Sliding Isolation System Research Articles

An innovative hybrid methodology for vibration control of inerter-assisted sliding isolation system under harmonic excitation

An innovative hybrid methodology for vibration control of inerter-assisted sliding isolation system under harmonic excitation

Experimental Investigation of Wear Effects on the Friction Coefficient of a Curved Surface Slider: Comparison of Small- and Full-Scale Tests

ABSTRACT The current practice to determine friction properties of sliding isolation systems is to perform displacement-controlled dynamic tests where the effects of several loading conditions with different amplitudes, loading velocities, and vertical forces are of concern. The number of cycles in these tests is generally three for most of the loading conditions assumed to be representative of seismic conditions. On the other hand, the isolator may undergo small-amplitude but large-cycles of service motions due to thermal deformations and accidental loads. In that case, the methodology requires to perform cyclic tests on small-scale samples of the slider material (not the isolator) considering very large accumulated sliding distances such as 1000 m for use in buildings, and 10,000 m for use in bridges. However, two unsettled issues are regarded: (i) the suitability of small-scale slider tests to estimate the characteristics of full-scale sliding isolation systems and (ii) the change in seismic performance of a sliding isolation system after it is subjected to a large amount of accumulated sliding distance. In the present study, both a full-scale double concave friction pendulum (DCFP) and small-scale sample composed of the slider of the DCFP are subjected to a total accumulated sliding distance of 1000 m. The corresponding variations in friction properties are comparatively presented, demonstrating that small-scale test results provide reasonable estimates for the friction properties of the tested full-scale DCFP. Moreover, the seismic response of the investigated DCFP remains almost the same regardless of the considered sliding distance.

Seismic Performance of Elastomeric and Sliding Friction Isolation System

The base isolation technique is widely used in the isolation of structures for providing efficient protection to structures concerning different loadings. This study aims to evaluate comparative performance and inelastic responses of the base-isolated structure for two types of isolation systems under the Far-field and Near-field earthquake. For this purpose, seismic response quantities like base shear, peak ?oor displacement, absolute acceleration, and isolator displacement for ten-story reinforced concrete building frame base isolated by lead rubber bearings (LRBs) are evaluated and compared with the seismic response of the same structure base isolated by Friction Pendulum Bearing Isolator. Nonlinear time history analysis is carried out to investigate the inelastic behavior of the base-isolated structure. The building frame was designed according to IS1893:2016 seismic code and IS 456:2000. To represent a wide range of assessments, a 10 storey building frame taking identical isolation parameters for elastomeric and sliding isolation system was analyzed in SAP 2000. It was observed that the responses of both the isolation system are nearly the same for all the three earthquakes.

Sliding Isolation Systems: Historical Review, Modeling Techniques, and the Contemporary Trends

Base isolation techniques have emerged as the most effective seismic damage mitigation strategies. Several types of aseismic devices for base isolation have been invented, studied, and used. Out of several isolation systems, sliding isolation systems are popular due to their operational simplicity and ease of manufacturing. This article discusses the historical development of passive sliding isolation systems, such as pure friction systems, friction pendulum systems, and isolators with other sliding surface geometries. Moreover, multiple surface isolation systems and their behavior as well as the effectiveness of using complementary devices with standalone passive isolation devices are examined. Furthermore, the article explored the various modeling techniques adopted for base-isolated single and multi-degree freedom building structures. Special attention has been given to the techniques available for modeling the complex phenomena of sliding and non-sliding phases of sliding bearings. The discussion is further extended to the development in the contemporary areas of seismic isolation, such as active and hybrid isolation systems. Although a significant amount of research is carried out in the area of active and hybrid isolation systems, the passive sliding isolation system still has not lost its appeal due to its ease of adaptability to the structures.

Analytical solutions of inerter-added sliding isolation structures to ground motions

