Rubber Isolators Research Articles

Hysteretic Dynamic Modeling and Vibration Characteristics Analysis of Metal-Rubber Isolators

A novel hysteretic constitutive model (HCM) with four parameters was proposed to reproduce the nonlinear elasticity and dry friction characteristics of metal–rubber isolators (MRIs). The HCM accurately characterized the nonlinear hysteretic behavior due to its intrinsic relationship with the geometric properties of the hysteresis loop. A physics-based parameter estimation strategy was developed to provide reasonable initial iteration values. Three MRIs with different design stiffnesses were tested to investigate their hysteretic behavior under various excitation levels. The HCM accurately reproduced the entire experimental hysteresis loops using only a subset of the experimental data. This exhibited higher precision and scalability compared to the classical dynamic model. Friction damping forces were employed to distinguish the stick-slip states of the three MRIs. Additionally, the identified parameters were used to simulate the steady-state vibration response of a complex MRI system. The resulting frequency response functions (FRFs) agreed well with the experimental data. The proposed model can effectively capture the amplitude-dependent effects in MRI systems with various design stiffnesses, enabling more accurate predictions of vibration responses.

Clutching inertial system for base-isolated liquid storage tanks: Seismic performance and optimal parameters

Liquid storage tanks (LSTs) are susceptible to significant damage during earthquake events, necessitating their continued functionality and additional protection through isolation techniques. The sloshing response and overall base shear of LSTs are critical factors, particularly in base isolated (BI) tanks. This study aims to enhance the seismic resilience of LSTs by leveraging a newly developed advanced inerter-based vibration control methodology for structures. This innovative approach integrates a supplemental clutching inertial system (CIS) with a laminated rubber isolator (LRB). Utilizing an equivalent linearization technique, the study evaluates the equivalent damping and inertance constants to account for the nonlinear behavior of the CIS. These equivalent parameters are then used to assess the stationary peak response of the isolated tank structure, which encompasses sloshing and bearing displacements, forces within the CIS and the isolator, and the total base shear. Further, the analysis employs the stationary power spectral density function (PSDF) model of earthquake excitation by Kanai-Tajimi and the performance of the inerter-based hybrid control strategy is examined by varying system parameters, such as isolation period, isolation damping, CIS inertance mass ratio, and the tank's aspect ratio (i.e., broad or slender). An optimal inertance of the CIS is identified, leading to the least overall base shear for both isolated tank configurations. The impact of these parameters inertance mass ratio of the CIS is also investigated. Subsequently, the isolated tanks are exposed to eleven near-fault (NF) and far-field (FF) real-time earthquake excitations. The study evaluates the CIS's performance as an auxiliary system during these seismic events and contrasts the outcomes with the seismic response under stochastic excitations. The results highlight the effectiveness of the advanced inerter-based hybrid control strategy in reducing the seismic response of isolated tank configurations.

A novel iterative model updating for jointed structures using nonlinear FRFs

A novel iterative model updating method is developed to identify the local nonlinear joint properties using the frequency response functions (FRFs) of assembled structures. In this paper, the least-squares fitting method was used to transform the sensitivity matrix into a square iteration matrix to match the dimensions of the objective functions and nonlinear joint model parameters. Leveraging the Newton’s iteration, the adaptive successive over-relaxation (A-SOR) was used to ensure iteration convergence while the multi-scale parameter adjusting (MPA) strategy was developed to degrade the ill-condition of the iteration matrix. Two updating examples of phenomenological equivalence models were applied to demonstrate the effectiveness of the proposed method. The nonlinear FRFs of a lap-type bolted joint beam system with Iwan model were simulated as the objective functions to identify the local nonlinear joint properties, as well as experimental investigations of a metal rubber isolation system with a high-order polynomial model. The proposed method was validated by the good agreement of the comparison results, and it indicated a better model updating performance with a much smaller condition number of the iteration matrix.

