Application Of Seismic Isolation Research Articles

Retrofitting Alternatives for an Existing Maillart-Arch-Type Bridge: A Case Study

This article examines different retrofit approaches for a still-in-use deck-stiffened arch bridge, the Viadotto Olivieri in Salerno (A3 Highway—South Italy). In its current state, the viaduct is characterized by a central Maillart-arch system, separated by 6 cm-deep joints from two lateral girder portions: the whole system works as an isostatic scheme on a global scale. Dating back to the 1960s, it derives from an early design approach, not including the effects of seismic actions. Considering the demands of current codes, also in light of recent bridge collapses and the resulting plan for assessing the structural safety and vulnerability of existing bridges, studies on seismic capacity become necessary to highlight the potentials and deficits of such complex structures. Analysing a still-in-use example of a Maillart-arch-type bridge, the article examines two different retrofit approaches. The first retrofit alternative includes the strengthening and partial modification of the original deck bridge: it exploits the beneficial effects of making the slender vault collaborate with a more rigid single deck, resulting from joint closure. Moving in the opposite direction, the second alternative considers the application of seismic isolation to the original scheme. An intermediate Isolation System (IS) has been postulated, inserting rubber devices—High Damping Rubber Bearings (HDRBs)—below the deck, at the top of the cross-walls. The advantages of an IS are clear, observing a great reduction of base reactions; moreover, the introduction of the IS completely modifies the original static scheme and exacerbates bridge deformability, at the expense of slender cross-walls, suffering for buckling. A comparison between these retrofit alternatives is argued in the article, evaluating the impact of different types of solution on the valuable original structural scheme.

Seismic Isolation Effects on Elevated and Ground-Supported Flexible Concrete Cylindrical Tanks Under Bi-Directional Excitation Using an Advanced Mechanical Model

In this paper, the effectiveness of seismic isolation using lead rubber bearings (LRBs) and friction pendulum systems (FPSs) for slender and broad, grounded and elevated tanks (two seat locations of isolation systems in elevated tanks) is investigated under bi-directional excitation of up to 10 records of earthquakes. An analytical mechanical model for a flexible, concrete cylindrical tank, taking into consideration the effect of wall mass and sloshing, is used. The assumptions underlying the mechanical model are basic equations of the motion according to the theory of fluid dynamics. So, the assumptions are more realistic and the results therefore are more accurate than the previous models. The results show that by selecting the best mechanical properties of base isolation systems, reductions of seismic base shear in the grounded broad tanks are around 35% and 30% and for the grounded slender tanks are around 55% and 58% in the x- and y-directions, respectively. Maximum total hydrodynamic pressure is reduced considerably by about 40% on average in all grounded and elevated models. As a result of isolation, elevated tanks are concluded to be better candidates in terms of more effective application of seismic isolation.

Framework for the design of seismically isolated National Building Code of Canada Part 9 structures

In Canada, most single-family wood-frame residential structures in seismically hazardous regions are constructed according to Part 9 of Division B of the National Building Code (or similar provincial standards) using nonengineering methods. These structures are expected to perform well during an earthquake regarding life safety but may sustain severe economic losses. Seismic isolation is an emerging technology that provides excellent life safety and economic performance. While this technology has proven effective at protecting structures from earthquakes, no nonengineering methodologies exist that are compatible with Part 9 methods. This limitation produces significant testing, design, and cost barriers that restrict the application of base isolation on vulnerable Part 9 structures. To eliminate or reduce these cost barriers, a program framework was developed to perform the engineering seismic design and analysis for a base-isolated Part 9 single-family residential structure. The proposed methodology further encourages the application of seismic isolation to Part 9 structures.

Numerical simulation of seismically isolated buildings with friction pendulum bearings

