Seismic Isolation Devices Research Articles

Frictional Slippage of Annular Elastomeric Disks Compressed Between Rigid Platens

Abstract Compression of compressible, linearly elastic, annular disks by flat rigid platens is analyzed. Coulomb (Amonton) friction is assumed to act at the interfaces between the disk and the platens. Slip may occur in an outer annular region while the inner annular (bonded, stick) region of the disk does not slip. The critical radius (slip boundary) is of major interest. The governing equilibrium equations in terms of the deflections are satisfied exactly. Approximations are made in some of the boundary conditions and the transition (matching) conditions at the critical radius. Numerical results are presented for nearly incompressible disks. The effects of the radius ratio, aspect ratio, and Poisson's ratio of the disk, and of the coefficient of friction at the platens, on the critical radius, effective compression modulus, stresses, and radial deflection are investigated. Applications include structural (especially bridge) bearings, seismic-isolation devices, mounting blocks and bushings, gaskets, and sealing components.

Proposal and Evaluation of Vertical Vibration Theory of Air Caster

Urbanization and human development have increased the exposure of seismic risk. Therefore, engineers need to develop new and more efficient technologies to protect people and objects from the disastrous consequences of earthquakes. Air casters have gained attention and have been utilized in the past decade as effective seismic vibration control devices. Although such active isolation systems perform well in mitigating horizontal input vibrations, they might cause excessive rocking motions, if not designed properly. This fact emphasizes the importance of exploring the vertical dynamic properties of air isolation systems. To gain such an understanding, this research examines and proposes a formula for the vertical stiffness and damping of air caster systems. Theoretical solutions to the vertical stiffness and damping of such systems have been explored. Computer simulations considering fluid-structure interaction have also been performed to understand the dynamic behavior of the supporting air layer. Results have been compared to validate the proposed dynamic quantities within the considered simulation range. It is also concluded that the instantaneous air layer thickness, representing the air chamber pressure, and the bearing inlet flow rate are the key factors in determining the dynamic properties of the air layer. It is concluded that to evaluate the performance of the air caster seismic isolation device and increase the probability that the qualified seismic isolation performance will be exhibited, it is necessary to investigate which parameters are greatly involved in the viscous damping coefficient and the spring constant of amass-spring-damper system equivalent to the air caster isolation system.

Experiment and analysis of air spring vertical seismic isolation device

To address the shortcomings of poor isolation performance in traditional rubber vertical seismic isolation devices and the large deformation in spring vertical seismic isolation devices, an air spring vertical seismic isolation device (ASVSID) utilizing compressed air for seismic isolation was proposed. The construction of the ASVSID was introduced, the material properties of the air spring (AS) capsule skin based on single and biaxial stress state were tested, the vertical mechanical properties of the ASVSID were experimentally studied, and the finite element (FE) method and the calculation method of the ASVSID based on biaxial stress state of the AS capsule skin were given. The research results show that the load displacement of the ASVSID exhibits nonlinear characteristics, and its vertical mechanical properties are obviously affected by air pressure of the AS. The material properties of the AS capsule skin are different under single and biaxial stress state. Through comparison with the test results, the proposed FE method based on biaxial stress state of the AS capsule skin can accurately simulate the ASVSID. In addition, the calculation method based on biaxial stress state of the AS capsule skin also can accurately calculate the vertical mechanical property parameters of the ASVSID.

Numerical Assessment of Bidirectional Roller Bearing Isolators under Near-Fault Earthquakes

In this research, a bidirectional seismic isolation device composed of sloped bearing plates and multiple rollers arranged in both orthogonal-in-plane directions is numerically studied. A previous analytical model of a single direction of roller bearing (RB) system is extended to a two-direction RB system. Several experimental tests in a physical building model with and without an RB system are used to validate the numerical model. The model is used to perform the nonlinear response of a four-story multi-column building when subjected to pairs of scaled near-fault earthquake records. The effect of the inclination angle of bearing plates in the range of 1.0° to 4.0°, the sliding friction force, and supplementary damping mechanisms ranging from 0.0 to 0.5 N/kg (i.e. friction force normalized with the structure mass) are also investigated. The results show that the proposed bidirectional RB system is suitable for reducing the seismic response of stiff and flexible multi-column structures. In particular, the RB system reduces the acceleration responses by 5% to 85% in flexible structures and 86% to 96% in stiff structures. Furthermore, bearing plates with an inclination angle greater than or equal to 3.0° have significant benefits in terms of self-centering capacity.

