Time-dependent Structural Reliability Research Articles

Connectivity-Based Optimal Scheduling for Maintenance of Bridge Networks

This paper addresses the issue of connectivity- and cost-based optimal scheduling for maintenance of bridges at the transportation network level. Previous studies in the same field have considered the connectivity just between two points or other network performance indicators, such as the total travel time. In this paper, the maximization of the total network connectivity is chosen as the objective of the optimization, together with the minimization of the total maintenance cost. From a computational point of view, several numerical tools are combined to achieve efficiency and applicability to real cases. Random field theory and numerical models for the time-dependent structural reliability are used to handle the uncertainties involved in the problem. Latin hypercube sampling is used to keep the computational effort feasible for practical applications. Genetic algorithms are used to solve the optimization problem. Numerical applications to bridge networks illustrate the characteristics of the procedure and its applicability to realistic scenarios.

Time-dependent reliability analysis of existing RC structures in a marine environment using hazard associated with airborne chlorides

In the design of reinforced concrete (RC) structures in a marine environment, it is important to consider the effects of this environment on structural long-term performance. In this paper, a time-dependent structural reliability analysis method taking the hazard associated with airborne chlorides into consideration is proposed. Also, a procedure to obtain the failure probabilities of RC structures in a marine environment updated by the Sequential Monte Carlo Simulation (SMCS) is indicated. In this procedure, the corrosion crack width and chloride concentration distribution by coring test are used as observational data. For illustrative purposes, time-dependent reliability analyses are presented for one-way RC slabs in a marine environment. Using SMCS, multiple random variables related to observation information can be updated simultaneously. This is realized by taking into consideration the joint probability density functions of the random variables. The effects of various marine environments, inspection results, and number of inspections on the updated estimates of an RC slab reliability are discussed in this paper.

A convenient approach for estimating time-dependent structural reliability in the load space

A procedure, formulated in the space of the load processes, is described for estimating the reliability of structures subject to multi-parameter time-varying loading. For most realistic reliability problems the load process space is of low order. As a result, the required multidimensional integration is significantly simplified. The proposed approach also has well defined steps. As a result, there is increased transparency and reduced problems of integration instability and non-convergence. Both loads and resistances are described in terms of random variable parameters and time dependent structural resistances can be considered. Numerical examples are given to illustrate the proposed method. Example applications are given for a fixed base rigid-plastic portal frame subjected to time dependent loads and resistances. Linear and non-linear limit state equations and Normal and non-Normal distribution of the random variables are considered and compared, in some cases, to the results evaluated using Monte Carlo simulation.

Computing in Civil Engineering—Lessons Learned from the 2007 ASCE International Workshop on Computing in Civil Engineering

On July 24–27, 2007, a group of approximately 150 researchers and practitioners met in Pittsburgh for the 2007 ASCE International Workshop on Computing in Civil Engineering to present and learn about current research and developments on IT/AIS: Information Technology Support to Advance Infrastructure Systems Management. The conference was geared toward academics and professionals who are interested in computing in a wide range of civil engineering research areas, such as sensing and sensor systems, mobile/wearable computing, data modeling, management, mining, and life-cycle assessment and sustainable infrastructure. The three keynote speakers presented fascinating and forwardlooking talks that provided insights on the future directions of the major conference topics. Dr. Steven B. Chase, the chief scientist of the Federal Highway Administration, talked about the role of information technology in the management of an aging highway infrastructure. He introduced the limitations in the data collection practice of bridge inspection and bridge management, and particularly in visual inspections. He then presented example applications of smart sensing technologies that help create smarter bridges. Dr. Dan M. Frangopol, the Fazlur R. Khan Endowed Chair of Structural Engineering and Architecture at Lehigh University, introduced a method for the integration of monitoring and maintenance management of civil infrastructure systems under uncertainty from a life-cycle perspective. He explained the importance of maintaining a satisfactory long-term performance not only of individual bridges, but also of the overall highway network. He presented a novel analytical and computational framework for network-level bridge maintenance management using optimization. This framework integrates time-dependent structural reliability prediction, highway network performance assessment, and life-cycle cost analysis by prioritizing the maintenance resources to deteriorating bridges through simultaneous and balanced minimization of three objective functions: maintenance cost, bridge failure cost, and user cost. The resulting multiobjective optimization problem is solved by a genetic algorithm. Dr. Edward J. Jaselskis, former program director at the National Science Foundation responsible for managing the information technology and infrastructure systems program, talked about

Optimizing Bridge Network Maintenance Management under Uncertainty with Conflicting Criteria: Life-Cycle Maintenance, Failure, and User Costs

