Seismic Isolation Effect Research Articles

Seismic isolation effect and parametric analysis of simply supported beam bridges with multi-level sliding friction adaptive isolation bearing

In response to the shortcomings of isolation bridge limit devices and friction dampers, a sliding friction bearing exhibiting multi-level working behavior (MSFB) is proposed. Its structure and mechanism are introduced, and a multi-condition quasi-static test is conducted using ABAQUS software. Through comparative analysis of theory and experiment, the theoretical model's accuracy and multi-level sliding friction mechanism of MSFB are verified. The mechanical parameters of MSFB are analyzed, clarifying the influence of various main mechanical parameters on the mechanical performance. The performance parameters of the MSFB are optimized based on a two-degree-of-freedom analysis model for a high-speed railway single-pier bridge equipped with MSFBs. The findings indicate that the seismic responses of MSFB is comprehensively affected by all the parameters, and the variation pattern is complex. By optimizing these performance parameters, MSFB can satisfy the multi-level performance demands of bridges subjected to varying earthquake intensities, and achieve the optimal control effect. The MSFB offers superior isolation efficiency during minor and moderate earthquakes and can substantially decrease the internal forces within the bridge substructure when utilized as a bridge isolation and limit device. During intense and infrequent earthquakes, the MSFB demonstrates remarkable displacement-limiting capacity and good self-centering and energy dissipation abilities.

Influence of pier height and ground motion parameters on seismic response and energy dissipation of isolated railway bridges

The overlap between high-speed railways and earthquake areas makes it necessary to implement isolation design for railway bridges. At present, the variation of seismic energy of railway bridges with structural and ground motion parameters is not clear. In this paper, the finite element models of railway bridges with different pier heights are established and verified by shaking table tests. Then, the nonlinear time history analysis of isolated and non-isolated models is carried out, and the differences in seismic response and energy dissipation between the two models under different parameters are compared. Finally, the isolation effect of hyperbolic friction pendulum bearing (HFPB) is evaluated by using the efficacy coefficient method. Results demonstrate that HFPB can not only reduce the seismic response of the girder and the pier, but also effectively reduce the seismic input energy, structural damping energy, and pier hysteretic energy. In addition, HFPB has a better seismic isolation effect when pier height is 3–15 m, site characteristic period is 0.25–0.45 s, and earthquake PGA is 0.2–0.5 g.

Comparative analysis of seismic isolation effects under three-way seismic actions for suspension core-tube structure and frame core-tube structure

In this paper, the suspension core-tube structure and frame core-tube structure are taken as the research objects, and the modal analysis of them and their basic seismic isolation structures are carried out firstly to explore the self-vibration characteristics and seismic isolation effect of the structures. Secondly, the nonlinear time-history analysis of the four structures under the action of rare earthquakes in the X, Y, and Z directions is carried out, and their inter-story drift angles, inter-story shear forces, base shear forces, maximum accelerations at the apex of the core-tube, and cantilever beam stresses are analyzed comparatively. Finally, the displacements and loads of the energy dissipators, the maximum horizontal displacements and tensile and compressive stresses of the seismic isolation bearings are analyzed to evaluate the performance of both of them under rare earthquakes. The results show that the suspension core-tube structure and the frame core-tube structure with base seismic isolation bearings can provide good control of their inter-story drift angles and internal forces, etc. The suspension core-tube structure is superior to the frame core-tube structure in controlling the maximum acceleration at the apex of the core tube response.

