Seismic Protection Of Structures Research Articles

Design and Experimental Assessment of a Prestressed Lead Damper with Straight Shaft for Seismic Protection of Structures

This study introduces a new energy dissipation device with a high damping capacity for the seismic protection of buildings. The device exploits the friction losses between a movable shaft and a lead core to dissipate the seismic energy and takes advantage of the prestressing of the lead material to control the friction force. Numerical analyses are introduced to evaluate the influence of prestressing on the axial force of the device. Cyclic tests performed on a prototype demonstrate the high damping capability, with an equivalent damping ratio ξeff of approximately 55%, a robust and stable response over repeated cycles and a low sensitivity of the mechanical properties to the frequency, suggesting that the proposed device may be a potentially effective solution for providing supplementary energy dissipation to structures in seismic areas. Moreover, the device is able to endure multiple cycles of motion at the basic design earthquake displacement, ensuring maintenance-free operation even in presence of repeated ground shakes.

A novel structural seismic protection system with negative stiffness and controllable damping

In this paper, an innovative controllable negative stiffness system (CNSS) integrating adaptive negative stiffness and controllable damping characteristics is proposed to realise desirable vibration protection and improve adaptability, hence being effective to various earthquakes. The force-displacement relationship of the CNSS is derived as the forward model to describe its nonlinear properties. Three representative control algorithms, i.e., Linear Quadratic Regular (LQR) control, H∞ control and Sliding Mode (SM) control, are utilised for the CNSS to attain optimal control force. Based on the Takagi-Sugeno-Kang (TSK) Fuzzy inference system optimised by Non-Dominated Sorted Genetic Algorithm II (NSGAII), a novel inverse model is proposed accordingly to obtain input current according to the required control force and real-time system responses. To demonstrate the feasibility and efficiency of the CNSS for structural seismic protection, a numerical case study is conducted on a three-storey building model with CNSS installed on its first floor. Four scaled benchmark earthquakes are employed as excitations for the case study. Ten evaluation criteria are adopted to assess and verify the performance of the CNSS, and comparisons are made with that of uncontrolled and passive controlled systems. The numerical results indicate that the proposed CNSS can significantly improve the vibration control performance on all evaluation criteria simultaneously in comparison with the other two conventional systems. In addition to having good suppression effects on peak floor displacement and peak inter-storey drift, the CNSS with the SM controller demonstrates superior performance on mitigating peak structure shear and peak acceleration response of the first floor.

Effectiveness of damaged viscoelastic dampers in seismic protection of structures under main shocks and aftershocks

It has been demonstrated through uniaxial reversal loading tests that damaged viscoelastic dampers are to some extent still able to possess stiffness and energy dissipation capabilities. Based on past performance test results, some analytical models originating from the fractional derivative method have been provided to account for the design, beyond-design, and residual performances of viscoelastic dampers. In this study, these models are employed for modelling the actual dynamic behavior of supplemental viscoelastic dampers installed at different stages in the numerical model of a practical high-rise steel building. Scenarios of main shocks and subsequent aftershocks are assumed as seismic inputs. The numerical results indicate that, even though viscoelastic dampers suffer damage during main shocks, the damaged dampers are still effective in reducing the structural acceleration and displacement responses compared with the undamped structural responses. It is assumed in the analytical model of viscoelastic dampers that the shear force will be immediately reduced to the beyond-design performance without hardening behavior when suffering damage at the beginning half-cycle. Thus, the damped structural acceleration control performance at that instant, particularly of the floors installed with the damaged dampers, might not be satisfactory but still superior to the undamped structural performance. Although some doubts are clarified in this study, it is emphasized that damaged viscoelastic dampers must still be appropriately repaired or even replaced before the next major earthquake occurs.

