Base-isolated Structures Research Articles

Seismic performance of a clutched inerter for structures with curved surface sliders

The performance of the clutched inerter in limiting the seismic response of structures isolated by curved surface slider (CSS) is investigated. The chosen structure is a flexible multi-floor building with an idealized linear shear-type behaviour. The equations governing the motion of an isolated structure with a clutched inerter under earthquake excitation have been derived. Initially, using the equivalent linearization technique, the isolated building's stationary floor absolute acceleration, isolator displacement, and device forces are evaluated. The stochastic earthquake excitation is considered to be a filtered white-noise Kanai-Tajimi model. The performance of the clutched inerter in mitigating the response of the isolated structure is studied by varying system parameters. The important parameters included are the inertance ratio of the clutched inerter, the period and friction coefficient of the CSS, and the flexibility of the superstructure. Further, there exists an optimum inertance of the clutched inerter for which the structure's highest floor absolute acceleration reaches its minimum level. The influence of important system parameters on the optimum inertance of the clutched inerter is also investigated. Finally, the performance of the clutched inerter as a supplemental device for the base-isolated structure is investigated when subjected to recorded earthquake motions consisting of near-fault as well as far-field types. The trends of results of isolated structures with clutched inerter under the recorded earthquake motions were in good agreement with that under stochastic excitation. It is demonstrated that the supplemental clutched inerter is effective in reducing the displacement response of base-isolated structures.

Modified endurance time method for seismic performance assessment of base-isolated structures

Endurance time (ET) method is a novel Time History Analysis‏ ‏(THA) approach in which structures are subjected to a set of intensifying excitations called endurance time excitation functions (ETEF). Although ‏various studies show ‏the efficiency of the ET method for the seismic evaluation of fixed base structures, this method has been less employed in isolated structures. The lack of coverage of high-intensity measures by existing ETEFs is the major obstacle to adopting the ET method in high-period structures such as isolated structures. It must be noted that high-intensity measures that are associated with large earthquakes are of paramount importance in performance assessment. This paper introduced a novel method called the modified endurance time (MET) method based on scaling existing ETEFs to alleviate this problem. By averaging multiple scaled ETEFs, the accuracy of the ET method is improved. Three steel structures with a different number of stories (6, 9, and 12), including Intermediate Moment Frames (IMFs), mounted on Triple Friction Pendulum Isolators (TFPIs) are considered to demonstrate the efficiency of the proposed method. These structures are analyzed under ETEFs with intensity multipliers 1 to 4 for three seismic hazard levels with return periods of 72, 475, and 2475 years. The effect of changing parameters such as isolator damping and period is also investigated on the results. The seismic responses obtained from the Endurance Time Analysis (ETA) are compared with the responses obtained from the nonlinear THA and pushover analysis. Results show that increasing the intensity multiplier of ETEFs can greatly improve the accuracy of results. However, it should be careful in the procedure of selecting the appropriate intensity multiplier. Because of the unbalanced changes in some ETEFs parameters such as PGV/PGA, the accuracy of results may also reduce by increasing the intensity multiplier. Therefore, the use of different combinations of results, obtained from several intensity multipliers, is investigated and proposed to reduce the error in results.

