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In this paper, an important feature of time variant reliability problems is identified. The concept of barrier failure dominance (BFD) is introduced to characterize those problems where an out-crossing or overload failure is more likely to be caused by a very small realization of the barrier (resistance) than by an exceptionally large realization of the load process. This result arises from a study of the ensemble out-crossing rate approximation, reported in a previous paper and which is reviewed herein. It is shown how the notion of BFD can be used to understand the limits of application of the ensemble out-crossing rate approximation. It is also suggested that the acknowledgement of BFD can support the choice of the appropriate simplified solution method for particular problems. A three-dimensional load combination and a resistance degradation problem are studied as examples. The ensemble up-crossing rate approximation is compared with load process-based approximations, using the time-integrated approach, the load combination rule of Turkstra and the point-crossing formula.

The present paper describes an interpretation of the variation in material loss of aluminium specimens in sea water immersion at 14 different locations worldwide. Careful examination of the conditions under which aluminium corrodes in very low velocity sea water suggests that the only significant variables are temperature and aeration. This allows the field observations obtained as part of an ASTM sponsored worldwide 'round robin' test programme to be viewed largely as a function of temperature. It is found that corrosion tends to be generally low except at temperatures around about 10°C and in the region 20–27°C with a local peak at around 23°C. This pattern applies for all exposures to 5 years.

No abstract is provided for this article.

The external corrosion of old cast iron water mains is a major concern for water industries in many older cities. To better manage these assets, good quality mathematical models, based on real-world observations, are required for predicting future corrosion. Herein a recently proposed model for the long-term maximum corrosion depth of cast iron buried in soil is presented. The model is based on the bimodal model, recently shown to be applicable for cast iron corrosion in soil. The model was calibrated to field data from 37 sites. It was found that the main factors influencing soil corrosion are, in order, time of wetness and inorganic nitrate concentration (for microbiological attack). Other parameters including chloride, phosphate and carbonate content were also considered, but were found to be less important. The potential influence of poor quality backfill and physical damage to the pipe on corrosion depth is also discussed.

Improvements on the approximate solutions for the standard multinormal or multivariate normal distribution function based on the first order structural reliability concepts are proposed. The numerical accuracy and efficiency of three methods of obtaining the solutions are compared. For parallel systems problems, it is shown that the suggested first order multinormal (FOMN) approach produces results significantly closer to the exact answer than either those of the crude or the improved FOMN solutions. The performance of the improved and general FOMN approaches when applied to high reliability series systems appears to be as good as or even better than those obtained by the well-known second order bounds. (Author/TRRL)

The sustainability of Royal Australian Navy (RAN) ships is affected by structural deterioration, including corrosion, which results in material loss through the oxidation of exposed steel. Deterioration through corrosion is one of the determining factors in developing the operational planning and economic aspects of structural maintenance management. The extent of corrosion depends on many environmental parameters making it difficult to predict efficient repair strategies using periodical time based maintenance. With this consideration, and the fact that the RAN owns an increasingly ageing fleet, new and innovative ways are required to effectively manage a ship. Presently there is no simulation tool available to the RAN that allows ship corrosion to be predicted. Tools such as these have been developed empirically for some commercial ships, however the corrosion loss models exhibit a high variability. By taking into consideration the operational parameters of the vessel a greater accuracy in modelling corrosion can be achieved.

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Life extension of ageing steel structures such as naval ships requires consideration of plate thickness losses due to corrosion, particularly when protective measures such as paint coatings and sacrificial protection are not entirely effective. Traditionally, corrosion prediction models for ships take no account of the operational profile. Consequently, the corrosion models have an inherently high variability with poor corrosion prediction capability. A new corrosion model for the prediction of corrosion loss in the seawater ballast tanks of naval vessels has been developed. The model incorporates previously available corrosion models for immersion corrosion and atmospheric corrosion and takes account of operational and environmental variables. Experimental validation is presented for a trial on an operational naval vessel.

No abstract is provided for this article.

Optimization of structures for design has a long history, including optimization using numerical methods and optimality criteria. Much of this work has considered a subset of the complete design optimization problem—that of the technical issues alone. The more general problem must consider also non-technical issues and, importantly, the interplay between them and the parameters which influence them. Optimization involves optimal setting of design or acceptance criteria and, separately, optimal design within the criteria. In the modern context of probability based design codes this requires probabilistic acceptance criteria. The determination of such criteria involves more than the nominal code failure probability approach used for design code formulation. A more general view must be taken and a clear distinction must be made between those matters covered by technical reliability and non-technical reliability. The present paper considers this issue and outlines a framework for rational optimization of structural and other systems given the socio-economic and political systems within which optimization must be performed.

This report presents a critical review of the various methods which have been suggested for the reduction of human error (and in particular gross human error) in structural engineering. The methods suggested have included a) education, b) complexity reduction, c) personnel selection, d) legal sanction and e) control. It is argued that only the latter two approaches have validity from a societal viewpoint, although all are desirable. The available objective knowledge about these latter approaches is reviewed and some suggestions for future research made. For the abstracts of parts I and II see TRIS Nos. 394165 and 394166. (Author/TRRL)

Examination of the conclusions which may be drawn from the study of cases of structural failure show these to be inconsistent between various investigators. It is suggested herein that to resolve these problems, detailed studies of the causes and underlying mechanisms for structural failure are required, even though this severely limits the data that can be employed. Starting from the development of a quite general model of the causes of structural failure, together with a set of plausible hypotheses, implications are derived for the type of information that can be obtained using limited data. It is suggested that the study of well- reported cases of failure can be useful in identifying error- causing- potentials in the conceptualization, detail design, documentation and execution of structural projects, but that only socially weighted relative values can be established from such a study. Particular attention is given to the relative importance of so- called uncertainty type (or gross) errors compared to errors arising from natural variability. Finally, it is suggested that the manipulation of control processes is likely to be an effective practical means of reducing structural failure. (Author/TRRL)

Solving some integro-differential equation we find the Laplace transformation of the first passage time for Filtered Poisson Process generated by pulses with uniform or exponential distributions. Also, the martingale technique is applied for approximations of expectations accuracy is veryfying with the help of Monte-Carlo simulations.

No abstract is provided for this article.

The reliability of structures composed of many members may be estimated by considering all ways in which the structure may fail. Procedures to achieve this have been extensively explored for structures composed of rigid-ideal-plastic materials or members. However, there has been rather less consideration for structures with more general member properties. The present paper shows that subject to certain simplifying assumptions, the limit state equations necessary for reliability analysis using the truncated enumeration method previously developed by the authors can be derived in a systematic manner by using an extension of the incremental load procedure due to F. Moses.

No abstract is provided for this article.

A discussion of a paper with the aforementioned title by Ahammed and Melchers, published in this journal (Volume 120, Number 6, November/December 1994), is presented. Discusser Prevost begins by suggesting that the authors confirm that the material of the pipes addressed is steel. He then moves on to discuss the two types of loadings separately, assuming steel pipes only are considered. Discusser Prevost also states that elastic limit is not a criterion of failure but a permanent feature. He concludes by pointing out that the paper lacks a discussion on jointing systems. Discussion is followed by closure from the authors.