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This paper investigates a steel moment resisting frame (MRF) with a novel type of self‐centering (SC) base isolators, wherein superelastic shape memory alloy (SMA) U‐shaped dampers (SMAUDs) work as core components. A two‐story steel MRF model equipped with two SMAUD‐based isolators was designed and built in the laboratory, and a series of shake table tests were conducted to examine the dynamic behavior and seismic performance of the frame. Throughout all the tests, no interventions, such as repair or replacement of frame or isolator members, were done. Shake table test results demonstrated that the SMAUD‐based isolators could withstand multiple strong earthquakes with stable SC behavior. The utilization of SMAUD‐based isolators provided effective protection for the frame, enabling it to restore its original position with minimal structural damage. A numerical model of the tested steel MRF with SMAUD‐based isolators was also built. The results obtained from the numerical analyses agreed with those of the shake table tests satisfactorily. A comparative study of the seismic performance between the MRF with SMAUD‐based isolators and the MRF with traditional steel U‐shaped damper‐based isolators was also conducted in the shake table tests. The results showed that SMAUD‐based isolators not only inherit the isolation function of conventional isolators to protect the frame but also possess an SC ability to eliminate residual isolator deformation effectively. Moreover, SMAUD‐based isolators demonstrate remarkable resilience to withstand multiple strong seismic events without any need for repair or replacement. [ABSTRACT FROM AUTHOR]

This paper investigates the implementation of supplemental vibration control systems (VCS) in base isolated (BI) structures, to improve their dynamic performance. More specifically, the aim of the VCS is to reduce the base displacement demand of BI structures, and at the same time mitigate the superstructure seismic responses. The purpose of the examined VCS is dual, and for this reason a multi-objective optimization methodology is formulated for the design of the VCS. The examined vibration absorbers include modifications of the KDamper concept. The KDamper is an extension of the traditional Tuned Mass Damper (TMD), and introduces a negative stiffness (NS) element to the additional oscillating mass of the TMD. The generated NS force is exactly in phase with the inertia force of the added mass, thus, artificially amplifying it. This way, lighter configurations are possible with an enhanced damping behavior. These VCS are designed based on engineering criteria and manufacturing constraints, while the excitation input used in the multi-objective optimization procedure is selected from a dataset of artificial accelerograms, designed to be spectrum-compatible with the EC8 design acceleration response spectrum. The effectiveness of the examined VCS is also assess with real near-fault earthquake records, and a comparison is performed with TMD-based VCS having 50 times larger additional masses. The numerical results demonstrate the superiority of the KDamper-based VCS in improving the dynamic behavior of BI structures over other mass-related systems (TMD). [ABSTRACT FROM AUTHOR]

The present study investigates the role of a simple inerter in supplemental devices for possible implementation in the mature seismic base isolation technique. Firstly, the response of the base-isolated structure with an optimally tuned mass damper inerter (TMDI) is investigated to see the tuning effects. The time required to tune the TMDI was found to be significantly longer than the duration of a strong-motion earthquake. There was still a reduction in the response of the isolated structure, which is primarily due to the added damping and stiffness (ADAS) of TMDI and not because of the tuning effects. Hence, it is proposed that the corresponding ADAS of the TMDI be directly added to the isolation device. Secondly, the response of the base-isolated structures to the fluid inerter damper (FID) is studied. It was observed that the inerter of the FID does not influence the displacement variance of an isolated structure under broadband earthquake excitation. It implies that the response of the isolated structure to FID is primarily controlled by its counterpart fluid damper (FD). The performance of optimal TMDI, ADAS, FID, and FD to mitigate the seismic response of the flexible multi-story base-isolated structure under real earthquake excitations is also investigated. In terms of suppressing the displacement and acceleration responses of the isolated structure, it has been found that TMDI and ADAS perform similarly. Comparing the response of the isolated structure with FID and FD demonstrated that the inerter in the FID has detrimental effects on the isolated structures, in which the top floor's acceleration and base shear are substantially increased. [ABSTRACT FROM AUTHOR]

