Life cycle structural integrity management of offshore structures

An overview of structural integrity management of offshore structures in the oil and gas energy sector is presented in this article. Based on relevant experiences with the hazards, accidents and means to control the associated risks are categorised from a technical and physical as well as human and organisational point of view. Structural risk relates to extreme environmental and accidental events, as well as structural degradation and can be controlled by use of adequate design criteria, inspection, repair and maintenance as well as quality assurance and control of the engineering processes. Such measures are briefly outlined, with an emphasis placed upon a quantitative design approach for dealing with a life cycle approach especially relating to crack degradation phenomena. The current status of risk and reliability methodologies to aid decisions in the safety management of novel and mature offshore structures is briefly reviewed.     

A Bridge Management System for Elevated Steel Highways

The Hanshin Expressway network extends some 200 km, forming the traffic arteries of the heavily urbanized Hanshin area surrounding Osaka, the second largest city in Japan. Due to restrictions on construction in mature cities, 93 percent of the total length of this network is elevated, and 77 percent of the elevated structures use steel girders that have numerous curves to allow complicated road alignments. These elevated structures are showing signs of damage after serving for almost 30 years under chronic overload conditions. This article describes the various types of damage that are frequently detected in elevated steel bridges and, focusing on typical fatigue-induced damage, reviews the repair process that begins with the investigation of causes and potential repair methods and continues through the implementation and inspection of the repair work. Propositions are presented that may enable the design of more durable steel bridges. In addition, this article briefly discusses a database system that is being used for the maintenance and management of steel bridges.     

Maintenance management of offshore structures using Markov process model with random transition probabilities

The robustness of an offshore engineering design is highly dependent on the maintenance management, where the latter needs a full knowledge of engineering analysis and predictions. An accurate estimation of offshore structural performance with time-varying effect is a keen technical issue. The traditional Markov chain model used for structural strength predictions suffers from the difficulty that some of the measurements or inspection data are largely different from the predicted damage condition. This paper presents a deterioration prediction method for maintenance planning in offshore engineering using the Markov models. Instead of traditional deterministic approaches, the Markov chain model is refined by expressing the transition probabilities as random variables. Through such development, the proposed model is able to estimate an interval for the deterioration of an offshore structure. An existing offshore structure located in South China Sea is used in this study for the demonstration purpose. The selection of transition periods of the Markov chain model is investigated. The use of the stochastic model in the prediction of maintenance timing is also discussed. The results show that the proposed approach can provide more reliable information on structural integrity compared to the conventional method.     

Bridge management in Turkey: a BMS design with customised functionalities

The overall design and customised functionalities of a bridge management system (BMS), developed in Turkey in 2009–2013 period (the so-called KYS), are presented. The novel design features are explained. Development of the web-based BMS involved the establishment of a bridge inventory database, a detailed multi-layer cost database with an itemised unit cost breakdown capability, inventory management, cost and planning modules, optimal allocation of maintenance-repair–replacement (MR&R) budgets while producing repair cost estimates at damage level, a network-level multi-criteria prioritisation implementation, establishment of a damage-level condition evaluation and rating model, 13 separate customised functionalities, and visual inspections and data entry for a pilot group of 200 bridges. Matrices containing bridge types versus element types and element types versus damage types are constructed. For each element, a dynamic list is developed that can expand or contract depending on an element's damage types. A check mark-based interactive decision-making capability is built, by which the user can overwrite the recommended decisions. BMS is being used by the bridge administration. Out of a total of 7514 bridges in Turkey, in 2014, the damage-level inspection data of over 3000 bridges is entered into the inventory. Entry of bridge and inspection data for the remaining bridge stock will be completed in 2015.     

