Railway Engineering

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Study on Improvement of the Existing Power Reliability of Addis Ababa Light Railway Transit
(Addis Ababa University, 2023-08) Eleni Sisay; Getachew Biru (PhD)
The DC Railway Traction Power Supply System is a widely used technology around the world, particularly in urban and inter-urban regions. The system operates on standard DC traction voltages of 750 V, 1500 V, and 3000 V, which require less electrical clearance than the AC Railway Traction Power Supply System catenary. However, power interruptions can have a significant impact on the system. In the case of AALRT, frequent power interruptions led to thousands of passengers being evacuated from subway cars and stranded at stations. This tesis analyses the reliability of the Addis Ababa Light Rail Transit (AALRT) Traction Power Supply System (TPSS) using interruption data collected from AALRT, Ethiopian Electric Power (EEP), and Ethiopian Electric Utility (EEU). The data includes the number of customers interrupted, number of trips cancelled due to power interruption, daily number of customers served, daily customer interruption duration, number of times the power interruption occurred, number of passenger flow in both lines, and number of passengers interrupted. The causes of power interruption from EEP and EEU sides and duration of power interruption from incoming line 132/15kV are also included. Then, reliability indices are calculated and analysis results indicate that the highest mean time between failures (MTBF) was 2688.98 hours on the East-West (EW) line in 2019 G.C. and 4705 hours on the North-South (NS) line in 2020 G.C from the collected data. The highest duration of power interruption recorded was 804.47 hours on NS in 2019 G.C, and the highest frequency of power interruption recorded was 154 interruption/year on NS in 2020 G.C. In this thesis, two power reliability improvement technologies, substation reconfiguration and distributed generation, were analysed. The thesis was modelled in Matlab Simulink and the results were compared and best reliability mitigation techniques were identified. Substation reconfiguration by using redundant line has been found the best alternative for improving the power reliability for AALRT. As per the model developed, system average interruption frequency index and system average interruption duration index of 10.0490 interruptions/year and 24.0280 hr/customer/year, respectively have been achieved. This method is optimal in terms its applicability and cost.
Modeling the Safety Conditions of a Railway Line: The Case of Ethio-Djibouti Railway
(Addis Ababa University, 2023-07) Kalkidan Teshome; Yonas Minalu (PhD); Biniyam Ayalew (Mr.) Co-Advisor
The Ethio- Djibouti railway line run from Addis Ababa to the port city of Djibouti (Negad). The construction of this rail infrastructure is essential for the economic growth and development of both countries. However, after the operation start the Ethio- Djibouti railway line faced so many challenges due to different safety issues that challenge the train speed to travel at less than the designed speed. This thesis concerns identifying and setting countermeasures for the major safety problem by developing a model. Safety problems are incidents that lead to accidents, collisions, and death. This is done by taking previous data, questionnaire results, and field data from video cameras that were installed on the train (CCTVs if any) and locating the major Land use accident analysis area by using QGIS and then developing a solution on the major accident locations. From other literature underpasses, overpasses, or providing fences on the railway crossing and implementing government laws are considered the major solution to prevent safety issues on railway property. So by considering the Ethiopian people‟s culture of living, developing new countermeasures are taken to solve the issues on the Ethio- Djibouti railway. Finally from this thesis, the extra expense cost by the Ethiopian Railway Company is deducted and solved. Once safety problems are solved the Compensation cost, unplanned purchasing cost, and also maintenance costs will be reduced, especially the compensation cost for the mortality of animals and person will be reduced once the location is identified providing the possible measures for the find out problems.
Passenger Ride Comfort Analysis of a Rail Vehicle Running with Polygonized Wheel Using Dynamic Simulations (A case study of Addis Ababa Light Rail Transit)
(Addis Ababa University, 2023-07) Mazuri Erasto Lutema; Haileleoul Sahle (PhD0
The railway transportation system is currently undergoing a significant expansion. As a result, train lines are upgraded, and the technical condition of the rail vehicles that use them is also taken into consideration. However, under certain circumstances, wheels on rail vehicles may sustain damage while in use. Then, depending on the kind and degree of flaws, the profile of the wheels is no longer circular but rather changes. The passenger's ride comfort is diminished when a rail vehicle with a damaged wheel is in operation. The research considered one type of railway wheel damage, which is wheel polygonization, and focused on analyzing the ride comfort for passengers based on results obtained from multibody dynamic analyses. Simulations and calculations were done in numerical and dynamic multibody software. The findings demonstrate that the wheel polygonization of 0.3 mm has a greater impact on ride comfort compared to the other amplitudes (0.1mm and 0.2mm). This implies that with an increase in polygonization amplitude, the ride index will also increase. However, running an overloaded carrying capacity vehicle has minimal comfort compared to an empty and rated carrying capacity vehicle when the wheel has a polygonization defect. Moreover, it found that with increasing vehicle speed, the ride index also increases, which means that at high speeds, the ride comfort will be diminished. Furthermore, it found that the orders of wheel polygonization have an effect on ride comfort. With the increasing order of polygonization, the ride index also increases. According to the findings, this study has a significant impact on the maintenance planning for wheels and rails as well as operation management.
