Numerical modelling of the deterioration of the Parisian metro infrastructures based on a new auscultation method

Many underground transport systems have aged and need heavy maintenance. Most of these tunnels have been affected by diverse weathering processes that have led to superficial or deep deterioration of the structure. To schedule maintenance operations, managers of these infrastructure networks need to assess the current state of tunnels. However, current diagnostic methods are mainly based on visual observations that cannot completely characterise the current state of these structures and predict the kinetics of degradation and its effect on the structural behaviour over time. In this context, we propose a methodology designed to obtain a state of deterioration of infrastructures and their evolution over time by integrating different parameters into the geometry of the tunnels and the value of the mechanical parameters of each zone (tunnel components and the ground). A numerical modelling procedure based on the parameters derived from a new methodology for auscultation is used to highlight the most damaged areas, which can disrupt the stability of the underground structures. The instantaneous decrease in the mechanical parameters of galleries is considered (from the initial state) to reproduce different states of alteration displayed on different surveys. Several scenarios are proposed to indicate the possible degradation observed on this underground.     

A deep reinforcement learning approach to mountain railway alignment optimization

The design and planning of railway alignments is the dominant task in railway construction. However, it is difficult to achieve self-learning and learning from human experience with manual as well as automated design methods. Also, many existing approaches require predefined numbers of horizontal points of intersection or vertical points of intersection as input. To address these issues, this study employs deep reinforcement learning (DRL) to optimize mountainous railway alignments with the goal of minimizing construction costs. First, in the DRL model, the state of the railway alignment optimization environment is determined, and the action and reward function of the optimization agent are defined along with the corresponding alignment constraints. Second, we integrate a recent DRL algorithm called the deep deterministic policy gradient with optional human experience to obtain the final optimized railway alignment, and the influence of human experience is demonstrated through a sensitivity analysis. Finally, this methodology is applied to a real-world case study in a mountainous region, and the results verify that the DRL approach used here can automatically explore and optimize the railway alignment, decreasing the construction cost by 17.65% and 7.98%, compared with the manual alignment and with the results of a method based on the distance transform, respectively, while satisfying various alignment constraints.     

Characterization of the masonry lining of an underground structure by geoendoscopy

Maintenance and sustainability of underground structures are the major tasks for infrastructure owners. To carry out these tasks, managers need to qualify the actual state of these facilities. There are very few operational methods to describe separately each component of an underground structure (structure lining, contact interface and surrounding soil). Therefore, most usual diagnosis methods are qualitative and focus the surveying operations on the tunnel intrados. In consequence, they collect limited quality information for maintenance decision.This article focuses on a new methodology for diagnosis of the lining status of an underground structure in order to obtain a mechanical characterization of materials.The methodology is based on an analysis of low diameter drillings on tunnel lining using geoendoscopy and automatic image recording. Then an automatic image processing, is applied on the recorded images in order to locate discontinuities and evaluate the tunnel lining condition. A definition of lining layers were adopted thanks to discontinuities rate criteria. In parallel, a comparative study of the mechanical parameters of old masonry materials by laboratory test cores’ samples was carried out Finally, based on the result of the geoendoscopy analysis and on the laboratory study the methodology establishes a link between the local state of the lining and the mechanical parameters of materials.The application of this methodology to carry out an evaluation of masonry lining of the Paris Metro System shows that the proposed method and tools are particularly well adapted to obtain masonry lining characterization at the local scale. It has been possible to identify each discontinuity leading to a grade of masonry alteration. Using this information it was possible to define a simplified model of lining by sectioning the masonry thickness on three homogenized layers with different mechanical properties.     

Development of improved railway track degradation models

There is a need among railway track maintenance programmers for a better understanding of the long-term behaviour of railway track systems and for improved predictive techniques. The use of accurate techniques to predict railway track conditions increases track safety and maintenance effectiveness. The aim of this research is to improve current track deterioration modelling techniques using a comprehensive field investigation. Statistical and engineering approaches are adapted for this research and comprehensive track field data is collected and analysed over a period of 2 years on approximately 100 km of railway line. Parameters that influence track degradation, including loading conditions, track maintenance status and track quality, are investigated, leading to the development of correlations between the effective parameters and the track degradation. These constructed correlations are then used to develop a new track degradation model in two formats. One format, based on track geometry, relies on data obtained from track geometry inspections. The other, based on track structure, relies on data obtained from visual inspections of the track structural conditions.     

