Optimisation model to schedule railway track renewal operations: a life-cycle cost approach

Besides high initial construction costs, ballasted railway tracks also have high investment requirements, related to maintenance and renewal (M&R) works. Decision support tools for railway track components that optimise these works are increasingly gaining in importance. This paper presents an optimisation model that integrates ballast, rail and sleeper degradation models in a mixed integer linear programming model. This model links the decisions to renew these components with their condition and takes advantage of the integrated planning of renewal works to minimise the railway track life-cycle cost (LCC). The practical utility of the model is illustrated with a case study involving the Portuguese Lisbon–Porto line. The results indicate a reduction in track renewal cost if the grouping of components, track segments and time interval for renewal operations are optimised. Furthermore, this paper demonstrates that possible annual budget restrictions for railway track M&R operations can have an important influence on the railway track LCC.     

Optimal intervention strategies for multiple objects affected by manifest and latent deterioration processes

In the existing infrastructure management systems, optimal interventions strategies (OISs) are determined for objects that deteriorate gradually (manifest deterioration process, MDPs), under the assumption that with appropriate inspection and intervention strategies the probability of failure of object can be neglected. Objects that deteriorate suddenly (latent deterioration process, LDPs), for example, due to scouring during a flood or earth movements during an earthquake are not considered. The determination of OISs for an object that deteriorates due to both MDPs and LDPs requires the consideration of both. The latter, however, means that the probability of failure of the object must be considered. In this article, a Markov model is presented that can be used to determine OISs for multiple objects of multiple types affected by uncorrelated MDPs and LDPs. The model is an extension of the model proposed by Mayet and Madanat (Incorporation of seismic considerations in bridge management systems. Computer-Aided Civil and Infrastructure Engineering, 17:185–193, 2002). In the model, a set of condition states (CSs) is used to describe the condition of objects of each type, where each set is composed of non-failure CSs and failure CSs. The probabilities of going from each non-failure CS to each failure CS are estimated using normalised fragility curves, and the probabilities of going from each non-failure CS to each non-failure CS are initially estimated using the Markov deterioration prediction model of Kobayashi, Kaito, and Lethanh (A Bayesian estimation method to improve deterioration prediction for infrastructure system with Markov chain model. International Journal of Architecture, Engineering and Construction, 1:1–13, 2012a) and later adjusted taking into consideration the probabilities of entering the failure CSs. The use of the model is demonstrated using a road link comprising one road section and one bridge.     

Optimal FRP-strengthening strategy for corrosion-affected reinforced concrete columns

Abstract

Deterioration of reinforced concrete (RC) structures is unavoidable after their long time in service, with corrosion being the major mechanism of deterioration. In order to ensure safety of deteriorated structures, an effective rehabilitation plan is essential. Although considerable research on strengthening of RC structures using fibre-reinforced polymers (FRPs) composites has been undertaken, more is on the methods of strengthening and effects of corrosion on strength of RC columns than that on the prediction of optimum strengthening time. This paper presents a methodology for determining the optimal strengthening time and the required number of FRP layers for corrosion-affected RC structures with application to columns. The methodology is based on the time-dependent reliability method and the renewal theory. An example is provided to illustrate the application of the proposed methodology. It is found in this study that an optimum point for the formulated objective function exists, and that outcomes of optimisation problem, i.e. strengthening time and number of required FRP layers, are sensitive to corrosion rate. The significance of the proposed methodology is that it provides guidance for practitioners and asset managers to decide when and how to strengthen deteriorated structural members.     

Evaluation and optimisation of receiver height in a compound parabolic collector with low acceptance angle

This research presents the method of finding an optimised location of a tubular receiver for a compound parabolic collector (CPC) with 6° acceptance angle. Due to low acceptance angle, reflected rays concentrate below the focus of a parabola. Graphical ray tracing (GRT) approach is implemented to execute the optical analysis with and without manufacturing error in the collector. It is performed on collector–receiver combinations by varying receiver height below the focus and they are compared on the basis of utilised area and projection ratios. The ideal cases of collector–receiver combinations which contribute high utilisation and projection ratio are selected and verified with the camera target method (CTM) performed on the actual set-up. It is built for water heater application to validate the results obtained from GRT and CTM. The thermal performance of CPC at various receiver heights is compared by thermal efficiency and therefore the optimum receiver height is concluded.     

