Seismic Base Isolation System Research Articles

Architectural Design of New Buildings with Seismic Base Isolation and Energy Damping Systems

Architectural Design of New Buildings with Seismic Base Isolation and Energy Damping Systems

Earthquake Resisting Building by using Base Isolation

Abstract: Natural disasters have been always been a part of human life since the beginning of time, causing destruction to our lives and properties. Earthquake plays a major role in wreaking this havoc upon us. Various challenges have occurred to withstand structures on earth due to sudden moment of ground it also results in collapse of structure, due to inappropriate design consideration of structure without any seismic resistance. Various techniques to make the building earthquake resistant as well as various shapes and materials are being considered to achieve required strength to resist seismic forces. Various techniques like shear walls, bearings and base isolation are used to withstand the structure against seismic forces. In this project we have used base isolation technique, it is also known as seismic base isolation or base isolation system is a prominent technique to protect the structure against earthquake.

Retrofitting Existing Masonry Structures by Using Seismic Base Isolation System

Retrofitting Existing Masonry Structures by Using Seismic Base Isolation System

Base isolation retrofitting design for the existing 2-story stone building and its Conversion into a 3-Story kindergarten

Recently the Armenian Missionary Association of America (AMAA) has approached the author of this paper with the request to carry out base isolation retrofitting design for the existing 2-story building with stone bearing walls and to simultaneously convert it into a 3-story kindergarten. In Armenia seismic isolation of existing buildings is becoming a more common method of providing protection from earthquake damage. Thanks to the author’s works in nowadays Armenia is well known as a country where seismic (base and roof) isolation systems are widely implemented in construction of new and retrofitting of existing buildings. The number of seismically isolated buildings per capita in Armenia is one of the highest in the world – second after Japan. The paper given below emphasizes that Armenia achieved significant results also in local manufacturing/testing of seismic isolation laminated rubber-steel bearings (SILRSBs). Several remarkable projects on retrofitting by base isolation of the existing buildings like apartment, school, hotel and hospital buildings are briefly mentioned in the paper to demonstrate the retrofitting experience accumulated in Armenia. Based on the gained experience further developments take place and unique base isolation structural concepts and technologies created by the author are applied more and more to the existing buildings. In this paper base isolation retrofitting design and analysis by the Armenian Seismic Code for the 2-story building with stone bearing walls is described. This will be a first application of base isolation retrofitting technology to an existing stone building with simultaneous increase of the number of its floors by one. The other important factor is that applied structural concept allows retrofitting by base isolation when reconstruction works in superstructure and construction of the additional 3-rd floor were going on in the same time.

Developing local rubber mixture for seismic base isolation system type high damping rubber bearing

The research objective is to develop a rubber mixture for the High Damping Rubber Bearing HDRB type of seismic base isolation system to resist seismic loads, and compare it with international companies’ brochures. Experiments were conducted on three HDRB models of 150 mm in diameter and 12 cm in height. These models were manufactured locally from natural rubber with other chemical additives and steel sheets. Load and unload tests (quasi-static) were conducted on the models simulating earthquake loads, first loaded with a vertical load of 110 kN, and then the base cyclic horizontally with an increasing amplitude of 25 % until 125 % of the shear strain. The vertical stiffness was 44,027 kN/m, the effective horizontal stiffness was 334 kN/m, and the damping ratio was 20.1 % experimentally. The results were within satisfactory ranges of the parametric values in the manufacturing design brochure, indicating the developed rubber mixture is convenient, giving a great motivation to manufacture seismic isolators locally at suitable prices.

Optimization of Seismic Base Isolation System Using a Fuzzy Reinforced Swarm Intelligence

The current study deals with the optimization of seismic isolation system parameters applied in base-isolated buildings. In this regard, to consider the more realistic condition, both near-fault and far-fault earthquake ground motions are taken into account by simultaneously imposing six different acceleration records during the direct time integration analysis of the structure. The minimization of the system's peak acceleration ratio is defined as the objective function of the optimization model. To get feasible results, the determining parameters of the isolator are restricted. Such that, while the isolation system period and damping ratio are kept within a predefined range, the maximum displacement of the system is monitored and limited during the optimization process. To solve the proposed optimization model, an enhanced version of the Deferential Evolution method so-called Fuzzy Differential Evolution incorporated Virtual Mutant (FDEVM) is employed. The FDEVM method applies a fuzzy decision-making mechanism to adopt its search behavior based on the governing conditions of the current problem. It also uses a new mutant vector called virtual mutant to contribute information of all population based on each agent's quality. So, the FDEVM works as a self-adaptive and parameter-free search algorithm. The acquired results show that the FDEVM works properly to find the optimal values for the dynamic parameters of the seismic base isolation system.

