Double-track Bridge Research Articles

Study on the aerodynamic performances and the operational safety of the vehicle-bridge system under the crosswind

The train operates in special environments such as large bridges and elevated viaducts. The fluctuations of the aerodynamic loads of the high-speed train (HST) are more intense and the possibility of the train derailment and overturning will increase when the train is running on the bridge under the crosswind. Thus, it is of utmost importance to study both the aerodynamic characteristics and the running safety of the train in this situation. This study uses the IDDES method to investigate the aerodynamic characteristics of the train running on the double track bridge in both up and down train directions at different speeds. The differences in the impact of aerodynamic loads on the train’s dynamic response indicators are discussed using the wind-vehicle coupling dynamic response calculation method. Based on these researches, the operational safety of the train under different operating conditions is evaluated from both flow field and dynamic perspectives. The results show that large-scale vortices fall off from the nose of the train and form a larger vortex structure on the leeward side and when the train is running under the crosswind. Its aerodynamic loads fluctuate intensely with time due to the complex wake flow of the train. The dominant frequencies of the unsteady aerodynamic loads are mostly concentrated in the range of 0–5Hz, which is close to the natural modal frequencies of the train. This will lead to the overturning of the train due to vehicle resonance. The derailment coefficient and wheel load reduction rate of the train increase with the speed. Their peak values exceed the limit of 0.8 while the peak duration of the derailment coefficient is less than 0.05s, which means the state of the leeward wheel will recover from a short derailment. However, the duration of derailment increases with speed. Therefore, appropriate measures should be taken to prevent accidents when the train is running at higher speed on the bridge to guarantee the operational safety of the HST.

Double Sub-Resonance Mechanism in Torsional–Flexural Vibrations of a Double-Track Short Bridge Under a Moving Train

Train-induced resonance of a railway bridge occurs when the train speed coincides with the primary resonance speed ([Formula: see text]) of the bridge, from which we can determine the sub-resonance speed as ([Formula: see text]). The primary resonance speed of a short bridge is generally much higher than the operation speeds of current high-speed trains but the corresponding sub-resonance speeds probably lie in the operation speed range. Such a resonance scenario can be observed from the vibration of a double-track bridge subjected to an eccentrically moving train, in which the deck vibration is combined by the vertical-flexural and torsional vibration modes of the bridge. Once the two modal sub-resonance speeds coincide with each other, a double sub-resonance will be developed on the bridge. In this study, an iteration-based train–bridge interaction finite element procedure will be presented to demonstrate the double resonance phenomenon. As expected, the double resonance may bring about a dramatic amplification on deck vibration. Such an excessive vibration is harmful to ballast stability and track maintenance of railway bridges.

On the vertical coupling effect of ballasted tracks in multi–span simply–supported railway bridges under operating conditions

This contribution investigates the vertical coupling exerted by ballasted tracks on the vertical response of bridges composed either of (i) several successive simply-supported spans with weak coupling between them due to the continuous track; or (ii) adjacent single-track decks conforming a double-track bridge, in which interaction effects are induced due to the transverse continuity of the ballast layer. To this end, 2 D and 3 D track-bridge interaction Finite Element models are implemented, which consider a three-layer discrete and explicit idealization of the track. The 2 D track-bridge interaction model is used to perform sensitivity analyses on the track parameters, which have revealed that the ballast shear mechanisms along the track may significantly affect the train-induced vibrations under resonant conditions. Then, the influence of the ballast coupling on the response of twin adjacent decks is investigated with a 3 D track-bridge interaction model. To this end, this model is updated based on the results of an experimental campaign performed on a real bridge composed of two SS spans and two single track twin adjacent decks. The numerical-experimental comparison shows an evident dynamic vertical coupling between the bridge decks and reveals the importance of including the ballasted track in the modelling process of these structures.

Hybrid Model for Railroad Bridge Dynamics

AbstractRailroads carry approximately 40% of the ton-miles of the freight in the United States. On the average, a bridge occurs every 2.25 km (1.4 mi) of track, making them critical elements. The primary load on the railroad bridges is the train, resulting in numerous models being developed to understand the dynamic response of bridges under train loads. However, because the problem is time-dependent and coupled, developing adequate models is challenging. Most of the proposed models fail to provide a simple yet flexible representation of the train, bridge, and track. This paper proposes a new hybrid model that is effective for solving the track–bridge interaction problem under moving trains. The main approach is to couple the finite-element model of the bridge with a continuous beam model of the track using the assumed modes method. Both single-track and multitrack bridges are considered. The hybrid model is validated against field measurements for a double-track bridge. This model is then used to predict...

Construction of Railway Bridge Over Velika Morava River Near Cuprija

The railway bridge over the Velika Morava River is located on the Belgrade – Nis main railway line, Gilje – Cuprija – Paracin section. It is a double-track bridge with track laid on crushed-stone ballast. The bridge over the Velika Morava River has five spans. The bridge structure is a steel truss continuous beam, with spans: 52.5 + 67.5 + 82.5 + 67.5 + 52.5, in the total length of 322.5 m. Truss structure height is constant (8.0 m), and the truss width is 10.0 m. Truss consists of diagonal members, without vertical members. All truss members are of box cross-section. Metal sheet is 12 - 36mm wide. Steel grade is S 235 J2G3 for less stressed members and S 355 J2G3 for highly stressed members in the area of supports and in the middle of the bridge. The Bridge deck is orthotropic deck with longitudinal trapezoidal stiffeners and cross girders spaced at 3.75 m. The bridge structure is completely welded, only steel connections of cross girders and joints of bottom and top bracings are made with 10.9 high-strength bolts applying full tightening force. Bridge bearings are of neoprene (pot bearings). Piers are founded on HW piles, Ø1500, 34 m maximum length. The structure is assembled on embankment (in front of the bridge) and successively longitudinally launched over piers without use of auxiliary trestle. The bridge was completed and put into service in 2016.

Fatigue Design in Consideration of Simultaneous Train Loading on Double-track Bridges

With the recent dramatic increase in the daily number of vehicles running on train lines, considering the effects of simultaneous train loading on double-track bridges has become a significant factor in fatigue design for railway steel bridges. In this research, we assessed the effects of simultaneous loading considering several parameters by applying Monte Carlo simulation, and evaluated each parameter's degree of contribution to fatigue damage in simultaneous loading. Using the results obtained, we proposed a new method for practical design calculation that can easily be adopted to consider simultaneous loading on double-track bridges using a coefficient.

Dynamic response of trains crossing large span double-track bridges

The alternating character of loads caused by trains crossing a bridge superstructure results in accelerations of the structure as well as of the train cars. These accelerations are not predictable on the basis of current design codes. Introduction of a model of train car suspension, enabled to calculate the transient state behaviour, thus simulating the structure and train vibration conduct. The model calculations were verified by comparing them to test results. Multiple application of the code resulted in the proposal of a set of formulas, enabling designers to predict the vibrational behaviour of train cars crossing double-track steel tied-arch railway bridges. The predicted values can be compared to recommended comfort quantities.