基于鲁棒性的地基土承载力设计研究

地基土承载水平的确定至关重要,而岩土工程设计中仅考虑了地基土承载能力,忽略了设计的安全度稳定水平。针对岩土参数的不确定性对地基土承载力及计算模式的不同及对地基土极限承载力稳定水平的影响,提出基于鲁棒性的地基土承载力设计思路。首先将岩土参数作为不确定因素,利用平均值及标准差考虑参数的不确定性;其次设定基础几何尺寸作为设计参数,将承载力极限状态方程作为功能函数进行地基土承载力设计。鲁棒性设计避免了传统设计方法忽略岩土参数不确定性的不合理性,将鲁棒性作为地基土承载力的安全性评价标准,并结合经济性对基础进行多目标优化设计。通过与传统设计对比分析,证明了基于鲁棒性的地基土承载力设计方法的合理性与重要性。     

A life cycle costing approach for discounting in age and interval replacement optimisation models for civil infrastructure assets

Civil infrastructure assets, such as roads, locks, bridges, treatment plants and storm surge barriers, are often characterised by long service lives and corresponding technical life cycles. When life cycles are long, the time value of money plays a role in asset management decision-making on capital investments and operation and maintenance expenditures. In this paper, a new life cycle costing (LCC) approach for discounting in two classes of maintenance optimisation models is developed. These models are the age replacement model and the interval replacement model. Three well-known LCC techniques, which are the present worth, the capital recovery and the capitalised equivalent worth, are combined and used to develop a stepwise methodology. This methodology is validated with the few case-specific mathematical equations that exist in the literature. The advantage of using this alternative LCC approach is its applicability and flexibility for reliability and maintenance engineers. The resulting LCC method builds on well-known LCC formula and enhances the understanding of the inclusion of discounting principles in reliability models. Understanding these principles makes the method flexible. Practitioners can extend or adapt the method to changing circumstances, such as additional cash flows and altering reliability modelling.     

A Petri-Net-based modelling approach to railway bridge asset management

Management of a large portfolio of infrastructure assets is a complex and demanding task for transport agencies. Although extensive research has been conducted on probabilistic models for asset management, in particular bridges, focus has been almost exclusively on deterioration modelling. The model being presented in this study tries to reunite a disjointed system by combining deterioration, inspection and maintenance models. A Petri-Net modelling approach is employed and the resulting model consists of a number of different modules each with its own source of data, calibration methodology and functionality. The modules interconnect providing a robust framework. The interaction between the modules can be used to provide meaningful outputs useful to railway bridge portfolio managers.     

浅谈施工机械设备的强制保养

阐述了铁路施工企业机械设备保养管理的重要性及现状,介绍了机械设备维护保养的几个阶段及其特点,并提出了实施机械设备强制保养的方法及推行"强保工程"的几点建议,以做好施工机械设备的强制保养工作。     

A stakeholder probability-based optimization approach for cost-effective bridge management under financial constraints

Management of bridges under uncertainty is an important issue for stakeholders. The use of probabilistic approaches enables one to consider uncertainties in the structural deterioration, assessment, and maintenance processes. Combined with optimization techniques, it is possible to determine management strategies that simultaneously minimize failure, assessment, maintenance, and rehabilitation costs. Nevertheless, there is a strong need in developing practical and efficient frameworks that enable stakeholders to optimize future allocation of budgets for facilities under uncertain structural parameters. In particular, providing an approach that is in agreement with stakeholders constraints still remains a challenge. Moreover, the use of structural health monitoring (SHM) in future management frameworks, to update structural performance, still needs further development. The objective of this paper is threefold: (a) provide management strategies in agreement with fixed budgets, (b) provide management strategies that consider the time delay between the assessment and the intervention schedule, and (c) include information provided by SHM in the decision process and analyze the impact of monitoring strategies on the structural analysis accuracy. An event tree based approach is proposed to consider various uncertainties in the decision process. Optimal solutions are associated with multiple criteria such as minimum expected failure cost, minimum expected inspection/SHM/maintenance costs, maximum agreement of expected inspection/SHM/maintenance costs to available budgets, and maximum accuracy of monitoring results. The approach is illustrated on an existing highway bridge.     