Design Strategy of Elastoplastic Dampers for Seismic Protection of Structures

Design Strategy of Elastoplastic Dampers for Seismic Protection of Structures

New structural seismic protection for high-rise building structures

Presented Structural Seismic Isolation Method (SSIM) aims to provide high safety for Highly Reliable Structures (HRS) against strong earthquakes including near-fault and long-period ground motions. The examined structure is converted to Structural Seismic Isolation System (SSIS) by the SSIM method which exhibited inverse pendulum behaviour. For this purpose, structure foot base and foundation contact surfaces have been designed as any curved surfaces (spherical, elliptical, etc.) depending on the earthquake-soil-superstructure parameters and this contact surfaces have been separated by elastomeric (lead core rubber or laminated rubber bearings) seismic isolation devices. It would allow the structure foot base to turn around gyration centre through rubber bearing contact and maintains similar behaviour to the super-structure. SSIS system provides the possibility of keeping the natural-period of the structure in a larger interval, which is greater than the predominant-period of the majority of possible earthquakes (including near-fault pulse) using currently existing conventional elastomeric isolators with up to 4 second period. Thus, the structure can sustain its serviceability after strong and long-period earthquakes. In this study SSIS system’s performance is presented for high-rise building structures, for this aim, the finite element model of the building (Bg) structure with SSIS system (SSIS-Bg) has been prepared and the nonlinear dynamic analysis of the model has been conducted using strong and long-period ground motions. Results indicate that the base and top accelerations, base shear and base moment responses of the SSIS-Bg structure is 23.21 %, 75.47 % and 85.74 % in average lower than the Conventional Application Method of Seismic Base Isolation Devices for Building (CAMSBID-Bg) structures respectively and it is not prone to resonant vibrations under long-period earthquakes related with the excessive deformation in the isolation layers in case of using CAMSBID-Bg structures. It should be noted that in this study with the presented SSIM method and SSIS system, it is aimed to protect only the Highly Reliable Structures(HRS) from the effects of strong and long-period ground motions and these structures (HRS) are classified as follows: 1) Nuclear Containment Structures; 2) High-rise buildings that contain information, operating systems, sensitive instruments, communication systems, routing systems, bank operating systems, databases, management systems and other similar facilities that are linked to the security and economy of a country; 3) High-rise hospitals etc.

Optimization of seismic response of steel structure using negative stiffness damper

Earthquakes of greater magnitude can cause stark destruction. Seismic protection of structures is one important tool to minimize damages and total collapse of structures. Researchers have made many attempts to achieve this goal with various techniques and one such strategy of seismic response control developed is introducing true negative stiffness in the structure. True negative stiffness is introduced with the help of negative stiffness damper (NSD). The NSD generates force in the direction of the displacement and hence it is called negative stiffness. The present study focuses on modelling NSD device in a commercial software tool (ETABS 2016). Further the device is implemented on 2D steel frame models and seismic parameters such as base shear, storey displacement and top storey acceleration are studied.

Multi-Span Steel–Concrete Bridges With Anti-seismic Devices: A Case Study

Seismic protection of structures in general, and bridges in particular, is very complex. In particular, the analysis of bridges with fluid viscous dampers and shock transmitting devices must be done on the best possible analytical model. Indeed a large number of factors must be treated accurately in order to be even more efficient in preserving human life. For complex structures, as is the case of the viaduct under examination, which contains numerous devices, consistent of fluid-viscous dampers and shock transmitters integrated with bearings, design assisted by testing is an almost necessary procedure. In this respect, the FE modelling of the viaduct have required a model updating procedure for its optimization. In fact, the viaducts built within the Caltagirone Project, can be fully defined as works of great interest due both to the construction methods adopted and to the techniques of stress control in the seismic stage. The design process allowed to solve seismic issues deriving from structural irregularities (altimetric and planimetric) as well as from the high seismicity of the area. The analyses have been carried out by a Capacity Design approach, using non-linear seismic dissipative devices integrated to supports and checking that the substructures maintain substantially elastic. For this reason the piers have been modelled upon their non-linear behaviour under Takeda's hysteretic model. Furthermore, fluid viscous dampers and shock transmitters integrated with bearings, have been designed in accordance with the different stiffness by the substructures, this allowing to limit and partially dissipating stresses induced by earthquakes, in order to keep the deck and the substructures substantially elastic for Life-Safety Limit state condition (at the Ultimate Limit State). The verifications carried out have demonstrated the capability of structures to withstand the stresses under the Collapse Limit State condition without damage, plus ensuring the curvature capability by piers. The comparisons between experimental and numerical results together with the demanding qualification tests carried out in this study, demonstrates that the hydraulic devices are an efficient solution to control the seismic stresses induced on the viaduct and in its substructures, confirming the reliability of the aforesaid devices, that ensure a better structural safety.

