tests were performed to estimate dynamic properties of a test bridge using trucks in a non-transportation state before opening of the bridge and by ordinary traffic loadings about one year later after opening of the bridge. The dynamic properties found from the results of the tests were compared with an analysis model. From the result of the ambient vibration tests of the cable supported bridge with R-FBI, it was confirmed that the dynamic properties were sensitive to the stiffness of the R-FBI in the bridge, and the seismic analysis model of the test bridge using the effective stiffness of the R-FBI was insufficient for reflecting the dynamic behavior of the bridge. In the case of cable supported bridges, the seismic design must follow the “Korean Highway Bridge Design Code (Limit State Design) for Cable supported bridges.” Therefore, in order to reflect the actual behavior characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure should be proposed.

Improvement of the Performance-Based Seismic Design Method of Cable Supported Bridges with the Resilient-Friction Base Isolation Systems

In areas of civil engineering, the resilient friction base isolator (R-FBI) system has been used due to its enhanced isolation performance under seismic excitations. However, because nonlinear behavior of the R-FBI should be reflected in seismic design, effective stiffness (Keff) of the R-FBI is uniformly applied at both peak ground acceleration (PGA) of 0.08 g and 0.154 g which use a multimodal response spectrum (RS) method analysis. For rational seismic design of bridges, it should be required to evaluate the dynamics of the R-FBI from in-field tests and to improve the seismic design procedure based on the performance level of the bridges. The objective of this study is to evaluate the dynamics of the R-FBI and to suggest the performance-based seismic design method for cable-supported bridges with the R-FBI. From the comparison between the experiments’ results and modal shape analyses, the modal shape analyses using primary (Ku) or infinite stiffness (fixed end) showed a great agreement with the experimental results compared to the application of Keff in the shape analysis. Additionally, the RS or nonlinear time history method analyses by the PGA levels should be applied by reflecting the dynamic characteristics of the R-FBI for the reasonable and efficient seismic design.

Seismic response control of base-isolated buildings using tuned mass damper

ABSTRACTEarthquake response mitigation of base-isolated (BI) buildings with a tuned mass damper (TMD) is investigated. Two-dimensional reinforced concrete buildings having multiple degrees of freedom are numerically modelled. The placement of a TMD is varied on different floor levels and the building response under earthquake excitations is studied. The laminated rubber bearing (LRB), lead rubber bearing (N-Z), friction pendulum system and resilient-friction base isolator (R-FBI) are used as isolation systems for the buildings with 5, 10 and 15 floor levels. Newmark’s step-by-step method of integration is used for solving differential equations of motion of the coupled buildings. Installation of a TMD at different story of the BI buildings mitigates the acceleration at the top level and displacement at bearings. It is found that at increased time period of the isolators the effectiveness of the TMD is reduced. Further, for low-rise buildings, the placement of TMD has no significant role in reducing the response of the buildings. However, the efficiency of TMD placement is more noticeable for buildings with a larger number of stories.

Performances of Various Base Isolation Systems in Mitigation of Structural Vibration Due to Underground Blast Induced Ground Motion

A comparative study is carried out on the performance of various elastomeric and frictional base isolation (BI) systems in the vibration mitigation of structures subjected to underground blast induced ground motion (BIGM). The parametric sensitivities of the base isolated structures to variations in the design parameters of the isolators are examined for different intensities of blast input. Results indicate that substantial reductions in both the acceleration and displacement responses of the structure can be achieved by the different base isolators. Generally, the Electricite de France (EDF) base isolator produces higher peak response reductions. However, peak bearing displacements are also largest here. The pure friction (P-F), resilient-friction base isolator (R-FBI) and friction pendulum (FP) systems produce lower values of response reductions but peak bearing displacements as well as residual displacements of isolators are also low. The New Zealand (N-Z) system provides good response reductions with a low to moderate value of peak bearing displacement. The present study indicates how a proper selection of the type of BI system with suitable design parameters can mitigate structural vibration due to different intensities of BIGM and restrict the unwanted characteristics of large isolator displacement and its permanent deformation.

