Seismic Reduction Effect Research Articles

Seismic reduction principle and response analysis of variable damping viscous damper system

PurposeA new type of variable damping viscous damper is developed to meet the settings of different damping parameter values at different working stages. Its main principle and design structure are introduced, and the two-stage and multi-stage controllable damping methods are proposed.Design/methodology/approachThe theoretical calculation formulas of the damping force of power-law fluid variable damping viscous damper at elongated holes are derived, aiming to provide a theoretical basis for the development and application of variable damping viscous dampers. For the newly developed variable damping viscous damper, the dynamic equations for the seismic reduction system with variable damping viscous dampers under a multi-degree-of-freedom system are established. A feasible calculation and analysis method is proposed to derive the solution process of time history analysis. At the same time, a program is also developed using Matlab. The dynamic full-scale test of a two-stage variable damping viscous damper was conducted, demonstrating that the hysteresis curve is complete and the working condition is stable.FindingsThrough the calculation and analysis of examples, the results show that the seismic reduction effect of high and flexible buildings using the seismic reduction system with variable damping viscous dampers is significant. The program developed is used to analyze the seismic response of a broadcasting tower using a variable damping TMD system under large earthquakes. The results indicate that the installation of variable damping viscous dampers can effectively control the maximum inter-story displacement response of TMD water tanks and can effectively consume seismic energy.Originality/valueThis method can provide a guarantee for the safe and effective operation of TMD in wind and vibration control.

Seismic Behavior of the Combined Viscous-Steel Damping System for a Long-Span Suspension Bridge Considering Wave-Passage Effect

This study investigates the working mechanism and seismic behavior of the Combined Viscous-Steel Damping System (CVSDS) considering the longitudinal wave-passage effect. In the CVSDS, the operational status of the fluid viscous damper (FVD) and the steel damper (SD) can be switched by the fuse–lock device (FLD), which is triggered by the output force of the FVD. The configuration and working mechanism of CVSDS are introduced in detail. A test model is manufactured and examined by cyclic tests to verify its fusing–locking function during cyclic motions. The numerical model of CVSDS is proposed based on the experimental result. The fusing–locking behavior and seismic reduction effectiveness of CVSDS installed in a long-span bridge is analyzed, in which the wave-passage effect is considered. The results show that the fuse–lock function under dynamic loading can be achieved by the proposed FLD. The occurrence condition of the locking mechanism activation depends on the viscous damping force. The traveling wave will induce a delay of the locking time, cause large locking intervals between CVSDSs installed at different positions, and lead to a larger required moving capacity of the CVSDSs. The mitigation effectiveness of CVSDS is significantly reduced due to the wave-passage effect.

Study on Seismic Reduction Measures of a Diaphragm Wall—Underground Structure System

In this paper, the seismic reduction and isolation measures are first proposed by setting a segmented isolation layer between the diaphragm wall and the side wall of the station structure. Although the segmented isolation layer can effectively improve the stress state of the side wall and slabs, the seismic reduction effect of the middle column is not obvious. In order to improve the overall seismic performance of the station structure, the reduction measures by combining the segmented isolation layer and new type bearing of the middle column are then proposed. At the same time of inserting the isolation layer between the diaphragm wall and the structure, the sliding bearing at the top of the column is set up to reduce the vibration. The results show that the segmented isolation layer can significantly reduce the internal force and damage at the top, bottom and side wall joints. In addition, the combined measures of segmented isolation layer and sliding bearing at the top of the column can effectively reduce the seismic damage of the middle column. The damage of the connection between the top plate, the middle plate and the middle column can be significantly decreased.