Bewertung der Ermüdungsfestigkeit von Baustrukturen in Offshore‐Windenergie‐Anlagen

Fatigue assessment of support structures for offshore wind energy converters. The structure of wind energy converters secures a reliable energy production. Hence an adequate reliability of the structure and additionally permanent assessment and maintenance is required. Within this paper methods for the assessment of the important damage mechanism fatigue in combination with monitoring of the fatigue reliability utilizing damage indicators are proposed. These methods comprise structural system, material degradation and probabilistic models as well as monitoring data of an offshore wind energy converter prototype. The structural reliability of the structure as designed is calculated based on an overall dynamic analysis using a SN‐approach. Herewith fatigue sensitive components are identified. Damage indicators for monitoring the fatigue reliability based on damage equivalent strains are presented.     

Modeling of risk-based inspection,maintenance and life-cycle cost with partially observable Markov decision processes

The utilization of Markov decision processes as a sequential decision algorithm in the management actions of infrastructure (inspection, maintenance and repair) is discussed. The realistic issue of partial information from inspection is described, and the classic approach of partially observable Markov decision processes is then introduced. The use of this approach to determine optimal inspection strategies is described, as well as the role of deterioration and maintenance for steel structures. Discrete structural shapes and maintenance actions provide a tractable approach. In-service inspection incorporates Bayesian updating and leads to optimal operation and initial design. Finally, the concept of management policy is described with strategy vectors.     

Time-dependent performance indicators of damaged bridge superstructures

The ability of a structure to survive an extreme event without collapse reduces in time due to deterioration processes. Therefore, in the lifetime management of structures and infrastructures, the resistance to sudden local damage has to be considered together with the effect of progressive deterioration. The aim of this paper is to present a framework for computation of time-dependent performance indicators of civil structures and infrastructures, with emphasis on bridges, including reliability, vulnerability, robustness and redundancy. A brief theoretical background and selected structural performance indicators regarding vulnerability, redundancy and robustness are presented. The approach is based on probabilistic performance assessment supported by finite element analysis and applied to an existing bridge. Time-variation of vulnerability, redundancy and robustness associated with various damage scenarios under uncertainty and the effects of several loading conditions on performance are investigated.     

Overview of the FEMA/SAC program for reduction of earthquake hazards in steel moment frame structures

Considerable research has been conducted worldwide to assess the unexpected damage to welded steel moment-frame buildings during the 1989 Loma Prieta, 1994 Northridge and 1995 Hyogo-ken Nanbu earthquakes, as well as to find effective and economical remedies that can be incorporated into analysis, design, and construction practices. A major 6-year program was undertaken sponsored by the US Federal Emergency Management Agency (FEMA) synthesized and interpreted the results of this research, and conducted additional investigations to develop reliable, practical and cost-effective guidelines for the design and construction of new steel moment-frame structures, as well as for the inspection, evaluation and repair or upgrading of existing ones. Topics investigated as part of this program included: (1) performance of steel buildings in past earthquakes; (2) material properties and fracture issues; (3) joining and inspection; (4) connection performance; (5) system performance; (6) performance prediction and evaluation; and (7) social, economic and political impacts. The project utilized a performance-based engineering framework and addresses issues pertaining to various types of steel moment-resisting frames including those utilizing welded, bolted, and partially restrained connections. Published late in 2000 by FEMA, the guidelines are applicable to regions of low, medium and high seismicity throughout the US. This paper reviews the overall organization and management of this program of research, guideline development, training and peer evaluation, the scope of the investigations undertaken, and the general organization and contents of the guidelines developed.     

Image‐based post‐disaster inspection of reinforced concrete bridge systems using deep learning with Bayesian optimization

Many bridge structures, one of the most critical components in transportation infrastructure systems, exhibit signs of deteriorations and are approaching or beyond the initial design service life. Therefore, structural health inspections of these bridges are becoming critically important, especially after extreme events. To enhance the efficiency of such an inspection, in recent years, autonomous damage detection based on computer vision has become a research hotspot. This article proposes a three‐level image‐based approach for post‐disaster inspection of the reinforced concrete bridge using deep learning with novel training strategies. The convolutional neural network for image classification, object detection, and semantic segmentation are, respectively, proposed to conduct system‐level failure classification, component‐level bridge column detection, and local damage‐level damage localization. To enable efficient training and prediction using a small data set, the model robustness is a crucial aspect to be taken into account, generally through its hyperparameters’ selection. This article, based on Bayesian optimization, proposes a principled manner of such selection, with which very promising results (well over 90% accuracies) and robustness are observed on all three‐level deep learning models.     

