High Damping Rubber Research Articles

Investigation of one dimensional multi-layer periodic unit cell for structural base isolation

Conventional base isolators like lead rubber bearing, high damping rubber bearing and friction pendulum bearing are not suitable for structures containing crucial pipelines and other sensitive structural components, since these structures with conventional isolators are usually subjected to large relative displacements between the superstructure and the base. Concepts from solid state physics have led to the evolution of a new technique of base isolation for civil engineering structures through the use of a foundation system consisting of periodic materials, namely periodic foundation. Periodic structures have the ability to block the passage of elastic waves within a certain frequency range through them. This frequency range is called the band gap or the attenuation zone of the periodic structure. Periodic foundations can be one dimensional (1D) or two dimensional (2D) or three dimensional (3D) periodic foundations depending of the arrangement of the periodic materials in the foundation. The band gap characteristics of 1D periodic foundations can be computed through the Plane Wave Expansion (PWE) method by expressing material properties in the form of Fourier series expansion in the reciprocal lattice space and obtaining the band gap through an eigenvalue problem using Bloch’s theorem. In the present study the PWE method has been formulated to analyse a generic multi-layer periodic unit cell. The generalized formulation has then been applied to the case of a 1D periodic foundation with three material layers. The results obtained from the analysis have shown wider attenuation zones with lower starting frequencies in the 1D three-layer periodic foundation as compared to a 1D two-layer periodic foundation. The effect of material and geometric parameters on the first attenuation zone of 1D three-layer foundation has also been investigated in the present study. Additionally, experimental studies on a single storey frame and numerical studies on a ten storey frame conducted with chosen configurations of periodic foundations showed that both 1D two-layer and 1D three-layer periodic foundations are effective in attenuating the vibration responses of structural systems.

Inerter dampers with linear hysteretic damping for cable vibration control

Long stay cables in cable-stayed bridges have low and close-spaced modal frequencies and are subjected to multimode vibrations, e.g., rain–wind vibrations and vortex-induced vibrations. Many types of dampers used in practice for cable vibration control can be described using a linear hysteretic damping model, e.g., high-damping rubber dampers and viscous-shear dampers. Such dampers are able to provide frequency-independent damping effects while the maximal achievable damping is limited due to their intrinsic stiffness effect. Therefore, this study investigates dampers with linear hysteretic damping enhanced by inerters for cable vibration control. A general inerter damper, consisting of a spring with complex stiffness and an inerter in parallel which is then connected to another inerter in series, is attached to a cable for dynamic analyses. Complex modal analysis is performed to appreciate cable damping. The optimal damping effect is discussed with reference to dynamic properties of the damper with respect to frequency, with comparison to the system of a cable with an inerter damper with viscous damping. It is found that two inerters, respectively in parallel and in series with a damper of linear hysteretic damping, can achieve a large improvement on multimode damping of a cable. The inertance of the inerter in series with the damper needs to be large for optimal performance while a small inertance of the other inerter is preferable. Furthermore, a case study based on a cable attached with a viscous-shear damper on the Sutong Bridge is conducted to show the feasibility of the inerter dampers.

Experimental study on seismic retrofit of a RC frame using viscoelastic dampers

The deformation capacity of a viscoelastic damper (VED) is generally limited by the thickness of the VE pad. In this study, a VED with fail-safe mechanism was developed and its seismic performance was evaluated by a series of experiments of full-scale two-story reinforced concrete (RC) frame before and after seismic retrofit. The VED is composed of high damping rubber viscoelastic pads and is installed vertically between stories. One bare frame and two retrofitted frames with different damper capacities were tested under cyclic loads to validate the effectiveness of the newly developed dampers. The Bouc Wen model was developed to simulate the seismic behavior of the damper, which turned out to represent the behavior of the VED accurately. As a case study, the proposed VED was applied to seismic retrofit design of a 4-story RC moment framed structure, and it was found that the proposed retrofit scheme could adequately improve the seismic performance of the structure by reducing both inter-story and residual displacements.

A simplified and versatile element model for elastomeric seismic isolation bearings

A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters’ identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.

