Over-track Buildings Research Articles

Train-Induced Vibration Predictions Based on Data-Driven Cascaded State-Space Model

Over-track buildings above metro depots have become common in megacities due to urban land shortages. The transmission of vibrations into the over-track buildings during routine train operations has the potential to adversely impact the occupants in terms of perceptible vibration and noise. There is a need to quantify the potential impacts before construction for planning and design purposes. Train-induced vibration measurements were carried out on a six-story over-track building at the Luogang metro depot in Guangzhou, China, which is located adjacent to the tracks. The measurements were used to develop a data-driven cascaded state-space model, which can be applied to planned over-track buildings located in track areas to predict and assess whether train-induced vibrations would adversely affect the buildings’ future occupants. Vibration levels in the platform of the building’s columns were used as inputs to the models, thereby avoiding the complexity of modeling the transfer behavior of the platform. The predicted vibration levels corresponded with measurements in the existing building. This comparison validated the use of the model for future residential buildings where the predictions indicate that the impacts on its occupants will be within the applicable criteria.

Vibration transmissions and predictions within low-rise buildings above throat area in the metro depot

Train-induced feelable vibrations can bring side effects to people living or working in the building, as well as to operation of precise equipment. As massive construction of over-track buildings above metro depots prevails in megacities, impacts from train-induced feelable vibration take more concern. Four standard-designed 4-story steel-framed offices above the throat area in the Qianhai metro depot in Shenzhen, China, are studied in this research. The field measurements were conducted to investigate the influences of track alignment and track location in the throat area on vibration responses of over-track buildings. Detailed vibration analyses using the finite element method have been conducted. Train-induced floor vibration assessments on human comfort are carried out based on a total of 54 train pass-bys operated in the morning and evening and on different tracks. It can be found that the track alignment primarily affected the higher frequency components of train-induced vibrations, where curved trackinduced vibrations have larger amplitudes. The variance of train-induced building vibrations among pass-bys on different track locations was reduced compared with that of ground vibrations because of the averaging effects caused by multiple transmitting paths within the massive platform and stiff transfer structures. Train-induced acceleration levels at mid-floor can be 20–25 dB larger than those near columns at floor resonance frequencies which are dependent on the structural design. This research gives a comprehensive insight into train-induced vibrations within low-rise steel-framed buildings above the throat area in the metro depot, which is a valuable reference for assessments before the construction of future similar over-track communities.

Isolation effects of vehicle-induced vibration tested by integral floating method

A set of integral floating vibration isolation methods was developed in this study to remedy the lack of effective measures for over-track buildings. The effect of vibration isolation pads was investigated experimentally; the resulting field measurements were used to determine the time-frequency dynamic responses of vehicle-induced vibration and isolation effects. The characteristics of the vibration source appear to significantly affect the frequency domain distribution of vibration inside the building. When no vibration isolation measures are taken, the internal vibration of the cultural center exceeds the limit. BSW vibration isolation pads R480, R550, and R800 are effective in the frequency range of 16–80 Hz. The vibration isolation level in the Z direction is between 5.6 and 7.3 dB. After floating vibration isolation treatment, the maximum Z vibration level of the cultural center is 56.4 dB in daytime hours and 52.9 dB at night, which satisfies the relevant standard. The proposed method is shown to effectively hinder the structural vibration caused by subways on surrounding buildings.

Experimental study on the characteristics of train-induced vibration in a new structure of metro depot.

