Seismic Isolation Devices Research Articles

Levitation Force Characteristics of Magnetic Levitation Type Seismic Isolation Device Composed of Radial Arrangement of HTS Bulks and Permanent Magnets

Levitation Force Characteristics of Magnetic Levitation Type Seismic Isolation Device Composed of Radial Arrangement of HTS Bulks and Permanent Magnets

New Structural Seismic Isolation for Nuclear Containment Structures

The new Structural Seismic Isolation System (SSIS) intends to provide high safety for important structures such as nuclear power plants, offshore oil platforms, and high-rise buildings against near-fault and long-period earthquakes. The presented SSIS 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 these contact surfaces have been separated by using elastomeric (lead core rubber or laminated rubber bearings with up to 4-second period) seismic isolation devices. It would allow providing inverse pendulum behavior to the structure. As a result of this behavior, the natural period of the structure will possess greater intervals which are larger than the predominant period of the majority of the possible earthquakes including near-fault zones. Consequently, the structure can maintain its serviceability after the occurrence of strong and long-period earthquakes. This study has investigated the performance of the SSIS for the nuclear containment (SSIS-NC) structure. The finite element model of SISS-NC structure has been developed, and nonlinear dynamic analysis of the model has been conducted under the strong and long-period ground motions. The results have been presented in comparison with the conventional application method of the seismic base isolation devices for nuclear containment (CAMSBID-NC) and fixed base nuclear containment (FB-NC) structures. The base and top accelerations, effective stress, and critical shear stress responses of the SSIS-NC structure are 48.67%, 36.70%, and 32.60% on average lower than those of CAMSBID-NC structure, respectively. The result also confirms that the SSIS-NC structure did not cause resonant vibrations under long-period earthquakes. On the other hand, there is excessive deformation in the isolation layers of CAMSBID-NC structure.

Performance-based seismic isolation design using the theory of spatially concave friction distribution

Seismic isolation devices were designed to protect three similar building structures, containing different objects with different fragilities, in a strong earthquake region. And a performance-based assessment framework, established by the PEER, was used to identify the seismic isolation efficiency of these devices. It optimized the ratios of spring part, viscous damping part and friction part in the seismic isolation devices, aiming at different functional buildings. Results show that a spatially concave friction distribution, combined with a weak spring, not only can reduce the structural acceleration response during earthquakes, but also decrease the structural residual displacement after earthquakes. Moreover, the spatially concave friction distribution can dissipate earthquake energy, but cannot hinder the recentering of structure like that of general uniform friction distributions. Consequently, the spatially concave friction distribution can partly or fully replace the viscous dampers, which are more expensive and short-lived. The reasonable combination of different components in the seismic isolation devices can satisfy different seismic requirements, aiming at different functional buildings.

Fatigue behaviors of the steel pipe tee in a nuclear power plant piping system under in-plane cyclic loading

The safety of a nuclear power plant against earthquakes can be improved by installing seismic isolation devices. As such seismic isolation devices handle seismic loads, however, displacements larger than those generated before the application of such devices may occur. Therefore, the seismic risks are likely to increase for some facilities. In particular, pipes that connect structures with seismic isolation devices to ordinary structures are likely to have higher seismic risks. The piping is affected by the behavior of the two supports, and damage may occur due to the displacement-dominant repeated behavior. In addition, to assess the low-cycle fatigue behavior of the piping system under seismic loads, it is essential to identify the relationships among the number of cycles, moment, and deformation angle until leakage occurs, through an in-plane cyclic loading test. In this study, an in-plane cyclic loading test was conducted to assess the fatigue behavior of a steel pipe tee against seismic loads from the correlation between the moment and the deformation angle.

Seismic isolation system of two hinged arch suspended-deck bridge: a case study on Kalikuto bridge - Indonesia

Seismic isolation systems are widely used in buildings, bridges, and industrial structures all over the world. The system is known for the efficiency to reduce earthquake demand and thus provide better seismic performance of the structures. In particular to application in an arch suspended-deck bridge, seismic isolation system can be a solution for the seismic resisting system due to the incapability of the cable hangers to transfer horizontal forces from excitation mass on the hanging deck to the main compression arches. Kalikuto arch bridge that is built in 2018 has implemented both Lead Rubber Bearings and Seismic Rubber Expansion Joints as the part of its seismic resisting system. These two seismic isolation devices were designed and engineered accurately to fulfil the seismic design requirements of the Kalikuto bridge. Finally, several performance tests were conducted to evaluate the design compliance of the manufactured devices.

