Rubber Isolators Research Articles

Shaking table test of a timber building equipped with a novel cost-effective, impact-resilient seismic isolation system

In most cases, construction of Light Frame Timber Buildings (LFTBs) in areas of high seismic hazard requires strong wood frame shear walls and continuous rod systems, which increases the cost of LFTBs. Frictional seismic isolation might be applied to protect LFTBs against extreme ground motions and mitigate the cost of continuous rod systems. However, there are no experimental studies on the response of LFTBs equipped with frictional isolation and subjected to extreme seismic ground motions that might cause impacts between the slider and the perimetral ring or between the isolated base and the perimetral moat wall.This study explores the potential of using impact-resilient frictional isolators as a feasible solution to alleviate stiffening and overturning costs of LFTBs while making them resilient to impacts in case of extreme events. This issue has been researched by evaluating the response of a 1:2 scaled 3-story LFTB isolated with a novel Impact Resilient Double Concave Frictional Pendulum recently developed by the authors. The specimen was subjected to a suite of shaking table tests (white noise, harmonics signals, and seismic records), including strong ground motions such as the Concepcion record (2010 Maule, Chile earthquake, Mw = 8.8) scaled to 130 %. Results indicate that despite being subjected to extreme excitations, peak acceleration ratios (i.e., the ratio of peak floor acceleration to peak ground acceleration) did not exceed 0.75, and story drift ratios were smaller than 0.52 % in most cases. Thus, the superstructure remained in the elastic range without damage. The study demonstrates the potential of achieving effective seismic protection of LFTBs using Impact Resilient devices. In addition, this paper presents a numerical model developed with experimental data, which provides insight into modeling issues such as, for instance, damping properties.

Research on Elastic Characteristics of Negative Pressure Rubber Isolator

Research on Elastic Characteristics of Negative Pressure Rubber Isolator

Shaking table test of vertical isolation performances of super high-rise structure under metro train-induced vibration

Metro systems are integral to improving transportation efficiency and providing convenience to the public; however, they cause environmental vibrations. To analyze the metro vibration propagation law and vibration isolation performance of a 120 m super high-rise structure positioned directly above two metro tunnels, a shaking table test at a 1/30 scale ratio is conducted in this study. First, a model for the shaking table test is designed and manufactured, and measurements of metro train-induced ground vibrations obtained on site are input into the model. Subsequently, vertical vibration tests are performed on the models with and without laminated rubber isolation bearings. Finally, their dynamic characteristics, vibration propagation law, and vibration isolation effect are analyzed, and the vertical vibration isolation mechanism of the structure is discussed. The results indicate that the metro vibration exerts a resonance effect on non-isolated super high-rise structures, thus resulting in the progressive amplification of the metro vibration response along the floors of the structure. The vibration isolation layer formed by the laminated rubber isolation bearings significantly reduces the vertical modal frequency and increases the vertical damping ratio of the super high-rise structure, thus effectively attenuating the vertical metro vibration. Unlike the non-isolated structure, the vibration-isolated structure can avoid severe structural resonance responses in the dominant frequency band of the metro vibration. This study aims to offer insightful considerations for evaluating metro vibrations in super high-rise structures and may serve as essential reference for vertical vibration isolation.

Hybrid simulation tests evaluating the seismic performance of lead high-damping rubber bearings at low temperatures

As a hybrid rubber isolation bearing, the lead high-damping rubber bearing (LHB) exhibits enhanced seismic isolation and energy dissipation performance by combining lead cores and high-damping rubber (HDR) in a single device. However, at low temperatures, the LHB exhibits the same hardening and self-heating problems as conventional lead rubber bearings (LRBs) and HDR bearings. The complicated thermo–mechanical coupled behavior of the LHB is difficult to predict and is an obstacle for designing and applying it in cold earthquake-prone areas. In this study, the mechanical characteristic variations of the LHB owing to a low temperature were evaluated in the cyclic loading tests, and the low temperature effect on the seismic behavior of a bridge isolated with LHBs was investigated in hybrid simulation tests using a loading system that can control the ambient temperature of the bearing.

