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Purpose: This study investigates the effects of exercises on sand on the frequency content of the lower limb muscles in individuals with anterior cruciate ligament reconstruction and pronated feet during walking. Methods: This was a semi-experimental and laboratory-type study. The study samples included 28 male students with pronated feet and anterior cruciate ligament reconstruction aged 22 to 25 years. The participants were randomly allocated into the following two groups: The experimental and the control group. The electrical activity of the lower limb muscles was recorded using an electromyography system before and after performing the exercises. The statistical analysis was done using a two-way analysis of variance method with a significance level of 0.05. Results: The findings showed that the main effect of time for the frequency content of the tibialis anterior, medial gastrocnemius, vastus medialis muscles during loading and push-off phases, the vastus lateralis muscle during the mid-stance, the rectus femoris at the mid-stance and push-off phases, semitendinosus muscle during the loading, mid-stance and push-off phases, biceps femoris muscle during the mid-stance and push-off phases, and gluteus medius muscle during the push-off phase (P

Featured Application: The conclusions of this article can be used to predict the uplift of tunnels or underground structures induced by soil liquefaction considering vertical earthquake motion. The uplift of underground structures induced by soil liquefaction can damage underground structure systems. Numerical simulations have shown that uplift is positively correlated with the energy of horizontal input motion. However, the effects of vertical input motion on uplift have not been studied comprehensively in the past. Previous studies on the vertical motion concluded that the effects of vertical motion on uplift depend on the overall characteristics of earthquake motion. These motion characteristics have only been studied separately in previous studies. A comprehensive study to explore the interactions and overall effects of these characteristics on the uplift of underground structures is essential. In this study, the FLAC program with the PM4Sand model was used as a numerical tool to explore the effects of vertical input motion on the uplift of underground structures. The numerical model was calibrated using centrifuge test results, and 48 earthquake motions were selected as input motions to study the effects of the overall characteristics of earthquake motions on the uplift of underground structures. The simulation results show that the frequency content characteristics of horizontal and vertical motion are the major factors affecting the uplift magnitude and the responses of liquefiable soils. However, most simulation cases show that the inclusion of vertical motion causes a 10% difference in the tunnel uplift, compared to cases without vertical motion. [ABSTRACT FROM AUTHOR]

Purpose: This study investigates the effects of exercises on sand on the frequency content of the lower limb muscles in individuals with anterior cruciate ligament reconstruction and pronated feet during walking. Methods: This was a semi-experimental and laboratory-type study. The study samples included 28 male students with pronated feet and anterior... [ABSTRACT FROM AUTHOR]

The Lombard effect is an unconscious reflex of speakers to increase vocal effort when disturbed by noise, aiming to enhance speech intelligibility. This study aims to evaluate the effect of noise with different energetic content and levels at various frequencies on the Lombard effect, communication disturbance, vocal comfort, and speech intelligibility. Twenty university students participated in the study, reading a six-sentence excerpt and performing an intelligibility test under 12 randomized noise conditions. These conditions included noises at low (20–500 Hz), medium (500–4000 Hz), and high frequencies (4000–20,000 Hz), at four levels (45 dB, 55 dB, 65 dB, 75 dB). After each condition, participants rated their perceived communication disturbance and vocal discomfort. The results indicated that noise with energetic content at medium frequencies produced the highest Lombard effect, produced the most detrimental effect on communication disturbance and vocal comfort, and caused the strongest decrease in speech intelligibility, whereas it was minimally affected by low- and high-frequency noise. In conclusion, this study highlights that medium-frequency noise has the greatest impact on vocal effort, communication disturbance, and vocal comfort, while low- and high-frequency noise has minimal effect on speech intelligibility.

The Lombard effect is an unconscious reflex of speakers to increase vocal effort when disturbed by noise, aiming to enhance speech intelligibility. This study aims to evaluate the effect of noise with different energetic content and levels at various frequencies on the Lombard effect, communication disturbance, vocal comfort, and speech intelligibility. Twenty university students participated in the study, reading a six-sentence excerpt and performing an intelligibility test under 12 randomized noise conditions. These conditions included noises at low (20–500 Hz), medium (500–4000 Hz), and high frequencies (4000–20,000 Hz), at four levels (45 dB, 55 dB, 65 dB, 75 dB). After each condition, participants rated their perceived communication disturbance and vocal discomfort. The results indicated that noise with energetic content at medium frequencies produced the highest Lombard effect, produced the most detrimental effect on communication disturbance and vocal comfort, and caused the strongest decrease in speech intelligibility, whereas it was minimally affected by low- and high-frequency noise. In conclusion, this study highlights that medium-frequency noise has the greatest impact on vocal effort, communication disturbance, and vocal comfort, while low- and high-frequency noise has minimal effect on speech intelligibility. [ABSTRACT FROM AUTHOR]

