Relative Displacement Response Research Articles

Experimental investigation of sliding-based isolation system with re-centering functions for seismic protection of masonry structures

A sliding-based isolation system is an efficient strategy to enhance the seismic performance of low-rise brick masonry buildings, a common type of construction across the globe. The previously developed isolation systems lack a proper re-centering mechanism. Therefore, in this study, a low-cost isolation system, termed reinforced cut wall (RCW) with an appropriate re-centering mechanism, is designed and tested experimentally using a shake table, which hasn’t been tested previously. Two unconfined reduced scale (1:3) brick masonry buildings were subjected to frequency-based seismic excitation, and the model's corresponding acceleration and displacement response were captured. Compared to the fixed base model, considerable reductions were observed in the acceleration and displacement response in the case of the isolated model. Similarly, the inter-story drift and floor relative displacement response was also reduced in the isolated model. Furthermore, the rebars used for the re-centering mechanism remained within the linear viscoelastic range. Based on the experimental validation, the proposed low-cost RCW isolator was found to be an efficient isolation strategy for low-rise masonry buildings in high seismic regions.

Predominant Frequency in Near-Field Strong Ground Motion by Analysis of Displacement Response Spectra

A literature review on the spectral content of seismic ground motion indicates that a clear predominant frequency in earthquakes is very difficult to define. Here, it is considered that this has been so because the usual seismic record or response quantity is always employed: acceleration. In this work, an attempt is made to define a single predominant frequency for strong seismic ground motion in the near field with a different idea. It is considered that this is possible if the concentration is on displacement rather than on ordinary acceleration. In particular, relative displacement response spectra will be studied, instead of the common acceleration one, and the existence of clear and neat maximum spectral displacements around, statistically, a single and general proposed predominant frequency will be investigated for a set of twenty very strong (magnitude larger than 6.5 MW) world events.

Structural vibration mitigation via an inertial amplification mechanism based absorber

This paper proposes a novel passive vibration control system, namely the Inertial Amplification Mechanism-based Absorber (IAM-A), to mitigate unwanted structural vibrations. With the help of the H2 and H∞ optimization methods, closed-form formulas for the design parameters of the proposed IAM-A are obtained. Parametric studies are conducted to evaluate the influence of the design parameters on the vibration mitigation performance of the proposed IAM-A. Finally, numerical simulations are performed to validate the efficiency of the IAM-A. For comparison, time history analyses of a structure with IAM-A, with TMD, and without control under earthquake ground motions are performed. Numerical results confirm that dynamic responses of the primary structure are suppressed when the TMD is introduced. But, the relative displacement responses between the primary structure and the absorber are relatively large. The proposed IAM-A outperforms the TMD. With respect to those of the TMD, dynamic responses of the primary structure with the proposed IAM-A are further suppressed. More importantly, the large relative displacement response of the absorber is reduced by more than half.

Shaking table test on seismic behavior of posttensioned precast segmental Concrete-Filled double skin steel tubular piers

Posttensioned precast segmental bridge piers have proven to be an attractive solution for accelerated bridge construction and seismic resilience. Although extensive research efforts have been made to understand the seismic performance of such piers under quasi-static loading and unidirectional/bidirectional ground motions, there is limited information available regarding to their dynamic behavior when subjected to tri-directional ground motions. Therefore, this study performed shaking table tests on an innovative posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) pier to explore its seismic behavior under a set of tridirectionally applied far-field ground motions. A total of six 1/5 scaled piers were investigated with different design details, including one monolithic pier as reference, two posttensioned precast segmental piers without internal energy-dissipating (ED) bars but different amounts of prestressing tendons, and three posttensioned precast segmental piers with different amounts of ED bars. It has found that the relative displacement responses decreased with increase in amounts of prestressing tendons or ED bars. The segmental piers without ED bars twisted obviously when PGA reached 0.3 g under tri-directional ground motion excitations, while the segmental piers with ED bars did not due to additional shear resistance across joints provided by ED bars. Moreover, the dynamic responses of segmental piers with and without vertical ground motion excitation were compared in details to investigate the effect of vertical ground motion on their seismic behavior. It has found that the change in vertical acceleration response due to vertical ground motion excitation was a significant importance compared to the change in lateral accelerations, relative displacements and tendon force increment. In consequence, the axial compressive force as well as shear resistance across joint provided by dead load reduced by almost 33% due to appearance of vertical ground motion at the PGA of 0.7 g.