检查井喷涂砂浆配合比设计及喷涂修复工艺

检查井是城市排水系统的重要组成部分.检查井破坏会严重影响排水系统的安全运营和正常功能需求,因此要定期对其进行检查和修复.目前,检查井的修复方式多种多样,本文针对喷涂修复展开相关研究.采用超高性能混凝土材料体系为基础,确定喷涂砂浆的基本组分,再通过砂浆流变性、粘结强度及回弹量等条件控制并确定喷涂砂浆的最优化配合比,同时结...     

Risikobasierter Ansatz zur Bewertung der Robustheit von Bauwerken

Ziel des vorliegenden Beitrages ist es, einen Überblick über die aktuellen Entwicklungen im Bereich der Bewertung und der Quantifizierung der Robustheit von Bauwerken zu geben. In diesem Sinne ist eine Zusammenstellung von Ansätzen und Ergebnissen aktueller Veröffentlichungen enthalten. Ein umfassender entscheidungstheoretischer Ansatz für die Berechnung und das Management der Robustheit wird vorgestellt. Dieser beinhaltet die Definition der Robustheit als eine Qualität eines Systems, welches das Bauwerk beinhaltet, d. h. eine Qualität, die auf der Grundlage einer Risikoanalyse bewertet werden kann. Um eine umfassende Risikoanalyse zu ermöglichen, wird ein szenarienbasierter Modellansatz eingeführt, welcher zwei Arten von Konsequenzen im System unterscheidet: direkte Konsequenzen (in Verbindung mit Schäden einzelner Komponenten des Systems) und indirekte Konsequenzen (in Verbindung mit einem Versagen des Systems). Die Definition des Systems spielt deshalb für die Risikoanalyse eine wichtige Rolle, und es wird diskutiert, wie die Robustheit für verschiedene Definitionen zu unterschiedlichen Ergebnissen und Erkenntnissen im Sinne des Managements der Integrität des Bauwerks im gesamten Lebenszyklus unter Berücksichtigung seiner Funktionalität führt. Weiterhin werden wichtige Aspekte der Standardisierung der Robustheitsanalyse, wie auch Anforderungen an die Robustheit, diskutiert und Vorschläge zum Umgang mit diesen Aspekten unterbreitet. Auf der Grundlage der vorgestellten Ansätze zur Berechnung der Robustheit eines Bauwerks wird beschrieben, wie Entscheidungen in Bezug auf den Entwurf, die Zustandsbewertung, auf Inspektionen und Wartung sowie in Bezug auf die Überwachung von Bauwerken, in Hinblick auf das Management der Risiken in allen Phasen des Lebenszyklus, optimiert werden können. Risk based approach for the assessment of the robustness of structures. The present paper serves as an overview of recent developments by the author on the assessment and quantification of robustness of structures; the paper aims in this sense not to present any new results but collects approaches and results from previous publications. A general decision theoretical approach to the assessment and management of structural robustness is outlined. Structural robustness is introduced as a quality of the system comprising the structure; a quality which can be assessed by means of risk assessments. To facilitate an appropriate risk assessment for structural systems a scenario based model approach is outlined which differentiates consequences into two different types: direct (related to damages to individual components) and indirect (related to collapse failures). The definition of the “structural system” thus plays an important role in the risk assessment and it is discussed how the robustness assessed according to different definitions of the structural system will lead to different results and insights of relevance for the lifecycle management of the structural integrity. Furthermore, the important aspects of standardization of robustness assessments as well as requirements to robustness are discussed and suggestions for the treatment of these are proposed. Based on the presented approach to the assessment of structural robustness it is outlined how decisions on design, condition assessment, inspection and maintenance as well as monitoring activities for structures can be optimized for the purpose of managing structural risks over all phases of the life‐cycle of structures.     

