Design Of Base Isolation System Research Articles

Flower Pollination Algorithm for Optimum Design of Base Isolation Systems under Near-Fault Effect

Flower Pollination Algorithm for Optimum Design of Base Isolation Systems under Near-Fault Effect

Risk‐based seismic design of base‐isolated structures with single surface friction sliders

AbstractChoosing friction pendulum isolators to avoid problems with device displacement capacity or boundary wall collision is a critical part of the seismic design of base isolation systems. This paper developed a probabilistic method to quantify the risk of failure in single friction pendulum bearing (FPB) devices. This was done by calibrating a demand‐intensity model for FPBs from numerical analysis for several device property combinations. These properties encompassed the dynamic friction coefficient and effective radius of curvature—key parameters impacting these FPB devices’ seismic response. Through this demand‐intensity model, a closed‐form and relatively simple approach to quantify the mean annual frequency of exceeding a given device displacement threshold, or risk of failure, was proposed. By applying this simplified method to several case study structures and comparing it with a more extensive assessment involving multiple stripe analysis (MSA) using hazard‐consistent ground motions, the proposed simplified approach could provide very accurate estimates of displacement‐based failure risk in FPB devices under the assumption of no non‐linear behaviour in the superstructure. This proposed approach implies that structural engineers can now quickly assess the actual failure rates of different FPB device combinations used in practice to give a more uniform level of safety or reliability when designing and assessing FPB‐isolated systems. It is also arguably much simpler, direct and accurate than currently available code‐based approaches.

Developing a simplified method for analysis and design of isolated structures with the novel quintuple friction pendulum system under bidirectional near-field excitations

Simplified analysis methods for seismically isolated structures proposed in recent structural codes and specifications are frequently used to reduce the computational effort and to simplify the design procedure, either directly for special cases or for checking the results of nonlinear response history analysis. Of the approximate methods, the equivalent lateral force procedure using the effective stiffness and effective damping is one of the best known. In this study, the simplified method is developed by combining the equivalent lateral force procedure with the capacity spectrum method and evaluated in terms of maximum isolator displacements and base shears for isolated structures with recently invented quintuple friction pendulum isolators , with different geometrical and frictional properties, under two different response spectra with corresponding two different sets of bidirectional near-field ground motions for stiff and soft soils site classes. In order to assess the accuracy of the simplified method, the delivered results of the ELF procedure are compared to those of nonlinear response history analysis, by modelling the quintuple friction pendulum isolator 3D element in OpenSees. Eventually, comments on the accuracy of the simplified method are given to make its applications more appropriate in practical design of base isolation systems.

Design of Base Isolation System for a Six Storey Reinforced Concrete Building

The aim of the seismic design is to protect the important building such as museums, hospitals, official buildings etc.., and reduce the damages after a seismic event. Many researchers have done a lot of research to get the best solutions to resist earthquakes and protect survival. One of those solutions is base isolation, the main goal of seismic isolation is to shift the fundamental frequency of a structure away from the dominant frequencies of earthquake ground motion and the fundamental frequency of the fixed base-superstructure, the other purpose of an isolation system is to provide an additional means of energy dissipation, thereby reducing the transmitted acceleration into the superstructure. In the present study, a six-story RCC building has been designed and analyzed according to IS Code for seismic analysis by (STAAD PRO V8i) software using response spectrum analysis, the study considered two models one of the models represents conventional building and the second model represents base isolation (BI) building. The results obtained shows the reduction in base shear and storey drift in both direction and increase in the displacement and the time period for the base isolated structure. Finally, parameters such as storey displacement, storey drift, mode and base shear are compared and obtained result where presented by both graphically and in tabular format.