A reliability-based methodology for considering corrosion effects on fatigue deterioration in steel bridges - Part I: Methodology -

It is known that the effects of corrosion on fatigue originate from two major sources: stress concentration due to corrosion discontinuities (CNF factor) and stress amplification due to loosing net section (NAF factor). In order to account for these effects, a performance function is developed which takes CNF and NAF factors into account and considers both random and time-dependent nature of the involved parameters. In order to consider real fatigue and environmental conditions, the available CNF-y and y-t functions are extended employing α and φ factors, respectively. In addition, some recommendations have been made to establish corrosion pattern of different steel sections. The final output of the methodology is development of a reliability-based procedure to establish time-dependent deterioration profile of a structural member, which assists in decision-making with regard to maintenance activities. The proposed methodology has been applied to Neka Bridge, a railway bridge in northern Iran, which is presented in Part II.     

高速公路软土路基沉降预测

软土路基沉降量的准确预测对高速公路施工与维护是非常重要的,但是影响路基沉降量的因素众多,并且沉降量之间具有高度复杂的非线性关系,用传统的数学、力学方法很难表示;将最新的机器学习技术-支持向量机应用于软土路基沉降量预测研究,提出了软土路基沉降量预测的支持向量机模型,该模型的应用结果表明,利用支持向量机进行预测是科学可行的,建立的模型很好地表示了沉降量之间的映射关系,并且提出的模型准确性高、推广预测能力强。     

Performance of strengthened hybrid structures renovated from old railway steel bridges

Structural repair or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges, which have been used beyond or approaching their design service life. A strengthening method for old steel railway bridges by integrating the new structural members was adopted in engineering practice in this context. Rubber–latex mortar, GFRP plates and rapid hardening concrete were integrated with the old steel railway bridge to increase its rigidity and reduce both stress levels and structure-borne sound levels of the old steel bridge. The purpose of the present study is to investigate the mechanical performance of the renovated hybrid railway bridge. The material test on aged structural steel, the static loading test on the strengthened bridge, and the impact hammer test on the old bridge before and after strengthening, were performed to confirm the effects of present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and the original steel bridge. Both experimental and numerical results indicate that the renovation method can greatly enhance the stiffness and reduce the stress levels of steel members, resulting in the extension of the service life of the old steel railway bridge. Furthermore, noise reduction effects by using concrete and rubber–latex mortar were confirmed in the impact test.     

Comparisons of the mechanical properties of timber,steel and concrete sleepers

In this research, the mechanical behaviour of steel, timber and concrete sleepers is investigated and compared by conducting several laboratory and field tests. The main sleeper design parameters including rail seat loads, sleeper-ballast contact pressures and sleeper bending capacities are considered in this investigation. New formulae for the calculation of sleeper design parameters are developed for steel, timber and concrete sleepers. Results indicate that the new formulae can improve the accuracy of current practices in the analysis and design of sleepers. Comparisons of the mechanical properties of steel, timber and concrete sleepers indicate the optimum sleeper type based on railway structural and operational conditions.     

A Condition‐Based Deterioration Model for the Stochastic Dependency of Corrosion Rate and Crack Propagation in Corroded Concrete Structures

Physics‐based models are intensively studied in mechanical and civil engineering but their constant increase in complexity makes them harder to use in a maintenance context, especially when degradation model can/should be updated from new inspection data. On the other hand, Markovian cumulative damage approaches such as Gamma processes seem promising; however, they suffer from lack of acceptability by the civil engineering community due to poor physics considerations. In this article, we want to promote an approach for modeling the degradation of structures and infrastructures for maintenance purposes which can be seen as an intermediate approach between physical models and probabilistic models. A new statistical, data‐driven state‐dependent model is proposed. The construction of the degradation model will be discussed within an application to the cracking of concrete due to chloride‐induced corrosion. Numerical experiments will later be conducted to identify preliminary properties of the model in terms of statistical inferences. An estimation algorithm is proposed to estimate the parameters of the model in cases where databases suffer from irregularities.     

