Seismic Isolation Effect Research Articles

Resilience-Based Retrofitting of Adjacent Reinforced Concrete Frame–Shear Wall Buildings Integrated into a Common Isolation System

Adjacent buildings of three to five stories with small spaces between them are widely used as offices, schools, and hospital wards. The seismic resilience of such buildings is critical, and retrofitting adjacent buildings by integrating them into a common isolation system is considered effective. The resilience-based retrofitting of adjacent RC frame–shear wall buildings was investigated through a case study. First, the critical engineering demand parameters (EDPs) dominating the resilience performance of such buildings were identified. An isolation scheme was designed to improve their seismic resilience, emphasizing control effect of seismic isolation on critical EDPs. The effect of the yield ratio of the isolation system on the seismic resilience of retrofitted buildings was investigated by comparing three cases. A yield ratio of 2.5% is preliminarily recommended as a valuable reference for the resilience-based retrofitting of adjacent RC frame–shear wall buildings.

上下振動の振動低減装置に関する基礎的研究

Earthquakes frequently occur in Japan so far. Therefore, seismic isolator is attracting attention to protect buildings. In order to reduce all direction of shakings, three-dimensional (3D) seismic isolator is needed. 3D seismic isolator is composed of isolator for horizontal direction and vertical direction. Because 3D seismic isolator can effectively reduce all shaking, it can protect people and objects in the building. If 3D seismic isolator is established, we will be closer to achieving sustainable society. However, there are not many studies on seismic isolation for vertical direction. In this study, to develop an effective vibration reduction device for vertical direction. A vibration reduction device using a nonlinear spring was invented in the past. According to experiment, devices with this mechanism were reducing vertical vibration. Analysis model is based on the device. To reduce vibration more effectively, analysis was conducted with different parameters such as spring constant or range of motion for vertical direction. Then, the differences in behavior and the effect of seismic isolation are examined from resonance curves obtained from analysis results. In addition, the experimental and analytical results will be compared to investigate the conditions necessary to improve the seismic isolation effect.

Shaking table test of space double-layer cylindrical reticulated shell with three-dimensional isolation bearing

Space double-layer cylindrical reticulated shells (SDLCRS) have undergone rapid development in the four three decades. Significantly different from conventional multistory high-rise structures, such structures are very sensitive to vertical actions. As a result, conventional seismic isolation techniques that aim to reduce horizontal seismic actions are notably insufficient for this kind of structure. In this study, a new three-dimensional seismic isolation bearing was developed that can simultaneously reduce the horizontal and vertical seismic responses of an SDLCRS. To examine the actual seismic isolation effectiveness of the three-dimensional seismic isolation bearing and provide important theoretical, technical and experimental support for practical engineering applications, comparative shaking table tests were performed on isolated and non-isolated SDLCRSs with lower supporting structures. The 2013 Lsf ground motion record during Lushan earthquake and the 1954 Taft ground motion record were selected as seismic inputs. The dynamic responses including acceleration, displacement and strain of the SDLCRS under the input ground motions with different amplitudes were obtained using the shaking table tests. In addition, the seismic damage of the isolated and non-isolated structures was examined to determine the acceleration amplification effect of the structures. The effectiveness in acceleration and strain responses demonstrated that the three-dimensional seismic isolation bearing was very useful for horizontal and vertical seismic isolation. Moreover, the maximum displacement responses of the bearing were less than half of the respective design displacements, suggesting that the bearing still had considerable reserve bearing capacity and could significantly improve the safety of an SDLCRS under seismic loads. The bearing developed in this study not only has excellent seismic isolation performance and post earthquake restoration capability but can also be easily installed and maintained. Thus, this bearing holds great promise for engineering applications and is suitable for SDLCRS that require both horizontal and vertical seismic isolation.

Effect of Seismic Isolation with Triple Friction Pendulum Isolator Device on Weight Optimization of Steel Plane Frames

In the study, the weight efficiency of the Triple Friction Pendulum Bearing (TFP) Isolators is investigated on optimal weight of planar steel frames. For this investigation, an optimization program based on Artificial Bee Colony (ABC) algorithm have been developed for this study. In the design of steel frames, the structure should satisfy strength, inter-story drift, top-story drift and geometric requirements that are implemented from LRFD-AISC. For the research, 8 different planar frames were optimized as seismic-isolated and fixed-based, which were diversified according to story height and bracing. According to the results, the frames with TFP isolators, especially non-braced ones are a lot more advantageous regarding the optimal weight.