Measurement, Modeling, and Analysis of the Dynamic Properties of Resilient Elements Used for Vibration Isolation

Abstract Resilient elements are widely applied for vibration and noise control in many areas of engineering. Their complex dynamic stiffness gives fundamental information to describe their dynamic performance and is required for predicting structure-borne sound and vibration using dynamic modeling. Many laboratory measurement methods have been developed to determine the dynamic properties of resilient elements. This paper presents a review of recent developments in the measurement methods from the perspective of force–displacement relations of the resilient element assembly rather than of their material properties. To provide context, the review begins with an introduction to modeling methods for resilient elements, especially for rubber and rubber-like isolators, and three standardized measurement methods are introduced. Recent developments are then discussed including methods to extend the frequency range, which are mainly developments of the indirect method. Mobility methods, modal-based methods, recent active frequency-based substructuring (FBS), and inverse substructuring (IS) methods to study the dynamic properties of resilient elements are also described. Laboratory test rigs and the corresponding identification methods are outlined. Methods to evaluate nonlinear dynamic properties of resilient elements by laboratory measurements are also discussed. Finally, the review is concluded by discussing the advantages and limitations of the existing methods and giving suggestions for future research.

Comparative Study on Seismic Response of Regular and Plan Irregular Base isolated structures

Earthquake is one of most destructing threat which cause severe damage to life and property. Recently, due to increasing demand and need for the present generations has made the designers and engineers to plan for structures having irregularities. It is impossible to avoid designing uneven buildings in reality. It is important to research how this irregular structure behaves in earthquake-prone areas, especially for structures with base isolation. When compared to regular structures with base isolation, structures with plan irregularity react differently. When a reinforced concrete building with varied plan configurations, such as an H, U, or L shape, is subjected to seismic loading, the impact of plan irregularity is explored. In the current study, a regular structure is also considered to compare the responses of the isolated irregular base structure. Building response spectrum analysis for seismic analysis was done in seismic zone III using IS 1893-2002 code [5]. The structural analysis software tool ETABS 18 was used to conduct the analysis. Among different types of isolators present, in the present study LRB isolator and friction isolators was used as a Nonlinear Support. The dynamic response of the structure such as base shear, time period and story displacement are used to compare the regular and irregular structures. The effectiveness of the base isolators in the structures in earthquake prone area is evaluated in the present study.

Theoretical dynamic reduction for steady-state nonlinear vibration responses of complex jointed structures having hysteretic contact behavior

A novel nonlinear dynamic reduction method was developed to determine the steady-state vibration responses of complex jointed structures having hysteretic contact behavior. By using the harmonic balance method to reformulate nonlinear dynamic equilibrium equations into a set of nonlinear algebraic ones, a dynamic reduction technique based on nonlinearity transformation was theoretically developed to iterate nonlinear vibration solutions in the local coordinate that was related only to the degree-of-freedoms of nonlinear joints. Only odd-order harmonic components were truncated to approximate the hysteretic nonlinear contact forces of joint interfaces, which was conducive to further dimension reduction of the nonlinear algebraic equations and iteration matrix. Then, a nonlinear dynamic reduction solver was developed to associate the steady-state nonlinear vibration responses of overall structures with the dynamic characteristics of underlying linear substructures, nonlinear joint models and external excitations. Combined with finite element analysis, the steady-state nonlinear vibration responses of a complex assembled structure with four reduced-order nonlinear joint models were numerically simulated to validate the proposed nonlinear dynamic reduction method by comparing with the literature. The comparative results of nonlinear frequency response functions exhibited good agreement, and the proposed method indicated higher computational efficiency. The experimental investigations of a rubber isolator system were also performed to validate the proposed method, which demonstrated good performance.

Investigation on active vibration isolation with multi-axis control: Analysis and experiment

Vibration isolators are usually used to attenuate the transmission of vibration of power machinery to the flexible foundation. Since vibration energy is transferred nearly through all the degrees of freedom of an isolator, it is difficult to guarantee sufficient vibration attenuation by the single-axis control at each active isolator. In order to enhance attenuation at each vibration isolator, a novel configuration of active vibration isolation is proposed. Each active isolator is composed of two rubber isolators and one intermediate rigid mass in which eight electromagnetic actuators and six error accelerometers are attached. Six control forces are applied on the intermediate mass to suppress its multi-axis vibration. Moreover, the weakened interaction between isolators allows independent local control at each isolator. A numerical model is established to verify the proposed active vibration isolation and the results show that the transmission of vibration from the source to the flexible hull structure can be nearly cut off when the error vibrations of each intermediate mass are attenuated completely. The effectiveness is also proved by an experimental active vibration isolation system and the proposed isolation configuration with multi-axis control can achieve more significant attenuation of vibration of the hull structure than the commonly used active vibration isolation with only single-axis control.

