Period Of Ground Motion Research Articles

On the displacement control performance of base-isolated structures incorporating nonlinear negative stiffness device

Low-frequency dominant far-field harmonic-like long period ground motions (FGMs) excitations have the potential to amplify the seismic response of base-isolated structures (BIS) and may result in isolator displacements exceeding their maximum limits. The application of negative stiffness devices (NSD) in isolated structures primarily focuses on SDOF systems, which fails to capture the displacement response of the superstructure on the isolation story. To address this issue, this study proposes the application of NSD to a 2DOF system in a BIS, with root mean square value as the metric for displacement transmissibility. Firstly, the displacement transmissibility of base-isolated structures with negative stiffness devices (BIS-NSD) and BIS is derived using the triple-harmonic balance (T-HB) method and the single-harmonic balance (S-HB) method, respectively. Subsequently, the applicability of the T-HB method and the S-HB method in obtaining analytical solution for the displacement transmissibility of BIS-NSD and BIS is revealed and validated through numerical solution. Parameters are selected based on fixed-point theorem for comparative analysis of the displacement and acceleration transmissibility between BIS-NSD and BIS. Finally, a comparative analysis between BIS-NSD and BIS under FGMs confirms the application advantages of NSD. The results indicate that compared to BIS, BIS-NSD significantly reduces the displacement transmissibility of the superstructure and the isolation story in the low-frequency range. As the primary resonance frequency decreases, NSD widens the vibration bandwidth of BIS. BIS-NSD effectively mitigates the increase in displacement caused by low-frequency ground motions. The acceleration transmissibility demonstrates that, without sacrificing the acceleration of the superstructure, it effectively controls the displacement of the isolation story.

Experiment and numerical simulation on the performance of multiple unidirectional single‐particle dampers under seismic excitation

AbstractThis study designed and manufactured a 1/5‐scale model of a three‐story steel frame structure. Various types of ground motions, including non‐long period (NLP) ground motions, near‐fault pulse type (NFPT) ground motions, and non‐pulse long‐period (NPLP) ground motions, were selected following the site conditions of the structure. The multiple unidirectional single‐particle damper (MUSPD) and its layout schemes were then designed. A series of shaking table tests for the three‐story steel frame with and without MUSPD were performed. Subsequently, a mechanical model of the multi‐degree‐of‐freedom structure with MUSPDs was established, and a corresponding numerical simulation method was proposed. The results revealed that MUSPDs achieved an average damping rate of 18.24% for peak and 27.41% for Root Mean Square (RMS). Notably, MUSPD exhibited a superior damping effect on the RMS of the structure compared to the peak. The distributing floor particle mass according to the first‐order mode of the structure resulted in excellent damping performance. Additionally, determining the particle movement distance for each floor involved calculating the optimal distance using a single‐degree‐of‐freedom structure. MUSPDs exhibited a better damping effect under NLP ground motions compared to NFPT and NPLP ground motions. The shaking table test results confirmed the rationality and feasibility of the proposed numerical simulation method, demonstrating a high level of accuracy.

Dynamic Response Analysis of Tunnel Underlain by a Soft Soil Layer Under the Near-Fault Pulse-Like Ground Motions

Affected by the near-fault pulse-like ground motions, the tunnels emerged in adverse geology, especially in an inhomogeneous strata are more vulnerable. However, the quantitative index effects on tunnel response during pulse identification are unclear and the propagation features of the near-fault pulse-like waves in a soft soil interlayer site are seldom revealed. In view of this, an improved energy-based pulse identification was used in this study to quantitatively extract the potential pulse energies emerged in velocity time-histories of ground motions. Subsequently, a series of numerical simulations were carried out to consider the critical parameters of soft soil layer and input ground motions. Finally, the dynamic response of the tunnel and interaction differences of soil and tunnel subjected to three types of ground motions were revealed. The result showed that the near-fault pulse-like ground motions pose a commonly severe damage to the tunnel, especially in the high pulse period ground motions based on the energy-based pulse identification method. The pulse energy of ground motions is an effective pulse index to analyze the seismic effects on tunnel when pulse periods of two different ground motions are uniform, and the index affects the tunnel in dynamic internal forces. More importantly, the existence of soft soil layer severely affects the propagation of input ground motions. At frequency domain, the ground response increases at high frequency component in the near-fault pulse-like ground motion, while the response shows a decreasing at low frequency component.