• Contribute unfulfilled analytical solutions of inerter-added sliding structures. • Reveal explicitly the role of additional inerter played in a sliding isolation system. • Derive explicit conditions for motion modes of inerter-added sliding isolation structures. • Recommend the trade-off between reduction of isolation displacement and acceleration. Previous studies have proven that adding an inerter to a sliding isolation structure can reduce the isolation displacement without compromising the control effect of the superstructure. However, due to the strong nonlinearity of the sliding isolator , approximate methods or numerical analyses are adopted to investigate inerter-added sliding isolation structures, which hinders the understanding of the inherent working mechanisms of such structures. This study derives exact analytical solutions during both sliding and stick motion states of inerter-added sliding isolation structures under harmonic ground motions and investigates the influence of an additional inerter on the motion states and responses of such structures. The main novelties of this paper are the employment of the inerter technique in a sliding system for performance improvement and explicit expressions of the dynamic responses and motion modes for inerter-added sliding isolation structures that assist in understanding the role of the additional inerter. Differential equations are established for both the stick and sliding motions of inerter-added sliding isolation structures subjected to harmonic ground excitations. The dynamic characteristics of the structure are analyzed, and accurate analytical solutions are derived for structural responses. The explicit forms for the occurrence conditions of three fundamental modes (i.e., the stick-stick, stick-slip and slip-slip modes) for the motion of the inerter-added sliding isolation structures are presented. Based on the derived analytical solutions, extensive parametric analyses are conducted to investigate the influences of the added inerter on the motion modes and responses of sliding isolation structures. By adding an inerter, a decreased natural frequency, a decreased damping ratio and a reduction in ground motion excitation are observed for the vibration of the superstructure in the inerter-added sliding isolation structure compared to that in the sliding isolation structure without an inerter. Furthermore, the inerter causes the slip-slip mode to occur more easily, which is preferred for sliding isolation structures when sliding occurs. An increasing inertance of the inerter is beneficial for reducing isolation displacement in general but contrary to reducing maximum acceleration in some frequency ranges and excitations with large amplitudes. The trade-off between the reduction of isolation displacement and acceleration is recommended for determining the inertance of the inerter in sliding isolation structures.

To Evaluate the Seismic Response of a Building Having Stiffness Irregularity and Plan Irregularity with Quintuple Friction Pendulum System

Abstract: Quintuple friction pendulum (QFPS) bearing is a new generation sliding isolation system having multiple spherical sliding surfaces. The friction isolation system with single sliding surface is designed for a specific level of ground shaking, which may prove ineffective in case of other hazard levels. The QFPS bearing on the other hand, exhibits adaptive behavior and imparts greater amount of flexibility to the designer for various levels of earthquake shaking. Here, the effectiveness of Quintuple Friction pendulum system is carried out to study the seismic demands of base-isolated building frames with stiffness irregularities and plan irregularities subjected to various earthquake ground motions i.e. Far field ground motion, near field ground motion with fling step and near field ground motion with forward directivity by comparing their estimates with the benchmark responses obtained by the Non-Linear Time History Analysis (NLTHA). SAP 2000 Software has been used for the same. The two soft storey buildings and two buildings with plan irregularity will be modelled and analyzed. The seismic demands namely, Inter story drift, peak storey acceleration, maximum base shear are considered for the study.The reduction in absolute acceleration is found more in case of PI as compared to SS for all the considered time histories. The reduction in Maximum Base-Shear is found more in case of Plan irregularity as compared to Stiffness Irregularity (Soft Story) in all the considered Time History. In isolated structure, the Inter-storey drift is found to be maximum in case of structure having soft storey as compared to plan irregularity 1 and 2. Keywords: Multi storied RC structures, Plan irregularities, Soft storey, Quintuple Friction Pendulum, Non linear Time History Method(NLTHM)

Sliding implant‐magnetic bearing for adaptive seismic mitigation of base‐isolated structures

Sliding isolation system is one of the widely used base isolation systems. Traditional pure sliding base isolation systems, however, lack restoring force and possess low damping energy-dissipation capacity. To overcome these disadvantages, a novel low-friction sliding isolation system with adaptive behavior using sliding implant-magnetic bearing (IMB) has been proposed in this paper. The isolation system consists of an upper block and a base block, both having polyurethane elastomer fillings and circumferentially implanted permanent magnets. This configuration allows an alterable damping force related to the eddy currents associated with bearing movement. Meanwhile, the interactions between magnets deployed in the upper and base blocks provide a capitalized repulsive force. A quasistatic test is performed to appraise the performance of the IMB system. Theoretical analysis and numerical simulation are carried out for quantification of the repulsive force, damping force, and Coulomb friction, which facilitates the modeling of the isolator. In order to verify the mitigation performance of the IMB deployed in seismic structures, a comparative study against the sliding hydromagnetic bearing (HMB) is carried out. It is revealed that the IMB exhibits reliable frictional performance and excellent damping energy-dissipation capacity, which commits the adaptability of the IMB in protecting the structures from severe vibration induced by high-frequency earthquake ground motions. Although exhibiting similar mitigation effectiveness to the HMB, the IMB has the capacity of fulfilling a more effective deformation constraint when subjected to pulse-type ground motions.