Positive Train Control with Headway Optimization on an Active Communication System-a case study of Addis Ababa Light Rail Transit
(Addis Ababa University, 2023-08) Mohamed Ali Hussein; Yihenew Wondie (PhD)
Reducing rail transit's headway effectively is of enormous practical value since it plays an increasingly significant part in the public transportation system. Some of the most important goals in railroad operations include safety, capacity, and timely schedules. The idea behind positive train control (PTC) is to use cutting-edge 2 information technologies to increase the safety and effectiveness of railroad operations. Except for increasing the average waiting time, headway irregularity may also result in additional energy consumption and more delay time. Active communications and other information technologies enable the deployment of a dynamic headway, which can increase track capacity and dispatching effectiveness while also enhancing safety. Minimum headway, which is the optima Interval time the following train can reach while tracking the lead train, is considered to be one of the main factors restricting operational capacity. We can run with better headways without increasing the operational speed; for example, the Addis Ababa LRT currently uses 15 minutes of headway when the speed is averaging 20-70 km/h. The calculated results show that this significant headway can be reduced by up to 4 minutes without slowing down operation As a result, dynamic headway control cannot be represented using existing modeling techniques that use fixed headways, especially when the dynamic headway only comprises a small portion of a single block. Minimum headway shall be a minimum period of time required for the station to carry out requisite train arrival and departure operations, which it is also essential that trains operating in this area are safe.
Reliability and sensitivity analysis of multibody system due to uncertainty parameters. A case study of Addis Ababa Light Rail Transit
(Addis Ababa University, 2023-08) Murungi Rodger; Haileleoul Sahle (PhD)
A multibody system is one of the complex mechatronic system whose dynamic performance is influenced by its connected components and the mechanical structure. However during the service life, the system is subjected to degradation of different components whose conditions may greatly impact the vehicles running characteristics like stability and reliability. The suspension system is one of the systems that ensure better and reliable running behaviors are achieved and hence any uncertain changes in its characteristics becomes of significant interest and must be treated with utmost attention. Hence this research aims carrying out reliability and sensitivity of multibody system due to uncertainties in the suspension system and provides a model which can be applied to evaluate the performance of the vehicle in terms of variation of suspension design parameters. The vehicle is modelled using SIMPACK dynamic software, incorporated with track irregularities from maintenance data and using statistical tools to vary suspension design parameters. The dynamic performance of the vehicle is evaluated by using dynamic indexes like derailment coefficient and vibration sensitivity to assess the level of reliability and sensitivity of the vehicle. The results showed that the running safety reliability is more sensitive at low values of damping and stiffness of the primary suspension and stability is achieved as they increase while vibration sensitivity increases with increase in damping and stiffness values of both primary and secondary suspension. Furthermore secondary suspension damping and stiffness greatly influence vibration sensitivity as opposed to primary suspension damping and stiffness which exhibits little influence on vibration sensitivity hence secondary suspension damping exhibits the greatest influence on vibration sensitivity while primary suspension stiffness exhibits the least influence on vibration sensitivity.