Seismic responses of super high-rise buildings under long-period ground motions

Super high-rise buildings usually exhibit low fundamental frequencies and are particularly susceptible to Long Period Ground Motions (LPGMs) characterized by rich components in long-period range. Previous seismic analyses of super high-rise buildings have primarily considered ordinary earthquake actions, overlooking the influence of LPGMs. To address this gap, the seismic responses of super high-rise buildings ranging in height from 400 m to 800 m are investigated when subjected to LPGMs. The effectiveness of earthquake intensity measures, which serve as indices connecting seismic hazards to structural responses, is evaluated in capturing the seismic effects caused by LPGM excitations. Firstly, this study introduces a statistical model for the response spectra of LPGMs. A simulation algorithm utilizing Continuous Wavelet Transformation (CWT) is then employed to generate LPGMs. Subsequently, simplified shear-flexural models are applied to serve as computational models for super high-rise buildings with varying heights. Furthermore, this study calculates, analyzes and compares typical seismic responses, such as lateral displacements and inter-story drifts, of these super high-rise buildings under simulated LPGMs and ordinary earthquake excitations. Additionally, a set of seismological ground motions is utilized to validate the seismic response analysis. The findings of this study reveal that LPGMs lead to significantly larger responses of super high-rise buildings exceeding 400 m in height compared to ordinary earthquakes. Furthermore, this study examines the correlation coefficients between various existing earthquake intensity measures and seismic responses under LPGM excitations. The results indicate a strong relationship between the LPGM induced responses and the spectral acceleration and velocity at the fundamental periods of the structures. The aim of this paper is to explore the seismic response of super high-rise buildings under LPGMs and provide a scientific basis for their seismic analysis and design.

Preliminary Study on Long Period Ground Motion in the Eskişehir Basin, Turkey

Effects of a basin structure on long period ground motion generation in Eskişehir region are studied by investigating the observed features of the 2011 Simav Earthquake (Mw:5.9) accelerograms. Spectral values and significant duration of ground motion at the basin center is much higher than the predicted mean values obtained by empirical models. 3-D wave propagation simulation of a small magnitude local event is accomplished utilizing a finite difference method and experimental velocity models. Simulation results indicate that the basin model produces more realistic waveforms than the flat layered model. Synthetic velocities agree with observed ones at two basin-center stations but considerable discrepancies exit at basin edge stations. These findings suggest that more careful definitions of basin boundaries are necessary for future models.

A Far-Field Ground-Motion Model for the North Australian Craton from Plate-Margin Earthquakes

ABSTRACT The Australian territory is just over 400 km from an active convergent plate margin with the collision of the Sunda–Banda Arc with the Precambrian and Palaeozoic Australian continental crust. Seismic energy from earthquakes in the northern Australian plate-margin region are channeled efficiently through the low-attenuation North Australian craton (NAC), with moderate-sized (Mw≥5.0) earthquakes in the Banda Sea commonly felt in northern Australia. A far-field ground-motion model (GMM) has been developed for use in seismic hazard studies for sites located within the NAC. The model is applicable for hypocentral distances of approximately 500–1500 km and magnitudes up to Mw 8.0. The GMM provides coefficients for peak ground acceleration, peak ground velocity, and 5%-damped pseudospectral acceleration at 20 oscillator periods from 0.1 to 10 s. A strong hypocentral depth dependence is observed in empirical data, with earthquakes occurring at depths of 100–200 km demonstrating larger amplitudes for short-period ground motions than events with shallower hypocenters. The depth dependence of ground motion diminishes with longer spectral periods, suggesting that the relatively larger ground motions for deeper earthquake hypocenters may be due to more compact ruptures producing higher stress drops at depth. Compared with the mean Next Generation Attenuation-East GMM developed for the central and eastern United States (which is applicable for a similar distance range), the NAC GMM demonstrates significantly higher short-period ground motion for Banda Sea events, transitioning to lower relative accelerations for longer period ground motions.

グリーン関数の震源位置依存性と強震動生成域の配置が計算地震動に与える影響

When we create input ground motions for building design, it is necessary to consider multiple cases for source parameters such as strong motion generation area (SMGA) arrangement and its area size, and multiple faults. Presently, it is difficult to cover all the possible cases of faults and source parameters Therefore, we often considered the safety side ground motions with the faults and SMGA placement close to the planned site. However, it has been reported that long period ground motions do not necessarily directly relate to the distance between the epicenter and the site, and the ground motions vary with the direction of the source and the depth of the hypocenter.