Study on Asphalt-Cement Isolation Layer for Shield Tunnels Using Seismic Fragility Curves

ABSTRACT For shield tunnels, seismic isolation layer is an effective countermeasure to reduce structural damage during earthquakes. In this paper, the physico-mechanical properties of asphalt-cement (A-C) materials applied to backfill grouting of shield tunnels were investigated by laboratory tests. Then, fragility curves were developed by analytical approach for shield tunnels before and after setting three typical A-C isolation layers (i.e. A-C Iso-layer1, 2, and 3), which were used to express the seismic vulnerability of tunnel lining and evaluate the seismic-reduction effectiveness under earthquakes. The results reveal that A-C isolation layers are effective in seismic-reduction under excitation of low input intensity (less than 0.5 g), while its effect is not significant at high-input intensity. The fragility curves for tunnel lining after setting A-C isolation layers show less vulnerability than not setting one at all seismic intensity levels. From the perspective of damage probability, the seismic-reduction effectiveness decreases with the increasing shear modulus of A-C isolation layer. The probability of minor damage of examined tunnel lining setting up with A-C Iso-layer1 decreased from 23% to 15% at most.

Experimental and Numerical Studies of AP1000 Shield Building considering Fluid-Structure Interaction

The gravity cooling water tank is a remarkable structural feature of third-generation pressurized water reactor nuclear power plant. To investigate the influence of fluid-structure interaction (FSI) on the seismic response of the structure, this study designed two 1 : 50 simplified models of the AP1000 shield building. A series of shaking table tests were conducted to study the seismic responses with and without FSI effect. The natural frequency, acceleration, strain, and hydrodynamic pressure of the two models were analyzed, and the seismic reduction effect of the water tank was evaluated. Moreover, the test data were compared with the results of numerical analysis using the ABAQUS software. The results show that the presence of water and the sloshing of water reduce the natural frequency and seismic response of the model structure. Thus, the gravity cooling water tank has a certain seismic reduction effect. The simplified model of water sloshing can be used to analyze the seismic response of the shield building.

Energy dissipation demand and distribution for multi-story buildings with fluid viscous dampers

The seismic response of structures with fluid viscous dampers (FVDs), which is a predominant type of structural control techniques, can be analysed from the perspective of energy. In such structures, the imposed seismic energy is mainly dissipated by the structural plastic energy, EP, and the energy dissipated by FVDs, Ed2, which quantify the structural cumulative damage and FVD’s seismic reduction effect, respectively. Research conducted in the past focuses on investigating the EP demand of systems without supplemental damping devices, but little knowledge is available for the EP and Ed2 demand in multi-story buildings equipped with FVDs. To fill this gap, this paper conducted a comprehensive investigation based on four steel-moment resisting buildings with different height (3-, 6-, 9-, and 20-stories, respectively) equipped with linear or nonlinear FVDs. The effect of structural property and FVDs properties, characterised by the supplemental damping ratio ξadd and velocity power α, on the EP and Ed2‘s overall demand and distributions among stories were illustrated. The results indicate coupling effects of structural property, ξadd and α, on the EP and Ed2 demands. In most cases, the increase of ξadd and the decrease of α can reduce the EP demand and increase the Ed2 response. However, the increasing of ξadd is not effective if it is larger than 20% and the FVDs with α = 0.3 are not recommended in relative high-rise buildings. The distribution pattern shows a trend of linearly decreasing along the height, but those in the high-rise buildings are disturbed by high-mode effects.

Vibration Reduction Performance of Structures with Viscous Dampers under Near‐Field Earthquakes

Near‐field pulse‐type ground motions (NPGMs) are characterized by a high‐energy pulse with large peak ground velocities and accelerations and need further studies to confirm whether structures with viscous dampers (VDs) are still applicable and effective for this type of ground motions. In this article, the vibration reduction performance of structures with VDs under near‐field earthquakes is investigated systematically. Displacement and acceleration spectra are developed for a single‐degree‐of‐freedom (SDOF) structure with and without VDs, while these influence factors, such as the nonlinear characteristic of structure, damper supports’ flexibility, and damper parameters, are considered. Additionally, the frequency domain characteristics of NPGM and the energy distribution of a multidegree‐of‐freedom (MDOF) structure with VDs are discussed to further reveal the action mechanism of NPGM on the structure. It is shown that the structure with VDs shows remarkable seismic reduction effect under the action of near‐fault pulse‐type earthquake, and the maximum interstorey drift decreased from 0.086 to 0.037 when the structure is equipped with VDs. However, the structure may still be difficult to completely dissipate the high‐energy generated by the earthquake pulse with a high pulse period in a short time, which can cause the structure to be damaged or even collapsed in a moment.

