High Damping Rubber Bearings Research Articles

Effect of near and far Field Earthquakes on performance of various base isolation systems

Civil engineering infrastructures are prone to natural disasters like earthquakes, floods and strong winds. Base isolation is one of the effective structural controlling technique for protection of structure during earthquake events. The concept of Base isolation is to insert a flexible layer between foundation and superstructure thus decoupling the building from damaging action of ground motion. This modifies the dynamic characteristics of the system. This paper presents comparative study of near and far field earthquakes on the performance of three types of passive base isolators namely High Damping Rubber bearing (HDRB, Damping Ratio: 13%), Low Damping Rubber Bearing (LDRB; Damping Ratio: 3%) and Lead Core Rubber Bearing (LCRB, Damping Ratio: 25%). For this purpose, an 8-storey structure has been analyzed using state space approach in MATLAB. Parameters like peak global drift, inter-storey drift, transmissibility of acceleration are compared for various base isolation systems under near and far field earthquakes. It is concluded that the dynamic response of the structure depends on the source of excitation and designer must consider this effect for efficient design. Moreover, the damping of the base isolator should be so adjusted that both the deformation and transmissibility ratio are minimized or in some cases a combination of different dampers may be used.

Experimental and analytical investigation of the influence of compressive load on rate-dependent high-damping rubber bearings

High-damping rubber bearings (HDRBs) have been widely accepted as a relatively novel type of seismic isolation devices in civil infrastructures construction, they are known to possess significant rate-dependent behavior and accommodate the gravitational load of the superstructure in typical applications. Hence, it necessitates better understanding of the mechanical behavior of HDRBs under coupling effect of compression and shear. The objective of the paper was to conduct experimental and analytical investigation to characterize the influence of compressive load on rate-dependent HDRBs. Firstly, a series of material tests including multi-step relaxation and monotonic shear tests were carried out on high-damping rubber, the strain rates and compressive stresses applied on specimens were varied and analyzed. Then, on the basis of experimental investigation, the classical Zener model was extended and a rate-dependent analytical model of HDRBs allowing for the consideration of compressive load was proposed. Finally, comparing the numerical simulations and experimental data obtained from both material tests and full-scale bearing tests, a reasonably good agreement was observed and the validity of the proposed model was demonstrated.

Modelling and Seismic Response Analysis of Italian Code-Conforming Base-Isolated Buildings

ABSTRACTThis paper reports on results of nonlinear analyses performed within the RINTC project on an RC building isolated with different systems (High Damping Rubber Bearings, High Damping Rubber Bearings and Flat Sliding Bearings, Friction Pendulum System) and designed according to the Italian design code. The seismic response has been evaluated under different seismic input levels of two sites with different hazard and by considering two Limit States: Global Collapse and Usability-Preventing Damage. The influence of seismic stoppers and modelling uncertainties is also evaluated. Results permit to compute the implicit collapse risk and to identify critical aspects of current design procedures.

Stochastic response of structures with hybrid base isolation systems

In 2004, two R/C residential buildings were retrofitted by using a hybrid base isolation system in Solarino, Sicily, and subsequently five free vibration tests were carried out in one of these buildings. The hybrid base isolation system combined high damping rubber bearings with low friction sliders. In terms of numerical modeling, a single-degree-of-freedom system is developed here with a new five-parameter trilinear hysteretic model for the simulation of the high damping rubber bearing, coupled with a Coulomb friction model for the simulation of the low friction slider. Furthermore, a shear beam type, four-degree-of-freedom model is used to numerically simulate the superstructure. Next, experimentally obtained data from the five initial-displacement, free vibration tests were used for the calibration of this six-parameter model describing the base isolation system. Following up on the model development, the present study employs Monte-Carlo simulations in order to investigate the effect of the unavoidable variation in the values of the six-parameter mechanical model on the response of both the hybrid base isolation system and the superstructure comprising the Solarino building. The calibrated parameters values from all the experiments are used as mean values, while the standard deviation for each parameter is deduced from the identification tests employing best-fit optimization for each experiment separately. The results of the Monte-Carlo simulations show that variation in the material parameters of the base isolation system produce a nonstationary effect in the response, which can be traced by the time evolution of its mean and standard deviation as computed from the response at different time instants. In addition, there is a magnification effect, since the coefficient of variation of the response, for most of the parameters, is larger than the coefficient of variation in the parameter values. The high level of nonlinearity in the base isolation system, as observed in the amplitude of vibration brought about by large initial displacements, helps explain the previously mentioned effects.