Retraction: Design of Base Isolation System for a Six Storey Reinforced Concrete Building (IOP Conf. Ser.: Earth Environ. Sci. 796 012034)

This article has been retracted by IOP Publishing following a request by the authors that this article may contain potential research errors. IOP Publishing has investigated in line with COPE guidelines, and during the course of the investigation were made aware the article contains potential similarities to other published works [1-4]. Due to the nature of the overlap identified, and the extent of the changes requested by the authors, the journal has lost confidence in the validity of the findings presented and agree this article should be retracted. The authors have neither confirmed whether they agree or disagree to this retraction. [1] A Hassan and S Pal, 2017, Performance Analysis of Base Isolation and Fixed Base Buildings, International Conferences on Emerging Technology in Structural Engineering (ETSE-2017) [2] Business Bliss Consultants FZE. (November 2018). Base Isolation Devices for Seismic Isolation. Retrieved from https://ukdiss.com/examples/base-isolation-devices-for-seismic-isolation.php?vref=1 [3] Ta-Chieh Wu, 2001, Design of Base Isolation System for Buildings, thesis, Massachuetts Institute of Technology [4] Y Mehani, A Benyoucef and B Chikh, 2015, Seismic Assessment demand of Isolated buildings, 7th International Conference on Seismology and Earthquake Engineering Retraction published: 21 November 2022

Stochastic optimal design of novel nonlinear base isolation system for seismic-excited building structures

A novel nonlinear isolation system is numerically investigated by employing a stochastic response evaluation and experimentally studied with a small-scale preliminary prototype. The stochastic response of isolated building structures is first derived using a nonstationary random process and time-dependent equivalent linearization, regarding the nonlinear restoring force behavior of the proposed isolator. A parametric study is then performed to evaluate the potential influences of earthquake excitations properties and the optimum force ratio of the isolator that adopts the widely used Kanai–Tajimi model. According to the insights from the parametric study, the optimal design for nonlinear isolation is proposed based on a stochastic optimization procedure with the convergence of different performance objectives. The stochastically optimized isolation system is numerically studied by first comparing the present nonlinear isolator and conventional bearings. The present isolator is systematically illustrated to perform advantageously compared with conventional passive isolators in terms of base drift and structural acceleration through a relatively large group of 40 recorded seismic motions. To further investigate the efficiency of the nonlinear isolator, a benchmark building for smart base-isolation is adopted, and a comparison of the results indicates comparable performances between the proposed passive isolator and the classical active isolation system. Furthermore, an original design of the base isolation system simulating an energy dissipation mechanism is presented with favorable force-deformation behavior from experimental testing on small-scale prototypes.

Use of active control algorithm for optimal design of base-isolated buildings against earthquakes

This study presents a new design method that concurrently determines the stiffness and damping coefficient in a base isolation system. This design method is developed based on the similarity between the active and passive control system. Then, the stiffness and damping coefficient are derived from the linear quadratic regulator control algorithm to a single degree of freedom superstructure and formed as a function of single weighting. The best design of a base isolation system is determined by optimizing this weighting from the minimum H∞-norm responses of base displacement and roof acceleration. A parametric study is performed to understand the influence of superstructures to the resulting optimized base isolation system. Moreover, this study also provides a numerical example to validate the optimal design of base isolation systems. The potential to design nonlinear lead-rubber bearings with added viscous dampers based on the proposed method is also investigated. As a result, the proposed method yields a high-performance base isolation system for a known superstructure.

Equivalent damping of bilinear hysteretic SDOF system considering the influence of initial elastic damping

The premise of equivalent linearization method is that the peak response of an inelastic system can be estimated as the peak response of a linear elastic system having reduced stiffness and increased damping.Different approaches have been used to determine the properties of the equivalent linear system, in particular the equivalent damping ratio. In general, equivalent damping is specified as the sum of elastic and hysteretic component, where the former is assumed to be constant, and the latter depends on the ductility and hysteresis model. It is found that, however, many studies only focus on the definition of hysteretic damping and omit the influence of elastic damping on the prediction accuracy of equivalent linearization method. Motivated by this limitation, comprehensive parametric analysis is performed in this paper based on bilinear hysteretic SDOF systems to identify the influence of elastic damping. Results show that elastic damping has significant influence on the estimation accuracy of equivalent linearization method. To improve the estimation accuracy of equivalent linearization method, improved method of equivalent damping is proposed by considering the influence of elastic damping. It is found that the proposed method is able to provide accurate and conservative values of equivalent damping for practical design of base isolation systems.

