Lead Rubber Bearing System 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.

Lead-rubber-bearing with negative stiffness springs (LRB-NS) for base-isolation seismic design of resilient bridges: A theoretical feasibility study

Advanced seismic isolation devices and systems have been recognized as promising measures toward resilient design of bridge structures. This paper proposes a base isolation system using lead rubber bearing with negative stiffness springs (LRB-NS), which is composed of traditional lead rubber bearing (LRB) and pre-compressed springs, installed at the bottom of bridge columns. These springs contain dual functionalities: (1) provide negative stiffness (NS) and negative restoring force during slight shakings and elongate the structural period that is determined by LRB products; and (2) offer significant restoring forces to prohibit excessive peak deformation and protect bearings from failure when subjected to strong earthquakes. Theoretical and analytical studies are first conducted to illustrate fundamental mechanics of the proposed LRB-NS device, followed by a series of parametric analyses to understand the influential factors of this device on structural behavior. Moreover, fragility analyses of typical highway bridges are conducted to demonstrate the feasibility of LRB-NS device via comparisons with non-isolated and traditional LRB systems. The results show that the LRB-NS device can be well designed to mitigate seismic demands of bridge columns, as well as highly effective to suppress the excessive deformation in bearings that often occurs in the traditional LRB system under strong excitations. The LRB-NS device can be used to facilitate the resilient seismic design of bridge structures.

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

A study on seismic isolation of building used LRB

Base isolation system with lead rubber bearing (LRB) is commonly used to prevent structure against to damage of earthquake. Design of LRB system is detailed in this study. The isolated building with LRB design according to Uniform Building Code (UBC-97) and fixed building were examined. The six-storey building with LRB and fixed building were modelled in SAP2000 with the same dynamic loads. The relative floor displacement and internal forces of the seismic isolated and fixed building are compared. In addition, transverse and longitudinal reinforcement of any axis of seismic isolated and fixed building are compared. Analyse results showed that effectiveness of using seismic isolation system on building. The weight of longitudinal and transverse reinforcement of isolated building is smaller than fixed building about 36%, 40% respectively.

An efficient approach for LCC-based optimum design of lead-rubber base isolation system via FFD and analysis of variance (ANOVA)

A framework for optimal design of lead rubber bearing (LRB) system is introduced based on the initial and life cycle cost of structures. The purpose of this framework is to minimize the initial and life cycle cost of building and simultaneously improve the seismic performance of the base isolated structure. Endurance time (ET) method is used to predict the seismic response of the building at continuous levels of hazard intensity. Before implementing the optimization process, a full factorial design is utilized, and the seismic performance of a total of 128 lead rubber base isolated structures with varying LRB design parameters is assessed using the ET analysis method. Accordingly, the parameters with the most significant impact on the responses are determined by the analysis of variance. These parameters are used as design variables in a multi-objective genetic algorithm to minimize the initial and life cycle cost of the building with LRB system. The cost analysis of the system requires evaluation of initial costs including the costs associated with the implementation of LRBs. To date, no appropriate cost model has been proposed for LRB systems in the literature; therefore, a simplified cost model for LRBs is developed. Also, a life cycle cost model is used to evaluate the structural performance in the form of economic measures based on the results obtained from the ET analysis. In order to illustrate the method, a prototype six-story building is studied here. According to the results, the proposed approach is found to be effective in reducing the initial and life cycle cost of the building with an acceptable amount of computational effort.

A combined control strategy using tuned liquid dampers to reduce displacement demands of base-isolated structures: a probabilistic approach

This paper investigates a hybrid structural control system using tuned liquid dampers (TLDs) and lead-rubber bearing (LRB) systems for mitigating earthquake-induced vibrations. Furthermore, a new approach for taking into account the uncertainties associated with the steel shear buildings is proposed. In the proposed approach, the probabilistic distributions of the stiffness and yield properties of stories of a set of reference steel moment frame structures are derived through Monte-Carlo sampling. The approach is applied to steel shear buildings isolated with LRB systems. The base isolation systems are designed for different target base displacements by minimizing a relative performance index using Genetic Algorithm. Thereafter, the base-isolated structures are equipped with TLDs and a combination of the base and TLD properties is sought by which the maximum reduction occurs in the base displacement without compromising the performance of the system. In addition, the effects of TLD properties on the performance of the system are studied through a parametric study. Based on the analyses results, the base displacement can be reduced 23% by average, however, the maximum reduction can go beyond 30%.