Optimization of Seismic Base Isolation System Using Adaptive Harmony Search Algorithm

In this study, a seismic isolator placed on the base of a structure was optimized under various earthquake records using an adaptive harmony search algorithm (AHS). As known, the base-isolation systems with very low stiffness provide a rigid response of superstructure, so it was assumed that the structure is rigid and the base-isolated structure can be considered as a single-degree of freedom structure. By using this assumption, an optimization method that is independent of structural properties but specific to the chosen earthquake excitation set is proposed. By taking three different damping ratio limits and isolator displacement limits, the isolator period and damping ratio were optimized so that the acceleration of the structure was minimized for nine cases. In the critical seismic analysis performed with optimum isolator parameters, the results obtained for different damping ratios and isolator periods were compared. From the results, it is determined that isolators with low damping ratios require more ductility, and as the damping ratio increases, further restriction of the movement of the isolator increases the control efficiency. Thus, it is revealed that increasing the ductility of the isolator is effective in reducing the total acceleration in the structure.

Study of isolation effectiveness of nuclear reactor building with three-dimensional seismic base isolation

PurposeIn recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. This paper aims to propose a new 3D combined isolation bearing (3D-CIB) to mitigate the seismic response in both the horizontal and vertical directions.Design/methodology/approachThe new 3D-CIB composed of laminated rubber bearing coupled with combined disk spring bearing (CDSB) was proposed. Comprehensive analysis of constitution and theoretical derivation for 3D-CIB were presented. The advantage of CDSB is that the constitution can be flexibly adjusted according to the requirements of the bearing capacity and vertical stiffness. Hence, four different combinations of CDSB were designed for the 3D-CIB and employed to isolate nuclear reactor building. A comparative study of the seismic response in terms of seismic action, acceleration floor response spectra (FRS), peak acceleration and relative displacement response was carried out.Findings3D-CIB can effectively reduce seismic action, FRS and peak acceleration response of the superstructure in both the horizontal and vertical directions. Overall, the horizontal isolation effectiveness of 3D-CIB was slightly influenced by vertical stiffness. The decrease in the vertical stiffness of the 3D-CIB can reduce the vertical FRS and shift the peak values to a lower frequency. The vertical peak acceleration decreased with a decrease in the vertical stiffness. The superstructure exhibited a rocking effect during the earthquake, and the decrease in the vertical stiffness may increase the rocking of the superstructure.Originality/valueAlthough the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted by different constitutions, the vertical stiffness should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. This study of isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of nuclear power plants.

Dynamic behavior of elevated and ground-supported, base-isolated, flexible, concrete cylindrical fluid containers

Liquid storage tanks are vital and have great importance in industrial facilities. One of the best ways to protect the fluid storage tanks against earthquake forces is the use of seismic isolation systems. These systems protect such structures against possible damage during an earthquake by allowing acceptable displacements at the base of the superstructures while preventing the superstructure from entering the nonlinear phases. One of the common methods for computer modeling of these structures is the use of equivalent mechanical models. It should be noted that, the mentioned equivalent mechanical models, are suggested for design of tanks by Standards and Codes. However, they are appropriate for rigid-wall tanks. On the other hand, the recent studies show that the seismic response of a rigid tank may be considerably less than that of a similar flexible tank. In this study, by using a state-of-the-art equivalent mechanical model of cylindrical concrete containers, that considers the issue of wall flexibility, the seismic responses of ground-supported and elevated concrete containers affected by the bi-directional horizontal motion of the earthquake is investigated. The results show that, by selecting the best mechanical properties of seismic base isolation systems, the seismic responses of these tanks can be greatly improved.

A hybrid seismic isolation system toward more resilient structures: Shaking table experiment and fragility analysis

The effectiveness of various vibration control strategies has always been a debate among structural engineers. Seismic base isolation systems and passive dampers are recognized as two of the most economical devices which have passive mechanisms in reducing the structural vibration and responses. To this end, comprehensive biaxial shake table testings have been carried out on a building frame with and without a proposed base isolation system. The proposed device has a novel combined isolation mechanism at the structure's base. By different methods of testing, natural frequencies and viscous damping for the frame model with and without the proposed system were identified. Both structures were intensively tested under various earthquake motions, and various structural responses were recorded. The experimental results indicated that the newly proposed system is very effective in controlling the vibration of building structures and can be used to increase the seismic resilience metrics. As a complementary investigation, the incremental dynamic analysis (IDA) was conducted to develop the seismic fragility curves under both near-field and far-field strong ground motions (SGMs). The fragility estimations indicated that the proposed system has a higher collapse margin ratio (CMR) compared to conventional fixed-base frames.