The effect of seismic base isolation on structural response of a 12-story hotel building in Padang, Indonesia

The amount of potential investment in Padang City, Indonesia since 2017 attracted many investors to contribute to the city. One of the investments is a 12-story hotel that will be constructed in By Pass Street of the city. The hotel is located in a high seismic zone area, so the seismic base isolation has been proposed to be used in the hotel building. The main aim of using a seismic base isolation device is to reduce the inertia forces introduced in the structure due to earthquakes by shifting the fundamental period of the structure out of dangerous resonance range and concentration of the deformation demand at the isolation system. An analytical study on the Reinforced Concrete (RC) hotel building with and without rubber bearing (RB) base isolation is carried out using the response spectrum and time history analysis methods. The results show that internal forces and inter-story drift of the building with high damping rubber bearing (HDRB) are lower than that of the fixed base with a remarkable margin. From this study, it is recommended to use the HDRB base isolation for medium and high rise buildings with soft soil in Padang City, Indonesia.

Hybrid seismic base isolation of a historical masonry church using unbonded fiber reinforced elastomeric isolators and shape memory alloy wires

One of the most promising devices for seismic base isolation of structures is the Unbonded Fiber Reinforced Elastomeric Isolator (UFREI) due to its low manufacturing cost and horizontal stiffness. This paper investigates the possibility of combining UFREIs and shape memory alloy (SMA) wires to increase the energy dissipation capacity of the isolation system for the seismic protection of a historical masonry church. Detailed 3D finite element (FE) analyses are performed to characterize the response of UFREIs under cyclic displacements. The behavior of SMA is simulated through a thermomechanical constitutive model implemented in a user-defined material (UMAT) subroutine available in the software package Abaqus. To reduce the computational effort in non-linear dynamic analyses of large isolated structures, an Abaqus user element (UEL) is developed to represent the 3D behavior of the isolation system proposed in this study. Non-linear dynamic time history analyses are then carried out to evaluate the seismic response of a historical masonry church in different configurations (fixed-base model and model equipped with different base isolation systems) for moderate and severe seismic intensity levels. Numerical results show that the damage observed in the masonry church can be considerably reduced through the insertion of UFREIs. The utilization of SMA wires with a specific pre-strain significantly increases the energy dissipation capacity of the base isolation system and decreases the horizontal displacements of the masonry church.

Dynamics of a new seismic isolation device based on tribological smooth rocking (TROCKSISD)

A novel isolation device is introduced to seismically protect slender structures or historic assets within the philosophy of Damage Avoidance Design (DAD). This device is conceived to allow smooth, controlled and damped rocking thanks to spherical contact surfaces, elastic springs which ensure re-centering, frictional layers and viscous elastic dampers able to dissipate energy during motion. The conceptual framework of the device is analyzed, and corresponding equations of motions obtained for the equivalent two degrees-of-freedom system. The proposed Performance Based Approach allows identifying geometric and mechanical features of the system. Extensive dynamic analyses with spectra-compatible ground motions are performed and the primary contribution of friction, developed by the relative slip of the two spherical surfaces, is discussed. Finally, the dynamic response under selected earthquakes is evaluated by comparing the isolated and the corresponding not isolated response, to highlight the beneficial effects produced by the proposed isolation technique.

Evaluation of Seismic Fragility Curve of Seismically Isolated Nuclear Power Plant Structures for Artificial Synthetic Earthquakes Corresponding to Maximum-Minimum Spectrum

In order to increase the seismic safety of nuclear power plant (NPP) structures, a technique to reduce the seismic load transmitted to the NPP structure by using a seismic isolation device such as a lead-rubber bearing has recently been actively researched. In seismic design of NPP structures, three directional (two horizontal and one vertical directions) artificial synthetic earthquakes (G0 group) corresponding to the standard design spectrum are generally used. In this study, seismic analysis was performed by using three directional artificial synthetic earthquakes (M0 group) corresponding to the maximum-minimum spectrum reflecting uncertainty of incident direction of earthquake load. The design basis earthquake (DBE) and the beyond design basis earthquakes (BDBEs are equal to 150%, 167%, and 200% DBE) of G0 and M0 earthquake groups were respectively generated for 30 sets and used for the seismic analysis. The purpose of this study is to compare seismic responses and seismic fragility curves of seismically isolated NPP structures subjected to DBE and BDBE. From the seismic fragility curves, the probability of failure of the seismic isolation system when the peak ground acceleration (PGA) is 0.5 g is about 5% for the M0 earthquake group and about 3% for the G0 earthquake group.