In order to improve the utilization rate of expensive and very limited urban land, a new structure system, underground metro depot, has been developed and applied in several cities in China. The underground metro depot, which is built underground, can be multiple stories, and allows other developments on top, has become increasingly popular in recent years. Since there are other developments on top, the vibration induced by the trains frequently entering and exiting the depot cannot be ignored. To better understand the characteristics of the train-induced vibration in the underground metro depot, a series of field tests were conducted on a two-story underground depot which is the largest underground metro depot in Asia. The results show that the main frequency components of vibration source are between 50 and 200 Hz and the level of that in the first floor underground is larger than that in the second floor underground due to the train floor structure interaction when the train running on the first floor underground. The vibration in the top platform decreases linearly with the distance from the measuring point to the center line of the track. When the train is running on the track at the edge area, the linear attenuation rate was about 0.2dB/m. It is easy to excite the vibration mode of the floor structure when the train is running on the first floor underground, so the vibration in the top platform induced by the train running on the first floor underground was much larger than the train running on the second floor underground. In the future design, if the underground depot has more than one floor, the structural dynamic behavior of over-track buildings induced by the train running on the floor slab underground should be the focus. The throat area has many rail joints and turnouts which can lead to a larger vibration level, the level easy to exceed the limit given for human vibration comfort. If developments are proposed on top of the throat area, the vibration level should be carefully checked in the area within 30 m from the track to avoid potential later vibration problem.

Predict the Influence of Environmental Vibration from High-Speed Railway on Over-Track Buildings

The vibration caused by railways is an environmental constraint in the development of over-track buildings. To study the influence of environmental vibration from the high-speed railway on over-track buildings, a finite element model including track, soil, and buildings was set up. Based on the vertical vibration acceleration sampled on the rail, the equivalent line load acting on rails vertically was obtained by a simplified model. On the basis of verifying the simulation model by measurement results, the vertical vibration induced by high-speed railways in over-track buildings was studied quantitatively. Through introducing correction terms relating to the thickness and height of the over-track platform, the story number, and the structure of the over-track building, an existing model released by the railway industry of China was improved. Compared with the existing model only being suitable for predicting vertical vibration of the first floor, the improved model can predict vertical vibration of different floors.

Efficient impedance model for the estimation of train-induced vibrations in over-track buildings

Rapid growth and the urban development of Chinese megacity in recent decades have led to land utilization challenges and the need for over-track buildings above metro depots that are part of the subway systems in these cities. Frequent subway operations into and out of the depots, which generate excessive vibration that transmits into the over-track buildings, can have adverse effects on the buildings’ occupants in terms of feelable vibration and noise. An efficient modeling procedure is presented for estimating vibration levels within the buildings before construction to determine whether vibration mitigation is required. Models were developed and validated based on vibration measurements in low-rise and high-rise buildings over a metro depot in Shenzhen, China. Impedance models were developed that characterize vibration transmission through the primary support columns or load-bearing walls into the building floors. Inputs to the model are vibration levels at the buildings’ foundation where the model estimates the transmission through individual support structures to the upper floors. Vibration estimates at different elevations within the building were compared with the measured levels during train pass-bys under the buildings with good agreement. Based on axial wave transmission impedances for column or load-bearing wall segments and simple impedance expressions for building floors, the closed-form analytical impedance model is an efficient and cost-effective tool for estimating floor vibration before construction.

Vibration isolation of over-track buildings in a metro depot by using trackside wave barriers

More and more cities consider to build superstructures over metro depots to comprehensively exploit the air space. However, metro train operations into and out of depots can generate excessive vibration and noise within the over-track buildings, which hampers the performance of vibration sensitive equipment and adversely affects the living quality of building occupants. This paper explores a systematic numerical investigation on the use of trackside wave barriers to isolate vibration transmission from the track into over-track buildings. A numerical model composed of a train-track dynamics sub-model and a track-soil-building finite element sub-model was developed to study the vibration isolation efficiency of various wave barriers including trenches and concrete walls. Utilizing this model, which was validated by previous field measurement results, parametric studies were further conducted to investigate the vibration isolation sensitivities of geometrical (depth, width and distance) and infilling material properties of trenches. Results showed that the open trenches performed best in building vibration isolation, and its isolation efficiency depended on the normalized depth. Geofoam trenches, i.e. soft material infilled trenches, were proved to be more effective than lightweight aggregate concrete trenches, i.e. hard material infilled trenches, in the dominant frequency range of 16–40 Hz. Concrete walls offered even worse vibration isolation performance than the hard material infilled trenches. These results can be used as a guideline in designing the geometry of wave barriers or the infilling materials of trenches in metro depots with over-track buildings.

Field measurement and evaluation of noise and vibrations induced by bridge cranes in full-scale over-track buildings.