Evaluation of the response of historical structures fitted with seismic-isolation

The paper highlights the performance of the seismic isolation devices installed on retrofitted buildings in reducing the seismic response when subjected to earthquakes. Two buildings from the beginning of the XXth century in Bucharest are chosen from many more, monitored over the city area. We discuss the response of these base-seismic isolated structures, relying on good quality data acquired from the recent strong earthquake (3 November 2022, MW = 5.0). Elastic response spectra computed from recordings at two levels of each structure are used, placed under and right above the isolating layer. At one building, the existence of previous recordings and the particularity of the sensors allow a comparison with the other two relatively recent medium-intensity earthquakes. The assessment is carried out in terms of maximum acceleration amax, measured at certain levels in each structure, spectral acceleration amplitude SAmax, and spectral-peak corresponding period. We find that the base-isolation methodology is effective in reducing the response of the building right above the isolating layer, an observation valid for both structures, all components of the recordings, and spectral acceleration values. Moreover, the outcomes from the modal evaluation performed prior to rehabilitation and the seismic isolation process are presented by pointing out a higher newly acquired fundamental period of the isolated structures.

Frictional slippage of elastomeric disks compressed between rigid platens and subjected to torsion

A new analysis is applied to compressible, linearly elastic disks that are compressed by flat rigid platens. The disks are not bonded to the platens and Coulomb (Amonton) friction is assumed to act at the interfaces between the disk and the platens. Slip may occur in an outer annular region, while the inner circular (stick) region of the disk does not slip. The critical radius (slip boundary) is of major interest. The governing equilibrium equations in terms of the deflections are satisfied exactly. Approximations are made in some of the boundary conditions and the transition (matching) conditions at the critical radius. Numerical results are presented for nearly incompressible disks, both for (a) compression only and (b) compression plus torsion. In the latter case, during twisting, either the compressed thickness of the disk is fixed while the compressive force varies, or the compressive force is fixed while the thickness varies. The effects of the aspect ratio and Poisson's ratio of the disk, the coefficient of friction at the platens, and the twist angle on the critical radius, stresses, compressive force, torque, and effective compression and shear moduli are investigated. Applications include structural (especially bridge) bearings, seismic-isolation devices, mounting blocks and bushings, and rheometry.

Parameter Optimization of Friction Pendulum Bearings Based on the Adaptive Genetic Algorithm Considering the Overall Evolutionary Status

Improper design of friction pendulum bearings can lead to poor seismic reduction performance and may result in the failure of local vulnerable components. And the parameter design of friction pendulum bearings mainly relies on experience and verification calculations at present. This paper proposes an adaptive genetic algorithm considering the overall evolution state of the population, adjusting crossover and mutation probabilities adaptively based on individual fitness and population diversity. Compared to traditional algorithms, it exhibits better global search capabilities and convergence efficiency. Combining the improved genetic algorithm with finite element models, a parameter optimization method is proposed. The parameters of friction pendulum bearings are optimized. In response to the situation in this paper, the optimal friction coefficient of the friction pendulum bearing is determined to be 0.01 and the optimal equivalent radius is 3.3 m. This can provide a reference for the design of seismic isolation devices.

Proposal for vertical distribution of seismic design load and equivalent isolation ratio for seismically isolated buildings with multiple types of dampers: Vertical distribution of seismic design load for seismically isolated buildings corresponding to diversity of seismic isolation devices, part 2

AbstractAs previously reported, we have proposed a vertical distribution of seismic design load for seismically isolated buildings (SIBs) corresponding to diversity of seismic isolation devices such as hysteretic dampers and velocity‐dependent dampers. This proposed seismic design load is obtained from the relationship between response amplification caused by higher mode responses and the isolation ratio which represents structural characteristics of SIBs. In this paper, we build a concept of the equivalent isolation ratio which has applicability to various dampers in order to simplify an evaluation formula of vertical distribution of seismic design load. Moreover, an effect of the combined application of various dampers on vertical distribution of shear force coefficient of SIBs is analyzed on the basis of the equivalent isolation ratio.