Improvement of the polyurethane spring isolation device for HV post insulators and its evaluation by fragility curves

A novel seismic base isolation system has been developed for high-voltage (HV) porcelain post insulators. The seismic isolation device consists of two steel plates, four polyurethane springs, and a steel rod, which are low-cost components compared to the post insulators. Two alternative designs of the device are experimentally and numerically assessed in this article. A simple and robust numerical model consisting of linear line elements and nonlinear springs was generated, and subsequently validated using the experimental results. Incremental dynamic analyses (IDAs) were then performed to obtain fragility curves. Ten historical earthquake profiles, scaled to intensities between 0.1 and 2.0 g, were then applied to the numerical models. The fragility curves, generated according to the latest version of IEEE-693, demonstrate that the seismic isolation devices are highly effective in diminishing the base moment of the porcelain insulator. It should be noted that relatively large displacements at the top of the pole must be accounted for by ensuring adequate slackness in the flexible conductors.

Base isolation design and analysis for the 7-story apartment building “Stepanakert-sections-4-5” with R/C monolithic load-bearing walls and asymmetric plan

In recent years seismic isolation technologies in Armenia were extensively applied in construction of multi-story residential, medical, hotel, airport, and business center complexes with parking floors and with floors envisaged for offices, shopping centers, fitness clubs, etc. To date there are 55 seismic isolated buildings in the country newly constructed or retrofitted by base or roof isolation systems. Of this number of buildings 48 were erected thanks to the works of the author of this paper and in nowadays Armenia is well known as a country where seismic (base and roof) isolation systems are widely implemented in civil construction. The number of seismically isolated buildings per capita in Armenia is one of the highest in the world – second after Japan. The paper given below emphasizes achievements also in local manufacturing/testing of seismic isolation laminated rubber-steel bearings (SILRSBs). Several remarkable projects on construction of base isolated buildings are briefly mentioned in the paper to demonstrate the experience accumulated in Armenia. Based on the gained experience further developments take place and unique base isolation structural concepts and technologies created by the author are applied more and more in construction of new buildings. In this paper base isolation design and analysis by the Armenian Seismic Code for the 7-story apartment building to be constructed in Stepanakert is described. This will be a first application of base isolation technology to a building the bearing system of which consists of reinforced concrete (R/C) monolithic load-bearing walls and building has an asymmetric plan. It is stated that suggested seismic isolation strategy will reduce the cost of construction of the given building on about 35% in comparison with the cost of conventional construction. Obtained results indicate the high effectiveness of the proposed structural concept of isolation system and the need for further improvement of Seismic Code provisions regarding the values of the reduction factors.

Innovations at Beijing Daxing International: the world’s biggest airport terminal

Beijing Daxing International, which officially opened in September 2019 after 5 years of construction, is the largest airport in China and has the world’s biggest airport terminal. It is also the first to feature double-deck arrival and departure lounges and an underground high-speed rail service. Engineering highlights include a world-class seismic base isolation system, a long-span irregular curved node truss structure, a glazed roof with 12 800 panes, eight hyperboloid C-shaped columns as the main load-bearing elements and multiple energy-saving systems.

Parameters Affecting Dynamics of Three-Dimensional Seismic Isolation

ABSTRACT Seismic base isolation systems are mainly used to reduce seismic demands and minimize earthquake effect on structure performance. In this study, the fundamental dynamic response of structures with three-dimensional (3D) isolation systems is explored using a simplified rigid block model. A parametric study is carried out to evaluate the effect of different site conditions, structure properties and 3D isolation parameters on structure and bearing response. The results show that the acceptable range of 3D isolation periods is 0.5–1.0 s for vertical direction with horizontal isolation period around 3–4 times the vertical period and 20% damping in both directions.

Phenomenological Model of Rubber Bearings With Variable Axial Loading

Seismic base isolation systems protect thousands of structures and infrastructures all over the world. Their effectiveness for seismic protection is widely recognized owing to acceleration reduction with a consequent minimization of the structural damage and of the ‘panic’ effect for the occupants. This work deals with the development of a model for simulating the horizontal response of rubber bearings, extending an existent procedure to the case of variable axial loading. A consolidated procedure from literature, demonstrated able to correctly reproduce the complex mechanical behavior of rubber bearing isolation devices under constant axial loading, represents the starting point. Available laboratory cycling tests at variable axial load allow to illustrate the new numerical formulation. An optimization process, based on both automatic and user-driven procedures, is used to identify at different loading conditions the model parameters and the functions to model their variation. The proposed formulation overcomes the limits of the original model in this respect. The developed new version of the bearing model is shown to be capable of simulating with reasonable accuracy the experimentally observed cyclic behavior under coupled vertical-horizontal loading conditions, and the consequences in terms of the device response in the case of a seismic vertical-horizontal concurrent excitations are highlighted.