An earthquake is a force which is unpredictable and can cause serious damage to a structure and its structural components. For improved safety, the seismic design of the building should be adequate, and measures should be taken for vibration control. In order to mitigate effects, baseisolation techniques must be provided to counter seismic loads; this is a seismic isolation technique which prevents the transfer of energy from the base of the structure to the upper stories. In the research, two similar 3D frame models were modelled with and without base isolators and analyzed following the provisions and codes. The real ground motion data of the earthquake was selected, then matched to a design spectrum to obtain the matched time history. The story response plots obtained after the time history analysis indicate that base isolation is a reliable and effective technology to improve the seismic performance of the building, particularly with inadequate seismic design. [ABSTRACT FROM AUTHOR]

This paper investigates the implementation of supplemental vibration control systems (VCS) in base isolated (BI) structures, to improve their dynamic performance. More specifically, the aim of the VCS is to reduce the base displacement demand of BI structures, and at the same time mitigate the superstructure seismic responses. The purpose of the examined VCS is dual, and for this reason a multi-objective optimization methodology is formulated for the design of the VCS. The examined vibration absorbers include modifications of the KDamper concept. The KDamper is an extension of the traditional Tuned Mass Damper (TMD), and introduces a negative stiffness (NS) element to the additional oscillating mass of the TMD. The generated NS force is exactly in phase with the inertia force of the added mass, thus, artificially amplifying it. This way, lighter configurations are possible with an enhanced damping behavior. These VCS are designed based on engineering criteria and manufacturing constraints, while the excitation input used in the multi-objective optimization procedure is selected from a dataset of artificial accelerograms, designed to be spectrum-compatible with the EC8 design acceleration response spectrum. The effectiveness of the examined VCS is also assess with real near-fault earthquake records, and a comparison is performed with TMD-based VCS having 50 times larger additional masses. The numerical results demonstrate the superiority of the KDamper-based VCS in improving the dynamic behavior of BI structures over other mass-related systems (TMD).

The present study investigates the role of a simple inerter in supplemental devices for possible implementation in the mature seismic base isolation technique. Firstly, the response of the base-isolated structure with an optimally tuned mass damper inerter (TMDI) is investigated to see the tuning effects. The time required to tune the TMDI was found to be significantly longer than the duration of a strong-motion earthquake. There was still a reduction in the response of the isolated structure, which is primarily due to the added damping and stiffness (ADAS) of TMDI and not because of the tuning effects. Hence, it is proposed that the corresponding ADAS of the TMDI be directly added to the isolation device. Secondly, the response of the base-isolated structures to the fluid inerter damper (FID) is studied. It was observed that the inerter of the FID does not influence the displacement variance of an isolated structure under broadband earthquake excitation. It implies that the response of the isolated structure to FID is primarily controlled by its counterpart fluid damper (FD). The performance of optimal TMDI, ADAS, FID, and FD to mitigate the seismic response of the flexible multi-story base-isolated structure under real earthquake excitations is also investigated. In terms of suppressing the displacement and acceleration responses of the isolated structure, it has been found that TMDI and ADAS perform similarly. Comparing the response of the isolated structure with FID and FD demonstrated that the inerter in the FID has detrimental effects on the isolated structures, in which the top floor’s acceleration and base shear are substantially increased.

In this article, a new full‐ and reduced‐order proportional–integral (PI) controller is developed such that the target‐tracking or command‐following problems become generic for a wide range of frequency inputs. The proposed controller has been developed for better control of seismic responses of structures. The integral part of the proposed controller in this case is formulated by proper factorization of relevant components in closed loop to avoid the presence of uncontrollable poles in the feedback system. Further, the controller–observer framework is designed through suboptimal H∞ control algorithm. The robustness and stability of the algorithm are evaluated in terms of tracking a wide range of frequency inputs, while mitigating the influence of sensor noise and modelling uncertainties at the same time. The efficiency of the proposed PI controller is established with respect to the suboptimal H∞‐based proportional controller in terms of reduction in error signal of a nominal and perturbed single degree‐of‐freedom spring–mass–damper system. Further, the applicability of the proposed controller in a realistic scenario is studied using a base‐isolated building under strong seismic excitation. The performance of the control algorithm is evaluated in terms of isolator displacement, inter‐storey drift and top‐floor drift of the nominal model. The results from this work highlight that the proposed controller has significant potential for practical implementation in civil engineering structures. [ABSTRACT FROM AUTHOR]