Probabilistic outlier detection for robust regression modeling of structural response for high-speed railway track monitoring

Outlier detection is an important procedure taken in structural health monitoring (SHM) to create clean and reliable data. A robust time series outlier detection method incorporating a Bayesian perspective and an extreme learning machine (ELM) neural network model is proposed, with application to long-term monitoring data of ballastless tracks for high-speed railway systems. A robust sparse Bayesian ELM (SBELM) model is first established by computing the posterior probability density function of the ELM weight parameters and then marginalizing over the prediction-error precision parameter to obtain a robust nonlinear regression model between the track temperature and structural response. Both the posterior mean and the associated uncertainties of the robust SBELM model are then taken into account to compute the outlier probability for each suspicious data point, which quantifies their degree of data “outlier-ness.” It effectively takes into account the prediction uncertainty of the SBELM regression model. The method is applied to long-term monitoring data for track temperatures, and track strain and relative displacement responses, from two high-speed rail track systems where there are both slight and serious outliers. The results demonstrate that the proposed method can reliably detect outliers by quantifying the outlier probability and that the final results are robust to the selection of the “thresholds.” It is also shown that our new algorithm produces significantly improved model prediction performance after the outliers are detected and removed.

Seismic evaluation of a traditional Chinese palace-style timber structure

To assess the seismic performance of a traditional Chinese palace-style timber structure, an extended discrete element method (EDEM) model has been established. The model has been applied to analyze a single-story and five-bay timber-frame palace architecture, where sliding isolation of the column foot, semi-rigid connections of mortise and tenon joints, and damping characteristics of bracket sets (known as Dougong in Chinese) have been considered. The study investigates the dynamic characteristics, seismic responses, and structural vulnerabilities of the palace building. Results show that an error of the natural frequency between the EDEM model and results from code-recommended empirical formulas is only 6.88%, highlighting the rationality of the EDEM model. Furthermore, the relative displacement response of each position increases with the increment of inputting acceleration of seismic waves. The inter-structural layer drift of the column-beam frame is the largest and that of the roof truss is smaller, while Dougongs are the smallest. The likelihood of moderate damage is highest during a small earthquake, while the structure is prone to severe damage under a medium earthquake, The structure is susceptible to collapse under a large earthquake.

Experimental study on seismic responses of tuned mass damper-applied real-scale piping system via shaking table tests

To secure the nuclear power plant (NPP) safety, it is essential to improve the seismic performance of piping systems. Accordingly, to achieve this purpose effectively, applying a tuned mass damper (TMD) to the NPP piping system has been attempted, but this is mostly limited to numerical analysis studies. Therefore, this study aimed to prove the TMD effect of reducing seismic responses of the real-scale NPP piping system through shaking table tests. As a result, it was confirmed that the TMD suppressed target and higher-order mode responses of the piping through the shaking table tests. In particular, the response control effects of the target mode and the higher-order mode were more pronounced when the earthquake motion intensity was larger. The application of the TMD showed reducing relative displacement responses in the harmonic motion excitation by about 80%-90%. This reduced peak relative displacement and normal stress responses by 33%-42% and 25%-37% on average, respectively, under random vibration excitation. Under the seismic excitation, peak relative displacement and normal stress responses were reduced by 7%-14% and 5%-27% on average, respectively. Finally, piping and piping-TMD finite element analysis models were successfully created and validated based on the shaking table test results.