Parameter Analysis and Optimization of Friction Pendulum Bearings in Underground Stations Based on Genetic Algorithm

ABSTRACT This paper analyses the influence of friction coefficient and equivalent radius on the seismic reduction effect of friction pendulum bearings in the underground station under far-field and near-field earthquakes with different strength. It is found that the parameters of the friction pendulum bearings will obviously influence seismic reduction effectiveness. By combining genetic algorithm with finite element method, the parameters of friction pendulum bearings in the station can be optimized. By using this method, the optimal parameters range can be obtained, which can provide reference for parameter design of friction pendulum bearings in underground stations.

Optimal Design of Negative Stiffness Devices for Highway Bridges Using Performance-Based Genetic Algorithm

Parameter optimization analysis on the negative stiffness device (NSD) installed in the benchmark highway bridge is carried out in this study. Key parameters and constrain conditions are determined in accordance with the characteristics of NSD, and an objective function is designed with safety and comfort being considered. Individual fitness value–related cross and mutation operators are designed to protect excellent chromosome and improve the efficiency and convergence of computation. The genetic algorithm is used to realize parameter optimization of the NSD used in a benchmark highway bridge. Dynamic responses of structure without NSD, with random NSD, and with optimal designed NSD are compared. By analyzing the time history of displacement and acceleration, it can be concluded that dynamic responses of the structure decrease obviously when the NSD is added, and a better seismic reduction effect can be reached when the NSD is designed optimally in accordance with the optimization method and different earthquake excitations have slight influence on the optimization results.

Research on Seismic Reduction and Isolation Measures for Urban Underground Station Structure

Based on a rectangle underground station structure, two-dimensional finite element models are established in this study to explore the effectiveness of different seismic reduction and isolation measures for underground structure, where Davidenkov model is adopted to consider the soil nonlinearity and the underground structure is considered elastic. The performances of the seismic reduction and isolation measures are evaluated by assessing the structure internal force and deformation responses. Depending on the ratio of wave impedance between the isolation layer and the structure, the isolation layers are divided into rigid and flexible types. The effects of the length and elastic modulus of rigid isolation layer as well as that of the thickness and shear modulus of flexible isolation layer are investigated. The results show that the seismic reduction effect of rigid isolation layer is better with the increase of stiffness, and the effect of flexible isolation layer is more obvious with the decrease of stiffness, which are consistent with the classical impedance theory. Furthermore, the middle column of subway station is usually the most vulnerable during seismic shakings, and one viable way to improve its seismic behavior is to reduce the column end constraints. Therefore, different column constraints consisting of swing, hinge, sliding connection and isolation bearing are considered. The numerical results suggest that among the different column end constraints considered, the sliding connection is comparatively more favorable, which can effectively limit the lateral deformation of column while imposing no horizontal reaction force.

Seismic Reduction Effectiveness of Friction Pendulum Bearings in Underground Station Structures

Setting friction pendulum bearings (FPB) at the top of central columns may be a good strategy to reduce the stations’ seismic responses. In this paper, the FPB is simulated in a detailed manner. The seismic reduction effectiveness of the FPB is studied with the three-dimensional dynamic time history analysis method. It is found that FPB can effectively reduce the maximum shearing force of the central columns and slightly reduce the maximum bending moment. It is stated that FPBs are also effective in the underground station structures.