Investigation of Conflicts Between Railway and Road Network Interaction and Their Impacts on the Operation: The Case Addis Ababa Light Rail Transit
(Addis Ababa University, 2023-07) Sibomana Aime Alphonse; Girmay Kahssay (PhD)
Due to quick financial growth, Addis Ababa city has a high traffic issue, which affects the movement of pedestrians, goods, and tracks where business is also affected. Addis Ababa Light Rail Transit (AALRT)has been involved in solving the problem. This research aims to investigate economic, social, and traffic conflicts caused by the alignment of AALRT and road network, suggest solutions for each conflict investigated, and mitigate for the next LRT project to avoid conflicts. Scenario 1 considered railway and road networks combined, and scenario 2 considered roads without LRT. The parameters for social conflicts were: pedestrians waiting time to cross, pedestrians travelled distance to access the next crossing level, the walkway distance between the railway and road network, safety and security at the crossing level, waiting area before the crossing level, and peak hours effects. The economic conflict parameters were: business owners crossing for services, vehicle supplying goods access to shops, customers and business owners’ vehicles access to shops and Railway alignment contribution on business around, interviews and questionnaires have been delivered, and statistical package for social science (SPSS) has been used to analyse the respondents’ feedback in qualitative aspects and Excel for quantitative aspects. After comparing the parameters of both scenarios, the following conflicts have been shown: long distance travelled to reach the crossing, long waiting time before crossing, insufficient walkway area between railway and road, insufficient security and safety signs at the crossing, difficulties of the vehicles to access shops and traffic congestion at turn bay. Solutions to the investigated conflicts are: to provide an inclusive pedestrian flyover bridge on every 150 m to 200 m of LRT and road network, to provide a walkway of 1.5 m width between railway and road, to install a signalling system at every crossing, to provide vehicles turn bay for freight vehicles and passengers’ vehicles on every 350 m of the systems which will make business easy and feasible. The future project must do a clear investigation during the planning phase; using tunnels and bridges to avoid alignment conflicts is better. The most cost-effective solution is constructing a turn bay that can be used as a zebra crossing and providing a signalling system at every turn bay. The other research can be focused on the design of suitable flyover bridges and turn bays.
Design of Synchronous Reluctance Motor for Light Rail Transit Traction
(Addis Ababa University, 2023-08) Takunda Victor Gadza; Abebe Teklu (PhD)
Trains play a crucial role in modern society transporting a significant portion of the freight and passengers transported worldwide. With increased urban populations, Light Rail Transit (LRT) systems have become one of the important means of transportation for large populations. Therefore, finding less expensive, reliable, and efficient ways of operating these trains is pivotal. In addition, there has also been a huge drive toward environmental conservation. This has resulted in standards and regulations that advocate for increased energy consumption efficiency and cleaner energy sources to reduce pollution-related environmental damage. Traction motors are one of the areas where these improvements may be introduced. Various types of traction motors have been used that include Direct Current (DC) motors, Alternating Current (AC) Induction Motors (IMs), and Permanent Magnet Synchronous Motors (PMSMs). However, these motors have shortcomings, such as inefficiencies in IMs due to rotor losses and expensive material costs in PMSMs due to rare earth permanent magnets. Therefore, finding alternatives with better efficiency and less cost is of paramount importance. One alternative is to replace the IM and PMSM with the Synchronous Reluctance Motor (SynRM). Therefore, this thesis designed a SynRM motor and drive system that can be used for the LRT application as an alternative. The design process includes investigating LRT traction requirements, investigating SynRM characteristics, design of a SynRM model for the LRT, optimizing the model’s performance, and evaluating it using Finite Element Analysis (FEA). The motor was designed for the Addis Ababa Light Rail Transit. A control for the SynRM was also generated using SyR-e software and simulated. The SynRM performed comparably to the reference IM with a 4% higher torque output and 5% higher efficiency. It is also three times smaller in volume, weighs 50% less, and the material cost is 40% less than the reference IM. However, the designed SynRM has less power factor than the IM. This is due to the rotor needing a high level of magnetization, leading to an increase in reactive power. This increase in reactive power can then cause a decrease in the motor's power factor.