Over-track buildings have been increasingly favored in the construction of metro depots and freight depots in China in the last decade due to advantages of intensive utilization of land resources and high-profits. However, due to the relatively heavy transportation mass and high-operating frequency of bridge cranes, over-track buildings are often complained by occupants for annoying noise and vibrations. So far this issue is rarely concerned and the characteristics of noise and vibrations under bridge crane loading remain unclear. In this study, field measurements of two full-scale over-track buildings, including a seven-story building over a metro depot and a three-story building over a freight depot, were conducted. Vibration characteristics of both the structure and the bridge crane were obtained. The transmission of vibrations from bridge crane system to the over-track building was obtained by transfer function (TF) of vibration from the column bracket towards the outdoor platform or building floors. The structure-borne noise inside the building was also captured and evaluated. The effect of bridge crane operational parameters (loading capacity and running velocity) and structural dynamic properties (non-structural components) on system responses was further discussed. Results show that the bridge crane-induced vibrations are comparable to the levels of train-induced vibrations. Besides, both buildings tested in this study suffer from unacceptable structure-borne noise, although the building vibration is acceptable. We recommend to carefully examining design of new over-track buildings to avoid annoying indoor noise and improve the living or working environment of occupants. It is demonstrated that vibrations of over-track buildings are more sensitive to running velocity than load capacity of bridge crane. It could be expected that the future increase of velocity will worsen the noise and vibration environment of over-track buildings. Furthermore, it is seen that non-structural components would remarkably affect dynamic responses of the building.

Experimental study of train-induced vibration in over-track buildings in a metro depot

Over-track buildings in Chinese metro depots have recently been designed to accommodate the rapid urbanization and massive construction of urban rail transit systems. However, train-induced vibration and noise impacts in over-track buildings need to be carefully assessed to provide comfortable working or living environments for the building's occupants. Vibration and noise measurements were carried out in a typical 28-story load-bearing wall supported residence and a 4-story steel-framed office building during train pass-by events in the Qianhai metro depot in Shenzhen, China. Measured points were set at ground level adjacent to the building support structures as well as on upper floors.Train induced noise levels were within both FTA and Chinese limits. Floor vibration levels in the low-rise building were within FTA limit but not the more stringent Chinese limit. Ground-borne vibration signals in the throat area contained high level, short duration impacts generated as cars passed over discontinuities in rails at a switch. Ground vibration levels near the columns under the low-rise building were significantly greater than at the load bearing walls of the high-rise building by 20 dB or more. Levels within the buildings near columns or walls were only 5 dB higher in the low-rise building. The low-rise building transfer structure apparently significantly reduced transmission into the building above the platform. Vertically aligned load bearing walls in the high-rise building more effectively transmitted vibration. The measured vibration reduction from floor to floor was meaningfully less than recommendations in FTA guidelines.This research enriches the database of train-induced vibration and noise in over-track buildings, provides insights into the vibration transmission process into and within over-track buildings and is of value for the design and construction for similar over-track buildings in future train depots.

Impedance model for estimating train-induced building vibrations

In recent years, the exploitation of over-track construction in populated Chinese cities has resulted in buildings being subjected to potentially disturbing vibrations from rail lines in metro depots. Building owners and engineers are concerned about occupants’ complaints related to structure-borne noise and vibration related to human comfort. Similar concerns exist for laboratory buildings and manufacturing plants that use vibration-sensitive equipment.In Chinese metro depots, the subway trains usually run on the bottom floor of the metro depot and the vibrational energy they generate transmits through the primary building support structures, including columns and load-bearing walls, to the upper floors of the over-track buildings. In order to predict train-induced vibration levels in over-track buildings, a new impedance model is presented. The model accounts for the propagation of axial and bending waves through the columns and load-bearing walls from the foundation into the upper floors. The primary mode of transmission is through higher impedance axial waves across impedance discontinuities at the floors; while the transmission due to bending waves is attenuated more rapidly by the floors. The input for axial wave transmission is the measured vertical vibration levels at the base of the column at the foundation. The contributions from multiple columns/walls into a given floor have been found experimentally to be statistically independent so that the total response of a floor is obtained from a simple energy summation of contributions from all columns/walls where the inputs to each may vary depending, in part, on their distance from the train track.Measured train-induced vibrations at the foundation level and on upper floors in 14-story and 25-story buildings in Shenzhen metro depot were used to validate model predictions of vibration levels at upper floors relative to the foundation vibration. The support structures for both buildings include both columns and load bearing walls where the transmission involves both in-plane shear and dilatation at various angles within the wall though a conclusion from this study is that axial propagation in the vertical direction dominates. The impedance model predictions are in good agreement with the measured floor vibration levels.