The uplift of underground structures induced by soil liquefaction can damage underground structure systems. Numerical simulations have shown that uplift is positively correlated with the energy of horizontal input motion. However, the effects of vertical input motion on uplift have not been studied comprehensively in the past. Previous studies on the vertical motion concluded that the effects of vertical motion on uplift depend on the overall characteristics of earthquake motion. These motion characteristics have only been studied separately in previous studies. A comprehensive study to explore the interactions and overall effects of these characteristics on the uplift of underground structures is essential. In this study, the FLAC program with the PM4Sand model was used as a numerical tool to explore the effects of vertical input motion on the uplift of underground structures. The numerical model was calibrated using centrifuge test results, and 48 earthquake motions were selected as input motions to study the effects of the overall characteristics of earthquake motions on the uplift of underground structures. The simulation results show that the frequency content characteristics of horizontal and vertical motion are the major factors affecting the uplift magnitude and the responses of liquefiable soils. However, most simulation cases show that the inclusion of vertical motion causes a 10% difference in the tunnel uplift, compared to cases without vertical motion.

Seismic sequence as a result of occurrence of strong and moderate earthquake ground motion in a short time strongly affects the seismic response of structures. This kind of excitation causes, in many cases, more deteriorated effects compared to the corresponding single ground motion. The aim of this paper is to investigate the effect of seismic sequence of earthquake ground motion on the seismic responses of steel moment frame structures considering soil-structure interaction (SSI). To this end, four steel moment frames with 8 and 16 stories are considered each of which have three and six bays. Soil-structure-interaction is considered by employing dampers and springs having specified damping and stiffness through cone method. For modelling SSI effects, three types of soil based on standard 2800 are considered. The time history of responses show that the relative displacement of structure is increased when the structure is subjected to the seismic sequence. As a result, the damage induced to the structure. It is noteworthy to say that the effect of seismic sequence is more in soft soil. The obtained responses show that a special attention should be paid for designing of steel structures in high seismic zone when they are subjected to seismic sequence excitation. Furthermore, soil-structure-interaction is an important parameter that should be considered for such conditions.Therefore, it is recommended that the effects of seismic sequence and soil-structure-interaction should be accounted for better estimation and evaluate accurate responses of steel shear frame.

Subsurface characterization has always been an interesting issue in Geotechnical and geological engineering, especially when there is a potential risk of subsurface anomalies such as cavities and sinkholes. Due to the low resolution and accuracy of seismic recorded data at higher depths, anomalies identification has become more difficult. In this paper, the effect of various types of seismic source loads such as hammer impact, short-time impact, sinusoidal source and Ricker wavelet with a peak frequency of 100, 50 and 20 Hz is evaluated to identify the subsurface cavities by using the Finite Element Method in Abaqus 6.14 software. In addition, The ability of R and P waves are compared after the filtering the waves to detect cavities at different depths of 2, 6, 10 and 20 m. The results show that the frequency content and peak frequency of source load have a significant effect on the penetration depth and wave field resolution. Furthermore, filtering methods and separating R and P waves could be more helpful to identify the shallow and high depths cavities. Also, Ricker seismic source with a central frequency of 100 Hz, hammer impact and short-time impact indicate suitable results for cavities located at depths of 2, 6 and 10 meters. Whereas, it is difficult to identify the backscattered R waves from the cavity at the depth of 20 meters. However, low-frequency seismic load, such as 20 Hz Ricker source load, provides backscattered R and P waves from the cavity at the depth of 20 m. In general, the acceptable results can be obtained by using a combination of P and R waves and applying seismic load proportional to the depth of identification.

Recently, a class of fractional multi-frequency oscillators, constructed based on using n integrators and n half-order ones, has been introduced, whose steady-state responses contain sinusoidal components with 0.5 (3 n - 1) number of selectable frequencies. In this paper, the structure of the introduced multi-frequency oscillator is modified such that, notwithstanding the frequency content preservation, the number of its involved integrators is reduced. With no effect on the frequency content of the generated oscillations, this modification causes that the circuitry implementation of the considered class of multi-frequency oscillators can be done with a less number of energy storage elements. [ABSTRACT FROM AUTHOR]

