Lead-rubber Bearing Isolation Research Articles

Application of a Novel Optimization Algorithm in Design of Lead Rubber Bearing Isolation Systems for Seismic Rehabilitation of Building Structures

Various mechanical and geometrical parameters have different effects on the isolation system's performance. Thus, a sensitivity study of the isolated structures' behavior is an essential matter. In this regard, the isolation systems should be designed using optimization approaches to consider the effects of the different factors. In this study, the optimal design of the lead rubber bearing (LRB) seismic isolation was conducted by considering mass irregularity and near-fault seismic excitation effects. Also, sensitivity analysis of the behavior of the considered isolated buildings was implemented concerning the mechanical parameters of the LRB system. A nonlinear time history dynamic analysis was used here, and the design optimization of the LRB isolator was programmed using the newly introduced grasshopper optimization algorithm (GOA). The main purpose was to investigate the ability of the GOA to optimize the design parameters of the LRB-isolated frames. The results proved the desirable ability of the GOA to solve optimal design problems for isolation systems. Also, the sensitivity analysis of the seismic behavior of LRB base-isolated structures showed that the yield base shear index had the most important effects. Also, the mass irregularity parameter showed a negligible influence.

Optimum arrangement investigation of LRB and FPS isolators for seismic response control in irregular buildings

The objective of a base isolation system is to decouple the building from the damaging components of the earthquake by placing isolators between the superstructure and the foundation. In this paper, an optimum arrangement of lead rubber bearing (LRB) and friction pendulum system (FPS) is investigated in irregular buildings, and its performance is compared with a regular case. For this purpose, 3 types of irregularities according to ASCE/SEI 7–16 and 3 types of story buildings have been performed. Accordingly, various possible combinations have been applied for the isolators in each model. Afterward, the numerical models have been analyzed using nonlinear time-history analysis. The obtained results show that the application of FPS and LRB isolators in outer and inner columns led to better performance compared to the other arrangements. In this configuration, the inter-story drifts and base shear are reduced, and also the energy dissipation is increased more than in other arrangements. The reason for the superiority of the selected combination is due to the characteristics of FPS isolators in balancing the applied forces with the building’s mass and preventing torsion occurrence in irregular structures. Unlike the irregular buildings, the application of FPS and LRB isolators in inner and outer columns, result in better performance by reducing the story drifts in regular structures.

Vibration Response Reduction of Seismic Forces Using Lead Rubber Bearing Isolators in Composite Buildings

Vibration Response Reduction of Seismic Forces Using Lead Rubber Bearing Isolators in Composite Buildings

Experimental and numerical investigations on hysteretic response of a multi-level SMA/lead rubber bearing seismic isolation system

This study investigates the response of a shape memory alloy (SMA)-based isolation system that combines multiple groups of SMA cables and a lead rubber bearing (LRB). The isolation device, named as multi-level SMA/lead rubber bearing (ML-SLRB), is designed such that it maintains its efficiency under frequent, design and extreme levels of seismic events. Two large-size ML-SLRB isolation devices were designed and fabricated. The response of the proposed isolation systems was evaluated together with a conventional LRB under increasing amplitudes of cyclic loads. The effects of loading rate and vertical pressure on the response of the ML-SLRB isolator were evaluated. Finite element models of the fabricated ML-SLRB isolators were developed and analyzed to assess the response of the different SMA cable groups at different stages of the loading. The test results, supported by the finite element analyses, revealed that the SMA cable groups used in a loop configuration in the ML-SLRB isolator are prone to stress concentrations and early damage. The ML-SLRB isolators that employed its main SMA cable groups in a straight configuration successfully achieved a multi-level performance where the stiffness of the isolator increased as the demands of the displacement increased. The developed isolator also exhibited lower residual drifts compared to the LRB isolator.