THE INVESTIGATION BASE ISOLATOR IN CONTROLLING THE RESPONSE OF THE STRUCTURES DURING EARTHQUAKES

<p>Base isolation systems are among the most successful and widely applied methods of mitigating structural vibration and damage during seismic events. These systems have been installed in numerous full-scale structures all around. There are three principal types of base isolators: Lead Rubber Bearing (LRB), High Damping Rubber Bearing (HDRB), and Friction Pendulum System (FPS). It is necessary to extensively examine the response of different LRB isolators—by combining them with re-centering and damping properties for isolated steel frame buildings experiencing several NF ground motions. The present research uses comparative-descriptive methodology and application in terms of objectives. The data needed for the study were collected using library references and through reviewing related studies conducted in the past in the same field.</p><p>Results of the current comparative investigation indicated significant reductions in the storey drift, shear, and acceleration and increment in the storey displacement. According to the findings of the current study, base isolators provide flexibility to massive structures against earthquakes. These structures are situated on rigid soils. Moreover, base isolation was found to be the most effective in controlling the response of the structures during earthquakes. Finally, shear, storey drift, and storey displacement reduce due to the use of base isolators as compared to the fixed-base structure.</p>

Study on seismic behaviour for high damping rubber bearings of continuous beam bridges

The seismic response of a viaduct has been analysed in order to investigate the seismic performance and influence of high damping rubber bearings. Nonlinear time-history method has been used to analyse the seismic behaviour of different bearings. The results show that the seismic behaviour of high damping rubber bearing was better than laminated rubber bearing under earthquakes of level E2. Laminated rubber bearing was not suitable to be used in high seismic intensity area as the oversize displacement and sliding resistance.

Numerical Solutions for Nonlinear High Damping Rubber Bearing Isolators: Newmark’s Method with Netwon-Raphson Iteration Revisited

AbstractNumerical methods for the solution of dynamical problems in engineering go back to 1950. The most famous and widely-used time stepping algorithm was developed by Newmark in 1959. In the present study, for the first time, the Newmark algorithm is developed for the case of the trilinear hysteretic model, a model that was used to describe the shear behaviour of high damping rubber bearings. This model is calibrated against free-vibration field tests implemented on a hybrid base isolated building, namely the Solarino project in Italy, as well as against laboratory experiments. A single-degree-of-freedom system is used to describe the behaviour of a low-rise building isolated with a hybrid system comprising high damping rubber bearings and low friction sliding bearings. The behaviour of the high damping rubber bearings is simulated by the trilinear hysteretic model, while the description of the behaviour of the low friction sliding bearings is modeled by a linear Coulomb friction model. In order to prove the effectiveness of the numerical method we compare the analytically solved trilinear hysteretic model calibrated from free-vibration field tests (Solarino project) against the same model solved with the Newmark method with Netwon-Raphson iteration. Almost perfect agreement is observed between the semi-analytical solution and the fully numerical solution with Newmark’s time integration algorithm. This will allow for extension of the trilinear mechanical models to bidirectional horizontal motion, to time-varying vertical loads, to multi-degree-of-freedom-systems, as well to generalized models connected in parallel, where only numerical solutions are possible.

Finite element model updating of base-isolated buildings using experimental results of in-situ tests

This paper builds on the results of in-situ release tests carried out on a 3-storey base-isolated reinforced concrete frame building located in the city of Augusta (Sicily). The isolation system consists of a combination of High Damping Rubber Bearings and Low Friction Flat Sliding Bearings. Suitable practice-oriented nonlinear models have been considered to describe the cyclic behavior of the isolation system and the infill panels. The results of ambient vibration and release tests have been used to calibrate the numerical models of superstructure and isolation system, respectively. Nonlinear response-history analyses of the calibrated model are then performed to compare the seismic response of the structure with the expected (design) seismic performance.

