Acceleration Time Histories Research Articles

A New Proxy for Near-Fault Acceleration Pulses and Implications on Inelastic Displacement Ratio

ABSTRACT This study develops new equations for predicting the constant-strength inelastic displacement ratio (C R ) by considering nonlinear single-degree-of-freedom systems subjected to near-fault ground motions. To this aim, an energy-based parameter, the MEA/MEV ratio, is firstly considered for characterizing the properties of pulse-like records. “MEA” and “MEV” represent the Maximum Energy of the half-cycle pulse in Acceleration and Velocity time histories, respectively. The effects of the MEA/MEV ratio on the C R spectra are investigated in terms of elastic-perfectly plastic hysteretic behavior. Finally, a simplified equation for estimating the C R spectra is developed, and its accuracy is evaluated by calculating the error measures.

A novel model order reduction-based two-stage damage detection paradigm for trusses using time–history acceleration

This paper presents a novel model order reduction (MOR)-based two-stage damage detection method for trusses employing time-series acceleration measured by limited sensors. In the first step, an acceleration-based strain energy indicator (ASEI) is newly proposed to evaluate the most doubtfully damaged candidates. Accordingly, the number of design variables defined in an inverse optimization problem of the second phase is reduced significantly. The location and severity of damaged members are then determined by minimizing an objective function with a newly added dynamic penalty parameter to achieve a faster convergence speed and better optimal solutions. Since acceleration signals are incompletely measured at limited sensors, the second-order Neumann series expansion (SNSE) is firstly employed to condense the proportionally damped trusses for inferring the unmeasured time–history information. An adaptive hybrid evolutionary firefly algorithm (AHEFA) is utilized to resolve the above inverse optimization problem. Four numerical examples of 2D and 3D trusses with various damage scenarios including noises are examined to demonstrate the reliability of the proposed methodology. Attained outcomes indicate that the suggested paradigm can reliably diagnose both multidamage sites and extents of trusses with only relatively short time histories and a few measurement sensors.

Baseline correction method of acceleration time history based on residual displacement and convex optimization

This paper proposes a time-domain baseline correction method of the acceleration time history based on the target residual displacement and convex optimization. The objective of the method is to reproduce accurately the displacement time history from the baseline corrected acceleration time history records. Compared with traditional time-domain methods, the proposed method can automatically determine the number of occurrence, the time of occurrence, and the amplitude of the baseline drifts, without manual intervention. Six acceleration time history records, including three ground-motions and three floor responses, were selected for numerical simulation. The simulation results suggest that the differences of the peak displacements between the reproduced displacement time history and the original time history are within 5%, and the Pearson Correlation Coefficients are more than 95%. The reproduction effect for floor responses is better than that of ground-motions owing to the characteristic of oscillation in the attenuation section. The form of the objective function and the influence of key parameters are discussed. Feasibility of this method was also verified by shaking table tests.

Vibration Serviceability of Large-Span Steel–Concrete Composite Beam with Precast Hollow Core Slabs Under Walking Impact

A large-span steel–concrete composite beam with precast hollow core slabs (CBHCSs) is a relatively new floor structure that can be applied to various long-span structures. However, human-induced vibrations may present serviceability issues in such structures. To alleviate vibrations, both the walking forces excited by humans and the associated floor responses must be elucidated. In this study, 150 load–time histories of walking, excited by 25 test participants, are obtained using a force measuring plate. The dynamic loading factors and phase angles in the Fourier series functions for one-step walking are determined. Subsequently, walking tests are performed on seven CBHCS specimens to capture the essential dynamic properties of mode shapes, natural frequencies, damping ratios, and acceleration time histories. The CBHCS floor system generally exhibits a high frequency (> 10 Hz) and low damping (damping ratio < 2%). Sensitivity studies using the finite element method are conducted to investigate the vibration performance of the CBHCS floor system, where the floor thickness, steel beam type, contact time, and human weight are considered. Finally, analytical expressions derived for the fundamental frequency and peak acceleration agree well with the experimental results and are hence proposed for practical use.