The ubiquitous brain oscillations occur in bursts of oscillatory activity. The present report tries to define the statistical characteristics of electroencephalographical (EEG) bursts of oscillatory activity during resting state in humans to define (i) the statistical properties of amplitude and duration of oscillatory bursts, (ii) its possible correlation, (iii) its frequency content, and (iv) the presence or not of a fixed threshold to trigger an oscillatory burst. The open eyes EEG recordings of five subjects with no artifacts were selected from a sample of 40 subjects. The recordings were filtered in frequency ranges of 2 Hz wide from 1 to 99 Hz. The analytic Hilbert transform was computed to obtain the amplitude envelopes of oscillatory bursts. The criteria of thresholding and a minimum of three cycles to define an oscillatory burst were imposed. Amplitude and duration parameters were extracted and they showed durations between hundreds of milliseconds and a few seconds, and peak amplitudes showed a unimodal distribution. Both parameters were positively correlated and the oscillatory burst durations were explained by a linear model with the terms peak amplitude and peak amplitude of amplitude envelope time derivative. The frequency content of the amplitude envelope was contained in the 0–2 Hz range. The results suggest the presence of amplitude modulated continuous oscillations in the human EEG during the resting conditions in a broad frequency range, with durations in the range of few seconds and modulated positively by amplitude and negatively by the time derivative of the amplitude envelope suggesting activation-inhibition dynamics. This macroscopic oscillatory network behavior is less pronounced in the low-frequency range (1–3 Hz). [ABSTRACT FROM AUTHOR]

Abstract Background The aim of this study is to quantify the frequency content of the blood velocity waveform in different body regions by means of phase contrast (PC) cardiovascular magnetic resonance (CMR) and Doppler ultrasound. The highest frequency component of the spectrum is inversely proportional to the ideal temporal resolution to be used for the acquisition of flow-sensitive imaging (Shannon-Nyquist theorem). Methods Ten healthy subjects (median age 33y, range 24–40) were scanned with a high-temporal-resolution PC-CMR and with Doppler ultrasound on three body regions (carotid arteries, aorta and femoral arteries). Furthermore, 111 patients (median age 61y) with mild to moderate arterial hypertension and 58 patients with aortic aregurgitation, atrial septal defect, or repaired tetralogy of Fallot underwent aortic CMR scanning. The frequency power distribution was calculated for each location and the maximum frequency component, fmax, was extracted and expected limits for the general population were inferred. Results In the healthy subject cohort, significantly different fmax values were found across the different body locations, but they were nonsignificant across modalities. No significant correlation was found with heart rate. The measured fmax ranged from 7.7 ± 1.1 Hz in the ascending aorta, up to 12.3 ± 5.1 Hz in the femoral artery (considering PC-CMR data). The calculated upper boundary for the general population ranged from 11.0 Hz to 27.5 Hz, corresponding to optimal temporal resolutions of 45 ms and 18 ms, respectively. The patient cohort exhibited similar values for the frequencies in the aorta, with no correlation between blood pressure and frequency content. Conclusions The temporal resolution of PC-CMR acquisitions can be adapted based on the scanned body region and in the adult population, should approach approximately 20 ms in the peripheral arteries and 40 ms in the aorta. Trial registration This study presents results from a restrospective analysis of the clinical study NCT01870739 (ClinicalTrials.gov).

Concrete ground tanks are widely used in storing water, sewage, oil, toxic chemicals and other liquids. Depending on their type of use, they are usually in the category of very important structures of lifelines; Therefore, the dynamic analysis of liquid storage tanks is one of the most important issues in earthquake engineering. On the other hand, the seismic behavior of the storage tanks and its interaction with liquid is very important. In this study, the water medium is modeled using smoothed particle hydrodynamics method and tank’s structure modeled by finite element method. The smooth particle hydrodynamics, which is a meshfree method, has many advantages over other traditional grid-based methods. For verification purposes, the modeling accuracy was compared with the available experimental and numerical results, the reasons and parameters that were effective on selecting the records were expressed, and then the time history analysis was performed on the modeled storage tank including records with different frequency content. The parameters of sloshing height, acceleration at the top of the tank’s wall, base shear, force per unit width and wall displacement were obtained for comparison. Finally, the effect of frequency content was studied considering the effect of water-structure interaction on the tank. The results showed that a record with low frequency content results higher sloshing height, while a record with moderate frequency content will cause larger responses on the tank’s structure despite of its lower sloshing height. The study also proved that the dominant frequencies of sloshing increases with decreasing frequency content of earthquake.

Background and Objective: The asymmetry index during walking can be used for clinical treatment. This study was done to determine the immediate and long-term effects of foot orthoses on asymmetry of ground reaction forces frequency spectrum in male children with flat foot during walking. Methods: This clinical trial study was done on fifteen children with flat foot. Subjects were randomly divided into without foot orthoses, immediate and long term usage of foot orthoses groups. The kinematic and kinetic data during three without foot orthoses, immediate and long term use of foot orthoses conditions were recorded by the motion analysis and force platform systems, respectively. Results: Asymmetry index of medio-lateral frequency spectrum component during walking without foot orthoses, immediate and long term use of orthoses in median frequency and band width were greater than 4 percent. There were not any significant differences in asymmetry index of ground reaction force frequency spectrum components, asymmetry index of essential harmony numbers, asymmetry index of essential harmony total powers, and asymmetry index of fundamental harmony number in vertical, anterior-posterior, and medio-lateral axes between without foot orthoses, immediate and long term use of foot orthoses conditions. However, asymmetry index of essential harmony total power in medio-lateral axis during immediate use of foot orthoses tend to be reduced than that walking without foot orthoses. However, this difference was not significant. Conclusion: Despite the high asymmetry index of the ground reaction force frequency spectrum in the medio-lateral component during walking without foot orthoses, immediate and long-term effects of foot orthoses in the median and bandwidth frequency variables, the acute or long term use of foot orthoses did not show any significant effect on improvement of asymmetry index of ground reaction force frequency spectrum components.