A multi-hazard-based design approach for LRB isolation systemagainst explosion and earthquake

Base isolation system is originally known as one of the most efficient earthquake-resistance control systems. Isolated strategic structures may also experience terrorist attacks during their lifetime. In this paper, a design method is proposed for lead rubber bearing (LRB) isolation system under multi-hazard of explosion and seismic. This method is based on transforming the design problem into an optimization problem. The seismic response of structure has been defined as objective function while the constraints have been applied on its blast response. To validate the effectiveness of the proposed design method, LRB is designed for controlling a four-story steel moment-resisting building. For comparison objectives, this control system has been also designed under seismic hazard without paying attention to its blast performance. The results show that the earthquake-based optimally designed LRB has effective performance under seismic hazard whereas its blast performance is not as good as its seismic performance. Therefore, this control system cannot be considered as a well-designed control system for multi-hazard. The multi-hazard-based optimally designed LRB shows excellent performance under both blast and seismic loadings, so the proposed design method can be introduced as an effective design approach for LRB under multi-hazard of explosion and seismic.

The Behavior of Elevated Water Tanks under Impact Loading

Because of the crucial role of elevated water tanks and their various uses, it is necessary to evaluate their structural behavior under threats to improve the durability performance of such tanks without putting them in jeopardy. In the present research, three open cylindrical concrete water tanks were modeled under an impact load (aerial blast) with the weight of 100 kg TNT explosive charge. The tanks were modeled in 3 forms: slender, middle, and broad (Aspect ratio = 1.28,1 and 0.85). Each tank contained various levels of water (non-water, half water, and full water) to estimate their structural behavior under blast loading. Moreover, the CEL (Coupled Eulerian-Lagrangian) approach was used to simulate water structure interaction in finite element program. For a comprehensive analysis of the structural behavior of water tanks, LRB (Lead rubber bearing) isolator device was also used to observe the effect of isolator under blast loading on elevated water tanks in all models. The results of this study show that the water level leads to stiffness of the structures that cause better performance under blast loading and also the intersection of the shaft and concrete column would be the critical section of this structure under blast loading. It is also concluded that Stress and Strain decrease as the water tanks level increase and stiffen (up to 33 %). Also, it is noticeable that the existence of the isolator has deteriorated the results because of the decreases in the structure’s stiffness and the increase of the displacements.

Life-cycle cost based design of bridge lead-rubber isolators in seismic regions

While rubber isolators are widely used for the seismic protection of bridges, their influence on the total life-cycle costs (TLCC) is generally neglected. This study aims to provide a framework to obtain the most cost-effective design solutions of Lead-Rubber Bearing (LRB) isolators for minimum objective functions based on the life-cycle cost of bridges. Also, a comprehensive analytical study is conducted to assess the effects of LRB characteristics on the total life-cycle costs (TLCC) consisting of the initial costs of LRB isolators and structural elements, traffic damage costs, and structural and non-structural damage costs due to possible earthquake events during the bridge life-span. While changing the lead core diameter, confined diameter, and the total thickness of the rubber layers could influence the TLCC of the bridges, the effect of lead core diameter is shown to be more significant. By using lead core diameter as the main design parameter, increasing the initial cost of LRBs up to a certain level can significantly reduce (up to 38%) TLCC of the bridges. However, beyond this limit, the TLCC may increase. Based on the results of over 13,000 Reinforced Concrete (RC) bridges under different earthquake hazard levels, the best design solutions are identified for different design objectives. The results of this study should prove the benefit of the proposed method for a more efficient design of bridges with lower TLCC.

Investigating the Performance of Isolation Systems in Improving the Seismic Behavior of Urban Bridges. A Case Study on the Hesarak Bridge

AbstractThis paper investigates the influence of isolation systems on the seismic behavior of urban reinforce concrete bridge. The performance of the Hesarak Bridge constructed in Karaj city, Iran with two isolation systems; i.e. the existing elastomeric rubber bearing (ERB) and a proposed lead rubber bearing (LRB) is discussed. The numerical model was implemented in the well-known FEM software CSIBridge. The isolated bridge has been analyzed using nonlinear time history analysis method with seven pairs of earthquake records and the results are compared for the two isolation systems. The LRB isolators are shown to have superior seismic performance in comparison with the existing ERB systems based on the response evaluation including force on the isolator, pier base shear, deck acceleration, bending moment, pier displacement, and energy dissipation.