An earthquake is a force which is unpredictable and can cause serious damage to a structure and its structural components. For improved safety, the seismic design of the building should be adequate, and measures should be taken for vibration control. In order to mitigate effects, base-isolation techniques must be provided to counter seismic loads; this is a seismic isolation technique which prevents the transfer of energy from the base of the structure to the upper stories. In the research, two similar 3D frame models were modelled with and without base isolators and analyzed following the provisions and codes. The real ground motion data of the earthquake was selected, then matched to a design spectrum to obtain the matched time history. The story response plots obtained after the time history analysis indicate that base isolation is a reliable and effective technology to improve the seismic performance of the building, particularly with inadequate seismic design.

Summary: The performance and optimal design of the base‐isolated structure supplemented with clutching inerter damper (CID) subjected to seismic loading are investigated. Because of the nonlinear force‐deformation behavior of the CID, the stochastic response of the isolated structure subjected to nonstationary earthquake excitation is obtained using the time‐dependent equivalent linearization technique. To investigate the effects of nonstationary earthquake characteristics, the isolated structure's nonstationary response is compared to the corresponding stationary response. For a given isolated structural system and excitation, there exists an optimum value of the CID inertance at which the root mean square absolute acceleration of the superstructure achieves a minimum value. The effects of key parameters like superstructure flexibility, isolation period, and isolation damping ratio on the CID's optimal inertance are examined. The seismic response of base‐isolated structures is also obtained under real earthquakes using the nonlinear model of the CID. The effects of the CID on the response of isolated structures under real earthquakes were found to be well correlated with those of stochastic analysis. Finally, for the approximate response and initial design of base‐isolated structures, a closed‐form expression for the equivalent damping of the CID is proposed. Using the equivalent inertance and damping of the CID, the bearing displacements and forces of isolated structures with the CID were found to be matching with that obtained by the nonlinear analysis. However, there can be an error in the prediction of structural acceleration and force in the CID by using this equivalent approach. [ABSTRACT FROM AUTHOR]

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Seismic base isolation is a passive structural control system that has been effectively utilized as an innovative seismic-resistant design method in the past decades. The properties of earthquake ground motions have significant effects on the response of the base isolation system. Many recent studies were dedicated to the influence of near-fault ground motions on the response of seismically isolated buildings. These previous studies concluded that near-fault ground motions mostly impose larger displacement on the seismic isolators and, in some cases, larger floor acceleration; furthermore, the velocity pulse period influences the seismic isolator displacement and the floor acceleration. Most of the previous studies were conducted using ground motions simulated with certain parametric conditions of near-fault ground motions and/or a limited number of real earthquake ground motions. This study intended to examine the conclusions of previous studies through response history analysis of a seismically isolated prototype building with lead–rubber bearing (LRB) isolators using a large number of real near-fault earthquake ground accelerations. It was found that no consistent resonance phenomenon can be observed when the velocity pulse period is close to the natural period of the isolated building in terms of floor acceleration and isolator displacement, in contrast to the findings of other studies. [ABSTRACT FROM AUTHOR]