Supplemental dampers in base-isolated buildings to mitigate large isolator displacement under earthquake excitations

The effect of viscous, viscoelastic, and friction supplemental dampers on the seismic response of base-isolated building supported by various isolation systems is investigated. Although base-isolated buildings have an advantage in reducing damage to the superstructure, the displacement at the isolation level is large, especially under near-fault ground motions. The influence of supplemental dampers in controlling the isolator displacement and other responses of base-isolated building is investigated using a multi-storey building frame. The coupled equations of motion are derived, solved and time history analysis is carried out on a building modeled with fifteen combinations of five isolation systems and three passive dampers. The seismic responses are compared with that of the fixed-base and base-isolated buildings. Based on the results, it is concluded that supplemental dampers are beneficial to control the large deformation at the isolator level. Parametric study is conducted and optimum ranges of damper parameters to achieve reduced isolator displacement without adverse effect on the other responses are determined. Further, it is concluded that the combination of the resilient-friction base isolator (R-FBI) and viscous damper is the most effective in reducing the bearing displacement without significant increase in superstructure forces.

A Novel Seismic Base Isolation System Consisting of a Lead Rubber Bearing in Series with a Friction Slider. Part I: Nonlinear Modeling of the System

In this paper a new seismic base isolator, called High Damping Hybrid Seismic Isolator (HDHSI), is proposed. It is obtained by the assembly in series of a Lead Rubber Bearing (LRB) and a Friction Slider (FS) with a high friction coefficient. The HDHSI device is in contrast with the Resilient-Friction Base Isolator (R-FBI) with the aim of optimizing the Electricité De France (EDF) system. The mathematical model of a structure base isolated by a HDHSI system is analyzed with a two Degree of Freedom System (2-DOF) in which the superstructure is assimilated to a rigid body. Nonlinear finite elements are adopted for modeling the HDHSI device. A dynamic nonlinear analysis is performed and the hysteretic cycles are derived and evaluated for the single components and for the innovative HDHSI device.

A Comparative Study on the Seismic Performance of Superelastic-Friction Base Isolators against Near-Field Earthquakes

This paper presents a comparative seismic performance assessment of super-elastic-friction base isolator (S-FBI) systems in improving the response of bridges under near-field earthquakes. The S-FBI system consists of a steel-Teflon sliding bearing and a superelastic shape memory alloy (SMA) device. The other isolation systems considered here are lead rubber bearing (LRB), friction pendulum system (FPS), and resilient-friction base isolator (R-FBI). Each isolation system is designed to provide the same isolation period and characteristic strength. Nonlinear time-history analyses of an isolated bridge are performed to compare the performance of various isolation systems. The results indicate that the S-FBI system shows superior performance in reducing deck displacement response and effectively limits permanent bearing deformation, whereas residual deformations are present for the other isolation systems in some cases. It is also observed that the LRB system has the largest deck drifts while the FPS system and R-FBI system produce the smallest peak deck acceleration and base shear.

A New Passive Seismic Control Device for Protection of Structures under Anomalous Seismic Events

In this paper, the possibility offered by the Base Isolation System, designed according to the strategy of limitation seismic force, in order to ensure a significant level of robustness to the isolated superstructure, has been analyzed. In according to the strategy of limitation seismic force, a new seismic isolator called HDHSI (High Damping Hybrid Seismic Isolator) is proposed, obtained by the assembly in series of a LRB (Lead Rubber Bearing) and a FS (Friction Slider) with high friction coefficient. The HDHSI device is in contrast to the R-FBI (Resilient-Friction Base Isolation) isolator and is the optimization of the EDF (Electricité De France) system. A modeling with HDHSI devise has been presented by using nonlinear finite elements NLlink (Nonlinear link) and nonlinear dynamic analysis for a SDOF system with harmonic force, in order to characterize the cycle-hysteretic behavior of the device for different levels of shear deformation, are performed. Nonlinear dynamic analysis for a RC structure, base isolated by the proposed devices, are performed. As seismic actions, have been adopted the following registrations: an anomalous earthquakes for intensity and in particular El Centro earthquake (N00W component, 1940) with different amplification factors; an anomalous earthquake for frequency content and in particular Erzincan earthquake (N90W component, 1992).