Experimental seismic performance assessment and numerical modelling of nonlinear inerter vibration absorber (IVA)‐equipped base isolated structures tested on shaking table

AbstractIn recent years, inerter vibration absorbers (IVAs), such as the tuned mass damper inerter (TMDI), attracted much attention in the literature for reducing seismic displacement demands of base isolated structures (BISs). Several theoretical studies reported reduced BIS seismic demands with increasing inertance endowed by a grounded inerter element, but adopted mostly idealized linear dynamical models. Herein, the potential of TMDI‐configured IVAs for seismic response reduction of BISs modelled as single‐mass structures is assessed under the combined effects of nonlinear inerter and structural behavior. To this aim, experimental data from a shaking table testing campaign are considered utilizing a custom‐built flywheel rack‐and‐pinion grounded inerter prototype with variable inertance, along with high damping rubber bearings in the isolation layer and in the BIS‐to‐absorber link. White noise excitation and an ensemble of six ground motions (GMs) with different frequency content are used in the tests for which bearings exhibit softening nonlinear behavior. Experimental results demonstrate improvement of BIS nonlinear seismic response in terms of displacement and base shear with increasing inertance for nonlinear and nonoptimally tuned IVAs. It is found though that the considered IVAs may be detrimental to BIS acceleration response depending on the GMs time‐varying frequency content signatures as captured by the continuous wavelet transform spectrogram. Finally, it is concluded that representing the inerter device by a simplified linear dissipative model as opposed to a nonlinear model with friction and gear backlash suffices to trace the BIS response with acceptable accuracy and, thus, can be used for optimal seismic TMDI design.

Suppression of vortex-induced high-mode vibrations of a cable-damper system by an additional damper

Dampers are widely used for mitigating cable vibrations, particularly for rain-wind vibrations which often occur in low-frequency modes with large vibration amplitudes. However, it has been observed in existing bridges that a long cable attached with a damper still experiences vortex-induced vibrations in high-frequency modes with a mode shape having a node close to the position of the damper. Therefore, this study proposes to add a device to suppress such high-mode cable vibrations. Three typical dampers are respectively considered as the additional device, i.e., a viscous damper (VD), a high-damping rubber (HDR) damper and a tuned mass damper (TMD). A theoretical model of a shallow cable under two transverse forces at different locations is applied for dynamic analysis. Multimode damping of a cable equipped with two dampers is investigated based on numerical solution of the system frequency equation, and maximal high-mode damping is pursued by optimizing parameters of the dampers on the cable consecutively and simultaneously. Results show that the three types of dampers can all improve damping of the cable modes vulnerable to vortex-induced vibrations. When an additional VD is installed between the original VD and the closer cable end, a decrease in the viscous coefficient of the original damper can improve damping of the higher-order modes. When an HDR damper is installed on the cable between the VD and the nearer anchorage, damping in more low modes is decreased as compared to the case when a VD is installed because of the stiffness of the HDR damper. The HDR damper mainly induces a change in the mode shape of high cable modes and hence the original damper can dissipate more vibration energy. In the case of adding a TMD, no adverse effect on cable damping is found in all the modes. Finally, the procedure for designing two dampers to control both low-mode and high-mode cable vibrations is provided.

Coupled structural and heat conduction FE analysis of laminated high damping rubber bearing

AbstractA framework for coupled structural and heat conduction finite element analysis is developed for laminated high damping rubber bearings (HDRBs), and coupled analyses are conducted for full‐scale tests of an HDRB using the shaking table at E‐Defense. An HDRB, which is used in base‐isolated buildings, is modeled using hexahedral solid elements. The high damping rubber is modeled as an overlaid viscohyperelastic and elastic‐plastic constitutive model. However, material parameters are identified using the results for the HDRB subjected to one‐directional loading, and temperature dependences of the parameters are taken into account by a simple method based on empirical formulae for the HDRB because no cyclic coupon test was conducted for the high damping rubber used in the full‐scale tests. The combined structural and heat conduction analyses are conducted for a number of loading cases. The same hexahedral mesh of the HDRB is used for both structural and heat conduction analyses. Analysis results are presented for a one‐directional cyclic loading test, two‐directional loading test with elliptical orbit, and earthquake loading test. The results obtained by the tests and those obtained by the coupled structural and heat conduction analyses are compared. The coupling effect of the mechanical and thermal behaviors is clearly shown in the analysis results, although reductions of the equivalent stiffness and damping are not large because the number of loading cycles in the present analyses is limited.

