Friction Pendulum System Research Articles

Development of an innovative three-dimensional vibration isolation bearing

This paper presented an innovative three-dimensional vibration isolation bearing (3D-VIB) to mitigate horizontal seismic action and rail-induced vertical vibration. The 3D-VIB was composed of a thick laminated rubber bearing acting as the vertical vibration isolation module and a friction pendulum acting as the horizontal seismic isolation module. The thick laminated rubber bearing was used as a part of the slider in the friction pendulum. The compression performance of 3D-VIB was decoupled from its shear performance by concentrating the compressive deformation into the thick rubber bearing while shear deformation occurred independently in the friction pendulum module. The bearing capacity, vertical and horizontal properties of a full-scale 3D-VIB specimen were tested. In the test, the ultimate bearing capacity of 3D-VIB was 7 times that of the design compressive load of normal service condition. The vertical stiffness of the specimen under seismic vibration and vertical rail-induced vibration were tested separately. It was found that the vertical stiffness of the specimen under rail-induced vibration was 1.55 times higher than the vertical stiffness under seismic vibration. The horizontal performance of the 3D-VIB was characterized by stable parallelogram-shaped hysteretic curves similar to that of the traditional friction pendulum system. A user-defined element was developed and incorporated into ABAQUS to simulate the mechanical behavior of the 3D-VIB under different loading conditions, and simulation results agreed with the test results. The responses of a steel structure equipped with the 3D-VIB, while subjected to earthquake ground motions and rail-induced vibrations, respectively, were analyzed and compared with the non-isolated one. The analysis results suggested that with the installation of the 3D-VIB, the maximum inter-story drift ratio of the structure under maximum considered earthquake was reduced by about 88%. The average maximum transient vibration value of the rail-induced vertical vibration at the typical points of the conventional model was 86.2 dB, while that in the 3D-isolated model was 78.6 dB, the vibration reduction was 7.6 dB.

Shaking table test to investigate the size effect on the seismic response of a low-cost friction pendulum system

To enhance the seismic resilience of reinforced concrete (RC) bridge piers, a novel friction pendulum system was developed. It consisted of a friction pendulum and a spherical sliding surface that were constructed from conventional steel and concrete. In comparison to commercial isolators, the complex spherical shape was realised using a three-dimensional printer to fabricate an acrylic glass mold, which allowed a significant cost savings in production. The system was distinguished by stable oscillation and a significant reduction in response accelerations on the flat surface. The inclined part acted as a restoring force that limited the residual displacement. However, these properties were confirmed experimentally using only small specimens. To characterise the fundamental properties of the system, a bidirectional shaking table test was performed in this study to investigate the size effect on the seismic performance of the proposed system. The test results demonstrate that the excellent performance in reducing the response acceleration and residual displacement is independent of the specimen size. In addition to the dependency of the friction coefficient on the sliding velocity and axial pressure, the impact force was observed to increase with the superstructure weight. Furthermore, a simplified method for estimating the maximum and residual displacements of the proposed system is presented.

Shaking table tests on the seismic response of truss structure with air spring‐FPS three‐dimensional isolation bearing

AbstractTo investigate the isolation effect of the friction pendulum system (FPS) horizontal isolation bearing and the air spring‐FPS three‐dimensional (3D) isolation bearing in truss structure and the influences of long‐period ground motions on the isolated structure, the shaking table test of a truss structure is designed and conducted. The ordinary ground motions, near‐fault pulse‐like ground motions, and far‐field long‐period ground motions with different spectral characteristics are chosen to input into the structure, and the dynamic characteristics such as the acceleration, displacement, and stress of the truss are compared and analyzed. The horizontal frequency of the horizontal isolated structure is reduced after the horizontal isolation, while the vertical frequency is further reduced after 3D isolation. The isolation effect of nodal acceleration, nodal displacement, and member stress under 3D isolation is better than that of horizontal isolation, especially the vertical seismic response is significantly improved. When the ground motion intensity is small, the FPS horizontal isolation bearing slides little, and reducing the seismic response of the structure is limited. There is a better isolation effect of 3D isolated structure. The vertical frequency ratio Rf under ordinary ground motions is far away from 1 and close to 3, basically avoiding the main energy segment of the ground motions. The advantage of 3D isolated structure is relatively reduced under long‐period ground motions, which lies in the rich low‐frequency components of long‐period ground motions which are difficult to isolate effectively.