Stochastic energy measures for hybrid base isolation systems

Two R/C residential buildings were retrofitted by using a hybrid base isolation system in Solarino, Sicily, in 2004 and subsequently five free vibration tests were carried out in one of these buildings. The hybrid base isolation system combined high damping rubber bearings with low friction teflon sliders. For numerical modeling purposes, a single-degree-of-freedom system was developed with a new trilinear hysteretic model for the simulation of the high damping rubber bearing response, coupled with a Coulomb friction model for the simulation of the low friction slider response. Five sets of data were obtained from initial-displacement, free vibration tests and were subsequently used for the calibration of this six parameter model. Following up on the numerical model development, the present study employs Monte-Carlo simulations in order to investigate the effect of variations in the values of the six-parameter model on the response of the hybrid base isolation system. The calibrated parameters' values from the experiments are used as mean values, while the standard deviation for each parameter is deduced from the identification tests employing best-fit optimization for each experiment separately. The results of the Monte-Carlo simulations show a non-stationary effect in the response, which can be traced by the time evolution of the standard deviation of various energy measures computed at different time instants. The high level of nonlinearity in the base isolation system response due to large initial displacements helps explain the previously described effects.

Effects of nonlinear modelling of the base-isolation system on the seismic analysis of r.c. buildings

Long-duration and high-amplitude horizontal velocity pulses are expected at sites located near an active fault; these are able to generate notable displacement at the level of the isolation system and pounding effects between closely spaced structural parts (e.g. in the case of an insufficient seismic gap between the elevator and building). A base-isolated commercial building, recently built in the Sicilian town of Augusta, designed in line with the former Italian seismic code, is considered as test structure. In particular, an r.c. framed structure with rectangular plan, composed of a basement and three storeys above ground level, is seismically isolated with a hybrid system including sixteen high-damping-rubber bearings (HDRBs) and twenty steel-PTFE low friction flat sliding bearings (LFSBs). An elevator shaft with steel framed structure crossing the isolation level is also placed in non symmetrical way along the longitudinal axis. A computer code for the nonlinear seismic analysis of base-isolated r.c. framed structures is improved by adding advanced nonlinear models of HDRBs and LFSBs. Finally, nonlinear dynamic analysis of the Augusta building is carried out with reference to near-fault earthquakes selected from the Pacific Earthquake Engineering Research center database and scaled in line with the design hypotheses adopted.

Study on Material Parameters for Coupled Structural and Heat Conduction Analysis of Laminated High Damping Rubber Bearing

Study on Material Parameters for Coupled Structural and Heat Conduction Analysis of Laminated High Damping Rubber Bearing

An experimental study on the shear property dependency of high-damping rubber bearings

This paper investigates the characteristics of high-damping rubber bearings (HDRBs) through various prototype tests. The characteristics were dependent on the displacements, number of load cycles, frequencies, vertical pressure, temperature, shear deformation capability, and vertical stiffness. The prototype tests showed that the displacement was the most influential factor on the characteristics of the HDRB. The effective stiffness and equivalent damping of the HDRB decreased with the displacement and increased with the frequency. The effective stiffness decreased at higher vertical pressure, while the equivalent damping increased. The equivalent damping was more dependent on the vertical pressure than the effective stiffness. The results show that careful examination is required to design the effective stiffness and equivalent damping ratio while considering the dependencies of the design displacement and excitation velocity.

Experimental assessment of sound velocity and bulk modulus in high damping rubber bearings under compressive loading

The present paper deals with the non-destructive evaluation of stressed High Damping Rubber Bearings (HDRB) in civil engineering. Such bearings are commonly made with alternating thin horizontal layers of High Damping Rubber (HDR) bonded to steel laminates. The influence of uniaxial compressive loading on pressure waves' velocity and bulk modulus is investigated for two types of bearings (with and without laminates). In the presence of laminates, bulk modulus increases with the applied compressive loading (e.g. ΔK = 20% at a mean stress σ = 16 MPa). In the absence of laminates, slipping on walls is visually observed in spite of their roughness and is thus confirmed by limitation in the increase of sound velocity. The feasibility of stress measurements using ultrasonic methods in HDRB is proved.