Comparative Studies of Base Isolation Systems Featured with Lead Rubber Bearings and Friction Pendulum Bearings

Due to the fact that safety is the major concern for civil structures in a seismic active zone, it has always been a challenge for structural engineers to protect structures from earthquake. During past several decades base isolation technique has become more and more popular in the field of seismic protection which can be adopted for new structures as well as the retrofit of existing structures. The objective of this study is to evaluate the behaviours of the building with different seismic isolation systems in terms of roof acceleration, elastic base shear and inter-storey drift under four benchmark earthquakes, namely, El Centro, Northridge, Hachinohe and Kobe earthquakes. Firstly, the design of base isolation systems, i.e. lead rubber bearing (LRB) and friction pendulum bearing (FPB) for five storey RC building was introduced in detail. The non-linear time history analysis was performed in order to determine the structural responses whereas Bouc-Wen Model of hysteresis was adopted for modelling the bilinear behaviour of the bearings. Both isolation systems increase the fundamental period of structures and reduces the spectral acceleration, and hence reduces the lateral force cause by earthquake in the structures, resulting in significant improvement in building performance; however the Lead Rubber Bearing provided the best reduction in elastic base shear and inter-storey drift (at first floor) for most of the benchmark earthquakes. For the adopted bearing characteristics, FPB provided the low isolator displacement.

Robust optimum design of base isolation system in seismic vibration control of structures under random system parameters

The optimum design of base isolation system to control seismic vibration considering uncertain system parameters are usually performed by minimizing the unconditional expected value of mean square response of a structure without any consideration to the variance of such responses due to system parameter uncertainty. However, the unconditional mean square response based designed may have larger variance of responses due to uncertainty in system parameters and the overall system performance may be sensitive. But, it is desirable that the optimum design should reduce both the mean and variance of dynamic performance measure under system parameter uncertainty. The present study deals with robust design optimization (RDO) of base isolation system considering random system parameters characterizing the structure, isolator and ground motion model. The RDO is performed by minimizing the weighted sum of the expected value of the maximum root mean square acceleration of the structure as well its standard deviation. A numerical study elucidates the importance of the RDO procedure for design of base isolation system by comparing the proposed RDO results with the results obtained by the conventional stochastic structural optimization procedure and the unconditional response based optimization.

The influence of damping on floor spectra in seismic isolated nuclear structures

Summary Seismic isolation is now being considered for nuclear power plant structures and has been applied to many nuclear structures including reactor buildings in France. A draft report entitled ‘Technical Considerations for Seismic Isolation Nuclear Facilities’ has been prepared by the USA Nuclear Regulatory Commission in 2010. It sets out to describe different types of isolators and recommends that lead plug isolators and FP isolators are acceptable choices for nuclear isolation systems. For the design of base isolation systems for nuclear structures, the design engineer is faced with very large design displacements for the isolators and supplementary dampers or highly damped isolators are prescribed to reduce them. These dampers reduce displacements but at the expense of significant increases in interstory drifts and floor accelerations in the superstructure. In this paper, an elementary analysis based on a simple model of an isolated structure is used to demonstrate this dilemma. The model is linear and is based on modal analysis, but includes the modal coupling terms caused by high levels of damping in the isolation system. Estimates of the floor response quantities are obtained by the response spectrum method. It is shown that as the damping in the isolation system increases, the contribution of the modal coupling terms becomes the dominant term. The results show that the use of damping in seismic isolation when the purpose of the isolators is to protect sensitive internal equipment is a misplaced effort, and alternative strategies to solve the problem are suggested. Copyright © 2014 John Wiley & Sons, Ltd.