The optimum damping and tuning frequency ratio of the tuned inerter damper (TID) for the base-isolated structure is obtained using the numerical searching technique under stationary white-noise and filtered white-noise earthquake excitation. The criterion selected for optimality is the minimization of the mean-square relative displacement and absolute acceleration of the isolated structure and maximization of the energy dissipation index. Explicit formulae for TID damping and tuning frequency for white-noise excitation are then derived using a curve-fitting technique that can be conveniently used for applications in dynamical systems. The error in the proposed empirical expressions is found to be negligible and hence these expressions are quite useful for the effective design of the base-isolated structure with supplemental TID. An optimally designed TID was found to be more effective for the base-isolated structures under soft soil conditions in comparison to the firm soils. Further, a comparison of the seismic response of the flexible base-isolated structure with and without TID was made under non-stationary earthquake excitation. It was observed that an optimally designed TID was found to be effective in controlling the displacement and acceleration response of the base-isolated structure and the effectiveness is observed to be increased for a higher inertance mass ratio. Finally, the close form expression for the bearing displacement of base-isolated structure with TID subjected to broadband earthquake excitation is proposed which will be helpful for initial optimal design. [ABSTRACT FROM AUTHOR]

The scope of this study is the comparison between experimental results of tests performed on a base isolated building using helical wire rope isolators (WRs), and results of Nonlinear Response History Analyses (NRHAs) performed using SAP 2000, a commercial software for structural analysis. In the first stage of this research, WRs have been tested under shear deformation beyond their linear range of deformation, and analytical models have been derived to describe the nonlinear response of the bearings under different directions of loading. On the following stage, shaking table tests have been carried out on a 1/3 scale steel model isolated at the base by means of curved surface sliders (CSS) and WRs. The response of the structure under ground motion excitation has been compared to that obtained using numerical analyses in SAP 2000. The feasibility of modelling the nonlinear behavior of the tested isolation layer using multilinear link elements embedded in SAP 2000 is discussed in this paper, together with the advantages of using WRs as supplemental devices for CSSs base isolated structures. [ABSTRACT FROM AUTHOR]

• A novel friction damper is presented for seismic response control of buildings. • The damper force can be controlled by an electromagnetic mechanism. • A semi-active controller is proposed to smooth the hysteretic behavior of the damper. • A current driver is designed to modify the control current, reducing the time delay. • Numerical results demonstrate the energy dissipation capability of the damper. This paper studies the use of a smart/semi-active electromagnetic friction damper (SEMFD) for the control of seismic response of multi-story base-isolated buildings. The SEMFD consists of a ferromagnetic plate and two similar arrays of thick rectangular ferromagnetic-core coils (FCs) connected in series. The FCs are attached to the two sides of the ferromagnetic plate through two non-magnetic friction pads. The force in the damper is developed because of the friction between the friction pads and the ferromagnetic plate when the FCs moves relative to ferromagnetic plate. The normal force between the friction pad and the ferromagnetic plate is caused by the attractive magnetic interactions between the FCs arrays and the ferromagnetic plate. The magnitude of this force is controlled by a proposed semi-active controller that is capable of varying the current flowing through the FCs in such a way that it is able to avoid stick-slip motion by smoothing the nonlinear hysteretic behavior of the SEMFD. The capability of the SEMFD and the proposed semi-active controller to control the seismic response of base-isolated buildings is demonstrated by implementing them into the dynamic model of a six-story base-isolated building supported on lead-rubber bearings (LRBs). The numerical results show that the SEMFD and its semi-active controller are capable of limiting the displacement of the base floor without noticeably increasing the inter-story drifts and absolute accelerations of the floors. It is demonstrated that the parallel actions of the LRBs and the SEMFD in the base floor create a smart base isolation system that is capable of fully protecting a multi-story building from ground motions with intensities at a level as that of the ASCE 7–10 Maximum Considered Earthquake (MCE). [ABSTRACT FROM AUTHOR]