Theoretical Research and Shaking Table Test on Nominal Aspect Ratio of the Isolated Step-Terrace Structure

With the installation of rubber isolation bearings in the upper and lower ground layers, an isolated step-terrace structure was created. Considering the ultimate bearing capacity of the rubber bearing under tension as the critical condition, a comprehensive framework was established to evaluate the overturning failure mechanisms present in isolated step-terrace structures. The bound of nominal aspect ratio was identified as the principal control index within this framework, which incorporates critical parameters such as height ratio (α), width ratio (β), vertical tensile stiffness to compressive stiffness ratio (γ), seismic coefficient (k), and nominal vertical compressive stress (σ0) to provide a thorough analysis of the structural responses and potential failure scenarios. In order to further investigate this matter, a scaled model of an isolated step-terrace concrete frame structure featuring two dropped layers and a single span within an 8° seismic fortification zone was meticulously crafted at a 1:10 similarity ratio. Subsequently, a series of shaking table tests were conducted to analyze the structural response under seismic excitation. The findings indicate that: utilizing the bound of nominal aspect ratio as a metric to gauge the anti-overturning capacity of isolated step-terrace structures is a justified approach. In instances where the height ratio remains constant, the bound of nominal aspect ratio for both positive and negative overturning trended upward with an increase in the width ratio. Notably, the bound of nominal aspect ratio for positive overturning consistently registered lower values compared to that of the negative overturning, underscoring the heightened susceptibility of step-terrace structures to positive overturning. Moreover, in scenarios characterized by higher height and width ratios, the structural integrity remained unscathed by any overturning effects arising from insufficient tensile strength in rubber bearings. Furthermore, the bound of nominal aspect ratio exhibited an ascending trend as the seismic coefficient, nominal vertical compressive stress, and vertical tensile stiffness to compressive stiffness ratio decreased. The outcomes derived from the shaking table test not only confirm the impressive seismic performance of the structure, but also, by closely examining the instantaneous stress variations within the upper and lower isolation layers of the model, substantiate the existence of a positive overturning hazard in scenarios marked by higher seismic coefficients (k). This observation aligns seamlessly with the theoretical projections, thereby substantiating the efficacy of the structural overturning failure theory through direct empirical verification.

Optimal design of low frequency rubber vibration isolator

Abstract Low frequency vibration isolator is a common structure vibration control device, widely used in transportation and machinery manufacturing fields. This paper is centered around enhancing the optimization design of rubber isolators operating at low frequencies. In the initial section, the paper introduces the structural framework and operational principles of rubber isolators. Furthermore, it delves into the analysis of their significance and potential applications within engineering contexts. Subsequently, the paper narrows its focus to address the design challenges concerning rubber isolators with low-frequency capabilities. A comprehensive three-dimensional model is constructed using ANSYS software, employing finite element analysis techniques. The paper employs a multi-objective optimization algorithm through a direct optimization module to facilitate the optimization design process. Within this study, the NSGA-II algorithm was employed to drive the optimization of design, with the objective of achieving a 10 Hz frequency for a series of dual rubber isolators, while simultaneously constraining static deformation to within 8 mm. The outcomes of this investigation emphasize the successful attainment of optimization goals by meticulously fine-tuning the structural dimensions of the isolators.

Visco-Hyperelastic Constitutive Modeling for High-Damping Rubber Materials During Combined Quasi-Static Compression–Cyclic Shear Deformation Process

High-damping rubber materials utilized in high-damping rubber isolation bearings are frequently subjected to multiple deformations during the occurrence of earthquakes. Typically, large combined compression–shear deformations of the material could potentially cause compressive shear damage to rubber bearings. During this process, visco-hyperelastic properties of rubber materials will greatly change, which would significantly impact the seismic performance of rubber bearings. Thus, to give out a deep insight into their variations, it is necessary and urgent to develop a high-performance numerical method to investigate this process. This paper proposed a visco-hyperelastic constitutive modeling approach for high-damping rubber materials based on the experimental assessment of combined quasi-static compression–cyclic shear deformation process. Within the thermodynamic framework, the Clausius–Duhem inequality associated with the intrinsic dissipation of the material was firstly derived in accordance with the Lagrangian formulism. Then, stress–strain relations were obtained upon considering the occurrence of entropy production due to viscous dissipation. In the model, Stumpf–Marczak strain energy density function, which satisfies the Baker–Ericksen (B–E) inequality, was harnessed to describe the hyperelasticity of the material. By introducing higher orders of strain and strain rates and taking their couplings into account, a generalized viscous dissipation potential was proposed to capture nonlinear strain and strain rate-sensitivity effects of the material. To identify constitutive parameters, the deformation gradient was particularized for the combined quasi-static compression–cyclic shear deformation process. And, an inverse identification procedure was carried out at different levels of compression stress. The prediction results revealed that the proposed model exhibits remarkable prediction ability and adaptivity for different rubber materials during this process. Several new insights were highlighted on the variations of visco-hyperelastic characteristics of high-damping rubber materials with respect to the compression stress. The accuracy of the model was further validated by design parameters including initial shear modulus, secant shear modulus and equivalent viscous damping factor. This work could provide a fundamental guideline for the optimization and reliability analysis of high-damping rubber isolation bearings used in the field of seismic engineering.

