||Study on environmental vibration and mitigation countermeasures caused by running high-speed train on railway viaduct
With the rapid economic and urban development, the high-speed railway system connecting majorcities serves as a vital role in the national transportation network. Due to its high speed, punctuality,safety, comfort, high transportation capacity and less land use, it has become a new trend of railwaydevelopment in the world especially in Asian and European countries. We have derived the benefits ofhigh-speed railways since Tokaido Shinkansen as first high-speed railway was began operations inJapan in 1964. The main railway lines usually pass directly over densely populated urban areas orhigh-tech industrial areas, where the railway structure mainly comprises elevated bridges. Consideringthe extremely high speed, the bridge vibration caused by running high-speed train (HST) is concerned.This long-term vibration may cause deterioration of the bridge structures, such as the cracking orexfoliation of concrete. On the other hand, the bridge vibration propagates to the ambient ground viafooting and pile structures, thereby causing long-term environmental problems. Those vibrations oftenbring annoyances to the residents alongside railway lines and malfunction to the vibration-sensitiveequipment housed in the nearby buildings. Furthermore, they can induce the secondary vibration of thebuildings, which seriously affect the structural safety of ancient buildings near the railway lines. Alongwith further urbanization and more rapid transport facilities, there is rising public concern about theenvironmental problems in modern Japan. Therefore, it is quite necessary to clarify the developmentand propagation mechanism of ground vibration caused by running HSTs on the rigid-frame viaducts(RFVs) to find out more effective countermeasures against the HST-induced vibration problems.In this study, the vibration issues related to the train-bridge-ground interaction system: the HSTinducedbridge vibration problem, the environmental vibration problem caused by running HSTs andthe vibration reduction method, have been investigated by the 3D numerical analysis approach.For the HST-induced bridge vibration problem, it is very important to perform effective predictionand diagnosis on the HST-induced vibration of either existing bridges or those in the planning stageand obtain some instructive information for the ground vibration analysis as well as the vibrationmitigation analysis. An analytical procedure to simulate the train-bridge coupled vibration problemwith considering the train-bridge interaction (TBI) as well as the effect of ground properties isestablished. The vibration responses of RFVs caused by running HSTs are analyzed in considerationof the wheel-track interaction including the rail surface roughness. The RFVs including the trackstructure are modeled as the 3D beam elements and simultaneous vibration differential equations ofthe bridge are derived by using modal analysis. The elastic effect of ground springs at the pier bottomsand the connection effect of the sleepers and ballast between the track and the deck slab are modeledwith double nodes connected by springs. A 3D HST model modeled as multi-DOFs vibration systemthat can appropriately express the lateral, vertical and rotational motions of the car body and bogies isdeveloped for the analyses. Newmark’s β method for direct numerical integration is applied to solvethe vibration differential equations. For the validation of the developed 3D HST model and theanalytical approach, the vibration response analysis of the TBI system is carried out and the analyticalresults are compared with experimental ones. Based on the simulation of TBI, the vibrationcharacteristics of the RFVs in both vertical and lateral directions including the fact where predominantvibration occurs are clarified. Frequency characteristics are clarified by Fourier spectral analysis and1/3 octave band spectral analysis. Furthermore, the parametric study of bridge vibration caused byrunning HSTs is performed to examine the vibration influences of different factors including trainspeeds, train types, track irregularities, rail types and damping based on their analytical results.For the environmental vibration problem caused by running HSTs, based on the developedanalytical procedure for the TBI, an approach to simulate ground vibration around the RFVs of thehigh-speed railway is established with considering the vibration interactions between the train and thebridge as well as the foundation and the ground. The TBI model established preciously is convenientlyused in this analysis. The entire train-bridge-ground interaction system is divided into two subsystems:the train-bridge interaction and the soil-structure interaction (SSI). In the stage of the TBI problem, thevibration responses of RFVs are simulated to obtain the vibration reaction forces at the pier bottoms ofiiRFVs. Then, applying those vibration reaction forces