Investigation of the Impact Properties of the Material of the Isolation on the Parameters of the Loaded Cable Lines

The thermodynamic model of work of the loaded cable line is presented. The received mathematical ratio allows to define the maximum allowed current loadings of the cable line in the form of a single-core cable product with the single-layer isolation depending on material and thickness of layer of isolation. It is constructed dependences of the maximum allowed current for a single-core wire of a certain section with one layer rubber (or polyvinilchloride) isolation from insulation layer thickness at various temperatures of the environment and the coefficients of the heat conductivity.

Seismic Isolation Measures of Plate-Shell Integrated Concrete Liquid-Storage Structure

In order to study isolation measures for plate-shell integrated concrete liquid storage structure (PSICLSS), shaking table tests were carried out to investigate the seismic responses of PSICLSS. The isolation performance of rubber isolation and sliding isolation bearings for PSICLSS was studied and shape memory alloy (SMA) was used to reduce the residual displacement of sliding isolation PSICLSS. The results show that the sliding isolation bearing can effectively reduce the seismic response of PSICLSS; however, there is a large residual displacement in the isolation layer. On the other hand, SMA-sliding isolation can provide a reliable recentering capability for isolating PSICLSS and does not cause amplification of structural response.

Efficacy of 3M-PTGL on low-temperature seismic performance of polyurethane elastomeric bearings for bridges

High-capacity casting polyurethane elastomeric (HCPUE) bearing is a new elastomer isolation bearing that features excellent durability, higher vertical capacity, and a simpler production process compared with traditional rubber isolation bearings. However, HCPUE bearing exhibits significant hardening behavior at low temperatures. To expand the application of HCPUE bearings in cold regional structures, this study developed an improved low-temperature resistant 3M-HCPUE bearing by incorporating 3-methyl tetrahydrofuran copolyether glycol (3M-PTGL) in the elastomer formulation. The low-temperature performance improvement of the 3M-HCPUE specimen was verified through characterization and mechanical property tests using six different compounding formulas. HCPUE materials with 15% and 25% 3M-PTGL were selected to prepare improved 3M-HCPUE bearings. The shear hysteretic behavior and ultimate deformation performance of the bearings were tested at different temperatures. Seismic fragility analysis of a three-span box girder bridge with 3M-HCPUE bearings was conducted using different isolation periods and ambient temperatures. The 3M-PTGLimproved 3M-HCPUE bearing exhibited excellent low-temperature performance and effectively alleviated the hardening behavior of the HCPUE bearing at low temperatures. The change rate in the equivalent stiffness for the 3M-HCPUE bearing with 25% 3M-PTGL was °C reduced from 106% to 44% at −20 °C compared with that at 23 °C. The equivalent damping ratio slightly decreased from 25.2% to 19.6%. The improved 3M-HCPUE bearings effectively reduced the failure probability of the pier at low temperatures, but increases the probability of bearing failure.

Structural optimization design of metal rubber isolator based on an ensemble surrogate model

The finite element simulation design of products depends on the computer’s processing power; hence an adequate model with acceptable accuracy can significantly reduce the calculation cost. The optimization method based on the surrogate model is a general method to solve this problem. Among them, the sampling point selection of the surrogate model plays a crucial role in the calculation efficiency and accuracy. Therefore, according to the applicable standards of metal rubber isolators, this paper proposes an improved sampling method based on the surrogate model method and then optimizes the structure of metal rubber isolators. The metal rubber isolator's performance and lightweight design requirements are considered based on satisfying the precision and boundary conditions.

Seismic isolation analysis and design of a plane irregular building structure in high earthquake intensity area

Taking the large commercial complex building of Changzhou Golden Eagle Plaza as the research object, this paper analyzes various parameters of typical special-shaped space structure under different isolation schemes under the conditions of earthquake protection, rare earthquake and extremely rare earthquake, compares three isolation layer design combinations of rubber isolation bearing, lead isolation bearing, rubber isolation bearing + lead isolation bearing, and studies the influence of different isolation layer arrangement schemes on the steel core and mass center of the building structure. The results show that the reasonable isolation design can obtain the reasonable arrangement pattern and rule of the plane irregular building structure in a high seismic intensity area by comparing and analyzing the arrangement schemes of different types and forms of isolation bearings in the isolation structure model.

