Mathematical model and results for seismicresponses of a nonlinear isolation system

Historical buildings are usually characterised by relatively low height and their natural vibration period is rather low. Hence if such buildings are located in seismically active zones, using seismic isolation systems is a very effective way for improving earthquake resistance of these structures. Seismic isolation is well known, however its practical implementation only began in the last few decades. The main advantage of a seismic isolation system is that no structural elements should be added to the building in order to strengthen it. This is a very attractive benefit, being especially important for historical buildings. A traditional seismic isolation system is presented by the following two types – bearings and pendulums. The design of seismic isolation systems and selection of their dynamic properties depend on the features of the isolated structure that can be obtained by non-destructive testing. A method for structural dynamic parameters assessment was previously developed by the authors. For this reason an impulse test was carried out on a three-story structural part of a building. Sometimes the displacements at the isolation level are rather big and exceed the allowed limits. In such cases it is recommended to add dampers to the isolation system. Different types of variable friction dampers were proposed and tested by the authors. These dampers significantly reduce the displacements at the isolator level and also yield further improvement in the dynamic response of a building.

Design charts for eurocode-based design of elastomeric seismic isolation systems

In this paper, the development of non-linear building isolation systems is overviewed. The study summarizes commonly used linear building isolation systems in two categories, which are building base isolation systems and building inter-storey isolation systems. Typical isolators including Lead-Rubber Bearings Friction Pendulum Bearings inter-storey viscous damper and Tuned Mass Damper are reviewed. The analysis and design of linear building isolation systems are also reported. After that, non-linear building isolation systems are introduced from two aspects based on their dynamic characteristics. They are (i) non-linear stiffness isolators including Quasi-Zero Stiffness isolators and Non-linear Energy Sink and (ii) non-linear damping isolators including power-law viscous dampers and magnetorheological dampers. Practical implementations of these non-linear isolators are introduced. Finally, the analysis and design of non-linear building isolation systems are discussed. Traditional equivalent linearization approaches and advanced non-linear frequency design approaches are introduced. The promising applications of the non-linear frequency design approaches to building isolation systems are also demonstrated in this review paper.

An important consideration for the design of seismic isolation systems composed of elastomeric and lead–rubber bearings is the safety of individual bearings for maximum considered earthquake shaking. One assessment of bearing safety involves the calculation of the vertical (or axial) earthquake load on the individual seismic isolation bearings. This paper investigates the influence of vertical earthquake excitation on the response of a bridge isolated with low-damping rubber and lead–rubber bearings through earthquake simulation testing. Response data collected from the experimental program are used to determine the vertical load on the isolation system due to the vertical component of excitation. A comparison of the normalized vertical load data to the vertical base acceleration showed significant amplification of the vertical response for each simulation and configuration. Disaggregation of the axial load history showed the summation of maximum values from the vertical earthquake load and overturning moment overestimates the maximum axial load because these maximum values are unlikely to occur simultaneously. Additionally, a spectral analysis procedure using the unreduced vertical stiffness of the bearings was shown to provide a reasonable estimate of the vertical earthquake load.

With the aim of unifying the damping concept and evaluating the amount of damping in a structure, this paper investigates whether friction action can be equivalent to traditional viscous damping. The research focused on purely concave friction distribution cases, uniform friction distribution cases, and their combination cases in a spring-friction isolation system. The dynamic responses of a numerical method using friction action were compared with those of another numerical methods using equivalent viscous damping under sine wave ground motions. The comparison of results shows that the friction action can be converted to the equivalent viscous damping action with some errors by using an equation. The conversion accuracy of uniform friction distribution cases using the first term of the equation is much worse than that of the purely concave friction distribution cases using the second term of the equation. The reason for this being that the uniform friction distribution can prevent the structure from sliding back to its center after the ground motion; however, the viscous damping action does not have such a negative function. The comparison errors, between using the friction action and using the equivalent viscous damping, are directly proportional to the ratio of the component of uniform friction distribution to the component of purely concave friction distribution.

This works attempts to implement artificial neural networks (ANN) for modeling Seismic-Isolation (SI) systems consisting of Natural Rubber Bearings and Viscous Fluid Dampers subject to Near-Field (NF) earthquake ground motion. Fourteen NF earthquake records representing two seismic hazard levels are used. The commercial analysis program SAP2000 was used to perform the Time-History Analysis (THA) of the MDOF system (stick model representing a realistic five-story base-isolated building) subject to all 14 records. Different combinations of damping coefficients (c) and damping exponents (α) are investigated under the 14 earthquake records to develop the database of feasible combinations for the SI system. The total number of considered THA combinations is 350 and were used for training and testing the neural network. Mathematical models for the key response parameters are established via ANN. The input patterns used in the network included the damping coefficients (c), damping exponents (α), ground excitation (peak ground acceleration, PGA and Arias Intensity, Ia). The network was programmed to process this information and produce the key response parameters that represent the behavior of SI system such as the Total Maximum Displacement (DTM), the Peak Damper Force (PDF) and the Top Story Acceleration Ratio (TSAR) of the isolated structure compared to the fixed-base structure. The ANN models produced acceptable results with significantly less computation. The results of this study show that ANN models can be a powerful tool to be included in the design process of Seismic-Isolation (SI) systems, especially at the preliminary stages.

This study consists of the development and presentation of example of seismic isolation system analysis and design for a continuous, 3-span, cast-in-place concrete box girder bridge. It is expected that example is developed for all Lead-Rubber Bearing (LRB) seismic isolation system on piers and abutments which placed in between super-structure and sub-structure. Design forces, displacements, and drifts are given distinctive consideration in accordance with Caltrans Seismic Design Criteria (2004). Most of all, total displacement on design for all LRBs case is reduced comparing with combined lead-rubber and elastomeric bearing system . Therefore, this represents substantial reduction in cost because of reduction of expansion joint. This presents a summary of analysis and design of seismic isolation system by energy mitigation with LRB on bridges.

