Xuhui He

Simulation Study on Train-Induced Vibration Control of a Long-Span Steel Truss Girder Bridge by Tuned Mass Dampers

Train-induced vibration of steel truss bridges is one of the key issues in bridge engineering. This paper talks about the application of tuned mass damper (TMD) on the vibration control of a steel truss bridge subjected to dynamic train loads. The Nanjing Yangtze River Bridge (NYRB) is taken as the research object and a recorded typical train load is included in this study. With dynamic finite element (FE) method, the real-time dynamic responses of NYRB are analyzed based on a simplified train-bridge time-varying system. Thereinto, two cases including single train moving at one side and two trains moving oppositely are specifically investigated. According to the dynamic characteristics and dynamic responses of NYRB, the fourth vertical bending mode is selected as the control target and the parameter sensitivity analysis on vibration control efficiency with TMD is conducted. Using the first-order optimization method, the optimal parameters of TMD are then acquired with the control efficiency of TMD, the static displacement of Midspan, expenditure of TMDs, and manufacture difficulty of the damper considered. Results obtained in this study can provide references for the vibration control of steel truss bridges.

Recent developments of high-speed railway bridges in China

Abstract China’s high-speed railway (HSR) construction industry has been experiencing a golden period of opportunities in the recent decades. Due to the necessity of protecting arable lands and the advantage of rapid construction, bridges (elevated structures) are predominantly used in China’s HSRs, which must meet the critical small settlement requirement. This article first reviews the main technical standards of small- to medium-span HSR bridges, where their comparison with the Japanese standard and International Union of Railway standards is highlighted. Then, the long-span HSR steel bridges are described and discussed case by case. Based on the engineering practice of HSRs, the main achievements and key technologies of HSR bridges in China are provided, followed by the opportunities and challenges of the current and future developments of HSR bridges.

Effects of friction-based fixed bearings on the seismic vulnerability of a high-speed railway continuous bridge

The fixed bearings of high-speed railway continuous bridges were vulnerable during earthquakes, since they transferred most of the seismic force between the superstructure and the piers. A type of friction-based fixed bearing was used and would slide during strong earthquakes. The influence of this sliding friction action on the seismic vulnerability curves of different components in the track-bridge system was analyzed in this article. Results show that the sliding friction action of the fixed bearings can protect other components from severe damage under earthquakes. This phenomenon is more significant when the friction coefficient on the friction-based fixed bearings is reduced. However, it increases the seismic relative displacement of the fixed bearings themselves. Finally, a sufficiently large displacement capacity and an appropriate friction coefficient between 0.2 and 0.3 are almost the best combination for the friction-based fixed bearings, which can effectively protect all components of the track-bridge system, including the track structure, piers, piles, and friction-based fixed bearings themselves.

Seismic Vulnerability Evaluation of a Three-Span Continuous Beam Railway Bridge

In order to evaluate the seismic vulnerability of a railway bridge, a nonlinear finite element model of typical three-span continuous beam bridge on the Sichuan-Tibet railway in China was built. It further aimed at performing a probabilistic seismic demand analysis based on the seismic performance of the above-mentioned bridge. Firstly, the uncertainties of bridge parameters were analyzed while a set of finite element model samples were formulated with Latin hypercube sampling method. Secondly, under Wenchuan earthquake ground motions, an incremental dynamic method (IDA) analysis was performed, and the seismic peak responses of bridge components were recorded. Thirdly, the probabilistic seismic demand model for the bridge principal components under the prerequisite of two different kinds of bearing, with and without seismic isolation, was generated. Finally, comparison was drawn to further ascertain the effect of two different kinds of bearings on the fragility components. Based on the reliability theory, results were presented concerning the seismic fragility curves.

Simulation of train–bridge interaction under wind loads: a rigid-flexible coupling approach

ABSTRACT This study proposed a rigid-flexible coupling method to simulate the train–bridge vibration under the actions of wind loads. Specifically, the numerical models of a rigid train and a flexible bridge were first established in the Multibody Dynamics Software SIMPACK and the Finite Element Software ANSYS, respectively. The bridge model was then integrated, using the virtual rigid body as an intermediate object, into the SIMPACK as a flexible body through the interface module FlexModal. The wind loads were applied to the coupled train–bridge system in the SIMPACK, and then the dynamic responses were obtained. The accuracy and efficiency of the proposed rigid-flexible coupling approach was verified by calculating the responses of the train–bridge system under various train speeds and comparing the results with those from FlexTrack module. The Xijiang Bridge on the Nanning–Guangzhou railway was employed as a case study to evaluate the dynamic indices under various combinations of the train and wind speeds.