Structural control can be used for protecting buildings and its vibration-sensitive contents from earthquakes. Seismic isolation is a passive control system that lowers effective earthquake forces by utilizing flexible bearings. However, supplemental damping in the isolation system may become necessary to reduce large isolator displacements under near-fault earthquakes. Semi-active dampers are preferred over passive dampers because of their capacity in minimizing possible amplifications in floor accelerations due to increased damping. Semi-active dampers are also preferred over the active ones because of their higher stability and lower power consumption. On the other hand, seismic performance of semi-active isolation may vary due to variations in the mechanical properties of semi-active devices and/or seismic isolators. Such uncertainties alongside the uncertainties associated with ground motion parameters should be taken into consideration to develop a realistic picture of the behavior of seismically isolated buildings equipped with semi-active control devices. The objective of this study is to examine the effectiveness of semi-active isolation in protecting vibration-sensitive equipment and integrity of a structure by considering the aforementioned uncertainties and present the reliability of semi-active seismic isolation under near-fault earthquakes. For this purpose, this paper introduces a method that uses synthetically generated near-fault earthquakes and Monte-Carlo Simulations. This method is used to determine the reliability of a 3-story and a 9-story benchmark buildings with semi-active isolation systems under near-fault earthquakes of various magnitudes and varying fault distances. The results are presented in the forms of comparative plots of probability of failure and reliability. [ABSTRACT FROM AUTHOR]

The paper analyses the applicability of seismic base isolation made of elastomeric bearings for the seismic mitigation of architectural heritage buildings. Due to the inestimable cultural and historical significance any remedial measures into such objects must be selected with care and are usually very limited. In an ideal situation only interventions with minimum visual impacts on the object and maximum potential for restoring its cultural values would be implemented. Historical structures were usually not designed accounting seismic hazard and might be seismically more vulnerable as modern buildings. The paper deals with seismic base isolation as a technique for increasing the seismic resistance of architectural heritage buildings made of unreinforced masonry. Typical base isolation devices represent special bearings that are usually installed bellow the foundations of the structure. If the isolation system is properly designed it can eliminate the need for using more invasive retrofit measures and techniques. The paper presents a relatively simple and computationally less demanding technique for the modelling and analysis of regular unreinforced masonry (URM) structures. This technique is based on the equivalent frame approach, while the complex seismic failure mechanism of masonry piers is expressed by a single failure mode interaction surface (an "FMI surface"), taking into account the influence of variation in the pier’s vertical loading, and it’s bending moment distribution. A single failure mode interaction plastic hinge (an "FMI hinge") for each masonry frame element is introduced by combining specific failure modes, taking into account their minimum envelope. In the final part of the work a case study of using base isolation for the seismic retrofitting of an existing three-story masonry building has been conducted. Some results obtained by the N2 method comparing the damage in fixed based and base isolated variant of the test building demonstrate the potential of used techniques for the seismic protection of masonry heritage buildings.

Summary: The tuned mass damper inerter (TMDI) couples the classical tuned mass damper (TMD) with an inerter, a mechanical device whose generated force is proportional to the relative acceleration between its terminals, thus providing beneficial mass‐amplification effects. This paper deals with a dynamic layout in which the TMDI is installed below the isolation floor of base‐isolated structures in order to enhance the earthquake resilience and reduce the displacement demand. Unlike most of the literature studies that assumed a linearized behavior of the isolators, the aim of this paper is to investigate the effectiveness of the TMDI while accounting for the nonlinearity of the isolators. Two nonlinear constitutive behaviors are considered, a Coulomb friction model and a Bouc‐Wen hysteretic model, representative of friction pendulum and of lead‐rubber‐bearing isolators, respectively. Optimal design is based on the stochastic dynamic analysis of the system, by modeling the base acceleration as a Kanai‐Tajimi filtered stationary random process and resorting to the stochastic linearization technique to handle the nonlinear terms. Different tuning criteria based on displacement, acceleration, and energy‐based performance indices are defined, and their implications in a design process are discussed. It is proven that the improved robustness of the TMDI reduces its performance sensitivity to the tuning frequency and to the earthquake frequency content, which are well‐known shortcomings of TMD‐like systems. This important feature makes the TMDI particularly suitable for nonlinear base‐isolated structures that are affected by unavoidable uncertainties in the isolators' properties and that may experience changes of isolators effective stiffness depending on the excitation level. [ABSTRACT FROM AUTHOR]