Postdisaster image‐based damage detection and repair cost estimation of reinforced concrete buildings using dual convolutional neural networks

Reinforced concrete (RC) buildings are commonly used around the world. With recent earthquakes worldwide, rapid structural damage inspection and repair cost evaluation are crucial for building owners and policy makers to make informed risk management decisions. To improve the efficiency of such inspection, advanced computer vision techniques based on convolutional neural networks have been adopted in recent research to rapidly quantify the damage state (DS) of structures. In this article, an advanced object detection neural network, named YOLOv2, is implemented, which achieves 98.2% and 84.5% average precision in training and testing, respectively. The proposed YOLOv2 is used in combination with the classification neural network, which improves the identification accuracy for critical DS of RC structures by 7.5%. The improved classification procedures allow engineers to rapidly and more accurately quantify the DSs of the structure, and also localize the critical damage features. The identified DS can then be integrated with the state‐of‐the‐art performance evaluation framework to quantify the financial losses of critical RC buildings. The results can be used by the building owners and decision makers to make informed risk management decisions immediately after the strong earthquake shaking. Hence, resources can be allocated rapidly to improve the resiliency of the community.     

Fatigue reliability of welded steel structures

In general, two different approaches to the formulation of the fatigue limit state are considered, the first based on S-N lines in combination with Miner’s damage accumulation rule, and the second based on fracture mechanics crack growth models and failure criteria. Often, the two approaches are used sequentially, with S-N being used at the design or preliminary assessment stage and fracture mechanics for more refined remaining life or inspection and repair estimates. However, it is essential to link the results, and the decisions made, at the design and assessment stages, and it is therefore important to develop compatible methodologies for using these two approaches in tandem. In doing so, it is essential to understand and quantify different uncertainty sources and how they might affect the robustness of the results obtained, and the subsequent decisions made about the structure. The objective of this paper is to highlight parts of recent research at the University of Surrey on the fatigue assessment of steel bridges. The work includes the development of a probabilistic fracture mechanics methodology for the prediction of fatigue reliability, using up-to-date crack growth and fracture assessment criteria and incorporating information on inspection and subsequent management actions.     

Residual strength of damaged steel ships and offshore structures

A review is made of various forms of structural damage which may occur in ships and offshore steel structures, with particular reference to the influence of such damage on stiffness and ductile strength. Consideration is given to damage in a ship's bottom or side shell as may be caused by collisions, grounding, hydrodynamic impact or explosions and to the influence of such damage on hull-girder bending strength. Reference is made to the effects of bending and denting of tubular members in offshore platforms and of collision damage in externally pressurised ring-stiffened cylinders as may be employed in submersibles and large-diameter tubulars. Some methods are suggested for evaluation of residual stiffness and strength with emphasis on approximate analysis techniques which can be applied quickly and economically to obtain an early assessment of damage effects.     

Risk Management of Large RC Structures within Spatial Information System

Abstract: The present article addresses the development of a spatial information system (SIS), which aims to facilitate risk management of large‐scale concrete structures. The formulation of the SIS is based on ideas developed in the context of indicator‐based risk modeling for concrete structures subject to corrosion and geographical information system based risk modeling concerning large‐scale risk management. The term “risk management” here refers in particular to the process of condition assessment and optimization of the inspection and repair activities. The SIS facilitates the storage and handling of all relevant information to the risk management. The probabilistic modeling utilized in the condition assessment takes basis in a Bayesian hierarchical modeling philosophy. It facilitates the updating of risks as well as optimizing inspection plans whenever new information about the condition of the structure becomes available. In the SIS, the various data of relevance for the risk management can be visualized in three dimensions. This feature and the other functionalities of the SIS are illustrated in an example considering the Danish Farø bridges.     