Modeling and model updating of a full-scale experimental base-isolated building

Large-scale seismic structural tests are crucial to validating both structural design methodologies and the effectiveness of seismic isolation devices. However, considering the significant costs of such tests, it is essential to leverage data from completed tests by taking advantage of numerical models of the tested structures, updated using data collected from the experiments, to complete additional studies that may be difficult, unsafe or impossible to test physically. However, updating complex numerical models poses its own challenges. The first contribution of this paper is to develop a multi-stage model updating method suitable for high-order models of base-isolated structures, which is motivated and evaluated through modeling and model updating of a full-scale four-story base-isolated reinforced-concrete frame building that was tested in 2013 at the NIED E-Defense laboratory in Japan. In most studies involving model updating, all to-be-updated parameters are typically updated simultaneously; however, given the observation that the superstructure in this study predominantly moves as a rigid body in low-frequency modes and the isolation layer plays a minor role in all other modes, this study proposes updating parameters in stages: first, the linear superstructure parameters are updated so that its natural frequencies and mode shapes match those identified via a subspace system identification of the experimental building responses to low-level random excitations; then, the isolation-layer device linear parameters are updated so that the natural frequencies, damping ratios and mode shapes of the three isolation modes match. These two stages break a large-scale linear model updating problem into two smaller problems, thereby reducing the search space for the to-be-updated parameters, which generally reduces computational costs regardless of what optimization algorithm is adopted. Due to the limited instrumentation, the identified modes constitute only a subset of all modes; to match each identified mode with a FEM mode, the second contribution is a procedure proposed to compare each identified mode with a candidate set of FEM modes and to select the best match. Further, nonlinear isolation-layer device models are proposed, updated and validated with experimental data. Finally, combining the isolation-layer devices’ nonlinear models with the updated superstructure linear FEM, the final result is a data-calibrated nonlinear numerical model that will be used for further studies of controllable damping and validation of new design methodologies, and is being made available for use by the research community, alleviating the dearth of experimentally-calibrated numerical models of full-scale base-isolated buildings with lateral–torsional coupling effects.

Shaking table test study on dynamic performance of a base-isolated frame structure under an isolation bearing removal scenario

Studies on the progressive collapse of structures have been at the forefront in structural engineering domain recently. The progressive collapse of isolated structures is quite different from that of conventional fixed-base structures. Once an initial failure occurs in the isolation layer which is the most vulnerable to accidental events due to the low horizontal stiffness, progressive failures at other locations may lead to a large-scale collapse of isolated structures. This paper presents a 1:4 scale model shaking table test of a three-story irregular plane reinforced concrete (RC) frame isolated structure to investigate the progressive collapse resistance of isolated structures. An edge bearing was removed quickly by an electromagnetic failure excitation device during the first seismic input case. The dynamic responses such as the macroscopic crack distribution, acceleration responses, displacement responses, internal forces of the isolation bearings, and concrete and reinforcement strains of the failure span beams were evaluated. The results show that the significant vertical deformation with dynamic impact response was produced at the failure point under multi-directional dynamic coupling excitation, i.e., the combined effect of the vertical unbalanced load caused by sudden failure of a bearing and horizontal earthquakes. This sudden failure of the isolation bearing not only had an impact on the internal forces of bearings adjacent to the failure bearing, but also on other non-adjacent bearings. As the tensile and compressive stress of adjacent bearings were more likely to exceed design limits under earthquakes, the risk of overturning collapse for isolated structures markedly increased following the failure of a few bearings. In addition, vertical and low-frequency components of earthquakes could have a significant influence on dynamic responses and damages of isolated structures, especially in the area of bearing failure. The experimental results obtained in this study act as important references for the progressive collapse design of isolated structures.

Seismic response of a mid-story-isolated structure considering soil–Structure interaction in sloping ground under three-dimensional earthquakes

A mid-story-isolated structure is developed from a base-isolated structure. Mid-story-isolated structures located in sloping ground have become a research hotspot in recent years. It is important to consider the soil–structure interaction (SSI) effects and multi-dimensional earthquakes on these structures. This paper established a model of the mid-story-isolated structure considering SSI in sloping ground. An elastic–plastic time history analysis was carried out under the one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) earthquakes. Under 3D earthquakes, the traditional 2D isolated bearing has limited damping capacity. Therefore, two kinds of 3D isolated bearings were designed. Results show that the seismic response of the mid-story-isolated structure considering SSI in sloping ground can be amplified compared with that of the mid-story-isolated structure without considering SSI. The seismic response of the structure under 3D earthquakes is more significant than that under 2D earthquakes and 1D earthquakes. For the two kinds of 3D isolated bearings, the minimum reduction rate of tensile and compressive stress is about 46% compared with that of the traditional 2D isolated bearings. When the 3D isolated bearings are used, the stress of the soil foundation decreases, which is more conducive to the stability of the soil foundation.