Seismic Behavior of Base Isolated Civil Protection Operative Center in Foligno, Italy

The analysis of the actual seismic behavior of the Operative Building of the Civil Protection Centre in Foligno, Italy, which is seismically isolated by means of high damping rubber bearings (HDRBs), is shown. An accelerometer network was installed on the structure. It recorded all the events of the seismic sequence that hit central Italy from August 2016 to January 2017. All the events had epicenters far from the building, so the effects at the site were quite low and the resonance frequencies measured were higher than the frequencies assumed in the design phase. The seismic filtering was effective. The strongest earthquake occurred on October 30, 2016, Mw=6.5, with epicenter at Norcia, was studied in detail. A nonlinear law for the rubber shear modulus was deduced, which fits quite well with experimental data and was used for a nonlinear dynamic analysis of the entire building. The model was first tested analyzing the effects of the acceleration time-histories recorded during the mentioned event at the building basement. The responses obtained numerically at the sensor locations were compared with those recorded at the same locations during the quake. Then the model was used to analyze the structural response to a strong earthquake.

Factors Affecting the Dependency of Shear Strain of LRB and SHDR: Experimental Study

In this research we conducted a sensitivity experimental study where we explored the dependency of the shear strain on the seismic properties of bearings, namely lead rubber bearing (LRB) and super high damping rubber bearing (SHDR). The factors studied were vertical pressure, temperature, shear modulus of the inner rubber (G value), loading frequency, and loading sequence. Six specimens were adopted, i.e., three LRBs and three SHDR bearings. A series of test plans were designed. The seismic characteristics of the bearings were captured through a cyclic loading test, which included post-yield stiffness, characteristic strength, area of a single cycle of the hysteretic loop, equivalent stiffness, and equivalent damping ratio. A whole analysis of variances was then conducted. At the same time, to explore certain phenomena caused by the factors, an extended discussion was carried out. Test results showed that the temperature is the most dominant feature, whereas the G value is the least contributing factor, with the effect of the loading frequency and the loading sequence found between these two. The increment of the post-yielded stiffness for LRB from 100% to 25% is a significant reduction from a low temperature to high one. The slope of the characteristic strength versus the shear strain for LRB under high temperature is larger than the one under low temperature.

Seismic retrofit of 3000 kVA power transformer using friction dampers and prestressed tendons

This study proposes a seismic retrofit system for large power transformers with 3000 kVA capacity. The seismic protection system is developed by combining rotational friction dampers and the pre-stressed tendons with high damping rubber pads at the base. The proposed system enhances the seismic performance of the transformer by limiting the lateral and vertical deflection during earthquakes. The numerical model of the retrofit system is developed and compared with the sub-assemblage test of the damper. The seismic performance of the 3000 kVA transformer retrofitted with the proposed retrofit system is evaluated by performing full-scale shaking table test, and the results are compared with those obtained by the analytical model. The experimental and numerical results demonstrate that the seismic retrofit system is effective in reducing the deflection and acceleration of the transformer when subjected to severe ground motions.

Analytical model for precast wall equipped with U-shaped steel channel connection

The stability and safety of precast concrete structures furnished with different types of connections has been a focus of researchers and engineers in the recent decade. In this study, the new design for connection of precast walls has been proposed by implementing and installing a pair of U-shape steel channels to each wall as male and female parts and tie to each other using bolts and nuts as a dry joint. The high damping rubber sheet has been implemented within the male and female U-shaped channel in order to dissipate vibration transferring within two precast wall when structure subjected to ground motion. The analytical model is developed in order to implement for numerical simulation of precast reinforced concrete (RC) structure with U-shaped wall connection using finite element method and evaluate the performance of proposed joint as energy dissipation systems for reduction of effect of earthquakes on precast structure. Therefore, the constitutive law and finite element (FE) model for proposed wall connection element have been formulated and the FE algorithm is developed to carry out inelastic analysis for precast RC structures equipped with proposed U-shaped connection under dynamic loading. The values for stiffness of connection were achieved by a series of experimental setup. Experimental results showed that the proposed connection failure mechanisms exception made for the specimen subjected to loading in X-direction for first degree of freedom demonstrates less damage in the connection zone due to huge stiffness of precast wall in that direction. This desired failure mechanism led to semi ductile failure in the structure. Finally, the efficiency of precast wall connections on performance of the RC building was carried during static and dynamic loading.