Comparison of different models for high damping rubber bearings in seismically isolated bridges

Steel-reinforced high damping natural rubber (HDNR) bearings are widely employed in seismic isolation applications to protect structures from earthquake excitations. In multi-span simply supported bridges, the HDNR bearings are typically placed in two lines of support, eccentric with respect to the pier axis. This configuration induces a coupled horizontal-vertical response of the bearings, mainly due to the rotation of the pier caps. Although simplified and computationally efficient models are available, which neglect the coupling between the horizontal and vertical response, their accuracy has not been investigated to date.In this paper, the dynamic behaviour and seismic response of a benchmark three-span bridge are analysed by using an advanced HDNR bearing model recently developed and capable of accounting for the coupled horizontal and vertical responses, as well as for significant features of the hysteretic shear response of these isolation devices. The results of the analyses shed light on the importance of the bearing vertical stiffness and how it modifies the seismic performance of isolated bridges. Successively, the seismic response estimates obtained by using simplified bearing models, whose use is well established and also suggested by design codes, are compared against the corresponding estimates obtained by using the advanced bearing model, to evaluate their accuracy for the current design practice.

Analyses of the Base Isolated Buildings; Nonlinear Model Time History Versus Codes' Methods

Multi-story hypothetical reinforced concrete buildings of variable geometric configurations (symmetrical, vertically irregular, horizontally irregular, with and without shear walls); with the isolated bases via high damping rubber bearing and friction pendulum systems, are analyzed using finite element method under seismic load function (North-South component of the ground motion that recorded at a site in El Centro, California in 1940) via SAP2000-V16 software. Four methods of analysis are adopted. The accuracy of the nonlinear model time history is compared with that recommended by the international codes, namely; nonlinear direct integration, equivalent lateral force, and response spectrum methods. The bilinear hysteretic model of base isolation system and the Rayleigh damping framework for superstructure are adopted. The results support the powerful nonlinear model time history analysis, due to the negligible deviations from those predicted by the robust nonlinear direct integration method. The response spectrum method is proved to be more reliable than the equivalent lateral force method which over predicts the displacement and rotation profiles for the isolated buildings.

Design approach of high damping rubber bearing for seismic isolation

Structural control through seismic isolation using elastomeric rubber bearing, which is also known as High Damping Rubber Bearing (HDRB), has seen an increase in use to provide protective from earthquake, especially for new buildings in earthquake zones. Besides, HDRB has also been used in structural rehabilitation of older yet significant buildings, such as museums and palaces. However, the present design approach applied in normal practice has often resulted in dissimilar HDRB dimension requirement between structural designers and bearing manufacturers mainly due to ineffective communication. Therefore, in order to ease the design process, most HDRB manufacturers have come up with catalogs that list all necessary and relevant product lines specifically for structural engineers to choose from. In fact, these catalogs contain physical dimension, compression property, shear characteristic, and most importantly, the total rubber thickness. Nonetheless, other complicated issues, such as the relationship between target isolation period and displacement demand (which determines the total rubber thickness), are omitted due to cul-de-sac fixing of these values in the catalogs. As such, this paper presents a formula, which is derived and extended from the present design approach, in order to offer a simple guideline for engineers to estimate the required HDRB size. This improved design formula successfully minimizes the discrepancies stumbled upon among structural designers, builders, and rubber bearing manufacturers in terms of variation order issue at the designing stage because manufacturer of isolator is always the last to be appointed in most projects.