Optimum design of slurry pipelines by genetic algorithm

Various applications of slurry transportation through pipelines exist. A transportation problem is formulated to determine the pipe diameters and amounts of transported slurry from the production to the consumption points. The minimisation of the cost consisting of the pipe and energy cost terms is considered as the objective function. Pipe cost is given as the function of pipe diameters and the energy cost is defined as the function of pipe diameters and slurry amounts. Energy cost is obtained by using the relation that is previously determined after the experimental studies have been made for the magnetite ore. Genetic algorithm is used as the optimisation method and to apply this method a commercially available software written in the C language is used and modified. The proposed methodology to solve this non-linear programming problem is applied to a transportation system and it is found that the proposed methodology has made the complex, labour-intensive solution process very convenient for the users.     

Optimising a modular expansion of a wastewater treatment plant

In the design of a wastewater treatment plant, engineers must estimate the future population that the plant will need to serve. When the population growth is uncertain, modular design can reduce up-front capital costs, operating costs and total expected present value costs. Models based on real option theory can provide insights to engineers/decision-makers that will not arise from standard net present value analysis. We consider a municipality faced with a plant expansion decision required to meet the demand of significant, uncertain growth. We present a model that optimises the size of the plant and its maximum modular size. The optimisation requires that multiple solutions be calculated at the decision time for the staged expansion. We utilise a moment matching technique to approximate the solution of the Asian-like option. The results show that as the uncertainty increases, a modular plant can save significant total costs for the municipality.     

A simulation optimisation tool for planning of low-income housing projects

Construction of low-income housing projects is a recurring process and is associated with uncertainties that arise from the unavailability of resources. This paper presents a case study that discusses how computer simulation and optimisation are used to aid government agencies and/or contractors in planning of such projects. It illustrates the optimisation of project objectives, taking into consideration the interaction amongst involved resources. As such, total duration and the associated total costs, including direct and indirect costs, can be estimated and optimised. One Youth Habitation project that is executed in 6th of October City in Egypt is analysed in a step-by-step procedure to demonstrate the capability of proposed computer simulation and optimisation prototype (named LIHouse{_}Sim) in the modelling construction of low-income housing projects using bearing block walls with hollow core technique. The presented tool proves its practicality to contractors in estimating the time and costs of the recurring process of low-income housing construction, considering complex interdependencies between construction resources and the uncertainties associated with construction activities. The LIHouse{_}Sim prototype is used to perform a wide analysis for the alternative of the effective optimisation criteria in the bearing block walls/hollow core technique and for the genetic algorithm optimisation approach elements.     

供热系统优化规划方法研究

提出了适用于供热系统的两级优化规划方法，即第一级的布局优化和第二级管网的多目标优化方法。运用最优化理论建立的布局优化模型和管网系统多目标优化模型及采用的求解方法，适用于所有具有“管一站”网络特征的系统。     

Multi-disciplinary collaborative building design—A comparative study between multi-agent systems and multi-disciplinary optimisation approaches

The importance of collaboration between different design disciplines has been widely recognised by the building industry. Traditionally this is achieved through physical meetings between the representatives of different design groups. However, this is facing more challenges when dealing with large and complex design problems. Various approaches have been introduced to tackle this problem, such as multi-agent systems (MAS) and the multi-disciplinary design optimisation (MDO) approaches. The former represents an advanced, ICT-based framework which facilitates collaborative design through communication, data and knowledge sharing and negotiation while the latter represents a theoretical modelling approach which facilitates collaborative design through a thorough analysis of the technical problems. By comparing the strengths and weaknesses of these approaches in facilitating collaborative design, this paper provides a roadmap study for the development of collaborative building design.