Steel brackets are customarily used to prevent sideways deformation or lateral-torsional buckling in the supporting components of structures such as ships and offshore platforms. The aims of this study are to undertake nonlinear finite element analysis to examine the ultimate-strength characteristics of steel brackets, and to develop a simple design formula to predict the ultimate strength of a steel bracket. The structural features of steel brackets in real ship structures are investigated. Finite element modelling techniques are developed to compute the ultimate-strength behaviour of steel brackets with different design variables, such as material type and breadth to height ratio. The findings of the research and the above-mentioned design formula have the potential to enhance the structural design and safety assessment of steel brackets in ship structures.

Evgeny Appolonov Krylov Shipbuilding Research Institute, Russia Jong-Hyun Baek Korea Gas Corporation, Korea Yong Bai Zhejiang University, China Amin Barari Aalborg University, Denmark Tadeusz Borzecki Gdansk University of Technology, Poland Kim Branner Technical University of Denmark, Denmark Tim Bunnik MARIN, The Netherlands Daejun Chang Korea Advanced Institute of Science and Technology (KAIST), Korea Fai Cheng Lloyd’s Register, UK Yoo Sang Choo National University of Singapore, Singapore Wei Cheng Cui China Ship Scientific Research Center, China Jerzy Czujko Nowatec AS, Norway Purnendu K. Das Universities of Glasgow and Strathclyde, UK M. C. Deo Indian Institute of Technology Mumbai, India Menglan Duan China University of Petroleum, China Gennadiy V. Egorov Marine Engineering Bureau, Ukraine Alberto Francescutto University of Trieste, Italy Paul A. Frieze PAFA Consulting Engineers, UK Carlos Guedes Soares Instituto Superior Tecnico, Portugal Raffaele Iaccarino CETENA SPA, Italy Atilla Incecik Universities of Glasgow and Strathclyde, UK Taek Soo Jang Pusan National University, Korea Jorgen Juncher Jensen Technical University of Denmark, Denmark Norman Jones University of Liverpool, UK Dale Karr University of Michigan, USA Yonghwan Kim Seoul National University, Korea Tae-Wan Kim Seoul National University, Korea Magnus Langseth Norwegian University of Science and Technology, Norway Seung Keon Lee Pusan National University, Korea Heba W. Leheta University of Alexandria, Egypt Inge Lotsberg Det Norske Veritas, Norway Yoshitaka Ogawa National Maritime Research Institute, Japan Guy Parmentier Bureau Veritas, France Philippe Rigo University of Liege, Belgium Jonas Ringsberg Chalmers University of Technology, Sweden Cesare Rizzo University of Genova, Italy Albert A. Rodger University of Aberdeen, UK Myung-Il Roh University of Ulsan, Korea Prasanta K. Sahoo Florida Institute of Technology, USA Emmanuel Samuelides National Technical University of Athens, Greece R. Ajit Shenoi University of Southampton, UK S. Surendran Indian Institute of Technology Madras, India Ken Takagi University of Tokyo, Japan Osman Turan University of Strathclyde, UK Ge Wang American Bureau of Shipping, USA Norio Yamamoto ClassNK, Japan Jianming Yang Shanghai Jiao Tong University, China Vedran Zanic University of Zagreb, Croatia Shengming Zhang Lloyd’s Register, UK

When considering an existing tanker for conversion to an FPSO with an expected service life of 15 or more years, a comprehensive reassessment of the hull structure should be conducted and appropriate corrosion margins for the hull girder and local scantlings should be established. Among all structural deteriorations incurred by trading tankers with an age of 10 years or more, corrosion wastage represents the most dominant one. There are two types of corrosion found to occur most frequently in aging tankers, namely general corrosion and pitting corrosion. In the case of general corrosion, the yielding and buckling strength of plating and structural members can be readily determined by deducting the corrosion wastage from the as-built scantling values. However, the determination of the strength reduction due to pitting corrosion is more difficult and complex, and the use of nominal loss of material may be insufficient. This paper discusses the findings from the authors' investigations of a number of different pitting corrosion distributions, and proposes recommendations for considering pitting corrosion effects during the establishment of renewal scantlings at the time of conversion.