Energy-efficient solution for the foundation of passive houses in earthquake-prone regions

In the paper, a new solution is proposed for reducing the seismic response of passive houses founded on layers of thermal insulation (TI) boards which, in such buildings, are usually installed beneath the RC foundations in order to prevent the occurrence of thermal bridges. This could be achieved by allowing controlled lateral sliding to occur along the horizontal surface between the individual layers of the TI boards, as a kind of seismic fuse. Depending on the size of the friction coefficient acting at this surface, three different seismic response scenarios can be foreseen: Scenario 1: Basic protection (“sliding prevention”), Scenario 2: Extended protection (“sliding controllable”), and Scenario 3: Full protection (“sliding isolation system”). Vertical and horizontal restraining elements are also introduced with the aim of preventing extreme lateral shifts or rocking phenomena. The nature of these three seismic response scenarios has been investigated by means of nonlinear dynamic analysis of some simplified parametric models, as well as of some realistic models of two, four and six storeyed RC passive house buildings. The results showed that the total base shear that might act on the superstructure could be reduced by permitting sliding between the layers of TI boards, thus reducing or even preventing the occurrence of damage. In the case of Scenario 2 the proposed seismic fuse could be used in modern energy-efficient houses practically without any additional costs.

Seismic response of triple friction pendulum bearing under multi hazard level excitations

Triple friction pendulum (TFP) bearing is a new generation sliding isolation system having multiple spherical sliding surfaces. The friction isolation system with single sliding surface is designed for a specific level of ground shaking, which may prove ineffective in case of other hazard levels. The TFP bearing on the other hand, exhibits adaptive behaviour and imparts greater amount of flexibility to the designer for various levels of earthquake shaking. Herein seismic response of TFP bearing is studied under 60 records comprising of service level, design basis and maximum considered earthquakes. Two types of surfaces having low and high friction in combination with three different displacement capacities of the bearing, resulting in six isolator design are considered. It is shown that although being a passive device, the TFP bearing stiffens at low input shaking, softens with increasing input reaching a minimum at the DBE, and then stiffens again at higher levels of input and thereby shows adaptive behaviour. Further, the increase of displacement capacity of bearing influences the response under MCE event, however, for DBE and SLE no significant change in demand is observed.

Development of sliding isolation system with multi-frictional plates and horizontal bidirectional behavior

Development of sliding isolation system with multi-frictional plates and horizontal bidirectional behavior

Analyzing Method Based on the Average Power of the Input Energy into Sliding Isolation System

An analyzing method is proposed to achieve a better study about the energy change which is inputted into a sliding base seismic-isolation system within any range of period during an earthquake. The proposed method is based on the average power index of the input energy into the sliding isolation system, and the corresponding formula are derived. The average power index is numerically estimated and analyzed for the different sliding isolation systems under a varity of conditions with the different duration period and friction coefficient. It is shown that the average input power depends strongly on the friction coefficient, and it can well reflect how much average energy are inputted in the sliding isolation system within any range of duration. So, the analyzing method based on the average power can be well used to study the natural property of the earthquake.

Experimental evaluation of supplemental viscous damping for a sliding isolation system under pulse-like base excitations

Near-fault earthquakes that usually contain a long-period pulse component may cause excessive responses to a base-isolated structure, especially with regard to its peak isolator displacement. Viscous-type dampers, whose damping force is proportional to the excitation velocity, can be used to mitigate the excessive responses of the isolated structure. In this study, the effect of viscous-type supplemental damping on a sliding isolation system subjected to pulse-like ground excitations is evaluated experimentally by a shaking table test. The test program involves a relatively rigid structure isolated by sliding-type isolators and a fluid viscous damper installed within the isolation layer. Seismic excitations with and without a long-period pulse component were imposed on the isolated system, and the experimental responses of the system with and without installation of the fluid damper were compared. The test results demonstrate that, for a rigid superstructure, the viscous damper is able to effectively suppress the peak isolator displacement induced by the long-period pulse component without increasing the acceleration level of the superstructure; however, it also slightly increases the structural acceleration in the seismic excitation without the pulse component. The results also show that a pulse-like ground motion is able to induce resonance-like behavior for the isolator displacement of a sliding system when the pulse period is close to the isolation period. However, this resonance-like behavior can be effectively mitigated by adding viscous damping to the isolation system. Finally, by using linear and nonlinear viscous models to simulate the experimental responses, the influence of the damper nonlinearity on the test results was also investigated.

