The details of footing design, the soil stiffness and the soil resistance all affect the rotation characteristics of column bases of structural frames. This can have a considerable influence on structural economics (strength design), structural deflections (serviceability design) and on structural stability. Of particular and increasing importance in structural design is the ability to predict structural deformations under serviceability load level conditions. However, only limited theoretical and experimental attention has been given to understanding the footing-soil interface behaviour of shallow footings for realistic foundation conditions. In this paper, a set of experimental results for shallow footing behaviour under load reversal is presented. Based on this work and on previous modelling attempts, a relatively simple theoretical model for predicting rotation behaviour of simple pad footings under the first loading condition is described.
The final discussion session of the Newcastle Earthquake Conference outlines changes that need to be made in relation to earthquake engineering, hazard analysis, and response. The recommendations are based on a broad feeling of consensus by conference participants. The discussion also includes feedback of problems currently facing industry and civic professionals involved in the Newcastle earthquake of 1989., i.e insurance assessment, continuing ground movement, demolishment vs. repair, and the public perception of engineers.
The directional-simulation procedure to estimate the zero-time failure probability and the outcrossing rate for structural systems is extended to structural frames subject to loads modeled as mixed Poisson pulse processes. The problem is formulated in the space of the load processes. The structural system resistance is represented by probabilistically defined region boundaries obtained from the presumed (known) limit state functions for the structure. The theory is applied to a simple rigid framed structural system acted on by two discrete load processes. The results obtained are compared with those derived from a consideration of bounds on the outcrossing rate for mixed sparse Poisson processes. A comparison with results published in the literature is also given. It is shown that there may be considerable differences. A detailed discussion of the reasons for these differences closes this paper.
Optimal corrosion and odour management has been hindered by limited understanding of several key in-sewer processes contributing to the problems, and the lack of tools and reliable technologies to support strategic decisions and cost-effective sewer operations. A major step forward to fill the above gaps is being taken in Australia with a $20mil collaborative research project funded by the Australian Research Council (ARC) Linkage Program, 11 water industry partners and 5 university partners. The project is called the Sewer Corrosion & Odour Research (SCORe) Project.In this paper, the state-of-the-art knowledge and practice based on both published and grey literature is reviewed and key knowledge gaps and challenges to be addressed in the SCORe Project are identified. Some of the early findings from this initiative are presented.
The corrosion of mild steel exposed to marine immersion conditions typically is not uniform although it is often idealized as such. Anodic regions and micro-pits develop very quickly after first exposure and eventually there is the development of shallow broad pits. This transition of the surface topography and the processes involved are still not completely understood. The present paper presents a number of images typical of the sequential evolution of the surface topology of mild steel corroding in sub-tropical coastal seawater. The sequence consists of the development of anodic areas, development of small pits and shallow broad pits, the apparent coalescence of small pits into larger localized corrosion and eventually the appearance of stepped or benched, perhaps irregular-shaped broad or macro-pits. This sequence is typical of that which has been observed many times and this suggests it is reasonable to infer a generic sequence that describes the changing surface of corroding mild steel in seawater. It will assist in developing a better understanding of the evolution of corrosion processes for mild steel in seawater and assist in identifying the various controlling processes.
For the management of infrastructure over long periods of time and for the assessment of infrastructure that is already deteriorating, structural engineers need to be able to predict the likely future deterioration of their structures. Conventionally they rely on mathematical models to do this. This paper deals with the development of such models for the marine corrosion of steel. They are based on corrosion science fundamentals and microbiological aspects. They invoke probabilistic notions to account for the inevitable uncertainties attached to enumerating the environment and other conditions and in prediction. Observations of long-term data, interpreting it and then invoking intuition and scientific principles are all involved in developing models consistent with expectations and with boundary conditions. They are then calibrated to data from the literature and using new data specifically collected as required. The approach taken herein for model development focuses on interpreting data in terms of an ‘a priori’ model in the sense of Bayes inferential theory, rather than using data alone to dictate a ‘model’, such as typically resulting from correlation studies. Some results obtained to-date illustrate that this approach can be successful in providing new interpretations and better understanding of empirical ‘field’ observations. A brief outline is given also of future research directions.