極配置法に基づく多質点１本棒せん断振動型建物モデルの支配方程式

Based on the pole allocation method in control theory, the authors’ previous research found out a fundamental closed-form equation governing a three-lumped-mass stick-shape shear model for a building. Through the selection of appropriate model parameters, the simplified model can represent an earthquake-resistant structure, a base-isolated structure, an interstory-isolated structure, or a passively controlled structure with a tuned mass damper or viscous interstory dampers. The equation explains how the model parameters are related to the control target and generally proves the trade-off relationship in the passive control effect. The present study similarly applies the pole allocation method to a multi-lumped-mass stick-shape model to provide the trade-off relationship with higher generality. The newly introduced equation has the same form as the previous research indicated. Next, this study discusses the installation distribution of interstory dampers from a viewpoint of modal damping as control target.

A physical model for dynamic analysis of structures equipped with variable curvature frictional isolators

During high magnitude ground motions, the internal lateral impact between inner sliders of frictional isolators and restraining rims of sliding surfaces may occur, jeopardizing the benefits of seismic isolation. In this study, a variable curvature friction isolator that exhibits a smooth-hardening behavior at large lateral displacements is evaluated as an alternative to mitigate the adverse effects of internal impacts. The geometry of the sliding surface is obtained by revolving a plane ellipse around a vertical axis. The pendular force transmitted by the isolator increases in stiffness as the device is laterally deformed. This research presents a physical model of variable curvature frictional isolators valuable for analyzing the three-dimensional dynamic response of structures equipped with variable curvature devices. The suggested physical model is capable of accounting for essential modeling features such as large deformations, P-∆ effects, sticking and sliding phases, uplift, kinematics constraints, and the lateral impact behavior. The presented force-displacement relationship of the frictional bearing with smooth-hardening behavior was validated using a Finite Element Model (FEM) under static and dynamic loads. An accurate representation of the coupling between the horizontal components of the pendular and frictional forces transmitted by the isolator is achieved by employing the physical model. The impact parameters of the physical model were calibrated to match the dynamics response of the FEM subjected to unidirectional and bidirectional ground motion inputs. Finally, a comparative example of a base-isolated three-dimensional structure is presented to show how the dynamic response is affected when variable curvature bearings form the isolation system.

Full-scale experimental tests on unbonded fiber reinforced elastomeric isolators under bidirectional excitation

Unbonded fiber reinforced elastomeric isolators (UFREIs) represent a lower-cost alternative to conventional steel reinforced elastomeric isolators (SREIs), in which the internal steel shims are replaced with fiber reinforcement and the installation is accomplished without anchorage bolts or dowels, but only relying on frictional mechanisms and interfacial roughness. In the literature, experimental tests on UFREIs were generally presented under unidirectional seismic excitation and considering small-scale devices. In this contribution, the hysteretic behavior of UFREIs is investigated experimentally by testing full-scale devices (diameter 620 mm) not only under unidirectional loading, but also including bidirectional orbits, thus quantifying the degree of biaxial coupling. A simple phenomenological model is then set up to numerically simulate the experimental outcomes. This model consists of a set of nonlinear springs arranged in a circular configuration. The spring parameters are calibrated by either curve-fitting 1D test results or considering 2D tests, thus selectively incorporating the lateral coupling. This model makes it possible to investigate the influence of bidirectional interaction of UFREIs on the seismic performance of base-isolated structures. Nonlinear time-history analysis on a regular three-dimensional reinforced concrete building with UFREIs modeled through the proposed approach demonstrates that the lateral coupling of the UFREIs leads to lower seismic response, of around 10-20%, in comparison to a simpler, uncoupled model that ignores the bidirectional interaction of the isolation devices.

Seismic response control of base-isolated structures with fluid inerter damper

Seismic response control of base-isolated structures with fluid inerter damper

Application of a Novel Optimization Algorithm in Design of Lead Rubber Bearing Isolation Systems for Seismic Rehabilitation of Building Structures

Various mechanical and geometrical parameters have different effects on the isolation system's performance. Thus, a sensitivity study of the isolated structures' behavior is an essential matter. In this regard, the isolation systems should be designed using optimization approaches to consider the effects of the different factors. In this study, the optimal design of the lead rubber bearing (LRB) seismic isolation was conducted by considering mass irregularity and near-fault seismic excitation effects. Also, sensitivity analysis of the behavior of the considered isolated buildings was implemented concerning the mechanical parameters of the LRB system. A nonlinear time history dynamic analysis was used here, and the design optimization of the LRB isolator was programmed using the newly introduced grasshopper optimization algorithm (GOA). The main purpose was to investigate the ability of the GOA to optimize the design parameters of the LRB-isolated frames. The results proved the desirable ability of the GOA to solve optimal design problems for isolation systems. Also, the sensitivity analysis of the seismic behavior of LRB base-isolated structures showed that the yield base shear index had the most important effects. Also, the mass irregularity parameter showed a negligible influence.