Modeling and Assessment of Project Risk Dynamics: A Case of Addis-Djibouti Railway Project
(Addis Ababa University, 2022-05) Tesfaye Gashaw; Kassu Jilcha (PhD)
Railway construction projects are characterized by large operations, long construction periods, complex processes, high financial intensity, dynamic environment, multiple stakeholder involvement, and exposure to the external environment. Due to their complexity and dynamic nature as well as the involvement of various stakeholders, the construction projects are exposed to the effects of numerous risk factors leading to delays and cost overruns. Several studies have been conducted on railway construction projects to analyze the impact of project risks. However, few attempts have been made to evaluate the overall dynamics, interrelationships, uncertainty, and feedback effects of risks on project objectives. The purpose of this research is to develop a dynamic risk assessment model that assesses the impact of project risks on delays and cost overruns of the Addis-Djibouti railway construction project. This research has conducted an extensive literature review on construction project risk assessment and the techniques of risk analysis of railway construction projects. From the literature review and experts’ opinion, forty-two construction project risk factors were identified and categorized into design, construction, management, resource, contractual and external risks. A structured questionnaire survey and pairwise comparisons of factors were conducted to obtain the opinions of domain experts on likelihood, impact on delays and cost overruns and interrelationships between risks. The model was developed using fuzzy synthetic evaluation, Bayesian belief network, fuzzy analytic network process, and system dynamics approach. Fuzzy synthetic evaluation and Bayesian belief network were employed to address uncertainty, subjective judgments, data unavailability, and interrelationships between risks and to determine the likelihood of project risks. A fuzzy analytic network process was also adopted to determine the impact of risks on project time and cost taking into account the interdependence and network of project risks. Then, the overall dynamics and feedback effects of the risks were analyzed using system dynamics. The dynamic risk analysis model was implemented on the case project and it was validated using different modeling tests. The findings of the research showed that contractor's lack of experience, right-of-way, incomplete contract details, poor quality of construction, payment delays, design changes, lack of coordination, and client's financial difficulties were identified as the significant risks that have a higher impact on delays and cost overruns. Based on their categories, the results showed that design, construction, and management-related risks have a significant impact on project objectives. The result of dynamic risk analysis showed that design-related risks were the most critical risks that had a greater impact on project cost and time. The proposed model is an effective tool for risk assessment to support project managers, clients, contractors, and stakeholders in decision-making and helps to forecast the impact of risks on delays and cost overruns. The model can be used as a project risk analysis tool for other construction projects to help managers identify significant risks and analyze the interdependence, dynamic, and feedback effects on project objectives. On this basis, it is recommended that design, construction, and management-related risks should be given due attention in managing railway construction projects. Moreover, it is also recommended that project managers should consider the interrelationship, dynamic, and feedback effects of risks to analyze their impact on project cost and time. Further research is needed to analyze the impact of risks on quality and other project objectives. The research made an original contribution to the body of knowledge in project risk assessment in terms of analyzing project risks in a holistic way taking uncertainty, interdependency, and dynamic and feedback effects of risks into account.
Behavior of Addis Ababa Light Rail Transit Embankments under Seasonal Changes in Suction
(Addis Ababa University, 2023-06) Tewodros Gemechu; Tezera Firew (PhD)
This research paper presents research on the behavior of selected embankment sections along the Addis Ababa Light Rail Transit (LRT) experiencing matric suction variation due to seasonal changes. In this study, an extended Mohr-Coulomb soil model in the MIDAS GTX NS software has been utilized to analyze the effect of precipitation on matric suction and by extension on slope stability and settlement prediction of a railway embankment along the North-South direction of the AALRT. The software implementation of the model was initially verified using an already published research on slope stability analysis of unsaturated soil. Climate data analysis has been conducted for a 40-year rainfall data acquired from the Ethiopian Meteorological Agency. Spatial and temporal simulation of matric suction variation has been carried out. The investigation's findings demonstrated that utilizing rainfall observations in the finite element analysis, it is possible to accurately anticipate how the matric suction distribution profile changes over time in an embankment. Results further indicate that as matric suction diminishes, stability is compromised, and settlement increases due to the upsurge in intensity, duration, and frequency of rainfall. The analysis's findings also indicate that one of the most crucial variables influencing rainfall infiltration for unsaturated slopes is rainfall intensity. It has also been made apparent that matric suction (and by extension slope stability and settlement) is highly affected by the location of ground water table. The factor of safety is amplified with raising depth of ground water table. Therefore, establishing the actual GWT is crucial in analysis and monitoring of actual embankments.
Wear Analysis of Freight Train Within Different Curve Parameters Case Study: Ethio Djibouti Freight Train
(Addis Ababa University, 2023-07) Tindiwensi Edison; Haileleoul Sahle (PhD)
This research deals with wear analysis along the Ethio Djibouti freight train under different parameter conditions. The main focus of this research is to understand how different parameters influence wear along the curve during operation, considering the effect of supervision, curve radius, and curving speed after a given distance of operation, such as 20000 km. The measured wear rates strongly correlate with superelevation. Below the equilibrium cant, wear rate rises exponentially as cant deficiency increases. However, further increasing cant beyond equilibrium provides diminishing wear rate returns. This research enhances the fundamental understanding of wheel rail wear mechanics in curves and provides validated tools to predict and mitigate wear.The results show that when the above distance is run under different curve radius creep, the wear volume increases from 6.8 mm to 3.7 mm as the radius increases from 600 to 1200 m, especially on the outside wheels. Wear increased from 6.6 to 7.8 mm as the speed increased from 40 to 100 km/hr. after a distance of 20000 km. Increasing the superelevation from 80 to 140 mm reduced wear due to improved curves from 7.1 to 6.7 mm after 20.00 km, and a significant decrease in wear volume from 8.9 to 2.3 mm outside wheels after a 20.00 km operational distance.