Dynamic Response of Deepwater Pile Foundation Bridge Piers under Current-wave and Earthquake Excitation

Pile foundation bridges are structures extending in the middle of the sea, so they are subject to currents, waves, and earthquake forces. This article presents a hybrid simulation that was used with input excitations of different current velocities, wave properties, and earthquake amplitudes to assess the non-linear dynamic behavior of pile foundation bridge piers. Based on the interface between MATLAB and ABAQUS software, the general formulations of fluid-structure interaction (FSI) under combined current-wave and earthquake loads are derived. Hydrodynamic and earthquake loading is consistently introduced by creating synthetic time histories of combined current-wave actions and spatially variable ground motion. The behavior of the dynamic model of a deepwater pile foundation bridge for the Songhua River in northeast China was adopted as an example of the study. The accuracy of the created model was verified using prior experimental and analytical computations. It is demonstrated how both linear and nonlinear dynamic behavior performs at various water depths under coupled current-wave-earthquake loading conditions. Revealing interesting aspects, particularly in terms of relative displacement, acceleration, shear, and moment response are shown. The results showed that the hybrid model is an efficient of simulating accurate predictions of the hydrodynamic pressure during earthquake actions for structures in coastal areas.

Study on Seismic Response and Parameter Influence in a Transformer–Bushing with Inerter Isolation System

In this paper, a mechanical model of a transformer–bushing with an inerter isolation system (IIS) is established. An IIS is composed of an inerter element, a damping element, and a spring element connected in parallel between the same two terminals. Vibration control equations and frequency response functions are also established. The influence of parameters on IIS, including inerter–mass ratio, damping ratio, and frequency ratio, was studied. In the extremum condition that represents the most efficient parameter set of inerter–mass ratio and damping ratio for relative displacement response ratio, an optimal design method was developed by exploiting a performance demand. Finally, the seismic response of the transformer–bushing with IIS was carried out to verify the isolation performance of IIS. The research shows that the equivalent mass coefficient and damping coefficient of IIS can be amplified by an inerter element and the inerter–mass ratio and damping ratio are reduced simultaneously under the conditions of meeting the performance demand after parameter optimization. Meanwhile, the parameter optimization design method proved to be effective for meeting the target demand of the relative displacement response of the bushing and tank, while base shear force and isolation displacement were reduced simultaneously. Based on the results from a response history analysis under ground motion records, IISs can significantly suppress the resonance response of a structure and the continuous vibration response in the stable state. The peak displacement can be reduced by 50% compared with a traditional isolation system.

Effect of simulation accuracy of shear keys shear state on seismic response of friction pendulum bearing

In order to study the effect of simulation accuracy of shear keys shear state on seismic response of friction pendulum bearing, a vertical spring-friction system composed of equivalent components is used to simulate the friction pendulum bearing effectively, and two numerical calculation programs are developed. A spring element with life-and-death characteristics is used to realize the simplified simulation of shear keys shear state in the program 1, while shear keys on both sides of the friction pendulum bearing in the same direction are considered independently in the program 2. By comparing the seismic responses of the two programs with different shear key shearing force, vertical spring stiffness and different peak ground acceleration (PGA) conditions, it can be concluded that the precise simulation of shear keys shear state can more accurately calculate the shear key shear time and the maximum acceleration of the structure, which is beneficial to seismic isolation design. When the shear key shearing force is large and the PGA is small, the relative displacement response of bearing will be small if the shear keys are simultaneously sheared off. Increasing the stiffness of the vertical spring can reduce the residual displacement of the friction pendulum bearing. The simulation accuracy of shear key shear state has little influence on the relative displacement response when the equivalent stiffness of friction pendulum bearing is large. In this case, the shear key shear state can be simplified.

