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The system reliability analysis of complex engineering structures remains a challenge in the field of reliability. In this work, a high-order moment method using generalized factorized dimensional reduction method (GF-DRM) and iterative maximum entropy method (IMEM) is proposed for structural system reliability assessment. Firstly, the performance functions are described uniformly by equivalent description methods for various system reliability problems. Secondly, a novel point estimation method (PEM) based on GF-DRM is proposed for the high-order moments estimation of the equivalent performance function. Thirdly, the system failure probability of the structures is accurately determined by using the IMEM, which can automatically determine the order of moments. Finally, four examples, including numerical and engineering cases, are investigated to demonstrate the accuracy and efficiency of the proposed method, in which results obtained from the proposed method are compared with some other existing moment methods and Monte Carlo simulation (MCS) method. The results of the examples show the proposed method has fairly high accuracy and efficiency for structural highorder moments estimation and system reliability analysis. [ABSTRACT FROM AUTHOR]

Contact wires are critical components of railway overhead infrastructure which provide power for trains. This paper proposes an innovative method to determine the service life of worn contact wires under three failure modes: tension, fatigue, and attrition. The tensile stress, fatigue damage, and cross-section loss of contact wire have been modelled as stochastic processes following lognormal distribution. The first-passage probability method is then used to determine the time-dependent failure probability for contact wires under each failure mode. The service life of the contact wire is determined through system reliability analysis. This method has then been applied to a case study to provide information on behaviour evaluation of contact wire. It has been found that the service life of contact wire can be underestimated without considering the wear effect on fatigue failure mode. Also, through sensitive analysis, it has been determined that the wear rate of contact wire can affect the probability of fatigue failure considerably in the longer term. The methodology proposed in this paper can help engineers and asset managers in making optimum decisions regarding the time of repair and/or maintenance of contact wire exposed to wear. [ABSTRACT FROM AUTHOR]

Fatigue is among the most critical forms of deterioration damage that occurs to steel bridges. The performance of steel bridges, which may be seriously affected due to fatigue, should be assessed and predicted. However, the code-based reliability assessment only provides a clear criterion for single details. The whole bridge or a splitting system from the bridge may contain many details which brings system impact on the fatigue assessment. In this paper the system reliability of steel bridges is addressed with focus on the influence of spatial correlations between similar fatigue sensitive details. The study is conducted on a typical riveted railway bridge, from which a subsystem is selected and modelled as a weakest link system. It is assumed that all details in the system are equicorrelated. An efficient modeling approach has been developed to quantify the correlation and help estimate the system reliability analytically. A parametric study was performed to determine the system effects on the fatigue reliability assessment and identify the decisive variables. [ABSTRACT FROM AUTHOR]

This article presents a novel system reliability-based framework for multi-objective optimisation of preventive maintenance (PM) management of in-service asphalt pavement. To accurately predict the international roughness index (IRI) sequence of pavement sections, a long short-term memory (LSTM) neural network that considers the spatiotemporal correlations between IRI sequences is trained with data retrieved from the long-term pavement performance (LTPP) program. Based on time-dependent limit-state functions (LSFs) incorporating the uncertainty associated with LSTM neural network prediction and the observational error involved in IRI measurement, Monte Carlo simulation (MCS) with importance sampling (IS) is adopted to calculate the reliability of pavement sections. Pavement sections located in New Mexico and Montana are selected as illustrative examples. Tri-objective optimisation processes are investigated by maximising user benefits (i.e. improved system reliability) and agency benefits (i.e. extended service life) while minimising the associated life-cycle cost (LCC) (i.e. user and agency costs) with multi-objective genetic algorithms (GAs). The obtained Pareto solution sets may assist decision-makers in the selection of well-balanced solutions to identify the optimal timing for applying PM treatments to in-service asphalt pavement. [ABSTRACT FROM AUTHOR]