Response of a High Damping Rubber Bearing to Multiaxial Excitation

Abstract A high damping rubber bearing fabricated as part of a seismic isolation system was tested at the Caltrans Seismic Response Modification Device Test Facility at the University of California, San Diego. The purpose of the test program, which consisted of 33 tests, was to assess the impact of multiaxial excitation and input rate on the response of the bearing. The test protocol consisted of unique tests, including testing the bearing in all six degrees of freedom (uncoupled and coupled) and testing the bearing dynamically to failure. This article examines the hysteretic response and resulting performance parameters of the bearing to the different tests. The most notable impacts on the bearing’s hysteretic response were the axial loading and coupling the lateral degrees of freedom, while the rotational degrees of freedom had minimal impact on the bearing’s response. The bearing’s hysteretic response to coupling input in the rotational degrees of freedom with lateral and axial degrees of freedom was consistent with the expected performance from superimposing the response to input from individual degrees of freedom. The bearing failed at almost three times the design shear strain and at a shear force over five times the shear force at the design shear strain during the dynamic test to failure.

Chlorinated butyl rubber/two-step modified montmorillonite nanocomposites: Mechanical and damping properties

Montmorillonite (MMT) was modified by ultrasound and castor oil quaternary ammonium salt intercalation method to prepare a new type of organic montmorillonite (OMMT). The surface structure, particle morphology, interlayer distance, and thermal behavior of the samples obtained were characterized. The modified OMMT was then added to chlorinated butyl rubber (CIIR) by mechanical blending, and a composite material with excellent damping properties was obtained. The mechanical experiment results of CIIR nanocomposites showed that the addition of OMMT improved their tensile strength, hardness, and stress relaxation rate. Compared with pure CIIR, when the content of OMMT was 5 phr (part per hundred of rubber), the tensile strength of the nanocomposite was increased by 677% and the elongation at break was also increased by 105.4%. The enhancement of this performance was mainly due to the dispersion of the nanosheets in CIIR rubber and the chemical interaction between the organoclay and the polymer matrix, which was confirmed by morphology and spectral analysis. OMMT also endowed a positive effect on the damping properties of CIIR nanocomposites. After adding 5 phr of OMMT, the nanocomposite owned the best damping performance, and the damping factor, tanδmax, was 37.9% higher than that of pure CIIR. Therefore, the good damping and mechanical properties of these CIIR nanocomposites provided some novel and promising methods for preparing high-damping rubber in a wide temperature range.

Performance of high-damping rubber bearings for seismic isolation of residential buildings in Turkey

The applicability of high-damping rubber bearings for seismic isolation of residential buildings in Turkey is studied using numerical and experimental approaches. Seismic isolation system composed of high-damping rubber bearings is designed according to the recently updated Turkish Building Seismic Code-2018 (TBSC2018). Three model buildings of different height at assumed seismically active area are chosen from an actual building database, on which, equivalent lateral force procedure, and time history analyses are carried out.The seismic responses of the buildings are evaluated and the seismic isolation system's efficiency is confirmed. It is pointed out that the requirements in the new code in terms of the maximum allowable shear strain of elastomeric isolators are excessively conservative for those isolators with much larger capacity which is verified by sufficient test data, and as a result, designed isolator size becomes larger than necessary from a practical aspect. In order to verify the isolator design without compliance of shear strain limitation in the code, full-scale prototypes of high-damping rubber bearings are specially designed, developed and are subjected to dynamic loading test under test protocol specified in the code. The specific values of test conditions, such as compressive force, shear displacement and frequency, are developed referring several projects in Turkey. The results are comprehensively discussed and the applicability of high-damping rubber bearing for seismic isolation of residential buildings in Turkey is concluded with numerical and experimental approaches and a possible modification of TBSC2018 regarding maximum shear strain is proposed.

Numerical study of visco-hyperelastic damper with high axial damping rubber subjected to harmonic loading

Structural control prevents structural damage and provides the desirable performance level through the ductility of components and using passive energy dissipation systems. In this paper, the performance of a recently introduced passive control device called Visco-Hyperelastic Damper (VHD) is investigated by ABAQUS FEM software. This device has the properties of both velocity-dependent and displacement-dependent dampers and provides additional energy dissipation for structures. This device consists of a viscoelastic material sandwiched between two metal rings dissipating energy through a combination of the elastic behavior of the viscoelastic material and the plastic deformation of the steel parts. In order to validate the numerical model, after separately testing the steel and rubber parts, their results are used in damper modeling. VHD performs desirably under different levels of excitation such that 82% to 99% of energy dissipation, depending on the type of loading, is observed by this device. The dynamic behavior of VHD can be further improved by modifying variable parameters such as dimensions and type of materials of the device.