Determination of seismic isolation effects on irregular RC buildings using friction pendulums

This study aims to evaluate influences of isolation made using friction pendulum type isolators on seismic behavior of irregular mid-rise RC frame buildings without shear walls. For this at first, a 4-storey 3D reference building model which have no irregularity is designed as residential building. Afterwards, models including heavy overhang, short column and soft storey irregularities are created through the reference building. A total of 88 nonlinear time history analyses of regular and irregular building models subjected to 11 pairs of ground motion records are performed for non-isolated and isolated cases. There has been a significant reduction in base shear ratios for isolated reference and irregular buildings. Roof drift ratios of isolated-base models are generally higher compared to fixed-base models for both regular and irregular buildings. Unlike the results of roof displacement demands, lower average interstorey drift ratios have been obtained for especially isolated reference and heavy overhang buildings. Evaluations on the effects of the isolation for floor accelerations, interstorey drift ratio (IDR) profiles and damages of structural elements are also given in the paper. This study emphasizes that advances are made in terms of behavior against earthquakes for irregular buildings thanks to isolation.

Influence of Vertical Equivalent Damping Ratio on Seismic Isolation Effectiveness of Nuclear Reactor Building

This paper aimed at evaluating the influence of different vertical equivalent damping ratios of a 3-dimensional combined isolation bearing (3D-CIB) as regards seismic response and isolation effectiveness. A comparative study of the seismic response in terms of acceleration floor response spectra (FRS), peak acceleration, displacement response of the nuclear reactor building, and dynamic response of the 3D-CIB was carried out. The results showed that: (1) the horizontal FRS is slightly influenced by the vertical equivalent damping ratio of 3D-CIB, whereas the increase of the vertical equivalent damping ratio has a significant effect on reducing the vertical FRS; (2) the peak vertical acceleration increased with the decrease in the vertical equivalent damping ratios of 3D-CIB and the difference of peak accelerations calculated by the damping ratio of 20 and 25% is within 10%; (3) the increase of the vertical equivalent damping ratio is capable of reducing the horizontal displacement and the rocking effect of the superstructure, and effectively controlling the vertical displacement amplitude; and (4) the vertical equivalent damping ratio of 3D-CIB has a slight effect on its axial force. Consequently, it is demonstrated that the increase of the vertical equivalent damping ratio is advantageous for isolation effectiveness. From the view of displacement control, it is suggested that the 3D-CIB with the vertical an equivalent damping ratio of 15~20% is appropriate and acceptable.

STUDY ON THE ISOLATION EFFECT OF SUBWAY COVER STRUCTURES

In order to study the seismic isolation effect of the subway superstructure comprehensively, a simplified two-degree-of-freedom model of the large base with multiple towers was presented, and the influences of mass ratio and period ratio on dynamic characteristics and seismic response of structures were investigated. In addition, a precise model of the subway superstructure was established by ETABS to study the effect of tower height, tower number, isolation floor stiffness, and viscous dampers on the structural dynamic characteristics, seismic isolation coefficient. The analysis results of the simplified two-degree-of-freedom model show that in the general period ratio range, the shear-weight ratio of the tower has almost no change with its mass variation, while the shear-weight ratio of the large base decreases when the tower mass increases. The analysis results of the precise model of the large base with multi-tower show that the seismic inertial force is evenly distributed along the height of the tower, and the building height has little effect on the earthquake action, and the seismic effect of the large base increases slightly as the height of the tower increases. As the number of towers increases, the seismic isolation effect of the tower decreases slightly, the seismic effect of the large base is less than that of non-seismic isolation structures. As the stiffness of the seismic isolation floor increases, the seismic effect of the tower increases and the seismic effect of the large base decreases. After viscous dampers are installed, the distribution of seismic force along the height of the tower changes significantly, the seismic action decreases at the bottom of the tower and the seismic action is significantly amplified at the top. Setting viscous dampers can effectively reduce the seismic action of the large base.

Research on Structural Design of an Isolated High-Rise Building with Enlarged Base and Multiple Tower Layer in High-Intensity Area

In the high intensity areas, the application of interlayer spacing technology can achieve the unity of quality and seismic performance of high-rise buildings with enlarged base and multiple tower layers. Through the comparison and analysis of the structural schemes of an enlarged base multiple tower-layer high-rise building, the ultimate seismic isolation scheme was adopted, and its seismic response and seismic performance were analyzed and studied. The results show that the overall seismic isolation effect of the story isolation technique is good, which can greatly reduce the seismic response, and is an effective means to improve the seismic safety of the structure. Considering the structural characteristics of the project, the improvement of the economy and the quality of the building, the use of story isolation technique in the enlarged base multiple tower-layer structure in the high-intensity region is an optimal scheme. Finally, several key technical issues such as the combined seismic isolation scheme of the enlarged base story isolation technique and the additional bending moment of the isolator and the tensile device of the isolator were discussed, which can provide some references for similar engineering practices.