Long period ground motion simulation and its application to the seismic design of high-rise buildings

Increasing attention is being paid to the adverse effects of long period ground motion (LPGM) on high-rise buildings. However, it is hard to quantitatively define this special ground motion in seismic design, especially in the cases of regions in which sufficient seismic observations have not been made. To this end, this paper proposes an innovative LPGM simulation method. This method not only involves probabilistic seismic hazard analysis (PSHA), but also overcomes the limitations of the original empirical relation-based method. Firstly, a large number of data taken from typical sedimentary basins are utilized to determine the basin amplification factor model, by which an improved response spectra attenuation formula is developed based on the site amplification mechanisms in different periods. Then, based on the statistical regression analysis of the basin correction factors, the modified group delay time empirical formula is obtained. Furthermore, the conventional PSHA model is refined to determine the scenario earthquake. Finally, the design LPGM is generated by the phase difference spectrum method and its impact on high-rise buildings is embodied via a case study. The satisfactory result proves that the proposed method can effectively simulate LPGM and may have great potential in practice.

Comparison of Near-Fault Velocity Pulse-Like Ground Motions from the 2018 Mw 6.4 Hualien, Taiwan, Earthquake with the Next Generation Attenuation (NGA)-West2 Ground-Motion Models and Directivity Models

ABSTRACTPulse-like ground motions cause severe damage in structures at certain periods. Hence, pulse effects need to be considered during probabilistic seismic hazard analysis and seismic design in the near-fault region. Traditional ground-motion models used to quantify the hazard posed by pulse-like ground motions may underestimate them, but they are relatively suitable for describing the residual ground motions after extracting pulses. Nevertheless, the applicability of Next Generation Attenuation-West2 Project (NGA-West2) models to pulse and residual ground motions has not been evaluated. Moreover, the applicability of recently developed directivity models, including the Shahi and Baker (2011; hereafter, SB2011), Chang et al. (2018; hereafter, Chang2018), and Rupakhety et al. (2011; hereafter, Rupakhety2011) models, has not been investigated for this event. Here, based on the abundance of pulse-like ground motions recorded during the Mw 6.4 Hualien earthquake, the applicability of NGA-West2 models and directivity models was quantitatively evaluated. In summary, (1) The applicability of NGA-West2 models to the observed original and residual ground motions varies significantly at different periods. The suggests that NGA-West2 models overestimate the original and residual ground motions for short periods (T<1.0 s), but are suitable for describing the residual ground motions yet underestimate the original ground motions for long periods (T≥1.0 s). (2) Pulse periods and amplification bands due to pulses are unusually larger than previous events. Similar to the Chang2018 model, the plateau of this event starts and ends at the periods of 0.70 and 1.1 times the pulse period. However, the Chang2018 and SB2011 models underestimate the constant ordinate of this plateau. Spectral ordinates of the spectral shape curve due to pulses for the short period (∼Tn<1.3 s) are smaller than the predictions from the Rupakhety2011 model. The trend was reversed for long periods (∼Tn>3.0 s). Compared with the Rupakhety2011 model, the peak location of the spectral shape curve is shifted to the long period. These results will be helpful for updating these models in the near future.

Development of Seismic Isolation Device for Long Period Ground Motion Using Non-linear Spring

Development of Seismic Isolation Device for Long Period Ground Motion Using Non-linear Spring

Study on Seismic Isolation Device with Magnetic Damper for Long Period Ground Motion

Study on Seismic Isolation Device with Magnetic Damper for Long Period Ground Motion

Performance based evaluation of an existing continuous reinforced concrete bridge – a case study

A performance-based evaluation was conducted on an eleven-span reinforced concrete bridge located in a high seismicity area. This bridge was designed using SNI 2833:1992 and to be checked using the updated Indonesian seismic hazard map. In addition, a non-linear time history analysis was conducted using eleven pairs of ground motions to evaluate the structural performance of the bridge pier for the anticipated service life. Elastic analysis shows that the existing bridge still satisfies the strength and serviceability requirement despite the increase in seismic demand. Meanwhile, by evaluating the average inelastic longitudinal reinforcement and concrete strain at bridge pier for selected eleven ground motions, this study suggests that the bridge is still “fully operational” and “life safety” when subjected to the lower level (100 year return period) and upper level (1000 year return period) ground motions, respectively.