Strength of offshore structures including FPSOs consists broadly of three aspects which are global intact and damaged strength, and local strength. Any of these strength aspects can be assessed by either prescriptive rule or finite element analysis (FEA). While many considerations relate to behavior in the linear elastic regime, the buckling and ultimate strength of both structural components (plate and stiffened panels) and structural systems can involve material and geometric nonlinearity behavior beyond the elastic region. With the development of computers and robust methods for nonlinear FEA, there has been a tremendous increase in the number of studies of structures under plastic or elasto-plastic behavior. However, even with today’s computers and software, nonlinear FEA of offshore structures remains complex and is not routinely applied in design analysis. Considerable effort therefore continues to be devoted to the development of simplified methods for rapid structural assessment and design analysis, instead of lengthy and complex nonlinear FEA. In this paper, various bucking and ultimate strength methodologies for plate and stiffener panels are first introduced. Each method is then compared with collected test data for buckling and ultimate strength of plate panels and stiffeners. Finally, conclusions are summarized based on the comparison study.

While it has been reportedly recognized that most casualties of marine structures including total losses have involved corrosion degradation, corrosion is one of the most important factors influencing safety and integrity of aging structures. Corrosion wastage also causes significant issues in terms of health, the environment, and financial expenditure. While the loss of a total system typically causes great concern, maintenance and repair of damaged structures is costly to society and the environment in general and important to the economic viability of the enterprises involved in particular. It is thus essential to develop advanced technologies that can allow for the proper assessment and management of corrosion. An overview of some recent developments in corrosion assessment and management for steel ships and offshore structures is addressed in the present paper. Relevant corrosion mechanisms, corrosion wastage models, design considerations (design corrosion-margin values), and preventive measures with the emphasis on marine structures are presented.

This paper is a logical sequel to the authors’ last two SNAME annual meeting papers (Paik et al. 2000, 2001) which dealt with the ultimate limit state design of ship plating and stiffened panels. It aims to deal with the advanced ultimate limit state design of ship hulls under vertical bending moments. Traditionally, design criteria and procedures were primarily based on allowable stresses and buckling checks. It is now well recognized that the limit state approach is a better basis for design, because it determines, in a more realistic way, the real safety margin of any economically designed structure. While the limit state design for steel structures uses limit states classified into four types, namely serviceability limit state, ultimate limit state, fatigue limit state and accidental limit state, the present paper is concerned with the ultimate limit state of ship hulls. In this paper, efficient and accurate methodology for the progressive collapse analysis of ship hulls is presented. The characteristics of progressive collapse behavior of a total of 10 typical merchant ships under vertical bending are then investigated using the analysis method presented. Effects of lateral pressure and horizontal moment on the hull girder ultimate vertical moment are studied. Closed-form ultimate strength formulations for the ultimate strength of ships are developed. Finally, the ultimate limit state design format for ships is addressed. ABS TECHNICAL PAPERS 2002 86 Ultimate Limit State Design of Ship Hulls INTRODUCTION During the last few decades, the emphasis in structural design has been moving from the allowable stress design to the limit state design, since the latter approach has many more advantages. A limit state is formally defined as a condition for which a particular structural member or an entire structure fails to perform the function that it has been designed for. From the special viewpoint of a structural designer, four types of limit states are considered, namely • Serviceability limit state (SLS) • Ultimate limit state (ULS) • Fatigue limit state (FLS) • Accidental limit state (ALS) SLS conventionally represents failures under normal operations due to deterioration of less vital functions such as • Local damage which may reduce the durability of the structure or affect the efficiency of structural or non-structural elements • Unacceptable deformations which affect the efficient use of structural or non-structural elements or the functioning of equipment • Excessive vibration or noise which causes discomfort to people or affect non-structural elements or the functioning of equipment • Deformations and deflections which may spoil the aesthetic appearance of the structure ULS (also called ultimate strength) represents the collapse of the structure due to loss of structural stiffness and strength related to • Loss of equilibrium in part or of entire structure, considered as a rigid body (e.g., overturning or capsizing) • Attainment of the maximum resistance capacity of sections, members or connections by gross yielding, rupture or fracture • Instability in part or of the entire structure resulting from buckling or plastic collapse of plating, stiffened panels and support members FLS represents fatigue crack occurrence in structural details due to stress concentration and crack damage accumulation under the action of repeated loading. ALS represents excessive structural damage as consequences of accidents, e.g., collisions, grounding, explosion and fire, which affect the safety of the structure and the environment. It is important to note that in limit state design of a structure, these various types of limit states may be required to have different safety levels. The actual safety level to be attained for a particular type of limit state is a function of its perceived consequences and ease of recovery to be incorporated in design. The structural design criteria against the ULS are based on plastic collapse or ultimate strength. The design of many types of structures including merchant ship structures has in the past tended to rely on estimates of the buckling strength of components, usually from their elastic buckling strength adjusted by a simple plasticity correction. This is represented by point A in Fig.1. In such a scheme, the structural designer does not use detailed information on the post-buckling behavior of component members and their interactions. The true ultimate strength represented by point B in Fig.1 is typically higher although one can never be sure of this. Proportional limit Buckling strength Ultimate strength Design load level Linear elastic response Displacement Fo rc e Design load level A B 1