線路上空建築物の方杖型ダンパ補強に関する実験的研究

This paper shows the shaking table test with the large scale test models which assumed over-track buildings reinforced with knee brace dampers. From the test results such as responses or hysteresis loops, we confirmed control effectiveness by knee brace damper. In addition, we grasped variation of vibration characteristics by estimating natural frequencies and damping factors with ARX model.

Train-induced field vibration measurements of ground and over-track buildings

Transit-oriented development, such as metro depot and over-track building complexes, has expanded rapidly over the last 5years in China. Over-track building construction has the advantage of comprehensive utilization of land resources, ease of commuting to work, and provide funds for subway construction. But the high frequency of subway operations into and out of the depots can generate excessive vibrations that transmit into the over track buildings, radiate noise within the buildings, hamper the operation of vibration sensitive equipment, and adversely affect the living quality of the building occupants. Field measurements of vibration during subway operations were conducted at Shenzhen, China, a city of 10.62 million people in southern China. Considering the metro depot train testing line and throat area train lines were the main vibration sources, vibration data were captured in five measurement setups. The train-induced vibrations were obtained and compared with limitation of FTA criteria. The structure-radiated noise was calculated using measured vibration levels. The vertical vibration energy directly passed through the columns on both sides of track into the platform, amplifying vibration on the platform by up to 6dB greater than ground levels at testing line area. Vibration amplification around the natural frequency in the vertical direction of over-track building made the peak values of indoor floor vibration about 16dB greater than outdoor platform vibration. We recommend to carefully examining design of new over-track buildings within 40m on the platform over the throat area to avoid excessive vertical vibrations and noise. For both buildings, the measured vertical vibrations were less than the FTA limit. However, it is demonstrated that the traffic-induced high-frequency noise has the potential to annoy occupants on the upper floors.

Measurement of ground and nearby building vibration and noise induced by trains in a metro depot

Metro depots are where subway trains are parked and where maintenance is carried out. They usually occupy the largest ground areas in metro projects. Due to land utilization problems, Chinese cities have begun to develop over-track buildings above metro depots for people's life and work. The frequently moving trains, when going into and out of metro depots, can cause excessive vibration and noise to over-track buildings and adversely affect the living quality of the building occupants. Considering the current need of reliable experimental data for the construction of metro depots, field measurements of vibration and noise on the ground and inside a nearby 3-story building subjected to moving subway trains were conducted in a metro depot at Guangzhou, China. The amplitudes and frequency contents of velocity levels were quantified and compared. The composite A-weighted equivalent sound levels and maximum sound levels were captured. The predicted models for vibration and noise of metro depot were proposed based on existing models and verified. It was found that the vertical vibrations were significantly greater than the horizontal vibrations on the ground and inside the building near the testing line. While at the throat area, the horizontal vibrations near the curved track were remarkably greater than the vertical vibrations. The attenuation of the vibrations with frequencies above 50Hz was larger than the ones below 50Hz, and the frequencies of vibration transmitting to adjacent buildings were mainly within 10–50Hz. The largest equivalent sound level generated in the throat area was smaller than the testing line one, but the instantaneous maximum sound level induced by wheels squeal, contact between wheels and rail joints as well as turnout was close to or even greater than the testing line one. The predicted models gave a first estimation for design and assessment of newly built metro depots.