Performance of Seismically Isolated Pile-supported Structures through 1 g Shaking Table Tests

This study fabricated friction pendulum (FP) and rolling pendulum (RP) seismic isolation systems using 3D printing to conduct 1g shaking table tests of pile-supported structure models incorporating these systems. The test results indicate that, when the FP bearing was applied to the pile heads, the acceleration response of the structure decreased once the FP bearing began to operate; as the input earthquake frequency increased (1, 3, and 10 Hz), the seismic isolation system engaged at lower input accelerations (0.16, 0.11, and 0.02 g, respectively), and the deck acceleration response decreased significantly (15, 37, and 65%, respectively) compared to that in the fixed pile head condition. Similarly, when the RP bearing was applied to the pile heads, a higher input earthquake frequency (1, 3, and 10 Hz) corresponded to a greater decrease in the deck acceleration response (82, 95, and 96%, respectively) compared to that in the fixed condition. However, a significant deck displacement was observed when using the RP bearing owing to the resonance phenomenon when the natural period of the structure was similar to the frequency of the input earthquake. Therefore, since applying RP bearing is not desirable in terms of structural displacement, it is appropriate to apply FP bearing, which can avoid resonance by changing the natural period during the operation of the seismic isolation system.

Seismic performance of isolated buildings with friction spring damper

The main objective of this paper is to introduce a new combination of passive seismic response control devices containing Friction Spring Damper (FSD) and Pot Bearing (PB) for buildings and compare this system with conventional seismic isolators such as Lead Rubber Bearing (LRB) and Friction Pendulum System (FPS). For this purpose, two benchmark buildings with different structural systems have been considered for implementing the devices. To capture the flag-shaped and self-centered behavior of FSD, new uniaxial material has been developed for OpenSees, and numerical verification of the material has been done based on a past experimental study. Nonlinear dynamic time-history analyses have been used to extract the seismic responses of models, including fixed-base structures, and isolated structures by FSD along with PB, LRB, and FPS. The results show that not only the proposed isolation system has the capability of reducing base shear and inter-story drift as well as both conventional seismic isolation systems compared to fixed-base structures, but also the system has even better performance than the isolated structures with LRB. Moreover, due to the self-centered behavior of FSD, the residual displacement of the proposed system is much lower than conventional isolation systems, which can lead to lower maintenance costs of isolators.

Inter-Storey Isolation Versus Base Isolation Using Friction Pendulum Systems

This study investigates the feasibility of utilizing the friction pendulum system based inter-storey isolation (FPS-I) strategy to replace the friction pendulum system base isolation (FPS-B) for high-rise structures’ vibration control against earthquakes. Both experimental verifications and computational analysis are carried out. A scaled nine-storey experimental model structure is constructed in accordance with the third generation Benchmark problem, and three aspects variant FPS with different slideway radius configurations are designed and manufactured based on the geometric similarity criterion. To assess the dynamic characteristics of FPS-B structure and FPS-I structure, four typical ground motions and four different intensities of peak ground acceleration (PGA) are considered. The findings show that FPS-I can effectively suppress the superstructure’s acceleration as well as affecting the lower substructure’s response. When the same earthquakes occur, the vibration reduction effect of FPS-I strategy is achievable between 50 and 60%, which is obviously superior to FPS-B scheme. The FPS-I technology is observed to have an even greater effectiveness on the entire structure’s vibration reduction during strong earthquakes than the traditional FPS-B technology. The basic mode as well as the higher-order mode responses of the high-rise structure can be controlled, resulting in the seismic response of the entire FPS-I structure at lower levels. The first-order mode contributes the most to the superstructure’s floor acceleration response. The location of the isolation layer changes the dynamic characteristics of the structure substantially. Finally, the finite element models for FPS-B structure and FPS-I structure are developed. It is demonstrated through the mutual comparison of experimental and numerical results that the finite element model is sufficient accurate for parametric studies. The numerical model can reproduce the dynamic characteristics of both isolation strategies with high fidelity. This research emerges the benefits of FPS with inter-storey isolation to address the issue of high-rise structures being prone to be over turned in the case of base isolation.

A novel bi-directional rail variable friction pendulum-tuned mass damper (BRVFP-TMD)