The present study was undertaken by the support from Ship Structure Committee (http://www.shipstructure.org), a North American-based interagency research and development committee, in association with SR-1446 project, and also from Alcan Marine, France. Empirical expressions are developed for predicting the ultimate compressive strength of welded aluminum stiffened panels used for marine applications. Existing data of the ultimate compressive strength for aluminum stiffened panels experimentally and numerically obtained by the SR-1446 project is used for deriving the formulations which are expressed as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. The formulae implicitly include the effects of weld induced initial imperfections, and softening in the heat affected zone.

1. Overview of ship-shaped offshore installations 2. Front-end engineering 3. Design principles, criteria and regulations 4. Environmental phenomena and application to design 5. Serviceability limit state design 6. Ultimate limit state design 7. Fatigue limit state design 8. Accidental limit state design 9. Topsides, mooring and export facilities design 10. Corrosion assessment and management 11. Inspection, maintenance and repair 12. Tanker conversion and decommissioning 13. Risk assessment and management Appendix 1. Terms and definitions Appendix 2. Scale definitions of winds, waves and swells Appendix 3. Probability of sea states at various ocean regions Appendix 4. Scaling laws for physical model testing Appendix 5. Wind tunnel test requirements Appendix 6. List of selected industry standards.

Ship-shaped offshore units are some of the more economical systems for the development of offshore oil and gas, and are often preferred in marginal fields. These systems are especially attractive to develop oil and gas fields in deep and ultra-deep water areas and remote locations away from existing pipeline infrastructures. Recently, the ship-shaped offshore units have been applied to near shore oil and gas terminals. This 2007 text is an ideal reference on the technologies for design, building and operation of ship-shaped offshore units, within inevitable space requirements. The book includes a range of topics, from the initial contracting strategy to decommissioning and the removal of the units concerned. Coverage includes both fundamental theory and principles of the individual technologies. This book will be useful to students who will be approaching the subject for the first time as well as designers working on the engineering for ship-shaped offshore installations.

Although substantial efforts are now being directed by the maritime industry toward the application of limit-state design approaches, the shipbuilding industry has traditionally used classification society rules for design of trading ships. On the other hand, the offshore industry has more extensively applied first-principles methods based on limit states. It may be said that the design approach for moored ship-shaped offshore structures, such as FPSOs, often takes a form that is a fusion of the two industry approaches.

The performance of a structure and its components is described using limit-state functions that separate desired states from undesired states. The physical effects of exceedance of a limit state may be either reversible or irreversible. For the reversible case, removal of the cause of the exceedance allows the structure to return to a desired state. For the irreversible case, the same is not true and certain consequences, such as damage, may occur depending on the nature of the limit state. The consequences may, in turn, be either recoverable or unrecoverable from the deformed state. For example, if the damage is limited, say, in the form of a localized permanent set in a case where the same is not desired, the condition may be repairable, for example, by replacing the affected parts.