Introduction. At present, in Tajikistan, buildings and structures are designed and constructed on the basis of passive methods of ensuring seismic resistance, which ultimately leads to an increase in stiffness and weight of structures and, accordingly, in seismic load. The present paper analyses seismic isolation of buildings provided by friction pendulum bearings. The dynamic model of the object under study is represented as a system consisting of a superstructure, substructure and seismic isolation.Aim. To contribute to the development of methods for analysis and evaluation of seismic isolation and earthquake protection of buildings and structures in order to justify the conditions for their effective application in earthquake-resistant construction on the territory of the Republic of Tajikistan.Materials and methods. The authors used methods of structural mechanics, structural dynamics, and numerical simulation. The research methodology involves mathematical modeling of the systems under consideration, numerical analysis, comparison of the obtained results with the available data. Experimental investigation was carried out on a building fragment model and a vibration platform.Results. The authors developed a mathematical model for investigating the stress-strain state of a building with friction pendulum bearings subjected to various external influences, including seismic ones. The differential equation system using successive approximations is transformed into a system of algebraic equations, which is solved at each time step. On the basis of the created algorithm, the authors developed a computer program in Fortran and obtained the numerical results of the dynamic calculation for a multistory building with friction pendulum bearings. The results from the action of an instantaneous impulse are obtained on the example of a 10-story frame building.Conclusions. The results show that the application of seismic isolation in the form of friction pendulum bearings leads to a significant reduction of internal forces in the support part, as well as to a reduction of velocity and acceleration in the upper part of the building compared to the model without seismic isolation bearings. At the same time, the deflections of both the lower and upper parts of the investigated object slightly increase.

Experimental and numerical assessment of grout-filled tennis balls as seismic isolation bearings

This paper describes the behavior of a low-cost seismic isolator comprising a grout-filled tennis ball rolling on concrete plates. The isolator could be used for isolating lightweight structures. Initially, the axial response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. Parameters of investigation were the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, the bearing temperature, the specimen-to-specimen variability, and the engagement of the displacement restrainer. Finally, a three-dimensional finite element model was developed to model in detail the response of the isolator and to explore the influence of the rubber thickness. This is the first study to characterize the above effects and to propose a finite element model of these isolators. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency) or temperature, and the isolators did not deteriorate under consecutive loading. The proposed displacement restrainer effectively limits the motion of the isolator. The developed finite element model accurately captures the experimental response. It was used to study the influence of the thickness of the rubber layer on the lateral response, to conclude that it is minimal, for rubber layers ranging from 3.4 to 7 mm.

Global torsional response of seismically isolated nuclear plants and evaluation of codal provisions

A major challenge in the application of seismic isolation to nuclear structures is the torsional response of base-isolated Nuclear Power plants (NPPs), which amplifies the isolator displacement around the periphery of the isolation system. Additionally, degradation in the mechanical properties of the isolator due to the response associated with extreme ground shaking may also affect the torsional response. This paper presents a comprehensive study on the torsional response of a NPP seismically isolated using lead rubber bearings with a focus on the isolation properties and eccentricity in the isolation system. Nonlinear response history analysis is conducted with different NPP model representations, which are derived from a benchmark NPP model for a range of eccentricities with different time periods and characteristic strengths. It was observed that torsional response in base-isolated NPPs could be controlled by using a flexible isolation system of higher characteristic strength, and it may be important to include the strength degradation in lead rubber isolators to correctly estimate torsional amplification to isolator displacements. The torsional amplification predicted by the nonlinear response history analysis was also compared with the provisions of ASCE 7 for buildings, and recommendations are provided on their suitability for seismically isolated NPPs.

Business Continuity in Data Centers and Seismic Isolation Applications

Economic losses from earthquakes raised many questions regarding the adequacy of the current seismic design and seismic isolation in data centers. Organizations accommodated new explicit seismic isolation applications in their business continuity and disaster recovery plans. These applications aim acceptable damage levels that correspond to acceptable business interruption for data centers in case of an earthquake. In this study, the authors aim to discuss the importance of seismic isolation applications that can be implemented for data centers within business continuity and disaster recovery planning contexts. To provide a clearer aspect on seismic isolation applications, the topic has been discussed within the framework of international standards. They conclude that GSA, ASCE, and Uptime Institute provide internationally recognized standards which make raised floors a good option for data centers. These standards provide technical documentation for service functioning with high levels of availability during an outage.

Double link sensor for mitigating tilt- horizontal coupling

The sensitivity of inertial sensors, intended for horizontal motion detection, to tilt due to gravity at low frequency is known as tilt horizontal coupling. This is crucial for numerous seismological studies and seismic isolation applications such as gravitational wave detection. This paper presents a new sensor architecture for mitigating tilt horizontal coupling when exposed to pure translation or tilt. The proposed Double Link (DL) sensor does not need any additional mechanisms and is only sensitive to the translation and negligibly sensitive to tilt. The sensor is in the form of a double pendulum hanging from a platform and the measured output is the relative motion between the two links. The simulations are carried out in Simscape environment and the results confirms the efficiency of the system. The study was carried out as a part of the ETEST project which is aimed at developing a prototype for the future Einstein Telescope Gravitational Wave detector.