Robust-to-Uncertainties Optimal Design of Seismic Metamaterials

Metamaterials, which draw their origin from a special class of structured (periodic) materials characterized by a dynamic filtering effect, have recently emerged as a prospective means for structural seismic protection. This paper explores such a periodic arrangement in the form of local adaptive resonators buried in the soil, serving as a seismic protection barrier. As a starting point, a simplistic representation is chosen herein that comprises chains of mass-in-mass unit cells. A robust-to-uncertainties optimization of such a chain, addressing uncertainties at the level of the excitation, the system properties and the model structure itself, is conducted. The optimization problem is formulated within the context of reliability assessment, where the objective function is the failure probability of the structure to be protected against seismic input. The problem is solved through adoption of the subset optimization algorithm enhanced through the simultaneous implementation of a stochastic approximation algorithm. It is demonstrated that not all parameters of the chain model require optimization, because the failure probability proves to be a monotonic function of a subset of the parameters. A primary objective herein lies in optimizing the internal unit-cell stiffness properties. It is further demonstrated that the effectiveness of the protection offered by the metamaterial is improved for spatially varying unit-cell properties. The optimization procedure is carried out in the frequency domain, with an example application confirming that a time domain optimization is expected to yield similar optimal configurations. A parametric study using a nonlinear model is also presented, offering a starting point for more refined future investigations.

Prototype Testing of a New Passive Energy Dissipation Device for Seismic Retrofit of Bridges

The increasingly demanding performance requirements trigger the development of new devices to eliminate the limitations concerning the post-earthquake performance of available seismic protection systems. The prerequisite for economical earthquake-resistant bridges is the structures’ capacity to absorb and dissipate a large amount of seismic energy. A widely considered strategy for enhancing this capacity is through the use of passive energy dissipation systems for seismic protection of structures. It has been known that majority of the available energy dissipation systems are non-usable after a major earthquake, which increases the risk of collapse during an aftershock. The focus of the current study is given to introduce a new type of passive energy dissipation device with a pending patent that is testified to have an improved energy dissipation capacity without suffering any damage while absorbing energy. Thus, the proposed damper does not require an immediate expensive replacement and keeps its operational capabilities and effectiveness during aftershocks. The paper presents the dynamic performance tests of the first full-scale prototype of the damper that eventually prove it to be a promising design with an improved energy dissipation capacity and stable behavior during and after the dynamic event.

A base isolation system for structures subject to extreme seismic events characterized by anomalous values of intensity and frequency content

In this paper the seismic response of a multi-storey reinforced concrete (RC) building base isolated by lead rubber bearings (LRBs) is compared with the seismic response of the same structure base isolated by an innovative seismic isolator which we called high damping hybrid seismic isolator (HDHSI). The study is performed in the context of passive structural control and seismic base isolation technique for the earthquake resistance of RC buildings. This novel high damping hybrid seismic isolator (HDHSI) is obtained by the assembly in series of a lead rubber bearing (LRB) and a friction slider (FS) characterized by a high friction coefficient. The base isolation system is realized by elastomeric materials and steel-teflon bearings. The nonlinear behavior of the composite devices is investigated by reporting a detailed analysis of the hysteretic cycles of the isolators.The purpose of the analysis is to highlight the features offered by the proposed HDHSI base isolation system compared to the traditional LRB base isolation system in the seismic protection of structures. Nonlinear dynamic analyses are performed for base isolated multi-storey RC structures. In the analysis the inputs of different seismic events are adopted which can be considered as extreme events in terms of peak ground acceleration and in terms of frequency content. The seismic records are related to seismic events obtained by suitably amplifying the El Centro earthquake. They are characterized by their high values of the peak ground acceleration. Another seismic event considered in the analysis is the Erzincan earthquake which is characterized by high energetic content at low frequencies. Accordingly, the seismic events adopted in the analysis are characterized by anomalous values of intensity and frequency content. A nonlinear dynamic analysis is illustrated for a multi-storey RC building base isolated by the proposed HDHSI system compared with the traditional LRB base isolation system. The time history of the base shear and the time history of the base displacement of the superstructure are illustrated for the different analyzed seismic events. The benefits of the presented composite HDHSI base isolation system are shown to be appropriate in conferring a suitable seismic protection to multi-storey RC buildings even under extreme seismic events.