Seismic Damage Analysis of Zamora Bridge in Ecuador

The Zamora Bridge, located in the Zamora-Chinchipe Province in the southeastern part of Ecuador, on the Pacific Rim seismic belt, serves as the sole river-crossing channel from the Mirador Copper Mine area to the exterior. Constructed and opened for traffic in 2013, this bridge is designed as a low-pier continuous girder bridge, featuring a three-span prestressed concrete continuous box girder for the main beam, with a span arrangement of 45.5+140+45.5 meters, and utilizes basin-type rubber bearings throughout. On May 6, 2019, and November 28, 2021, the Zamora Bridge experienced two significant seismic events. The initial seismic damage investigation revealed that the piers and foundation maintained their load-bearing capacity largely intact; the basin-type rubber bearings predominantly suffered shear failure and displacement, losing their horizontal limit capacity. Additionally, abutment blocks sheared, padstones cracked locally, and the main girder exhibited residual displacement. Following the first earthquake, repair work was undertaken based on the damage results, switching to friction pendulum seismic isolation bearings to enhance the seismic resilience of bridge. The subsequent seismic damage assessment indicated the overall stable condition of the bridge, with no observable damage, deformation, or settling to the main structure, thus maintaining basic traffic functionality. However, shear and deformation occurred to the bolts and pins fixing the direction of the friction pendulum isolation bearings, along with residual displacements after the activation of the seismic isolation function, and cracks developed in the abutment padstones and mortar layers. To delve into the performance and damage probability of vulnerable components of low-pier continuous girder bridges under various seismic intensities, numerical models of the Zamora Bridge equipped with basin rubber bearings and friction pendulum bearings were separately established using OpenSees finite element software. An analysis of the bearings' longitudinal seismic susceptibility was conducted by integrating the demand-capacity ratio and IDA method. The findings indicate that bearings, padstones, and anchor bolts are the vulnerable components necessitating reinforcement for such bridges. Compared to the basin rubber bearings, friction pendulum bearings significantly reduce the probability of bearing damage and demonstrate an excellent seismic isolation effect.

Seismic design optimization of space steel frame buildings equipped with triple friction pendulum base isolators

To increase the seismic resilience of structures, it is necessary to utilize seismic isolation to increase structural periods and reduce story drifts. When seismic isolation is implemented, structures are capable of deforming by remaining within safe limits. Thus, more seismically resilient designs are achieved compared to conventional fixed-based structures since lighter structural design weights are attained. The principal aim of this study is to achieve the comparative design optimization of space steel frame buildings equipped with seismic base isolation and to examine the effect of seismic base isolation on optimum structural design weight by comparing the same structures with conventional rigid-based ones. For seismic base isolation, triple friction pendulums are implemented into steel frame buildings. For this aim, four different space steel frame buildings with 4-, 6-, 8-, and 10-story are treated as design examples. A novel design optimization algorithm is encoded, which includes nature-inspired metaheuristic artificial bee colony, crow search, and Archimedes optimization algorithms to achieve design optimizations of triple friction pendulums equipped with seismic-isolated space steel frame buildings. The practice code provisions of load and resistance factor design specification for structural steel buildings have been applied to control the structural design constraints of inter-story drift, top-story drift, strength, displacement, and connections geometry of beams and columns. Eventually, it has been remarked that seismic base isolation significantly reduces the structural optimal design weight of space steel frame buildings.

Shaking table tests on seismic performance of a five-story reinforced concrete frame structure with MoS2 sliding bearings and steel dampers

The seismic performance of friction isolated structure is greatly affected by the friction coefficient, and the combination of low friction material and limit device is an available option. Via the Motion State module simulating the friction conditions and the Bouc Wen model describing the restoring characteristic of the steel dampers, a single-degree-of-freedom model was established to investigate the influence of the friction coefficient and limit stiffness on the isolation effect. Then, for the evaluation of the seismic performance of the proposed isolation system with molybdenum disulfide (MoS2) sliding bearings and steel dampers, the shaking table tests of a 1/5 scaled five-story reinforced concrete frame structure model, subjected to three ground motions with different peak ground acceleration, were implemented to obtain the isolation layer drift, absolute acceleration, inter-story shear and damage energy of the structure under the testing conditions of free sliding, limited sliding, multi-dimensional seismic excitation, and top additional layer sliding. It is found that the ideal friction coefficient for sliding isolated structure is 0.03–0.07, and the corresponding reasonable elastic stiffness of steel dampers is (0.2–0.5) Ks that is the stiffness of the structural standard story, and the proposed MoS2 sliding bearing presents remarkable low-friction characteristic with a friction coefficient of 0.04–0.05. The appropriate steel dampers can reduce the isolation layer drift without obviously increasing the acceleration. The low-frequency components in the ground motion significantly increase the isolation layer drift, while the high-frequency components cause the superstructure acceleration to show a K-shaped distribution along the height. Moreover, the proposed isolated system can be effectively used for structural protection under multi-dimensional earthquakes, the sliding additional layer on the roof can be considered as the second defense line in the structural seismic design, and the seismic energy the superstructure bears can directly estimate the seismic isolation effect that is consistent with the analysis result of dynamic response.

