Chayut Ngamkhanong

Fatigue Life Assessment Method for Prestressed Concrete Sleepers

Concrete sleepers are one of the most important applications of a railway track system. Researchers have previously studied the impact load characteristics and ultimate load carrying capacity of a prestressed sleeper but research on the fatigue life of prestressed concrete sleepers is limited. Prestressed concrete sleeper fatigue damage is mainly due to the accumulation of defects, caused by the repeated load of wheel-rail interaction. Fatigue load, fatigue characteristics and the existing design methods of prestressed concrete sleeper are summarized in this paper. The commonly used fatigue assessment methods of concrete structures are also evaluated. Based on the results of former research result, this article presents a convenient fatigue life assessment method for a prestressed concrete sleeper, and contrasts with the test results. The insight information gained can be used to evaluate the service performance and predict the fatigue life of the concrete sleeper, as well providing design flexibility and broadening the design principle. The outcome of this study may also improve the rail track maintenance and inspection criteria, in order to establish an appropriate track condition monitoring network in practice.

The effect of ground borne vibrations from high speed train on overhead line equipment (OHLE) structure considering soil-structure interaction

At present, railway infrastructure experiences harsh environments and aggressive loading conditions from increased traffic and load demands. Ground borne vibration has become one of these environmental challenges. Overhead line equipment (OHLE) provides electric power to the train and is, for one or two tracks, normally supported by cantilever masts. A cantilever mast, which is made of H-section steel, is slender and has a poor dynamic behaviour by nature. It can be seen from the literature that ground borne vibrations cause annoyance to people in surrounding areas especially in buildings. Nonetheless, mast structures, which are located nearest and alongside the railway track, have not been fully studied in terms of their dynamic behaviour. This paper presents the effects of ground borne vibrations generated by high speed trains on cantilever masts and contact wire located alongside railway tracks. Ground borne vibration velocities at various train speeds, from 100u202fkm/h to 300u202fkm/h, are considered based on the consideration of semi-empirical models for predicting low frequency vibration on ground. A three-dimensional mast structure with varying soil stiffness is made using a finite element model. The displacement measured is located at the end of cantilever mast which is the position of contact wire. The construction tolerance of contact stagger is used as an allowable movement of contact wire in transverse direction. The results show that the effect of vibration velocity from train on the transverse direction of mast structure is greater than that on the longitudinal direction. Moreover, the results obtained indicate that the ground bourn vibrations caused by high speed train are not strong enough to cause damage to the contact wire. The outcome of this study will help engineers improve the design standard of cantilever mast considering the effect of ground borne vibration as preliminary parameter for construction tolerances.

Impact capacity reduction in railway prestressed concrete sleepers with vertical holes

Railway prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground as well as to secure rail gauge for dynamic safe movements of trains. In spite of the most common use of the prestressed concrete sleepers in railway tracks, the concrete sleepers are often modified on construction sites to fit in other systems such as cables, signalling gears, drainage pipes, etc. This is because those signalling, fibre optic, equipment cables are often damaged either by ballast corners or by tamping machine. It is thus necessary to modify concrete sleepers to cater cables internally so that the cables or drainage pipes would not experience detrimental or harsh environments. Accordingly, this study will extend from the previous study into the design criteria of holes and web openings. This paper will highlight structural capacity of concrete sleepers under dynamic transient loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The outcome of this study will improve the understanding into dynamic behavior of prestressed concrete sleepers with vertical holes. The insight will enable predictive track maintenance regime in railway industry.