ResCol‐Versuche zur Prüfung der dynamischen Langzeitstabilität von TA/TM‐Böden unter Eisenbahnverkehr

Application of resonant column tests for the investigation of the dynamic long‐term stability of clays under railway traffic. Some resonant column tests have been done on the clays, which were taken from the foundation zones of open cut in the new railway line Nuremberg–Ingolstadt (under construction). From the tests, basic dynamic parameters were determined for the evaluation of dynamic long‐term stability of railway foundation by using a new approach, which has been developed by using well‐known soil dynamic knowledge. With the help of the test results, the practical controlling criteria in regard to the long‐term dynamic stability have been derived for construction site. In the paper presented, the design criterion, the test results and their application in practice are described.     

Modelling concentration fluctuations and individual exposure in complex urban environments

One of the key problems in coping with deliberate or accidental atmospheric releases, which in many cases are short or/and result in high concentrations, is the ability to reliably predict the individual exposure during the event. Furthermore, for consequence assessment and countermeasures application, it is more realistic to rely on the maximum expected dosage rather than on the actual dosage. Recently, Bartzis et al. (2008) have introduced an approach relating maximum dosage to parameters such as concentration variance and turbulence integral time scale. The need for an estimation of these parameters poses new challenges to CFD models. In the CFD RANS model ADREA, new approaches have been implemented recently, where the parameterization of the dispersion of a pollutant emitted from a point source depends not only on the parameters of turbulence, but also on the pollutant travel times. In this study the new methodology is tested against MUST and FLADIS field experimental data, which consist of high resolution concentration time series enabling the production of short term dosage data. The present comparisons further strengthen the evidence that the applied methodology is capable of dealing properly with complex transient dispersion phenomena.     

Modal parameter identification for closely spaced modes of civil structures based on an upgraded stochastic subspace methodology

Based on a recently developed stochastic subspace identification methodology equipped with an alternative stabilization diagram and a hierarchical sifting process, this research aims to improve this approach for more efficiently identifying the modal parameters of civil structures with closely spaced modes. The concept of a doubly folded stabilization diagram is proposed to combine the advantages of both the conventional and alternative stabilization diagrams for achieving better computational efficiency. In addition, the hierarchical sifting process is further refined to more properly handle closely spaced modes. The investigated cases for the occurrence of extremely close modes in civil engineering structures include axially symmetric stay cables, a symmetric cable-stayed bridge with respect to the pylon, and a uniformly arranged office building. Applying the upgraded SSI methodology established in this study, it is demonstrated that the modal parameter identification of civil engineering structures with extremely close modes can be elevated to an advanced level with a frequency space index at the order of 0.1%. Such an accurate identification and distinction is particularly important in the practical applications of structural health monitoring to prevent the false alarms resulting from the confusion of two extremely close modes. Furthermore, this approach also performs well in the determination of mode shape vectors for closely spaced modes to provide an excellent tool for observing their corresponding orthogonality property and high sensitivity.     

邢临高速公路机电系统的维护

随着我国科学技术的不断发展和创新,一些先进的高速机电技术设备应运而生,因此,不断地提高维护人员的技术水平,不断地优化机电系统已经成为目前的重要课题。论文在邢临高速以往的维护管理中总结出了一些经验和观点在此与大家探讨。     

Capacity loss evaluation of reinforced concrete bridges located in extreme chloride-laden environments

This article provides a comprehensive procedure for the structural performance evaluation and life-cycle cost (LCC) analysis of reinforced concrete highway bridges located in extreme chloride-laden environments. An integrated computational methodology is developed to simulate the chloride intrusion and to estimate the corrosion initiation time. The effects of various influential parameters on the chloride diffusion process are examined and the changes in geometry and material properties of structural members are calculated over the entire life of the bridge. In order to evaluate the global structural degradation due to the corrosion mechanisms, an inventory of bridges with different structural attributes are investigated. The extent of capacity loss is calculated using the moment-curvature and nonlinear static (pushover) analysis. Results of this study are then utilised to find the LCC of bridges. Different inspection and maintenance strategies are considered to minimise the total LCC, which includes the initial construction cost, inspection and maintenance costs and service failure costs. The proposed approach indicates the inspection and maintenance intervals in a way that the inspection and maintenance costs are optimised while the safety of the bridge is ensured.