Reliability-based design of steel moment frame structures isolated by lead-rubber bearing systems

This paper puts forward a reliability-based approach to seismic design of steel moment frame structures isolated with lead-rubber bearing (LRB) devices. The system is modeled as an equivalent two-degree-of-freedom system in which the superstructure is assumed to remain elastic, while a bilinear behavior is assigned to the isolation level. Furthermore, the uncertainties associated with the superstructure properties including mass and stiffness are taken into account by adopting appropriate probability density functions. To design the base-isolated structure, the paper proposes “reliability curves” that given a target reliability, return the two key design parameters: the natural period of the super-structure and the target base displacement. Given these two key parameters, the paper proposes a regression equation that predicts the optimal design variables of the base-isolation system, i.e., the initial stiffness and the yield force. This equation is calibrated against a set of optimally-designed base-isolated systems using the genetic algorithm. The proposed approach is showcased for an example steel moment frame structure located in Los Angeles, California.

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.

Seismic reliability-based design of inelastic base-isolated structures with lead-rubber bearing systems

In this paper, a seismic reliability-based approach is proposed to design inelastic steel moment frame structures isolated by lead-rubber bearing (LRB) systems. An equivalent two-degree-of-freedom system is assumed in which a bilinear behaviour is assigned to both the superstructure and the base. Furthermore, uncertainties associated with the equivalent superstructure mass, stiffness, and yield properties are taken into account by employing proper probability density functions. The proposed design approach is twofold: 1) Reliability curves that return the key design parameters of the inelastic base-isolated structure including: the period of the superstructure, the target base displacement, and the ductility-dependent strength reduction factor for a given target reliability. 2) Regression equations, which estimate the displacement ductility demand of the inelastic superstructure and the optimal design properties of the lead-rubber bearing system including: the total initial stiffness and the total yield force. These regression equations are calibrated against a large set of optimally-designed base-isolated buildings using Genetic Algorithm.

The effects of lead rubber bearing (LRB) systems on the earthquake response of high-rise building

The base isolation systems set sight on mitigating the effects of forces triggered by an earthquake through neutralizing the interaction between building and ground by means of earthquake isolators. This study aims to determine the effects of base isolation systems on the earthquake response of a high-rise building. In the content of the study firstly the high-rise building is designed for different sized isolators under the framework of earthquake isolator technique, and then scrutinize the earthquake response of the same building by comparing its configurations equipped with different sized isolators and fixed support. The building has 122.5 m tall and 35 stories and 16´20 m2 habitable inner space, which is properly considered in line with vertical settlement movement widely seen in the world metropolises, is punctiliously designed and diffusively probed within the concept of fixed support. During the following stage, 2 different diameter size of 21 cm. tall lead rubber bearings are added to the structure, its unpredictable behaviors and forces transferredto the building under 1999 Kocaeli Earthquake highlighted from the study that LRB systems provide better structural response to building compared to fixed system, and then the critical parameters such as acceleration, lateral displacements, base and shear forces are compared with each other. Figs.: 9. Refs.: 13 titles.Keywords: base isolation; lead rubber bearing system; earthquake response; high-rise building.

English

English

Optimum design of lead-rubber bearing system with uncertainty parameters

In this study, a non-stationary random earthquake Clough-Penzien model is used to describe earthquake ground motion. Using stochastic direct integration in combination with an equivalent linear method, a solution is established to describe the non-stationary response of lead-rubber bearing (LRB) system to a stochastic earthquake. Two parameters are used to develop an optimization method for bearing design: the post-yielding stiffness and the normalized yield strength of the isolation bearing. Using the minimization of the maximum energy response level of the upper structure subjected to an earthquake as an objective function, and with the constraints that the bearing failure probability is no more than 5% and the second shape factor of the bearing is less than 5, a calculation method for the two optimal design parameters is presented. In this optimization process, the radial basis function (RBF) response surface was applied, instead of the implicit objective function and constraints, and a sequential quadratic programming (SQP) algorithm was used to solve the optimization problems. By considering the uncertainties of the structural parameters and seismic ground motion input parameters for the optimization of the bearing design, convex set models (such as the interval model and ellipsoidal model) are used to describe the uncertainty parameters. Subsequently, the optimal bearing design parameters were expanded at their median values into first-order Taylor series expansions, and then, the Lagrange multipliers method was used to determine the upper and lower boundaries of the parameters. Moreover, using a calculation example, the impacts of site soil parameters, such as input peak ground acceleration, bearing diameter and rubber shore hardness on the optimization parameters, are investigated.

