An extended recursive decomposition algorithm for dynamic seismic reliability evaluation of lifeline networks with dependent component failures

https://doi.org/10.1016/j.ress.2021.107929Get rights and content

Highlights

  • An algorithm is proposed to evaluate dynamic reliabilities of lifeline systems.

  • Complex and large-sized systems with dependent failures can be analyzed.

  • Joint probabilities of paths and cuts of systems can be effectively calculated.

  • Most reliable paths of the systems with dependent failures can be singled out.

  • Faster convergence rate is obtained by selecting subgraphs to be decomposed.

Abstract

An extended recursive decomposition algorithm (e-RDA) is proposed to evaluate the dynamic seismic reliabilities of the complex and/or large-sized lifeline network systems with dependent component failures. To effectively analyze statistical dependence of failures of system components, multivariate extreme value response distributions of the components and joint occurrence probabilities of the (disjoint) shortest paths and cuts of systems, a multivariate Gumbel Copula is developed and introduced into the original recursive decomposition algorithm (RDA). Based on the established joint occurrence probability formula of the paths and cuts, two techniques that may accelerate convergence of the upper and lower reliability bounds of complex and/or large-sized systems are developed and embedded into the RDA. Illustrative examples are presented to demonstrate the accuracy, effectiveness and use of the extended RDA for the node weight (only node-type components may fail), edge weight (only line-type components may fail) and general weight (both node- and line-type components may fail) lifeline network systems.

Introduction

The fast and accurate evaluation of the seismic reliabilities of complex and/or large-sized lifeline network systems, such as electrical power networks, gas transmission networks, water supply networks, etc., is of important interest for assessing seismic risk and enhancing seismic resilience of a society. A key issue of the reliability evaluation is to calculate the node-pair connectivity probabilities of the systems under the actions of random earthquake loads. When the considered earthquake loads are modeled by the random processes, the lifeline systems can be considered as the random vibration systems. In this situation, the failures of the system components should be analyzed by using the random vibration theory, e.g., the first passage probability analysis of their nonlinear random seismic responses, and are usually statistically dependent due to the consistent or spatially correlated random earthquake excitations. In the present study, this kind of node-pair connectivity probability evaluation of lifeline network systems is named as the dynamic reliability evaluation of lifeline network systems.

To evaluate the network system reliabilities, one can use the naïve Monte Carlo (MC) simulation method [1]. This method first generates K samples, xk=(x1k,,xmk),k=1,,K, of the m-dimensional component state vector from the mK independent samples drawn from a uniform random number generator and vector, p=(p1,,pm), of component operating probabilities, and then calculate the number K^ of vectors xk,k=1,,K for which the structure function of the network Φ(xk)=1 by the deterministic network connectivity analysis. Then an unbiased estimator for the network reliability R is R^=K^/K and its variance is bounded above by R(1R)/K. Reduction of the variance of the MC simulation results can be obtained by several standard MC sampling techniques [2], [3], [4]. However, the main limitations of the MC methods are that they usually require a large number of simulations to achieve an acceptable level of convergence when the reliabilities of system components or systems are high. In addition, the sampling technique is usually difficult to estimate conditional probabilities. Hence the MC methods were often used in the early reliability analysis of lifeline systems [5,6].

Besides the simulation methods, the non-simulation methods have been also developed in the last decades to evaluate the network system reliabilities, such as the exact algorithms, heuristic algorithms, recursive decomposition algorithm (RDA), recursive compounding method, etc. The exact algorithms usually need to examine all states or generate all paths and/or cuts of the considered networks [7], [8], [9]. Essentially the exact calculation of the network reliabilities is a non-deterministic polynomial (NP) hard problem, hence the exact algorithms are quite inefficient for the complex and/or large-sized lifeline network systems. If the component state variables in the expressions of the system reliability given by the path-and-cut method are substituted by the corresponding component reliabilities, then the Esary-Proschan upper and lower bounds are produced and the true value of the network reliability lies between these bounds [10]. As the numbers of the paths and cuts increase, there will be an intersection of the upper and lower bounds, which offers the approximation to the true system reliability value. Based on this principle, the heuristic algorithms have been developed [11,12]. The shortcoming of the heuristic algorithms is that they cannot determine with what precision the reliability is estimated. In order to overcome the shortcomings of the simulation methods, exact algorithms and heuristic algorithms, the RDA was developed [13], [14], [15], [16]. The RDA is on the basis of the techniques of the generation and disjoint operation of the shortest paths and cuts, evolution and decomposition of the graphs as well as the approximation of the upper and lower reliability bounds. Since it was proposed, the RDA has been continuously extended and widely used in the seismic reliability assessment of complex and/or large-sized lifeline systems [17], [18], [19], [20]. The recursive compounding method successively compounds the system components from the node to the destination node until one single super component representing the connectivity of the source and terminal nodes is obtained [21,22]. This method is suitable for the middle-sized statistically correlated lifeline network systems, which the joint failure probabilities of the system components can be described by the multivariate Normal distributions or Normal Copula.