In this article, the effect of earthquake frequency content and noise effects on damage detection is inspected. For this purpose, the damage was defined as nonlinear behavior of beams and columns, and several ground motion records were scaled so that some elements yield under the applied excitation. Consequently, the acceleration response data of each floor obtained through the nonlinear dynamic analysis. Using the discrete wavelet analysis, the occurrence and time of damage in a frame can be detected based on the spikes appearing in the wavelet details plots acquired from discrete wavelet decomposition. The mean period (Tm) was utilized to compute the frequency content of earthquakes. The implications of this parameter for the analyses with dissimilar ground motion records were investigated and the results indicates that the records with low Tm are more suitable for structural damage detection. In order to examine the effect of noise or measurement errors on damage detection process, the discrete wavelet analysis was repeated with a noise introduced to the acceleration response data.

Background: The evaluation of balance measures can help identify postural control processes, but traditional data collection for the center of pressure (COP) may not reveal differences in postural control mechanisms. This study aimed to evaluate the reliability of the frequency component of postural sway using wavelet analysis of COP signals. Methods: Fifteen healthy male subjects (average age: 39.16±7.2 years, average weight: 72±11.06 kg, average height: 171±6.31 cm) participated in this project. They were requested to perform three trials of single-leg and tandem stance conditions for 20-second with and without vision on a force plate. The frequency content of COP signals, including the energy, root mean square (RMS), and velocity of the COP in four frequency bandwidths of postural sway, was evaluated. The test-retest reliability of COP parameters was tested using the intraclass correlation coefficient (ICC). Results: Among different COP parameters, the energy of the COP within a moderate (1.56–6.25 Hz) frequency band (.79≤ ICC ≤.97) with standard error measurement (SEM) ranged from .14 to .23, the RMS of COP within low (.39–1.56Hz) (.79≤ ICC ≤.93) and ultralow (< .10 Hz) (SEM ranged from .000 to .002) (.78≤ ICC ≤.94) in a tandem stance and the RMS of COP in a bandwidth of < .10 Hz (SEM=.00) in a single-leg stance (.70≤ ICC ≤.99) with the eyes closed and open showed good to excellent reliability. Conclusion: The results of this study showed moderate to excellent reliability of wavelet-based COP measures; therefore, these parameters can be used for the identification of postural control mechanisms.

Objective: The link between frequency content of gait ground reaction forces and hearing loss is not well understood. The objective of this study was to investigate the effects of hearing loss on gait ground reaction force frequency content. Methods: Thirty male children were equally divided into a healthy group and a group with hearing loss problems (Deaf group). Frequency content of ground reaction forces were analyzed during barefoot walking. Independent samples t-test was used for between group comparisons. The significance level was set at p0.05). Conclusion: The results reveal that gait ground reaction force frequency content in deaf children may have clinical values for rehabilitation of these subjects.

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The authors propose in this work to formulate multicomponent amplitude modulation (AM)–frequency modulation (FM) representations as a sparse approximation (SA) problem, which is solved using orthogonal matching pursuits (OMP) and least angle regression (LARS). The approach appears to be an efficient tool to separate the frequency content of linear and non‐linear signals and behaves in a better way like the well‐known data‐driven empirical mode decomposition (EMD). Contrary to related works where AM–FM models and/or EMD are used to improve sparsity or learned dictionaries, they propose instead a sparse approach framework in AM–FM modelling and EMD. Recasting EMD as a SA problem provides a new framework towards its comprehension, formulation, and convergence since OMP and LARS converge. Doing so presents an alternative to getting rid of the interpolation process that EMD terribly suffers from. Conducted experiments show noticeable improvements in terms of frequency separation of linear and non‐linear signals, tone separation capability and robustness in a noisy environment. [ABSTRACT FROM AUTHOR]

Dynamic testing of bridges has as target to establish their response on pulse forces between the wheels and unevenness of road surface. Generally, during the tests, real time accelerations or deformations are to be measured and which through successive processing methods lead to other data as velocities, displacements, dynamic impact factor, but also the damping ratio. In order to validate the bridge response following testing, the measured data are compared both with allowable limits existing in standards and with the results obtained using analytical or numerical models.