建(构)筑物加固设计失误与规范管理

分析了建(构)筑物修复、加固、改造设计中失误增多的问题,提出应加强加固设计的监督管理.建议有关部门尽快制定加固设计监督管理条例和相应的管理机构,尽快配齐各种结构加固设计规范.     

Das Sandwich‐Platten‐System (SPS)

Sandwich Plate System (SPS). SPS was initially developed to provide impact resistant plating for offshore structures, ice islands, working in the Canadian Beaufort Sea. Research and development over the last thirteen years has focused on basic research into structural behaviour and performance, material characterization, fire resistance and fire engineering analyses, as well as development of design rules and energy absorption design philosophies. In addition connection details specific to sandwich plate structures and methods for in‐situ installations (SPS Overlay), repair, prefabrication and inspection have been developed. This work summarized in this paper, clearly demonstrates that not only SPS plates can be designed to be structurally equivalent to stiffened steel plates, but that the implied economical use of SPS plates provides a number of further advantages with respect to performance and safety.     

On the assessment of robustness

A framework for assessing robustness is proposed, taking basis in decision analysis theory. Robustness is assessed by computing both direct risk, which is associated with the direct consequences of potential damages to the system, and indirect risk, which corresponds to the increased risk of a damaged system. Indirect risk can be interpreted as risk from consequences disproportionate to the cause of the damage, and so the robustness of a system is indicated by the contribution of these indirect risks to total risk. A framework is presented for measuring robustness in this way, and implications for system modelling and acceptable levels of robustness are discussed. Numerical studies of idealized structural systems are performed using this framework, to demonstrate the use of the proposed robustness index and provide insight into system properties affecting robustness. Considered exposures include the design live load and an extraordinary exposure representing a fire or explosion that causes the loss of one or more system components. The results indicate that properties affecting system reliability, such as number of components or the stochastic properties of the load, also affect robustness. Perhaps more interestingly, it is seen that properties such as failure consequences and time to repair a damaged system also affect this measure of robustness. The assessment framework is applied here to study damage tolerance, but the procedure can be applied as well to other aspects of robustness such as tolerance to human error in design or construction.     

On the robustness to corrosion in the life cycle assessment of an existing reinforced concrete bridge

Management of existing structures has traditionally been based on condition assessment, based on visual inspections, disregarding the susceptibility of different structural types to aging and deterioration. Robustness, as a measure of the effects of unpredictable damage to structural safety can be a complementary information to the results of inspection. Although robustness has mostly been used to evaluate the consequences of extreme events, a similar framework can be used to investigate the result of aging, allowing a better understanding of the potential effects of deterioration and allowing a better allocation of available maintenance funding. In this work, a probabilistic structural robustness indicator is used to quantify the susceptibility of structures to corrosion. The methodology is exemplified through a case study comprising an existing reinforced concrete bridge deck, heavily damaged due to reinforcement corrosion, and finally demolished due to safety concerns. Robustness measures the bridge deck safety tolerance to reinforcement corrosion. The principal effects of corrosion, including loss of area and bond between concrete and steel are modelled using a non-linear finite-element model, coupled with a Response Surface Method to compute the bridge reliability as a function of the corrosion level, and finally used to assess robustness. Results show that the redundancy of the bridge allows significant redistribution of loads between elements with different corrosion levels. As a result, the bridge presents significant robustness and tolerance to reinforcement corrosion.     

Spatial variability of damage and expected maintenance costsfor deteriorating RC structures

The paper develops a technique to predict life-cycle costs, using probabilistic information about the likelihood and extent of corrosion-induced cracking to reinforced concrete (RC) structures. The present paper focuses on the likelihood and extent of severe cracking as the criterion for the timing and cost of maintenance. The life-cycle cost and expected maintenance cost considers multiple repairs and various inspection intervals over the service life of the structural element. A repair cost function is also developed. Two common maintenance strategies are considered: repair and rehabilitation. It was found that for a 2% discount rate the benefits of delaying the timing of repairs outweigh the cost of increased extent of damage, for maintenance of a RC bridge deck.