Mechanism and optimum design of shared tuned mass damper for twin‐tower structures connected at the top by an isolated corridor

SummaryThe concept of shared tuned mass damper (STMD) for twin towers linked by a sky corridor using flexible joints is proposed in this paper. The analytical expressions of the transform functions and random earthquake responses of the flexibly connected structures are derived using a three‐degrees‐of‐freedom model system. The seismic reduction mechanism of the STMD is revealed using comparative analysis between the structures with STMD and those connected using a viscoelastic damper. The effect of the nondimensional parameters such as the frequency ratio of the two primary structures, mass ratio, tuning frequency ratio of the corridor, and damping ratio of the passive control devices on the structural seismic response is investigated. Optimum parametric analysis is performed using the principle of minimizing the displacements of both towers, and the optimal parameter formulas are established. Numerical analysis is conducted to verify the control effectiveness of the connected multi‐degree‐of‐freedom system subjected to the El Centro earthquake ground motion. The results show that the earthquake responses of the towers can be effectively reduced if the parameters of the flexible connecting elements are appropriately selected for a certain corridor mass. Moreover, a remarkable seismic reduction effect can be achieved if the towers have similar dynamic properties.

Seismic performance of high‐rise building with a rock‐slip isolation system with cables

SUMMARYTo avoid the overturning hazard of high‐rise buildings with traditional isolation technology, a rock‐slip structure with cables (RSSC) was proposed to improve their seismic performance. The mechanical model was established, and the motion behaviour equation of the RSSC was derived. Shake‐table tests of the RSSC were performed, and the results were compared with the corresponding finite‐element model simulations. The influences of key structural parameters and earthquake motion characteristics were analysed. The study results showed that the RSSC could effectively reduce the internal seismic force response and interlayer deformation under a severe earthquake, as well as decrease the overturning probability. The seismic reduction effect was influenced by the prestressed force, the aspect ratio of the structure, and the friction coefficient between the superstructure and foundation as well as seismic site type. The motion equation derived in this paper can be used to theoretically predict the motion behaviour of RSSC.

Study on Energy Dissipation of Viscous Damper for Long-Span Suspension Bridges

Viscous dampers are important devices to dissipate the vibration energy of long-span bridges. In the paper, nonlinear time history analysis was used to study the effects of this type of dam-per on suspension bridges. The influence of nonlinear viscous dampers on the seismic response of long-span suspension bridges was analyzed, which was based on a real project. The quantitative relationship between the displacement of the bridge girder and the tower with the damping coefficient and velocity index was investigated. The results showed that the displacement of the bridge girder under earthquakes can be effectively reduced by selecting the appropriate damping coefficient and velocity index of the nonlinear viscous dampers, and the best energy dissipation and seismic reduction effect for long-span suspension bridges can be obtained.

Performance evaluation of existing isolated buildings with supplemental passive pseudo-negative stiffness devices

A new configuration for passive pseudo-negative stiffness device (PPNSD) is proposed to work as a supplemental device for the seismic protection of existing isolated buildings. The proposed PPNSD reproduces the hysteretic behaviors of semi-active pseudo-negative stiffness devices (PNSD). Using the ratchet-pawl mechanism, a prototype was realized and tested under cyclic loading, validating the feasibility of the proposed PPNSD. Seismic reduction effect of the PPNSD on single-degree-of-freedom (SDOF) systems was verified through seismic response analysis. The PPNSD shows superiority in suppressing the peak acceleration response of long period structures, which is unlikely to be achieved even with large supplemental damping. Then, the performance of isolated buildings with PPNSD was evaluated in comparison to those of isolated buildings with traditional passive isolators under far-field (FF), near-fault pulse-like (NFP), and near-fault non-pulse-like (NFNP) ground motions. It is shown that the use of PPNSD not only simultaneously reduced the base drift and the acceleration of superstructures, but also was effective for all the FF, NFNP, and NFP motions.