An experimental study on a generalized Maxwell model for nonlinear viscoelastic dampers used in seismic isolation

Long-stroke fluid dampers may be installed under seismic isolation systems to provide supplementary damping. Due to the larger vibration amplitude and velocity, highly nonlinear viscoelastic behavior may exist in a long-stroke fluid damper. In order to accurately simulate the hysteretic behavior of such a damper, this paper presents and experimentally verifies a mathematical model called the generalized Maxwell model (GMM). Similar to the classic Maxwell model, the GMM is composed of a stiffness and a viscous elements connected in series. However, nonlinearity is incorporated into both elements of the GMM by assuming that their resistant forces are exponential functions of the relative velocity and deformation of the damper. By adjusting the two exponential coefficients, the GMM is able to simulate the more complicated viscoelastic behavior of fluid dampers. The GMM is reduced to the Maxwell model when both exponential coefficients are set to one. To verify the GMM, both an element test with harmonic excitations and a shaking table test with seismic excitations were conducted for a long-stroke fluid damper with highly nonlinear viscoelastic behavior. The result of the element test confirms that the GMM model is very accurate in simulating the hysteretic property of the fluid damper under a wide range of excitation frequencies, while the classic Maxwell and the viscous models may only be accurate under a certain excitation frequency. Moreover, the shaking table test, in which the fluid damper is used to provide supplementary damping for a sliding isolation system, demonstrates that the GMM is able to more accurately predict the amount of energy dissipation by the damper and also the peak isolator drift of the isolation system, especially for an earthquake with a long-period pulse.

Study on a Simple Self-Resetting Sliding Isolation

This paper presents a simple Self-resetting sliding isolation system, which is composed of graphite sliding device and simple rubber bearing. Theoretical analysis is carried out. Shaking table test for a typical brick masonry structure in village of China is performed on a 1:4 scale. Results show that the proposed new isolation system can achieve a favorable level of performance.

Optimal design of superelastic‐friction base isolators for seismic protection of highway bridges against near‐field earthquakes

AbstractThe seismic response of a multi‐span continuous bridge isolated with novel superelastic‐friction base isolator (S‐FBI) is investigated under near‐field earthquakes. The isolation system consists of a flat steel‐Teflon sliding bearing and a superelastic NiTi shape memory alloy (SMA) device. The key design parameters of an S‐FBI system are the natural period of the isolated bridge, the yielding displacement of the SMA device, and the friction coefficient of the sliding bearings. The goal of this study is to obtain optimal values for each design parameter by performing sensitivity analysis of a bridge isolated by an S‐FBI system. First, a three‐span continuous bridge is modeled as two‐degrees‐of‐freedom with the S‐FBI system. A neuro‐fuzzy model is used to capture rate‐ and temperature‐dependent nonlinear behavior of the SMA device. Then, a set of nonlinear time history analyses of the isolated bridge is performed. The variation of the peak response quantities of interest is shown as a function of design parameters of the S‐FBI system and the optimal values for each parameter are evaluated. Next, in order to assess the effectiveness of the S‐FBI system, the response of the bridge isolated by the S‐FBI system is compared with the response of the non‐isolated bridge and the same bridge isolated by pure‐friction (P‐F) sliding isolation system. Finally, the influence of temperature variations on the performance of the S‐FBI system is evaluated. The results show that the optimum design of a bridge with the S‐FBI system can be achieved by a judicious specification of design parameters. Copyright © 2010 John Wiley & Sons, Ltd.

Double variable frequency pendulum isolator for seismic isolation of liquid storage tanks

The paper describes the behaviour of liquid storage slender and broad tanks isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is a double sliding isolation system having elliptical sliding surfaces. The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion and energy balance equation of the tank-isolation system subjected to bilateral ground excitation are derived and solved in the incremental form. In order to investigate the behaviour of the DVFPI, the response is obtained under different parametric variations for a set of 20 far-field earthquake ground motions. Four different combinations of the DVFPI design cases having different isolator geometry and coefficient friction at top and bottom sliding surfaces are studied and the criterion to optimize its performance is proposed based on minimum responses and energy quantities. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces and the tank aspect ratio are investigated. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface with high initial stiffness relative to the bottom one and the coefficient of friction of both sliding surfaces to be equal for a slender tank whereas both surfaces should be designed with equal initial stiffness and coefficient of friction for a broad tank.