This study presents a newly developed modular system for control of power electronic amplifiers in high-power, high-frequency power hardware in the loop experiments. The proposed design comprises computational nodes connected via multi-gigabit fibre-optic links. Nodes are modular and reconfigurable, allowing interfacing with a range of sensors and actuators, typically voltage and current sensors, and switching converters. The system has been designed for scalability to permit arbitrarily high power ratings and fidelity to be achieved through paralleling and interleaving of multiple power converter modules, targeting an ultimate sample and control rate of 1 MHz. Experimental validation is presented using a two-node configuration to facilitate a power electronic experiment operating at 120 V(rms) and 10 A(rms), with a fundamental frequency of 50 Hz and frequency content up to the 11th harmonic.

This study presents a newly developed modular system for control of power electronic amplifiers in high-power, high-frequency power hardware in the loop experiments. The proposed design comprises computational nodes connected via multi-gigabit fibre-optic links. Nodes are modular and reconfigurable, allowing interfacing with a range of sensors and actuators, typically voltage and current sensors, and switching converters. The system has been designed for scalability to permit arbitrarily high power ratings and fidelity to be achieved through paralleling and interleaving of multiple power converter modules, targeting an ultimate sample and control rate of 1 MHz. Experimental validation is presented using a two-node configuration to facilitate a power electronic experiment operating at 120 Vrms and 10 Arms, with a fundamental frequency of 50 Hz and frequency content up to the 11th harmonic. [ABSTRACT FROM AUTHOR]

Background and Objective: The asymmetry index during walking can be used for clinical treatment. This study was done to determine the immediate and long-term effects of foot orthoses on asymmetry of ground reaction forces frequency spectrum in male children with flat foot during walking. Methods: This clinical trial study was done on fifteen children with flat foot. Subjects were randomly divided into without foot orthoses, immediate and long term usage of foot orthoses groups. The kinematic and kinetic data during three without foot orthoses, immediate and long term use of foot orthoses conditions were recorded by the motion analysis and force platform systems, respectively. Results: Asymmetry index of medio-lateral frequency spectrum component during walking without foot orthoses, immediate and long term use of orthoses in median frequency and band width were greater than 4 percent. There were not any significant differences in asymmetry index of ground reaction force frequency spectrum components, asymmetry index of essential harmony numbers, asymmetry index of essential harmony total powers, and asymmetry index of fundamental harmony number in vertical, anterior-posterior, and medio-lateral axes between without foot orthoses, immediate and long term use of foot orthoses conditions. However, asymmetry index of essential harmony total power in medio-lateral axis during immediate use of foot orthoses tend to be reduced than that walking without foot orthoses. However, this difference was not significant. Conclusion: Despite the high asymmetry index of the ground reaction force frequency spectrum in the medio-lateral component during walking without foot orthoses, immediate and long-term effects of foot orthoses in the median and bandwidth frequency variables, the acute or long term use of foot orthoses did not show any significant effect on improvement of asymmetry index of ground reaction force frequency spectrum components. [ABSTRACT FROM AUTHOR]

Time–frequency (TF) representations are very important tools to understand and explain circumstances, where the frequency content of non-stationary signals varies in time. A variety of biosignals such as speech, electrocardiogram (ECG), electroencephalogram (EEG), and electromyogram (EMG) show some form of non-stationarity. Considering Priestley's evolutionary (time-dependent) spectral theory for analysis of non-stationary signals, the authors defined a TF representation called evolutionary Slepian transform (EST). The evolutionary spectral theory generalises the definition of spectra while avoiding some of the shortcomings of bilinear TF methods. The performance of the EST in the representation of biosignals for the blind source separation (BSS) problem to extract information from a mixture of sources is studied. For example, in the case of EEG recordings, as electrodes are placed along the scalp, what is actually observed from EEG data at each electrode is a mixture of all the active sources. Separation of these sources from a mixture of observations is crucial for the analysis of recordings. In this study, they show that the EST can be used efficiently in the TF-based BSS problem of biosignals.

The main purpose of this study is to investigate the influences of the duration and frequency content of ground motions on the seismic performance of high-rise intake tower considering structures-reservoir-foundation interactions. Thirty earthquake records matched with the standard design response spectrum according to Chinses code for seismic design of hydraulic structures of hydropower project were selected as ground motion input. The nonlinear seismic responses were classified according to the duration to investigate the effects of ground motion duration; while the nonlinear dynamic response under other fourteen earthquake records matched with previous standard design response spectrum with different response spectrum curves and characteristic periods were compared to study the effects of frequency content. The results show that the duration and frequency content in the seismic input can have significant effects on the seismic performance of high-rise intake towers. [ABSTRACT FROM AUTHOR]