During the past decade, a variety of bridge maintenance management methodologies have been developed to cost-effectively allocate limited budgets to deteriorating highway bridges for performance enhancement and lifespan extension. In most existing research and practice, however, bridges are treated individually rather than collectively as integral parts of a transportation network. In addition to safety issues, failure of bridges renders a highway network inaccessible, either partially or completely. This may lead to considerable economic consequences, ranging from agency costs caused by repair/reconstruction to user costs as a result of disrupted network service (e.g., congestion and detour). Therefore, it is both natural and important to maintain the satisfactory long-term performance of not only individual bridges but the highway network. In this paper, a novel analytical/computational framework for network-level bridge maintenance management using optimization is presented. This framework integrates time-dependent structural reliability prediction, highway network performance assessment, and life-cycle cost analysis. Failure occurrences of individual bridges and their effects on the overall performance of the highway network are evaluated probabilistically. The maintenance resources are prioritized to deteriorating bridges through simultaneous and balanced minimization of three objective functions, i.e., maintenance cost, bridge failure cost, and user cost. Each of these cost metrics is computed as the present value of the expected economic expenditure accrued over the specified time horizon. The resulting multiobjective optimization problem is solved by a genetic algorithm. An application example is provided for maintenance management of deteriorating reinforced concrete deck slabs of an existing bridge highway network in Colorado. It is shown that the proposed methodology is effective for enhancing the bridge maintenance management practice at network-level through probabilistic quantification and preferred balance of various life-cycle costs.

Time-dependent reliability of textile-strengthened RC structures under consideration of fuzzy randomness

The reliability of civil engineering structures is time-dependent. By means of strengthening it is possible to improve the load-bearing capacity and serviceability of structures and simultaneously to increase structural reliability. In this paper, we focus on the time-dependent reliability assessment of RC structures strengthened by textile-reinforced fine-grade concrete layers. The paper starts with a short introduction concerning textile strengthening of RC structures and the underlying mechanical model. The uncertain material parameters of textile-strengthened structures are then investigated. The uncertain parameters are quantified as fuzzy variables or fuzzy random variables. In order to take account of the latter in the assessment of the time-dependent reliability a new fuzzy probabilistic safety concept is presented. The fuzzy adaptive importance sampling (FAIS) method is introduced. The algorithm is demonstrated with an example. The uncertainty of the input parameters is comprehensively reflected in the uncertainty of the computed fuzzy reliability index. The assessment of the uncertain results is discussed.

A time-dependent corrosion wastage model for seawater ballast tank structures of ships

For assessment of time-dependent reliability or risk of aging ship structures, it is essential to have a mathematical model which provides the statistical characteristics (mean, variance, distribution) of corrosion wastage as a function of time (i.e., ship age). The aim of the present work is to develop such a model for low alloy carbon steel plates used for the structure of seawater ballast tanks in ships. Measurement data of structural wastage due to corrosion for such ship steel plates is collected and the statistical characteristics of corrosion loss and rate are quantified by statistical analysis in terms of ship age. The results and insights developed in the present study will be useful for predicting the wastage of corrosion in seawater ballast tank structures of ships. They will also be useful for designing corrosion tolerant structures subjected to the seawater environment.

Time-Dependent Reliability Analysis of Steel Miter Gates

This article deals mainly with identification of a suitable method for time-dependent reliability and analysis of navigation structures based on a detailed literature review, application of the method to a miter gate, and comparison of results with the existing results in the the literature. The aspect of corrosion is considered in the study. This work is a continuation of the work on rolled steel sections reported by the authors at an international conference in Canada. Detailed computer programs in FORTRAN have been developed as part of this research study. It has been found that the existing results and the results of the present investigation compare very well.

Modelling Infrastructure Deterioration Risks Using Bayesian Mixtures

A major aspect of assessing the long-term reliability of deteriorating structures is the need to integrate the results of different inspections in time, within the models used to analyse the progress of deterioration. This article presents a framework for such an analysis. The article focuses on reinforced concrete structures subject to chloride corrosion, as this represents the single largest form of deterioration of infrastructure in Europe and North America. The analysis focuses on special extensions of the Empirical Bayes method where the nonobservable parameter is a discrete random variable with a relatively small number of outcomes. Various likelihood functions are derived. They are based on mixtures of “deterioration scenarios.” The authors show how the method can be used to calibrate the response of a stochastic deterioration model, and to update a time-dependent structural reliability analysis. An example relating to long-term chloride corrosion in a reinforced concrete bridge slab is presented.

Assessment of the time-dependent structural reliability of buried water mains

Abstract The structural performance of civil engineering constructions is assessed by comparing its state behaviour as a function of time to one of several limit states.The method presented is based essentially on the analysis of interference data and evaluates current and future structural reliability using a multidimensional time dependent failure surface. It takes into account the stochastic nature and the variation in time of past and future loads, and the randomness in strength due to degradation resulting from different environmental stressors.This methodology has been implemented in the case of grey cast-iron buried water pipes.