Full-scale shaking table tests and numerical studies of structural frames with a hybrid isolation system

A typical hybrid isolation system (HIS) incorporating natural-rubber bearings (NRBs) and nonlinear fluid viscous dampers (NFVDs) is proposed for seismic protection of critical equipment in nuclear power industrial buildings (NPIBs) under strong earthquakes. Design procedure with a parametric study towards the HIS considering various stiffness and damping values is first investigated via extensive nonlinear time history analyses. Then a preliminary recommendation for the specific structural demands of the considered system is proposed to direct the seismic design for both member- and system-level tests. Through a suite of full-scale shaking table tests on two typical NPIBs, the efficiency and reliability of the HIS are verified, in comparison to the structure with conventional rubber isolation system (RIS). The shaking table test results exhibit a superior behavior of the HIS in structural dual control strategies, i.e., transient acceleration control in critical equipment and bearing deformation control. Also, the HIS presents stable and resilient performances in both negligible residual bearing deformation and undetectable damage to structural/nonstructural components (containing the seismic isolated devices, i.e., NRBs and NFVDs). Finally, a three-dimensional finite element (FE) structural model and a single-degree-of-freedom (SDOF) system are successively developed to simulate the dynamic responses of the test structures. The well-validated SDOF FE model, serving as a reliable alternative for the isolated NPIBs, can be further utilized to facilitate practical design.

Influence of ambient temperature on seismic performance of elastomeric isolation structural system

As one of the most innovative technology in the field of structural engineering, rubber isolation system has been widely used in engineering structures. However, the mechanical performance of elastomeric rubber bearing is severely affected by temperature, which is not considered in the seismic isolation design in most areas and may lead to serious accidents in severely cold and seismically active areas. This study aims to evaluate the seismic performance of the elastomeric isolation structure with rubber bearings at different ambient temperatures. First, the mechanical properties of the high-performance rubber bearings used in the structure are tested at −40, −25, 0, 20, and 40 °C. Then, based on a three-dimensional finite element model of the isolation structure, the influence of bearing temperature dependence on the seismic performance of the elastomeric isolation structure is evaluated. Finally, seismic fragility assessment is conducted to probabilistically evaluate the impact of temperature on the seismic response of the elastomeric isolation structure. The results show that temperature has a significant influence on the mechanical properties of the rubber bearings; the maximum values of the base shear force, the isolating coefficient, the maximum story drift and the acceleration of the superstructure at −25 °C increase by 46.09%, 43.92%, 51.53%, 45.64%, respectively, compared with that at 20 °C in the case study; Therefore, the influence of the bearing temperature dependence on the seismic response of the elastomeric isolation structure cannot be ignored.

Damage Rule of Marine Isolator under Secondary Shock Vibration

To study the damage of the shock vibration generated by the ship hull to the internal equipment of the ship under the secondary explosion impact, a three-dimensional simulation model of the BE rubber isolator was established. The signal of the impact vibration load was loaded by the AUTODYN software. And the relationship between the damage of the isolator under the primary vibration impact and the frequency, amplitude, and attenuation of the loading signal was found. It is revealed that the damage law curve of the isolator under the secondary shock vibration conforms to a rational function. Based on this discovery, a mathematical model of the secondary shock vibration signal that can predict the isolator damage through the primary shock vibration is established.

Research on dynamic characteristic of compressor RIP under thermal oxygen aging and variable preload conditions

The dynamic characteristics of rubber isolation pad (abbreviated as RIP) after service under the high temperature thermal oxygen aging and the variable preloads have preload dependence and thermal oxygen aging dependence, which is a crucial problem for matching the vibration isolation system of air conditioner compressor to reveal the dynamic characteristic mechanism of the RIP with different preloads and thermal oxygen aging conditions. The Peck model is first introduced to characterize the thermal oxygen aging factor, the fractional derivative Kelvin-Voigt thermal oxygen aging-perturbation model (FDKVTPM) and the Coulomb frictional thermal oxygen aging-perturbation model (CFTPM) are established to describe the frequency dependence and the amplitude dependence, respectively. The thermal oxygen aging-dynamic characteristic model of the RIP is built by considering the influence of variable preloads, the model parameters under different preloads are further identified, the validity of the model was examined by the experimental data. The concepts of the stiffness transition point (STP) and the stiffness transition frequency (STF) are innovatively proposed to better describe softening effect of the RIP under variable preload and variable amplitude working conditions. The results show that the static stiffness of RIP increases by 20.7%, the dynamic stiffness increases by 9.3%, and the loss factor decreases by 35% after thermal oxygen aging under different preload conditions, which can lay a theoretical foundation for in-depth study of the stiffness matching and optimization of air conditioner compressor with the RIP.