A low-cost bonded scrap tire rubber isolator in rural regions: Experimental, numerical and theoretical analysis on mechanical behavior

The utilization of low-cost scrap tire pads (STP) made from recycled tires presents a promising alternative to traditional rubber isolators (i.e., fiber-reinforced elastomeric isolators) in rural construction. However, the STP was limited in application to practicing structures due to stability with a shear strain level of 100 % and the significant variability of the mechanical behavior at the same parameters. For these issues, this paper presents a bonded scrap tire rubber isolators (BSTRIs), based on earthquake demand parameters for rural area buildings. In addition, a series of vertical compression and horizontal shear tests were conducted to evaluate the dependency of mechanical behavior on surface pressure (σ0), the first and the second shape factor (S1 and S2). Then, a finite element (FE) model of BSTRIs was developed and validated. The experimental and FE results show that the σ0, S1, and S2 overwhelmingly effect on mechanical behavior (i.e., critical pressure, vertical stiffness, horizontal stiffness, and damping ratio). Moreover, the new theoretical formulations on critical pressure, vertical stiffness, and horizontal stiffness were developed to evaluate the stability of BSTRIs. Finally, based on experimental result, a nonlinear dynamic response was conducted including the BSTRIs-supported and based-fixed unreinforced masonry (URM) buildings under 22 far-field and 28 near-field seismic excitations. The results indicated that the base shear of the BSTRIs-supported URM were decreased by 66.5 % and 50.1 % in far- and near-field record, respectively, compared with the response of the fixed-base URM building.

Elastic constant ratio for fatigue evaluation on rubber isolators

AbstractIn this study, a new concept of the elastic constant ratio was introduced to derive an S‐N base function, which has removed the requirement of the shear modulus to be measured in previous work, allowing much wider applications in fatigue prediction with significant reduction in the costs involved in conducting experiments and acceleration of the design process in industries. In this approach, the damage parameter was the effective tensile stress verified for both positive and negative R ratios (the ratio between the minimum stress and the maximum stress). Existing work only provided a general description of the criterion without detailed explicit equations, which does not provide sufficient clarity to the reader and could lead to variable fatigue life predictions. Here, detailed equations are introduced on the calculation procedure to allow accurate results to be obtained for fatigue assessment. The applicability of the approach was validated using two industrial components, that is, the Metacone spring and the bush spring. The maximum values of the damage parameter corresponded to the same failure locations observed in the experiments. The suggested S‐N base function, correlated with different materials and failure cycles, could be applied in a fatigue design stage and failure analysis for rubber isolators.Highlights For the first time, an elastic constant ratio is introduced on different rubbers. There is no additional test required for the material constants to save cost. The approach is experimentally validated on two industrial isolators. Monitoring stiffness in tests cannot determine the crack initiation accurately.

Base Isolation and Energy Dissipating System in Earthquake Resistant Building Design

The utilization of base isolation is a crucial strategy for enhancing seismic resilience in structures. The method involves installing isolators and energy-absorbing devices beneath a building's superstructure to mitigate the destructive effects of earthquakes. When base isolation is implemented in a building, it not only makes the structure stronger and more stable, but also helps to safeguard lives and properties. This technique is particularly valuable for seismic retrofitting of historical buildings. In the present study, software called simulation of seismic isolation systems in structural analysis is employed, considering isolator characteristics, whether they exhibit nonlinear or equivalent linear behavior. Adhering to the IS 1893:2016 Code, the analysis utilized the SAP 2000 software package. A study was carried out to compare the effectiveness of base isolation systems versus fixed-base buildings in dealing with seismic activity. The study focused on analyzing various seismic indicators such as joint displacement, shear force, bending moment, building torsion, and the period of natural frequency. Results showed that models utilizing base isolation systems had significantly higher base shear values than those with a fixed-base building configuration. However, there was a significant 35% reduction in story shear values for the rubber isolation system and a 40% decrease for the friction pendulum model. Additionally, there was a 25% reduction in story drift for the rubber base model and a 30% decrease for the friction pendulum model. The friction pendulum model demonstrated the most effective control of these parameters across various seismic zone conditions. Key words: The topic of discussion pertains to Seismic Isolation with Rubber Bearing System and the Friction Pendulum Technique. Additionally, it includes SAP2000 Analysis, Story Drift Measurement, and Shear Force Evaluation in relation to these techniques.