Simulation of strong earthquake characteristics of a scenario earthquake (MS7.5) based on the enlightenment of 2022 MS6.9 earthquake in Menyuan

The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan MS6.9 earthquake that occurred on January 8, 2022 had a major impact on the local infrastructure and transportation of this region. Due to the high possibility of similar strong earthquakes occurring in this area in the future, preliminary assessment of the seismic intensity characteristics of destructive earthquakes in this region is essential for effective disaster control. This paper uses the empirical Green′s function (EGF) method as a numerical simulation tool to predict the ground motion intensity of Datong Autonomous County under the action of the scenario earthquake (MS7.5). Seismic records of aftershocks of the 2016 Menyuan MS6.4 earthquake were used as Green’s functions for this simulation. The uncertainties associated with various source parameters were considered, and 36 possible earthquake scenarios were simulated to obtain 72 sets of horizontal ground motions in Datong County. The obtained peak ground acceleration (PGA) vs. time histories of the horizontal ground motion were screened using the attenuation relationships provided by the fifth-edition of China's Seismic Ground Motion Parameter Zoning Map and the NGA-West2 dataset. Ultimately, 32 possible acceleration-time histories were selected for further analysis. The screened PGA values ranged from 78.8 to 153 cm/s2. The uncertainty associated with the initial rupture point was found to greatly affect the results of the earthquake simulation. The average acceleration spectrum of the selected acceleration-time history exceeded the expected spectrum of a intermediate earthquake, which means that buildings in Datong County might sustain some damage should the scenario earthquake occur. This research can provide reliable ground motion input for urban earthquake damage simulation and seismic design in Datong County. Growing the dataset of small earthquakes recorded in this region will facilitate the large-scale simulation of ground motions under different earthquake scenarios.

Ground Motion Simulations for the 19 January 2020 Jiashi, China, Earthquake Using Stochastic Finite‐Fault Approach

AbstractA 6.0‐magnitude (Mw) earthquake was reported to have occurred in Jiashi County, Xinjiang at 21:27 on 19 January 2020, Beijing time (13:27 UTC). This study applied a stochastic finite‐fault approach based on the dynamic corner frequency (EXSIM) to simulate 23 near‐field stations within a distance of 120 km from the epicenter. The stochastic finite‐fault approach is the simplest and most effective method for simulating high‐frequency ground motions. According to studies and empirical relationships, we estimated a region‐specific parameter (κ0) for use in simulations. In this study, two different slip models, namely, random and inverted slip models, were used to explain their influence on the simulation results. For most stations, the simulated seismic characteristics, such as the peak ground acceleration (PGA), pseudo spectral acceleration ,and Fourier acceleration spectrum, are highly compatible with the observed values in the frequency range (f &gt; 1 Hz), indicating that the stochastic finite‐fault approach is not highly sensitive to input slip distributions and fault dimensions. The simulation results indicated no significance between the two slip models under high‐frequency conditions. Finally, based on the predicted PGA values of 1891 field points selected near the fault, the acceleration field of the Jiashi earthquake is plotted. The results show that the use of the acceleration time history predicted by modified EXSIM is feasible and practical in the high‐frequency band above 1 Hz.

Shaking table experimental study on models of steel buildings with different types of joints

The aim of this paper is to study the response of models of steel buildings with destroyed and non-destroyed joints. The study was conducted experimentally using the shaking table tests. Two steel models were considered. Several types of joints were taken into account: totally destroyed joints, partially destroyed joints, welded joints and joints stiffened with additional metal. Six ground motions were taken into account. The acceleration time histories were measured at the top of these two models of steel buildings. The results of the study show that the steel models with partially destroyed joints experienced higher levels of accelerations at their top, as compared to the steel models with totally destroyed joints. It was also concluded that the steel models experienced higher peak accelerations at their top in the case of welded joints and stiffened joints, as compared to the case with totally destroyed joints and partially destroyed joints.