Evaluation of equivalent linearization analysis methods for seismically isolated buildings characterized by SDOF systems

Although peak response of seismic isolation systems can be obtained through nonlinear time history analysis method, approximate linear elastic analysis method is frequently proposed in recent structural codes to reduce the computational effort and to simplify the design procedure. Of the approximate methods, the equivalent linearization (EL) method is best known. In this study, fourteen EL methods proposed in the literatures are assessed based on single-degree-of-freedom (SDOF)systems with bilinear hysteretic behavior. A large number of numerical simulations are performed using a program developed by MATLAB in combination with OpenSees to evaluate the influence of ductility ratio and initial period on the accuracy of EL methods to estimate the maximum inelastic displacement of bilinear SDOF systems when subjected to 12 earthquake ground motions. A set of 20 ductility ratios ranging from 2 to 50 are considered, as well as 15 initial natural periods between 0.1s and 1.5s. Ratios of approximate to exact maximum displacement corresponding to each EL method are averaged over the considered ground motions, and the standard deviation of investigated ratios is also calculated to measure the degree of dispersion. Eventually, comments on the accuracy of different EL methods are given to make their applications more appropriate in practical design of base isolation systems.

Optimal design of Base Isolation System considering uncertain bounded system parameters

The optimum design of base isolation system considering model parameter uncertainty is usually performed by using the unconditional response of structure obtained by the total probability theory, as the performance index. Though, the probabilistic approach is powerful, it cannot be applied when the maximum possible ranges of variations are known and can be only modelled as uncertain but bounded type. In such cases, the interval analysis method is a viable alternative. The present study focuses on the bounded optimization of base isolation system to mitigate the seismic vibration effect of structures characterized by bounded type system parameters. With this intention in view, the conditional stochastic response quantities are obtained in random vibration framework using the state space formulation. Subsequently, with the aid of matrix perturbation theory using first order Taylor series expansion of dynamic response function and its interval extension, the vibration control problem is transformed to appropriate deterministic optimization problems correspond to a lower bound and upper bound optimum solutions. A lead rubber bearing isolating a multi-storeyed building frame is considered for numerical study to elucidate the proposed bounded optimization procedure and the optimum performance of the isolation system.

Robust optimum design of base isolation system in seismic vibration control of structures under uncertain bounded system parameters

The optimum design of a base isolation (BI) system in the framework of total probability theory cannot be applied in many real situations when the required detailed information about the uncertain parameters are limited and the maximum possible ranges of variations are only known and can be modeled as an uncertain but bounded type. The interval analysis based bounded design optimization usually applied in such cases are the worst case measures and unsuitable for practical design. Moreover, such a design method does not consider the variation of the performance of an isolated system due to uncertainty and may not correspond to an optimum design yielding maximum performance with its minimum dispersion. The robust optimization requiring only the bounds on the magnitude of the uncertain parameters will be a viable alternative in such situations. The present study deals with the robust optimization of BI system for seismic vibration mitigation of structures characterized by bounded uncertain parameters. The robust optimization is performed by using a two-criteria equivalent optimization problem, where the weighted sum of the nominal value of the maximum root mean square acceleration of the superstructure and its dispersion is optimized. The bounded design optimization is also performed to demonstrate the effectiveness of the proposed robust optimization approach. A five-storied building frame with attached isolator elucidates the effectiveness and importance of the proposed design approach by comparing the present robust optimization results with the results obtained by the bounded design optimization procedure.