A meshfree particle approach, namely moving particle semi-implicit (MPS) method is used to investigate the sloshing behavior in a partially filled liquid container. The validity of the numerical model is checked by comparing the sloshing motion in tanks undergoing sinusoidal and earthquake excitations with the published results. A comprehensive study of seismically excited violent sloshing motion and wave impact using a particle method, not reported in open literature, were taken up in the present study. Three ground acceleration time histories of varying characteristics were selected as the external excitations to the liquid tank system. The influence of the frequency content of ground acceleration on the violent sloshing characteristics was studied by scaling the peak ground acceleration to a fixed value for all the earthquake events. The assessment of dynamic responses, such as base shear, overturning moment, pressure load exerted on tank walls and ceiling, and slosh displacement arising out of vicious sloshing phenomenon, was competently carried out subjected to the selected ground excitations. A higher magnitude of dynamic responses, such as impact pressure load, base shear, and overturning moment, was evaluated for low frequency-content earthquake compared with that of a high frequency-content earthquake. [ABSTRACT FROM AUTHOR]

Main purpose of this study is to numerically simulate a three-dimensional soil–structure–liquid interaction problem in order to scrutinize the dynamic behavior of base-isolated concrete rectangular tanks under horizontal seismic excitations. It has been deduced that in many earthquakes, the isolation systems reduce the earthquake effects on structures by lengthening their fundamental natural periods against excessive drifts of the superstructure. However, in exceptional cases of the soil stiffness and shaking frequency, the base-isolation systems could have noxious effects. Therefore, the numerical seismic response of rectangular liquid tank system isolated by bilinear bearings is investigated under three real earthquakes with different frequency characteristics in this paper. To this end, finite shell elements for tank wall and boundary elements for liquid and soil are used. Subsequently, fluid–structure–soil equations of motion are coupled with isolator governing equation in the time domain, to gain the whole system response. For different concrete tanks from slender to broad ones, the variations of base forces, sloshing responses, shell radial displacements, and hydrodynamic pressures are illustrated under various system parameters such as the flexibility of the isolation system and the soil properties, to censoriously scrutinize the effects of various system parameters on the utility of the base-isolators. From the analyses, author has concluded that the base-isolation effect is intimately dependent on the earthquake characteristics and may amplify or control the structural responses. [ABSTRACT FROM AUTHOR]

A sample of healthy wind turbines from the same wind farm with identical sizes and designs was investigated to determine the average vibrational signatures of the drive train components during normal operation. The units were variable-speed machines with three blades. The rotor was supported by two bearings, and the drive train connected to an intermediate three-stage planetary/helical gearbox. The nominal 2 MW output power was regulated using blade pitch adjustment. Vibrations were measured in exactly the same positions using the same type of sensors over a six-month period covering the entire range of operating conditions. The data set was preliminary validated to remove outliers based on the theoretical power curves. The most relevant frequency peaks in the rotor, gearbox, and generator vibrations were detected and identified based on averaged power spectra. The amplitudes of the peaks induced by a common source of excitation were compared in different measurement positions. A wind speed dependency of broadband vibration amplitudes was also observed. Finally, a fault detection case is presented showing the change of vibration signature induced by a damage in the gearbox.

One of the brilliant and exquisite structures in Iranian architecture is the Gonbad-e Qabus tower which was built on the Gorgan Plain in 1006 AD. Because Iran is located on the Alpide seismic belt and due to the presence of many faults in the region, as well as the historical, cultural, and tourism importance of the tower, examining the behavior of this structure under earthquake conditions is an important matter. To investigate the performance of the tower under various earthquake loadings, this study uses the finite-element method and nonlinear dynamic analysis as well as field and experimental tests to determine the mechanical properties of masonry blocks and the soil around the building. Accordingly, after the modeling of the tower and the surrounding soil, modal analysis, as well as static and time history analysis, was carried out under seismic records with different frequency contents. The results showed that the records with low frequency contents produced higher displacements and stresses in the tower, such that Tabasrecord, with high frequency content, and Loma-Yerba earthquake, with low frequency content, produced the maximum displacements of 13.88 and 27.57 cm, respectively. Stress contours resulting from the earthquake records in all cases exceeded the compressive and tensile strength of the tower's materials, which indicate the necessity of seismic rehabilitation. [ABSTRACT FROM AUTHOR]

In this paper, an A P / V P specific equivalent viscous damping model is proposed through regression analysis to predict the maximum inelastic displacement of base-isolated buildings characterized by SDOF system. In order to present comprehensive results, a large number of parameters are specified for bilinear SDOF systems, i.e., 8 initial natural periods between 0.1 s and 1.5 s, 16 ductility ratios ranging from 2 to 50 and 4 post-to-pre-yield stiffness ratios: 0.0, 0.05, 0.1 and 0.2. A total of 45 earthquake ground motions are selected as seismic input and classified into three groups according to different frequency contents represented by peak ground acceleration to peak ground velocity ratios ( A P / V P ). Results show that the A P / V P ratio is of significant importance for the estimation accuracy of equivalent linearization method, especially for buildings with relatively small post-to-pre-yield stiffness ratio. Finally, the estimation accuracy of the proposed model is verified through comparison with other models. [ABSTRACT FROM AUTHOR]