The Influence of Wheel Flat for Low-Speed train Performance due to Contact Load: A Case Study of Ethio-Djibouti Railway (EDR
(Addis Ababa University, 2023-04) Yared Wondiye; Mulugeta Habtemariam (PhD); Awel Mohammed Seid (Mr.) Co-Advisor
Wheel flats are the most common defect that occurs during train operation. When a train wheel is locked during braking, wheel sliding happens, and as a result, wheel flat rises this wheel flat causes severe impact load on both the vehicle and track components, which leads to excessively damaged railway vehicles and tracks. In this scenario, the Low-speed performance of a train generates higher friction on the wheel/rail contact, which causes wear and defects like wheel flat. The rigid multi-body system dynamics simulation considered wheel flat defect and track irregularity were established based on SIMPACK software. The present research work is validated based on measurements and relevant research literature. The current work considered the changes in vehicles running speeds from 40km/hr to 100km/hr and wheel flat lengths from 25 mm to 85 mm and studied the dynamic response (vertical force, lateral force & acceleration of the car body), comfort (vertical/lateral), Ride index (vertical/lateral), the influence of speeds. The results of the analysis showed that the impact load typically rises with running low-speeds and wheel flat lengths, while other parameters, such as vertical acceleration along with its amplitude and power spectrum density rise and reach a maximum value at a specific speed of 70 km/hr, after which it begins to significantly decline. Finally, the results of impact force for the railway vehicle running at different low speeds and with different wheel flat lengths were analyzed with the warning and alarm limts of impact force that can damage the vehicle and tarck components to classify the running condition as safe, moderate and severe operating condition based on the maximum impact force due to the defects.
Strengthening of Pre-Stressed Girder of Railway Bridge Using Carbon Fiber Rein-Forced Polymer
(Addis Ababa University, 2023-06) Awet Tekle; Abraham Gebre (PhD)
The use of composites to strengthen and renew infrastructure is widely accepted around the world. Traditional methods of strengthening structures are expensive, time-consuming, and la-bour-intensive. Carbon fiber reinforced polymers (CFRP) are in use nowadays because they are light and strong materials that are also corrosion-resistant. Carbon Fibre Reinforced Poly-mers (CFRP) plates are regarded as a suitable alternative to strengthen girders due to their high tensile strength and good modulus of elasticity. In this study, prestressed concrete girders were loaded with a static load and reinforced with carbon fiber reinforced polymers (CFRP) sheets. The carbon fiber reinforced polymer (CFRP) plates and sheets used in this study were adhered to the tensile sections of pre-stressed concrete girders with epoxy adhesive. The results, ob-tained from ANSYS numerical analysis, showed that using carbon fiber reinforced polymer (CFRP) plates with epoxy adhesive increases the load carrying capacity of a prestressed girder bridge by 11.4%, 22.36%, and 27.63% when it is strengthened with one layer, two layers, and three layers of carbon fiber reinforced polymers (CFRP), respectively.
Finite Element Analysis of Rail Bending Stress and Deformation Under The Effect of Unsupported Sleeper
(Addis Ababa University, 2023-06) Bethelhem Bekele; Celestine NKundineza (PhD)
Ethiopia, one of the developing countries in the world, has put large affinity towards basic infrastructures like buildings, roads, power supplies needed for the society wellbeing. Among these, railway is one mode of transportation. In several countries, the traditional railway track system is the ballasted track, i.e., consists of rail, rail pad, and concrete or wooden sleeper on ballast and sub-grade. Railway sleepers and ballast are the main structural elements of railway track. The ballast-sleeper interactions include pressure distribution and load transfer to ballast, railway sleepers are aimed to maintain track gauge, guarantee lateral stability of the track and contribute to better geometrical conditions of the track. However, in the case of lose sleeperballast contact, these function of the interaction will be affected. This study examines the effect of rail vehicle speeds and unsupported sleeper as a result of ballast stiffness variation on rail stresses and vertical displacements. The Finite element model which was composed of a single train wheel rotating on a rail supported by evenly spaced five sleepers, laid on a 300mm thick ballast layer, was used. The results show that the decrease in ballast modulus leads to an increase in rail deflections. It is also found that increase in speeds results in an increase of rail deflection and stress. For the deflection of the rail as the speed increases the deflection also increases. In this project considering the speed variation for example at ballast modulus of 120 MPa, for the speed of 20, 40 and 80Km/hr the deflection are 0.187, 0.207 and 0.266mm respectively. In the presence of unsupported sleeper, the rail bending stress increased by 32% and the maximum von-mises stress on rail which is 181.52 MPa occurred when the ballast modulus is 90MPa with a rolling speed of 80Km/hr. For a train moving on 80Km/hr speed, the rail bending stress increases from 51.12 MPa to 72.23 MPa in the existence of unsupported sleeper.