Research on dynamic response characteristics and control effect of mega-sub controlled structural system under long-period ground motions

New structure system, named as Mega-Sub Controlled Structure System (MSCSS) is proposed after the combination of structural response control theory and the construction principle of megastructures. This newly proposed structure, MSCSS, is based on a new structural response control mechanism and has a significant response control effect. The response control effect of the structure under long-period ground motions is studied in this work. Firstly, Hilbert-Huang transform (HHT) is employed to analyze the time–frequency power spectral density characteristics of three typical ground motions, and their spectrum distribution is discussed. Under long- period ground motions, Single-Degree-of-Freedom system showed different trend in its response spectrum. Subsequently, a reasonable cross-section was designed for MSCSS and a finite element model was established using SAP2000 and ABAQUS software respectively and the accuracy of the MSCSS finite element model was verified. Three structural response control indexes are defined and the response control characteristics of MSCSS under long-period ground motion are explored. The results show that the response control rate of MSCSS under the action of long-period ground motions is above 10%, and the control rate of base shear force is about 20%, which reflects the good energy dissipation effect of MSCSS. In addition, this study provides a basis for the dynamic matching design between the mega-structure and substructure of MSCSS.

A New Method to Calculate Additional Damping Ratio considering the Effect of Excitation Frequency

The additional damping ratio (ADR) is an important indicator for evaluating the damping effect of structures with energy‐dissipation devices. Most existing methods for determining the ADR require an analysis of the structural dynamic response and complex iterative calculations. An innovative simplified calculation method for determining the ADR of a structure supplemented by nonlinear viscous dampers is proposed. This method does not require the dynamic response of the structure to be calculated and only requires the structural characteristics, excitation frequency, and damper parameters. In this study, several typical calculation methods for the ADR were analysed. Then, a calculation formula for the ADR was derived with consideration of harmonic excitation under the condition where the excitation frequency is equal to the structural natural frequency, without calculation of the structural dynamic response or an iterative process. The effect of the excitation frequency on the calculated value of the ADR with different damping exponents was studied. Accordingly, the response spectrum average period (RSAP) was considered as the excitation period of ground motion to evaluate the excitation frequency, and a simplified calculation method for the ADR considering the effect of the excitation frequency characterised by the RSAP of the ground motion was established. Finally, the accuracy and effectiveness of the proposed method were verified by comparison with ADRs calculated using other methods.

Ground motion simulations of Hope fault earthquakes

This paper examines ground motions for a major potential Mw7.51 rupture of the Hope Fault using a physics based simulation methodology and a 3D crustal velocity model of New Zealand. The simulation methodology was validated for use in the region through comparison with observations for a suite of historic small magnitude earthquakes located proximal to the Hope Fault. Simulations are compared with conventionally utilised empirical ground motion models, with simulated peak ground velocities being notably higher in regions with modelled sedimentary basins. A sensitivity analysis was undertaken where the source characteristics of magnitude, stress parameter, hypocentre location and kinematic slip distribution were varied and an analysis of their effect on ground motion intensities is presented. It was found that the magnitude and stress parameter strongly influenced long and short period ground motion amplitudes, respectively. Ground motion intensities for the Hope Fault scenario are compared with the 2016 Kaik¯oura Mw7.8 earthquake, it was found that the Kaikoura earthquake produced stronger motions along the eastern South Island, while the Hope Fault scenario resulted in stronger motions immediately West of the near-fault region and similar levels of ground motion in Canterbury. The simulated ground motions for this scenario complement prior empirically-based estimates and are informative for mitigation and emergency planning purposes.

Mapping of ground motion amplifications for the Fraser River delta in Greater Vancouver, Canada

The Fraser River delta in Greater Vancouver, Canada consists of deep soft deposits of silts and clays, and it is well known that the deep soil deposits can amplify the low frequency contents of ground motions. This study aims to investigate the effects of deep soil deposits in the delta on ground motion amplifications by using thorough site response simulations that account for the full soil profiles and a suite of recorded ground motions that covers a wide range of intensity levels. Based on both equivalent-linear and nonlinear site response simulations, the effects of soil depth (represented by natural period of the soil, TS) on ground motion amplifications for various spectral periods are clearly demonstrated. The ground motion amplification maps for various spectral periods and rock ground motion intensity levels are also generated to be used in the regional seismic hazard assessment for infrastructure. It is found that ground motions for long periods are substantially amplified in the center of the delta, while those for short periods are de-amplified when input rock motions are large.