Effect of material characteristics of lead rubber isolators on seismic performance of box girder bridge

Near-field (NF) earthquakes have distinct ground motions, forward directivity pulses, and fling-step motions, causing structural responses to differ from far-field (FF) earthquakes. Seismic isolation is regarded as a developed and successful technology that may be applied to enhance a structure’s functionality and safeguard it against catastrophic earthquake effects. The variation in mechanical properties of seismic isolation also significantly influences bridge seismic response. The study investigates the influence of lead rubber (LRB) isolators and the characteristics of ground motions on seismically isolated bridges, aiming to determine optimal parameters for minimal earthquake response. Key parameters include ground motion characteristics, characteristic strength (Q), and isolator flexibility. The study modeled the force-deformation behavior of isolators using bilinear behavior, reflecting the Bouc-Wen hysteric model. CSI Bridge was used to model seismically isolated steel box girder bridges, with eight natural accelerograms assessing a 2% probability of exceedance in 50 years. The peak responses of pier displacement (MPD), isolator hysteric energy (HED), base shear, and deck acceleration are chosen as the response parameters for the comparison. To evaluate the response parameters, the earthquake data are scaled to the three studied peak ground acceleration (PGA) levels of design level (0.2 g), extreme level (0.4 g), and rare-extreme level (0.8 g). The findings offer insight on the relevance of isolator stiffness and its influences on the seismic performance of isolated bridges. The study identifies minimum values for pier displacement, hysteric energy, deck acceleration, and base shear at specific Q/weight sustained by isolator (W) and time period (T) values. Recommendations are made for the preliminary seismic isolation design of bridges with LRB isolators, highlighting the importance of PGV to PGA ratio in earthquake damage assessment.

Fatigue characteristics of rubber isolation layers used in high speed railway ballastless tracks: A theoretical and experimental study

In order to enhance operational conditions for high-speed trains on long-span bridges, the utilization of rubber under-ballast mats were taken as a novel isolation layer in ballastless tracks. Due to the increased train axle load, it is imperative to conduct investigation into the fatigue properties of the rubber isolation layer, so as to ensure the smoothness of the railways. In this work, a series of fatigue tests were performed on the rubber isolation layer to obtain the influence of stress amplitude and loading cycles on its fatigue performance. The results demonstrate a pronounced non-linear load–displacement relationship of the rubber isolation layer with increasing load, while the fatigue endurance significantly decreases with escalating the stress amplitude. Moreover, considering the hyperelastic properties of rubber material, the Mooney-Rivlin constitutive model was employed in finite element simulations. Subsequently, the stress distributions of the rubber isolation layer were analyzed, and the fatigue life was evaluated based on Luo stress method. The rubber isolation layer exhibits localized damage that does not affect the overall performance after 32 years of normal service condition. Therefore, the fatigue performance of the rubber isolation layer remains reliability, providing assurance for the application in ballastless tracks on high-speed railway long-span bridges.

Tests and Seismic Response Analysis of Guided-Rail-Type Anti-Tensile Rubber Bearing

When subjected to seismic activity, tall isolated buildings with a high aspect ratio are susceptible to overturning as a result of the failure of rubber isolation bearings under tension. In order to address this issue, a guided-rail tension device (GR) has been developed to enhance the tensile strength of rubber bearings. Furthermore, a novel guided-rail isolation rubber bearing (GR&RB) has been proposed as a potential solution. Quasi-static tests have been conducted to investigate the mechanical properties of the GR, as well as the GR&LNR600 and LNR600. Additionally, numerical finite element analysis has been employed to study the seismic response of the GR&RB under El Centro seismic action in a high-rise building with an aspect ratio of approximately 4. The experimental results suggest that the inclusion of GRs has a limited effect on the horizontal mechanical attributes of rubber isolation bearings. Nevertheless, it simultaneously enhances their tensile strength, demonstrating a significant augmentation of 4.23 times. Moreover, the mechanical behavior of the GR aligns with the Hook model. The numerical analysis suggests that the utilization of GR&RB can mitigate the tensile stress levels of rubber isolators. Furthermore, it is recommended to augment the elastic tensile stiffness of the GR while reducing the open value to enhance the tensile efficiency, with the potential to attain up to 75% efficiency in tensile performance.