Modified Adaptive Negative Stiffness Device with Variable Negative Stiffness and Geometrically Nonlinear Damping for Seismic Protection of Structures

Adaptive negative stiffness device is one of the promising seismic protection devices since it can generate seismic isolation effect through negative stiffness when it is mostly needed and achieve similar vibration mitigation as a semi-active control device. However, the adaptive negative stiffness device generally combined with linear viscous damping underpins the drawback of degrading the vibration isolation effect during the high-frequency region. In this paper, a modified adaptive negative stiffness device (MANSD) with the ability to provide both lateral negative stiffness and nonlinear damping by configuring linear springs and linear viscous dampers is proposed to address the above issue. The negative stiffness and nonlinear damping are realised through a linkage mechanism. The fundamentals and dynamic characteristics of a SDOF system with such a device are analyzed and formulated using the Harmonic Balance Method, with a special focus on the amplitude–frequency response and transmissibility of the system. The system with damping nonlinearity as a function of displacement and velocity has been proven to have attractive advantages over linear damping in reducing the transmissibility in the resonance region without increasing that in the high-frequency region. The effect of nonlinear damping on suppressing displacement and acceleration responses is numerically verified under different sinusoidal excitations and earthquakes with different intensities. Compared with linear damping, the MANSD with nonlinear damping could achieve additional reductions on displacement and acceleration under scaled earthquakes, especially intensive earthquakes.

Seismic response reduction analysis of large chassis base-isolated structure under long-period ground motions

Long-period structures (e.g. Isolated structures) tend to produce pseudo-resonance with low frequency components of long-period ground motions, resulting in the increase in damage. Stiffness mutation occurs due to the set-back in the upper body of the large chassis structure. In the parts with stiffness mutation, the torsion effect caused by the tower is far greater than that of the chassis itself. In this study, a total of 273 ground motions are collected and then filtered into four types, including the near-field ordinary, near-field pulse, far-field ordinary, and far-field harmonic. An 8-degree (0.2 g) fortified large chassis base-isolated structure is established. Furthermore, ETABS program software is used to conduct nonlinear time history analysis on the isolation and seismic model under bi-directional earthquake ground motions. The comparison results show that the seismic isolation effect of the base-isolated structure under long-period ground motions is worse than that associated with ordinary ground motions when the seismic response reduction rate of the large base floor significantly decreases compared with that of the tower. When the inter-story displacement angle and the displacement of isolation layer of the chassis exceeds the limit of Code for Seismic Design of Buildings (GB 50011-2010), it is recommended to adopt composite seismic isolation technology or add limit devices. Under the condition of long-period ground motions, the base-isolated structure reduces the lateral-torsional coupling effect of the large chassis structure, while the torsion response of large chassis’ top layer increases. Under long-period ground motions with the same acceleration peak, the response of the base-isolated structure increases much more than that of the seismic structure and the consideration of this impact is suggested to be added to the Code.

Model Test on the Vibration Reduction Characteristics of a Composite Foundation with Gravel Cushion under Different Seismic Wave Amplitudes

Gravel cushions have been introduced as a practical and efficient seismic isolation technology to ensure the safety of nuclear power plants. This study investigated the seismic isolation effect of a gravel cushion by conducting a series of shaking table tests on a model foundation with a cushion built of three different types of graded aggregates (single-sized (2–5 mm), two-sized (2–5 mm:5–10 mm = 3 : 1), and continuously graded) under input El Centro seismic waves with three different peak accelerations (0.1 g, 0.2 g, and 0.3 g). The testing results showed that the seismic isolation effect of the gravel cushion increased with the peak seismic acceleration. The gravel cushion built with single-sized aggregates had better seismic isolation performance than gravel cushions built with two-sized or continuously graded aggregates. Under input seismic waves with 0.1 g peak acceleration, the single-sized aggregate gravel cushion still had a seismic isolation effect with a vibration reduction rate of approximately 11.81%, whereas the other two gravel cushions had no effect. Under input seismic waves with peak accelerations of 0.2 g and 0.3 g, all three gravel cushions had seismic isolation effects with vibration reduction rates of approximately 18.63% and 17.92%, respectively. An empirical model is proposed for predicting the vibration reduction rate of the cushion. Under input seismic waves with 0.3 g peak acceleration, the ultimate vibration reduction rate of the gravel cushion fell between 20.44% and 31.33%. The gravel cushion is an excellent option for nuclear power plant foundations with high requirements for seismic isolation, provided that the required bearing capacity is satisfied.

