Committee III.1: Ultimate Strength
Authors: Hess Paul E. , An Chen , Brubak Lars , Chen Xiao , Chiu Jinn Tong , Czujko Jurek , Darie Ionel , Feng Guoqing , Gaiotti Marco , Jang Beom Seon , Kefal Adnan , Makmun Sukron , Ringsberg Jonas , Romanoff Jani , Saad-Eldeen Saad , Schipperen Ingrid , Tabri Kristjan , Wang Yikun , Yanagihara Daisuke 
Published: April 2023

Committee Mandate

Concern for the collapse behaviour of ships and offshore structures and their structural components under ultimate conditions. Uncertainties in strength assessment shall be highlighted. Attention shall be given to the influence of response to load combinations including accidents; fabrication imperfections; life-cycle effects; and user approach. Consideration shall be given to the practical application of methods.

Introduction

Determining the ultimate strength of ship and offshore structures involves the ability to predict and measure component, sub-system, and system structural maximum capacity beyond which the capacity diminishes. The purpose of this committee is to present a summary of recent work published after the time period covered by the 2018 committee that addresses these goals within the guidance of the Committee Mandate. Effective consideration of these factors requires definition of terms and description of the use of ultimate strength calculations and measurements prior to directly addressing the objectives set forth in the Mandate.

1.1 Definitions

The ultimate strength of a structure is defined as the maximum load carrying capability beyond which the load carrying capacity reduces. This may be viewed as the definition of failure for ultimate strength of any structure. This committee mainly focused on compressive buckling failure mechanisms vs tensile failure that would lead to fracture, which is addressed in Technical Committee III.2.

The majority of marine structures are a type of thin-walled structure, where the maximum load carrying capability of one component might be reached prior to the system reaching its ultimate limit. Defining the boundaries of the structure whose strength is being assessed is important both to support the analysis process, but also to communicate this information for use in decision- making. For example, a stiffener-plate combination that reaches ultimate strength would not necessarily coincide with collapse of an entire grillage or hull girder cross-section. Both of these failure modes are used in limit state equations to support decision-making, but representing very different assessments of structural performance, reliability, or risk.

1.2 Report Structure

The report is organized into 7 Chapters and an Appendix, with the primary technical chapters being Chapters 2 through 6, covering fundamentals, materials and life-cycle effects, and ship and offshore structures, culminating in a unique benchmark in Chapter 6 and the Appendix.

Chapter 2 covers Fundamentals, introducing aleatory and epistemic uncertainty quantification and effects, elements of strength prediction tools with a focus on high fidelity numerical modeling and reduced order modeling, and experimentation.

Material and life-cycle effects are addressed in Chapter 3, highlighting issues related to degradation such as corrosion and cracking, consideration of distortion, damage or repair effects, and residual stresses resulting from the manufacturing process.