177 research outputs found
Minimization of railhead edge stresses through shape optimization
No full textThe railhead is severely stressed under the localized wheel contact patch close to the gaps in insulated rail joints. A modified railhead profile in the vicinity of the gapped joint, through a shape optimization model based on a coupled genetic algorithm and finite element method, effectively alters the contact zone and reduces the railhead edge stress concentration significantly. Two optimization methods, a grid search method and a genetic algorithm, were employed for this optimization problem. The optimal results from these two methods are discussed and, in particular, their suitability for the rail end stress minimization problem is studied. Through several numerical examples, the optimal profile is shown to be unaffected by either the magnitude or the contact position of the loaded wheel. The numerical results are validated through a large-scale experimental study
Effect of Central Queensland sands on the shear capacity of concrete masonry containing damp proof course
No full textThe damp proof course (DPC) effectively breaks the bond between the masonry units and mortar Joints. The actual shear capacity that includes the shear bond strength and the frictional resistance is evaluated for hollow concrete block masonry joints containing DPC from seventy-two wallet tests. The effect of three mortar sands that are representative of the region of central Queensland is also investigated. It is shown that the type of sand in the mortar affects the shear capacity considerably. Other variables that affect the shear strength include the level of vertical stress and the inclusion ofDPC in mortar joint.constitutive relations for materials under complex 3D states of stress by judiciously designing an experimental setup involving complex shapes of structures with simple load application, which will significantly reduce the costs of generating complex 3D loading on simple shapes of specimens as traditionally followed. The material parameters obtained are more realistic as they account for the true status of the structures
Research outcomes for improved management of insulated rail joints
No full textInsulated Rail Joints (IRJs) are safety critical component of the automatic block signalling and broken rail detection systems. IRJs exhibit several failure modes due to complex interaction between the railhead ends and the wheel tread near the gap. These localised zones could not be monitored using automatic sensing devices and hence are resorted to visual inspection only, which is error prone and expensive. In Australia alone currently there are 50,000 IRJs across 80,000 km of rail track. The significance of the problem around the world could thus be realised as there exists one IRJ for each 1.6 km track length. IRJs exhibit extremely low and variable service life; further the track substructure underneath IRJs degrade faster. Thus presence of the IRJs incur significant costs to track maintenance. IRJ failures have also contributed to some train derailments and various traffic disruptions in rail lines. This paper reports a systematic research carried out over seven years on the mechanical behaviour of IRJs for practically relevant outcomes. The research has scientifically established that stiffening the track bed for reduction in impact force is an ill-conceived concept and the most effective method is to reduce the gap size. Further it is established that hardening the railhead ends through laser coating (or other) cannot adequately address the metal flow problem in the long run; modification of the railhead profile is the only appropriate technique to completely eliminate the problem. Part of these outcomes has been adopted by the rail infrastructure owners in Australia
Sleeper embedded insulated rail joints for minimising the number of modes of failure
No full textInsulated rail joints (IRJs) identify broken rails and train locations in railway signalling circuitry, which are critical to the rail safety operation. Unfortunately, IRJs exhibit several failure modes due to complex interaction between their components, the load spectra and the support conditions. A novel idea of simplifying the design of the IRJs consisting of only two pieces of insulated rails embedded into a concrete sleeper in such a way that the free ends of the rails at the gap attain stiffness commensurate to that of the current designs where the gapped rails are connected with two joint bars (also known as fishplates) one on each side of the rail web with the assembly resting on top of sleepers. The advantages of the new design are that it exhibits stability levels comparable to the current designs with fewer components and hence fewer failure modes. A multi-objective optimisation framework was used for the development of the new design that enables safe passage of train wheels across the gap between the rails embedded in concrete sleepers. Feasibility of the sleeper embedded gapped insulated rails under traffic loading is demonstrated through a dynamic analysis of a rail wheel rolling on top of a selected optimal design from the Pareto front. The deformation components of the rail edge at the gap of the new design are shown to be lower than that of the classical insulated rail joints
Dynamics of railway wagons subjected to braking torques on defective tracks
No full textIt is well known that track defects cause profound effects to the dynamics of railway wagons; normally such problems are examined for cases of wagons running at a constant speed. Brake/traction torques affect the speed profile due to the wheel–rail contact characteristics but most of the wagon–track interaction models do not explicitly consider them in simulation. The authors have recently published a model for the dynamics of wagons subject to braking traction torques on a perfect track by explicitly considering the pitch degree of freedom for wheelsets. The model is extended for cases of lateral and vertical track geometry defects and worn railhead and wheel profiles. This paper presents the results of the analyses carried out using the model extended to the dynamics of wagons containing less ideal wheel profiles running on tracks with geometry defects and worn rails
Studies on the existing in-plane shear equations of partially grouted reinforced masonry
No full textThis paper provides critical analyses of the presence of the reinforced grout cores within the masonry walls with particular reference to the existing in-plane shear design expressions in several national standards; these expressions comprise terms which define the shear strength of masonry, the vertical load and the area of reinforcement. \ud
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These expressions treat the wall height to length ratio (termed as wall aspect ratio) as a prime factor in their respective masonry strength terms. The consideration of the wall aspect ratio in these design expressions implies existence of a compression strut along the wall diagonal, although such a phenomenon is not established in the literature. \ud
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In this paper, through an extensive analyses of partially grouted reinforced masonry shear walls using a validated nonlinear finite element model, it is shown that the aspect ratio of the unreinforced masonry panels inscribed within the vertical and the horizontal reinforced grouted cores has profound effect on the in-plane shear capacity of the walls. \ud
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It is also shown that the horizontal and the vertical reinforcements do never yield and hence their inclusion in the in-plane shear capacity expressions is not justified. A recently reported expression by the authors is also reviewed and compared with the other international design expressions
Modelling the failure of thin layered mortar joints in masonry
No full textThis paper deals with the failure of high adhesive, low compressive strength, thin layered polymer mortar joints in masonry through a contact modelling in finite element framework. Failure due to combined shear, tensile and compressive stresses are considered through a constitutive damaging contact model that incorporates traction–separation as a function of displacement discontinuity. The modelling method is verified using single and multiple contact analyses of thin mortar layered masonry specimens under shear, tensile and compressive stresses and their combinations. Using this verified method, the failure of thin mortar layered masonry under a range of shear to tension ratios and shear to compression ratios has been examined. Finally, this model is applied to thin bed masonry wallettes for their behaviour under biaxial tension–tension and compression–tension loadings perpendicular and parallel to the bed joints
Analysis of Rail Ends under Wheel Contact Loading
No full textThe effect of the discontinuity of the rail ends and the presence of lower modulus insulation material at the gap to the variations of stresses in the insulated rail joint (IRJ) is presented. A three-dimensional wheel – rail contact model in the finite element framework is used for the analysis. It is shown that the maximum stress occurs in the subsurface of the railhead when the wheel contact occurs far away from the rail end and migrates to the railhead surface as the wheel approaches the rail end; under this condition, the interface between the rail ends and the insulation material has suffered significantly increased levels of stress concentration. The ratio of the elastic modulus of the railhead and insulation material is found to alter the levels of stress concentration. Numerical result indicates that a higher elastic modulus insulating material can reduce the stress concentration in the railhead but will generate higher stresses in the insulation material, leading to earlier failure of the insulation materia
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