Publications

Bacteriological influence in the development of iron sulphide species in marine immersion environments

Bacteria and microbiological consortia play an important role in the corrosion of steel in marine environments. There are laboratory based experimental findings and images verifying the presence of such consortia but there are few images in the literature of the interaction between bacteria and corrosion processes. The present paper considers the marine immersion corrosion of steel and presents a number of new images which appear to show steps in the metamorphosis of the iron in the steel to forms of iron oxide and to iron–sulphur compounds. These transformations appear to involve interaction with bacteria. Scanning electron microscope images were obtained for the specimens which were exposed to actual seawater conditions. Energy dispersive spectroscopy and X-ray diffraction were used to analyse the corrosion products. Inferences are made about the role of bacteria in the transformations from iron to iron–sulphur compounds.

Directional Simulation for Time-Dependent Reliability Problems

No abstract is provided for this article.

MICROBIAL CORROSION OF SEWER PIPE IN AUSTRALIA- INITIAL FIELD RESULTS.

Column-base response under applied moment

In the emerging interest in the serice ability of steel structures, the ability to predict structural deflections under various loading scenarios requires knowledge of the response of the connections employed in the steel frame. Although there have been extensive research efforts for beam-column connections, surprisingly little is known at present about the behaviour of nominally ‘pinned’ baseplate connections. The paper presents the results of 10 moment reversal tests on nominally ‘pinned’ steel bases for 200 U B 25 columns and presents a simple mathematical model for the prediction of elastic stiffness of the connection. The model is based on the reported test results as well as on earlier tests on considerably larger column sections and thicker base plates. Both two-bolt and four-bolt connections are considered. A discussion of implications for practical design closes the paper.

Corrosion and pitting of 6060 series aluminium after 2 years exposure in seawater splash, tidal and immersion zones

New longer-term observations of corrosion and pitting of 6060-grade aluminium alloy showed that the most intensive pitting and corrosion occurred in the marine immersion zone. After 2 years exposure the corrosion morphology included shallow and deep pits, intergranular corrosion and crystallographic attack. The deepest pits showed complex morphologies, spatially and with depth. This is considered the result of localized anoxic conditions formed under accumulated corrosion products. Less severe corrosion was observed in the splash and tidal zones. For these the pit morphologies were less complex.

Mechanisms and conditions for the formation of rusticles on steel immersed long-term in natural waters

Stalactite-like rust formations, known as 'rusticles' have been observed on some ocean shipwrecks usually after extended exposures and sometimes associated with microbiological influences. Herein that possibility is examined using field observations for some 40 different shipwrecks in seawaters and open freshwaters. Comparison is made to somewhat similar rust formations, known for more than 100 years as 'tubercles', that are mounds of highly non-uniform corrosion product found both in freshwaters and in seawaters. The data show that tubercles are widespread in occurrence but that rusticles form only in seawaters and that their typical stalactite-like formation is possible only in quiescent exposure conditions, caused by the extended build-up of rusts resulting from the oxidation of downward migration of ferrous chloride, itself generated by pitting corrosion under localized anaerobic seawater conditions. The processes in the formation of rusticles and tubercles are otherwise similar. Microbiological processes may be involved but are not essential.

Human error in structural design

No abstract is provided for this article.

FORM for discontinuous and truncated probability density functions

The common iterative FORM algorithm deals with random variables having continuous and smooth probability density functions. In some cases when the algorithm is applied to problems with discontinuous probability density functions difficulties may occur with convergence. For truncated density functions the routine may breakdown completely. Some examples illustrating these potential problems are given and the reasons described. Modifications to the standard iterative FORM algorithm are proposed.