Effects of seismic isolation on the dynamic behaviour of the DTT torus complex during earthquake events

The Divertor Tokamak Test (DTT) fusion machine is currently under construction at ENEA site in Frascati (Italy). The location has been identified as being at high seismic risk. Preliminary analyses, using both static equivalent and dynamic methods, of seismic effects from local response spectra have been carried out on the structure, namely the cryostat base, supporting the vacuum vessel, the magnets and the cryostat, and a reference design has been obtained. An update of the geological seismic surveys for the site showed a more severe local seismic response than previously considered. The analyses based on the updated seismic response revealed potential structural criticality for the base. Therefore, two possible seismic isolation solutions were considered to reduce the stress state. Finally, a comparison in terms of displacement and stress fields between the non isolated configuration and the two isolated ones is presented.

Seismic modeling and performance evaluation of seismically isolated building considering large strain effects under near-fault earthquakes

Lead rubber bearings (LRBs) have been widely used in seismically isolated buildings to mitigate earthquake damages in highly earthquake-prone regions. The deformation of the LRBs has been generally recognized to conform to the bilinear model under moderate shear deformation. However, when the bearings are loaded with large strain deformation, LRBs exhibit a significant increase in stiffness and strength due to the hardening characteristics of the rubber. Nevertheless, the dilemma in engineering practice is that most of the existing LRB models in design software cannot capture complex hardening behaviors under large strain loadings. Furthermore, although some LRB models can consider the large strain effects, they require many calibrated parameters. For this reason, a concise generalized Bouc–Wen model was proposed (hereinafter referred to as BoucWenG model) in this work, which can improve the aforementioned limitations of the traditional LRB models while retaining the favorable features of the Bouc–Wen model. The detailed features of the BoucWenG model were introduced first. Then, the generalized model was verified using the experimental results of LRBs with different sizes under cyclic large strain loadings. Furthermore, considering the large strain effects, we examined the seismic performance of the base isolation system using two comparative isolated reinforced concrete frame buildings, in which the base isolation bearings were simulated by the traditional Bouc–Wen and the proposed BoucWenG models. Next, we conducted seismic fragility analyses of these two isolated buildings through incremental dynamic analysis, in which the near-fault (NF) ground motions characterized by large-amplitude velocity pulse were also considered. The comparison results reveal that the proposed BoucWenG model can well represent the large strain hardening and strength degradation properties of LRBs. Furthermore, the dynamic responses of the superstructure and the isolation system significantly tend to vary when the large strain effects of the bearings are considered under strong earthquakes. The traditional LRB model, which ignores the large strain effects, may highly overestimate the shear deformation of the isolation layer and lead to poorer-than-expected seismic isolation effects for the superstructure, especially under strong NF earthquakes.