Source parameters and scaling relations for small earthquakes in mainland Gujarat region of Western Deccan Volcanic Province, India

The return period of large earthquakes in intraplate regions is more in comparison to the interplate regions. Also, the intraplate region is less instrumented and hence, these regions are devoid of acceleration time histories of large and great earthquakes. The mainland Gujarat region is one of such intraplate regions for which acceleration time histories are not available, however, is vulnerable for earthquakes of M ∼ 6.0. Simulation is performed in these scenarios and the prerequisite is the knowledge of source parameters and scaling laws. We analyzed the spectra of the P- and S-waves recorded by the stations of Gujarat Seismic Network for the mainland Gujarat region of western Deccan Volcanic Province, India. Additionally, we developed scaling laws based on the obtained source parameters. We analyze 177 digital records from 43 local earthquakes during the period 2007–2016 with a magnitude of Ml = 2.5–4.3, which are located in a distance range of 10–250 km, using Brune’s seismic source model (Brune 1970, 1971). According to our study, the calculated stress drop values do not vary considerably with seismic moment values and are generally between 1 and 100 bar for most of the events. Therefore, the earthquakes in this region adhere to the law of self-similarity. As widely observed for conventional earthquakes, we find an inverse relationship between seismic moment and corner frequency for these events. Based on a linear regression analysis between the assessed seismic moment (M 0) and corner frequency (fc), we developed the scaling relation M 0 f c 3 = 2.29 × 1015. Scaling relations developed here are in agreement with those developed for the nearby Kachchh region and various other seismically active areas around the world. Use of regional scaling is recommended instead of global scaling laws for better estimation of seismic hazard. The source parameters and scaling laws presented here can be used for a variety of applications in mainland Gujarat, including the assessment of seismic hazards and the development of earthquake scenarios.

Seismic Safety Assessment of Arch Dams Using an ETA-Based Method with Control of Tensile and Compressive Damage

The seismic safety assessment of large concrete dams remains a significant challenge in dam engineering, as it requires appropriate analysis methods, modern performance criteria, and advanced numerical models to simulate the dam seismic behavior. This paper presents a method for seismic safety assessment of arch dams based on Endurance Time Analysis (ETA), using tensile and compressive damage results from a robust formulation for seismic analysis considering joint opening/sliding and concrete non-linear behavior (finite element program DamDySSA, under development in LNEC). The seismic performance is evaluated by controlling the evolution of the damage state of the dam, according to predefined performance criteria, to estimate acceleration endurance limits for tensile and compressive damage. These acceleration limits are compared, respectively, with the peak ground accelerations prescribed for the Operating Basis Earthquake (OBE) and Safety Evaluation Earthquake (SEE), aiming to evaluate the dam seismic performance relative to both earthquake levels efficiently, using a single intensifying acceleration time history. The ETA-based method is applied to the cases of Cabril Dam (132 m-high) and Cahora Bassa Dam (170 m-high), confirming its usefulness for future seismic safety studies, while the potential of DamDySSA for non-linear seismic analysis of arch dams is highlighted.

Research on rockfall impact process based on viscoelastic contact theory

Rockfall collision is the most complex and unpredictable movement pattern in rockfall movement. By examining the rockfall collision process, it will be possible to accurately forecast the route of the rockfall and direct the selection of protective measures. There is no unified quantitative theoretical solution, and the primary research approaches for determining rockfall collision characteristics are experiments and numerical simulation. In this paper, the rockfall is simplified as a sphere, and the rockfall impact mechanics model is constructed based on the viscoelastic contact theory. The time history solution method of the rockfall collision parameters is theoretically obtained by the differential equation solution method in combination with the initial conditions of the rockfall collision. Further research results show that the rockfall impact acceleration, impact velocity and impact displacement time history solutions derived in this paper are close to the logistic method. Finally, the results demonstrate that the results of this study are accurate when compared to the widely used rockfall maximum impact force algorithm. In conclusion, in this study, the rockfall collision process is theoretically quantified, and the general solution form of the time-history law of rockfall impact load is obtained, which has engineering applications.