For a bridge, its columns or piers, which are the main seismically resistant members of the bridge, are generally retrofitted to improve seismic performance. However, retrofitting may cause unexpected damage to the non-retrofitted components/members. Therefore, a corresponding retrofitting of these components/members should be considered as part of any retrofitting method to eliminate unexpected damage. This work is to develop an estimating procedure of the seismic reliability of the system for a bridge considering the seismic reliability of each specified component/member. Additionally, the damage state of bridge for the system reliability analysis is built based on the engineering judgement. For the convenience of the calculation, the seven-point estimation method and the Nataf transformation method are combined to calculate the first four moment values of a specified limit state function in the moment-based system reliability analysis. For determining the retrofitting strategy, this work also presents a method for calculating the relationship between the resilience in functionality and seismic intensity that is achieved using a particular retrofitting method. Moreover, the system reliability and recovery time of each damaged component/member are considered in a resilience analysis. Finally, a bridge is selected as an example to demonstrate the application of this work. [ABSTRACT FROM AUTHOR]

Reliability assessment is an indispensable task in risk-based corroding ship maintenance planning. For simplicity and computational efficiency it is commonly assumed that the reliability of a ship is computed as a component-based reliability problem defined by the plastic collapse of the one-bay section at mid-ship. However, this assumption may underestimate the likelihood of ship failure since there are many bays of sections subjected to very high vertical bending moments near the mid-ship and the failure of any section can lead to the loss of the entire ship. The failures of the individual one-bay sections are spatially dependent due to the spatial variability of variables, such as corrosion and yield strength, among others. Therefore, system-based reliability is more appropriate for describing the safety level of ships under uncertainty. This paper utilises an improved first-order reliability method (FORM) recently developed to assess ship system reliability. The methodology developed is demonstrated on a double hull girder tanker subjected to corrosion. The effect of the spatial dependence among the variables associated with different sections on the computed failure probability of the ship is studied by parametric analysis. The results indicate that the dependence of the model error for predicting the bending capacity associated with different sections impacts the failure probability significantly, and the underestimation of this probability can be non-trivial if only a single one-bay section is considered. [ABSTRACT FROM AUTHOR]

The cables in a cable-stayed bridge are critical components supporting the long-span girders and ensuring their functionality. However, cables are prone to fatigue damage and atmospheric corrosion, which directly affect the bridge safety. This study presents a framework for system reliability evaluation of in-service cable-stayed bridges subjected to cable degradation. The effect of cable strength degradation on the system reliability is demonstrated through simulation on a parallel-series system representation. Learning machines are utilised to approximate the non-linear and dynamic response functions of critical components due to cable rupture, and the system reliability is finally evaluated from the event tree established by the β-unzipping method. Both short-span and long-span cable-stayed bridges are selected as prototypes to investigate the influence of cable degradation on the system reliability. On this basis it is revealed that cable degradation can significantly influence the collapse mechanism of a cable-stayed bridge and thereby lead to a significant reduction in the system reliability. This phenomenon is associated with cable spacing, where a spare cable system seems more sensitive to cable gradation. It is demonstrated that the consideration of cable corrosion and correlation is essential for lifetime safety evaluation of in-service cable-stayed bridges. [ABSTRACT FROM AUTHOR]

Civil infrastructure systems provide physical supports to a community’s functionalities and are expected to achieve acceptable safety levels subjected to extreme load effects. However, these systems may deteriorate with time as a result of aggressive environmental or operating conditions in service, implying that the system reliability may decline beyond the baseline as assumed for design. Moreover, the increasing trend of the external loads may also contribute to the reduction of the system reliability. In this paper, a semi-analytical method is proposed for assessing the reliability of aging systems subjected to non-stationary loads. The series system is considered, where the system failure is defined as the failure of any single component (structure) among the system. The application of the proposed method is illustrated using a representative series bridge network with several individual bridges. The role of parameters such as the variations in the load intensity, resistance correlation and number of components under attack in the system reliability are investigated. [ABSTRACT FROM PUBLISHER]

A methodology that employs the first-order reliability method is proposed to evaluate the time-dependent system reliability of a segment of a pressurised steel pipeline containing multiple active corrosion defects. The methodology considers the leak and burst failure modes of the pipe segment and takes into account the correlations among limit state functions at different corrosion defects. The methodology involves first constructing two linearised equivalent limit state functions for the pipe segment in the standard normal space and then evaluating the probabilities of leak and burst of the segment incrementally over time based on the equivalent limit state functions. The applicability and accuracy of the proposed methodology is illustrated through system reliability analyses of three pipeline examples, each containing ten active corrosion defects whose growth over time is characterised by the linear, nonlinear and homogeneous gamma process-based models. [ABSTRACT FROM PUBLISHER]