The above-mentioned RDAs or recursive compounding method were developed to evaluate the static seismic reliabilities of the large- or middle-sized lifeline systems with statistically independent or dependent component failures. However, as far as we know, there are no the efficient methods for evaluating the dynamic seismic reliabilities of complex and/or large-sized lifeline network systems with dependent component failures. The analysis of the seismic reliabilities of structures is a quite complex issue, which involves the definition of failure modes, solution of structural responses, estimate of the probabilities of failure, etc. [23,24]. In addition, it also involves various epistemic and aleatory uncertainties such as uncertainty of the mechanical behavior of building material, uncertainty of earthquake load and uncertainty of calculation method [25,26]. If the failures of lifeline components are defined as the first passage of their responses over the critical threshold levels [27,28] and only uncertainty of earthquake load is considered, then the evaluation of the dynamic seismic reliabilities of lifeline network systems will require estimation of the (joint) first passage probabilities of the (nonlinear) random responses of the lifeline components to the random earthquake excitations. In the last decades, many efficient methods have been developed for estimating the probabilities, such as the stochastic averaging method [29], probability density evolution method [30], moment method [28,31], subset simulation method [32], tail equivalent linearization method [33], asymptotic sampling method [34] and extreme value theory-based simulation methods [35], [36], [37], [38]. Simultaneously, multivariate extreme Copulas have been also developed for estimating the joint failure probabilities of system components [39], [40], [41], which can be used to estimate the joint first passage probabilities of the nonlinear random responses of lifeline components. The challenging issue is how to combine the existing computational methods of network reliabilities and structural dynamic reliabilities to develop an efficient algorithm for evaluating the dynamic seismic reliabilities of complex and/or large-sized lifeline network systems with dependent component failures, especially for the general weight (both node- and line-type components may fail) lifeline systems. The present study aims to solve this issue.

The rest of this paper is organized as follows. Section 2 provides the structure function-based expressions for the original RDA, which can facilitate the derivation of the formula for calculating the joint occurrence probabilities of disjoint shortest paths and cuts. Section 3 derives the expressions of the expectations of the structure functions of disjoint shortest paths and cuts based on the developed Gumbel Copula model, whereby the joint occurrence probabilities of the paths and cuts of systems can be calculated. Section 4 describes the techniques of selecting the most reliable paths and subgraphs to be decomposed, which may accelerate convergence of the upper and lower reliability bounds of systems. In Section 5, the dynamic seismic reliabilities of two illustrative network systems are analyzed to demonstrate the accuracy, effectiveness and use of the extended RDA for the node weight (only node-type components may fail), edge weight (only line-type components may fail) and general weight lifeline network systems. Finally, Section 6 summarizes the present study and provides main conclusions.

Section snippets

Node and edge weight networks

Consider first a node weight lifeline network system, i.e., only the node-type components such as the electrical equipment items of transformer substations may fail and all the line-type components such as the buses or electricity lines of transformer substations are perfectly operative. The network can be described by a directed or undirected graph G(V,E) where V and E respectively denote the sets of the nodes and edges in the graph. Suppose the m nodes have binary states, that is, operative

Expectations of the structure functions αj(x,y) and βj(x,y)

As mentioned earlier, in the present study the failure of a lifeline component is defined as the state that its nonlinear random seismic response first exceeds in magnitude the critical threshold level in a reference duration T. The dynamic seismic reliabilities of the node- and line-type lifeline components can be then expressed as [27,37,38]:ri=E(xi)=1P{τ[0,T]:Xi(τ)>bi}=P{max0tTXi(τ)bi}=FZi(bi)andrj=E(yj)=1P{τ[0,T]:Yj(τ)>bm+j}=P{max0tTYj(τ)bm+j}=FZm+j(bm+j)for i=1,,m and j=1,,n,

Selection of the most reliable paths and subgraphs to be decomposed

In order to accelerate convergence of the lower and upper reliability bounds of lifeline network systems, a selective RDA has been developed [18]. This method uses the most reliable path of the original graph and subgraphs as well as the subgraph which has the greatest contribution to the system reliability and failure probability in the recursive decomposition procedure. However, the selective RDA is developed on the basis of the assumption of independent component failures and only suitable

Simple directed network

This example investigates the accuracy and effectiveness of the extended RDA in evaluating the dynamic seismic reliabilities of node, edge and general weight lifeline network systems with independent and dependent component failures. Fig. 3 shows a directed network system with 6 nodes and 11 edges, in which the source and terminal nodes are node 4 and node 6, respectively. The dynamic reliabilities of the system components ui=FZi(bi),i=1,,17 and values of the parameter θ of the Gumbel Copula

Conclusions

An extended RDA is proposed in the present study to effectively evaluate the dynamic seismic reliabilities of complex and/or large-sized node, edge and general weight lifeline network systems with dependent component failures. The extended RDA uses a multivariate Gumbel Copula with the margins are GEV distributions to model the multivariate extreme value responses of system components to random earthquake loads, whereby the joint occurrence probabilities of the (disjoint) shortest paths and

CRediT authorship contribution statement

Jun He: Conceptualization, Methodology, Software, Data curation, Writing – original draft, Investigation, Validation, Writing – review & editing.

Declaration of Competing Interest

The author declare that has no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The present work has been supported by a grant of the National Natural Science Foundation of China (No. 51978397), which is gratefully acknowledged.

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