Finite element study of effect of parameters on stress distribution of steel shim in elastomeric bearings

Elastomeric bearings are widely used in various structures as a type of seismic isolation device, and accurately assessing the state of their stress is an essential step in the design of elastomeric bearings. This article aims to better understand the influencing factors of stress distribution on the steel shims and the effect of steel shim thickness on the critical behaviour of elastomeric bearings. First, theoretical analysis is conducted for investigating the influencing factors of the bearing’s critical load capacity and stress distribution on the steel shim thickness. Then, a series of finite element models is employed to study the influence of steel shim thickness on the global performance of bearings, the stress distribution on steel shims at different locations and the effect of steel shim thickness on stress distribution. Combining the results of theoretical analysis and finite element analysis, we conclude that steel shim thickness has little obvious effect on the mechanical properties of the bearing under normal working conditions, but it has a significant influence on the distribution and change of the local stress. Especially, when the vertical load and the horizontal displacement of the bearing increases, the growth rate of stress on the upper steel shims is very fast and may enter the yield state first or even resulting in local damage.

Response modification factors of concrete bridges with different bearing conditions

One of the shortcomings of seismic bridge design codes is the lack of clarity in defining the role of different seismic isolation systems with linear or nonlinear behavior in terms of R-factor. For example, based on AASHTO guide specifications for seismic isolation design, R-factor for all substructure elements of isolated bridges should be half of those expressed in the AASHTO standard specifications for highway bridges (i.e., R=3 for single columns and R=5 for multiple column bent) but not less than 1.50. However, no distinction is made between two commonly used types of seismic isolation devices, i.e., elastomeric rubber bearing (ERB) with linear behavior, and lead rubber bearing (LRB) with nonlinear behavior. In this paper, five existing bridges located in Iran with two types of deck-pier connection including ERB and LRB isolators, and two bridge models with monolithic deck-pier connection are developed and their R-factor values are assessed based on the Uang\'s method. The average R-factors for the bridges with ERB isolators are calculated as 3.89 and 4.91 in the longitudinal and transverse directions, respectively, which are not in consonance with the AASHTO guide specifications for seismic isolation design (i.e., R=3/2=1.5 for the longitudinal direction and R=5/2=2.5 for the transverse direction). This is a clear indicator that the code-prescribed Rfactors are conservative for typical bridges with ERB isolators. Also for the bridges with LRB isolators, the average computed Rfactors equal 1.652 and 2.232 in the longitudinal and transverse directions, respectively, which are in a good agreement with the code-specified R-factor values. Moreover, in the bridges with monolithic deck-pier connection, the average R-factor in the longitudinal direction is obtained as 2.92 which is close to the specified R-factor in the bridge design codes (i.e., 3), and in the transverse direction is obtained as 2.41 which is about half of the corresponding R-factor value in the specifications (i.e., 5).

Failure Strain Measurement of the Piping System of a Nuclear Power Plant Using Image Signals

When seismic isolation devices are installed in piping systems, it is expected that such devices will be subjected to larger displacement than before their installation because they handle seismic loads, and it is likely that the seismic risks of some facilities will be increased by such displacement increase. In particular, it is highly likely that the seismic risks of piping systems, which connect seismic-isolated structures with conventional ones, will be increased. Previous studies have revealed that the vulnerable part of piping systems is the elbow, and that failures occur due to the low-cycle ratcheting fatigue in the hoop direction. Therefore, in this study, the ultimate state of the elbow was defined as a leakage, and an in-plane cyclic loading test was conducted. In addition, the hoop-direction strain of the steel pipe elbow was measured using an image measurement system, and the failure strain, which cannot be measured using the conventional sensors, was also measured.

Verification of Hybrid Seismic Isolation Device with Resistance to Earthquake

Verification of Hybrid Seismic Isolation Device with Resistance to Earthquake

Rolling devices for seismic isolation of lightweight structures and equipment. Design and realization of a prototype

Rolling devices for seismic isolation of lightweight structures and equipment. Design and realization of a prototype

Experimental and analytical investigation of the influence of compressive load on rate-dependent high-damping rubber bearings

High-damping rubber bearings (HDRBs) have been widely accepted as a relatively novel type of seismic isolation devices in civil infrastructures construction, they are known to possess significant rate-dependent behavior and accommodate the gravitational load of the superstructure in typical applications. Hence, it necessitates better understanding of the mechanical behavior of HDRBs under coupling effect of compression and shear. The objective of the paper was to conduct experimental and analytical investigation to characterize the influence of compressive load on rate-dependent HDRBs. Firstly, a series of material tests including multi-step relaxation and monotonic shear tests were carried out on high-damping rubber, the strain rates and compressive stresses applied on specimens were varied and analyzed. Then, on the basis of experimental investigation, the classical Zener model was extended and a rate-dependent analytical model of HDRBs allowing for the consideration of compressive load was proposed. Finally, comparing the numerical simulations and experimental data obtained from both material tests and full-scale bearing tests, a reasonably good agreement was observed and the validity of the proposed model was demonstrated.

