Our knowledge to model, analyse, design, maintain, monitor, manage, predict and optimise the life-cycle performance of structures and infrastructures under uncertainty is continually growing. However, in many countries, including the United States, the civil infrastructure is no longer within desired levels of performance and safety. Decisions regarding civil infrastructure systems should be supported by an integrated reliability-based life-cycle multi-objective optimisation framework by considering, among other factors, the likelihood of successful performance and the total expected cost accrued over the entire life-cycle. The primary objective of this paper is to highlight recent accomplishments in the life-cycle performance assessment, maintenance, monitoring, management and optimisation of structural systems under uncertainty. Challenges are also identified.

Life-cycle performance, management, and optimisation of structural systems under uncertainty: accomplishments and challenges 1

Risk assessment in maritime transportation

Aluminum sandwich construction has been recognized as a promising concept for structural design of lightweight transportation systems such as aircraft, high-speed trains and fast ships. The aim of the present study is to investigate the strength characteristics of aluminum sandwich panels with aluminum honeycomb core theoretically and experimentally. A series of strength tests are carried out on aluminum honeycomb-cored sandwich panel specimen in three point bending, axial compression and lateral crushing loads. Simplified theories are applied to analyze bending deformation, buckling/ultimate strength and crushing strength of honeycomb sandwich panels subject to the corresponding load component. The structural failure characteristics of aluminum sandwich panels are discussed. The test data developed are documented.

The strength characteristics of aluminum honeycomb sandwich panels

Offshore wind is a source of clean, renewable energy of great potential value to the power industry in the context of a low carbon society. Rapid development of offshore wind energy depends on a good understanding of technical issues related to offshore wind turbines, which is spurring ongoing research and development programmes. Foundations of offshore wind turbines present one of the main challenges in offshore wind turbine design. This paper reviews the present state of knowledge concerning geotechnical and structural issues affecting foundation types under consideration for the support structures of offshore wind turbines, and provides recommendations for future research and development.

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Foundations of offshore wind turbines: A review

This paper develops an efficient methodology to perform reliability-based design optimization (RBDO) by decoupling the optimization and reliability analysis iterations that are nested in traditional formulations. This is achieved by approximating the reliability constraints based on the reliability analysis results. The proposed approach does not use inverse first-order reliability analysis as other existing decoupled approaches, but uses direct reliability analysis. This strategy allows a modular approach and the use of more accurate methods, including Monte-Carlo-simulation (MCS)-based methods for highly nonlinear reliability constraints where first-order reliability approximation may not be accurate. The use of simulation-based methods also enables system-level reliability estimates to be included in the RBDO formulation. The efficiency of the proposed RBDO approach is further improved by identifying the potentially active reliability constraints at the beginning of each reliability analysis. A vehicle side impact problem is used to examine the proposed method, and the results show the usefulness of the proposed method.

A direct decoupling approach for efficient reliability-based design optimization

The aim of this study is to derive a simple analytical formula for predicting the ultimate collapse strength of a single- and double-hull ship under a vertical bending moment, and also to characterize the accuracy and applicability for earlier approximate formulations. It is known that a ship hull will reach the overall collapse state if both collapse of the compression flange and yielding of the tension flange occur. Side shells in the vicinity of the compression and the tension flanges will often fail also, but the material around the final neutral axis will remain in the elastic state. Based on this observation, a credible distribution of longitudinal stresses around the hull section at the overall collapse state is assumed, and an explicit analytical equation for calculating the hull ultimate strength is obtained. A comparison between the derived formula and existing expressions is made for largescale box girder models, a one-third-scale frigate hull model, and full-scale ship hulls.

A simple formulation for predicting the ultimate strength of ships

Estimation of ship motions using closed-form expressions

The objective of this paper is to develop a modified Paik–Mansour formula for the ultimate strength calculations of ship hulls subject to vertical bending moments. The method is based on a credible bending stress distribution over the hull cross-section presumed at the ultimate limit state. The accuracy of this method is demonstrated through comparison with computations obtained using more refined methods, such as non-linear finite-element method, intelligent super-size finite-element method, and idealised structural unit method. Statistical analysis of the hull girder ultimate strength based on comparisons among the various computations is carried out in terms of their mean values and coefficients of variation. The original Paik–Mansour method is found to be inapplicable to the case of a pure vertical bending moment depending on the ship's hull type and/or vertical bending direction, but the modified Paik–Mansour method is more general and is able to resolve this issue.

Modified Paik–Mansour formula for ultimate strength calculations of ship hulls

Dans la conception de navires, un critere de fiabilite consiste en general en une inequation dont les deux membres sont des fonctions de variables aleatoires et qui doit etre satisfait avec une probabilite suffisante. On obtient l'expression de la variance de chacune de ces fonctions par un developpement en serie de Taylour autour de sa valeur moyenne, limite aux termes du premier degre

Implementation of reliability methods to marine structures

This paper provides a demonstration on the use of probability- bases ship structural safety analysis and enumerates the benefits in comparison with traditional methods. Reliability techniques are developed to determine safety levels of existing vessels, taking into consideration uncertainties in loads, strength and calculation procedures. Ultimate, serviceability and fatigue limit states are developed and applied to an existing tanker. The corresponding load models are examined and, in some instances, further developed. Safety indices associated with yielding, buckling, and fatigue are calculated. Conclusions are drawn regarding the benefits and drawbacks of using probability-based ship safety analysis.

Alaa E. Mansour

Papers

A simple formulation for predicting the ultimate strength of ships

Estimation of ship motions using closed-form expressions

Modified Paik–Mansour formula for ultimate strength calculations of ship hulls

Implementation of reliability methods to marine structures

Probability-based ship structural safety analysis