Seismic Protection of Structures with Supplemental Rotational Inertia

AbstractThis paper investigates the alternative strategy of suppressing ground-induced vibrations with supplemental rotational inertia. The proposed concept employs a rack-pinion-flywheel system where its resisting force is proportional to the relative acceleration between the vibrating mass and the support of the flywheels. This arrangement, known in the mechanical networks literature as the inerter, complements the traditional supplemental damping and stiffness strategies used for the seismic protection of structures. The paper shows that the seismic protection of structures with supplemental rotational inertia has some unique advantages, particularly in suppressing the spectral displacements of long period structures—a function that is not efficiently achieved with large values of supplemental damping. The paper shows that this happens at the expense of transferring appreciable forces at the support of the flywheels and proceeds by examining to what extent the finite stiffness and damping of the suppor...

A comparative study on parameter identification of fluid viscous dampers with different models

Fluid viscous dampers are extensively adopted as efficient and cheap energy dissipation devices in structural seismic protection. If we consider the usefulness of these passive control devices, the exact recognition of their mechanical behavior is of outstanding importance to provide a reliable support to design a very efficient protection strategy. In scientific and technical applications, many different constitutive models have been proposed and adopted till now to represent fluid viscous dampers, with different levels of complexity and accuracy. This paper focuses on parameter identification of fluid viscous dampers, comparing different existing literature models, with the aim to recognize the ability of these models to match experimental loops under different test specimens. The identification scheme is developed evaluating the experimental and the analytical values of the forces experienced by the device under investigation. The experimental force is recorded during the dynamic test, while the analytical one is obtained by applying a displacement time history to the candidate mechanical law. The identification procedure furnishes the device mechanical parameters by minimizing a suitable objective function, which represents a measure of the difference between the analytical and experimental forces. To solve the optimization problem, the particle swarm optimization is adopted, and the results obtained under various test conditions are shown. Some considerations about the agreement of different models with experimental data are furnished, and the sensitivity of identified parameters of analyzed models against the frequency excitation is evaluated and discussed.

Seismic protection of critical infrastructures through innovative technologies

Development of new technologies for seismic protection will better support the sustainable urban systems. The paper focuses on development of an innovative technology for seismic protection of bridges using smart materials. The seismic protection of structures with the use of special devices is widely accepted as a very effective technique, both for new constructions and for retrofitting of existing ones. Shape memory alloys show the potential to eliminate the limitations of the present technologies, presenting broader application domain. Damper cum restraining device with recentering capabilities has been developed within the laboratory and shake table experiments were conducted on an equivalent SDOF system for a specific narrow band spectrum. The model was subjected to a strong resonant earthquake ground motion in the horizontal direction and analytical investigations were carried out. The damper is found to be very effective for seismic performance enhancement of critical facilities like bridges offering great benefits for the sustainable development of urban systems.

Recentering Shape Memory Alloy Passive Damper for Structural Vibration Control

This paper presents a preliminary study on the evaluation of an innovative energy dissipation system with shape memory alloys (SMAs) for structural seismic protection. A recentering shape memory alloy damper (RSMAD), in which superelastic nitinol wires are utilized as energy dissipation components, is proposed. Improved constitutive equations based on Graesser and Cozzarelli model are proposed for superelastic nitinol wires used in the damper. Cyclic tensile-compressive tests on the damper with various prestrain under different loading frequencies and displacement amplitudes were conducted. The results show that the hysteretic behaviors of the damper can be modified to best fit the needs for passive structural control applications by adjusting the pretension of the nitinol wires, and the damper performance is not sensitive to frequencies greater than 0.5 Hz. To assess the effectiveness of the dampers for structural seismic protection, nonlinear time history analysis on a ten-story steel frame with and without the dampers subjected to representative earthquake ground motions was performed. The simulation results indicate that superelastic SMA dampers are effective in mitigating the structural response of building structures subjected to strong earthquakes.