Application research of seismic isolation device in long-span continuous beam bridge

The three-dimensional finite element model of pre-stressed concrete continuous girder bridge with span (76+144+76)m is established by using finite element structural analysis software Ansys in this paper. The dynamic time history analysis method is used to study the influence of viscous dampers and friction pendulums with different parameters on the seismic response of long-span continuous beam bridges, which provides a basis for rational selection of seismic isolation measures. The results show that reasonable seismic isolation measures can effectively reduce the seismic response of long-span continuous beam bridges; both the viscous damper and the friction pendulum can have good seismic isolation effects, but the damping effects are related to their parameter settings.

Numerical modeling of the dynamics of multi-storey buildings with elastoplastic seismic insulators

The work is devoted to the problems of reducing the intensity of seismic impacts on multi-storey buildings. The main difficulties in solving the problems of seismic isolation of buildings and structures lie in the field of creating mathematical models of the dynamic interaction of the systems “foundation - seismic isolation device - construction”. One of the most effective ways to reduce the level of seismic effects on buildings is to equip them with special devices - seismic isolators, a successful way of implementing which is the use of elastoplastic systems. The method of calculation for seismic actions of multi-storey buildings equipped with elastoplastic seismic insulators is proposed. Numerical modelling of the alternating loading of which uses the rheological model of N N Davidenkov. Modelling of dynamic processes is carried out by means of a mathematical description of the dynamics of two linear multidimensional subsystems that approximate the structures located under seismic insulators and above seismic insulators. The dynamics equations are formed on the basis of the D’Alembert principle. Horizontal seismic effects are considered. The presented technique makes it possible to determine the movements of the nodes of the system at any time of the seismic action specified in the form of a digitized seismogram. The above algorithm is implemented as a software module Proxima. The results of calculations are presented on the example of a model of a 24-storey building designed for the conditions of building in the city of Irkutsk.

Seismic Response Evaluation of Mid-Story Isolation System According to the Change of Characteristics of the Seismic Isolation Device

Seismic Response Evaluation of Mid-Story Isolation System According to the Change of Characteristics of the Seismic Isolation Device

Seismic Response Analysis of an Isolated Structure with QZS under Near‐Fault Vertical Earthquakes

Seismic isolation devices are usually designed to protect structures from the strong horizontal component of earthquake ground shaking. However, the effect of near‐fault (NF) vertical ground motions on seismic responses of buildings has become an important consideration due to the observed building damage caused by vertical excitation. As the structure needs to maintain its load bearing capacity, using the horizontal isolation strategy in vertical seismic isolation will lead to the problem of larger static displacement. In particular, the bearings may generate large deformation responses of isolators for NF vertical ground motions. A seismic isolation system including quasi‐zero stiffness (QZS) and vertical damper (VD) is used to control NF vertical earthquakes. The characteristics of vertical seismic isolated structures incorporating QZS and VD are presented. The formula for the maximum bearing capacity of QZS isolation considering the stiffness of vertical spring components is obtained by theoretical derivation. From the static analysis, it is found that the static capacity of the QZS isolation system with vertical seismic isolation components increases when the configurative parameter reduces. Seismic response analyses of the seismic isolated structure model with QZS and VD subjected to NF vertical earthquakes are conducted. The results show that seismic responses of the structure can be controlled by setting the appropriate static equilibrium position, vertical isolation period, and vertical damping ratio. Adding a damping ratio is effective in controlling the vertical large deformation of the isolator.

Seismic vulnerability assessment of a continuous steel box girder bridge considering influence of LRB properties

Bridges are one of the most crucial facilities of transportation networks. Therefore, evaluation of the seismic vulnerability of bridge structures is perpetually regarded topic for researchers. In this study, we developed seismic fragility curves for a continuous steel box girder bridge considering the effect of different levels of mechanical properties of lead rubber bearing (LRB) devices including initial stiffness and yield strength on the seismic performance of such structure. A powerful framework for an earthquake engineering simulation, OpenSees, is used to perform nonlinear analyses of the bridge model. In order to construct fragility curves for this structure, a set of 20 ground acceleration records is adopted and various scales of the peak ground acceleration (PGA) from 0.1 to 1.6 g are considered. Besides, a series of damage state of the bridgeis defined based on a damage index, which is expressed in terms of the column displacement ductility ratio. Fragility analyses result reveals that reducing the initial stiffness of LRBs reduces the seismic vulnerability of bridge piers and vice versa. Meanwhile, the changes of the yield strength of LRBs have trivially effected on the seismic behaviour of the bridge piers. On the other hand, the short pier has performed more susceptibly than those of the high pier in both seismically-isolated and non-isolated bridge cases. Lastly, the results in this research also indicate that the bridge structures equipped with seismic isolation devices (e.g. LRBs) significantly mitigated the damages due to earthquakes.