Optimum Design of Lead-Rubber Bearing System Under the Non-Stationary Random Earthquake Ground Motion

Optimum Design of Lead-Rubber Bearing System Under the Non-Stationary Random Earthquake Ground Motion

Seismic Behaviour Of Base Isolation System Using Lead Rubber Bearing

Nowadays the main cause of damage of reinforced concrete frames in the countries which are located on the seismic line area is earthquake even though they are designed due to the enactment of seismic codes. To provide a solution to these problems, Lead Rubber Bearing (LRB) system has been utilized in the construction of the buildings. Hence, the objective of this study is to determine the best configuration of the LRB in the structure by calculating the response of the structure, roof level acceleration and inter-story displacement based on the ground motion records. The study consists of determining the structure, calculating the weight of structure, modelling the LRB in the structure and obtaining the output from the dynamic analyses. The comparison of the inter-story displacement, drifts frames and top level acceleration response of the LRB system with the Fixed Base System (FBS) using spectrum and time history analysis shows that the base shear reduces by 65–75% in response spectrum analysis, while in time history analysis base shear reduces by 75–85%. The proposed method is based on the LRB system that reduces the response of the structure because of high damping and stiffness used in the Base Isolation System (BIS) and capable to be used for super structure located in the seismic line area. This system would help in reducing the cost in the long time and increase the safety of the structure.Â

A Novel Seismic Base Isolation System Consisting of a Lead Rubber Bearing in Series with a Friction Slider. Part II: Application to a Multi-Storey RC Building and Comparison with Traditional Systems

In a parallel paper a new High Damping Hybrid Seismic Isolator (HDHSI) has been proposed and obtained by the assembly in series of a Lead Rubber Bearing (LRB) and a Friction Slider (FS) characterized by a high friction coefficient. In the present paper, within the context of seismic base isolation techniques for the earthquake resistance of Reinforced Concrete (RC) buildings, a multi-storey RC building is analyzed as base isolated by the seismic isolator HDHSI (High Damping Hybrid Seismic Isolator). The seismic response of this base isolated RC building is compared with the seismic response of the same structure isolated by a LRB (Lead Rubber Bearing) isolator. The analysis is developed by considering different seismic events in terms of intensity and in terms of frequency content with regard to a supervening collapse. The purpose of this comparative analysis is to highlight the features offered by the HDHSI system compared to the LRB system in the seismic protection of structures. Accordingly, a nonlinear dynamic analysis is performed for a RC structure base isolated by means of the proposed device. In the analysis anomalous seismic events are considered. They are the El Centro earthquake (N00W component, 1940) which is characterized by high intensity and the Erzincan earthquake (N90W component, 1992) which is characterized by anomalous frequency content. The comparison between the two base isolation systems is presented by analyzing the time history of the shear force and the time history of the displacement at the base of the superstructure. The benefits of the HDHSI system in conferring protection to the structure are shown to be significant even under extreme seismic events.

A Comparative Study on the Seismic Performance of Superelastic-Friction Base Isolators against Near-Field Earthquakes

This paper presents a comparative seismic performance assessment of super-elastic-friction base isolator (S-FBI) systems in improving the response of bridges under near-field earthquakes. The S-FBI system consists of a steel-Teflon sliding bearing and a superelastic shape memory alloy (SMA) device. The other isolation systems considered here are lead rubber bearing (LRB), friction pendulum system (FPS), and resilient-friction base isolator (R-FBI). Each isolation system is designed to provide the same isolation period and characteristic strength. Nonlinear time-history analyses of an isolated bridge are performed to compare the performance of various isolation systems. The results indicate that the S-FBI system shows superior performance in reducing deck displacement response and effectively limits permanent bearing deformation, whereas residual deformations are present for the other isolation systems in some cases. It is also observed that the LRB system has the largest deck drifts while the FPS system and R-FBI system produce the smallest peak deck acceleration and base shear.