Experimental Methods for Selecting Base Isolation Parameters for Public Buildings

As a rule, public buildings should have higher safety level compared to residential ones. Hence, using base isolation systems is an effective and widely known way for improving dynamic response of such buildings. The idea of base isolation was known hundreds years ago, however practical implementation of base isolators started in the last few decades. The main advantage of a base isolation system is that no elements should be added to an isolated building, which is especially important for heritage architecture, forming a part of public buildings. Traditional base isolation system is obtained by using two main base isolator types – elastomeric bearings or friction pendulums. Hundreds of buildings all over the world are provided by such isolators and proved enhanced dynamic behavior. Design of base isolation systems and selection of their properties usually depend on dynamic characteristics of the isolated building. The last can be obtained, for example, by non-destructive impulse testing of the structure before its protection. An appropriate method for structural dynamic parameters experimental estimation was developed by the authors. For this reason an impulse test was carried out on a three-story structural part of a building designed for a seismic region. Another method, which is also discussed in the paper, is based on seismic monitoring of a building in a waiting regime. In some cases the displacements at the base isolation level are rather big and exceed the allowed limits. In such cases it is recommended to add dampers to the base isolation system. Effective variable friction dampers were proposed and tested by the authors. These dampers significantly reduce the displacements between the first floor column and foundation and additionally yield further improvement in the structural seismic response.

“Smart” Base Isolation Strategies Employing Magnetorheological Dampers

One of the most successful means of protecting structures against severe seismic events is base isolation. However, optimal design of base isolation systems depends on the magnitude of the design level earthquake that is considered. The features of an isolation system designed for an El Centro-type earthquake typically will not be optimal for a Northridge-type earthquake and vice versa. To be effective during a wide range of seismic events, an isolation system must be adaptable. To demonstrate the efficacy of recently proposed ''smart'' base isolation paradigms, this paper presents the results of an experimental study of a particular adaptable, or smart, base isolation system that employs magnetorheological ~MR! dampers. The experimental structure, constructed and tested at the Structural Dynamics and Control/Earthquake Engineering Laboratory at the Univ. of Notre Dame, is a base-isolated two-degree-of-freedom building model subjected to simulated ground motion. A sponge-type MR damper is installed between the base and the ground to provide controllable damping for the system. The effectiveness of the proposed smart base isolation system is demonstrated for both far-field and near-field earthquake excitations.

The role of damping in seismic isolation

In the current code requirements for the design of base isolation systems for buildings located at near-fault sites, the design engineer is faced with very large design displacements for the isolators. To reduce these displacements, supplementary dampers are often prescribed. These dampers reduce displacements, but at the expense of significant increases in interstorey drifts and floor accelerations in the superstructure. An elementary analysis based on a simple model of an isolated structure is used to demonstrate this dilemma. The model is linear and is based on modal analysis, but includes the modal coupling terms caused by high levels of damping in the isolation system. The equations are solved by a method that avoids complex modal analysis. Estimates of the important response quantities are obtained by the response spectrum method. It is shown that as the damping in the isolation system increases, the contribution of the modal coupling terms due to isolator damping in response to the superstructure becomes the dominant term. The isolator displacement and structural base shear may be reduced, but the floor accelerations and interstorey drift are increased. The results show that the use of supplemental dampers in seismic isolation is a misplaced effort and alternative strategies to solve the problem are suggested. Copyright © 1999 John Wiley & Sons, Ltd.

Base Isolation: Linear Theory and Design

The idea that a building can be uncoupled from the damaging effects of the ground movement produced by a strong earthquake has appealed to inventors and engineers for more than a century. Many ingenious devices have been proposed to achieve this result, but very few have been implemented and the concept now referred to as base isolation or seismic isolation has yet to be generally accepted by the engineering profession. Although most of the proposed systems are unacceptably complicated, in recent years a few practical systems have been developed and implemented. While some of these systems have been tested on large-scale shaking tables, none have to date been tested as-built by a strong earth tremor. The shake table testing and related static testing of full-scale components such as isolation bearings, however, has led to a certain degree of acceptance by the profession and it is possible that the number of practical implementations of base isolation will increase quite dramatically in the next few years. This paper describes recent implementations of base isolation and describes an approximate linear theory of isolation which can be used for the design of base isolation systems that use multilayer elastomeric isolators.