Vertical Ground Vibration Research Articles

Experimental study on seismic behavior of reinforced concrete exterior beam-column joints under varying axial load

The majority of low-cycle loading tests on reinforced concrete (RC) beam-column joints were currently conducted under constant axial loads. During earthquake shaking, the axial load on the joints fluctuates due to the overturning moment and vertical ground vibration. Particularly in exterior beam-column joints, where beam shear occurs on only one side, the range of axial load variation is significantly larger. To elucidate the impact of varying axial loads on the seismic performance of exterior beam-column joints, low-cycle loading tests were conducted on four groups of full-size beam-column subassemblage specimens. Two identical specimens from each group underwent low-cycle loading tests with constant and varying axial loads, respectively. Based on the experimental findings, this paper examines the differences in cyclic behaviors among comparison specimens, focusing on damage characteristics, joint shear strength, stiffness degradation, displacement ductility, and longitudinal bar slip. The study suggests that compared to specimens subjected to constant axial loads, the comparison specimens exhibit variations in load-carrying capacity corresponding to the fluctuations in axial load. Furthermore, varying axial loads accelerate post-peak stiffness and strength degradation, leading to reduced ductility. Additionally, specimens in one of the comparison groups exhibited different failure models when subjected to varying axial loads and constant axial loads, specifically beam failure and joint failure, respectively. Numerical simulations of the corresponding beam-column subassemblages were conducted on the Opensees platform to elucidate how the two axial loading methods affect the transformation of failure modes. A subsequent parametric study focusing on the axial compression ratio was performed to further explore the impact of varying axial loads on the seismic behavior of beam-column joints.

Structural vibration characteristics of the historical building in a nearby blasting test

The tunnel construction by the drill-and-blast method can have a significant impact on the adjacent buildings, especially the historical buildings with poor structural performances. Based on a special explosive case of Nanjing Metro Line 4, an in-situ blasting test for vibration safety evaluation on the Nanjing Drum Tower was carried out. According to the site geological investigation, the location of the blasting test was selected near the planned tunnel. 6 blasting was carried out in terms of sing-hole blasting and millisecond-delay blasting. The attenuation of the ground vibration and the structural vibration responses of the historical Drum Tower were analyzed. The test results also showed that the Nanjing Drum Tower was not damaged by this blasting test. For single-hole blasting tests, the peak particle velocity increased with the increasing of the explosive charge, but decreased remarkably when using the millisecond-delay blasting technology. The horizontal and vertical ground vibration attenuation patterns were consistent, which can be described by the Sadowski formula. The ground vibration response was dominated by the horizontal vibration, and the velocity amplification factor in the case of the single-hole test with a charge quantity of 400 g reached 2.4, which was observed the most remarkable amplification effect.

Analysis of phase data from ground vibration measurements above a leaking plastic water pipe

One way to locate a buried plastic water pipe is to measure the surface vibration due to a leak in the region above the pipe, and to process the data to infer the pipe location. This paper investigates the physical mechanisms that propagate leak noise through the pipe and the surrounding soil to the ground surface. An analysis is carried out of the relative phase between vertical ground vibration measurements at points in a grid above the pipe. The study involves experimental measurements from a site in the UK with a more realistic leak mechanism compared to recent research, a simplified analytical model to gain insight into the underlying physics, and a numerical model to validate some of the assumptions made in the derivation of the analytical model. Three waves are principally involved in propagating leak noise to the ground surface from the pipe, namely the predominantly fluid-borne wave in the pipe, and the shear and compressional waves in the soil radiating from the pipe. Their influence on the ground surface vibration is investigated through measured and simulated phase contours over a rectangular grid of surface velocity measurements. It is shown how shear and compressional waves combine to affect the shape of the lines of constant phase on the ground. The results demonstrate the potential of the proposed analytical and numerical models to investigate wave radiation from buried water pipes, and possible pipe location strategies using phase data from surface vibration measurements.