Performance of Base Isolators and Tuned Mass Dampers in Vibration Control of a Multistoried Building

Earthquakes create vibrations on the ground that are translated into dynamic loads which cause the ground and anything attached to it to vibrate in a complex manner and cause damage to buildings and other structures. Civil engineering is continuously improving ways to cope with this inherent phenomenon. Conventional strategies of strengthening the system consume more materials and energy. Moreover, higher masses lead to higher seismic forces. Alternative strategies such as passive control systems are found to be effective in reducing the seismic and other dynamic effects on civil engineering structures. The present paper focuses on the performance evaluation of a few passive control systems such as base isolation systems and tuned mass dampers in the vibration control of a linear multi storied structure under harmonic and earthquake base motions. Base isolators such as Lead Rubber Bearing (LRB) system and Friction Pendulum System (FPS); and, a tuned mass damper (TMD) are designed for a ten storied reinforced concrete building. The building is modelled as a 10 degrees of freedom shear building model and Bouc Wen model is used to describe the hysteretic behaviour of base isolators. The performance of LRB system, FPS and TMD are evaluated numerically and compared. The frequency response characteristics of the systems are also studied.

Full-scale pseudo-dynamic test for bridge retrofitted with seismic isolations

The authors examine retrofitted bridge pier performance with a seismic isolation present. Retrofitted bridge seismic performance experimental validation was done through fabrication and testing of four full-scale reinforced concrete bridge piers with fixed support conditions. To simulate the superstructure dead load, a static vertical load was applied to the bearing top and several different bearing systems were installed. Conventional pot bearing was also considered in addition to lead rubber bearing (LRB) and rubber bearing (RB) systems. To simulate earthquake loading, a horizontal loading was applied to the specimen using a pseudo-dynamic testing method. Isolated RB and LRB system specimen seismic response was compared to that of the conventional pot bearing specimen. That the seismic isolation system this study considers is effective in magnitude reduction of transferred substructure forces and period bridge shifting is shown in the results. The peak acceleration transmitted to the structure can be effectively reduced by the LRB structure, which under earthquake loading is less than those with RB system. That the proposed seismic retrofit method was found to be valid can be concluded through the test results.

“Smart” Base Isolation Systems

A base isolation system (SBIS) is proposed and shown to effectively protect structures against extreme earthquakes without sacrificing performance during the more frequent, moderate seismic events. The proposed SBIS is composed of conventional low-damping elastomeric bearings and controllable (semiactive) dampers, such as magnetorheological fluid dampers. To demonstrate the advantages of this approach, the SBIS is compared to lead-rubber bearing isolation systems. The effectiveness of the isolation approaches are judged based on computed responses to several historical earthquakes scaled to various magnitudes. The limited performance of passive systems is revealed and the potential advantages of smart dampers are shown. Two- and 6-degree-of-freedom models of a base-isolated structure are used as a test bed in this study. Smart isolation is shown to achieve notable decreases in base drifts over comparable passive systems with no accompanying increase in base shears or in accelerations imparted to the superstructure. In contrast to passive lead-rubber bearing systems, the adaptable nature of the SBIS provides good protection to both the structure and its contents over a wide range of ground motions and magnitudes.

Recent research and applications of seismic isolation in New Zealand

In New Zealand, seismic isolation, the technique in which the structure is decoupled from earthquake-induced ground motions, has now advanced to the point where it is often considered for the protection of both new and existing buildings, bridges, and to a lesser extent, industrial plant.
 Many of the devices used in these applications have been developed in our laboratory. We describe here how the lead-based devices operate, and we give some examples of the application of seismic isolation to structures m New Zealand.
 Current interest is focused on the application of seismic isolation to three buildings in central Wellington. In July 1993, the construction of the seismically isolated Museum of New Zealand was started on the Wellington waterfront. All of the lead-rubber isolators have now been tested and installed. Nearby the NZ Parliament Building and Library have been retrofitted with a lead-rubber bearing system.
 To support the continuation of improvements to the seismic resistance of structures a number of research programs are operating in the Universities of Auckland and Canterbury, the Engineering Seismology Section of the NZ Institute of Geological and Nuclear Sciences, Works, a number of engineering consultants and in our company.
 Very strong support for the principles of seismic isolation is given by the fact that of the ten hospitals affected by the 1994 Northridge earthquake in Los Angeles, only the hospital seismically isolated by a lead-rubber bearing system was able to continue to operate. Further support is given by the excellent behaviour of two isolated buildings in the 1995 Hyogo Ken-Nanbu earthquake.