In the present study two base isolation systems, i.e. lead-rubber and elastomeric bearings are analyzed and their seismic applicability is compared with reference to a liquid-filled conical elevated container undergoing different ground motions. The drilled shaft system is unlinked either from the base or from the top-mounted bowl by means of damping devices and the impact of such amendment on seismic performance of elevated liquid tank is examined by carrying out time-dependent finite element (FE) analyses on several pedestal-container systems. The developed FE procedure is competent in assaying the precise three-dimensional performance of the isolated elevated containers including the hysteretic performance of bi-linear isolation devices. For the input ground motions, the impacts of various parameters on the efficiency of the seismic bilinear hysteretic members are inspected. The results obtained from the FE analysis are validated against available numerical predictions in the time domain, and a good agreement is found between two methods. The sensitivity of induced forces, the internal hydrodynamic pressure, base moments and displacements in regard to some system parameters comprising lateral versus vertical isolation and locations of isolation devices, have been highlighted. Finally the numerical procedure suggests that earthquake response spectrum in various intensity levels has an influential role in the performance of elevated containers and special attention should be given to the dynamic analysis of such structures. • The performance of thin-walled elevated tanks isolated by bilinear bearings under lateral earthquake loading is examined. • Time-dependent nonlinear analyses are performed via 3D finite element models. • The impacts of lateral versus vertical isolation, locations of isolators, and frequency characteristics of earthquake are studied. • Comparisons are made on shear/moment forces, and cross drifts and new practical findings have been offered. • Depending on the earthquake characteristics , amplified responses due to ground exaction can be efficiently controlled. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of duration and frequency content of earthquakes on the collapse risk of post-mainshock buildings accounting for four damage states. The 5–95% significant duration D s and the mean period T m are selected as the index parameters to represent the duration and frequency content of ground motions, respectively. The modified Ibarra–Krawinkler hysteretic model is used in the structural models to capture strength and stiffness degradation associated with structural damages. The ground motion intensity is measured by inelastic spectral displacement ( S di ) to implicitly capture the spectral shape effect. Structural collapse capacities are determined using a suite of 62 records with a broad range of earthquake ground motion characteristics. The results demonstrate that both the duration and frequency content of ground motion play a significant role in structural collapse capacity. The degree of influence of aftershock characteristics on post-mainshock building collapse capacities becomes more significant as the structural damage level from the mainshock increases. As a result, post-mainshock structures with more serious damage states may be more fragile when subjected to the aftershocks with longer duration and lower frequency. Aftershocks are usually characterized by shorter duration and higher frequency than those of the corresponding mainshocks, thus the collapse risk of post-mainshock buildings may not be properly estimated using seeding scaled mainshock record as an aftershock compared to those using as-recorded mainshock–aftershock sequences. [ABSTRACT FROM AUTHOR]

 Abstract  The existence of containers on buildings in large cities with high earthquake risk has caused many damaging problems during past earthquakes. In addition to financial losses, it might induce uncontrolled fire, water cut and local or global failure of the structure. In this study, the dynamic interaction of water containers built on roof of structures, is investigated by means of a nonlinear software based on Finite Element Method. The tank shell and its water have been modeled as a composite system and the interaction of container and water have been examined.  This seismic control system with its limited potential capability as a tuned liquid damper (TLD) has been employed for 5 and 15-story structures, subjected to various earthquakes. The results gained from the present study can be helpful in investigating the tankâs support conditions and its installation. Based on the numerical results obtained in this paper, frequency content and other earthquake characteristics highly affect the role of water tanks on the seismic performance of lower rise buildings.