Experimental and Theoretical Investigations of a Displacement‐Amplified Torsional Damper

In this work, a displacement‐amplified torsional damper (DATD) is proposed for improving the seismic capacity of the beam‐column joints of a frame structure. The proposed DATD uses common steel, lead, and high‐damping rubber. This damper exhibits good energy dissipation under small earthquakes. Under strong earthquakes and large displacements, the strengthening of the high‐damping rubber can improve the overall stiffness of the damper and increase the energy dissipation. In order to investigate the performance of the proposed DATD, theoretical analyses, simulations, and cyclic loading tests were performed, and their results were compared, showing an overall good agreement.

Study on the cyclic shear behavior of damping layer joint for the infilled masonry wall

Damping Layer Joint (DLJ) is the core element of Damped Infilled Wall (DIW), which is used to improve the seismic performance of Infilled Masonry Wall (IMW). The aim of this study is to find a better combination of material and bonding method to make DLJ and bond DLJ-brick bonding interface (DBI) respectively. The influence of DBI effectiveness, material types (i.e. modified asphalt waterproofs (MAW) and high damping rubber (HDR)) in terms of the cyclic and monotonic behavior were investigated. The results indicate that failure of DBI may lead to a deterioration in loading with a better energy dissipation feature. Also, failure of DBI may change mechanism to the coupled shear deformation and the sliding at DBI. It is recommended to make DLJ as a material with much lower stiffness and shear force compared to mortar bed-joint and to bond DBI by one type of epoxy resin.

Effect of various aspects on the seismic performanceof a curved bridge with HDR bearings

The performance of an isolated horizontally curved continuous bridge with High Damping Rubber (HDR) Bearings has been investigated under seismic loading conditions. The effectiveness of response controls of the bridge by HDR bearings for various aspects viz. variation in ground motion characteristics, multi-directional effect, level of earthquake shaking, varying incidence angle, have been determined. Three recorded ground motions, representative of historical earthquakes along with near-field, far-field and forward directivity effects, have been considered in the study. The efficacy of the bearings with bi-directional effect considering interaction behavior of bearing and pier has also been investigated. Modeling and analysis of the bridge have been done by finite element approach. Sensitivity studies of the bridge response with respect to design parameters of the bearings for the considered ground motions have been performed. The importance of the nonlinearity of HDR bearings along with crucial design parameters has been identified. It has been observed that the HDR bearings performed well in different variations of ground motions, especially for controlling torsional moment. However, the deck displacement has been found to be increased significantly in case of Turkey ground motions, considering forward directivity effect, which needs to be paid more attention from designer point of view.

Coupled Bilateral Hysteretic Behavior of High-damping Rubber Bearings under Non-proportional Plane Loading

ABSTRACT The hysteretic behavior of high-damping rubber bearings under different non-proportional plane loading paths is experimentally examined. Compared with unilateral reversal loading test results, non-proportional plane loading will make the rubber of high-damping rubber bearings have additional regional shear strain, thus leading to quite different mechanical properties and hysteretic behavior. A previously developed mathematical model is further modified for appropriately characterizing the unilateral and bilateral behavior of high-damping rubber bearings. The applicability and generalization of the further modified model are examined and demonstrated by comparing its predictions using a unique set and different sets of identified coefficients with the test results.

Evaluation of mechanical properties considering hysteresis characteristic of high damping rubber bearing

Recently, laminated rubber bearings are widely used as seismic isolators for road bridges. Although many studies have been conducted on the dynamic model of High Damping Rubber (HDR) bearings, few models can reflect phenomena such as the dependency of experienced shear strain on initial history. To develop a model that can represent the dependency of the experienced shear strain of HDR and a dynamic loading test was conducted using HDR specimens. The hysteresis characteristics of HDR was measured by applying a horizontal vibration using a hybrid actuator under a constant vertical load. Based on the cyclic shear test, the mechanical properties of HDR were calculated such as absorbed energy, hysteresis loop area, equivalent stiffness, equivalent damping ratio. Dynamic analysis was also performed from the experimental results. The dynamic model applied in program analysis is a bilinear type double-target model. This model can express the nonlinear characteristics related to the initial history of HDR bearings. The parameters required for dynamic analysis were determined from the experimental results. Through this dynamic analysis, the effectiveness of the bilinear type double target model was verified. In this research, a high damping rubber specimen was used.