The shape of hysteretic loops for a friction pendulum system transforms when excited by bi-directional motion, which exhibits unexpected dynamic behavior compared with unidirectional motion. Therefore, a novel bidirectional rail variable friction pendulum-tuned mass damper (BRVFP-TMD) with two independent rails that satisfied the purpose of bidirectional structural response control and provided a full bidirectional friction force was proposed. The variable friction arrangement was applied to the rails so that the BRVFP-TMD could be accomplished with a linear hysteretic damping property that is contributed by the displacement-dependent variable friction force. Using unidirectional harmonic excitations with attack angle as bi-directional loading, illustrations were created to investigate the control effect of traditional pendulum friction TMDs with a spherical sliding surface. This demonstrated the collapse of hysteretic loops of traditional pendulum friction TMDs and superiority of BRVFP-TMD in terms of mechanism. For the BRVFP-TMD with a lightly damped structure, the optimizations of the fixed-point theory were accessed to obtain the closed-form solutions of the optimal parameters of the BRVFP-TMD. Numerical verifications based on bidirectional motions were conducted to evaluate the performance of the BRVFP-TMD. The bidirectional earthquake results indicated stable and excellent performance of the BRVFP-TMD in terms of either frequency response reduction or friction energy dissipation efficiency. Meanwhile, bidirectional wind-induced vibrations confirmed the correctness of the optimization and the stable robustness of the optimized BRVFP-TMD.

Experimental investigation of FPS inter-storey isolation control for assembled steel structure with high aspect ratio

A comprehensive experimental investigation of high-rise structure employing the friction pendulum system (FPS) in accordance with inter-storey isolation control strategy are presented in this paper. A test assembled steel structure is constructed in accordance with the third generation Benchmark model. Three types of FPS systems with varied slideway radius are designed and manufactured. Through shaking table tests, seismic performance of the FPS inter-storey isolation (FPS-I) strategy for structure with a high aspect ratio was examined. The test cases involve eight isolation layer locations, six ground motions, and four types of peak ground accelerations (PGA). The test results demonstrate that using FPS-I scheme to control vibration of assembled steel structure with an aspect ratio greater than four is feasible and effective. Furthermore, when the FPS is installed on the 6th to 8th floors of the structure, the top floor’s acceleration attenuation rate is approaching 67%, leaving the controlled structure’s response is only one third of the uncontrolled structure. The dynamic characteristics of the controlled structure are impacted by the isolation layer's location, which is indicated in the changing of the ratio of the modal participation mass coefficients. By regulating the contribution factor of each mode, the FPS-I scheme effectively lessens the structural high-order mode’s contribution to structural response.

Performance Comparison Analysis of a Bridge Installed with Anti-seismic Devices using PVDF/MgO Friction Material According to Friction Analysis Models

In this study, structural analyses were conducted to analyze the performance of a bridge to which friction pendulum systems (FPSs) were applied using different friction models. A Coulomb friction model and a rate dependent friction model were constructed using the friction coefficient of a PVDF/MgO friction material to analyze the effect of different friction analysis models. The Coulomb friction model uses a single friction coefficient regardless of friction velocity, while the rate dependent friction model can reflect the change in the friction coefficient with friction velocity. Nonlinear time history and seismic fragility analyses were conducted to confirm responses of the bridge. The seismic responses of a deck and a column were used to evaluate the performance of the base isolated bridge, and a friction model that can effectively evaluate the performance of isolated bridges was analyzed.

Shaking table test of multiple-type isolation control strategies for high-rise structure based on friction pendulum

Given the difficulties associated with deploying isolation technique in high-rise structures, this article conducts a comprehensive comparison of three operating systems: friction pendulum system (FPS) base isolation form: FPS-B, FPS inter-story isolation form: FPS-I, and FPS hybrid isolation form: FPS-H. A 9-layer scaled test model is constructed by using third generation benchmark model, and the accompanying FPS model is created and fabricated using the geometric similarity criterion. Considering four typical ground motions and four peak ground acceleration (PGA), the structural seismic responses of the three control systems were analyzed. The result demonstrates that FPS-H technology greatly decreases the superstructure’ top floor acceleration and even the substructure's acceleration impact in both mild and major earthquakes. The working mechanism of FPS-H technology in terms of vibration reduction is similar to the conjunction of tuned mass damper (TMD) and FPS-B structure. The inertia force of superstructure suppresses the substructure since superstructure has FPS inter-story isolation form, and even the substructure is an FPS-B form that can extend the structural period and segregate earthquake energy. The FPS-H technology, which reduces the acceleration response of the structure's 1st -order mode and restrains the dynamic reaction of the high-order mode by changes the dynamic characteristics of whole structure, is primarily responsible for the long-period structure's effective damping.