Effect of scour erosion on mode shapes of a 5 MW monopile-supported offshore wind turbine

This paper investigates the influence of scour erosion on the mode shapes of the National Renewable Energy Laboratory (NREL) 5 MW offshore wind turbine (OWT) in varying soil conditions, where modes are derived from wind and wave-induced accelerations. A numerical model, which considers aerodynamic and hydrodynamic loading with soil-structure interaction (SSI) and servo-dynamics, is developed. The superstructure is modelled using OpenFAST and the foundation is modelled with SESAM, where SSI is incorporated using Winkler (p-y) springs. The foundation stiffness is subsequently integrated in OpenFAST using mudline interface springs. The influence of soil density, scour hole depth, and loading on the derived mode shapes is studied. Accelerations are extracted at nine locations along the tower. The first two system natural frequencies and mode shapes are estimated using frequency domain decomposition (FDD) applied to the acceleration time-histories for each scour depth and soil condition. Modal Assurance Criterion (MAC) values are calculated to evaluate the changes in mode shapes that occur due to scour. It is shown that the mode shapes present consistent changes as scour depth increases, and the second mode shape exhibits more sensitivity to scour. The sensitivity of mode shape changes to scour under variations in wind speed and measurement noise are also investigated.

Effects of stochastic generation on the elastic and inelastic spectra of fully non-stationary accelerograms

Nonlinear dynamic analyses are a state-of-the-art tool to assess the performance of earthquake-resistant structures. Inevitably, the validity of the predicted seismic response depends on the fidelity of the computational model to the actual structural behavior and the representativeness of the time histories of ground acceleration as realizations of the seismic hazard for the site under consideration. The generation of artificial time histories is generally allowed by international seismic codes and represents a valid alternative to recorded accelerograms, provided that the key features in the expected seismic input are preserved in the generated signals. Different stochastic generation methods of fully non-stationary accelerograms have been proposed in the literature. Two alternative randomization strategies are compared in this paper, based on (i) wavelets analysis and (ii) evolutionary power spectral density (PSD) functions. The analyses are focused on the aleatory variability observed in the generated elastic and inelastic response spectra in relation to different modeling choices, offering qualitative and quantitative information to designers using stochastically generated accelerograms.

Seismic Damage Index Spectra Considering Site Acceleration Records: The Case Study of a Historical School in Kermanshah

The frequency content and time duration of earthquakes are as effective as the peak ground acceleration on structural damage. Therefore, using rapid seismic vulnerability assessment methods that consider the earthquake acceleration time history is noticeable. Kermanshah is a historical city that is generally affected by far-field earthquakes. Therefore, it is necessary to consider the effect of the low-frequency shocks in evaluating the vulnerability of buildings in this city. Herein, a historic school in Kermanshah is assumed as a case study and two well-known damage index formulas are used for determining the damage index spectra of this structure, considered as a single degree of freedom system. Then, the effective parameters of the damage index, including ductility, relative degradation of stiffness, and dissipated energy are determined from a nonlinear analysis of the structure under the effect of the most probable earthquake acceleration records. Finally, the damage index spectra can be used for rapid seismic vulnerability assessment of masonry buildings on similar sites with various fundamental periods for large-scale assessments. The result shows that the building tends to collapse at a peak ground acceleration of 0.15 g. Furthermore, results confirm the seismic resistance reduction effect of flexible floors.

Region- and Site-Specific Measurements of Kappa (κ0) and Associated Variabilities for Iran

ABSTRACT Spectral parameter kappa (κ) is widely used to model the decay slope of the Fourier acceleration spectrum at high frequencies. This study presents estimates of κ0, often referred to as the site-related contribution in κ, for the Iranian strong-motion dataset. For our analysis, we use 2798 acceleration time histories from 325 earthquakes (between 1976 and 2020, inclusive) in the magnitude range M 3–7.4 and recorded over 285 stations at distances up to 100 km. The main objective of this study is to estimate κ0 and associated uncertainties at Iranian strong-motion stations. We investigate different sources of uncertainty that contribute to the higher scatter in the station-specific measurements of κ0. According to our results, the choice of frequency range used to approximate linear decay of acceleration spectrum contributes significantly to measurement-related uncertainty. Moreover, our measurements exhibit regional variations in (average) κ0 within Iran; in particular, for Zagros, the average κ0(=0.036) is found to be lower than that for northern Iran (κ0=0.044) and central-eastern Iran (κ0=0.04). In terms of between-station variability, there is a weak negative correlation between κ0 and VS30. The within-station uncertainty (i.e., standard deviation of κ0 values at individual stations) is also found to be decreasing with increasing VS30. The fundamental frequency of the site (f0) also appears to affect both measurement-related uncertainty and between-station variability at stations that exhibit significant 1D soil response behavior.

