Lead-core Rubber Bearings Research Articles

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.

Analysis of seismic response of a large-scale isolated LNG tank considering dynamic soil-pile interaction

Seismic safety is a critical issue for liquefied natural gas (LNG) tanks. It is essential to investigate the effect of the isolation system on the seismic response of LNG tanks, considering dynamic soil-pile interaction, especially for tanks located in the deep soil site. This study aims to quantitatively evaluate the effects of isolation system (e.g., lead-core rubber bearings) on various aspects of a large LNG tank located on a deep soil site under horizontal bi-directional seismic action. Specifically, the evaluation includes outer tank acceleration, inner tank base shear, overturning moment, and pile force distribution. The findings demonstrate that the isolation system can effectively minimize the transfer of inertial interaction from the superstructure to the pile foundation, optimize the internal force distribution within the pile foundation, mitigate the pile group effect, and enhance the safety margin of the structure. Moreover, the isolation system can effectively suppress the transmission of seismic energy in medium and high frequencies, but amplify it in the low-frequency domain. Consequently, it is recommended that it is needed to avoid the site's natural frequency in the design of seismic isolation bearings for LNG tanks.

Study on the seismic mitigation effects of inerter isolated storage tanks

Liquefied Natural Gas (LNG) storage tanks can ensure national energy sufficiency, but they are vulnerable to earthquakes. Although ordinary seismic isolation bearings can effectively reduce the base shear force and overturning moment, they tend to amplify the height of the sloshing wave. In this paper, a hybrid vibration control method for LNG storage tanks is proposed, paralleling the series viscous mass damper (SVMD) devices with Lead-core rubber bearings (LRB). The seismic mitigation effects of this parallel seismic isolation scheme were investigated. First, three-dimensional finite element models of fixed base, LRB isolated and SVMD isolated tanks were established, and nonlinear time history analyses were performed for the three types of tanks to compare the seismic responses. It was concluded that SVMD can effectively control the sloshing wave height. In addition, the effects of site types, storage liquid heights, and SVMD's performance parameters on the seismic mitigation effects were also studied. It was found that the softer the site soil, the higher the storage liquid height would make seismic isolation less efficient. The increase of SVMD's additional equivalent mass reduces the sloshing wave height, increases the shear-to-weight ratio, and has little influence on the base displacement. The increase of SVMD's additional equivalent damping reduces the sloshing wave height, base shear force, and base displacement of the tank. The final conclusion is that SVMD can effectively control the sloshing wave height and has a good seismic mitigation effect.

Effects of Building Height and Seismic Load on the Optimal Performance of Base Isolation System

AbstractSeismic isolation has been widely accepted as one of the techniques that can be used to protect structures during earthquake ground motions. However, some challenges still exist such as the optimal control of excessive isolator shear strains imposed by some ground motions. The main purpose of this study was to assess the effects of building height variation and earthquake ground motion type on the optimal performance of the seismic isolation using lead core rubber bearing (LCRB). Nonlinear time history analysis for building models of various storeys isolated by LCRB and exposed to different real earthquakes was performed. To achieve this, the equations governing the motion of the isolated three different building models were presented, and an approach for solving the equations while taking into consideration of the optimized mechanical properties of the LCRB was developed. The LCRB performance was measured in terms of elastomer shear strains, derived after an optimal criterion leading to reliable substructure and superstructure responses was reached. The results showed that the combined effects of the earthquake type and building height significantly affect the substructure responses (maximum isolator displacement, energy dissipation capacity, maximum isolator force) and the superstructure responses (storey shear forces, storey drifts, floor displacements, and floor accelerations), which in some cases lead to a need for adding a fluid damper. In this regard, an attempt to couple the LCRB with nonlinear fluid viscous damper was made, and the performance of the hybrid was assessed. It was generally found that the hybrid can positively improve the substructure responses, thereby reducing the unwanted large elastomer shear strains without adversely affecting the superstructure responses.

Probability Distribution Characteristics of Horizontal and Vertical Mechanical Properties of Rubber Bearings.