Effectiveness of friction pendulum system on the seismic behavior of high-rise building with shear wall

Effectiveness of friction pendulum system on the seismic behavior of high-rise building with shear wall

Seismic Performance of Irregular Building with different Variable sliding isolators and Semi active Dampers

The comparative performances of semiactive friction and stiffness dampers with different control laws in the base-isolated Irregular building subjected to bi-directionally acting strong earthquakes have been studied. The Irregular building is hybridly isolated with rubber bearings and friction pendulum system (FPS) or variable frequency pendulum isolator (VFPI) or variable curvature friction pendulum system (VCFPS). The shear type base-isolated Irregular building is modeled as three-dimensional linear elastic structure having three degrees-of-freedom at each floor level. Time domain dynamic analysis of the building has been carried out with the help of constant average acceleration Newmark-Beta method and non-linear isolation forces has been taken care by fourth-order Runge-Kutta method. The effects of variation of characteristic properties of semiactive dampers on their hysteresis loops and on the structural response of Irregular building is studied through parametric study. Comparative performances of different semiactive dampers with sliding isolation systems for seismic control of Irregular building have been observed through time history plots and peak response performance indices. It has been found that semiactive electromagnetic friction damper work efficiently with VFPI and VCFPS in comparison FPS for the Irregular building for near field earthquakes as it not only reduces base displacement at lower control force but also give lower base shear and story drift in base-isolated Irregular building. The control laws based on modulated homogeneous friction control semiactive friction dampers better than the predictive control law.

Application of MR damper in Base-isolated Irregular Building with different variable sliding Isolators

Application of Electromagnetic induction (EMI) based passively controlled and some local response governed MR dampers in controlling the isolator displacement in base-isolated Irregular building have been studied and compared with the Lyapunov controller. The Irregular building is hybrid isolated with elastomeric rubber bearings and a variety of sliding isolators subjected to strong near field earthquakes acting bi-directionally in horizontal plane. The shear type base-isolated Irregular building is modelled as three-dimensional linear elastic structure having three degrees-of-freedom at each floor level. Time domain dynamic analysis of the building has been carried out using constant-average acceleration Newmark-Beta method and non-linear isolation forces has been taken care by fourth-order Runge-Kutta method. It is observed that the EMI based passive controller performs better than the Lyapunov controller though it reduces less base displacement but gives lower structural response among all the controllers. Local response governed Hyperbolic and Aly’s controller require only velocity and displacement at controller locations sound simpler in application as compared to Lyapunov controller especially to civil engineering structures like Irregular building. The Hyperbolic controller restrains base displacement comparable to the Lyapunov controller but gives less base shear and story drifts to Irregular building. Variable frequency pendulum isolator (VFPI) and variable curvature friction pendulum system (VCFPS) sliding isolators perform better with MR damper control in comparison to conventional friction pendulum system (FPS) in base–isolated Irregular building.

Seismic performance of reinforced concrete bridge using friction pendulum bearing under different friction coefficients

Application of seismic isolation system is important in bridges design, primarily in seismically active countries. Bridges are prone to damage from seismic forces. Elastomeric isolation bearings have been applied in short-span bridges for some time in most countries. These bearings are preferred because of the low maintenance cost. However, these bearings are not reliable when subjected to large displacement and low temperatures. In the other hand, friction sliding bearings shows better performance under the former circumstances despite its use is still limited to long-span bridges and has not been explored further. This paper describes a performance evaluation of seismically-isolated short-span reinforced concrete bridge using friction pendulum system (FPS). Seismic performances of non-isolated and isolated models from the reference bridge functioning as light rapid transit (LRT) bridge in Jakarta are investigated using nonlinear time history analysis. The results demonstrate that isolated bridges with FPS performed better than non-isolated bridges under 1000-year earthquake as shown by reductions of base shear force, absolute deck acceleration, and acceleration amplification ratio. Comparisons of isolated bridges with different FPS friction types and arrangement have demonstrated that the reference bridge with all Type A friction (�0 = 0.050) applied, performed the best among all other configurations.

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.

Seismic design and performance evaluation of typical lightweight and heavyweight RC girder bridges with friction pendulum bearing in Indonesia

Seismically isolated bridges have shown better seismic performance than bridges with conventional bearings during large earthquakes. While elastomeric type of isolation has been introduced in various new highway bridges in the country, the use of friction pendulum system for bridge bearing is not yet common in Indonesia, a highly seismically active country. In this paper, design and seismic performance evaluation of two typical reinforced concrete bridges seismically isolated by single concave friction pendulum (SCFP) bearings system and designed according to Indonesian seismic code is described. The reference bridges are selected from typical light rapid transit (LRT) bridge and highway reinforced concrete (RC) bridge in Indonesia. Seismic performances of SCFP-isolated bridges with different bearing configurations and the conventional non-isolated bridges under 1000-year design earthquake were investigated and compared using nonlinear finite element analyses. The results show that SCFP-isolated bridges performed better than non-isolated bridges under design earthquake as shown by reductions in the base shear force, absolute deck acceleration, and deck acceleration amplification ratio. Effects of SCFP on the seismic performance of isolated bridge was evaluated by comparing the moment and rotation values of each pier and the possible formation of plastic hinges. Performance comparisons of SCFP-isolated bridges with various friction types and arrangements revealed that the LRT bridge with all higher friction and the highway bridge with lower friction have the best seismic performance among all isolated bridge models analyzed.