Propagation characteristics of vibration induced by medium-low-speed maglev train running on subgrade

As a new generation of urban transit system, the medium-low-speed maglev transport entered a rapid development stage. However, the report about the ground vibration due to running medium-low-speed maglev train (mlsMT) is very limited. Therefore, an in-situ experiment and numerical analysis are systematically carried out to investigate the vertical and horizontal ground vibrations induced by mlsMT running on subgrade. The experiment was performed on the Changsha Maglev Express under different train load conditions. The numerical analysis is carried out by using the two-step analysis method. In the first step, the mlsMT-guideway spatially coupled dynamics model is developed to obtain the rail supporting forces during train passing. In the second step, a three-dimensional finite element model of guideway-subgrade-ground system is established, and then the rail supporting forces are taken as the external loads to calculate the ground vibration. After well validated by the experiment, the two-step analysis method is employed to study the time- and frequency- domain characteristics of the vertical and horizontal vibrations propagating from guideway to ground, under the conditions of different train speeds and double line operation. Results show that the vibrations induced by mlsMT are significantly different from those induced by the traditional wheel/rail steering train and the high-speed maglev train. The horizontal ground vibrations are not only more serious than vertical ones, but also have obvious vibration amplification phenomenon. Besides, the subgrade can obviously decrease the vertical and horizontal vibrations propagating to ground. With the increasing distance to the guideway centerline, both the decaying rate of ground vibration and the influences of the train load, running speed and double-guideway operation mode are gradually reduced. This works could contribute to the evaluation of the vibration annoyance caused by mlsMT operation.

Field Testing on active isolation of vibrating foundations in Middle-frequency range

Open or in-filled trenches are usually used for suppressing disturbing ground vibrations induced by various man-made sources such as construction activities, transportation systems and power plants. However, using a trench to suppress low-frequency excitations, may be either impractical or inefficient. This study evaluates different mitigation strategies to suppress middle-frequency ground vibrations (i.e. between 25 and 40 Hz), generated by a rotating mass vibrator mounted on a shallow foundation in the field. The mitigation strategies encompassed placing isolating materials including sand-rubber mixture (SRM) in bags and block-type EPS geofoam, in sidewalls and bottom of a cubic pit excavated underneath the vibrating foundation and then backfilling the pit. Using EPS geofoam resulted in up to 30% and 20% reduction in ground vibration amplitudes of vertical and horizontal components, respectively. However, SRM-filled bags provided better efficiency which increased with rubber content. For instance, up to 40% and 50% reduction were observed, respectively in vertical and horizontal ground vibrations, when a SRM mixture with 25% rubber content was used. The excavation depth in current study was comparably lower than that of an open trench, for the same vibration reduction level, and thus considerably reduced the earthwork volume.

The study of ground motion amplification based on an SMASS array site

There is a consensus in earthquake engineering that different soil structures have significant effects on ground motion. Three main methods can be used to study this issue: theoretical analysis, numerical simulation, and earthquake records analysis. Notably, the combined analysis of strong-motion records and station site information appears to be the most effective and reliable approach. In this study, we used site information from the Seismic Monitoring Array of Site and Structure (SMASS) of the Institute of Disaster Prevention and a record of the earthquake that occurred in Guye, China: a point on the bedrock was considered as reference for studying the amplification effect of the soil structure on ground motion through traditional spectral ratio analysis. Our main conclusions are the following. (1) The SMASS array data indicated that the shallow soil had an amplifying effect on ground motion: the frequency bands amplifying the horizontal ground motion were mainly those between 3.4 and 6.8, 11.3–13, and 15–20.8 Hz, while the frequency bands amplifying the vertical ground vibration were mainly those between 5 and 9.9, 13.5–15.9, and 18.5–21.9 Hz (2) The SMASS array data indicated that the influence of the deep soil on the horizontal ground motion frequency component was more significant than that of vertical ground motion. (3) Overall, the SMASS array site amplified the effects of both the high (3.4–20.8 Hz) and low (0.4–2.2 Hz) frequency components of ground motion with the depth decreases of buried depth; notably, the amplification effect of the high-frequency components grew much faster than that of the low-frequency components. (4) The groundwater table had an amplification effect on the vertical ground motion; therefore, its influence is also important to consider.