Effect of Building Height on Torsional Rotation of Base Isolated Structures

The effect of height variation of a base isolated building on torsional response has been studied in the paper Also response of lead rubber and friction pendulum base isolator on torsional rotation has been compared. For the study, building rests on friction pendulum system (FPS) and lead rubber bearing (LRB) has been considered. The height of the building is varied successively and subjected to bi-directional seismic excitation. The torsional response of isolated structure is studied for each increment in the storey height for both LRB and FPS isolators and compared with fixed base structure. The result indicates that, base isolated structures reduces torsional rotation. It is also found that torsional rotation for buildings of ten to fifteen stores have significant reduction compared to other models considered in present study. Beyond this, the effectiveness reduces. It is also observed that FPS base isolator has effectively reduced torsional rotation when compared to LRB.

Potential Design of Seismic Vulnerable Buildings Incorporating Lead Rubber Bearing

The seismic hazard of vulnerable regions warrants the investigation of new technologies, such as base level isolation by lead rubber bearing (LRB) devices, that can help to mitigate structural damage on seismic prone buildings. The behavior adopting such technologies can be dynamically observed in simulated environments and thus serves as a valuable metric for their feasibility. LRB base isolators were incorporated into the design of 16 model buildings to better understand how they affected a building’s seismic response while also providing information on the structural parameters. A total of 12 different types of bearing systems were tested in base isolated (BI) buildings against conventional fixed-base (FB) isolated buildings. The system of each model high-rise building was represented by the finite element package. Static as well as dynamic analysis were conducted using response spectrum analysis (RSA) based on the seismic excitation to determine the influence of the model type in the aseismic design and the alteration in superstructure behavior. The study reveals that the LRB isolators can potentially diminish respective story accelerations, story inertia, and base shear. Use of LRB isolators in BI buildings resulted in a 10–20% reduction in base shear compared to FB buildings. A notable lateral shift of superstructure is offered by LRB-induced flexibility. The reduction of story acceleration for response spectrum varies 30% on lower stories up to 70% on upper stories. The LRB systems with higher characteristic strength and relatively less isolation periods shows better productivity to minimize displacements in the bearing face for dropping structural shift. However, the LRB with comparatively lower characteristic strength and high isolation periods shows the most efficiency in controlling base shear, offering least story accelerations and consenting lower story inertia forces.

Response modification factors of concrete bridges with different bearing conditions

One of the shortcomings of seismic bridge design codes is the lack of clarity in defining the role of different seismic isolation systems with linear or nonlinear behavior in terms of R-factor. For example, based on AASHTO guide specifications for seismic isolation design, R-factor for all substructure elements of isolated bridges should be half of those expressed in the AASHTO standard specifications for highway bridges (i.e., R=3 for single columns and R=5 for multiple column bent) but not less than 1.50. However, no distinction is made between two commonly used types of seismic isolation devices, i.e., elastomeric rubber bearing (ERB) with linear behavior, and lead rubber bearing (LRB) with nonlinear behavior. In this paper, five existing bridges located in Iran with two types of deck-pier connection including ERB and LRB isolators, and two bridge models with monolithic deck-pier connection are developed and their R-factor values are assessed based on the Uang\'s method. The average R-factors for the bridges with ERB isolators are calculated as 3.89 and 4.91 in the longitudinal and transverse directions, respectively, which are not in consonance with the AASHTO guide specifications for seismic isolation design (i.e., R=3/2=1.5 for the longitudinal direction and R=5/2=2.5 for the transverse direction). This is a clear indicator that the code-prescribed Rfactors are conservative for typical bridges with ERB isolators. Also for the bridges with LRB isolators, the average computed Rfactors equal 1.652 and 2.232 in the longitudinal and transverse directions, respectively, which are in a good agreement with the code-specified R-factor values. Moreover, in the bridges with monolithic deck-pier connection, the average R-factor in the longitudinal direction is obtained as 2.92 which is close to the specified R-factor in the bridge design codes (i.e., 3), and in the transverse direction is obtained as 2.41 which is about half of the corresponding R-factor value in the specifications (i.e., 5).