Dominant failure modes in stochastic structural systems

In an analysis of redundant structural systems in which either or both loading systems and/or member resistances are stochastic variables, all modes of failure are potentially of significance in the calculation of structural reliability. In practice, however, many modes do not contribute very much, and a problem has been to identify those modes which are stochastically dominant. In this paper a general, iterative procedure called the Truncates Enumeration Method [TEM] to determine the most stochastically dominant modes is derived from successive systematic curtailment of the results which would be obtained by complete enumeration. In this way, it is shown that the procedure presented has the capability to produce all dominant modes to within the accuracy of the criteria used for curtailment. The method is similar to that proposed by Murotsu et al. It is also shown that the incremental load method (ILM), proposed by Moses et al., has certain features common to TEM, that both techniques are essentially incremental in nature and that both methods produced the same mode failure probability statement, each using quite distinct procedures. It is finally argued that the methods are not restricted merely to the materials behaviour properties studied thus far by their proponents.

Discussion of SEI 3/93: Structural Analysis: Elastic or Plastic?

"Discussion of SEI 3/93: Structural Analysis: Elastic or Plastic?." Structural Engineering International, 3(4), p. 260

Radial Importance Sampling for Structural Reliability

In Cartesian coordinates importance sampling has been remarkably effective in improving the efficiency of Monte Carlo simulation techniques for reliability calculations in structural engineering. The approach is extended in this paper to the (hyper‐) polar coordinate system, firstly using an importance sampling function that has its mean at the radial distance, from the mean vector, where the limit‐state functions are expected to lie. This approach is then refined by using interpolation to estimate the location of the crucial limit state along any radial direction and to censor sampling not in the failure domain. The third development is to approximate, in a radial direction, the "tail" of the original probability density function by an appropriate Gaussian probability density function, and then to apply the established theory for directional simulation. Example applications for a linear limit‐state function and for a circular limit‐state function are given.

Observations About the Performance of Reinforcement in Marine Environments

The corrosion of reinforcement bars and prestressing strands in concrete structures is a significant issue in coastal environments. The conventional wisdom is that time to initiation of such corrosion is governed by the rate of diffusion of chlorides and other aggressive species to the reinforcement. However, the rate of reinforcement corrosion is not significantly affected by the presence of chlorides. A review is given of recent observations of the lack of serious reinforcement corrosion for some older structures in marine environments. These and new experimental results for concretes in actual seawater exposures show that the time to initiation of corrosion of reinforcement is delayed for concretes with high calcium carbonate content. Observations from on-gong experimental investigations for the effect of low heat cement, water and aggregate cement ratios and the level of salinity of salt water in the concrete mix also are presented.

On the theory of optimal, constant thickness fibre-reinforced plates—II

The investigation of optimal fibre reinforcement layouts begun earlier1 is continued and extended to another important combination of support conditions. It is also shown that all the deflected shapes for the slabs discussed in the previous paper are everywhere both displacement and slope continuous, and hence are global optima.

Trends in Longer-Term Corrosion Loss of Magnesium Alloys

The corrosion of magnesium alloys is often considered to differ in behaviour and development with time from most other metals and alloys because they show evolution of hydrogen right from first exposure. However, data extracted from the open literature indicate that magnesium alloys develop corrosion mass-loss trends with time that are consistent with the so-called bimodal pattern, which is topologically similar to those of other alloys. Examples are given of such trending for magnesium alloys under immersion, half-tide and various atmospheric exposure conditions. The critical roles of corrosion pitting and its development into localised corrosion are discussed. For high-purity magnesium alloys, the transition to longer-term corrosion, which is rate-controlled by the hydrogen evolution cathodic reaction, occurs quickly, within days. Comments are made about the application of measurements of hydrogen evolution and of electrochemical methods to make rapid estimates of shorter-term corrosion rates.

Structural Optimization in a Non- Deterministic Setting

No abstract is provided for this article.

STRUCTURAL RELIABILITY ASSESSMENT FOR MAJOR STRUCTURES.

Keywords NEWCASTLE UNIVERSITY NSW STRUCTURAL, RELIABILITY, ASSESSMENT, STRUCTURES, ECONOMICS, DECISIONS, THEORY, METHODS, PROCEDURE, TECHNIQUES, MONTE CARLO, SYSTEMS, ALGORITHMS, LIMIT STATE, EQUATIONS, SIMULATION, SAMPLING, CALCULATIONS... Show All

First Passage Time of Filtered Poisson Process with Exponential Shape Function

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.

Probabilistic Modelling of Marine Corrosion of Steel Specimens