Shaking table test and numerical analysis of nuclear piping under low- and high-frequency earthquake motions

A nuclear power plant (NPP) piping is designed against low-frequency earthquakes. However, earthquakes that can occur at NPP sites in the eastern part of the United States, northern Europe, and Korea are high-frequency earthquakes. Therefore, this study conducts bi-directional shaking table tests on actual-scale NPP piping and studies the response characteristics of low- and high-frequency earthquake motions. Such response characteristics are analyzed by comparing several responses that occur in the piping. Also, based on the test results, a piping numerical analysis model is developed and validated. The piping seismic performance under high-frequency earthquakes is derived. Consequently, the high-frequency excitation caused a large amplification in the measured peak acceleration responses compared to the low-frequency excitation. Conversely, concerning relative displacements, strains, and normal stresses, low-frequency excitation responses were larger than high-frequency excitation responses. Main peak relative displacements and peak normal stresses were 60%–69% and 24%–49% smaller in the high-frequency earthquake response than the low-frequency earthquake response. This phenomenon was noticeable when the earthquake motion intensity was large. The piping numerical model simulated the main natural frequencies and relative displacement responses well. Finally, for the stress limit state, the seismic performance for high-frequency earthquakes was about 2.7 times greater than for low-frequency earthquakes.

Floating slab track with inerter enhanced dynamic vibration absorbers

This paper proposes an inerter enhanced dynamic vibration absorber (IDVA) to improve the low-frequency vibration mitigationperformance of the floating slab track (FST). To this aim, the inerter is coupled to a dynamic vibration absorber (DVA) to form the IDVA. Analytical derivations of the FST-IDVA are given. Considering the random property of the wheel-rail interaction, the H2 optimization is performed and closed form solutions for the optimal parameters of the IDVA are obtained. Parametric studies are conducted to evaluate the influences of the inerter on the performances of the FST-IDVA. Numerical simulations are performed to validate the efficiency of the proposed FST-IDVA. Time history analyses of FST, FST-DVA, and FST-IDVA under moving metro vehicle load are computed and compared. When using the FST-DVA, it is found that dynamic responses of the track slab and the force transmitted to the ground are suppressed, but the relative displacement response of the absorber isrelatively large; conversely, when using the FST-IDVA, dynamic responses of the track slab and the force transmitted to the ground are furthersuppressed, more importantly, the relative displacement response of the absorber is mitigated greatly. Overall, the FST-IDVA overperforms the FSTDVA, even the small-mass-ratio absorber is used.

Study on a Novel Variable-Frequency Rolling Pendulum Bearing

Seismic isolation is a technique that has been widely used around the world to decouple the superstructure from the ground motions during earthquakes. However, the attention of seismic isolation is mostly focused on the protection of the building structures. Acceleration-sensitive devices or equipment, which are in desperate need of seismic protection, are still not fully emphasized. Meanwhile, the stiffness and frequencies of the conventional rolling- and sliding-type isolation bearings demonstrate an upward trend as the isolation layer displacement increases, which may bring self-centering and resonance issues. Thus, a novel variable-frequency rolling pendulum bearing is developed for the protection of acceleration-sensitive equipment. The rolling-type isolation bearing is selected to enhance the self-centering capacity, and additional viscous dampers are incorporated to improve the system damping. Moreover, the theoretical formulas of several typical variable-frequency rolling pendulum bearings are derived and presented to figure out the dynamic characterization of the device. The isolation efficiency of the proposed device under different parameters is also validated using shake table tests. Test results demonstrate that the newly proposed devices show excellent isolation performance at reducing both acceleration and displacement responses. Finally, the numerical model of this isolation system is proposed in detail. The simulated results, including relative acceleration responses, relative displacement responses and movement locus of the upper plates, are consistent with test results, which demonstrates this simplified model could be used for further studies.

Lateral force–displacement response of buried pipes in slopes

A series of full-scale experiments was conducted to estimate lateral soil constraints on pipes buried in dense sandy slopes at different burial depths. The experimental data indicated that the soil force on the pipe increases with increase in the slope grade and burial depth ratio. The lateral soil force against relative pipe displacement response observed from the experiments is presented and compared to those arising from level ground conditions. The study was extended to larger burial depth ratios by simulating pipes under sloping ground conditions using a numerical (finite-element) model that was initially calibrated using the results from physical modelling. The findings from the study in terms of the variation of peak lateral soil restraint as a function of the slope grade and burial depth ratio are presented for consideration in pipeline design.

