Numerical and experimental investigations into time-dependent effects of prestressed concrete sleepers

It is commonly believed that railway is the safest transportation system for either passengers or freight. Rail operators consistently demand better performance and durability of prestressed concrete sleepers to compete effectively with other transport modes. Track structures guide the safe, economical, and comfortable transit of trains. At present, the use of prestressed concrete sleepers is on the rise around the world as they are more durable, with a life span of 50 years worldwide (70 years in the UK), economical as compared to wood and steel, and easier to manufacture. However, over a long-term service, railway prestressed concrete sleepers are subject to various time-dependent actions, which results in the reduction of durability and capacity. Over decades, the premature failures of traditional railway sleepers have significantly increased track maintenance costs. Due to the need for increased service loads and faster train speed being applied to conventional tracks, the current designs of prestressed concrete sleepers for long-term services may be estimated, largely due to the lack of thorough understanding into the mechanisms of sleeper degradation. In order to study the mechanisms of sleeper degradation over time, significant research effort for railway engineering and technologies has been conducted to perform comprehensive investigations of prestressed concrete sleepers subject to time-dependent actions. The structural performance, material, loading conditions, capacity, support conditions, and environmental conditions of prestressed concrete sleepers have been considered fully. Collaborative research between the University of Birmingham (UoB) and other international railway research institutions such as China Academy of Railway Sciences (CARS), Southwest Jiaotong University (SWJTU), Tsing Hua University (THU), Beijing Jiaotong University (BJJTU) has investigated such important issues as the deformation due to time-dependent actions in prestressed concrete sleepers and capacity of prestressed concrete sleepers. The comprehensive literature review highlights the extremely limited research that has previously been conducted in this field of research. The investigations have been carried out in order to enhance the understanding into time-dependent behaviours of prestressed concrete sleepers. Moreover, this thesis provides an intensive review aimed at predicting time-dependent behaviours in different design codes. Experimental and numerical investigations into the time-dependent behaviours of prestressed concrete sleepers are presented in this thesis. A series of full-scale experiments were conducted in a laboratory and at a railway sleeper factory in order to validate and calibrate the numerical models. The deformation measurements were carried out to predict creep and shrinkage behaviour. Capacity tests has been conducted to identify crack propagation and cumulative damage has been identified in order to calculate fatigue life. The effect of environmental factors on time-dependent behaviours is also presented, while numerical investigations of the time-dependent behaviours of prestressed concrete sleepers have been undertaken to supplement the experimental results in this thesis. The key findings will enhance the development of inspection criteria for railway prestressed concrete sleepers subject to time-dependent actions, improve safety and reliability of railway infrastructures in long-term service.