Abstract The earthquake-resilient design of a reinforced concrete framed building is presented in this paper as a case study. A non-conventional application of the base isolation in conjunction with a tuned-mass-damper (TMD) located at basement, below the isolation floor, is studied for improving the seismic performance of the building. The seismic base isolation is implemented below the first story, with low-damping rubber isolators mainly placed throughout the perimeter of the building. At the center of the building a large-mass TMD is inserted, which consists of a box filled with large aggregate concrete. The box is located at basement and is connected to the base isolation system via an auxiliary set of lead-core rubber isolators, the latter playing the role of damper and spring elements of the TMD. The TMD box is disconnected from the ground via low-friction flat sliding devices. Optimal design parameters of the auxiliary TMD isolators are detected by minimizing an objective function that is based on the stochastic dynamic analysis of a simplified three-degree-of-freedom system comprising the main structure, the base isolation and the TMD. Four different objective functions are investigated, including the main structure displacement relative to the ground, the interstory displacements, the total acceleration and an energy-based indicator. The effectiveness of this design philosophy and of the related optimization procedure, first time applied to a real case, is demonstrated via nonlinear time-history analyses with simulated accelerograms being consistent with the response spectrum of the installation site. Advantages of this structural system over both the fixed-base building and the conventional application of the base isolation are shown in terms of a variety of response indicators summarizing the seismic performance of the building, including the deformation of the isolators, the displacement demand of the structure, the base shear, the interstory drifts, and the shear forces and bending moments on the beam-column members. Highlights • A low-damage structural system implemented in a RC building is presented as a case study. • A non-conventional application of the base isolation in conjunction with a TMD. • Four different optimization procedures of the TMD are scrutinized. • Improvements over the conventional base isolation demonstrated via time-history analyses. • A very high level of earthquake protection is achieved with the proposed system. [ABSTRACT FROM AUTHOR]

In this paper, the seismic response of base-isolated liquid storage tanks subjected to real and simulated near-fault ground motions is investigated. It is assumed that the tanks are seismically isolated by single surface Concave Sliding Bearings (CSB) with different isolation periods. For the input data, the recorded and simulated ground motions having pulse type characters and their dominant waveforms are considered. For each case considered, numerical analyses are carried out to calculate the critical demand parameters such as base shear values, bearing and sloshing displacements of the tank. The results revealed that, the base shear response of the slender tank to real and simulated ground motions and equivalent pulses tend to approach each other at isolation periods around 3 s and then remain constant in higher periods. Similar findings are not observed for the broad tank. Depending on the special case considered in this study, it can be said that, for the preliminary design of slender tanks in the near-fault regions, the real earthquakes can be replaced by equivalent pulses especially for isolation periods larger than 3s. [ABSTRACT FROM AUTHOR]

Summary: In seismic base isolation, most of the earthquake‐induced displacement demand is concentrated at the isolation level, thereby the base‐isolation system undergoes large displacements. In an attempt to reduce such displacement demand, this paper proposes an enhanced base‐isolation system incorporating the inerter, a 2‐terminal flywheel device whose generated force is proportional to the relative acceleration between its terminals. The inerter acts as an additional, apparent mass that can be even 200 times higher than its physical mass. When the inerter is installed in series with spring and damper elements, a lower‐mass and more effective alternative to the traditional tuned mass damper (TMD) is obtained, ie, the TMD inerter (TMDI), wherein the device inertance plays the role of the TMD mass. By attaching a TMDI to the isolation floor, it is demonstrated that the displacement demand of base‐isolated structures can be significantly reduced. Due to the stochastic nature of earthquake ground motions, optimal parameters of the TMDI are found based on a probabilistic framework. Different optimization procedures are scrutinized. The effectiveness of the optimal TMDI parameters is assessed via time history analyses of base‐isolated multistory buildings under several earthquake excitations; a sensitivity analysis is also performed. The enhanced base‐isolation system equipped with optimal TMDI attains an excellent level of vibration reduction as compared to the conventional base‐isolation scheme, in terms not only of displacement demand of the base‐isolation system but also of response of the isolated superstructure (eg, base shear and interstory drifts); moreover, the proposed vibration control strategy does not imply excessive stroke of the TMDI. [ABSTRACT FROM AUTHOR]