Seismic responses of base-isolated flexible rectangular fluid containers under horizontal ground motion

This paper focuses on analyzing, the results and arguments about the analysis of seismic base-isolated flexible rectangular containers. An equivalent mechanical model of rectangular containers with three lumped masses and six degrees of freedom is used. Lead rubber bearing (LRB) and friction pendulum system (FPS) are two types of seismic isolators, used to isolate the storage tank base. Results show that seismic base isolation can be an efficient way to reduce seismic responses such as base shear, wall deflection and hydrodynamic pressure, but it can adversely affect the free surface sloshing height. The seismic responses of isolated tanks under unidirectional excitation (No interaction) and bidirectional excitation (Interaction) are not considerably different and the results are not very sensitive to the interaction effect of the bearing forces. In any case, the careful choice of the number and the mechanical characteristics of seismic base isolation systems is suggested to achieve good responses.

A Simplified Parametric Study on Occupant Comfort Conditions in Base Isolated Buildings under Wind Loading

Vibrations in buildings can cause occupant discomfort in the form of annoyance, headache, or sickness. While occupant comfort is considered in international standards regarding the design of high rise buildings against wind loading, it is neglected in the design of buildings with seismic protective base isolation systems. Nevertheless, due to their low flexibility, base isolated buildings can be prone to wind-induced vibrations, which makes occupant discomfort a potentially significant serviceability limit state. This paper presents a study on occupant comfort conditions in wind-excited base isolated buildings. A numerical simplified parametric procedure is proposed in order to evaluate the return period of wind events causing human discomfort. A parametric investigation is then presented to evaluate the effects of salient parameters on comfort conditions. The procedure is based on (i) the nonlinear dynamic analysis of the structure modeled as a single-degree-of-freedom oscillator with hysteretic base isolators, (ii) the digital generation of time histories of turbulent wind velocity, and (iii) comfort evaluations based on international standards. Results demonstrate that discomfort conditions can occur a few times in a year, depending upon the wind-exposure of the site, what suggests considering this serviceability limit state in the design of base isolated buildings.

Mohr Circle-based Graphical Vibration Analysis and Earthquake Response of Asymmetric Systems

The maximum seismic response of torsionally coupled plan asymmetric structures can be rationally visualized and computed through a Mohr Circle Response Spectrum Analysis (MCRSA). This is done combining the graphic modal properties of the torsional dynamic equations of motion with the structural earthquake demand in terms of a displacement spectrum as a function of the modal eigenvalues SD(ω2). A compact representation of the modal properties and of the response envelope is built and visualized in the Mohr plane. The maximum modal responses are then combined using a graphic adaptation of the SRSS and CCQ combination rules based on the elastic response spectrum. This Graphic Dynamic rule proves to be an effective response prediction tool, and is particularly suited to estimate the response of seismic base isolation systems.

The efficiency of using a seismic base isolation system for a 2D concrete frame founded upon improved soft soil with rigid inclusions

2D finite element models were developed to analyze the effect of improved soft-soil foundation on the efficiency of a base-isolated concrete frame. Static and dynamic analyses were performed for a frame on raft foundation. Non-improved and improved soft-soil foundation using rigid inclusions were considered, as well as the use of high damping rubber bearing as base isolation. Results show that the use of rigid inclusions increases the efficiency of base isolation; base shear is reduced by 38% and maximum acceleration at the top of the frame by 30%.

Application of damage locating vectors approach on monitoring shock isolation system

Structural damage detection based on the changes of dynamic properties is a major topic for structural health monitoring. In this paper, efforts are made to extend the flexibility-based damage localization methods, especially the damage locating vectors (DLVs) method, to the case of earthquake vibration, where the finite element model and mass matrices are not available. First, a new method using continuous Cauchy wavelet transform (CCWT) and ARX (autoregressive with exogenous input) model is applied to identify the modal parameters of a five-storey steel frame with seismic base isolation system LRB from its simulated acceleration responses under 10% and 100% of Chi-Chi Earthquake excitation (Taiwan, 1999). The DLVs, which determined from the change of flexibility matrix between two cases, are then used to monitor the shock isolation device in the structure through a weighted relative displacement index (WRDI). The proposed scheme is also proved to be superior to mode shape based methods (MAC, COMAC) in monitoring shock isolation system.