Feasibility Study on Re-Using Tennis Balls as Seismic Isolation Bearings

This paper presents an experimental study of a low-cost seismic isolator that can be used for the protection of residential structures in low-income countries. The isolator is based on mortar-filled, used tennis spheres, rolling on flat or spherical concrete surfaces. The tennis spheres serve as permanent, spherical molds to cast mortar, and they are not removed after casting. The thin rubber shell of the tennis sphere offers increased damping and reduces stress concentrations at the contact areas. At the same time, this procedure creates a promising solution for the re-use of tennis spheres. Using a closely-spaced grid of such spheres may allow for avoiding the diaphragm slab at the isolation level, or reducing its thickness. Avoiding the cost of this additional, heavily reinforced isolation slab is crucial for making seismically isolated low-rise dwellings economically feasible in low-income regions of the globe. Initially, the tennis isolators were subjected to monotonic uniaxial compression to examine their behavior under vertical loading. Different mixes and low-cost reinforcement approaches to increase their strength were tested. Subsequently, cyclic tests were performed to obtain the lateral force-displacement diagram of the isolation system. The effects of the geometry of the rolling surface (i.e., flat or concave) and of the applied compressive load (i.e., 2.08, 3.23, 4.74, or 8 kN/sphere) on the cyclic behavior were investigated. It was found that the restoring force of such systems mainly originates from the curvature of the concrete surface. However, the vertical motion induced by the compressed sphere and its local casting imperfections is not negligible. When surface imperfections become significant, the force-displacement loops deviate from the bilinear curves that a rigid-body model suggests. When the spheres are properly cast, they experience zero damage even under 8 kN of compressive force, and their loops have a bilinear form. For the tested configurations, the rolling friction (defined as the ratio of lateral to vertical force at zero displacement) was in the range of 4.7–7.2%, thus suitable for seismic isolation applications. The cost of the tested tennis ball isolators was 0.05 $ per sphere.

Earthquake-Resilient Design of Seismically Isolated Buildings: A Review of Technology

Earthquake Seismic isolation plays an important role in achieving sustainable earthquake resilience communities. Seismic isolation method is a justified, mature, and reliable performance enhancement strategy for a wide range of structural systems and valuable contents. As a result of the targeted response modification, high-performance expectations and earthquake resilience can be achieved during the service life of the structures that are compliant with the design code requirements. Design and analysis procedures of isolation systems in standards were evolved substantially to expand the use of isolation technology and quantify the benefits of isolation systems to overcome the existing impediments. Strictly speaking, new tools are offered to the engineering community to highlight the possible issues that may appear in isolation units beyond the design basis earthquake level to improve the accuracy of response prediction. This paper aims to overview the characteristics of frequently used isolation systems in the industry with mathematical models, design criteria toward sustainable communities, the current state of practice along with the set forth design requirements of selectively well-known standards with special emphasis to the ELF procedure from the perspective of performance-based design philosophy. Additionally, two large-scale seismic isolation applications in the world are given as benchmark studies for the new construction and upgrading scheme in the content of the study.

Shear stress distribution of unbonded reinforced elastomeric bearings after lift-off occurs

Reinforced elastomeric bearings (REBs) are widely used to accommodate displacements in bridges as well as for seismic isolation applications. For unbonded REBs, lift-off (i.e. separation between the superstructure and the bearings) could occur under certain combinations of large rotations and relatively low axial stress. Canadian and American bridge design codes (i.e. CSA S6 and AASHTO) have inconsistent requirements in the regulation of lift-off. The objective of this study is to validate the existing analytical solution of the moment-rotation relationship for unbonded REBs considering lift-off by finite element analysis (FEA). The analytical solution, which accounts for the compressibility of the elastomer and extensibility of the reinforcement, has not yet been validated. The shear strain distribution in the elastomeric layers of unbonded REBs is derived and validated by FEA. Eight infinite strip-shaped bearings with different number of layers are investigated. The results show that the numerical curves fit well with the analytical curves in terms of the overall tendency. The analytical solutions could be used to predict the behaviour of unbonded REBs subjected to lift-off. The numerical results of the moment-rotation relationship were more agreeable to the analytical solutions for the unbonded bearings with fewer number of layers and under smaller loads.