Experimental validation of a simplified numerical model to predict train-induced ground vibrations

This study evaluates the effect of high-speed train (HST)-induced environmental vibrations using simplified computational models and validates the test results in full-scale field conditions. Experimental investigations and in-situ measurements were performed at the Istanbul-Ankara high-speed railway section to examine the effect of ground vibrations from HSTs on the surrounding residential lands. In this study, ground-borne free-field surface motion at different distances from the railway track was realized using accelerometers. The experimental results of vertical and horizontal ground vibration accelerations induced by HSTs with a velocity of 250 km/h were analyzed. In the first part of the study, a two-dimensional (2D) numerical model based on finite element method (FEM) was used to investigate ground vibrations and validate the experimental results. To minimize artificial reflections and dissipate vibrational energy at the boundaries, the lateral extension of an infinite domain was modeled with viscous absorbing boundaries. A dynamic analysis of the proposed railway-soil coupled model was performed in the time domain under plain-strain conditions using Plaxis 2D, a commercial FEM software. For the verification, the experimental results were compared with those obtained from the numerical analysis. The simplified computational model validated by the test results may help researchers determine further investigation strategies to develop cost-effective mitigation measures for structures with sensitive devices near the railway track and significantly contribute to understanding complex wave propagation problems. In the second part of the study, train-induced environmental ground vibrations were analyzed for different types of soil conditions using a 2D FE model. Computational analyses were performed with four types of soil: soft, medium, dense, and rock, based on the Turkish Earthquake Code. The HST was used as a dynamic source to observe the differences in vibration generation and wave transmission in different types of soil. The HST load on the slab track was simulated to study the effect of operational loads on ground-borne vibrations. Based on the dynamic analysis results, the response of the free-field motion was investigated to obtain the relative acceleration time histories for different points of soil. According to the results, the peak acceleration values of train-induced vibrations at soft, medium, and dense soil sites increased dramatically when compared to the rock site. Vibration measurement data collected from parametric experiments with a simple numerical model for various soil characteristics can be particularly useful when planning residential and industrial facilities at new locations near railroads, to avoid the adverse effects of environmental vibrations caused by HSTs.

Large air pressure changes triggered by P-SV ground motion in a cave in northern Taiwan

Acoustic-gravity waves are generally considered to be one of the major factors that drive changes of the total electron content in the ionosphere. However, causal mechanisms of couplings between sources in the lithosphere and responses in the atmosphere and the ionosphere are not fully understood, yet. A barometer in the cave of the SBCB station records an unusual phenomenon of larger amplitudes in air pressure changes inside than those at the Xinwu station (outside). Accordingly, the comparison between the recorded data at the SBCB and Xinwu station can drive investigations of potential sources of the unusual phenomenon. Analytical results of phase angle differences reveal that the air pressure outside the cave at the Xinwu station often leads air pressure changes inside at the SBCB station at relatively low frequency bands. In contrast, the larger pressure changes at frequencies > ~ 5 × 10–4 Hz inside the cave at the SBCB station lead smaller changes outside at the Xinwu station. To expose causal mechanisms of the unusual phenomenon, continuous seismic waveforms are further conducted for examination. When the horizontal and vertical ground velocities of ground vibrations yield a difference in the phase angle close to 90°, coherence values between the air pressure changes and ground vibrations become large. This suggests that the pressure-shear vertical ground vibrations can drive air pressure changes. Meanwhile, the results shed light on investigating the existence of acoustic waves near the Earth’s surface using a partially confined space underground due to that the assumptions of the waves can propagate upward into the atmosphere driving changes in the ionosphere.

Earthquake Resisting Elements and Techniques in High Rise Buildings

An earthquake resisting elements are the components that are introduced in a structure to improve its seismic resistance and method of application of these elements are said as techniques. Though structures are designed and detailed as per code provision there remains some possibility of damage or failure in strong earthquake. Performance of buildings may be improved using earthquake resistant elements and techniques. An earthquake produces seismic waves on earth surface of earth due to releases of large energy from lithosphere which produces waves in earth surface causing disturbance in structures resulting failure of seismically weak structures. Seismic waves then travels in horizontal and vertical direction. It causes horizontal and vertical ground movement or vibration. These seismic waves cause disturbances in in buildings. The disturbance caused depends on position of building with respect to the center of disturbance called as epicenter. Intensity of these seismic waves is maximum at center and goes on reducing away from epicenter. Generally horizontal waves are of stronger than vertical so buildings are designed to horizontal seismic forces. These valves travel in any direction but from design purpose it is resolved in two orthogonal directions. Few constructional precautions may help to avoid or minimize damage in buildings. Earthquake resistance of building may be improved with proper design and construction of structures. Some earthquake resisting elements like shear wall, moment resisting frame or innovative techniques like base isolation, or energy dissipation system are used in many high rise buildings to avoid or minimize damage and hence loss of lives and properties. Shear walls are RC member generally introduced in a structure during construction in symmetrical manner. Base isolators in the form bearings are placed between sub and super structure to reduce stiffness of structures. Structures are braced with seismic dampers in energy dissipation system. Composites are used by mixing in concrete or as a warp. All these techniques are reviewed herewith with special attention on shear walls.