Investigating the Influence of Wheel Wear on Vehicle Dynamic Behavior by Introducing Yaw and Track Irregularity
(Addis Ababa University, 2023-02) Biruk Yifru; Daniel Tilahun (PhD); Awel Mohammed (Mr.) Co-Advisor
This research intends to indicate the influence of wheel wear due to yaw and track irregularity on vehicle dynamic behavior demonstrated in terms of waer depth, derailment coefficient and ride index. Software simulation-based and wear data validation was used. A Hertzian contact model was used for the wheel-rail contact while SIMPACK and in house made MATLAB code of Archard wear model were used for multibody modeling and analysis of wear depth of each wheel. Main influencing factors involved in the analysis were curvature radius, speed, yaw, and track irregularities variations which were demonstrated in terms of wear depth and vehicle dynamic behavior expressed in derailment coefficient and ride index. A 1 km track long specified curve radius, speed, and yaw damper values were devised for the analysis process with a wear factor of 10,000 applied for the wear depth calculation. Based on the analysis, re-profiling analysis was performed till 60,000km with 10,000km interval data extraction and wear depth was found to match close to the values from wear data collected from AALRT. Further case studies also confirmed that 50m radius of curvature resulted the highest wear depth (6.18mm) and higher derailment coefficient (1.01) and unconfortable despite the existence of yaw damper or track irregularity. Yaw at lower running speeds on the other hand didn’t affect much the ride index while it improved the derailment coefficient. But when speed becomes higher and its value increased, wear depth reduced and both ride index and derailment coefficient deteriorated. Finally, track irregularity alone brought only slight disturbance to the derailment coefficient and ride index. But it has significant increase to both values when combined with factors like yaw. As a result, measures shall be taken to minimize the combined effect of yaw and track irregularity.
Modeling and Analysis of Rail Pad Stiffness on Ballasted Railway Track
(Addis Ababa University, 2023-07) Chebaran Jonex; Henok Fikre (PhD)
Railway infrastructure, has become the most competitive transport means due to its unique advantages (efficiency, transportation capacity, low environmental impact, etc). Rail pad is the regularly used resilient element, and is very crucial as it act as a softening medium between rail and sleeper. A soft rail pad permits a larger rail deflection which lead to the fatigue of this component or others like the fastener system but allows the axle load from the train to spread over more sleepers/ties. In contrast, stiff pads cause larger dynamic actions on the infrastructure components such as sleeper and ballast material. Low stiffness rail pads of less than 100 kN/mm have been recommended in a number literature implying a potential neglect of associated problems of excessive rail displacement caused by very soft rail pads. This is the basis for motivation of this study to analyze the effects of rail pad stiffness on ballasted railway track so as to recommend rail pad stiffness that contributes towards minimal rail displacement and sleeper acceleration. A 3D numerical model was established using ABAQUS/CAE 6.14 to carry out the investigation. The FEA model entails a rolling wheel, UIC 54 rail, rail pads, concrete sleepers, ballast and subgrade. The prepared model was verified with a laboratory experiment that replicated a ballasted track section (from one reference paper [1]). The basic parameters used in the model were synonymous to that of the experimental test and was in compliance with literature and the different standards such AS1085.14, AREMA and other acknowledged publications. Track behavior was noted in the form of stress, displacement, acceleration and corresponding rail seat loads to categorize the stiffness of the rail pad, that limits the negative extremes in track behavior. Parametric studies were executed with various rail pad stiffness to understand their consequence on the behavior of track components; rail and sleeper. This study showed that, with increase in rail pad stiffness at 200 and 300 kN/mm rail pad stiffness, the rail vertical displacement decreases by at least 64-73% and 79-83%, rail vertical acceleration decreases by 37-56% and 56-77%, while rail vertical stress increased by 44-57% and 68-73%, the rail seat loads increased by 52-56% and 68-74% under static loading and increased by 37% and 55% under dynamic loading, the sleeper vertical acceleration increased by 55% and 62%. Due to correlation behavior of most of the out puts with increasing stiffness of rail pads, rail vertical displacement and sleeper vertical acceleration were chosen as the two criteria for selecting the most suitable rail pad stiffness. Even though some researchers recommend soft rail pads below 100 kN/mm rail pad stiffness, which could increase rail movements and deflection, this research study has recommended rail pad stiffness of 150 kN/mm with 48% reduction in rail displacement and 44% increase in sleeper acceleration. This is also in an agreement with recommendation of Nazmul Hasan (2019) [2], that the softest rail pad should not be less than 100 kN/mm and desired range is 116-256 kN/mm.