Analytical and experimental studies on an innovative steel damper reinforced polyurethane bearing for seismic isolation applications

Isolation bearings are widely applied to mitigate the seismic response of civil structures under strong earthquakes. With the development of material science, various advanced materials have been applied in isolation bearings to meet special demands. In this paper, a steel damper reinforced polyurethane bearing (SDRPB) for protection of structures from earthquake damages is developed by innovative usages of steel damper to reinforce a newly developed polyurethane bearing, simultaneously combining the advantages of hysteretic steel and polyurethane elastomer. This paper first presents a general description and illustration of the SDRPB which is composed of a polyurethane bearing and four specially designed C-shaped steel dampers. Then, mechanical modeling of the SDRPB is derived to fundamentally define its cyclic behavior and obtain essential mechanical parameters, with a particular attention on describing the mechanical behavior of C-shaped steel dampers. Subsequently, a series of quasi-static compression, friction, and cyclic shear tests are conducted to comprehensively investigate the mechanical behavior of SDRPB. The test results show that SDRPB exhibits high strength and energy dissipation capacity, and the accuracy of the proposed mechanical model of SDRPB is examined by comparing the hysteretic loops between the experimental and analytical results. Finally, the SDRPB was applied in a typical multi-span continuous isolated bridge to numerically validate its isolation effects in real engineering scenarios. In conclusion, the SDRPB is expected to be served as a promising option with both large vertical bearing and energy dissipation capacities, making it particularly suitable for seismic isolation applications.

Parametric studies on the behaviour of reinforced elastomeric bearings considering the compressibility and extensibility index, shape factor, and lift-off

Reinforced elastomeric bearings (REBs) are widely used in bridges as well as for seismic isolation applications. Analytical solutions for the critical design properties of REBs (e.g. compression and bending modulus, stress distributions) have been derived based on the assumptions of the pressure solution. In all cases, the analytical solutions can be expressed as functions of the dimensionless compressibility and extensibility index. This parameter accounts for the influence of the compressibility of the elastomer and the extensibility of the reinforcement. Together with the shape factor, these variables are highly influential on REB design. The objective of this study is to investigate mechanical behaviour of bonded and unbonded REBs with the same compressibility and extensibility index but different other parameters and the influence of the shape factor by finite element analysis (FEA) including lift-off. For unbonded REBs, lift-off (i.e. the separation between the superstructure and the bearings) can occur under certain combinations of large rotations and relatively low axial stress. Three different loading cases (pure compression, pure bending and the combined case) are considered. The results show that REBs with the same compressibility and extensibility index but different other parameters have similar behaviour under the same loading condition. Available analytical solutions have good agreement with numerical results provided an appropriate shear modulus is selected and the level of rotation is reasonable for structural applications.

Application of seismic isolation for multi-story buildings in moderate seismicity areas like Vietnam

Multi-story buildings are important components of urban infrastructures due to their undeniable advantages. However, their structures are characterized by the mass distributed in height and a great slenderness leading to its earthquake vulnerability. Further, their typical structures designed by the conventional method provide low earthquake resistance. The seismic isolation bearings are considered as an effective solution for the structure located in regions of high and moderate seismic activity. The paper presents the procedure to calculate the isolated building structure located in the moderate seismicity areas such as Vietnam. The bilinear hysteretic model is employed to determine the properties of the isolator through the simplified procedure. Three-dimensional model of a typical 11-story building structure is analyzed to evaluate the effect of the isolator on seismic responses of building. The modal analysis and time history analysis are performed using Etabs V17, with the input record taken according to the earthquake ground motion in Hanoi-Vietnam, calculated by the Vietnamese code. The result shows the high effectiveness of isolator on reducing the seismic effect.

Experimental and Numerical Study of a New Proposed Seismic Isolator Using Steel Rings (SISR)

ABSTRACT The seismic isolation technique is one of the most effective methods to control the seismic vibrations of structures by isolating them from the ground. In this research, an experimental and numerical study of a proposed elastomeric seismic isolator is presented. The proposed seismic isolator is composed of three components: rubber, top, and bottom connection plates, as well as steel rings, to enclose the rubber elements. Compared to common LRB isolators, the lighter weight of the proposed isolator and lower cost are the main features of these new bearings. The goal is to provide a low-cost seismic isolator for one or two-story masonry buildings, reservoirs containing hazardous materials, sensitive equipment, and other applications of seismic isolation for light to medium weights. In this research, a low- damping type natural rubber is used in the fabrication of the proposed seismic isolator with steel rings (SISR). First, using a preliminary FE modeling of the rubber material, the strain energy function (SEF) and the Yeoh hyper-elastic material, the required dimensions of two sizes of the proposed SISRs, to carry 25 kN and 80 kN vertical loads, for two cases of structural application, are determined and two samples for each size of the SISRs are fabricated. Prototype tests of the specimens subjected to the predefined vertical and lateral load patterns are carried out and the performance of SISR specimens is evaluated. The complete testing process of two sizes of the proposed SISR is also simulated by finite element analysis and the numerical results are presented. The force-displacement curves of SISRs, obtained from the tests and numerical analyses, show a satisfactory correspondence and satisfy the requirements of isolator units in accordance with ASCE 7 standard.