The effect of seismic isolation on performance of a residence building

The effect of seismic isolation on performance of a residence building

Investigating the seismic isolation effect of the cushioned pile raft foundation in soft clay through dynamic centrifuge tests

Cushioned pile-raft foundation (Cushioned-PR) is a new type of foundation for sea-crossing bridges in deep water (more than 50 m in depth). Cushioned-PR is able to tolerate a certain amount of slide that occurs between the raft and the piles under strong earthquakes. This characteristic could reduce the seismic motion transmitted to the superstructure to maintain the integrity of the bridge. Thus, Cushioned-PR has become popular for bridges under the threat of strong earthquakes. However, the dynamic responses of the Cushioned-PR under various earthquake intensities in soft clay have not been thoroughly understood. It is essential to better evaluate the isolation effect of Cushioned-PR to improve the design. In this study, the non-linear behavior of Cushioned-PR and the isolation effect of its interposed layer are evaluated using centrifuge tests. A series of dynamic centrifuge tests are performed with a 3 × 3 pile group foundation embedded in soft clay under different earthquake motions. Both the cushioned pile raft foundation system (Cushioned-PR) and the connected pile raft foundation system (Connected-PR) are tested in the centrifuge tests. Acceleration and residual displacement of the super-structure, and bending moment of columns and piles, are monitored during the experiments. The results show that the interposed layer in Cushioned-PR has a significant impact on the bending moment and residual displacement of the pile-raft system. Based on the observation from this study, the maximum bending moment of the column in the Cushioned-PR is around 28%–54% of the values from the Connected-PR. On the other side, the maximum horizontal displacement of Cushioned-PR is about 2–10 times larger than that of the Connected-PR. The results show that Cushioned-PR can effectively reduce the seismic excitation transmitted to the super-structure if the seismic intensity is high. However, the benefit of Cushioned-PR is marginal under low-intensity earthquakes.

Effect of seismic isolation on random seismic response of High-Speed railway bridge based on probability density evolution method

In order to evaluate the effect of seismic isolation on random seismic response characteristics of a track-bridge system, in this paper, a three-dimensional detailed nonlinear dynamic model consists of rail, CRTS II slab ballastless track, high-speed railway simple supported bridges, isolated bearings, piers, pile foundations from top to bottom, is established by OpenSEES. The stochastic process of ground motion constructed by the random harmonic function is taking as random excitation, and the probability density evolution method (PDEM) is applied to investigate and analyze the system from the random perspective. On this basis, the influence of FPB bearing and the different FPB parameters (such as equivalent radius) on the random seismic response of the track-bridge system is studied. Thereby, aplenty probabilistic information (probability density evolution function, mean value and standard deviation) can be gained of seismic response of isolated bridges with different isolation parameters and non-isolated bridges of the high-speed railway track-bridge system under the excitation of random earthquakes by case study. Through the comparison of random seismic responses of non-isolated bridge and isolated bridges with different parameters under random ground motions, the favorable and unfavorable effects of seismic isolation for high-speed railway bridges are explored and demonstrated from a random point of view. The comparison of the random seismic response under different cases are discussed and significant outcomes are drawn. Results show that: The use of isolation bearing can reduce the response of track structure and pier, but meanwhile, increase the response of bearings. The change of the equivalent radius of the isolation bearing has no obvious influence on the random response of the pier and the track structure, but will to some extent bring the change of the bearing response. The results can be used for the seismic design and maintenance of the railway high-speed bridge.

On the effect of seismic base isolation on seismic design requirements of RC structures

According to the basic concept of seismic isolation, the base-isolated structures must remain elastic during an earthquake. On the one hand, the existing technical documentation and codes strongly noted that the superstructure of isolated buildings should be designed the same as a fixed base structure. The only difference is the isolator. So, its period is higher, and consequently the applied acceleration is lower. One of the criteria for designing fixed-base structures is a seismic design and especially compact transverse rebars for beams and columns near the support. In the present study, 12 structures of 8 to 24 stories were designed in both fixed and isolated forms. Then, a program was written in MATLAB that calculated “moment-curvature” and “P-Mx-My interaction” curves for concrete beam and column sections with any amount of transverse rebars (Av/s). Having these curves, the structures were push-over analyzed in three sway conditions “ordinary”, “intermediate” and “special”. The results also showed that, unlike fixed-base structures, the response modification factor (Ru) of the isolated structures was not affected by the seismic design level of beams and columns. Also, in the two “target” and “final” displacements, the number of plastic hinges formed in IO or thereafter, in the isolated structures was much less than the fixed ones.