Influence of shape memory alloy on seismic behaviour of hollow-section concrete columns

The influence of shape memory alloy (SMA) reinforcement on the non-linear static and dynamic responses of hollow-section concrete columns to earthquakes was investigated. The seismic performance of concrete columns reinforced with steel and with a mix of SMA and steel was compared by assessing their ductility ratios, dissipated energies, strain recovery capacities and collapse drifts. The influence of near- and far-field ground motions on the static and dynamic responses of the test columns was also investigated. To verify the results, the columns were subjected to a near-field ground motion related to an existing earthquake and the relative displacement response history was compared with experimental results. Compared with the steel-reinforced column, it was found that the use of the hybrid SMA–steel reinforcement was more effective at recovering strains and reduced the residual deflections. On the other hand, the steel-reinforced column had a greater ductility ratio and energy dissipation capacity. It is therefore important to find an optimal combination length for the two types of reinforcement in a concrete column. The results indicated that the optimum reinforcement configuration involves replacing steel with SMA at 15–20% of column height, which includes the probable plastic hinge length.

Study of isolation effectiveness of nuclear reactor building with three-dimensional seismic base isolation

PurposeIn recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. This paper aims to propose a new 3D combined isolation bearing (3D-CIB) to mitigate the seismic response in both the horizontal and vertical directions.Design/methodology/approachThe new 3D-CIB composed of laminated rubber bearing coupled with combined disk spring bearing (CDSB) was proposed. Comprehensive analysis of constitution and theoretical derivation for 3D-CIB were presented. The advantage of CDSB is that the constitution can be flexibly adjusted according to the requirements of the bearing capacity and vertical stiffness. Hence, four different combinations of CDSB were designed for the 3D-CIB and employed to isolate nuclear reactor building. A comparative study of the seismic response in terms of seismic action, acceleration floor response spectra (FRS), peak acceleration and relative displacement response was carried out.Findings3D-CIB can effectively reduce seismic action, FRS and peak acceleration response of the superstructure in both the horizontal and vertical directions. Overall, the horizontal isolation effectiveness of 3D-CIB was slightly influenced by vertical stiffness. The decrease in the vertical stiffness of the 3D-CIB can reduce the vertical FRS and shift the peak values to a lower frequency. The vertical peak acceleration decreased with a decrease in the vertical stiffness. The superstructure exhibited a rocking effect during the earthquake, and the decrease in the vertical stiffness may increase the rocking of the superstructure.Originality/valueAlthough the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted by different constitutions, the vertical stiffness should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. This study of isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of nuclear power plants.

Dynamic behavior and seismic performance of base-isolated structures with electromagnetic inertial mass dampers: Analytical solutions and simulations

The newly-developed electromagnetic inertial mass damper (EIMD) consisting of an inerter element and a damping element can significantly enhance the seismic performance of frame structures. However, whether an EIMD can enhance the seismic performance of a base-isolated structure (BIS) remains largely unknown. This paper presents a comprehensive theoretical study of the BIS with an EIMD, stressing on the dynamic behavior, parameter optimization, and seismic performance. Based on a simplified two-degree-of-freedom model, we derive the closed-form solutions of the dynamic characteristic parameters, modal participation factors, and dynamic amplification factors. A parametric study is conducted to investigate the effects of the EIMD parameters on the dynamic behavior of the system, through which the seismic response control mechanism of the EIMD in BIS is comprehensively analyzed. When the BIS subjected to a total of 20 earthquake records, the parameters of the EIMD are optimized for minimizing the interstory drift of the superstructure, the absolute acceleration response of the superstructure, and the relative displacement response of the base floor, individually. The effectiveness of the EIMD in enhancing the seismic performance of base-isolated structures is validated via numerical simulation of a five-story isolated building structure. Under a typical earthquake ground motion, the peak relative displacement of the base floor is reduced by up to 56.57% in comparison to traditional BIS; whereas the peak relative displacement and the absolute acceleration of the superstructure are reduced by up to 60.00% and 52.11%, respectively. Both analytical and numerical results demonstrate that the EIMD can significantly reduce the dynamic responses of both the base floor and the superstructure.