Crossing Phenomena in Overhead Line Equipment (OHLE) Structure in 3D Space Considering Soil-Structure Interaction

Nowadays, the electric train becomes one of the efficient railway systems that are lighter, cleaner, quieter, cheaper and faster than a conventional train. Overhead line equipment (OHLE), which supplies electric power to the trains, is designed on the principle of overhead wires placed over the railway track. The OHLE is supported by mast structure which located at the lineside along the track. Normally, mast structure is a steel column or truss structure which supports the overhead wire carrying the power. Due to the running train and severe periodic force, such as an earthquake, in surrounding area may cause damage to the OHLE structure especially mast structure which leads to the failure of the electrical system. The mast structure needs to be discussed in order to resist the random forces. Due to the vibration effect, the natural frequencies of the structure are necessary. This is because when the external applied force occurs within a range of frequency of the structure, resonance effect can be expected which lead to the large oscillations and deflections. The natural frequency of a system is dependent only on the stiffness of the structure and the mass which participates with the structure, including self-weight. The modal analysis is used in order to calculate the mode shapes and natural frequencies of the mast structure during free vibration. A mast structure with varying rotational soil stiffness is used to observe the influence of soil-structure action. It is common to use finite element analysis to perform a modal analysis. This paper presents the fundamental mode shapes, natural frequencies and crossing phenomena of three-dimensional mast structure considering soil-structure interaction. The sensitivity of mode shapes to the variation of soil-structure interaction is discussed. The outcome of this study will improve the understanding of the fundamental dynamic behaviour of the mast structure which supports the OHLE. Moreover, this study will be a recommendation for the structural engineer to associate with the behaviour of mast structure during vibration.

Impact Capacity Reduction in Railway Prestressed Concrete Sleepers with Surface Abrasions

Railway sleepers (also called railroad tie in North America) embedded in ballasted railway tracks are a main part of railway track structures. Its important role is to transfer the loads evenly from the rails to a wider area of ballast bed and to secure rail gauge and enable safe passages of rolling stocks. By nature, railway infrastructure is nonlinear, evidenced by its behaviours, geometry and alignment, wheel-rail contact and operational parameters such as tractive efforts. Based on our critical review, the dynamic behaviour of railway sleepers has not been fully investigated, especially when the sleepers are deteriorated by excessive wears. In fact, the ballast angularity causes differential abrasions on the soffit or bottom surface of sleepers (especially at railseat zone). Furthermore, in sharp curves and rapid gradient change, longitudinal and lateral dynamics of rails increase the likelihood of railseat abrasions in concrete sleepers due to the unbalanced loading conditions. This paper presents a structural capacity of concrete sleepers under dynamic transient loading. The modified compression field theory for ultimate strength design of concrete sleepers under impact loading will be highlighted in this study. The influences of surface abrasions, including surface abrasion and soffit abrasion, on the dynamic behaviour of prestressed concrete sleepers, are firstly highlighted. The outcome of this study will improve the rail maintenance and inspection criteria in order to establish appropriate and sensible remote track condition monitoring network in practice. Moreover, this study will also improve the understanding of the fundamental dynamic behaviour of prestressed concrete sleepers with surface abrasions. The insight into these behaviours will not only improve safety and reliability of railway infrastructure but will enhance the structural safety of other concrete structures.

Static and dynamic behaviours of railway prestressed concrete sleepers with longitudinal through hole

As the crosstie beam in railway track systems, the prestressed concrete sleepers (or railroad ties) are principally designed in order to carry wheel loads from the rails to the ground. Their design takes into account static and dynamic loading conditions. It is evident that prestressed concrete has played a significant role as to maintain the high endurance of the sleepers under low to moderate repeated impact loads. In spite of the most common use of the prestressed concrete sleepers in railway tracks, there have always been many demands from rail engineers to improve serviceability and functionality of concrete sleepers. For example, signalling, fibre optic, equipment cables are often damaged either by ballast corners or by tamping machine. There has been a need to re-design concrete sleeper to cater cables internally so that they would not experience detrimental or harsh environments. Accordingly, this study will investigate the effects of through hole or longitudinal hole on static and dynamic behaviours of concrete sleepers under rail shock loading. The modified compression field theory for ultimate strength design of concrete sleepers will be highlighted in this study. The outcome of this study will enable the new design and calculation methods for prestressed concrete sleepers with holes and web opening that practically benefits civil, track and structural engineers in railway industry.

