640 publications from this institution
There are essentially two periods when microbiological activity is important for the corrosion of steel coupons in marine environments. The first commences soon after first exposure but becomes ineffective after some months, for reason(s) not yet elucidated. The second period commences when sufficient rust layers have built-up on the corroding surface to permit new microbiological activity under suboxic and anoxic conditions. Since microbiological activity depends on the availability of appropriate micro-environments and on the rate of supply of necessary nutrients, it is argued that the first period concludes as a result of the changing micro-environment caused by the build-up of corrosion products. This interferes both with the metabolite flux and the availability of iron as a necessary nutrient for bacterial metabolism. A model consistent with field observations is proposed.Keywords: MICCORROSIONBACTERIANUTRIENTSSTEELSEAWATER
Microbiologically influenced corrosion (MIC) of reinforced concrete sewer systems is a major issue for waste water authorities world-wide. Global repair costs are estimated at billions of dollars per year. Advanced stages of corrosion may trigger structural failure with potentially serious operational, economic and societal consequences. The fundamental issues involved in concrete sewer deterioration are reasonably well-understood but much less developed is the quantitative prediction of the rate at which deterioration is likely to occur under particular operating environments. An outline is given of a current industry-sponsored research project that aims to develop a phenomenological model of the sewer corrosion process for use in estimating the reliability and the expected remaining service life of concrete sewers. The model will be based on corrosion science but to ensure relevance to use in industry it will be calibrated to field observations and specific laboratory testing. This will also involve historical records and the experience of the industry participants. Parameters of particular interest include H2S levels, temperature and humidity and the effect of odour control measures.
Considerable attention has been given to the plastic design of plates and grillages of uniform depth for minimum reinforcement material consumption, but very little has been given to nonuniform depth structures. This paper attempts to fill some of this gap. It will be shown that the optimality conditions for plates of nonuniform thickness can be derived quite simply from the Marcal-Prager-Shield associated structure optimization theory. These conditions are applied to an axisymmetric plate or grillage with predefined thickness variation, a square simply supported flat plate with differing reinforcement depths and to the more practical problem of an infinite flat plate with drop panels, supported on finite columns. Some remarks about the practical application of the results close the paper.
The variation of structural reliability with time is developed for a simple portal frame structure in the context of low-cycle fatigue under high level but short duration overloading occurring at random intervals during the design life of the structure. Inelastic fracture mechanics theory is employed for the analysis of low-cycle fatigue, and Monte Carlo simulation used for the reliability analysis. Some indicative results are given, limitations inherent in the present analysis are noted. (Author/TRRL)
A method for reliability assessment of deteriorating reinforced concrete slab bridges is presented. The method is based on the combination of a nonlinear finite element structural model and the first-order method for reliability estimation. Deterioration of bridges due to corrosion of embedded reinforcing steel is considered, including spalling and debond between concrete and the corroded reinforcement. The influence of uncertainties in material properties, geometry, loads, and corrosion parameters on the estimate of the bridge reliability is taken into account. Two examples illustrating application of the method are provided.
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.
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.
It has been observed in the shipping industry that the rate of corrosion of steel plate may increase with longer duration of exposure, typically over many years. This effect has been attributed to the flexure of ships plates causing the loss of protective rust layers. The present paper describes the results of laboratory experiments in which plates with pre-existing rusts were subject to high levels of tensile strain, with and without subsequent exposure and corrosion. All rusts were obtained by exposing the steel to a natural marine environment, including the atmospheric and tidal zones. Careful observation of the rusts under tensile strain conditions showed that only strains near and beyond the elastic limit of the steel have the capacity to cause significant damage to the rust layers. Subsequent short-term exposure tests on pre-corroded and pre-strained steel coupons showed that there can be a moderate (10–15%) increase in the short-term corrosion rate.
Data collected from ageing ships indicate that the rate of corrosion of ship's plating may increase with long periods of exposure when combined with plate flexure. The reasons for this have not been clarified. Herein, the possibility is investigated that the observed effect is due to the loss of protective rusts under high strains in the steel plating, as might be caused by high sea-states and during loading and unloading. Recently, relatively short-term exposure studies of the tensile strain-induced fracture of rusts formed on structural steels during natural marine exposure show an increase in corrosion rate of some 10–15%, but only when the strains are near and beyond the elastic limit of the steel. This has implications for ship management. An interpretation is given for the corrosion loss curves reported in the literature and it is shown that, qualitatively at least, they are consistent with earlier observations and models for the corrosion of steel in marine environments. It is proposed that the validity of the conclusions be tested using long-term exposures under corrosion and flexure conditions in actual ships.