Rubber bearings are widely used to protect civil structures from destructive earthquakes. The mechanical properties of the bearings are the key technical parameters that determine the seismic isolation performance of isolated structures. To estimate the probability distribution of the mechanical properties related to rubber bearings (including horizontal stiffness, vertical stiffness, post-yield stiffness and yield force) under seismic events. Typical natural rubber bearings (NRBs) and lead-core rubber bearings (LRBs) were designed and fabricated, and the bearings were subjected to repeated load tests using a compression-shear testing machine. The test results of the horizontal and vertical mechanical properties of the bearings in the tests were basically consistent with the design values, and the rubber bearings showed stable mechanical behavior under repeated cyclic loading. The statistical analysis of the test results revealed that the relevant mechanical properties of the NRB and LRB specimens followed a lognormal or general extreme distribution with coefficients of variation mainly ranging from 0.86% to 5.6%. The dispersion of the yield force of LRB was the largest in the repeated tests of many mechanical parameters of typical rubber bearings.

Seismic Response of a Large LNG Storage Tank Based on a Shaking Table Test

In order to study the dynamic response of the LNG storage tank under the action of seismic load and the seismic isolation effect of the lead-core rubber bearing, this paper establishes the experimental storage tank model with reference to the structural form of the large-scale LNG storage tank, and the seismic response of the test tank is obtained using a shaking table test. Simplified mechanical models of non-isolated and isolated storage tanks are proposed and the seismic responses of the corresponding storage tanks are calculated using the Newmark-beta method. Under the action of seismic waves with different acceleration peaks, the results show that (a) more excitation directions of the seismic wave can lead to the greater acceleration and displacement response of the tank and (b) the isolation bearing has a damping effect on the acceleration response of the storage tank, but it has an amplifying effect on the displacement of the storage tank. Comparing the results of the simplified model and the shaking table test, it is found that the change trend of the acceleration response of the experimental results and simplified mechanical models is the same. The spectral characteristic curve of them is not large, which verifies the effectiveness of the simplified model.

Rubber bearing isolator with granular and polymer filler core and application on a building

In the present study, a new core-and-filler system was proposed to use in elastomer bearings as a substitution to hazardous lead core while improving the performance of base isolators. The proposed system utilizes steel core and filler consists of either granular or polymer materials in relation to this proposal, both pure sand and epoxy are used as filler. Special design procedure for the proposed bearing was developed to determine the required dimension for elastomeric bearing under considered design loads according to the code of practice.The finite element model of the designed elastomeric bearing was developed to evaluate performance of the proposed bearings under design condition through nonlinear dynamic analysis. Then, parametric study was conducted to simulate various material properties and loading conditions that may occur during the manufacturing and service life of base isolation.Substantial improvement in performance of proposed bearing with core-and-filler system was observed in comparison to the lead rubber bearing. By reducing the volume of sand filler, the damping bearing of proposed sand and steel core mechanism can be improved. By manipulating the sand packing condition during manufacturing, improvement in term of effective stiffness is achievable. Trilinear constitutive curve for fully sand filled bearing revealed that, the increment in effective stiffness of bearing is higher for the shear strains more than 150%. Therefore, the core-and-filler system with full sand filler provides superior resistance against high shear strain in comparison to the lead-core rubber bearing, and achieve the purpose of limiting lateral displacement.Application of proposed elastomeric bearings in the 5-story building as base isolator has been proven the effectiveness and suitability of implementing bearing with core and fully filled sand and also with epoxy filler as alternative isolator to the lead core elastomer bearings.