Analysis of Rope Sway during Travel of Elevator

An elevator for a high-rise building ought to perform emergency operation when the elevator rope is oscillated by the sway of the building caused by wind force or long – period ground motion. In recent years, techniques for directly measuring rope amplitude in real time have been utilized. Thereby, it has become possible to perform apposite emergency operation based on the rope sway condition. On the other hand, the rope sway changes continuously every moment during the travel of elevator. Therefore, it is very important to grasp the changing tendency of rope sway for the efficient judgment of emergency operation. In this research, we constructed a simulation model which quantitatively simulates the rope sway motion during a travel of an elevator.

Ground motion and site effect observations in the wellington region from the 2016 Mw7.8 Kaikōura, New Zealand earthquake

This paper presents ground motion and site effect observations in the greater Wellington region from the 14 November 2016 Mw7.8 Kaikōura earthquake. The region was the principal urban area to be affected by the earthquake-induced ground motions from this event. Despite being approximately 60km from the northern extent of the causative earthquake rupture, the ground motions in Wellington exhibited long period (specifically T = 1 - 3s) ground motion amplitudes that were similar to, and in some locations exceeded, the current 500 year return period design ground motion levels. Several ground motion observations on rock provide significant constraint to understand the role of surficial site effects in the recorded ground motions. The largest long period ground motions were observed in the Thorndon and Te Aro basins in Wellington City, inferred as a result of 1D impedance contrasts and also basin-edge-generated waves. Observed site amplifications, based on response spectral ratios with reference rock sites, are seen to significantly exceed the site class factors in NZS1170.5:2004 for site class C, D, and E sites at approximately T=0.3-3.0s. The 5-95% Significant Duration, Ds595, of ground motions was on the order of 30 seconds, consistent with empirical models for this earthquake magnitude and source-to-site distance. Such durations are slightly longer than the corresponding Ds595 = 10s and 25s in central Christchurch during the 22 February 2011 Mw6.2 and 4 September 2010 Mw7.1 earthquakes, but significantly shorter than what might be expected for large subduction zone earthquakes that pose a hazard to the region. In summary, the observations highlight the need to better understand and quantify basin and near-surface site response effects through more comprehensive models, and better account for such effects through site amplification factors in design standards.

両端から全長の1/<i>N</i>の位置に変位拘束部材を有する弦の自由振動（<i>N</i>が奇数，弦と変位拘束部材との間にギャップがある場合）

In high-rise buildings, the elevator rope may resonate with the building's sway induced by wind forces and/or by long period ground motion. Therefore, suppression of elevator rope vibration is desired. In previous paper, an exact solution to the free vibration of the rope with vibration suppressors located at 1/N from both ends of the rope was presented in the case where the gap between rope and vibration suppressor was zero. However, in the case where N is an odd number and the gap between rope and vibration suppressor is not zero, no exact solution of the free vibration has yet been obtained. In this paper, an exact solution to the free vibration of this case (N is an odd number and gap between string and vibration suppressor is not zero) is presented, when the center position of the rope is pulled. The rope is modeled with string. Finite difference analyses of the rope vibration with vibration suppressor are also performed. The calculated results of the finite difference analyses are in good agreement with those of the exact solution.

Seismic performance of reinforced concrete frame buildings in Bhutan based on fuzzy probability analysis

Seismic performance of reinforced concrete (RC) frame buildings is mostly assessed based on the distinct interstorey drift limits defined by many existing guidelines. In reality, damage of a structure is a continuous process under the action of the load and also depends on a number of factors. Therefore damage can be more logically defined with a fuzzy performance level than a distinct interstorey drift limit. In this paper, probability and fuzzy set theory are used to estimate the realistic failure probabilities of the RC buildings in Bhutan by considering randomness in material and geometrical parameters and fuzziness in the damage criteria. Three typical RC frame buildings in Thimphu, Bhutan and the ground motions predicted at the generic soil sites in Thimphu are used for the structural response prediction. Rosenbluth Point Estimate Method is used for modelling the statistical variation of the input parameters and the computer program Perform 3D is used for carrying out the dynamic nonlinear analysis of the buildings. Monte Carlo Simulation is employed to validate the accuracy of the Rosenbluth Point Estimate Method and determine the statistical distribution of the response quantities. Soil structure interaction (SSI) is considered at the soft soil site using the uncoupled spring model. Based on the mean and standard deviation of the intersotrey drifts obtained from the analyses, the fuzzy failure probabilities of the buildings are estimated. It is found that under the 475 year return period ground motions, typical buildings experience a high probability of irreparable and severe damages, while the high probability of severe damage and complete collapse are predicted under the 2475 year return period ground motions. SSI is found to be detrimental to the 3 storey building, while no significant effect is observed to the 6 storey building.