Condition Monitoring of Overhead Line Equipment (OHLE) Structures Using Ground-Bourne Vibrations from Train Passages

The most modern railway systems have fully adopted clean energy for train and track operations. Trains or rolling stocks are powered by electricity through the overhead wire or the third rail on ground. Commonly, the overhead line equipment (OHLE), which supplies electric power to the trains, is widely adopted in new railway networks around the world since its system enables trains to operate smoothly while track inspectors can safely work on tracks. The OHLE is supported by mast structure, which is located at the lineside along the track. The mast structure is often made of steel structure built on mat or pile foundation. Due to the train passages, ground-bourne periodic forces may cause damage to the OHLE structure especially mast structure, connections and its foundation, which can lead to operational failure of train electrification. On this ground, the structural integrity of mast structures must be inspected regularly. In this study, the modal analysis is used in order to identify the mode shapes and natural frequencies of the mast structure. A mast structure with varying rotational soil stiffness is used to construct dynamic influential lines for soil-structure integrity prediction. Finite element model updating technique has been used to perform modal analysis and modal parameter identification. This paper presents the integrated numerical of three-dimensional mast structure considering soil-structure interaction to evaluate the condition of OHLE structures for maintenance planning. The outcome of this study will help civil and track engineers to effectively and efficiently inspect OHLE structures using ground borne vibrations from train passages.

Dynamic Properties Evaluation of Railway Ballast Using Impact Excitation Technique

Railway ballasted track, traditional railway track, consists of steel rails, sleepers, fastener system, ballast, sub-ballast and subgrade. Railway ballasted track has been widely used in railway system around the world. Ballast, which supports the sleepers uniformly, is highly experienced deterioration. [...]

Far-Field Earthquake Responses of Overhead Line Equipment (OHLE) Structure Considering Soil-Structure Interaction

Overhead line equipment (OHLE) is the components for the electric train which supply the electric power to the train. For one or two tracks, OHLE is normally supported by cantilever mast. The cantilever mast, which is made of H-section steel, is slender and has a poor dynamic behaviour by nature. Nonetheless, the mast structures, which located alongside the railway track, have not been fully studied on the dynamic behaviour. This paper presents the effects of far-field excitations on cantilever mast and overhead contact wire. The five far-field earthquake records at various magnitudes between 6.5 and 8 Mw are considered. A three-dimensional mast structure with varying support stiffness is made using finite element modelling. It is interesting that support stiffness plays a role in the dynamic responses of OHLE during far-field earthquakes due to the change of its properties. Surprisingly, the earthquakes can cause damage to the overhead contact wire which lead to the failure of electric system. In this case, the train cannot run until the broken wire and electric system is cleared. This occurs when there are the losses of support stiffness due to the failure of support connection or soil degradation. Moreover, beating phenomenon, which normally occurs in the tall building, is obviously observed in OHLE during the occurrence of earthquake. This is the world first to demonstrate the effects of far-field earthquakes on the cantilever mast structure and the response of OHLE. The insight in this earthquake response of OHLE and its support has raised the awareness of engineers for better design of cantilever mast structure and its support condition. The outcome of this study will provide a new earthquake detection method using OHLE.

Time-Dependent Topology of Railway Prestressed Concrete Sleepers

The railway sleepers are very important component of railway track structure. The sleepers can be manufactured by using timber, concrete, steel or other engineered materials. Nowadays, prestressed concrete has become most commonly used type of sleepers. Prestressed concrete sleepers have longer life-cycle and lower maintenance cost than reinforced concrete sleepers. They are expected to withstand high dynamic loads and harsh environments. However, durability and long-term performance of prestressed concrete sleepers are largely dependent on creep and shrinkage responses. This study investigates the long-term behaviours of prestressed concrete sleepers and proposes the shortening and deflection diagrams. Comparison between design codes of Eurocode 2 and AS3600-2009 provides the insight into the time-dependent performance of prestressed concrete sleepers. The outcome of this paper will improve the rail maintenance and inspection criteria in order to establish appropriate sensible remote track condition monitor network in practice.