Development of Elastomeric Rubber Bearing Utilizing Core-and-Filler System

Elastomeric bearing is the most common base isolation system for structures and bridges to dissipate effect of applied vibration and ground motion. To improve performance of the base isolators, lead core is implemented in the rubber bearings and it successfully enhances the damping and stiffness of elastomeric bearing.However, the most notable disadvantage of lead-core rubber bearing is the lead toxicity impact on extensive environmental contamination, which restrained application of lead in construction industry.Therefore, in the present study, an attempt has been made to develop a new elastomeric laminated bearing utilizing core-and-filler system instead of lead core to improve the performance of bearing. Two types of filler, namely granular and shape memory polymer are implemented. Granular filler is prepared by using silica sand, while shape memory polymer filler is prepared by using epoxy resin. Also, steel core is implemented to improve the stiffness of filler.The performance of proposed bearing utilizing with core-and-filler system is evaluated using finite element simulation. The numerical results revealed the efficiency of bearing with proposed system by providing considerable damping and stiffness. The replacement of lead core with fully filled granular and shape memory polymer showed improvement in terms of stiffness, and this proved core-and-filler system is effective in limiting lateral displacement.Also, the prototype of base isolation devices with both granular and shape memory polymer fillers are fabricated and tested via cyclic shear test. The results are compared with finite element analysis results, and good agreement between experimental tests results and numerical simulation response is shown. The experimental testing results proved that implementation of core-and-filler system improves the lateral resistance of proposed elastomeric bearing. In overall, it can be concluded that the implementation of core-and-filler system provides a reliable improvement to the performance of conventional elastomeric bearing and can be considered as alternative system to lead core rubber bearings.

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.

Seismic performance and effective isolation of a large multilayered underground subway station

In this paper, the seismic performance of a reinforced concrete (RC)-framed underground subway station structure which has three stories and three spans was analyzed firstly under strong earthquakes. It was found that the central columns in the top and the bottom stories were the weakest seismic components in this type of underground structure. Thus, lead-core rubber bearings (LRBs) were installed at the central column-tops of the structure, and the seismic performance of the underground station structure with LRBs was also studied. The results show that LRBs can reduce the seismic damage to the central columns and interior slabs and the lateral deformation of the central columns effectively. While the installation of LRBs will also change the internal force transfer characteristics and energy distribution of the large underground structure and increase the seismic damage to the top and bottom slabs and side walls to some extent. In particular, when LRBs were only set on the central column-tops in the top and bottom stories, which have the most unfavorable seismic performance in the underground structure, the seismic damage to the central columns without LRBs was significantly exacerbated. The isolation method of installing LRBs at the top of the central columns in each story was clearly superior and could ensure that the underground station structure would not collapse due to serious damage of the columns under strong earthquakes.

Assessing the three-dimensional seismic behavior of the multi-degree-of-freedom (MDOF) structure with LCRB and LRB control systems

The main objective of this study was to investigate the dynamic behavior of isolated structures with lead core rubber bearing (LCRB) and laminated rubber bearing (LRB) isolators under the influence of different earthquakes. First, a three-dimensional finite element model of the seismic isolator was created and analyzed using ABAQUS software based on a developed model. The hyper-viscoelastic properties were used for rubber layers in this modeling. Then, a 5-story base-isolated building on a laboratory scale was modeled on a well-verified isolator, which was once with core (LCRB) and then without the core (LRB). In this study, the isolation system was analyzed by dynamic explicit approach in ABAQUS and the behavior of the considered isolated building has been studied when subjected to Kobe, Northridge, and El Centro earthquakes. Finally, it was found that LCRB has a significant effect on reducing the amount of displacement and acceleration in the upper floors. However, it should be noted that the responses of the base-isolated building may unexpectedly appear reversely in some earthquakes and increase the responses.

Natural Rubber Bearing Incorporated with Steel Ring Damper (NRB-SRD)

The present paper is aimed to investigate the behavior of Natural Rubber Bearing incorporated with steel ring damper (NRB-SRD). These types of dampers are integrated of several steel rings which are considered with two configurations namely, continual steel ring damper and separate steel ring damper and are inserted between top and bottom plates. The performance characteristics of the system such as effective horizontal stiffness, energy dissipation, equivalent viscous damping and residual deformation are calculated and then compared with the results of high damping rubber bearings and also shape memory alloy (SMA)-lead core rubber bearing (SMA-LRB). The results show that the energy dissipation in steel rings are mainly based on plastic deformation due to flexural behavior of the rings. NRB-SRD shows better performance in energy dissipation comparing to SMA-LRB and HDRB. These additional dampers show higher stability and energy dissipation in low shear strains due to developing of link between structure and substructure having desirable initial stiffness under weak earthquakes and wind loads and also in higher shear strains due to creation of higher energy dissipation, stability and secondary stiffening.