Experimental Study on Effectiveness of a Prototype Seismic Isolation System Made of Polymeric Bearings

Seismic isolation is identified as one of the most popular and effective methods of protecting structures under strong dynamic excitations. Base isolators, such as Lead Rubber Bearings, High Damping Rubber Bearings, and Friction Pendulum Bearings, are widely used in practice in many earthquake-prone regions of the world to mitigate structural vibrations, and therefore minimize loss of life and property damage during seismic events. The present paper reports the results of the comprehensive experimental investigation designed to verify the effectiveness of a prototype base isolation system made of Polymeric Bearings in reducing structural vibrations. In order to construct seismic bearings considered in this study, a specially prepared polymeric material with improved damping properties was used. The dynamic behaviour of a single-storey and two-storey experimental model, both fixed-base and base-isolated, under a number of different ground motions, was extensively studied. The reduction in lateral response was measured by comparing the peak accelerations recorded at the top of the analyzed model structures with and without a base isolation system. The results of this research clearly demonstrate that the application of the prototype Polymeric Bearings leads to significant improvement in seismic response by reducing the lateral acceleration.

Experimental and analytical studies of seismic response of highway bridges isolated by rate-dependent rubber bearings

The mechanical behavior of a majority of rubber bearings used for seismic isolation is known to exhibit rate dependence. Although this feature has been known for years, few studies have attempted to quantitatively evaluate the influence of this characteristic on the seismic response of an isolation system at the structural level. In this study, experimental and analytical investigations were conducted to probe the seismic response of highway bridges isolated by rate-dependent rubber bearings. Three types of such bearings were investigated: natural rubber bearings, high damping rubber bearings (HDRBs), and super high damping rubber bearings (SHDRBs). To achieve the study objective, real-time hybrid simulation (RTHS) tests were performed on a typical multi-span continuous girder highway bridge under various earthquake ground motion intensities. In the RTHS tests, a velocity loading method was adopted and the bearings were physically tested in a real-time scale and larger time scales such that the bearings were exerted under different loading rates. The influence of the rate-dependent behavior of bearings on the seismic response of the bridge was investigated by conducting a series of parametric studies. The test results indicated that the seismic response of the bridge was significantly affected by all three types of rate-dependent rubber bearings, especially HDRBs and SHDRBs. Finally, a newly proposed rate-dependent analytical model and the traditional rate-independent bilinear model for rubber bearings were used in the numerical simulation. A comparison of the simulation results indicated that the proposed model performed better than the bilinear model in the seismic response analysis.

Experimental investigation on the effectiveness of laminated rubber bearings to isolate metro generated vibration

Vibration control is important in maintaining the functionality of the buildings surrounding a metro. Among the many methods of vibration control, track isolation is by far the most efficient approach. However, for buildings constructed near a metro line which has no track isolation, base isolation of the building structures is useful to alleviate metro generated vibration. Laminated rubber bearings are commonly used for seismic isolation of building structures; however, their effectiveness in isolating metro generated vibration has not yet been well explored. In this study, scaled model tests were carried out to investigate the isolation effectiveness of laminated rubber bearings in base isolated building structures. Specifically, four types of laminated rubber bearings, i.e. thick natural rubber bearings, thin natural rubber bearings, thick high damping rubber bearings, and thin high damping rubber bearings, were tested. Tests were carried out under the designed compressive stress, 70% of the design compressive stress and at various excitation intensities. Our results show that the isolation effectiveness of both thick natural rubber bearings and thick high damping rubber bearings were significant and stable, while thin rubber bearings offered insignificant and unstable isolation.

Experimental study on mechanical properties of high damping rubber bearing model

A high damping rubber bearing was designed and manufacturedin order to reduce the seismic response of the bridge structure. The experimental study on its mechanical properties was carried out. The results show: the horizontal equivalent damping ratio is 16.77% when the shear strain is 175%. If the shear strain is larger, the post yield stiffness will be smaller as well as the horizontal equivalent stiffness. However, the equivalent damping ratio and yield force will be larger. If the vertical compressive stress is greater meanwhile the loading frequency is faster, and number of repeated loading is smaller, the equivalent stiffness and the post yield stiffness will be larger as same as the equivalent damping ratio. Destruction didn’t occur if the shear strain was no more than allowable shear strain (250%), and the ultimate shear strain was 350%. Compression destruction came when pressure stress was 10MPa. In the case of failure, the bearing was stable, but had large, nonrecoverable vertical and horizontal deformation. The study results can be used as the basis for shaking table test of seismic isolated continuous girder bridge with high damping rubber bearing and the reference for relative seismic isolated bridge design.