INCE/J Vibration Measurement Manual for Buildings—Part 1: A commentary on the manual for vibration measurement

Vibration Regulation Law in Japan has regulated vertical ground vibration caused by road traffic, operation of a factory machine, and construction work since 1976. However, inhabitants perceive vibrations not on the ground but in buildings which are residential spaces. For the purpose of assessing building vibrations, technical committee on Environmental Vibration Evaluation in the Institute of Noise Control Engineering (INCE/J) organized Vibration Manual for Buildings. The manual is desired to provide technical materials contributing to effective measures for the vibrations to be solved. To achieve the aim, the manual concerns the method of measurement of the following vibration characteristics: propagation of ground vibrations, transmission of house vibrations, and vibration exposures to inhabitants according to vibration sources. In addition, the accumulation of detailed measurement data contributing to the revision of vibration index in the future is an important issue. Specifically, items of the manual are the following: scope, measurement (measurement unit, instrument, location direction, time zone, and notices) and calculation of measurements. For example, measurement unit is based on one-third octave band analysis. The vibration shall be measured at the location in building where the inhabitants perceive highest magnitude of the vibration.

Experimental investigation of the vibration-attenuating effect of rail suspension fasteners on environment vibration induced by subway

A field test of environment vibration due to subway was carried out so as to investigate the vibration-alleviating effect of rail suspension fasteners in both time and frequency domains. The experimental results show that the time-domain vertical ground vibration accelerations would transform from several concentrated vibrations to the decentralized and uniform ones after replacement of common rail fasteners with rail suspension fasteners. Moreover, rail suspension fasteners have more significant vibration-mitigation effect on the time-domain peak particle accelerations (PPAs) at the nearer positions than at the farther ones, and the minimum PPA induced by common rail fasteners is still higher than the maximal PPA caused by rail suspension fasteners at all measuring positions. In frequency domain, the vibration-reduction effect of rail suspension fasteners is more remarkable in the dominant 1/3 octave center frequencies of 50-125 Hz than in the non-dominant ones from 1 to 40 Hz. Compared with common rail fasteners, the highest vibration acceleration levels (VALmax) in the dominant 1/3 octave center frequencies between 50 and 125 Hz at all measuring positions decrease by 8.7-21 dB after adoption of rail suspension fasteners. Additionally, the integrated VLzs in 1/3 octave center frequencies of 1-125 Hz at all measuring positions are ranged from 77.1 dB to 66.5 dB, evidently higher than the China’ standard threshold of 65 dB, before replacement of common rail fasteners, while the integrated VLzs are framed between 68.3 and 57.3 dB, mostly less than the threshold, after application of rail suspension fasteners.

Experimental study of the frequency-domain characteristics of ground vibrations caused by a high-speed train running on non-ballasted track

An in-situ test to obtain vertical, transversal and longitudinal ground velocities and accelerations caused by high-speed trains was performed alongside the Chinese high-speed railway line between Beijing and Shanghai. The test results indicate that due to excellent track quaity and consolidated infrastructure, whether if the train speed is below or above the Rayleigh wave speed, the dominant frequencies of both the vertical ground velocity and acceleration are both integral multiples of the trainload frequency generated by the centre distance of two neigbouring cars. The frequency-domain distribution of the ground velocity is more sensitive to soil stiffness than is the ground acceleration; this is especially the case for the first dominant frequency. Whether the frequency amplitudes of the vertical ground vibration are higher than the horizontal vibrations depends on the soil stiffness. The greater the soil stiffness, the higher is the frequency-range of the vertical ground vibration compared with that for the horizontal vibration, and the smaller is the difference between the three-dimensional frequency-weighted ground vibration level and the vertical vibration. Thus, effects of horizontal ground vibrations cannot be ignored when the foundation soil is soft.