Seismic control of benchmark cable-stayed bridge using passive hybrid systems

Earthquake response of benchmark cable-stayed bridge with passive hybrid control systems is investigated. The passive hybrid system consists of high damping rubber bearing, lead-rubber bearing, friction pendulum system and resilient-friction base isolator (R-FBI) supplemented with the linear and non-linear viscous fluid damper (VFD). Considering the phase-I benchmark problem, the ground acceleration is only applied in the longitudinal direction acting simultaneously at all supports. The seismic response of benchmark bridge is obtained by solving the governing equations of motion by Newmark's step-by-step integration method. A comparative performance study among the four hybrid control systems for seismic response control of bridge is carried out by finding the various evaluation criteria under different parameters of the hybrid control system. Significant reductions in the base shear, overturning moment and other responses (especially deck displacements) were observed by using the passive hybrid control s...

Performance of a multi-story structure with a resilient-friction base isolation system

Complex frequency response functions and excitation–response relations for stationary random process are formulated to estimate responses of multi-story superstructures isolated with resilient-friction base isolation (R-FBI) system. The equivalent linearization technique is also used to linearize the nonlinear governing equations of motion of R-FBI system occurred between the parallel actions of the resiliency of rubber and friction of Teflon-coated plates. In this approach, the spectral density functions for both the relative displacement response and absolute acceleration response of N degrees of freedom systems are derived. The applicability and accuracy of the proposed methodology are examined by comparing the resulting responses obtained from this study with those calculated from time history analysis based method. These two studies demonstrate good agreement in terms of characteristics of peak responses. Extensive sensitivity analysis to find the influence of various important structural parameters on the behavior of structures isolated with R-FBI system is also carried out.

A COMPARATIVE STUDY OF PERFORMANCE OF VARIOUS ISOLATION SYSTEMS FOR LIQUID STORAGE TANKS

A comparative study of performance of various isolation systems for liquid storage tanks is investigated under real earthquake ground motions. The various base isolation systems considered are the laminated rubber bearings (with and without lead core) and sliding isolation systems (with and without restoring force). The isolated liquid storage tank is idealized with three-degrees-of-freedom associated with convective, impulsive and rigid mass under uni-directional earthquake excitation. Since the force-deformation behaviour of the isolation systems is non-linear, as a result, the equations of motion are solved numerically by step-by-step method. In order to measure the effectiveness of the isolation systems, the seismic response of the isolated liquid storage tanks is compared with the corresponding response of non-isolated tanks. Further, the effectiveness of the isolation is also explored for wide range of practical liquid storage tanks considering the influence of tank aspect ratio. It is observed that the isolation systems are quite effective in attenuating the earthquake acceleration transmitted to the tank, which reduces the design seismic forces significantly. Further, it is also found that the sliding type isolation systems are more effective in controlling the response of liquid storage tanks in comparison to the elastomeric bearings. Among the various sliding systems, the resilient-friction base isolator is found to be most effective for seismic isolation of the tanks.

A comparative study on aseismic performances of base isolation systems for multi-span continuous bridge

Various base isolation systems (BISs) such as the pure-friction, laminated rubber bearing, lead rubber bearing, resilient-friction base isolator and electricité de France systems, which have been used or are considered to have considerable potential for wide applications, are systematically compared and discussed for aseismic performances of multi-span continuous bridge in this study. Sensitivity analyses of the bridge employed the devices are carried out to choose the appropriate design parameters of various devices. It is possible to recommend the appropriate ranges of the natural period and the friction coefficient of the various BISs. Therefore, the recommended ranges of the design parameters are presented in this study. The design parameters such as the first natural period of the isolated bridge and the friction coefficient of the bearing are determined by the reciprocal relationship between the peak deck displacement and the peak overturning moment of the bridge in the recommended ranges, and then the relative effectiveness of the bearings is described for the selected design parameters under the different ground motions. The peak responses of the bridge with the friction-type bearing are less sensitive to substantial variations in the frequency range and the intensity of the ground excitation than those with the rubber-type bearing due to characteristics of the friction element within the range of this study.