Multivariable probabilistic seismic demand models for parametric fragility prediction of isolated bridges portfolios under pulse-like GMs

The wide application of friction isolation bearings has led to a rapid increase in the number of frictional isolated bridges. Therefore, the traditional method of seismic fragility analysis based on nonlinear time-history analysis (NLTHA) may not suitable for bridge portfolios. For this purpose, this study developed a multivariable probabilistic seismic demand model (MV-PSDM) for friction isolation bearings conditioned on the earthquake parameters (peak pulse velocity, pulse period), bearing parameters (effective radius) and pier parameters (bending stiffness, pier numbers, pier height), in which a novel formula is adopted to calculate the seismic demand and the dispersion is also estimated. This MV-PSDM can be applied to investigate the influence of various parameters (earthquake parameters, friction bearing parameters, pier parameters) on the seismic demand, sensitivity and the vulnerable range of the bearing. Finally, an efficient parametric fragility prediction method for friction isolation bearing is proposed based on the MV-PSDM, and the flow chart is also provided. In this method, only earthquake parameters, bearing parameters and pier parameters are required to obtain the seismic fragility of friction isolation bearings, which avoids the FE modeling and NLTHA.

Comparison and Correlation of Corynespora cassiicola Populations from Kiwifruit and Other Hosts Based on Morphology, Phylogeny, and Pathogenicity.

Corynespora leaf spot, which is caused by Corynespora cassiicola (Berk. & M. A. Curtis) C.T. Wei (C. cassiicola), has been globally reported in many plant species. 'Hongyang' was reported as highly sensitive kiwifruit cultivar to C. cassiicola. This cultivar is an important germplasm resource in the Actinidiaceae family and is widely cultivated throughout China. Even though C. cassiicola has been identified as the pathogen associated with kiwifruits in China, the C. cassiicola population from kiwifruit has not been characterized based on morphology, phylogeny, and pathogenicity. In this study, 133 and 48 representative C. cassiicola isolates from kiwifruit and 11 other hosts, respectively, recovered from symptomatic leaves were classified into eight morphological subgroups based on host origins. Using three loci (rDNA ITS, caa5, and act1), a phylogenetic tree showed that C. cassiicola isolates in Sichuan Province were grouped into three clades. All kiwifruit isolates were genetically identical to the rubber isolates from different countries. However, most isolates from other hosts in this study were genetically identical to the cucumber, soybean, and cowpea isolates in China, Brazil, and the United States, and two strawberry isolates clustered with isolates from tomato and other hosts in China, Brazil, and the United States. Furthermore, we confirmed host shift of C. cassiicola among different plant species in this study. Although 51 isolates from kiwifruit and different hosts were pathogenic to kiwifruit, blueberry, cucumber, and soybean, virulence levels of the pathogen were diverse for four hosts. Kiwifruit isolates exhibited host specificity with regards to the original host in degree. In addition, those isolates revealed a correlation between morphology and pathogenicity. The results suggest that C. cassiicola in Sichuan Province were derived from three different phylogenetic lineages. Promotion of the susceptible 'Hongyang' cultivar led to the emergence of a regnant C. cassiicola population from kiwifruit. In conclusion, rapid development of the C. cassiicola-sensitive crop in agricultural systems led to the emergence of a regnant C. cassiicola population. In some dominant populations (e.g., the C. cassiicola population from kiwifruit in this study), host origin was found to be a key factor influencing the morphologic, genetic, and pathogenic characterization of C. cassiicola.

Effectiveness of Tuned Mass Damper in Reducing Damage Caused by Strong Earthquake in a Medium-Rise Building

A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced concrete (RC) building is presented. The aim of the study was to investigate the effectiveness of the TMD in changing the structural behavior of medium-rise existing buildings from dissipative to non-dissipative in order to eliminate reparation or demolition costs resulting from damages caused by strong earthquakes. The TMD mass is made by a RC slab lying on flat surface sliders. Horizontal stiffness and damping of the TMD are both provided by lead rubber isolators in the first proposed solution and by low-damping rubber isolators and viscous linear dampers, respectively, in the second. The improvement in the building’s structural behavior attained with the installation of the TMD was assessed by considering the flexural demand over capacity ratios of structural elements and the energy dissipated by the TMD. These results are compared with those of the same building retrofitted with a base isolation system. In both of the proposed solutions, TMD remarkably changed the modal behavior of the considered building, improved the flexural verifications, and dissipated most of the input seismic energy. It is therefore demonstrated that a TMD is a valid solution for the retrofit of medium-rise existing buildings.