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

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

Seismic isolation technology of shallow buried large section utility tunnel with soft soils in seismically vulnerable area

Shallow utility tunnels with exceptionally large cross-sections in weak soil can face significantly more severe seismic risks compared to conventional deep tunnels in seismic hazard areas. This study investigates the seismic response and isolation technologies applied to a large section utility tunnel with 4 compartments in one layer, employing seismic simulations. The engineering context, dynamic motions, and measuring points of the numerical simulation were introduced. Subsequently, the finite element method was employed to explore the seismic behaviors of the large section utility tunnel when subjected to strong earthquake excitations under four conditions. The study explored and comparatively evaluated the seismic isolation effectiveness of three proposed schemes: the grouting scheme, the buffer layer, and the assembly of three-quarters buffer layer, cushion and grouting. The analysis included various indexes such as the deformation, the principal and shear stress, and the safety factor. The finding reveals that the assembly seismic scheme exhibits the most significant seismic effect (95.39%), followed by the buffer layer (38.82%), and the grouting scheme (25.66%). The assembly seismic scheme is recommended for the seismic design in the current large-section utility tunnels. These conclusions provide valuable scientific guidance for the seismic design of large-section utility tunnels, aiding in enhancing earthquake resilience.

Preliminary design and evaluation method for the seismic isolation layer of a shield tunnel

Theoretical analyses and numerical simulations, proposed to increase the efficiency of tunnel seismic isolation measures, are too complex for solving practical problems. Herein, a simplified design method for a tunnel isolation layer is developed for preliminary calculations of the required physical parameters based on the surrounding rock conditions and seismic isolation performance. The internal force response of a shield tunnel in homogeneous ground before and after the installation of a seismic isolation layer is determined using the proposed method, considering the coupled effect of the isolation layer and surrounding rock by calculating the equivalent elastic modulus. The effectiveness of the derived method is verified using wave function expansion and finite element numerical simulation methods. The results obtained using the simplified design formulae are consistent with those obtained using the wave function expansion method. Furthermore, the effects of the seismic wave frequency, surrounding rock type, elastic modulus, and thickness of the seismic isolation layer on the seismic isolation effect are examined via parametric analysis. The proposed method could be applied to preliminary design and evaluation of seismic isolation layers for shield tunnels with different surrounding rock types.

Geotechnical seismic isolation based on high-damping polyurethane: centrifuge modelling

Geotechnical seismic isolation (GSI) is a new category of low-damage resilient design methods that are in direct contact with geomaterials and of which the isolation mechanism primarily involves geotechnics. Various materials have been explored for placing around the foundation system in layer form to facilitate the beneficial effects of dynamic soil-foundation-structure interaction, as one of the GSI mechanisms. To reduce the thickness of the GSI foundation layer and to ensure uniformity of its material properties, the use of a thin and homogeneous layer of high-damping polyurethane (HDPU) was investigated in this study via centrifuge modelling. HDPU sheets were installed in three different configurations at the interface between the structural foundation and surrounding soils for realising GSI. It was found that using HDPU for GSI can provide excellent seismic isolation effects in all three configurations. The average rates of structural demand reduction amongst the eight earthquake events ranged from 35 to 80%. A clear correlation between the period-lengthening ratio and the demand reduction percentage can be observed amongst the three GSI configurations. One of the configurations with HDPU around the periphery of the foundation only is particularly suitable for retrofitting existing structures and does not require making changes to the structural systems or architectural features.

Finite Element Analysis of Geotechnical Isolation System Finite-Element Analysis on the Geotechnical Seismic Isolation (GSI) System

In order to verify the effectiveness of the Geotechnical Seismic Isolation (GSI), a series of finite element parameter studies were carried out. The finite element calculation model of the GSI system and superstructure is established. The finite element analysis conditions consist of two kinds of confining pressures, three kinds of RSM ratios and three kinds of seismic wave inputs, a total of 32 kinds of conditions. Comparing the analysis results of the parameters, it can be seen that the dynamic shear modulus of the RSM sample increases with the increase of the confining pressure, but the degree is affected by the input of seismic waves. The greater the peak value of the input acceleration, the more obvious the isolation effect; As the RSM ratio increases, it decreases, but it is not greatly affected by the input of seismic waves, and the isolation effect remains basically the same. The numerical simulation results verify the isolation effect of GSI, which can be used as a reference for practical engineering applications in the future.