Risk assessment of transmission line structures under severe thunderstorms

To assess the collapse risk of transmission line structures subject to natural hazards, it is important to identify what hazard may cause the structural collapse. In Australia and many other countries, a large proportion of failures of transmission line structures are caused by severe thunderstorms. Because the wind loads generated by thunderstorms are not only random but time-variant as well, a time-dependent structural reliability approach for the risk assessment of transmission line structures is essential. However, a lack of appropriate stochastic models for thunderstorm winds usually makes this kind of analysis impossible. The intention of the paper is to propose a stochastic model that could realistically and accurately simulate wind loading due to severe thunderstorms. With the proposed thunderstorm model, the collapse risk of transmission line structures under severe thunderstorms is assessed numerically based on the computed failure probability of the structure.

Time-Dependent Structural Reliability Analysis Based on Directional Simulation.

This paper outlines an improved simulation method for a time-dependent reliability analysis of structural systems subjected to stochastic loads. Strengths of structural elements are assumed to degrade with time proportionally during the life cycle of the structural system, and stochastic load events are modeled as Poisson processes. The structural failure probabilities are estimated through the life cycle simulation, in which the directional simulation method is applied just to sample random load variables to execute each life cycle simulation efficiently. Numerical examples are presented and results are compared with those obtained by the crude Monte Carlo simulation to show the effectiveness of the proposed method. It is shown that the proposed method is effective for the assessment of the time-dependent failure probability of structural systems.

Computation of the failure probability of deteriorating structural systems

Structural system deterioration is one of the least attended topics in time-dependent structural reliability analysis. There are basically two types of problems in structural deterioration analysis; one is the need for models to simulate the behaviour of deteriorating structural material. This will be done through case by case study in this paper. The other problem is that when both the applied loads and resistance vary with time, the current methods to generate limit state functions for the structural system need validating. To avoid this problem, an alternative formulation for time-dependent reliability is proposed, where the reliability analysis of a deteriorating structural system is based on the reliability of its structural members, which constitute a failure sequence for the structure. The advantage of the proposed approach is that it has effectively obviated the use of global limit state functions and that it is applicable to structures subject to various types of loads and with different structural material properties. An application example is given to illustrate the computation procedure.

Time-dependent reliability of rock-anchored structures

Time-dependent reliability of rock-anchored structures

Probability of plastic collapse of a structural system under nonstationary load processes

This paper deals with the reliability analysis of a complex structural system, in which the failure of the system is due to plastic collapse. Of particular interest herein is the computation of the time-variant probability of the structural system failure under nonstationary load processes. The theoretically most attractive approach for this type of problem in time-dependent structural reliability analysis is to employ the concept of first passage probability in stochastic process theory. Because the use of the generalized Rice formula poses some difficulty, the outcrossing problem will be formulated herein in another way, i.e., using the original Rice formula directly. This situation allows the multidimensional integral to be reduced to a one-dimensional integral. Also it can include smooth nonstationary processes as well as time-variant domain boundaries. An example is given to illustrate the method.

A simulation method for time-dependent structural reliability

A one-dimensional simulation procedure is developed for use in estimating structural reliability in multi-dimensional load and resistance space with the loads represented as stochastic process. The technique employed is based on the idea of using ‘strips’ of points parallel to each other and sampled on the limit state hyperplanes. The ‘local’ outcrossing rate and the zero time failure probability P f (0) associated with the narrow strips are derived using the conditional reliability index. When the domain boundary consists of a set of limit states, second order bounds are used to obtain a lower bound approximation of the outcrossing rate and P f (0) associated with the union of a set of λ strips. It is shown by examples that for high reliability problems, λ may be much less than the number of limit states without significant loss of accuracy and with considerable saving in computation time. It was also found that the rate of convergence of the simulations is quite fast even without using importance sampling.

Outcrossings from Convex Polyhedrons for Nonstationary Gaussian Processes

This technical note concerns the estimation of the outcrossing rate of nonstationary Gaussian vector processes from a convex polyhedral limit-state surface enclosing the origin. The theoretically most attractive approach for this type of problem in time-dependent structural reliability analysis is to employ the concept of first-passage probability in stochastic-process theory. Because the use of the generalized Rice formula poses some difficulty, the outcrossing problem is formulated in another way; i.e., using the original Rice formula directly. This situation allows the multidimensional integral to be reduced to a one-dimensional integral. This then allows the formulation (which applies also to smooth nonstationary processes) to be extended to time-dependent domain boundaries. An example is given to illustrate the method.