Development of novel high damping rubber damper under axial compression dynamic load for energy-dissipation application

High Damping Rubber (HDR) has been a reliable and durable material used in bearings as seismic isolation devices for several decades. However, there has been no development of HDR as dampers to mitigate structural response caused by earthquake excitations, specifically by dissipating the induced energy applied to structures under direct axial load. This paper aims to address this gap by developing a novel HDR damper utilizing Hyper Elastic Composite Material (HECM) and conducting experimental investigations to determine its damping ratio, compressibility, and elasticity behaviour under axial dynamic compression load for effective dissipation of dynamic loads. The research methodology involved performing response spectrum analysis (RSA) on a model of actual building structures, following the guidelines of National Annex to MS EN 1998–2017. Subsequently, the dampers were incorporated into the model to achieve a seismic base shear value without seismic actions, as determined by the RSA. Full-scale dampers were then developed using three different HECM variants (NR- A, B and C), selected based on their achievement of a damping ratio of more than 10% as bearing isolators using the shear method according to EN 15129:2009 cl. 8.2.4.1.5. The developed dampers underwent testing for damping and wind load in accordance with EN 15129 cl. 7.4.2.7 and cl. 7.4.2.8, respectively, incorporating the testing parameters derived from the model's RSA. Finite element models (FEM) were developed and accurately simulating the hysteresis curves and damping properties of the HDR damper. The properties of HECM in the FEM were derived from the simulation results and can be utilized for future damper design, ensuring compliance with industry requirements. Additionally, an empirical formula will be developed to enable structural designers to estimate the mechanical properties of the tested damper. The testing shows that NR-C HECM damper is able to achieve 10.46% under 1.8 Hz requirement and able to exceed more than10% damping ratio up to frequency 2.3 Hz, thus providing an alternative energy dissipation damper in the building industry.

Shaking table tests on seismic behaviors of a single-layer spherical lattice shell with shape memory alloy-controlled friction pendulum bearings

An innovative seismic isolation device incorporating a friction pendulum bearing (FPB) and vertically aligned shape memory alloy (SMA) strands is proposed for the seismic control of spherical lattice shells located in strong-earthquake regions. To validate the effectiveness of the proposed SMA-FPBs experimentally, a 1/10-scale single-layer spherical lattice shell test structure and a set of isolators were designed and fabricated. A shaking table was used to apply various three-dimensional seismic excitations to test structures equipped with and without different isolation bearings (SMA-FPBs or bare FPBs). Significant seismic behavior enhancements were observed when such isolation systems were used. However, bare FPBs cannot accommodate excessive displacements induced by high seismic intensities owing to their lack of adaptive control. In contrast, SMA-FPBs exhibited satisfactory control performance in terms of the peak and residual bearing displacements under fortification and rare seismic actions, and the adaptive properties of the SMA-FPBs protected the isolators from disassembly owing to excessive sliding displacements under extremely rare earthquakes, even though their re-centering abilities decreased slightly because of the failure of several SMA wires. Finally, the larger number of SMA wires in an SMA-FPB enhanced its restraining capacity against peak bearing displacement rather than improving the seismic responses of structural nodes and members.

Research on Isolation Design of Ultra-High Voltage Converter Transformer

To assess the performance of the bushings in UHV converter transformers, a finite element time analysis was performed on a ±800 kV UHV converter transformer with or without the implementation of horizontal seismic isolation devices. The simulation results show that the maximum stress response value of the root of the alternating current bushing is 68.96 MPa, when the horizontal seismic isolation device is not installed, and the stress response values of the root of the two direct current bushing are close, with 26.06 MPa and 25.89 MPa respectively; when the direct current bushing is not vertically arranged, the angle between the direct current bushing axis and the horizontal X-direction is smaller, the relative displacement response is smaller in the X-direction; After installing the horizontal with seismic isolation device, the stress at the root of the bushing is significantly reduced compared with the without seismic isolation results, and the peak stresses at the root of the alternating current bushing, direct current bushing-1 and direct current bushing-2 are reduced with seismic isolation: 72.17%, 51.76% and 51.49%, respectively, all of which meet the requirement of seismic isolation efficiency greater than 50%. The research results provide technical support for the seismic resistance of UHV converter transformers and promote seismic research and the seismic isolation level of power facilities.