Seismic isolation effect of tunable friction pendulum system in bridge

ABSTRACT A Tunable Friction Pendulum System (TFPS) was proposed to investigate its seismic isolation control performance in bridge structures. First, the structural design and theoretical model of TFPS are given. Second, the mechanical properties of TFPS are studied through finite element simulation. Then, the above TFPS is introduced into the bridge structure, and the analysis model is established based on SAP2000. Finally, a nonlinear time-history analysis is carried out on the bridge structure, and the seismic isolation performance of TFPS is evaluated by using the dynamic characteristic response index of the bridge structure. Theoretical derivation and finite element analysis results show that TFPS can adjust the dynamic characteristics in real time according to the spectral characteristics of the ground motion input and the response of the structure itself, so that the friction force can be continuously adjusted and energy consumption can be adjusted.

Shaking Table Testing of a Scaled Nuclear Power Plant Structure with Base Isolation

To investigate the seismic performance and isolation effect of a high-temperature gas-cooled reactor, a 1/20 scale model including a reactor, a spent-fuel plant, and a nuclear auxiliary plant was fabricated. In addition, 220 mm lead-rubber bearings were designed and produced for use in the shaking table test, which included both isolated and nonisolated conditions. Two historical earthquake records and three artificial earthquake motions were used to input the ground motion in the tests. The results demonstrated that the seismic performance of the plant was better and that the structure was in an elastic state, under a safe shutdown earthquake event. Isolation bearings were found to effectively reduce the dominate frequency of the structure. The acceleration amplification factor of the superstructure was found to be less than 1. The isolation test results showed that the peak of the floor response spectrum at the pressure vessel support was less than 0.1 g. In the nonisolation test, the peak of the floor response spectrum was greater than 1 g. In the isolation test, the relative displacement of the structure was less than 1.1 mm, which was relatively small. The structure maintained a good isolation performance and exhibited improved safety under extreme ground motion.

Seismic isolation effect of unconnected piles-caisson foundation: Large-scale shake table tests

The seismic response and isolation mechanism of a new unconnected pile-caisson foundation (UPCF) suitable for supporting deep-water large-span bridges under seismic loading were investigated by large shaking table tests. Five scaled models were constructed utilizing different cushion material (aggregate), cushion thickness and piles configuration. Each model was tested under 18 different seismic loading conditions. The tests observations were analyzed to evaluate the seismic response characteristics and isolation mechanism of UPCF. The maximum displacement of UPCF and the peak acceleration of the input ground motion were linearly related. Under strong ground motions, the foundation soil and cushion displayed a significant softening behavior manifested in reduced natural frequencies and prolonged periods, which resulted in lower acceleration amplification. However, the stiffnesses of soil and cushion were largely restored after the ground shaking ended. The cushion model with larger aggregate particles performed better in terms of the caisson residual displacement and displacement restoration rate of the caisson. It was found that the UPCF constructed with a thin cushion layer comprised of large, rounded aggregate particles exhibited acceptable seismic isolation effect and reduced the peak seismic acceleration by up to 26.7%. It was also observed that the front and middle piles experienced larger loads, and accordingly, their peak moment envelopes were greater and the location of peak moment was shallower.

Anti-liquefaction mechanisms in buildings with shallow foundations with a focus on lowering the ground water table

This study simulates and discusses the behavior of low-rise buildings on liquefiable ground with different ground water table levels during earthquakes via centrifuge modeling. The test results reveal that lowering the water table can effectively limit the settlement of structures on liquefiable ground. However, this also reduces the seismic isolation effect of soil liquefaction. As the water table is lowered, the acceleration amplification in structures increases slightly. In addition to this, the effect of reinforcing the first floor slab was studied and the results show that such reinforcement can generate a significant anti-liquefaction effect in areas with a high water table. Engineers can use this combination of improvement methods to achieve better designs.