Probabilistic Behavior Assessment of Base-Isolated Buildings and Base Isolation Systems Subjected to Various Earthquakes with Different Components

One of the greatest challenges of researchers is to understand the behavior of base isolation systems and base-isolated buildings under the conditions of different ground motions. The specific objective of this study is to evaluate the seismic response of multi-story base-isolated buildings with lead core rubber bearings (LCRBs) and buildings that are not isolated when subjected to different types of ground motions with different components. Under these conditions, the equations of motion of buildings with isolation systems are obtained, and LCRB force–deformation behavior is modeled as bilinear in MATLAB. Then, the behaviors of the base isolation system and base-isolated buildings are evaluated for 45 different earthquake scenarios, which are categorized into three different groups with regard to the ratio of peak ground acceleration to peak ground velocity (PGA/PGV). The dissipation of energy by a base isolation system, which is induced by the earthquake, varies for three different ranges of the PGA/PGV ratio. Despite the fact that by increasing the number of stories, the effectiveness of the isolator system decreases, this paper shows the most important finding to be that the damage limitation requirement is kept below 1% according to Eurocode 8, which is the requirement for buildings at the upper limit on the inter-story drift ratio under seismic loading, and the inter-story drifts significantly decreases for the base-isolated buildings and even for high-rise buildings.

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.

Natural Seismic Protection Properties of Historical “Walled Obelisk” Structure in Istanbul: Modeling-Numerical Approach

The “Walled Obelisk” is a 32.77-meter high, 2x2 meter mean square, rough-cut limestone monument that is becoming thinner to the four-sided hill. This monument is in a very sensitive seismic region of the World-Istanbul and remains intact from the time of its construction (approximately tenth century) to the present despite all seismic activity during that time. The current study extracts and investigates a mathematical model of the monument, which reveals that support of the structure incorporates a “natural seismic isolator” that demonstrates behavior similar to current used lead-core rubber-bearings isolator (LRB). The total height of the “natural seismic isolator” is 3.44 m. and consists of three–steps of rough-cut limestone and a massive marble stone that forms four sliding surfaces bonded with Horasan mortar. The components of the “natural seismic isolator” form four sliding surfaces and appear to function similar to LRB’s combined layers of steel plates and hard rubber. The massive marble stone appears to function like the lead cylinder core of the LRB. The “natural seismic isolator” demonstrates fully plastic behavior and differs from the LRB by maintaining the monument’s upper part in equilibrium during earthquake excitation, which also varies near zero equilibrium. During this study’s comparison of the isolator’s use of the expression, “similar” is frequent used in this meaning, and the comparison uses a fixed base model of the monument that cannot reciprocate during recovery from earthquakes over the 1000-year history. The proposed model of “natural seismic isolation” from historical experience (for this monument, 1000 years), suggests that the easily constructed natural isolator requires no special maintenance, and is suitable for modern structures in seismic regions.

Effect of a Near Fault on the Seismic Response of a Base-Isolated Structure with a Soft Storey

AbstractThis study focuses on the soft-storey behavior of RC structures with lead core rubber bearing (LRB) isolation systems under near and far-fault motions. Under near-fault ground motions, seismic isolation devices might perform poorly because of large isolator displacements caused by large velocity and displacement pulses associated with such strong motions. In this study, four different structural models have been designed to study the effect of soft-storey behavior under near-fault and far-fault motions. The seismic analysis for isolated reinforced concrete buildings is carried out using a nonlinear time history analysis method. Inter-story drifts, absolute acceleration, displacement, base shear forces, hysteretic loops and the distribution of plastic hinges are examined as a result of the analysis. These results show that the performance of a base isolated RC structure is more affected by increasing the height of a story under nearfault motion than under far-fault motion.