Experimental investigation into ground vibrations induced by very high speed trains on a non-ballasted track

A field measurement of ground vibration was performed on the Beijing−Shanghai high-speed railway in China. In this paper, the experimental results of vertical ground vibration accelerations induced by very high speed trains running over a non-ballasted track on embankment with speeds from 300 to 410km/h are reported and analyzed in detail for the first time. Characteristics of ground vibration accelerations in both time and frequency domains are analyzed based on the test data. It is shown that the periodic exciting action of high-speed train bogies can be identified in time histories of vertical accelerations of the ground within the range of 50m from the track centerline. The first dominant sensitive frequency of the ground vibration acceleration results from the wheelbase of the bogie, and the center distance of two neighboring cars plays an important role in the significant frequencies of the ground vibration acceleration. Variations of time–response peak value and frequency-weighted vertical acceleration level of ground vibration in relation with train speed as well as the distance from the track centerline are also investigated. Results show that the time-domain peak value of ground vibration acceleration exhibits an approximately linear upward tendency with the increase of train speed. With the increasing distance from the track centerline, the frequency-weighted vertical acceleration level of the ground vibration attenuates more slowly than the time-domain peak value of the ground vibration acceleration does. Severe impact of high-speed railway ground vibration on human body comfort on the ground occurs at the speed of 380–400km/h. The results given in the paper are also valuable for validating the numerical prediction of train induced ground vibrations.

Analysis on Ground Vibration Induced by Subway under Three Track Structures

On the purpose of investigation for damping effect of different track supporting, In-situ experiments of vertical ground vibration acceleration induced by underground railway traffic under three track structures were performed at line 8 in shanghai. Time history and 1/3 octave for ground vibration were analyzed and the variation between ground vibration and track supporting structure as well as train velocity was summarized. The results show that reducing vibration effects of different track structure is determined to its own stiffness, various track velocity has little influence to VLzmax of ground vibration. The study result in this paper has important theoretical significance and reference value for the application of track structure in vibration reduction of subway.

Research on the Laws of the Environmental Vibration Induced by Elevated Rail Transit

Established the Car Line - Bridge coupling dynamic model, then entered the actual parameters of train, track and bridge structural, obtained the dynamic excitation at the rail bridge pier bottom when the train passes. On this basis, established the pier - soil - building coupling dynamic model by combining finite element method and infinite boundary element method, analysed the vibration characteristics of soil and buildings surrounding the elevated rail way, brought an in-depth study to the effects of elevated rail transit train running on the environment. The results show that: 1)The the environmental vibration induced by elevated rail transit is low-frequency vibration, the vertical ground boils down to low-frequency vibration of 10 - 25Hz, the transverse vibration of housing column is fundamental frequency vibration near 10Hz, the vertical floor boils down to low-frequency vibration of 10 - 25Hz. 2) The vertical ground vibration response level decreases with the increase of distance to the rail centerline when the train passes. 3) With the increase of vibration wave propagation distance, components of higher frequency decay more quickly.

Experimental study of ground vibrations induced by Brussels IC/IR trains in their neighbourhood

In this paper, railway-induced ground vibrations are analysed experimentally with the aim of addressing questions raising from the planning of a new RER network, available in the near future in order to alleviate pollution and the traffic jams. Free field ground vibrations are measured during the passing of InterCity and InterRegion trains. Various sites along the main line L161 Brussels-Luxembourg are chosen and investigated, with specific differences about the track and soil configurations. In order to compare these results with numerical ones, a deep dynamic characterisation of the track, the soil and the train is first performed. The analysis of horizontal and vertical ground vibrations measured during the passage of domestic trains (AM96, AM86, AM80, AM75, HLE27/M4 or M5) at various speeds (from 40 to 120 km.h-1 ) is then presented. The results show that the ground vibration amplitude depends on various factors: soil configuration, train type and speed, direction of measurement, track quality. In a particular case, a local defect (rail joint) induces large deformations of the soil.