3D-Finite element modeling of lead rubber bearing using high damping material

Lead Rubber Bearing (LRB) has been widely applied for seismic protection of mid and high-rise buildings around the world. Its excellent energy dissipation becomes the most important aspect of this isolation system thanks to the plasticity and recovery behavior of the lead core. Aiming to develop a deeper knowledge on the behavior of LRB’s, a 3D detailed finite element (FE) modeling is performed in Abaqus FE software. Some important parameters involved in the model are plasticity of the lead core and hyper-elasticity and viscosity of the rubber material. The parameters for rubber material are derived from the results of experimental works in the laboratory, including uniaxial tensile test and relaxation test. The bearing model is then subjected to a cyclic shear-test under constant vertical load. The result of the 3D-FE model is then compared with the analytic-Abaqus model for LRB isolators, developed in the literature. Finally, both 3D-FE model and analytic model result in a good agreement on the shear behaviour of the presented LRB.

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>

Seismic response variation of multistory base-isolated buildings applying lead rubber bearings

The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

English

English

Seismic analysis and parametric study of SDOF lead-rubber bearing (LRB) isolation systems with recentering shape memory alloy (SMA) bending bars

Base isolation has been considered one of aseismic design methodologies based on belief that it is feasible to separate the superstructure from the supporting ground, thereby preserving structural members and their internal contents from damage caused by earthquake motions. Although remarkable progress was achieved in this isolation technique towards the end of the century, a number of catastrophic building failures are still found where earthquake with severe ground motion attacked. In particular, high-rise buildings that have been currently constructed in urban area are very vulnerable when exposed to such impulsive events, and thus large relative displacement occurs at the isolator interface. The obstacles in or in the vicinity of the isolator interface destroy seismic performance. In this study, the innovative isolation systems incorporated with superelastic Shape memory alloy (SMA) bars functioning as seismic restrainers are suggested in order to more effectively maintain structural integrity. The superelastic SMA bending bars supply recentering force to the base isolator that accordingly makes a significant contribution to reducing permanent deformation over entire structure. The base Lead-rubber bearing (LRB) isolators with superelastic SMA bars are considered as inelastic behavior reproduced by component spring elements. The response of the proposed base isolators are compared with those of the conventional LRB isolators. Through the observation of the analysis results, it can be concluded that recentering LRB isolators create the improvement of seismic performance in terms of strength, energy dissipation and recentering effect.

Improving the Seismic Behavior of Symmetrical Steel Structures Under Near-Field Earthquake Using a Base Isolation Method Lead Rubber Bearing Isolator

<p>In this study, the function and application of seismic isolation system through lead rubber bearing isolator (LRB) in near-fault earthquakes are compared with fixed-base structures. As a result of their high frequency content, near-fault earthquakes impose huge energy on structures and cause severe damages. One of the appropriate solutions for this issue is the use of LRB which decreases the amount of imposed energy on structures. To improve the function of isolated structures under the near-fault earthquakes, isolators are designed in a way to tolerate the vertical component of earthquakes. To this purpose, we limit the displacements due to the horizontal movements of isolator through Gap spring which acts as a retaining wall and prevent shocks to other buildings. Moreover, this approach decreases the vertical movements of isolators and indirectly improves their behavior. In the current study, three buildings with four, eight, and 12 floors (with and without gap spring) were included. Isolators were manually designed in accordance with AASHTO-LRB regulations and the behaviors of both isolators and buildings are considered non-linear. Then we analyzed and compared the amount of energy, displacement, and acceleration of structure at the center of roof. The results indicated a significant decrease in the results of base shear, the acceleration of roof center, floors drift and energy imposed on the structure in the isolated system in comparison with the fixed-base structure.</p>