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.

Special Issue on Design and Analysis of Structures with Seismic Damping Systems

The papers in this special issue focus on the theme of design and analysis of structures with seismic damping systems, the intent being to provide a summary of current research activities within the general field of seismic energy dissipation systems. The special issue originated within the ASCE-SEI Task Committee on Supplemental Damping Systems for Seismic Applications, a committee serving under the ASCE-SEI Committee on Seismic Effects. Two members of the task committee, Finley A. Charney and Andrew S. Whittaker, were particularly helpful in developing the special issue, assisting with its early development, and the soliciting manuscript reviews. Their efforts are gratefully acknowledged. In addition, the general membership of the Seismic Effects Committee supported the efforts of the task committee by serving as reviewers for many of the manuscripts. Their collective efforts are sincerely appreciated. The special issue begins with a lead paper, “Energy Dissipation Systems for Seismic Applications: Current Practice and Recent Developments,” which is coauthored by a mix of academicians and practitioners Symans, Charney, Whittaker, Constantinou, Kircher, Johnson, and McNamara. The lead paper provides an overview of current practice and recent developments in the application of passive energy dissipation systems for seismic protection of structures, with particular attention given to the application of such systems within the framing of building structures. Furthermore, emphasis is given to descriptions of viscous, viscoelastic, metallic, and friction damping systems, including recent applications of such systems. In the paper “Design Formulations for Supplemental Viscous Dampers to Building Structures,” Hwang, Huang, Yi, and Ho examine the accuracy of existing design formulas for determining the damping coefficients corresponding to a specified added damping ratio. They conclude that the effect of flexural deformations of a building is as significant as the shear deformations and that neglecting flexural deformations leads to inaccurate damping ratios. New design formulas are presented that account for both flexural and shear deformations, providing more accurate predictions of the damping ratio contributed by linear viscous dampers and ensuring a more conservative design for buildings that employ nonlinear viscous dampers. In “Comparison of Methods for Computing Equivalent Viscous Damping Ratios of Structures with Added Viscous Damping,” Charney and McNamara demonstrate that the approach used to compute modal damping ratios can have a significant influence on the computed values and that the axial flexibility of toggle-brace linkages can result in reduced system damping as the damping constant of the damper increases, a phenomenon that is readily observed through examining complex-valued mode shapes. In their paper “Seismic Protection of Frame Structures by Fluid Viscous Damped Braces,” Sorace and Terenzi present results from experimental testing of two three-story building frames, one constructed of steel and the other of reinforced concrete, each containing a bracing system employing fluid viscous dampers. The method by which the damping coefficient of the dampers was selected is discussed and evaluated by comparing the target response with the experimentally measured response. An analytical study entitled “Fluid Dynamics and Behavior of Nonlinear Viscous Fluid Dampers” is presented in the paper by Hou. In this study, the dynamics of the fluid flow are evaluated through solving the Navier-Stokes equations, and the shear-thinning effect and viscoelasticity of the fluid are considered. Comparisons with experimental data show that both the nonlinear viscous and restoring force behavior can be captured. The seismic response of a three-story reinforced concrete frame with viscous wall dampers is investigated by Lu, Zhou, and Yan in their paper “Shaking Table Test and Numerical Analysis of RC Frames with Viscous Wall Dampers.” In addition, the effect of the wall dampers on the seismic performance of a partially damaged reinforced concrete frame is examined. The test results demonstrate that the viscous wall dampers add significant damping while also providing some increase in stiffness, reducing the test structure displacements, and in some cases, increasing accelerations.