Six-degree of freedom active pneumatic table based on time delay control technique

Precision equipment is sensitive in general to both horizontal and vertical ground vibrations and, thus, equipment manufacturers specify limits on the vibrations of the floor so that such equipment can be operated satisfactorily. When the floor vibrations are unacceptably high, various types of passive or active vibration isolation tables can be used. A three-degree of freedom active pneumatic table with time delay control was developed for control of heaving, pitching, and rolling motions in a previous study by the authors. The isolation performances achieved were very good for both ground and table excitations in the vertical directions. Limitations of the three-degree of freedom active pneumatic table, however, were that it is vulnerable to excitations of the floor and table in the horizontal directions. Hence, a six-degree of freedom active pneumatic table was required in order to tackle ground and table excitations in the horizontal as well as vertical direction. In this paper, a study on the six-degree of freedom active pneumatic table supported by four air-springs for both vertical and horizontal vibration control is presented. Its performance is evaluated by ground and table excitation tests. The physical meaning of the singular value decomposition approach in transmissibility analysis on a multi-input/multi-output vibration isolation system is presented using a simple two-degree of freedom example and applied to the actual six-degree of freedom active pneumatic table. It is also shown that settling time in the case of table excitations in both vertical and horizontal directions can be effectively reduced by the proposed six-degree of freedom control.

Prediction of high-speed train induced ground vibration based on train-track-ground system model

The development of analysis on train-induced ground vibration is briefly summarized. A train-track-ground integrated dynamic model is introduced in the paper to predict the ground vibration induced by high-speed trains. Representative dynamic responses of the train-track-ground system predicted by the model are presented. Some major results measured from two field tests on the ground vibration induced by two high-speed trains are reported. Numerical prediction with the proposed train-track-ground model is validated by the high-speed train running experiments. Research results show that the wheel/rail dynamic interaction caused by track irregularities has a significant influence on the ground acceleration and little influence on the ground displacement. The main frequencies of the ground vibration induced by high-speed trains are usually below 80 Hz. Compared with the ballasted track, the ballastless track structure can produce much larger train-induced ground vibration at frequencies above 40 Hz. The vertical ground vibration is much larger than the lateral and longitudinal components.

Studies on Ground Environmental Vibration Induced by Urban Rail Transit

In order to offer theoretical basis for the vibration prevention and noise reduction for the area along urban rail traffic line, the propagation laws of environmental vibration are summarized by analyzing observation data in time and frequency domain based on actual field observation data in Beijing. The mathematical statistics method under the criterion of least-squares has been used to study the vibration propagation and to establish the empirical formula of vertical ground vibration. The results obtained from the empirical formulas proposed agree with the results of field observation well. The vertical ground vibration level is much higher than that of horizontal. So the vertical ground vibration level is the most important aspect when evaluating ground environmental vibration level. The field response near the rail depends on the high frequency vibration caused by moving train and that far from the rail is dominated by the natural vibration frequency of train and the field vibration. The response amplitude of environmental vibration would be changed when load changed.

Inverted pendulum as low-frequency pre-isolation for advanced gravitational wave detectors

We have developed advanced seismic attenuation systems for Gravitational Wave (GW) detectors. The design consists of an Inverted Pendulum (IP) holding stages of Geometrical Anti-Spring Filters (GASF) and pendula, which isolate the test mass suspension from ground noise. The ultra-low-frequency IP suppresses the horizontal seismic noise, while the GASF suppresses the vertical ground vibrations. The three legs of the IP are supported by cylindrical maraging steel flexural joints. The IP can be tuned to very low frequencies by carefully adjusting its load. As a best result, we have achieved an ultra low, ∼12 mHz pendulum frequency for the system prototype made for Advanced LIGO (Laser Interferometer Gravitational Wave Observatory). The measured quality factor, Q, of this IP, ranging from Q∼2500 (at 0.45 Hz) to Q∼2 (at 12 mHz), is compatible with structural damping, and is proportional to the square of the pendulum frequency. Tunable counterweights allow for precise center-of-percussion tuning to achieve the required attenuation up to the first leg internal resonance (∼60 Hz for advanced LIGO prototype). All measurements are in good agreement with our analytical models. We therefore expect good attenuation in the low-frequency region, from ∼0.1to ∼50 Hz, covering the micro-seismic peak. The extremely soft IP requires minimal control force, which simplifies any needed actuation.