The papers addresses a novel passive vibration control system combining seismic base isolation with a tuned inerter damper (TID) system. The latter, by analogy with the tuned mass damper (TMD), is a dynamic vibration absorber in which the physical mass of the TMD is partly or entirely replaced by an apparent mass, also called inertance, created by a particular arrangement of mechanical gearings—the inerter . By attaching a TID to the isolation floor, not only the displacement demand of base-isolated structures can be significantly reduced, but also the superstructure response (e.g. interstory drift, base shear) is effectively controlled. Optimum parameters of this system are found based on a simplified three degree-of-freedom model that reflects the dynamic properties of both the isolation system and the TID while accounting for the flexibility of the base-isolated superstructure. Within a probabilistic framework, the influence of soil conditions is investigated by modeling the seismic ground motion as a filtered Gaussian random process. Different filter parameters are considered that may be associated with firm, medium or soft soil conditions depending on the frequency content of the power spectral density function. A wide parametric study is performed in order to detect the optimal TID parameters depending on the soil conditions for a variety of isolation ratios, mass ratios and damping ratios of both the superstructure and the isolation system. Finally, a multi-story building equipped with the proposed passive vibration control system is examined. Effectiveness of the proposed system is assessed via the evaluation of the structural response in the time domain. Detuning effects are investigated via a sensitivity analysis. Comparison with alternative passive vibration control systems proposed in the literature and based on different arrangements of TMD and inerter-based device is discussed. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the effect of the geomembrane/geotextile interface on the seismic response of small-to-moderate height structures. Three building models with first-mode natural frequencies changing between 2-4 Hz (representing two, three and four storey structures) were tested with and without the addition of geomembrane/geotextile interface using the shaking table test setup by employing harmonic and modified/scaled ground motions. Experimental results showed that the geomembrane/geotextile interface significantly reduced the floor accelerations, especially at moderate-to-high ground shaking levels. The interaction between the first-mode natural frequency of the model and the predominant frequency of the input motion is significant, and the interface is most effective when these two frequencies are close to each other. This effect is more clearly seen when the harmonic motions are employed during the tests compared to the modified/scaled ground motions. The results of the tests with modified/scaled ground motions were used to evaluate the efficiency of the composite liner system in reducing the spectral accelerations in the frequency domain. The results presented here document that the geomembrane/geotextile interface reduces the floor accelerations in a certain frequency range and underline the potential of this interface to be used as a base isolation material. [ABSTRACT FROM AUTHOR]

The article discusses methods of building frame constructions modeling by finite element method, taking into account seismic isolation systems. It presents data of the calculation in the two software systems. The calculation results are compared by analyzing of the individual elements stress-strain state. Recommendations about the calculation schemes and software systems selection are given on the base of results analyzing. The achieved results allow us to evaluate the effectiveness of seismic base isolation and can be used for wide application of such systems in building area.

The paper presents a series of experimental tests on ANCO R250-3123 shaking table from the Faculty of Civil Engineering and Building Services of Iaşi, in order to identify the structural response of a base isolated model with a multi-stage system made of four layers of elastomeric bearings. In the first phase of the experimental program, the dynamic characteristics of the structural model were determined and in the second phase the behaviour under different seismic actions of the base isolated structure with multi-stage system was evaluated. Three sinus beat actions and an artificial accelerogram were applied in the longitudinal direction of the experimental model. Following the results interpretation, a significant reduction of accelerations recorded at the top of the structure was achieved compared with the maximum acceleration recorded at the platform level. The experimental model behaved like a rigid body (the displacement values from the top and the bottom of the structure are approximately equal). [ABSTRACT FROM AUTHOR]