Research on the Seismic Isolation Effect of the Ring Spring–Friction Pendulum Bearing in the Dakai Underground Subway Station

During strong earthquakes, the vertical seismic force becomes an essential factor affecting shallow underground structures that cannot be ignored. In this situation, it is proposed that ring spring–friction pendulum two-way seismic isolation bearings be set up at the bottom of such structures. Targeting the Dakai underground station and the Kobe earthquake, a soil-structure force model was established based on the damage to the underground structure and dynamic simulation was carried out using Abaqus software. The advantages of the ring spring–friction pendulum bearing over the ring spring bearing alone and the friction pendulum bearing alone were compared. The simulation results showed that the structure displayed a good seismic isolation effect in both horizontal and vertical directions after setting the ring spring–friction pendulum bearing. The deflection in the midspan of the roof reduced to less than 5 cm, the horizontal relative displacement of the structure reduced to less than 3 cm, there was no obvious damage to the structure, the axial pressure ratio of the mid-pillar reduced to less than 0.5, the axial force on the mid-pillar reduced by more than 50%, and the shear force reduced by more than 30%. In addition, by comparing the damage to the structure after setting the annular spring bearing and the friction pendulum bearing, we found that a vertical seismic isolation device is more crucial than a horizontal seismic isolation device for shallow underground structures. Setting a vertical damping device can make the structure retain part of the ductility and reduce the damage to the structure, so the ground vertical seismic mitigation design should be strengthened when a shallow underground structure is designed.

On the Adaptability and Effect of High Damping Rubber Bearings in the Seismic Resistance of Large Aqueducts

Being the critical hydraulic structure in the construction of national water diversion projects, the large-scale aqueduct is one of the indispensable buildings in the rational allocation of water resources. Moreover, its safe operation during an earthquake is related to the success of the national water network’s construction. In this paper, HDRBs (high damping rubber bearings) have been used as the seismic isolation device for the large aqueduct, considering the FSI (fluid solid interaction) between the water and the walls of the aqueduct, and the mechanical model of HDRBs has been constructed by the bilinear model. The dynamic responses of the large aqueduct under different ground motion excitations, including different peak ground accelerations (PGAs) and operating conditions, have been calculated using the precise integration method. At the same time, the influence of RB (rubber bearings) and HDRBs, two kinds of bearings, on the seismic response of the large aqueduct is compared and analyzed. The maximum reduction in natural frequency with HRDB is about 72%, compared with the use of RB under different working conditions. When there is substitution of HDRB for RB, the stresses in the concrete at the corresponding positions decrease from 1.87 MPa to about 0.71 MPa. The analysis shows that HDRBs are equipped with well seismic isolation and energy dissipation performance, which can effectively reduce the seismic responses and improve the seismic performance of the large aqueduct. In addition, it shows that HDRBs have well adaptability to different operating conditions, ground motion excitation, and PGA, which can be extended to the constructions of aqueduct projects with high seismic intensity and complex geological conditions.

Deep learning model for prediction of non-linear cyclic hysteresis of seismic isolation devices: Full-scale experimental validation

Recurrent neural networks predicting the non-linear hysteresis behavior of specific triple pendulum bearing (TPB) and lead rubber bearing (LRB) seismic isolation devices, are developed, and tested in this paper. Experimental datasets of full-scale isolators were derived from a shake-table test program of a five-story building specimen, performed at the Hyogo Engineering Research Center of Miki, Japan. Data measured during several table motions of different amplitudes, frequency content, and durations, are appropriately processed to construct a substantial TPB/LRB dataset of 158/55 samples. A comprehensive framework is proposed to process the data, to optimize the network architecture, and to train, validate, and to test the machine learning models. The comparisons with reference experimental data showed that developed models could predict the two-dimensional hysteresis behavior of studied isolators with a very good accuracy. The R2 value of the TPB/LRB model was of 0.83/0.96 on new unseen dataset. The illustration of representative predictions showed the power of a single model to capture different and irregular hysteresis patterns, performed by a typical isolator under variable and realistic loading conditions and that can't be described by conventional analytical models. The generalization capability of these surrogate models on such a substantial data, revealed the benefit of applying machine learning to solve complex structural engineering problems.