Influence of Earthquake Parameters on the Bi-directional Behavior of Base Isolation Systems

The introduction and development of the base isolation systems, especially the friction isolator device, were done recently to improve the capacity of adaptive behavior. The efficiency of multi-phase friction pendulums comes from their complexity, which helps reduce the structural responses and enhance structures' energy dissipation under lateral loads. Nevertheless, the influence of various earthquakes' properties on the behavior of base-isolation systems subjected to bi-directional seismic loading is still unclear. Hence, further research and studies regarding the behavior and capability of these systems under bi-directional loading are still necessary before incorporating this device in real-life practical applications. Therefore, this paper is intended to investigate the bi-directional behavior of the friction isolator subjected to various ground motion records. In order to do so, different versions of the friction pendulum system are selected and compared within the study context. Generally, the study's results have shown that the behavior of the friction isolator is highly dependent on low values of the PGA/PGV ratio. Besides, pulse-like earthquakes considerably impact the response of the isolator compared to non-pulse-like ones. Doi: 10.28991/CEJ-2022-08-10-02 Full Text: PDF

Performance evaluation of FPS and LRB isolated frames under main and aftershocks of an earthquake

The seismic behaviour of a 10-storey building frame isolated with the Friction Pendulum System (FPS) and Lead Rubber Bearing (LRB) is investigated under the mainshock and a single aftershock of (i) far-field earthquakes with narrow and broadband characteristics; (ii) near field earthquake with directivity effect; and (iii) near field earthquake with the fling step effect. In order to make the investigation, a realistic one, the FPS and LRB are so designed that their dynamic characteristics are quite comparable. The difference in seismic responses (maximum and residual values) between the FPS and LRB isolated frames is calculated to assess the relative performances of the two systems. A non-linear time history analysis is performed to determine the response parameters which include base shear, peak top storey displacement, absolute acceleration, isolator displacement and the number of hinges formed. The effect of µslow (Friction coefficient at low sliding velocity) which controls the re-centring capability of the FPS and earthquake intensity parameter (PGA) of earthquakes on the difference in responses is demonstrated. It is concluded that better re-centring capability of the FPS isolated frame is observed for lower values of µslow (friction parameter) and higher values of PGA as compared to the LRB isolated frame. Further, less number of plastic hinges are formed in the FPS isolated frame for lower values of µslow.

Geometrically nonlinear analysis of friction pendulum systems under tri-directional excitation

A three-dimensional formulation for a mass sliding with friction on a concave spherical surface is presented and used to describe the behavior of friction pendulum systems under extreme tri-directional excitation. The proposed approach accounts for large deformations and includes a procedure for handling the characteristic stop-and-go, or stick-slip, motion of friction-based systems. A set of numerical examples are carried out comparing the results of the proposed formulation with available analytical solutions. Where these are not available, such as in the case of earthquake excitation, the convergence rate of Newton’s method and energy balance plots illustrate the accuracy of the computed solutions. Tri-directional earthquake simulations demonstrate the vulnerability of friction pendulum systems to nearly-periodic, and near-fault, long-period ground motions.

Elastic and viscous bumpers for seismic mitigation of base-isolated liquid storage tanks in near-fault zones

The use of friction pendulum system (FPS) as a base isolation system is one of the efficient and reliable techniques for seismic response reduction of liquid storage tanks. However, recent studies have shown that the FPS may experience substantial displacements under pulse-like near-fault earthquakes, which could lead to the collision of its articulated slider against the retainer ring. This internal impact in the FPS can make the isolation system less effective or even damaged. The best solution to this problem is to provide an appropriate displacement capacity of the FPS bearing to accommodate the resulting movements. However, due to any practical limitation or under extreme ground motions, the base displacement may exceed the displacement capacity provided and an internal impact may occur. This paper proposes and investigates the use of elastic and viscous bumpers in FPS-isolated tanks subjected to near-fault earthquakes to limit excessive bearing displacements and to prevent direct impact with the retainer. The material properties of the bumpers and their initial gap distance are used as variable parameters in the nonlinear time-history analyses of selected isolated tanks with different aspect ratios. The results, while showing the advantages of viscous bumpers over elastic ones, indicate the effectiveness of both shock absorbers in isolated tanks that are subject to large displacement demands. Based on the results of the parametric study, design recommendations are given for the use of such bumpers in FPS-isolated tanks.