Parameter optimization analysis of plane friction coupling effect

When the ground motion is input into a Spring-Viscous damping-Coulomb friction plane isolation system with XY shear keys along a certain inclined angle, XY shear keys will be sheared asynchronously, which will lead to the structural violent curvilinear movement in the plane, resulting in the plane friction coupling effect. In this paper, the influence of the plane friction coupling on the relative displacement response of the structure is studied, and the variation of the structural peak relative displacement with the spring stiffness coefficient, damping constant and friction coefficient is analyzed in detail, so as to find the optimal parameter design of the plane isolation system under the plane friction coupling effect. The results indicate that the plane friction coupling can amplify the peak relative displacement, and the smaller the peak ground acceleration is, the more significant the amplification effect is. Although the mechanism of friction and viscous damping is different, the peak relative displacement will decrease with the increase of friction coefficient or damping constant, and it will decrease rapidly at first and then slowly, so the optimal parameters can be obtained at the cutoff point of the reduction rate. However, with the increase of spring stiffness coefficient, the amplification effect of relative displacement caused by plane friction coupling will be significantly reduced, and the amplification effect will decrease rapidly at first, and then decrease slowly, so there is also a dividing value for spring stiffness coefficient, and this value will not cause resonance phenomenon.

Design and analysis of isolation effectiveness for three-dimensional base-seismic isolation of nuclear island building

In order to investigate the application of 3D base-seismic isolation system in nuclear power plants (NPPs), comprehensive analysis of constitution and design theory for 3-dimensional combined isolation bearing (3D-CIB) was presented and derived. Four different vertical stiffness of 3D-CIB was designed to isolate the nuclear island (NI) building. This paper aimed at investigating the isolation effectiveness of 3D-CIB through modal analysis and dynamic time-history analysis. Numerical results in terms of dynamic response of 3D-CIB, relative displacement response, acceleration and floor response spectra (FRS) of the superstructure were compared to validate the reliability of 3D-CIB in mitigating seismic response. The results showed that 3D-CIB can significantly attenuate the horizontal acceleration response, and a fair amount of the vertical acceleration response reduction of the upper structure was still observed. 3D-CIB plays a significant role in reducing the horizontal and vertical FRS, the vertical FRS basically do not vary with the floor height. The smaller the vertical stiffness of 3D-CIB is, the better the vertical isolation effectiveness is, whereas, it will increase the displacement and the rocking effect of superstructure. Although the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted, it should be designed by properly accounting for the balance between the isolation effectiveness and displacement control including rocking effect. The results of this study can provide the technical basis and guidance for the application of 3D-CIB to engineering structure.

Wind-induced vibration fragility of outer-attached tower crane to super-tall buildings: A case study

To gain insight into the wind-induced safety concerns associated with attached tower cranes during the construction of super-tall buildings, a 606 m level frame-core tube super-tall building is selected to investigate the wind-induced vibration response and fragility of an outer-attached tower crane at all stages of construction. The wind velocity time history samples are artificially generated and used to perform dynamic response analyses of the crane to observe the effects of wind velocity and wind direction under its working and non-working resting state. The adverse effects of the relative displacement response at different connection supports are also identified. The wind-resistant fragility curves of the crane are obtained by introducing the concept of incremental dynamic analysis. The results from the investigation indicate that a large relative displacement between the supports can substantially amplify the response of the crane at high levels. Such an effect becomes more serious when the lifting arm is perpendicular to the plane of the connection supports. The flexibility of super-tall buildings should be considered in the design of outer-attached tower cranes, especially for anchorage systems. Fragility analysis can be used to specify the maximum appropriate height of the tower crane for each performance level.