Aim of this paper is to discuss on the T phases generated after the mb 6.5 earthquake that shook Algeria on May 21, 2003. The seismograms, recorded by a cluster of seismic stations located on the coast facing the Ligurian Sea, Northern Italy, some 800 km N-NE from the source, represent a good database able to shed some light on the recognition, propagation and characteristics of these quite uncommon phases. The occurrence and the recording of T phases are in fact due to particular conditions, and require both particular characteristics of the bathymetric slope and the existence of a clear path between the instruments and the earthquakes source: these constraints are exactly realized in the north-western part of the Mediterranean Sea, whose coasts have been affected several times in the past by similar events. The preliminary investigations on the complex recorded seismogram show two different behaviours for stations close the coast and inland. In both cases, two distinct T phases (namely T1 and T2) are observed. In one case they have apparent velocities close to an average SOFAR channel, and are thus the recording of direct T phases. In particular, T1 is probably a precursor due to some scattering, while T2 is the direct T wave. Conversely, the recordings of the stations inland show apparent velocities that suggest back conversion of the original T to P and S waves and a crustal path. The frequency content of the T phases, as derived from the spectral analysis, reveals marked amplitude peaks also in the range 1-3 Hz, conversely to what was proposed by other authors for similar occurrences in other parts of the world. Since the geometry and shape of the SOFAR channel vary, it is highly likely that the spectrum is biased by the water conditions and the frequency content might change in different seas. Finally, the attenuation of the T phase does not depend on the actual distance of the receiver from the source but rather from the backconversion point: the amplitude varies thus with the in-land path and decreases proportionally to x?1.

Abstract: The dynamic response of railway bridges is known to be influenced by a combination of factors including the bridge natural frequency, train speed, and bridge and carriage lengths. However, the intrinsic relationships among these parameters have seldom been elaborated in common dynamics terms so as to enable more effective implementation in practice. This paper attempts to approach this classic problem from a frequency perspective, by investigating into the frequency characteristics in the bridge response as well as in the moving trainloads. In particular, the significance of the so-called “driving” and “dominant” frequencies arising from the moving load is examined. Based on numerical results and a securitization using a generalised trainload pattern, it is demonstrated that the primary frequency contents in the trainload, and consequently in the dynamic response of the bridge, is largely governed by the bridge-to-carriage length ratio. Namely, for short bridges (with a length ratio below the order of 1.5), well-distributed frequency peaks occur at a number of dominant frequencies, whereas for longer bridges the main frequency peak tends to concentrate towards the lowest dominant frequency. Such a characteristic affects directly the resonance condition and resonance speeds for bridges of different length categories, and this observation echoes well the predictions of the resonance severity using a so-called Z-factor. For the special case of bridge response under a single carriage/vehicle, the influence of the carriage mass is examined in association with the concept of critical speed, and the abnormal acceleration spikes that could occur when the vehicle moves at the critical speed is highlighted. [Copyright &y& Elsevier]

This paper presents a relationship between the focal depth in terms of Rayleigh-wave wavelength and the dominant frequency of Rayleigh waves generated in a homogeneous half-space. Rayleigh waves were simulated using a (2, 4) staggered grid P-SV wave finite difference algorithm with VGR-stress imaging technique as a free surface boundary condition. VGR is an acronym for vertical grid-size reduction. The simulated seismic responses using P-wave and SV-wave sources at different focal depths revealed Rayleigh-wave generation up to certain focal depth only for the considered frequency bandwidth. A shift of normalized spectral shape of Rayleigh wave towards lower frequency with increasing focal depth was inferred. Largest spectral amplitude was obtained in the wavelength for which the ratio of focal depth to the wavelength of Rayleigh wave was around 0.17 in the case of P-wave source and 0.9 in the case of SV-wave source. An exponential decrease of spectral amplitude of Rayleigh wave with the departure of the ratio of focal depth to Rayleigh wave wavelength from the above mentioned values was obtained. [ABSTRACT FROM AUTHOR]

Resonant ground motion has been observed in earthquake records measured at several parts of the world. This class of ground motion is characterized by its energy being contained in a narrow frequency band. This paper develops measures to quantify the frequency content of the ground motion using the entropy principle and the dispersion index. These measures are based on the geometric properties of the power spectral density function of the ground acceleration. The application of these measures to quantify the frequency content of random earthquake models is demonstrated first. Subsequently, these measures are used to quantify the frequency content of the ground acceleration for near-field records measured at rock and soil sites, short-duration and long-duration earthquakes. [ABSTRACT FROM AUTHOR]

This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function (PSDF) of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records. [ABSTRACT FROM AUTHOR]

The frequency content of earthquake ground motion is very important because it affects the dynamic response of structural systems. In the paper, we use five scalar parameters (the response spectral predominant period T p, smoothed spectral predominant period T o, Fourier amplitude spectral mean period T m, equivalent pulse period T v, and the pseudo-velocity spectral predominant period T pv) reflecting the characteristics of frequency content of strong ground motion to examine the near-fault three-component motions during the 1999 Chi-Chi earthquake. The result indicates that the frequency content of near-fault motions at the Hanging wall is less than that at the foot wall; T p shows a smaller value than that of T o and T m and it emerges a reverse relation of three-component motions as compared with that of T o and T m; T v and T pv of the near-fault motions at the north end of the rupture display a similar trend to that generated by the rupture directivity effect of strike-slip faulting. We therefore conclude that these observations are useful in the formulation of near-fault design spectra for seismic codes and in zoning studies in seismic risk. [ABSTRACT FROM AUTHOR]