Seismic assessment of bridge structures isolated by a shape memory alloy/rubber-basedisolation system

This paper explores the effectiveness of shape memory alloy (SMA)/rubber-based isolationsystems for seismic protection of bridges against near-field earthquakes by performing asensitivity analysis. The isolation system considered in this study consists of a laminatedrubber bearing, which provides lateral flexibility while supplying high vertical load-carryingcapacity, and an auxiliary device made of multiple loops of SMA wires. The SMA deviceoffers additional energy dissipating and re-centering capability. A three-span continuousbridge is modeled with the SMA/rubber-based (SRB) isolation system. Numericalsimulations of the bridge are conducted for various near-field ground motions thatare spectrally matched to a target design spectrum. The normalized forwardtransformation strength, forward transformation displacement and pre-strain level ofthe SMA device, ambient temperature and the lateral stiffness of the rubberbearings are selected as parameters of the sensitivity study. The variation of theseismic response of the bridge with the considered parameters is assessed. Also,the performance of the SRB isolation system with optimal design parametersis compared with an SMA-based sliding isolation system. The results indicatethat the SRB isolation system can successfully reduce the seismic response ofhighway bridges; however, a smart isolation system that combines sliding bearingstogether with an SMA device is more efficient than the SRB isolation system.

Improvement of near-fault seismic isolation using a resettable variable stiffness damper

A seismic structure isolated by a conventional passive isolation system is usually a long-period structural system; therefore, although its dynamic response may be effectively mitigated in a regular earthquake, the responses may be considerably amplified in a near-fault earthquake with long-period characteristics, due to the low-frequency resonant effect. In order to overcome this problem, a sliding isolation system equipped with a new type of the semi-active damper called a resettable variable stiffness damper (RVSD) is proposed in this study. An RVSD damper is similar to a conventional resettable stiffness damper, except that it has a variable stiffness part. By controlling the variable stiffness, the damper force provided by the RVSD will follow a target force that is determined on-line by a general, active control law. As a result, the RVSD damper is able to prevent the abrupt changes of the damper force that inevitably exists in a conventional resettable damper. The harmonic and seismic responses of an isolation system with the RVSD are studied numerically and compared with the other types of isolation systems. The simulated results demonstrate that the RVSD is able to attenuate the low-frequency resonance behavior of the seismic isolation system induced by long-period ground motions. As compared with an isolation system with a conventional resettable damper, the study shows that isolation with the RVSD is superior in reducing the acceleration response due to a near-fault earthquake, while maintaining its effectiveness in the suppression of the isolator displacement.

A STUDY ON SEISMIC ISOLATION SYSTEM WITH ROBUSTNESS FOR INCREASING GROUND MOTION LEVEL

The development of seismology and recent observation records have been evolving the ground motions to be considered in structural engineering. The future research will seems to require quite an amount of revisions in ground motions. Since it is difficult to envisage the goal of seismology, some measures to deal with increasing levels of ground motions must be included in structural engineering. Consideration of excessive strength in structural engineering is not economical. However, making extra margin in sliding bearings for seismic isolation devices require less expenditures in structural design. The authors have conducted analytical study of this kind of system and have confirmed the sliding isolation system has the potential to keep isolation characteristics for large input ground motion level. However, the maximum displacement and residual displacement become quite large, especially when the elements to provide restoring force are not employed, it was over 1.0m. The authors think this level of displacement can be considered in the structural design of foundations to withstand P-Delta effect by building weight. From this study, the authors concluded that if the foundations are well designed to accept P-Delta moment in isolation interface, sliding bearings can be a potential candidate to provide robustness to deal with excessive level of input ground motions.

Earthquake Simulator Testing of Base-Isolated Power Transformers

This paper presents a comprehensive study involving triaxial earthquake simulator testing on seismic isolation of electric power transformers. In this study, two isolation systems were developed: one using sliding bearings combined with rubber bearings and the other segmented high-damping rubber bearings. Triaxial earthquake simulator testing was performed using a large-scale transformer model equipped with a real bushing. The effectiveness of the base isolation system in reducing the response acceleration of power transformer systems was demonstrated. Important observations were made on the seismic responses of the transformer and bushing. In particular, the vertical component of the ground motion induced a high-frequency response of the bushing when the transformer was isolated with the sliding isolation system. This is because the vertical motion changes the friction forces in the sliding bearings that excite high modes in the transformer-bushing system. Furthermore, the effect of the interaction with the bushing connecting cables on the response of the bushing in the base-isolated system was experimentally evaluated. In conclusion, the base isolation technology, when properly designed, is a highly effective measure for seismic protection of power transformers.