Effects of uncertain characteristic periods of ground motions on seismic vulnerabilities of a continuous track–bridge system of high-speed railway

The high-speed railway in China has to pass through the site surrounded by several known faults. Different earthquake mechanics of those faults and propagation paths cause different ground motions, including different peak ground accelerations (PGA), durations and characteristic periods, acting on the high-speed railway bridges. However, the previous seismic vulnerability analysis mainly aimed at the influence of PGA instead of characteristic periods on the seismic fragilities of bridge structure rather than track–bridge system. By taking a typical and common continuous bridge recommended in Chinese criterion as example, the effects of the uncertain characteristic periods of ground motions on the seismic responses and fragilities of track–bridge system were analyzed based on a numerical method. The results indicate that the probabilities exceeding any damage state of most components, including the bridge and track parts, increase with the characteristic period of ground motions. The uncertain characteristic periods of ground motions should be fully considered for the seismic design of track–bridge system, especially when the uncertain characteristic periods change around a small value. In the seismic vulnerability analysis, the uncertain of the designed characteristic period of ground motions should be developed by considering the different earthquake mechanics of several known faults surrounding the bridge site and the complex propagation paths of ground motion waves through different soils. Using a constant characteristic period of ground motions only considering the soil profile at the local site of bridge possibly leads to an unsafe result in the current criterion.

Measurement of Non-Stationary Characteristics of a Landfall Typhoon at the Jiangyin Bridge Site

The wind-sensitive long-span suspension bridge is a vital element in land transportation. Understanding the wind characteristics at the bridge site is thus of great significance to the wind- resistant analysis of such a flexible structure. In this study, a strong wind event from a landfall typhoon called Soudelor recorded at the Jiangyin Bridge site with the anemometer is taken as the research object. As inherent time-varying trends are frequently captured in typhoon events, the wind characteristics of Soudelor are analyzed in a non-stationary perspective. The time-varying mean is first extracted with the wavelet-based self-adaptive method. Then, the non-stationary turbulent wind characteristics, e.g.; turbulence intensity, gust factor, turbulence integral scale, and power spectral density, are investigated and compared with the results from the stationary analysis. The comparison highlights the importance of non-stationary considerations of typhoon events, and a transition from stationarity to non-stationarity for the analysis of wind effects. The analytical results could help enrich the database of non-stationary wind characteristics, and are expected to provide references for the wind-resistant analysis of engineering structures in similar areas.

Evolutionary power spectral density analysis on the wind-induced buffeting responses of Sutong Bridge during Typhoon Haikui:

Recent field measurements on long-span bridges during typhoon events have captured strong nonstationary features in the buffeting responses. In this study, the buffeting responses of Sutong Bridge during Typhoon Haikui in 2012 recorded by structural health monitoring system are analyzed to represent the nonstationary characteristics. As an accurately measured state variable, the acceleration response of the main girder is first selected to evaluate its own original stationarity in different time intervals using the run test method. The acceleration response of the main girder can be regarded as a zero-mean nonstationary random process which is in demand to extract its transient features in time–frequency domain. Hence, the evolutionary power spectral density (EPSD) of the acceleration responses, which can present the local turbulence energy distribution in both frequency and time domains, is estimated using the wavelet-based method. Also, an average wavelet spectrum is obtained by averaging the square values of wavelet coefficients along the time axis, and the comparison between the average wavelet spectrum and Fourier spectrum shows a great conformance which indirectly verifies the validity of the obtained evolutionary power spectral density. The results of this study exhibit that there are strong nonstationary characteristics existing in the buffeting responses of Sutong Bridge during Typhoon Haikui, and it is essential to incorporate the nonstationary features of winds in the analysis or design of long-span bridges from an aerodynamic viewpoint.

Earthquake Isolation of a Spring-Damper-Friction System with a Convex Friction Distribution

When a structure is isolated by rubber bearings and viscous dampers, some of those bearings are often destroyed by an earthquake, causing a rough friction interface with large friction coefficients, while other contact surfaces around the damaged bearings are very smooth with smaller friction coefficients. A typical spring-damper-friction isolation system with a convex friction distribution is formed because the viscous dampers and other undamaged bearings can still work normally to provide the damping and restoring forces, respectively. The seismic isolation trend of this system is analyzed by artificially supposing the friction distribution to be theoretically and linearly convex. The calculation results validate that the convex pattern of friction distribution reduces the earthquake isolation efficiency and should be avoided in the actual projects.

Interaction between continuous welded rail and long-span steel truss arch bridge of a high-speed railway under seismic action

Abstract Track–bridge interaction under the seismic excitation is a dominant factor to the design and operation of railway bridges. A spatial model integrating rails, deck system, stringers, cross beams, suspenders, main trusses, piers and foundations was established in this paper, adopting non-linear springs to simulate the longitudinal resistance between the track and the bridge. The improved Penzien model was utilised to simulate the soil-pile interaction effect and a computer program was developed to generate artificial seismic waves. Comparison of natural vibration characteristics for the track–bridge system with and without considering the track constraint was made. Furthermore, the effects of sensitive parameters were investigated, including the ballast resistance, friction of movable bearings, location of rail expansion joint (REJ), etc. Present study results indicate that the track–bridge interaction enhances the structural integrity and induces relatively higher natural frequencies of the bridge. In general, the response obtained by the ballast resistance specified in the Chinese code is smaller than that by UIC code. Neglecting the friction of movable bearing will lead to over-estimated rail stresses and under-estimated internal forces of some piers in the system. Setting REJ at both beam ends is more efficient to release the seismic stress of the rail on the bridge.