Experimental Study of the Mechanical Properties of Full-Scale Rubber Bearings at 23 °C, 0 °C, and -20 °C.

In this study, the effects of ambient temperature on the horizontal mechanical performance of isolated rubber bearings were investigated using high-speed reciprocating loading methods. A comprehensive series of 54 experimental trials are performed on the full-scale (900 mm-diameter) isolation rubber bearings, encompassing a range of temperatures (-20 °C, 0 °C, and 23 °C), shear pressures (50%, 100%, and 250%), and frequencies (0.20 Hz, 0.25 Hz, and 0.30 Hz). Because the compression-shear tests were conducted at high velocities and pressures (specifically, vertical compressive stress of 15 MPa), the equipment used in these tests was capable of generating substantial inertial and frictional forces. Appropriate correction methodologies for the precise determination of mechanical performance metrics for bearings are presented. Then, a comprehensive investigation of the effects of various loading conditions on the characteristic strength, post-yield stiffness, horizontal equivalent stiffness, and equivalent damping ratio of LRB900 (lead-core rubber bearings 900 mm-diameter) and LNR900 (linear natural rubber bearings 900 mm-diameter) is conducted. The empirical results show a discernible relationship between these characteristics and ambient temperature as the number of loading cycles increases, except for the equivalent damping ratio. Finally, empirical fitting formulations incorporating the influence of ambient temperature are presented for each performance indicator. These formulas are intended to assist designers in performing seismic design analyses by allowing them to take into consideration the effects of ambient temperature comprehensively.

Research on the effectiveness of a new-type bearing for structural seismic and vibration dual control

The burgeoning expansion of subway systems has heightened the significance of subway-induced vibrations and their impact on nearby structures. Addressing the dual challenges of mitigating subway-induced vibrations and ensuring structural seismic safety is garnering increasing attention. This study introduces a new-type seismic and vibration dual control isolation bearing that leverages the deformability of rubber. This bearing consists of a thick rubber bearing and a traditional horizontal rubber bearing, which are decoupled in motion and responsible for vertical vibration isolation and horizontal seismic isolation, respectively. A scaled model was constructed of an actual structure to assess the effectiveness of this bearing, conducting shaking table tests with inputs simulating typical subway-induced vibrations and seismic motions. Our findings reveal that the bearing successfully meets predefined isolation and vibration control objectives. Regarding subway-induced vibration loads, it markedly diminishes peak vertical acceleration responses. Frequency-wise, it effectively attenuates high-frequency responses while amplifying low-frequency ones. Notably, increasing damping does not significantly improve vertical vibration isolation. Regarding seismic loads, by aptly configuring the horizontal seismic isolation parameters, the bearing achieves targeted seismic isolation objectives. Furthermore, this new bearing demonstrates certain vertical isolation capabilities, distinguishing it from traditional horizontal rubber isolation bearings.

Sound transmission loss through steel-framed building partitions

Load-bearing steel-stud walls pose a unique acoustical challenge because both the spacing and the mil thickness of the studs can significantly affect the acoustical performance of these walls. A single wall type in a load-bearing steel building may actually include many acoustically distinct walls as the stud spacing and mil thickness change from floor to floor in the building due to the different loads. This can be especially challenging on delegated design projects where the final selection of the steel studs is left to the framing contractor and may not be included in the project documents supplied to the acoustical consultant, if there even is one on the project. In prior ASA presentations, Ben Shafer has clearly documented the effects of steel stud spacing and mil thickness on acoustical performance. This presentation adds to Ben’s prior work by investigating the effects of resilient sound isolation clips on wall performance. Clips are a unique application because the spacing of both the clips, and the hat channels does not change with changing stud spacing and because the low stiffness of the rubber isolators should reduce the effect of stud stiffness. This presentation will present the results of recent lab tests of walls with resilient sound isolation clips and compare the results to the data previously presented by Mr. Shafer.