THE BEHAVIOUR OF SMA ISOLATION SYSTEMS BASED ON A FULL-SCALE RELEASE TEST

Two full-scale isolation re-centring devices, embodying NiTi Shape Memory Alloy elements, were designed and manufactured as the final product of a European research project for the exploitation of SMA's in the seismic protection of structures (MANSIDE Project). The devices were subjectod to several experimental tests aimed at verifying the feasibility and evaluating the mechanical properties of SMA-based devices for the passive seismic protection of buildings and bridges. In order to fully check the applicability of SMA-based isolation systems in real situations, the two devices were temporarily installed in a small base-isolated building, at Rapolla, Southern Italy, which was subjected to several in situ release tests. The complete SMA-based isolation system consisted of the SMA re-centring devices and steel-PTFE lubricated sliding bearings. The release tests were carried out by moving the superstructure and then suddenly releasing it. Numerical seismic simulation analyses have also been carried out to evaluate the effects of the variations of the mechanical characteristics of the isolation systems, including those due to temperature, on the seismic behaviour of the building. Based on these results, a proposal for the improvement of the performances of SMA based isolation systems is made and verified by numerical simulations.

Theoretical and Experimental Studies for the Application of Shape Memory Alloys in Civil Engineering

Shape memory alloys (SMAs) have great potential for use in the field of civil engineering. The authors of this paper have been involved, from 1996, in several experimental and theoretical studies of the application of SMAs in civil engineering, for national and international research projects. This paper provides an overview of the main results achieved, consisting of the conceptual design, implementation, and testing of three families of SMA-based devices, namely: (i) special braces for framed structures, (ii) seismic isolation devices for buildings and bridges, and (iii) smart ties for arches and vaults. The main advantage of using SMA-based devices in the seismic protection of structures comes from the double-flag shape of their hysteresis loops, which implies three favorable features, i.e., self-centering capability, good energy dissipation capability, and high stiffness at small displacements. The main advantage of smart ties comes from the thermal behavior of SMA superelastic wires, which is opposite to that of steel rod. This implies a strong reduction of the force changes caused by variations of air temperature.

ゴムと建築・建設材料 建築免震用積層ゴム支承

Destructive earthquakes may happen anytime anywhere at. Many lives and property were lost, and public traffic and life-lines suffered from damages in the past seismic events. Seismic isolation technology has gained popularity in the recent decade as one of the measures fo+r seismic protection of structures, and elastomeric isolators are the essential devices which construct seismic isolation systems. In this paper, principle of seismic isolation, actual records obtained in seismic-isolated structures, characteristics and requirements of isolators, basic issues of rubber materials and aging properties, and recent activity regarding development of ISO standards are introduced.

Efficiency of base isolation systems in structural seismic protection and energetic assessment

AbstractThis paper concerns the seismic response of structures isolated at the base by means of High Damping Rubber Bearings (HDRB). The analysis is performed by using a stochastic approach, and a Gaussian zero mean filtered non‐stationary stochastic process is used in order to model the seismic acceleration acting at the base of the structure. More precisely, the generalized Kanai–Tajimi model is adopted to describe the non‐stationary amplitude and frequency characteristics of the seismic motion.The hysteretic differential Bouc–Wen model (BWM) is adopted in order to take into account the non‐linear constitutive behaviour both of the base isolation device and of the structure. Moreover, the stochastic linearization method in the time domain is adopted to estimate the statistical moments of the non‐linear system response in the state space. The non‐linear differential equation of the response covariance matrix is then solved by using an iterative procedure which updates the coefficients of the equivalent linear system at each step and searches for the solution of the response covariance matrix equation.After the system response variance is estimated, a sensitivity analysis is carried out. The final aim of the research is to assess the real capacity of base isolation devices in order to protect the structures from seismic actions, by avoiding a non‐linear response, with associated large plastic displacements and, therefore, by limiting related damage phenomena in structural and non‐structural elements.In order to attain this objective the stochastic response of a non‐linear n‐dof shear‐type base‐isolated building is analysed; the constitutive law both of the structure and of the base devices is described, as previously reported, by adopting the BWM and by using appropriate parameters for this model, able to suitably characterize an ordinary building and the base isolators considered in the study.The protection level offered to the structure by the base isolators is then assessed by evaluating the reduction both of the displacement response and the hysteretic dissipated energy. Copyright © 2003 John Wiley & Sons, Ltd.