Editorial: Recent Advances and Applications of Seismic Isolation and Energy Dissipation Devices

Editorial: Recent Advances and Applications of Seismic Isolation and Energy Dissipation Devices

SEISMIC ISOLATION OF WHOLE CITY QUARTERS FOR AN EFFECTIVE AND PRESERVATIVE RECONSTRUCTION

The post-earthquake reconstruction should solve the problem to rebuild with safety but preserving the historical aspect of buildings and landscapes. This paper proposes a particular application of seismic isolation for the reconstruction of entire urban quarter or entire small centers with integral seismic protection. This involves the construction of large floating slabs having the size of entire compartments supported by seismic isolators and/or dampers, above which to construct buildings that can present the aesthetic and constructive characteristics of the collapsed traditional ones. The solution is suited for the reconstruction of villages or quarters collapsed or damaged. Buildings of any type (masonry, stone, r/c, steel, wood) and of different characteristics also significantly irregular can be freely built above slabs and all of them will be fully protected from the consequences of future expected quakes. Paper illustrates a case study related to a quarter of a historic town in Central Italy.

Evaluation and research needs for seismically isolating nuclear power plants

AbstractThe main focus of this paper was to examine some of the principal advantages and disadvantages cited for the application of seismic isolation to nuclear power facilities. This discussion is followed by an examination of the potential relative impacts on cost and schedule of a conventional fixed‐base design approach vs one based on seismic isolation. This examination considers issues associated with planning, design, operation, and decommission. Some of the challenges related to design and maintenance (during normal operations and following a significant earthquake) are then discussed, and specific research and development topics are identified that are necessary to allow seismic isolation to be pursued with confidence. Finally, overall conclusions and recommendations are offered.

Special Issues in the Application of Seismic Isolation to Nuclear Power Plants

While seismic isolation is one of the principal approaches used to mitigate the risks associated with earthquake ground shaking, it has found only limited application in the construction of nuclear power plants (NPPs). As a new application, it is necessary to understand how the overall process works and figure out potential difficulties in all stages of managing isolated NPPs. Several manufacturers, experts, and representatives from engineering firms were contacted and interviewed to better understand potential difficulties in the application of seismic isolation to NPPs. In addition to this firsthand knowledge, studies and research conducted in the area of radiation exposure and the area of general durability are reviewed. According to these materials, this paper summarizes some issues related to the durability of the isolators, radiation, and other environmental effects on devices and raises some understanding and special issues in the planning, design, analysis, procurement, installation, operations, and maintenance stages of managing a seismically isolated NPP. These topics are expected to provide a certain guiding significance on future application of seismic isolation for NPPs.

Comparison of different models for high damping rubber bearings in seismically isolated bridges

Steel-reinforced high damping natural rubber (HDNR) bearings are widely employed in seismic isolation applications to protect structures from earthquake excitations. In multi-span simply supported bridges, the HDNR bearings are typically placed in two lines of support, eccentric with respect to the pier axis. This configuration induces a coupled horizontal-vertical response of the bearings, mainly due to the rotation of the pier caps. Although simplified and computationally efficient models are available, which neglect the coupling between the horizontal and vertical response, their accuracy has not been investigated to date.In this paper, the dynamic behaviour and seismic response of a benchmark three-span bridge are analysed by using an advanced HDNR bearing model recently developed and capable of accounting for the coupled horizontal and vertical responses, as well as for significant features of the hysteretic shear response of these isolation devices. The results of the analyses shed light on the importance of the bearing vertical stiffness and how it modifies the seismic performance of isolated bridges. Successively, the seismic response estimates obtained by using simplified bearing models, whose use is well established and also suggested by design codes, are compared against the corresponding estimates obtained by using the advanced bearing model, to evaluate their accuracy for the current design practice.