Ground Vibration Acceleration Research Articles

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.

The Influence of Amplitude- and Frequency-Dependent Stiffness of Rail Pads on the Random Vibration of a Vehicle-Track Coupled System

The nonlinear curves between the external static loads of Thermoplastic Polyurethane Elastomer (TPE) rail pads and their compressive deformations were measured. A finite element model (FEM) for a rail-fastener system was produced to determine the nonlinear compressive deformations of TPE rail pads and their nonlinear static stiffness under the static vehicle weight and the preload of rail fastener. Next, the vertical vehicle-track coupled model was employed to investigate the influence of the amplitude- and frequency-dependent stiffness of TPE rail pads on the vehicle-track random vibration. It is found that the static stiffness of TPE rail pads ranges from 19.1 to 37.9 kN/mm, apparently different from the classical secant stiffness of 26.7 kN/mm. Additionally, compared with the nonlinear amplitude- and frequency-dependent stiffness of rail pads, the classical secant stiffness would not only severely underestimate the random vibration acceleration levels of wheel-track coupled system at frequencies of 65–150 Hz but also alter the dominant frequency-distribution of vehicle wheel and steel rail. Considering that these frequencies of 65–150 Hz are the dominant frequencies of ground vibration accelerations caused by low-speed railway, the nonlinear amplitude- and frequency-dependent stiffness of rail pads should be taken into account in prediction of environment vibrations due to low-speed railway.

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.

大型振动台阵的振动影响实测研究

为研究某大型土木实验室内四点振动台阵正常运行所致的振动影响，对实验室内部和外部进行表面加速度的实地测试。测试内容主要分为两个时段，一是设备静止时段，二是设备运行时段，两个振动台满布刚性质量，最大加载质量接近60 T，施加1~40 Hz的多条正弦波激励，最大水平加速度0.5 g。根据室内外各测点的表面加速度振动衰减曲线的实测结果，得到了不同频率下的基础结构阻尼比，验证了大质量刚性基础减振方案的有效性。In order to evaluate the effect of vibration induced by large scale shaking table array, site test on the ground vibration acceleration was done inside and outside the civil lab. Two conditions, as no table working and 2 tables working with sines input of different frequencies from 1 to 40 Hz and peak acceleration of 0.5 g are included. By vibration attenuation curve from the test result, the damping ratio of different frequency is got and the effectiveness of the large mass stiffness is also verified for vibration reduction.

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.

Excitation Source Function of Ground Vibration from Urban Railway Traffic by an Inversion Procedure

The exciting source of ground vibration from urban rail generally consists two parts, a quasi-static load moving through the railway, and a dynamic interaction between wheel and rail. The latter is caused mainly from the wheel-rail unevenness, and usually described by a power spectral density function, PSD in brief. From the three dimensional point of view, this kind of exciting source can hardly be measured directly. A procedure is proposed to invert the source function from the ground vibrations observed at array. A dynamic coupled train-track-3D ground model is adopted to calculate the vibrations from given PSD. The Micro-Genetic Algorithm including the operators of the tournament selection, the uniform crossover and the re-initialization together with an elitist strategy is schemed to the inversion. The object function is designed as minimum of the sum of residua between calculated and observed ground vibration acceleration levels of 18 center frequencies, at 4 ground points and twice trains. The result shows that the ground vibration acceleration levels calculated from the obtained excitation source function agree with those from the observed data quite well, even for an additional point where the observed data have never been adopted in the inversion process.

Piling in fine and medium sand—a case study of ground and pile vibration

The paper presents the results of the measurement of ground and pile vibrations from a field investigation of prototype piling in which a steel casing of 600 mm diameter was driven in fine and medium sand for a depth of 16.4 m by impacting a hammer of mass 4100 kg dropped from a height of 2.4 m by a motorised winch fitted in a pile rig. In the case of ground vibration, both horizontal and vertical accelerations at 3 m, and vertical velocity at 15 m on the ground surface from the driven pile were measured. So also, vibration of the top of the already installed pile at 6.25 m from the driven pile was measured. Vibrations were measured using piezoelectric accelerometers and recorded using a 16-channel RT 145D DAT recorder. The recorded data were processed and acquired using DASYLAB data acquisition system. Time history plots of velocity and acceleration of ground were obtained. The maximum peak ground vertical velocity measured at a distance of 25 times the diameter of pile from the driven pile was 126.2 mm/s. The maximum vertical acceleration of the already installed pile situated at a distance of 10.42 times diameter of pile was 123.42 m/s 2 indicating the resonance of pile due to shock wave propagating in the soil medium. The time history of the ground vibration indicates its impulsive dynamic nature of short duration in contrast to the random periodic nature of ground waves generated by earthquake. Spectral analysis of the time histories of ground accelerations shows a dominant vertical frequency of 35.21 Hz and horizontal 25 Hz. The vertical frequency of pile was observed to be 25 Hz. Based on these spectral frequencies and going by the permissible vibration limits prescribed in various standards and codes, it has been found that the ground and pile vibrations were quite severe. Such severe ground vibration has got the potential of inflicting damage to structures in the vicinity. The problem can be quite serious in the midst of cluster of buildings in the urban habitat in the vicinity of pile driving.