Evaluation of Remaining Fatigue Life of Pre-Stressed Concrete Railway Bridge
(Addis Ababa University, 2023-06) Gebremedhin Kidus; Abrham Gebre (PhD)
Nowadays reinforced bridges are being replaced by pre-stressed bridges because of their cost efficiency and serviceability. Pre-stressed concrete railway bridges are widely used in various parts of the world. Their main function is to transfer load coming from the track supper structure to the sub-structure part like of that pier through bearing. The bridges are mostly failed by fatigue failure as a result of repeated cyclic load. Previously, the fatigue life of the railway bridges subjected to design and operational loading on these loading capacities, has not been well investigated on the Addis Ababa LRT. The general objective of this thesis is to estimate the remaining fatigue life of pre-stressed concrete railway bridge subjected to operational cyclic load. The study addresses the fatigue life of pre-stressed concrete railway bridge of Addis Ababa Light Rail Transit as a case study. Imperative issues like load application, bearing profile and arrangement of static analysis results to generate the data for fatigue evaluations have been studied. To implement this numerical approach, ANSYS 2020 was used. The minimum fatigue life obtained is 1e8 cycles. These number of cycles correspond to about 114.16 years which is 14 percent more than the design life of the railway bridge. The railway bridge serves more than the design life of 100 years (175,200,000 cycles). However, other parts of the railway bridge, especially the steel bearing section can attain life greater than 1e10 cycles (infinite life).
Fatigue Life Prediction of a Railway Bogie Frame due to Wheel Out-of-Roundness. A Case Study of Ethio-Djbouti Railway
(Addis Ababa University, 2023-08) Hakizimana Jean De Dieu; Haileleoul Sahle (PhD)
Railway transportation is one of the most common effective, safe and efficient mode of transportation used in many countries around the world. However, the failure of a bogie frame as a vital component that supports almost overall weight of the vehicle, can significantly affect the operation system. Mostly, it fails due to fatigue phenomenon brought on by various impact. The purpose of this research is to predict the fatigue life of a bogie frame due to wheel out-of-roundness (OOR). This research was focused on a freight bogie at Ethio-Djibouti railway (EDR), mostly faced with fatigue failure due to high load compare to a passenger vehicle. Wheel OOR cases have been integrated into a multibody system model with SIMPACK where dynamic loads that act on a frame have been extracted and applied to the finite element model with ANSYS to get stress and strain distributions used to predict lifecycles. Through the simulation scenarios with three cases of out-of-roundness with maximum radius deviation of 1 mm, 2 mm and 5 mm, the results show that the wheel OOR with high amplitude induce high non-monotonic impact forces that account for high stresses and reduce the life of a bogie frame. The results from this study show that the lifecycles are 8.2e7, 7.2e6 and 4.4e5 cycles for the case of out-of-roundness with 1 mm, 2 mm and 5 mm radius deviation, respectively. It shows that the bogie frame can operate below recommended fatigue lifecycles which is 2e6 cycles at the case of OOR with 5 mm and the study recommend to operate at wheel OOR with radius deviation below 2 mm. This study has significant to the maintenance department to enhance the countermeasures for minimizing the effects of OOR on bogie frame’s life.