Design spectra to be used in Base Isolation Design in light of recent strong motion records

Strong motion records have shown an increase of the maximum values of PGA and PGV, also associated to the increase of the archived strong motion records. Nowadays, the worldwide largest PGA values are: 3,94g (vertical) and 2,75g (horizontal), from the 2008 Iwate-Miyagi and 2011 Tohoku earthquakes, while the current PGV maxima are larger than 2.0 m/s (horizontal and vertical). These unforeseen values have encouraged a more conscious approach in BIS design, being necessary to move to larger design periods and to face wider design displacements. Many changes have occurred in the history of BIS, as indicated in Design Recommendations for Seismically Isolated Buildings by AIJ (2016), tracing the improvements of BIS in Japan, and in De Luca and Guidi (2019). In this excursion, a significant contribution has been given by Miyazaki (2008) that defined a “Next Generation of seismic isolation” to counteract the unprecedented spectral values of displacement and acceleration. In this perspective, the paper analyzes the acceleration, velocity and displacement spectra of different sets of strong motion records to provide suggestions for seismic design of base-isolated structures in the light of higher spectral values. In particular, we will consider: the set defined in Trevor Kelly (2001), that divided motions into pre-1971 and post-1971; the set of FEMA307 (1999), in which three categories of ground motion are considered (short duration, long duration and forward directivity); the set used by Miyazaki (2008) for the Next Generation of Seismic Isolation; the set defined by Suzuki and Iervolino (2017) to trace the history of largest PGA and PGV; the set used by De Luca and Guidi (2019) to trace the improvements in BIS design and propose a classification of BIS in three successive generations. A comparison between results, for different periods, will lead to possible design indications for BIS.

Gaussian process regression-based surrogate modelling for direct loss-based seismic design of low-rise base-isolated structures

Seismic base isolation has gained popularity in the last decades. As a result, many structures are now equipped with base isolation systems to offer enhanced seismic performance and meet the needs of risk-aware stakeholders. However, a robust performance-based seismic design of these types of structures is generally not carried out due to the iterative nature of common design approaches and the time/computational resources required for such iterations, which are incompatible with the preliminary design phase. Indeed, seismic risk/loss is often just assessed at the end of the design process as a final verification step. This paper offers an overview of a simplified methodology for the seismic design of low-rise structures equipped with a base isolation system to achieve a predefined level of earthquake-induced economic loss while complying with a predefined minimum level of structural reliability. The main advantage of the proposed methodology is that it requires no design iterations. The procedure is enabled by Gaussian-process-regression-based surrogate probabilistic seismic demand modelling of equivalent single degree of freedom systems (i.e., the probability distribution of peak horizontal displacements and accelerations on top of the isolation layer conditional on different ground-motion intensity levels). Combined with simplified loss models for the base isolation system and the structural and non-structural components of the superstructure, this approach allows mapping a range of structural configurations to their resulting seismic loss. A designer can then select one of the identified combinations of the strength of the superstructure and properties of the isolation system conforming with the loss target, and reliability requirements, and consequently detail the superstructure and isolation system accordingly. This paper introduces the implemented surrogate probabilistic seismic demand models and provides an overview of a tentative Direct Loss-based Design procedure for low-rise base-isolated structures.

Response of base–isolated structures-evaluation of different isolation systems

Base isolation is a seismic mitigation technique that separates the structure from the ground motion by placing isolators between the foundation and the superstructure. This creates a flexible base that allows the structure to move independently of the ground, reducing the seismic forces transmitted to the superstructure. Different isolation systems have been developed, each with advantages and disadvantages. This paper evaluates the seismic response of base-isolated structures with varying isolation systems under various earthquake ground motions. The results show that base isolation can significantly reduce the seismic response of structures and that the effectiveness of different isolation systems depends on ground motion characteristics.