This study is aimed to investigate the seismic performance of low-rise precast wall system with base isolation. Three types of High Damping Rubber Bearing (HDRB) were designed to provide effective isolation period of 2.5 s for three different kinds of structure in terms of vertical loading. The real size HDRB was manufactured and tested to obtain the characteristic stiffness as well as damping ratio. In the vertical stiffiiess test, it was revealed that the HDRB was not an ideal selection to be used in isolating lightweight structure. Time history analysis using 33 real earthquake records classified with respective peak ground acceleration-to-velocity (a/v) ratio was performed for the remaining two types of HDRB with relatively higher vertical loading. HDRB was observed to show significant reduction in terms of base shear and floor acceleration demand in ground excitations having a/v ratio above 0.5g/ms-1, very much lower than the current classification of 0.8g/ms~'. In addition, this study also revealed that increasing the damping ratio of base isolation system did not guarantee better seismic performance particularly in isolation of lightweight structure or when the ground excitation was having lower a/v ratio. [ABSTRACT FROM AUTHOR]

The effects of soil–structure interaction on the performance of a nonlinear seismic base isolation system for a simple elastic structure are examined. The steady-state response of the system to harmonic excitation is obtained by use of the equivalent linearization method. Simple analytical expressions for the deformation of the base isolation system and of the superstructure at resonance are obtained in terms of an effective replacement oscillator characterized by amplitude-dependent frequency, damping ratio, and excitation. Numerical results suggest that the seismic response of a structure resting on an inelastic base isolation system may be larger when the flexibility of the soil is considered than the corresponding response obtained by ignoring the effects of soil–structure interaction. It is shown that, in the undamped case and in the absence of soil–structure interaction effects, a critical harmonic excitation exists beyond which the steady-state resonant response of the isolators and structure become unbounded. [ABSTRACT FROM AUTHOR]

In this article, the optimization of isolation system parameters via the harmony search (HS) optimization method is proposed for seismically isolated buildings subjected to both near-fault and far-fault earthquakes. To obtain optimum values of isolation system parameters, an optimization program was developed in Matlab/Simulink employing the HS algorithm. The objective was to obtain a set of isolation system parameters within a defined range that minimizes the acceleration response of a seismically isolated structure subjected to various earthquakes without exceeding a peak isolation system displacement limit. Several cases were investigated for different isolation system damping ratios and peak displacement limitations of seismic isolation devices. Time history analyses were repeated for the neighbouring parameters of optimum values and the results proved that the parameters determined via HS were true optima. The performance of the optimum isolation system was tested under a second set of earthquakes that was different from the first set used in the optimization process. The proposed optimization approach is applicable to linear isolation systems. Isolation systems composed of isolation elements that are inherently nonlinear are the subject of a future study. Investigation of the optimum isolation system parameters has been considered in parametric studies. However, obtaining the best performance of a seismic isolation system requires a true optimization by taking the possibility of both near-fault and far-fault earthquakes into account. HS optimization is proposed here as a viable solution to this problem. [ABSTRACT FROM AUTHOR]

SUMMARY This paper investigates numerically the seismic response of six seismically base-isolated (BI) 20-story reinforced concrete buildings and compares their response to that of a fixed-base (FB) building with a similar structural system above ground. Located in Berkeley, California, 2 km from the Hayward fault, the buildings are designed with a core wall that provides most of the lateral force resistance above ground. For the BI buildings, the following are investigated: two isolation systems (both implemented below a three-story basement), isolation periods equal to 4, 5, and 6 s, and two levels of flexural strength of the wall. The first isolation system combines tension-resistant friction pendulum bearings and nonlinear fluid viscous dampers (NFVDs); the second combines low-friction tension-resistant crosslinear bearings, lead-rubber bearings, and NFVDs. The designs of all buildings satisfy ASCE 7-10 requirements, except that one component of horizontal excitation, is used in the 2D nonlinear response history analysis. Analysis is performed for a set of ground motions scaled to the design earthquake and to the maximum considered earthquake (MCE). At both the design earthquake and the MCE, the FB building develops large inelastic deformations and shear forces in the wall and large floor accelerations. At the MCE, four of the BI buildings experience nominally elastic response of the wall, with floor accelerations and shear forces being 0.25 to 0.55 times those experienced by the FB building. The response of the FB and four of the BI buildings to four unscaled historical pulse-like near-fault ground motions is also studied. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]