Investigation of Ballast Degradation on Bike- Dewele Railway Line
(Addis Ababa University, 2023-10) Yohannes Embibel; Henok Fikre (PhD)
Rail tracks are often placed on ballast which offers the desirable resiliency to cyclic loads. Modernization of railway transportation in terms of increasing axle load and speed focused on ballast layer as a key component of conventional railway track. The ballast layer undergoes gradual and continuing degradation with usage and time due to increasing traffic passage, loads and speed. The rate and magnitude of ballast degradation depends on ballast quality, environmental exposure, geometry profile, speed, and number and magnitude of axle loadings. Intolerable degradation cause track geometry deterioration due to track settlement as a result of excessive permanent deformation of the ballast layer. Understanding the degree of ballast bed degradation under cyclic loadings helps to either making standardization or planning for maintenance schedule. This study was conducted to determine the extent of ballast degradation along the Bike-Dewele section of the Ethio-Djibouti railway line following five years of operation. This study collects data on ballast degradation through visual inspections in the field and laboratory tests. Visual inspections were conducted following such as vegetation growth, surface fines, crib and shoulder ballast missing, cobles on the main track, more degraded ballast sections. On samples of ballast collected from ten (10) locations along the Bike-Dewele sections, laboratory tests including gradation (sieve analysis), Los Angeles Abrasion, shape tests (Elongation and Flakiness) and Fouling index were conducted, as well as design and as-built data reviewed. Gradation was determined by calculating the percentage shift of each PSD curve from the as-built PSD curve limits. Additionally, other tests were compared to the recommended standard at each location. The investigation discovered that the ballast on the Bike-Dewele section within five years of operation, there is significant deterioration of ballast, as shown by the PSD curves shifting above the as-built maximum values of 40-115 percent. Improper ballast aggregate addition has been found, as indicated by PSD curves dropping below the as-built minimum value of 41-180 percent. The majorities of ballast aggregates throughout the Bike-Dewele stretch are broadly graded and fall within as-built data, while others are even more broadly graded than as-built data. The resistance of the present ballast to abrasion is between 76 and 87%, when the values are compared to the recommendations in various standards, it can be concluded that the ballast is still capable of carrying the imposed loads. The shape property index tests show that particle shape has been rapidly changing (highest FI value is 37% and highest EI value is 46%) and the material is deteriorating. While conducting a field investigation, discovered that several portions of the ballast were highly fouled, but that sampling was not permitted.
Zone-based Fare Integration for Public Transport in the Case of Addis Ababa City
(Addis Ababa University, 2022-06) Toyiba, Mohammed; Sosina, Mengstu (PhD)
The most important technique to establish an efficient and modernized public transportation system is to conduct studies on it. In terms of economic and social growth, public transportation is essential. Furthermore, providing integrated fare systems is critical for creating effective public transportation that enables the pursuit of objectives such as maximization of demand, maximization of revenue, profit, and social welfare. The goal of this research is to propose a fare integration system of public transportation using a zone-based fare structure in the case of Addis Ababa city. The study reviewed the current fare system, identify economic and social problems due to the lack of a fare integration system, examined the best zone partition and zone-based fare setting approaches, and proposed, identified, and verified the main benefits of the applying zone based fare integration system of public transportation such as maximization of revenue, maximization of profit, reduction of fare, and minimization of passengers waiting time. In order to create the fare integration system, the zone is partitioned analytically using the value of the weighted mean travel distance of the ride in a city and the K-means clustering algorithm is employed to model the segmented zone and the zone-based fare also determined based on the principle distance- based expense. Accordingly, the new proposed system for users' 16.66% reduction of fares, 32.33% minimization of passengers waiting time and for operators' maximization of revenue by 31.52% and maximization of profit by 75.77% against the existing system. And the result clarified using a numerical explanation with a graph.
Design of C/SiC Composite Brake Disc for AALRT Finite Element Method
(Addis Ababa University, 2016-06) Tekle, Asegehegn; Daniel, Tilahun (PhD)
Gray cast iron is commonly used brake disc material with high density that increase fuel consumption. It also generates heat easily during braking due to its lower specific heat capacity which affects its mechanical properties. The ever increasing demand for high speed trains from passengers and reduction of maintenance costs by operators means a compelling need to develop new disc brake materials with higher friction performance and longer service life. An interesting alternative are C/SiC composite materials characterized by lower wear rate and higher resistance to thermal shock. During braking kinetic energy transforms in to thermal energy resulting to intense heat and high temperature in the brake disc-pad interface. Thus, induced thermal loads determine thermo-elastic behavior of the railway disc brake structure. This paper is mainly concerned with design analysis of C/SiC composite material to study and evaluate the performance under severe braking conditions and there by assist in brake disc design and analysis. Geometric dimensions of AA LRT train disc are taken on to CATIA where the 3D model is imported to ANSYS for determining the temperature distribution, variation of stresses and deformation produced in the disc brake after applying the boundary conditions. The main boundary and initial condition are the heat flux on the braking surface of the disc and the force of the brake clamps. Two different disc designs are used, one solid and other the ventilated existing one to demonstrate the material response for each variant. The aim is to investigate the structural deformation of the brake disc due to combined effect of thermal expansion when subjected to temperature change during the braking cycle and thereby assist the railway industry in developing optimum and effective disc brake material. The results were found to be satisfactory.

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