In Japan, applications of seismic isolation systems to new generation nuclear power plants and fast breeder reactors have been expected in order to enhance seismic safety. However there are lots of restrictions for design of isolation systems, such as strong design seismic wave, deformation of piping between an isolated structure and a non-isolated structure, and so on. In addition combination of horizontal and vertical isolation has possibility to cause rocking motion if a three-dimensional isolation system is applied. Therefore isolation systems should be designed properly. Moreover the design of seismic isolation system has to consider influence on inner equipment and piping. This paper describes investigation regarding required properties and performance of seismic isolation system for nuclear power plants. The investigation is carried out by numerical analysis. In the analysis, various isolation devices such as friction pendulum bearings and so on are applied as well as natural rubber bearings.

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

<p>The protection of the existing and new structures in earthquake prone areas is one of the key priorities for the protection of human lives and for the reduction of associated economic losses. The effects of earthquakes can be mitigated by the reduction of the induced seismic loads, and this can be effectively achieved by the introduction of suitable seismic isolation and response control devices. However, the extensive use of seismic isolation and response control systems is a challenging task because the knowledge of the characteristics of these devices is not widespread but also due to the lack of expertise in the design process. IABSE SED 19 ‘Seismic Isolation and Response Control’ [1] is focused on the description of various seismic isolation and response control systems in addition to applications to new and existing structures aiming to provide a practical guideline for the selection and design process. This publication presents a collection of the most commonly used seismic isolation and response control systems in addition to a critical evaluation of the main characteristics of these systems. The design methodology for the application of these systems in new structures is also presented in detail offering a critical evaluation of the main differences of the examined technologies. The application of seismic isolation systems and response control systems for the retrofitting of existing structures is also examined, followed by numerous case studies in Greece, Japan Mexico New Zealand, and Turkey. </p>

Robust design of seismic isolation system using constrained multi-objective optimization technique

The concept of the vibration and seismic isolation of heavy mining machines, buildings, and structures with rubber seismic blocks is considered. The concept of the seismic isolation of structures is very topical. In Japan, New Zealand, France, Greece, England, USA, and in a number of other countries, it is successfully used for the earthquake protection of such important structures as nuclear power stations, schools, bridges, museums, office and residential buildings. Seismic isolation systems including rubber blocks are most commonly used. The known publications in these countries do not present analytical calculations and technological peculiarities of manufacturing elements. In Ukraine, this concept was extended by developing seismic isolation blocks for the earthquake protection of residential buildings and vibration isolation blocks for the vibration protection of heavy equipment (weight of up to 300 t, used in Russia, Ukraine) and residential buildings. Results of static and dynamic tests of a parametric series of rubber seismic blocks for the vibration protection of residential buildings are presented. A pile design with anti-vibration rubber mounts is considered. Developed and tested rubber seismic block designs were used to protect against subway and motor vehicle induced vibrations two dwelling houses in Kiev (a ten-section ten-storey and a three-section 27-storey dwelling house) and three houses in Lvov. Vibration and seismic isolation with rubber seismic blocks provides a natural vibration frequency of building in the horizontal plane of under 1 Hz, which complies with the requirements of the state building codes and Eurocode 8 for the design of seismic isolation systems for buildings.

Theoretical and experimental analysis of an electromagnetic seismic isolation system

The benefits of seismic isolation are many. Structures that are isolated from the ground seismically perform better than those that are not. They experience reduced floor accelerations and drifts and are less likely to experience damage to structural elements. Additionally, their contents are better protected from the effects of earthquakes. The selection and design of seismic isolation devices are complex and require a good understanding of how they behave during earthquakes. This study investigates the effect of various isolation system parameters and ground motion characteristics on the seismic response of base isolated structures in order to develop rational procedures for design and analysis. Additionally, the study investigates the problem of optimal design of seismic isolation systems through parametric nonlinear dynamic analysis. Results showed that the maximum base shear and displacement were velocity-sensitive and that the peak ground velocity controls the motion. The largest maximum base shear occurred when using isolation systems with high yield strength levels and low degrees of nonlinearity, while the smallest maximum base shear occurred when using low yield strength levels and high degrees of nonlinearity. Results from the study can be used to select the appropriate isolation devices and design them correctly to achieve the benefits they provide.

The given paper presents a new approach in design of seismic isolation systems of base isolated buildings. The idea is to install not one big size rubber bearing under the columns and/or shear walls, or one by one with certain spacing under the load-bearing walls, but to install a group/cluster of small size bearings, in order to increase the overall effectiveness of the isolation system. The advantages of this approach are listed and illustrated by the examples. Also the results of analyses of some buildings where the approach on installation of clusters of rubber bearings was used in their isolation systems are given for two cases: i) when the analyses are carried out based on the provisions of the Armenian Seismic Code, and ii) when the time history analyses are carried out. Obtained results are compared and discussed. Paper also presents, as an example, detailed analysis and design of the 18-story unique building in one of the residential complexes in Yerevan. Earthquake response analyses of this building were carried out in two versions, i.e. when the building is base isolated and when it is fixed base. Several time histories were used in the analyses. Comparison of the obtained results indicates the high effectiveness of the proposed structural concepts of isolation systems and the need for further improvement of the Seismic Code provisions regarding the values of the reduction factors. A separate section in the paper dedicated to the design of high damping laminated rubber-steel bearings and to results of their tests.