Seismic Response and Performance Evaluation of Self-Centering LRB Isolators Installed on the CBF Building under NF Ground Motions

This paper mainly treats the seismic behavior of lead-rubber bearing (LRB) isolation systems with superealstic shape memory alloy (SMA) bending bars functioning as damper and self-centering devices. The conventional LRB isolators that are usually installed at the column bases supply extra flexibility to the centrically braced frame (CBF) building with a view to elongate its vibration period, and thus make a contribution to mitigating seismic acceleration transferred from ground to structure. However, these base isolation systems are somehow susceptible to shear failure due to the lack of lateral resistance. In the construction site, they have been used to be integrated with displacement control dampers additionally withstanding lateral seismic forces. For this motivation, LRB isolation systems equipped with superelastic SMA bending bars, which possess not only excellent energy dissipation but also outstanding recentering capability, are proposed in this study. These reinforced and recentering LRB base isolators are modeled as nonlinear component springs, and then assigned into the bases of 2D frame models used for numerical simulation. Their seismic performance and capacity in the base-isolated frame building can be evaluated through nonlinear dynamic analyses conducted with historic ground motion data. After comparative study with analyses results, it is clearly shown that 2D frame models with proposed LRB isolators generally have smaller maximum displacements than those with conventional LRB isolators. Furthermore, the LRB isolation systems with superelastic SMA bending bars effectively reduce residual displacement as compared to those with steel bending bars because they provide more flexibility and recentering force to the entire building structure.

Response of Seismically Isolated Steel Frame Buildings with Sustainable Lead-Rubber Bearing (LRB) Isolator Devices Subjected to Near-Fault (NF) Ground Motions

Base isolation has been used as one of the most wildly accepted seismic protection systems that should substantially dissociate a superstructure from its substructure resting on a shaking ground, thereby sustainably preserving entire structures against earthquake forces as well as inside non-structural integrities. Base isolation devices can operate very effectively against near-fault (NF) ground motions with large velocity pulses and permanent ground displacements. In this study, comparative advantages for using lead-rubber bearing (LRB) isolation systems are mainly investigated by performing nonlinear dynamic time-history analyses with NF ground motions. The seismic responses with respects to base shears and inter-story drifts are compared according to the installation of LRB isolation systems in the frame building. The main function of the base LRB isolator is to extend the period of structural vibration by increasing lateral flexibility in the frame structure, and thus ground accelerations transferred into the superstructure can dramatically decrease. Therefore, these base isolation systems are able to achieve notable mitigation in the base shear. In addition, they make a significant contribution to reducing inter-story drifts distributed over the upper floors. Finally, the fact that seismic performance can be improved by installing isolation devices in the frame structure is emphasized herein through the results of nonlinear dynamic analyses.

Multi-objective fuzzy control of smart base isolated spatial structure

Base isolation systems are used widely to reduce the dynamic responses of structures subjected to a seismic load. Recently, research has been conducted actively on smart base isolation systems that can effectively reduce the dynamic responses of isolated structures without accompanying increases in the base drifts. On the other hand, control performance of smart base isolation systems for spatial structures has not attracted significant attention. This study examined the dynamic response reduction capacity of a smart base isolation system for a spatial structure subjected to seismic excitation. MR dampers and low damping elastomeric bearings were used to compose a smart base isolation system, and its vibration control performance was compared with that of the optimally-designed, lead-rubber bearing (LRB) isolation system. A fuzzy controller was used to effectively control the spatial structure with a smart base isolation system. The dynamic responses of the spatial structure with an isolation system conflicted with the base drift. Therefore, these two responses were selected as the objective functions to apply a multi-objective genetic algorithm to optimize a fuzzy controller. The numerical simulation results showed that the smart base isolation system proposed in this study can reduce drastically the base drifts and seismic responses of the example spatial structure compared to the optimally designed LRB isolation system.