This paper investigates the effects of post-failure material behaviour on redundancy factor for the design of structural components in nondeterministic systems. The procedure for evaluating the redundancy factors of components of ductile and brittle nondeterministic systems is demonstrated using systems consisting of two to four components. The effects of the number of brittle components in a mixed (ductile–brittle) system and the post-failure behaviour factor on the redundancy factor are also studied using these systems. An efficient approach for simplifying the system model in the redundancy factor analysis of brittle systems with a large number of components is proposed. In order to generate standard tables to facilitate the design process, the redundancy factors and the associated component reliability indices of nondeterministic ductile and brittle systems with large number of components are calculated considering three correlation cases and two probability distribution types. Finally, a bridge example is used to demonstrate the application of the redundancy factor in the design of steel girders taking into account their post-failure behaviour. [ABSTRACT FROM PUBLISHER]

This paper presents a methodology for evaluating the time-dependent system reliability of a pressurised gas pipeline segment containing multiple active metal-loss corrosion defects. The methodology incorporates three distinctive failure modes of the pipe segment due to corrosion, namely small leak, large leak and rupture. The growth of the depth of individual corrosion defect is assumed to follow a power-law function of time. The Bayesian updating and Markov Chain Monte Carlo (MCMC) simulation techniques are used to quantify the parameters of the power-law growth model based on data obtained from multiple inspections carried out at different times. The simple Monte Carlo and MCMC techniques are combined to evaluate the system reliability. A numerical example involving an in-service gas pipeline located in Alberta, Canada, is used to illustrate the proposed methodology. Results of the sensitivity analysis suggest that the use of a defect-specific or segment-specific growth model for the defect depth has a marked impact on the evaluated system reliability. The proposed methodology can be incorporated in reliability-based pipeline corrosion management programmes to assist integrity engineers in making informed decisions about defect repair and mitigation. [ABSTRACT FROM PUBLISHER]

The deteriorating state of highway bridges is traditionally ignored in estimating the seismic reliability of transportation networks. In this study, the present day seismic reliability of ageing bridges in highway networks is evaluated through a time-dependent seismic fragility analysis of typical bridge classes. An efficient algorithm based on finite-state Markov Chain Monte Carlo simulations is also presented to assess the reliability of large ageing highway bridge networks without the need to simplify the network topology. The criticality of ageing bridges is then assessed through different proposed ranking strategies to arrive at an optimised seismic retrofit prioritisation. A case study on an existing bridge network with 515 bridges in the state of South Carolina, USA reveals striking differences between results of the proposed ranking strategies and those from state-of-the-practice methods. Such differences emphasise the significance of accounting for network-level importance in seismic retrofit programs of ageing transportation networks. [ABSTRACT FROM AUTHOR]

In efforts to estimate the risk and reliability of a complex structure or infrastructure network, it is often required to evaluate the probability of a ‘system’ event, i.e. a logical function of multiple component events. Its sensitivities with respect to design parameters are also useful in decision-making processes for more reliable systems and in reliability-based design optimisation. The recently developed, matrix-based system reliability (MSR) method can compute the probabilities of general system events including series, parallel, cut-set and link-set systems, and their parameter sensitivities, by use of efficient matrix-based procedures. When the component events are statistically dependent, the method transforms the problem into an integral in the space of random variables which cause the statistical dependence, termed as the common source random variables (CSRVs). One can identify CSRVs by fitting a generalised Dunnett-Sobel (DS) model to a given correlation coefficient matrix. This article introduces two further developments of the MSR method: First, for efficient evaluation, it is proposed that the integral in the CSRV space can be performed using the first- or second-order reliability methods. Second, a new matrix-based procedure is developed to compute the sensitivity of the system failure probability with respect to the parameters that affect the correlation coefficients between the components. In addition, an extensive parametric study is performed to investigate the effect of the error in fitted generalised DS model on the accuracy of the estimates by the MSR method. The further developed MSR method is demonstrated by two examples: system reliability analysis of a three-storey Daniels system structure, and finite element reliability analysis of a bridge pylon system. [ABSTRACT FROM PUBLISHER]