The influence of pier height on the seismic isolation effectiveness of friction pendulum bearing for Double-Track railway bridges

Friction pendulum bearing (FPB) is a sliding-based isolator, widely used in the seismic design of the bridge structure. However, there is neither unified standard nor complete evaluation system to evaluate the specific isolation effectiveness of FPB-isolated bridges with different pier heights. In this paper, the prototype bridge finite element models (FEM) of the typical simply supported girder bridges on the double-track railway in China, are established and studied. These bridge FEM differ in the pier height range of 4–60 m. Each FEM adopts two types of bearing: FPB (isolated bearing) and spherical steel bearing (non-isolated bearing). The nonlinear time history analysis is carried out to compare the seismic responses of FPB-isolated and non-isolated bridges. Based on the comparison results, the seismic isolation ratios of FPB are defined and obtained. In addition, a new criterion index is presented to quantifiably measure the effectiveness of the seismic isolation of FPB-isolated bridges with different pier heights, which is beneficial to the further popularization and application of FPB in the seismic design of bridge engineering.

Analysis of Seismic Isolation Effects on a Reverted L-shaped Pier Bridge in High Seismic Intensity Region with Finite Element Simulation

The seismic response of urban special-shaped bridges is large, and the consequence of these bridges’ failure is very influential, therefore, the seismic response of this kind of bridges must carefully be calculated and seismic measures of isolation should be used for them. Simulation methods was studied for common used seismic isolation structures such as the rubber bearing, high damping rubber bearing, friction pendulum bearing and block. Four layouts of those seismic structures were set up for an actual reverted L-shaped pier bridge, which were correspondingly four simulation cases. The seismic responses of the bridge were analyzed and comparatively studied in all simulation cases, as a result, the seismic performance and seismic isolation effects of those structures were researched for the bridge, and the isolation design methods were gained. The results show that measures of isolation can reduce largely the seismic response of this kind of special-shaped bridge, high damping rubber bearings have remarkable effect and make the responses among piers more even, and setting reasonably blocks with clearance can make full use of the seismic performance of structures of the bridge.

A numerical investigation on the seismic isolation effect of flexible wooden cushion

This paper proposes a finite element simulation of wooden structures with flexible cushion. Applied with different loads, the seismic isolation effect of the cushion is analyzed. By changing the thickness and elastic modulus of the cushion, the dynamic effect of the cushion under various conditions was analyzed. The Pi theorem is used to obtain the non-constant parameter that affects the vibration isolation result.

Improvement of the Performance Based Seismic Design Method of Cable Supported Bridges with Resilient-Friction Base Isolation Systems (II-Proposal for the Seismic Design Procedure)

In a previous paper, ambient vibration tests were conducted on a cable stayed bridge with resilient-friction base isolation systems (R-FBI) to extract the dynamic characteristics of the bridge and compare the results with a seismic analysis model. In this paper, a nonlinear seismic analysis model was established for analysis of the bridge to compare the difference in seismic responses between nonlinear time history analysis and multi-mode spectral analysis methods in the seismic design phase of cable supported bridges. Through these studies, it was confirmed that the seismic design procedures of the “Korean Highway Bridge Design Code (Limit State Design) for Cable Supported Bridges” is not suitable for cable supported bridges installed with R-FBI. Therefore, to reflect the actual dynamic characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure is proposed that applies the seismic analysis method differently depending on the seismic isolation effect of the R-FBI for each seismic performance level.

Shaking table test study on the seismic isolation effect of a hybrid passive control system

Abstract In this paper, the effects of control of a hybrid passive control system with energy consumption between the isolated structure and the adjacent structure, which was proposed recently by other researchers, is studied by shaking table test. Compared with a single seismic isolation system, this hybrid control system combines seismic isolation technique with damper energy dissipation and has strong robustness with application to seismic waves in different frequency domains. By inputting seismic waves in different frequency domains through shaking table tests, the effects of the control systems with different vibration reduction and isolation schemes under different frequency domain ground motions are studied. Finally, the finite element numerical simulations are compared with the test results. Research results show that, compared with ordinary periodic seismic waves, the long-period seismic waves have more obvious effects on structural displacement and acceleration, the overturning effect of high-rise isolated structures and the possibility of displacement over-limit of isolation bearings. For isolated structures, the multiple isolation has the best effect of vibration control. After connecting adjacent structure with viscous dampers, the hybrid passive control system is established and the seismic isolation performance of the isolated structure is further strengthened. The hybrid passive control system studied in this paper can effectively solve the problems existing in high-rise isolated structures, such as structural overturning and bearing displacement overrun and so on, and has a better control effect on structural responses under different frequency domain seismic excitations.