Friction pendulum-strengthened tuned liquid damper (FPTLD) for earthquake resilience of isolated structures

Conventional base isolation has been commonly used to protect structures against destructive earthquakes. However, base-isolated structures can be vulnerable to ground motions, including resonant frequency components, which cause significant displacement of the isolation floor and a weakened isolating effect. To address this issue, this study develops a friction pendulum-strengthened tuned liquid damper (FPTLD) as a hybrid isolating system that comprises a friction pendulum subsystem mounted at the bottom of a liquid tank with sloshing liquid inside. Its configuration and theoretical analysis model are established, based on which the experimental test of the tuned liquid subsystem and finite element simulation of the complete FPTLD are conducted for validation. The nonlinear stochastic response analysis is performed for an FPTLD-equipped isolated structure within a probabilistic framework. Correspondingly, the dual-modal and lightweight-based control benefits of the FPTLD over conventional and TLD-equipped isolation systems are clarified by an extensive parametric analysis. Based on the simultaneous control of the isolation floor and the superstructure, a multiperformance-based design framework is presented for the FPTLD, and an easy-to-use design formula is obtained by fitting its numerical design results. To illustrate the effectiveness of the developed device and the design method, the FPTLD is used in a typical base-isolated building subjected to various seismic excitations. The obtained results show that the optimized FPTLD with adjustable tuning degrees—liquid sloshing and friction pendulums—is highly effective in simultaneously enhancing the multiple seismic performances of the superstructure and the isolation floor. In particular, compared with conventional and tuned liquid damper-equipped isolation systems, the FPTLD facilitates sufficient utilization of the entire liquid for efficient energy absorption by implementing friction pendulums, reducing the deformation demand of an isolation floor. Benefitting from the friction pendulums with a constant isolating period, the FPTLD demonstrates a robust multiperformance mitigation effect against the variation in the liquid height. It thereby presents a practical solution to the retrofitting or new construction of a base-isolated structure using a nonspecific designed liquid tank or landscape.

Performance of Supplemental Inertial Devices for Base-Isolated Structures

The seismic response of base-isolated structures with supplemental inertial devices subjected to stationary and real earthquake excitation is presented. Three types of devices, namely inertial mass damper (IMD), tuned mass damper-inerter (TMDI), and clutching inerter damper (CID), are considered. The seismic response of the base-isolated structure with and without inertial devices is compared to assess their effectiveness. Under stationary white-noise excitation, the optimum parameters of these devices were obtained. The criterion selected for optimality is the minimization of the mean-square relative displacement and absolute acceleration of the isolated structure. An equivalent linearization method was used for base-isolated structures with CID under stochastic excitation. It was observed that the IMD is not very effective in controlling the response of base-isolated structures. Optimally designed TMDI, on the other hand, was found to be effective in controlling the displacement and acceleration response of the isolated structure, with the effectiveness increasing as the inertance mass ratio increased. The CID involved in the base-isolated structure reduces the structural natural frequency and increases structural damping, thereby reducing isolator displacement and structural acceleration. The high-frequency components were present in the absolute acceleration of base-isolated structure with inertial devices (more pre-dominating for IMD and CID), which may have detrimental effects on installed high-frequency sensitive equipment.

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.

Shaking Table Test of a Base-Isolated Frame Structure under Near-Fault Ground Motions

A five-story moment frame structural model with a base isolation system was tested on a shaking table. The isolation system comprised both linear natural rubber bearing (LNR) and nonlinear viscous dampers (NLVDs). Seven ground motions were employed: including three far-fault (FF) and four near-fault (NF) earthquake ground motions. The performance of the isolation system was evaluated by measuring the displacement and base shear of the isolation bearings. Furthermore, the axial force and displacement of the NLVDs were measured. The evolution of the fundamental dynamic frequency of the frame during the test was also determined. During strong earthquakes, NF ground motions caused larger story drifts and floor accelerations of the superstructure than FF ground motions. The displacement and base shear of the isolation base was very large when the isolated structure was subjected to Kobe_TAK000 and ChiChi_TCU102/278 pulse-like NF ground motions. Furthermore, the LNR s experienced tension and uplift when the PGA of input earthquake ground motions was larger than 0.80 g. Although the NLVDs performed very well in combination with the LNRs, the severe responses of the isolation bearings were caused by NF ground motion with a pulse period Tp neighboring the fundamental period of the isolated structure.