Displacement reduction effect and simplified evaluation method for SDOF systems using a clutching inerter damper

SummaryThis study evaluates the response reduction effect of linear single degree of freedom systems with a clutching inerter damper (CID) via parametric analysis under harmonic excitations and real earthquake records. The cause of the displacement reduction effect of a CID is inherited from the inertial mass damper (IMD)—reducing the nominal load intensity by increasing the mass by inertance. Additionally, the displacement reduction effect is further enhanced by the clutching effect, which speeds up the decreasing of the velocity response from an instantaneous extremum to 0. Thus, the CID is more effective than the IMD at reducing displacement responses. For example, the displacement response for a long‐period structure with a CID can be reduced by approximately 53%, while for an IMD, it can only be reduced by approximately 24%. Additionally, the linear single degree of freedom system with a CID is a weak nonlinear system reserving homogeneity, indicating that the response reduction factor will provide enough information to reveal the seismic reduction effect of the CID and that there is no need to consider the amplitude of the input excitations. To simplify the analysis of such nonlinear systems, an equivalent linearization method and a simplified formula of displacement reduction factors for code‐based designs are proposed and validated by another independent set of records from the European Strong‐motion Database.

Connecting parameters optimization on unsymmetrical twin-tower structure linked by sky-bridge

Based on a simplified 3-DOF model of twin-tower structure linked by a sky-bridge, the frequency response functions, the displacement power spectral density (PSD) functions, and the time-averaged total vibration energy were derived, by assuming the white noise as the earthquake excitation. The effects of connecting parameters, such as linking stiffness ratio and linking damping ratio, on the structural vibration responses were then studied, and the optimal connecting parameters were obtained to minimize the vibration energy of either the independent monomer tower or the integral structure. The influences of sky-bridge elevation position on the optimal connecting parameters were also discussed. Finally, the distribution characteristics of the top displacement PSD and the structural responses, excited by El Centro, Taft and artificial waves, were compared in both frequency and time domain. It is found that the connecting parameters at either end of connection interactively affect the responses of the towers. The optimal connecting parameters can greatly improve the damping connections on their seismic reduction effectiveness, but are unable to reduce the seismic responses of the towers to the best extent simultaneously. It is also indicated that the optimal connecting parameters derived from the simplified 3-DOF model are applicable for two multi-story structures linked by a sky-bridge with dampers. The seismic reduction effectiveness obtained varies from 0.3 to 1.0 with different sky-bridge mass ratio. The displacement responses of the example structures are reduced by approximately 22% with sky-bridge connections.

Vertical pseudo-dynamic experimental study on long-span reticulated structures with multi-dimensional earthquake isolation and mitigation devices

The multi-dimensional earthquake isolation and mitigation device (MEIMD) for long-span reticulated structures is a newly invented passive vibration control device. In order to explore the vertical earthquake isolation and mitigation ability of the device, vertical pseudo-dynamic tests on a 1:3 scaled long-span reticulated structure with and without devices are carried out. In the tests, dynamic responses of the structure with the devices are compared with those without the devices under different earthquake waves. It can be seen from experimental results that the devices can obviously reduce the displacement, acceleration, and members’ strain responses of a long-span reticulated structure. Moreover, the finite element analyses are also performed to verify the seismic reduction effect of MEIMD. The numerical results fit well with the experimental results and this indicates that the finite element analysis has high simulation precision.

Optimization analysis on parameters of multi-dimensional earthquake isolation and mitigation device based on genetic algorithm

Parameter optimization analysis on the multi-dimensional earthquake isolation and mitigation device (MEIMD) installed in reticulated structures is carried out in this study. First, optimization parameters and constrain conditions are determined in accordance with the characteristics of MEIMD, and an object function is derived from the energy equation. Then, the genetic algorithm is used to realize parameter optimization of the MEIMD added in a cylindrical reticulated shell. Finally, in order to verify the effectiveness of the proposed optimization method, dynamic responses of structures without devices, with devices possessing random and optimal parameters are compared, and the sensitivity to the earthquake excitations of the optimization method is studied. It can be concluded that dynamic responses of the structure decrease obviously when adding the MEIMD, and a better seismic reduction effect can be reached when the MEIMD is designed optimally in accordance with the optimization method, and different earthquake excitations have slight influence on the optimization results.