Mild steels exposed to marine immersion conditions in which carbonate solubilities are exceeded, leading to deposition of calcareous material, have been shown to exhibit much-reduced corrosion rates compared with corrosion under conditions in which there is no exceedance of solubility limits and therefore no calcareous deposition. However, the differences in corrosion including the potential effect of microbiologically influenced corrosion (MIC) in these conditions have not been examined systematically in the literature. The study reported herein involves short- to medium-term marine immersion exposures (up to 18 month) of mild steel coupons in natural seawater (control) and in environments using the same seawater source dosed with (1) CaCO3, acting as an inorganic particulate suspension representative of that encountered in seawater with elevated calcareous content; and (2) a nitrate salt, acting as an industrial pollutant and bacterial nutrient source. The results show the extent to which the deposition of particulate CaCO3 from suspension in seawater onto and into the rusts reduces the rate of corrosion of mild steel; a rate that was found to be dependent on the coupon orientation within the seawater. Coupons that were permanently buried beneath a cap of settled CaCO3 particles exhibited a 70% reduction in corrosion rate compared with the representative control coupons. The results also show that for these exposure durations and conditions, while iron-related bacteria and sulfate-reducing bacteria populations were identified in high concentrations (respectively ∼1 × 106 cfu/g and ∼1 × 102 to 4 × 106 cfu/g, depending on coupon orientation) within the rust products themselves after 18 month of exposure, there was no clear evidence of MIC. These findings indicate that short and medium-term (nonaccelerated) studies of MIC for mild steel are insufficient or even misleading for the prediction of long-term corrosion rates in these environments.
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.
With the increasing emphasis on attempting to retain in service ageing infrastructure models for the description and prediction of corrosion losses and for maximum pit depth are of increasing interest. In most cases assessment and prediction will be done in a probabilistic risk assessment framework and this then requires probabilistic corrosion models. Recently, novel models for corrosion loss and maximum pit depth under marine immersion conditions have been developed. The models show that both corrosion loss and pit depth progress in a non-linear fashion with increased exposure time and do so in a non-monotonic manner as a result of the controlling corrosion process changing from oxidation to being influenced by bacterial action. For engineers the importance of this lies in the fact that conventional ‘corrosion rates’ have no validity, particularly for the long-term corrosion effects as relevant to deteriorated infrastructure. The models are consistent with corrosion science principles as well as current understanding of the considerable influence of bacterial processes on corrosion loss and pitting. The considerable practical implications of this are described.
The response of a ship or other vessel to surface sea waves, including extreme waves, may compromise crew and vessel safety and long-term operational capability. Herein, a novel high-fidelity numerical time-dependent simulation approach is presented using Smoothed Particle Hydrodynamics (SPH) for modelling sea waves coupled with Finite Element Analysis for modelling vessel structural response under wave loading conditions. The results are compared with physical scale model wave tank test results. Good agreement was obtained for heave and pitch motions and vertical bending moments for various forward (head) speeds in regular head waves, heave and pitch motions, and vertical bending moments. High computational demands can be met by the increasing availability of computation power. Ongoing research is outlined. The implications for the design of vessels such as ships and for through-life assessment are discussed.
AbstractRust layers found on shipwrecks after long term exposure to immersion or tidal conditions have characteristics that suggest that Fe ions were transported away from the corroding surface during the corrosion process and were deposited elsewhere. This is supported by observations of corroded steel and corrosion products recovered from very old steel shipwrecks. It is hypothesised that bacterial activity is involved in this process. Support for the hypothesis comes from well documented characteristics of iron related bacteria. These are reviewed and related to the movement of iron particles, ions and compounds. Reference is also made to the recently discovered magnetotactic bacteria and to the possible influence that these may have on iron migration.Keywords: CORROSIONLONG TERMSTEELBACTERIAION MIGRATIONSHIPWRECKS
A soil/structure interaction model for the simulation of the structural response, including wall cracking, of lightweight masonry structures to expansive soil movements is described. The simulation of swell and shrink in expansive soils due to changes in soil suction is discussed. The model is capable of reproducing the essential features of the structural response observed in full scale experiments. Simple modeling assumptions and the use of static condensation of the global stiffness equations allow fast solution speeds to be achieved. The soil/structure interaction model is thus suitable for use in sensitivity studies and probabilistic analyses of masonry walls with a wide range of possible structural geometries and crack locations. The model has potential applications for studying the behavior of one or two story structures of masonry veneer, full brick/block, or cavity construction, particularly in a probabilistic framework. Although designed specifically for the simulation of expansive soil movements, the effects of various other sources of foundation deformation such as differential settlement and mine subsidence can also be studied.
After the Newcastle earthquake in December 1989 CSIRO's National Building Technology Centre and the Department of Civil Engineering at the University of Newcastle were assigned the project of assessing the evidence of how buildings react under earthquake stress. This report is a full description of the study team's observations and recommendations. As such, it provides a much-needed analysis of how Newcastle's buildings reacted in the earthquake, why they sometimes failed, and the lessons to be learned from the tragedy.
Importance sampling as a technique to improve the Monte Carlo method for probability integration can be shown to be extremely efficient and versatile. This paper addresses the accuracy and efficiency of the method, and its application to series and parallel systems in structures.
A sandwich plate is considered in which the reinforcement fibers are located entirely within the outer faces of the plate. The layout of the fibers is determined within the faces of the plate to minimize the total fiber consumption. The variation of fiber material within the optimal plate to resist the internal stress resultants due to a given loading may be obtained once the fiber layout has been determined. Only one loading case is considered for a simply supported plate, clamped plate, and simply supported annular plate.