Numerical and Experimental Investigation of the Seismic Effect of a Two-Stage Seismic Isolation Method

In order to improve the post-earthquake resilience of bridge structures, a Two-Stage seismic isolation method is proposed in this paper. According to the method, the restoring force and horizontal stiffness are smaller in the first stage and become much larger in the second stage. Therefore, a new kind of seismic isolation device, Two-Stage Friction Pendulum Bearing (TSFPB for short), is invented based on the traditional friction pendulum bearing (FPB for short). In this paper, the geometry configuration, sliding states and hysteresis characteristics of the bearing are first introduced with a theoretical approach. Then the hysteresis curve of the TSFPB is verified experimentally and the simulation method of the bearing in an FEM software is proposed. Last, a numerical analysis for an actual highway girder bridge is carried out to compare the seismic design method recommended in this paper with the conventional seismic isolation method. It is found that the Two-Stage seismic isolation method has an adaptive restoring force, horizontal stiffness and energy dissipation mechanism for different seismic intensity levels and better seismic performance compared with a conventional seismic isolation method. In addition, bridges with TSFPBs have smaller residual displacements and better post-earthquake resilience than those with traditional FPBs.

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.

Simulation of the structure of a multistory building with seismic isolation and the testing technique on a laboratory bench under dynamic ((seismic) impacts)

The article presents the main provisions of modeling multi-story buildings with seismic isolation, the characteristics of the seismic isolation device, structural elements and materials, the methodology for conducting experimental studies on a laboratory vibro-stand under dynamic (seismic) effects and the results of the modeling.

Hysteretic restoring force model of high damping rubber bearings including thermo-mechanical coupled effect

In the application of High Damping Rubber (HDR) bearings as seismic isolation devices for bridges in cold regions, there are concerns about the low temperature effect on the hysteresis performance of HDR bearings and the resulting deterioration in bridge performance under strong ground motions. The stiffness and damping ratio of the HDR bearing significantly increase at lower ambient temperatures, and the stiffness reduces as the inner temperature of the bearing increases due to the self-heating of rubber material under repeated cyclic loading, resulting in a complicated thermo-mechanical coupled hysteresis behavior which is not expressed by the currently available restoring force models of HDR bearings. In this study, a simplified thermo-mechanical coupled hysteretic restoring force model of HDR bearings is newly developed. The model parameters are identified from the shear strain–stress curves of HDR bearings obtained in quasi-static cyclic loading tests at three different ambient temperatures. Accuracy of the improved model is verified by comparing the numerical result of seismic response analysis of a bridge model using the proposed restoring force model with the result of hybrid simulation of the same bridge model including the HDR bearing loading test under low-temperature conditions.

Seismic Isolation Devices for Protecting RC Buildings: The Frangipane School in Reggio Calabria

Seismic isolation devices, as known, are particularly efficient tools for the protection of newly designed or existing buildings and infrastructures and for the mitigation of maximum effects due to earthquakes. The highest is the vulnerability of a given existing construction, and the higher is the benefit in structural terms due to a possible retrofit intervention based on base isolation. This is especially the case of reinforced concrete (RC) building frames built in the 1960s in the Italian context and originally designed with a code of the first generation (“Regio Decreto Legge 25 Marzo 1935, n. 640”) in a city characterized by a long history of severe earthquakes (as the Reggio Calabria and Messina earthquake in 1908), and thus recognized as highly seismic regions. In this paper, a case-study application is proposed for the Frangipane school constructed in Reggio Calabria (Italy) and recently subjected to a major renovation intervention for its retrofit against the high seismic hazard.

The Padma Multipurpose Bridge: Construction Challenges and Sustainable Management

An iconic building linking Bangladesh's southwest to its northern and eastern areas is the Padma bridge, which spans the third-largest river in the world with a complicated topology. By boosting production, employment, transportation, and the national and regional economy, this multipurpose bridge is projected to boost GDP growth by 1.2%. This study's primary goal is to pinpoint the greatest challenges encountered during Padma Bridge's construction and explain how sustainable management procedures might be put in place to address such difficulties. The most challenging tasks included finding a suitable site, dealing with complex river morphology, overcoming geotechnical barriers, controlling unfavorable environmental conditions, assembling massive construction equipment and materials, maintaining the construction schedule, and dealing with the COVID epidemic. To resolve these construction challenges, massive river training works and a unique pile foundation design that consists of six floating heaps and one center pile with the largest raking pile in the center were both utilized. To get around the difficulties in superstructural design, longer pre-assembled steel truss girders, pre-tensioned Super-T girders in viaducts, seismic isolation devices, and the largest friction pendulum bearings in the world were all made. Only a small number of people experienced COVID-19 without any fatalities or causing delays in the construction schedule since the Project was kept operational during the COVID-19 period by tightly enforcing the COVID laws and limits on people's mobility. The field of construction management would undergo a paradigm shift with this sustainable management of construction-related difficulties, which might later be used to design more intricate bridges.