Interlayer Isolation Structures Considering Soil–Structure Interaction under Long-Period Ground Motions: An Experimental Analysis

After coupling long-period seismic motions with the soil–structure interaction (SSI) effect, isolated structures can easily be resonated, and the seismic response of the structure is significantly enhanced. The SSI effect can alter the dynamic characteristics of a structure, resulting in a deviation between the assumed seismic-isolation effect of the rigid foundation and the theoretical results. To investigate the dynamic characteristics and seismic-response laws of interlayer structures considering SSI under long-term seismic motion, four types of ground motions (near-field ordinary, far-field ordinary, near-field pulse, and far-field harmonic ground motions) were selected, and two structural models (rigid-foundation and soft soil foundation interlayer seismic-isolation structure models) were established. Experiments were conducted using a combination of shaking-table tests and finite-element simulations. The results show that the use of the SSI effect caused the decrease in the acceleration response of the upper structure of both models under four types of seismic motions and increased the seismic peak ground acceleration (PGA). In addition, the weakening of the acceleration response of the upper structure under ordinary seismic motion is significant for longer periods of seismic motion. Furthermore, when considering the SSI effect, the displacement response ratio under long periods and ordinary ground motions is greater than that of rigid foundations, and the horizontal deformation of the isolation layer under long-period ground motions is greater than that under ordinary ground motions. This shows that the SSI effect weakens the interlayer shear force under ordinary seismic action more than that under long-period seismic action. When PGA increases, the interlayer shear force response of the interlayer isolation structure model with a soft soil foundation under a long-period seismic action may be smaller than that of the rigid-foundation model.

Mechanical Behaviors and Numerical Simulation Analysis of a New Isolation System

Finite element analysis is one of the key steps in evaluating the effectiveness of an isolation system. The aim of this paper is to research the mechanical properties of sliding and rolling friction systems and their application for isolating frame structures. A hybrid seismic isolation system is proposed, which aims to protect the superstructure by reducing dynamic response. The effect of different parameters on the friction coefficient of the isolation bearing was tested using a compression-shear testing machine, and the results showed that various parameters significantly affected the friction coefficient. In addition, a numerical analysis finite element model was established using SAP2000 software to compare the seismic isolation performance of the hybrid isolation system with that of traditional seismic-resistant structures. The results showed that the composite isolation system not only effectively reduced inter-story shear and acceleration, but also slightly enhanced the seismic isolation effect as the friction coefficient decreased.

Research on the Seismic Isolation Effect of the Ring Spring–Friction Pendulum Bearing in the Dakai Underground Subway Station

During strong earthquakes, the vertical seismic force becomes an essential factor affecting shallow underground structures that cannot be ignored. In this situation, it is proposed that ring spring–friction pendulum two-way seismic isolation bearings be set up at the bottom of such structures. Targeting the Dakai underground station and the Kobe earthquake, a soil-structure force model was established based on the damage to the underground structure and dynamic simulation was carried out using Abaqus software. The advantages of the ring spring–friction pendulum bearing over the ring spring bearing alone and the friction pendulum bearing alone were compared. The simulation results showed that the structure displayed a good seismic isolation effect in both horizontal and vertical directions after setting the ring spring–friction pendulum bearing. The deflection in the midspan of the roof reduced to less than 5 cm, the horizontal relative displacement of the structure reduced to less than 3 cm, there was no obvious damage to the structure, the axial pressure ratio of the mid-pillar reduced to less than 0.5, the axial force on the mid-pillar reduced by more than 50%, and the shear force reduced by more than 30%. In addition, by comparing the damage to the structure after setting the annular spring bearing and the friction pendulum bearing, we found that a vertical seismic isolation device is more crucial than a horizontal seismic isolation device for shallow underground structures. Setting a vertical damping device can make the structure retain part of the ductility and reduce the damage to the structure, so the ground vertical seismic mitigation design should be strengthened when a shallow underground structure is designed.