A frequency-dependent variable damping control method for base-isolated structures under ground motions with different frequency characteristics

The base isolation technique is commonly adopted to protect important structures from earthquake damages. Typically, a high damping ratio for the base isolation layer is useful in reducing the structure's resonance effect under low-frequency (long-period) ground motions, and a low damping ratio is preferred in minimizing the acceleration response under high-frequency (short-period) ground motions while not causing significant displacement response. To realize optimal control for base-isolated structures under ground motions with different frequency characteristics, the semi-active control is adopted and a frequency-dependent variable damping (FVD) control method based on a transmissibility weighted fast Fourier transform (TWFFT) spectrum is newly proposed. The FVD control method considers the influences of different frequency components of ground motions on base-isolated structures by developing the TWFFT spectrum of the detected ground accelerations. A series of shaking table tests for a base-isolated steel frame structure with semi-active control were carried out to evaluate the effectiveness of the FVD control method. The test results demonstrated that the FVD control method could realize optimal control of the structure under various types of ground motions, and it was more effective than the ON-OFF control method which only considered the dominant frequency characteristics of the ground motions.

Improved Response Spectrum Method Based on Real-Complex Hybrid Modal Superposition for Base-Isolated Structures

A novel real-complex hybrid modal response spectrum method (RCHM-RSM) based on the modal superposition of the superstructure is proposed for base-isolated (BI) structures in this paper. In contrast to the traditional analysis method, the method can increase the accuracy of the structural response and avoid complex calculations. Additionally, the direct use of the damping matrix of superstructures for BI structures was found to cause an overestimation of the damping effect and consequently underestimate the deformation of the superstructure. Thus, a new scheme is proposed for determining the damping matrix for BI structures, and general expressions of the damping matrix of the superstructure and the damping constant of the isolation layer are presented. Using the proposed method to construct the damping matrix of BI structures, the equivalent load associated with the coupling damping between the structure and support can be determined when the displacement–velocity input model (D–VIM) is adopted. Analytical expressions of structural matrices are presented for a shear-type model of a BI structure, and a numerical investigation is conducted to demonstrate the feasibility and effectiveness of the proposed methods. The results show that the proposed method (RCHM-RSM) has the advantages of simple calculations and high accuracy. The numerical results obtained also confirm that the direct use of the damping matrix of superstructures for the BI structure will underestimate the superstructure response, while the displacement input model (DIM) overestimates the deformation of the isolation layer and underestimates superstructure responses, the analysis results by using D–VIM are consistent with the acceleration input model (AIM), so the D–VIM should be used instead of the DIM.

Multihazard response of unbonded fibre-reinforced elastomeric isolator-isolated structures

Unbonded fibre-reinforced elastomeric isolator (UFREI) as laminated elastomeric isolator is a relatively new approach to base-isolation devices with improved efficiency, cost-effectiveness and ease. Base-isolated structures become more susceptible to wind loads due to an increase in the period of the structure, and UFREIs have been found to be effective in mitigating occasional wind loads on isolated structures with the help of supplemental devices. This study investigates the multi-hazard response of benchmark structures isolated using UFREIs and subjected to several hazards over a period of time. Hazard timelines consisting of probable prominent seismic and long-term wind events are generated for the analysis. Since fibre layers in UFREI are flexible in bending, the bond strength demand between elastomer and fibre layer decreases by a huge margin, which delays any delamination failure. Thus, fatigue losses in the elastomer layers are used to characterise the damage induced in the UFREI due to multiple hazards throughout the timeline. Maximum principal strain in elastomer layers at various displacement amplitudes is calculated using finite-element modelling, and it is further used to characterise the fatigue damage in elastomer layers. The final fatigue life of the designed UFREI is predicted using the obtained damage indices.