Sensitivity analysis on mechanical characteristics of lead-core steel-reinforced elastomeric bearings under cyclic loading

This research conducts a sensitivity analysis on the mechanical properties of lead core rubber bearings (LCRBs). Here, the input variables include: number of rubber layers, lead core radius and lead core material properties. A full factorial numerical experiment is designed and the hysteretic behaviour of a total of 81 LCRBs with varying parameters is captured through numerical simulation. The material models used in those models were first validated with experimental results from published literature. Operational characteristics of the studied bearings include: the vertical and horizontal stiffness, and the equivalent viscous damping ratio. An analysis of variances is then conducted in order to quantitatively express the effectiveness of each parameter. Among the three considered input variables, the lead core radius is the most dominant parameter in affecting LCRBs’ performance, whereas the number of rubber layers has the least contribution. It is observed that the lead core influences bearing’s vertical stiffness the most, compared to other input variables.

Comparing Seismic Performance of Steel Structures Equipped with Viscous Dampers and Lead Rubber Bearing Base Isolation under Near-Field Earthquake

In the present research, seismic behaviours of a steel frame equipped with either viscous damper or lead-core rubber bearings (LRB) isolator were evaluated and compared under the effect of near-fault earthquake records. For this purpose, three buildings of 5, 10, and 15 stories equipped with lateral bearing systems composed of steel moment-resisting frames were subjected to 7 near-fault earthquake accelerogram pairs at earthquake hazard levels 1 and 2, so as to evaluate their responses under three scenarios, namely without any energy dissipation system, with viscous damper, and with LRB isolator, using dynamic analysis of time history utilizing PERFORM 3D v5 software. The results were indicative of enhancement in seismic performance of the viscous damper-equipped structures at earthquake hazard level 1, as the corresponding performance level was enhanced from life safety to uninterrupted usability, while no significant seismic performance level enhancement was determined at seismic level 2. Seismic isolator-equipped structures were also associated with seismic performance level enhancement from life safety to uninterrupted usability at both earthquake hazard levels. Relative lateral displacement at floor levels in damper-equipped structures and seismic isolator-installed buildings were found to be about 29% and 68% improved over that of the structure with no energy dissipation system. Results of distribution of shear forces within structures equipped with viscous damper and seismic isolator, as compared against that of the structures with no energy dissipation system, indicted increased and decreased shear forces, respectively..

Soft-Story Effects on the Behavior of Fixed-Base and LRB Base-Isolated Reinforced Concrete Buildings

In Turkey, the entry stories of reinforced concrete (RC) structures are usually used for commercial purposes because they are slightly higher than other stories. Therefore, these RC structures sometimes exhibit what is called soft-story behavior. The best examples of this behavior are observed in the severe damage or collapse of RC structures with soft stories during the 1999 Marmara and Duzce earthquakes. To prevent this type of damage, seismic isolation systems can be used in the construction of new structures. This study focuses on the soft-story behavior of RC structures with fixed-base and lead core rubber bearing (LRB) systems under different seismic loads. The superstructure is modeled using the Turkish Seismic Regulation (TEC 2007). Because there is no detailed information concerning LRB isolators in the Turkish Seismic Regulations, the Uniform Building Code (UBC 97) is used to model the substructure system under consideration. In this study, four different structural models are designed to study the effect of the soft-story behavior. The dynamic analysis of the time domain on these frame systems is conducted using Ruaumoko software, and the influences of soft-story behavior in fixed-base and LRB base-isolated systems are investigated. The period of the frame system, story accelerations, inter-story drift ratio, base shear forces, and distribution of plastic hinges and their damage conditions are evaluated.

Seismic Performance of Base-Isolation Building Subjected to Near-Fault Ground Motion with Velocity Pulse

The seismic response of the base-isolated structure can be reduced significantly in the far-field region compared to the conventional seismic structure. However, near-fault ground motions with velocity pulse may cause the adverse influence on the seismic performance of the base-isolation building, which needs to be investigated deeply. In this paper 6 ground motions with velocity pulse are selected as the input, and the seismic response of a 9 layers conventional seismic RC frame building and comparative base-isolation building with lead-core rubber bearings are obtained by nonlinear time history analysis. The result indicates that base-isolation building with lead-core rubber bearings are of good aseismic performance under the near-fault ground motions with velocity pulse.