Vibration isolation characteristics of a rubber isolator in the deep water condition

Vibration isolation characteristics of a rubber isolator in the deep water condition

Advancements in base isolation for seismic mitigation: Perspectives on elastomeric and lead rubber bearings

Base isolation represents an environmentally sustainable and highly effective technique for mitigating structural responses to strong seismic forces generated by plate boundary tectonic activities. Its primary benefits include preventing structural collapse, minimizing property damage, and safeguarding human lives during severe earthquakes. This passive, energy-efficient approach is often complemented by supplementary dampers to further reduce seismic impact. This study provides a comprehensive overview of elastomeric and lead rubber isolators, covering their theoretical, experimental, and numerical aspects. The paper examines the seismic response of structures equipped with elastomeric and lead rubber bearings, including a discussion of their pros and cons. This paper presents the comparison of fixed base and rubber isolated base in SAP 2000 to assess the effectiveness of base isolation. Additionally, it presents findings from shaking table tests, relevant building codes, and practical applications, considering the impact of events beyond initial design parameters. The review delves into the historical evolution of elastomeric and lead rubber-bearing systems, offering valuable insights into their contemporary understanding. Furthermore, the paper introduces three-dimensional isolators designed to attenuate ground motion responses in both horizontal and vertical directions. It investigates the effects of soil-structure interaction and evaluates isolator responses under blast and impact aircraft loading conditions. Notably, specific types of bearings exhibit exceptional energy dissipation capabilities during catastrophic seismic events, leading to reduced floor acceleration and inter-storey sway at critical levels. In conclusion, the study offers future recommendations and identifies potential constraints in this field

Seismic behavior of base-isolated building structures with lead rubber bearings (LRBs)

This study is designed to evaluate the efficacy of multi-storey buildings in mitigating seismic responses, particularly through the implementation of a base isolation system. Our focus centers on two reinforced concrete structures, one eight stories high and the other ten stories high, both outfitted with a base isolation system featuring lead rubber isolators to proactively minimize seismic risks. The primary objective of introducing a base isolation system is to curtail the potentially destructive impact of earthquakes on a building by attenuating the transmission of seismic forces from the superstructure to the foundations. This seismic protection technique involves strategically installing isolators between the building's superstructure and its foundations. The integration of lead rubber bearing (LRB) isolators into the building's base constitutes a pivotal approach to significantly augmenting the seismic performance of a structure. This method boasts several advantages, chief among them being a notable reduction in floor drift, a critical factor for ensuring the safety and stability of a structure amidst seismic activity. The outcomes of our study underscore the remarkable effectiveness of base isolation in substantially decreasing the overall seismic responses of buildings in the studied region. The observed reductions range from 50% to 70%, affirming the robustness and resilience that this innovative approach imparts to buildings in earthquake-prone areas.

Numerical investigation and optimisation of a combination of a rubber isolator and steel U-shaped dampers

Numerical investigation and optimisation of a combination of a rubber isolator and steel U-shaped dampers

PRELIMINARY EVALUATIONS OF AIR TEMPERATURE EFFECTS ON THE RESPONSE OF SEISMICALLY ISOLATED BRIDGES EMPLOYING ELASTOMERIC BEARINGS

Laminated rubber bearing is a common seismic protection device for bridge structures based on its high vertical stiffness, low horizontal and rotational stiffness, and significant lateral restoring capacity. However, the mechanical behavior of elastomers, particularly the material's shear stiffness, is significantly influenced by variations in air temperature. The cyclic behavior of elastomeric isolators is affected by variations in air temperature and this is considered by current seismic codes through requiring upper and lower bound analysis using relevant modification factors. As a result, it significantly impacts the seismic responses of structures employing laminate rubber isolators. However, this aspect is not frequently considered when designing seismic isolation in most locations. This article aims to evaluate the effect of air temperature on the seismic response of isolated bridges. A parametric study, with varying temperature conduction, is carried out. The responses of a seismically isolated bridge are evaluated by the peak value of lateral force and displacement. Results indicate that air temperature has considerable effects on the behavior of rubber isolators and seismic responses of isolated bridges.