as input excitation forces in the SSI problem, theground vibration around the RFVs in both vertical and lateral directions is simulated and evaluated bymeans of using a general-purpose program named SASSI2000. Based on the simulation of TBI andSSI, the characteristics of ground vibration including the fact where predominant vibration occurs areclarified. The ground vibration is rapidly attenuated along with the increase of propagation distance inthe near field and their vibration influence in the vertical direction is much more serious than that inthe lateral direction. The predominant frequency components are basically same for differentobservation points and they are determined by those of bridge vibration. Frequency characteristics arealso clarified by Fourier spectral analysis and 1/3 octave band spectral analysis. It is verified that theprimary vibration frequency component is dependent on the speed of HST in relation to the length ofcar and the higher frequency components are integer multiples of the primary one. The lowerfrequency band mainly exists in the vicinity of bridge piers and reduces quickly along with theincrease of propagation distance. The lateral vibration is mainly affected by the higher frequencycomponents. Furthermore, the parametric study of ground vibration caused by running HSTs is alsocarried out to examine the vibration influences of different factors including train speeds, train types,track irregularities, rail types and damping based on their numerical results.Based on the vibration characteristics related to the above-mentioned vibration issues, two kinds ofvibration reduction countermeasure are proposed to reduce the HST-induced vibration to meet therequirement of environmental vibration. One kind is to reinforce the hanging parts of RFVs to firstlyreduce the HST-induced bridge vibration. The other one is to install a new barrier called reinforcedconcrete vibration isolation unit (RCVIU) to directly isolate the HST-induced ground vibration. Then,according to 3D numerical analysis approach of the entire train-bridge-ground interaction system, themitigation analyses are carried out to comparatively investigate the HST-induced vibration responsesfor three reinforcement methods and a double-layer RCVIU. Their vibration screening efficiencies areevaluated by the reduction of vibration acceleration level (VAL) based on 1/3 octave band spectralanalysis and the reduction factor on the maximum acceleration from three aspects such as vibrationfrequency, train speed and propagation distance. Furthermore, the combined vibration reductionmethod with strut and RCVIU is proposed to involve the source motion control and the wavepropagation obstruction. It is an effective vibration reduction method to reduce the HST-inducedground vibration around the RFVs in both vertical and lateral directions. The reduction of VAL is9.67dB and 2.78dB at 25m in the vertical and lateral direction, respectively. In particular, aboutvibration frequency, it is more effective to mitigate the ground vibration at 25m in the lower frequencyband and the high frequency band such as 1-2.5Hz and 6-25Hz. The largest reduction of VAL is11.35dB at 8Hz and 13.68dB at 12.5Hz in the vertical and lateral direction, respectively. But it is smallaround the primary frequency component 3.15Hz.According to the ground vibration response, the environmental vibration evaluation is performedby means of the VAL from two aspects: vibration frequency and train speed. Taking advantage of thefrequency-dependent base curves of perceptible vibration from ISO 2631-2:1989 and the threshold70dB of environmental vibration for Shinkansen railway in Japan, the environmental vibration iscomparatively investigated through the 1/3 octave band spectral analysis. The parametric effectsincluding train speeds, train types, track irregularities, rail types and damping are also investigated forthe environmental vibration caused by running HSTs. Furthermore, the assessment for vibrationreduction methods is carried out to clarify the effectiveness of improvement of environmentalvibration. The results show: the VALs in the lateral direction are below the base curves and far lessthan those in the vertical direction; the VALs in the vertical direction easily exceed the smallest basecurves in the range of 8Hz to 25Hz and the threshold 70dB at the border for Shinkansen railway. Thevarious impact factors can cause the change of the HST-induced vibration but the change for the railtype is very small. In particular, the train speed can easily cause the variation of predominantfrequency components; the train type and damping ratio can easily cause the variation of magnitudes;track irregularity can cause the variation of both predominant frequency components and magnitudes.Finally, the application of vibration reduction countermeasures is useful to reduce the HST-inducedvibration to satisfy the requirement of environmental vibration in the vibration-sensitive areas.
Hokkaido University（北海道大学）. 博士(工学)