Assessment of Passenger Security in Paratransit Buses

The main objective of this study was to assess usefulness of 3-D, nonlinear dynamic, explicit computer codes for transit safety and security research. An analysis of response of a paratransit bus structure under loading caused by high explosive (HE) detonation is presented. It was assumed that the cubic HE charge detonates in the air near the bus. The ground was modeled as a rigid stationary wall. The problem was studied using LS DYNA, an explicit, 3-D, dynamic, nonlinear finite element program. The HE detonation and the processes of shock propagation in the air were modeled using the mesh with the Euler’s formulation. The Euler’s mesh was modeled as a rectangular prism sufficiently large enough to cover the entire bus structure. The nonreflecting boundary conditions on the top and side surfaces of the Euler’s domain and the sliding interface on the bottom side for the contact with the ground were assumed.A finite element model of the Ford Eldorado Aerotech 240 paratransit bus was developed for this study. This model consisted of 73,600 finite elements and had 174 defined properties (groups of elements with the same features) and 23 material models.Computational analysis provided useful information about dynamic deformations and damage inflicted to the bus structure under load blast wave activated by the HE detonation. It allowed for detailed, rigorous analyses of time histories of accelerations, velocities, deformations, and stresses. Resulting acceleration and overpressure histories were correlated with expected blast injuries of the bus passengers. The data obtained can be used to improve passenger safety and to reduce the threat of suicidal terrorist attacks against public transit. Changes in the bus structure and replacement of some materials to build a safer class of vehicles can be carefully considered and implemented.

Design and performance evaluation of steel beam members with plate‐type locally resonant metamaterials for vibration control

AbstractIn this study, a plate‐type locally resonant metamaterial (PTLRM) is proposed to control bending vibrations and low‐frequency noise of civil members. Considering the ease of design, installation, and workability, the PTLRM was fabricated using high‐density and soft materials. The PTLRM design includes a resonance frequency calculation of the unit and band gap estimation of the PTLRMs‐coupled structure. Three indicators were developed and experimentally analyzed to evaluate the vibration attenuation performance of the PTLRM: the response suppression in the resonance of PTLRMs, peak response suppression ratio, and distance between peaks. Experimental results of a 5‐m long steel beam with PTLRMs indicated that the bending modal responses of the steel beam were suppressed at frequencies closer to the local resonance of the PTLRM. This showed reasonable agreement with the results of the estimation. The acceleration of the PTLRMs‐coupled beam was reduced by up to 98.58% in the frequency response function. The time history of acceleration also decreased significantly over the entire time period. The damping of the soft material had little effect on the bandwidth of the band gap. However, it was found that a proper increase in the damping of the soft material could increase the vibration suppression performance.

Seismic evaluation of frictional FRP piles in saturated sands using shaking table tests

This manuscript presents results of two shaking table tests that were used to characterize seismic performance of Fibre-Reinforced Polymers (FRP) pile groups in saturated sand. A laminar shear box with a dimension of 1.0 m × 1.0 m and a depth of 1.0 m was employed to contain the soil medium and allow the soil to respond in the same fashion as the free field. Two types of composite group piles (2 × 2) made of Carbon FRP (CFRP) and Glass FRP (GFRP) along with a series of Aluminum model piles were manufactured and embedded as frictional piles within the soil. The pile-soil models were subjected to acceleration time histories adopted from the 2010 Val-des-Bois Earthquake in Canada and the 1995 Kobe Earthquake. The foundation motions recorded along the model piles showed significantly higher levels of excitation compared to the accelerations recorded within the soil at the same level. This was attributed to strong interaction between the soil and the foundation, and higher flexural stiffness of the model piles. Pile material was also found to influence the seismic response of pile caps and its superstructure through kinematic soil-pile interaction and possible rocking motion. The aluminum pile cap experienced significantly higher acceleration response compared to the FRP piles. Among the FRP piles, GFRP piles were shown to provide slightly better performance and could be an appropriate alternative piling material for frictional traditional piles especially in liquefiable soils.

