Optimising strategy selection for the management of railway assets

In the railway industry a main concern is how to manage efficiently and effectively the railway assets under budget constraints. Optimal asset management involves decision making and selection of the best inspection, maintenance and renewal interventions for each asset along the network. This paper presents an optimisation method for supporting the decision making process. The method is based on a two-level approach. At a lower level, asset models combining degradation and intervention processes are used in order to evaluate the effects of different intervention strategies on the evolution of the asset state over time. On a system-level, a Knapsack-type optimisation model is developed to selects the optimal combination of intervention strategies to apply to all assets in the network in order to deliver the required level of performance while minimising the whole lifecycle costs

A Petri net model for railway bridge maintenance

This article describes the application of the Petri net modelling approach to managing the maintenance process of railway bridges. The Petri net model accounts for the degradation, inspection and repair processes of individual bridge elements in investigating the effectiveness of alternative maintenance strategies. The times governing the degradation and repair processes considered are stochastic and defined by the appropriate Weibull distribution. The model offers a capability for modelling the bridge asset which overcomes the limitations in the currently used modelling techniques reported in the literature. The bridge model also provides a means of predicting the future asset condition as a result of adopting different maintenance strategies. The solution of the Petri net model is performed using a Monte Carlo simulation routine. The application of the model to a typical metal railway bridge is also presented in the article

Optimising strategy selection for the management of railway assets

In the railway industry a main concern is how to manage efficiently and effectively the railway assets under budget constraints. Optimal asset management involves decision making and selection of the best inspection, maintenance and renewal interventions for each asset along the network. This paper presents an optimisation method for supporting the decision making process. The method is based on a two-level approach. At a lower level, asset models combining degradation and intervention processes are used in order to evaluate the effects of different intervention strategies on the evolution of the asset state over time. On a system-level, a Knapsack-type optimisation model is developed to selects the optimal combination of intervention strategies to apply to all assets in the network in order to deliver the required level of performance while minimising the whole lifecycle costs

Linear ViscoElastic (LVE) Behaviour of Pure Bitumen via Fractional Model

By fitting experimental data from static creep/recovery carried out on pure bitumen, it is shown that the fractional model proposed enables the description of both creep and recovery behaviour with fewer parameters than those needed by other models in the literature. In particular, the model is fitted to experimental data of complex modulus |G*| and phase angle δ° obtained from Dynamic Mechanical Analysis. Lastly, it is demonstrated that when the fractional model is used, complex modulus isotherms for a range of frequencies can be created simply starting from isochronals at f = 1Hz

Experimental validation of a fractional model for creep/recovery testing of asphalt mixtures

Prediction of asphalt mixtures\u2019 behavior during their service life is a challenge due to its complexity and sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements arranged in series or in parallel (analogical models) have been proposed and specified for both bitumen and asphalt mixtures. The corresponding constitutive laws always involve first order derivatives of time with exponential type solutions but problems in setting parameters arise when both the creep and recovery behavior have to be modeled. In this paper it is shown that experimental creep data follow a power decay law, rather than an exponential one. As a consequence, a simple fractional model is here proposed for predicting creep/recovery behavior of asphalt mixtures with a small number of parameters and low computational efforts with respect to the classical analogical models. The proposed model is then calibrated by a best fitting procedure on experimental data from creep and creep/recovery tests carried out on asphalt mixtures under different load and temperature conditions

New helicoidal spindle for mixing and viscosity measurements of tyre rubber modified binders

The use of modified bituminous binders, in place of pure bitumen, is a common practice to enhance performance of road pavements. The measurement of rheological properties of the modified binders is often challenging due to presence of suspended solids. Phase separation during the course of measurements makes viscosity of non-homogeneous blends, such as tyre rubber modified bitumens, difficult to ascertain. In this study, a new spindle was designed and manufactured to be used with a rotational viscometer in order to adapt the viscometer as a low shear mixer and to guarantee reliable viscosity measurements of samples which contains suspended particles. This helps optimize the modification process of tyre rubber modified bitumen by having a reliable real-time viscosities measurement. Spindle geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain investigate this. Development of prototype spindles was undertaken using a layer based manufacturing technique which allows the rapid realisation of a design intent which could not be achieved in another fashion. In this case nested features are created in a prototype to verify the design before a fully functional prototype is produced using conventional 4-axis machining. The new spindle allows the Brookfield viscometer to be used as a low shear mixer of small volumes of bitumen-rubber blends while allowing real-time reliable measurements of the viscosity