Study on the Measure of Reducing Noise and Vibration of Over-Track Buildings Induced by Crane Load

Big vibration will be cause by train load and crane load in the over-track buildings, and then generate structure-borne moise in the buildings, which will affect the live quality of the people lived in the buildings greatly. Focusing on this proble, three finite element method is established based on a practical engineering. The measures of reducing noise and vibration is proposed according the characteristics of the building, which is to replace the steel column as concrete column. The dynamic responses of the building under the two cases are calculated and analyzed. The computation results show that the measurement can reduced structure vibration significantly, and accordingly, the structure-borne noise is also reduced greatly. The research results in the paper have strong engineering practicability and can provide some references for some other projections in China in future.

Seismic Retrofitting Effects of Reinforcing Over-track Buildings with Knee-brace Dampers

The study presented in this paper verifies the seismic retrofitting effects of reinforcing over-track buildings with knee-brace dampers. Firstly shaking table tests were carried out on large-scale test models, to simulate over-track buildings reinforced with knee-brace dampers. Resulting responses or hysteresis loops, confirmed the seismic retrofitting effects of knee-brace dampers. In addition, natural frequencies and damping factors of the models were estimated by ARX model. Furthermore, analytical study of over-track building models simulating true structures confirmed the seismic retrofitting effects of knee-brace dampers.

SEISMIC DESIGN AND EVALUATION OF PERFORMANCE BASED ON MEASUREMENT OF RESPONSE-CONTROLLED AND LINKED STRUCTURAL SYSTEM OF OVER-TRACK BUILDING

Response-controlled and linked structural system is suggested to over-track buildings as a system with the applicability. About the example that applied response-controlled and linked structural system to an over-track building, possession performance as the building was identified by earthquake response analysis. At the same time by analysis of the maximum earthquake prescribed in design standard for railway structure, the performance was inspected as the railway structure. By an examination in a station building, vibration characteristic of an over-track building was evaluated and inspected the effectiveness of the adopted system.

SEISMIC RESPONSE CHARACTERISTICS BASED ON ENERGY BALANCE OF RESPONSE-CONTROLLED AND LINKED STRUCTURAL SYSTEM OF OVER-TRACK BUILDING

As a simple damage control structure to apply to over-track buildings with many restrictions on design and construction, response-controlled and linked structural system is effective. In order to make fixed quantity evaluation of the response reduction effective, the validity of the response evaluation by energy balance can be verified by lumped mass system model. Large effect of energy absorption is provided by the combination that is off the most suitable setting in linear range. The effect becomes small in non-linear range, but also large energy absorption is provided by using together with the vibration system including internal damping mechanism.

Application of Seismic and Vibration Isolation Structure System to Design of Over-Track Buildings

Over-track buildings require seismic performance enhancement as well as minimization of the vibration propagated by trains running below them. To this end, we have proposed a structural system for a building with functions to isolate both seismic and vibration effects. In this system, laminated rubber bearings that are softer in the vertical direction than general ones are set into the middle story of the building. Through response analysis, this study demonstrates a high level of seismic performance, and the reduction of train-induced vibration is confirmed using model experiments and numerical analysis.

線路上空利用建築物への免震・防振構造システムの適用

In over-track buildings, it is necessary not only to enhance the resistance against earthquake but also to reduce the train-induced vibration propagated to the buildings, which will be caused by trains running under the buildings. Therefore, we have proposed a structural system of a building with functions of both seismic and vibration isolation. In this structural system, laminated rubbers are set in the middle story of the building, which are softer in the vertical direction than general laminated rubbers. In this study, it has been made clear by response analysis that the resistance against earthquake is high and the reduction of train-induced vibration has been confirmed with model experiments and numerical analysis.

地中梁の無い線路上空建築物の構造設計法(構造)

This report introduces a new structural design method for over-track low-rise buildings without footing beams. We investigated the structural performance of existing over-track buildings, and grasped the seismic response and load-carrying capacity of a number of building models by analytical studies. The results were reflected in the revision of "Standard for Structural Design of Over-Track Low-Rise Buildings." In the new design method, the push-over analysis of soil-structure interaction models are used, and the seismic performance of buildings is made clear. As a result, it is possible to construct a building without footing beams both perpendicular and parallel to tracks.