Pseudo-Dynamic Test on Composite Frame with Steel-Reinforced Recycled Concrete Columns and Steel Beams

Pseudo-dynamic tests were conducted on a 2/5-scaled, three-story, two-span frame with steel-reinforced recycled concrete (SRRC) columns and steel beams. The El-Centro earthquake waves, Taft earthquake waves, and Lanzhou artificial earthquake waves were considered as the main loads to study the seismic behavior. The failure modes, displacement and acceleration time history curves, hysteretic characteristics, energy dissipation, stiffness degradation, and inter-story drift capacity of the composite frame were analyzed. Results showed that the composite frame did not show plastic deformation during the whole test process, and the steel beams and columns basically did not yield. Under the action of three seismic waves, the displacement response, acceleration response, and restoring force response of the composite frame were increased with seismic intensity, while the hysteretic curves and energy dissipation were different as the seismic wave changed. The seismic response of the composite frame was greatly affected by the spectral characteristics of the loading ground motion and the hysteretic energy mainly consisted of recoverable elastic deformation energy. Under the action of Taft wave with the input peak acceleration of 400 gal (rare earthquake), the stiffness degradation of composite frame was the largest, which reduced to 47% of the initial stiffness. This indicated that the composite frame had good energy dissipation performance in the elastic and elastic-plastic stages, and still possessed good rigidity after a rare earthquake, fully achieving the design purpose of “no collapse in major earthquake”.

Free-field soil response to bidirectional horizontal non-uniform ground motion from multi-point shaking table tests

This paper assesses the dynamic nonlinear free-field soil response under bidirectional horizontal non-uniform excitation through a series of multi-point 1 g shaking table tests. The soil bed was enclosed in an innovative soil box supported by an array of three shake tables and was subjected to uniform and non-uniform ground motions in one and two horizontal directions. The soil response to bidirectional and unidirectional excitations, both uniform and non-uniform, were compared and discussed in terms of acceleration time history and Fourier spectra, acceleration amplification factor and soil settlement, as well as shear stress-shear strain behavior. The comparison of soil responses to bidirectional and unidirectional shakings demonstrated that the trends of peak acceleration amplification factors are similar along soil depth, but the response difference between bidirectional and unidirectional shaking is increasingly higher along the soil profile towards the ground surface, especially for uniform excitation. The variations of soil settlement, shear stress-strain and damping curves under bidirectional excitation were similar to that under longitudinal excitation; however, they were much different than those observed under transverse excitation. The soil damping in Y-direction under non-uniform excitation was larger than that under uniform excitation. These different site response characteristics under bidirectional non-uniform excitation should be properly considered in the seismic design of extended infrastructure.

Transfer Learning for CNN-Based Damage Detection in Civil Structures with Insufficient Data

Among various methods proposed for health monitoring of structures, deep learning-based techniques with their powerful performance have attracted considerable attention in recent years. However, a major problem with these methods is that they usually need large amounts of data in the training phase, while such data may not be available in real applications. In this study, compact one-dimensional (1D) convolutional neural networks (CNNs) are utilized that require less data for training. The study is comprised of two parts: the first stage aims to develop a compact CNN that can recognize damages in a structure with high accuracy, when data are provided to some extent. The problem of inadequate training data in health monitoring of experimental and real-life structures is then investigated in the second part. Transfer learning is used to deal with this problem. A compact CNN is utilized as the source domain network and the target domain network receives all of its knowledge from this source. Acceleration time histories from a numerical model, an experimental structure, and a full-scale bridge are utilized to validate the proposed methodology. According to the results, the compact CNN can reach 100% accuracy when data are available for training. Also, for the case of insufficient data, using a compact network as well as transfer learning causes considerable improvement (about 95%) in the accuracy of damage detection.