Seismic response of rotating machines-structure-RFBI systems

The seismic response of a critical rotating machine either rigidly attached to a floor or independently isolated housed within an initially aseismically designed or uncontrolled structure are investigated. A particular isolation system, the Resilient-Friction Base Isolator (RFBI), is employed. Finite element formulations of a rotor-disk-bearing model on a rigid base are developed. The equations of motion for the combined rotating machine–structure–RFBI systems are presented. Parametric studies are performed to investigate the effects of variations in system physical properties including friction coefficient, mass ratio, shaft flexibility, bearing rigidity, bearing damping and speed of rotation on the response of rotating machines for the combined rotating machine–structure–isolator systems. Comparative studies in the peak response of the rotating machine supported on various isolation systems and the corresponding fixed base system are carried out. The study indicates that the Resilient-Friction Base Isolator can significantly reduce the seismic response of rotating components to potentially damaging ground excitations. Copyright © 2000 John Wiley & Sons, Ltd.

Effects of Isolation Damping on Stochastic Response of Structures with Nonlinear Base Isolators

Optimum isolator damping required to minimize absolute acceleration responses to stochastic ground motions in buildings with non-linear resilient-friction base isolation (R-FBI) devices is studied. Using a stochastic equivalent linearization technique, an analytical expression is developed for estimating optimum material damping values in an R-FBI system for a rigid superstructure. This optimum damping value depends on the effective time period and friction coefficient of the R-FBI system and the design earthquake intensity. The fixed base structural time period, damping, and the number of stories also affect the optimum isolator damping values, if the superstructure is flexible. However, the analytical expression mentioned above provides an upper-bound optimum isolator damping value for any superstructure with an R-FBI system subjected to a given earthquake intensity. Comparison of optimum damping values for a linear isolator and the R-FBI system, with identical lateral stiffness properties, illustrates the beneficial effect of sliding friction in reducing the optimum damping in the latter type of isolator, for a given earthquake intensity.

Non Gaussian closure techniques for the analysis of R‐FBI isolation system

AbstractThe Resilient‐Friction Base Isolator (R‐FBI) stochastic response under severe ground motion modelled as a stationary and non‐stationary zero mean stochastic white noise processes is performed. The moment equation approach is applied and the non‐normal response is obtained by means of a non‐Gaussian closure technique, based on the Gram‐Charlier asymptotic expansion of the response probability density function. Results are compared with the equivalent non linearization technique and with results obtained by means of Monte Carlo simulation.

OPTIMUM DAMPING IN A NON-LINEAR BASE ISOLATION SYSTEM

Optimum isolation damping for minimum acceleration of a base-isolated structure subjected to earthquake ground excitation is investigated. The stochastic model of the El-Centro1940 earthquake, which preserves the non-stationary evolution of amplitude and frequency content of ground motion, is used as an earthquake excitation. The base isolated structure consists of a linear flexible shear type multi-storey building supported on a base isolation system. The resilient-friction base isolator (R-FBI) is considered as an isolation system. The non-stationary stochastic response of the system is obtained by the time dependent equivalent linearization technique as the force-deformation of the R-FBI system is non-linear. The optimum damping of the R-FBI system is obtained under important parametric variations; i.e., the coefficient of friction of the R-FBI system, the period and damping of the superstructure; the effective period of base isolation. The criterion selected for optimality is the minimization of the top floor root mean square (r.m.s.) acceleration. It is shown that the above parameters have significant effects on optimum isolation damping.