Marine immersion corrosion observations for archaeological and other data, including from shipwrecks, wrought iron anchors, and cast iron bridge piers are used to estimate corrosion losses in natural unpolluted coastal and near-coastal seawaters for exposures up to about 600 y. Empirical functions for the development of corrosion loss with time were then developed, standardized to 20°C mean seawater temperature. The resulting slightly nonlinear corrosion loss trend, represented by a modified form of the power law, is consistent with phase 4 of the previously proposed bi-modal corrosion model. These observations support the notion that the rate of long-term corrosion is controlled by outward diffusion, through the rust layers, of gaseous hydrogen generated by the cathodic hydrogen evolution reaction under predominantly anaerobic corrosion conditions. The power-law trend also provides good extrapolation from shorter-term data. For practical purposes for exposures <100 y in seawaters with a mean temperature of around 20°C, a linear model, with a longer-term corrosion rate 0.06 mm/y at 20°C, is sufficiently accurate.
Earlier papers have considered optimal solutions for various layout shapes of plate but with the edges supported in the classical manner—either simple supports, fixed edges or free edges in various combinations. In these cases there is no work done by supported boundary moments or edge normal reactions. The present study focuses attention on the optimal layouts appropriate to cases where the plate edge is supported on (deflecting) edge beams and hence work is done and energy is stored or dissipated in the boundary zone.
Abstract Through-wall pitting is the most common failure mode of concern for high-pressure pipelines as used in the oil and gas industry, both offshore and onshore, potentially allowing loss of containment and environmental pollution. Pipe burst under pressure is also of concern, particularly in high-safety class pipelines. Semiempirical models for predicting pipeline burst capacity vary in their fidelity. Mostly, this has been estimated by benchmarking burst capacity prediction models of undefined conservatism against burst pressure derived from finite element analysis (FEA) of steel pipes with wall defects, such as those caused by corrosion. The most recent of these comparative assessments is reviewed herein, and areas of concern are noted. This is followed by a statistical analysis for performance assessment of several burst capacity models, by comparing their predictions against FEA-generated data, for which both the modeling and the input data appear to have been correctly applied. The results of the analyses allow a more accurate ranking of burst capacity models, considering both predicted mean values and estimates of variability, and provide a basis for making logically consistent comparisons. They also form a basis for the application of safety factors to provide measures of the relative probability of pressure pipe bursts.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
Elevated concentrations of dissolved inorganic nitrogen (DIN) that stimulate microbiologically influenced corrosion (MIC) likely much increase longer-term seawater immersion corrosion of mild and low alloy steels. In contrast, in shorter-term exposures, DIN less than about 0.25 mgN/L concentration usually has little or no effect. This is illustrated with data for 12 independent cases with corrosion loss trending interpreted using the bimodal model. Its early part is predominantly under oxygenated conditions suitable primarily for iron and sulphur oxidising bacteria that are less aggressive for corrosion. These conditions also are suitable for the nitrogenous components of DIN to act as corrosion inhibitors. Longer-term exposure conditions predominantly are anaerobic suitable for sulphate-reducing microorganisms, typically the main actors in MIC. The results demonstrate it is problematic to extrapolate short-term (days – months) observations to long-term corrosion, particularly when MIC or DIN are involved. The results also highlight that the change from oxygen reduction as the critical cathodic reaction in shorter exposures to water reduction (or hydrogen evolution) as the critical cathodic reaction in extended exposures has a profound effect on the effect of DIN concentration and its effect on corrosion.
A parallel structural system is one in which more than one critical section must reach a limiting state before the structure as a whole can reach a limit state. An obvious example is the plastic analysis of redundant frameworks in which individual member strengths can be maintained while the structure deforms to mobilize the strength of all those members which can add to its ultimate load capacity. In a reliability analysis, the effect of member strength correlation may be an important parameter governing the reliability of the whole system. This aspect is investigated in this paper. It is shown by means of a series of examples of relatively simple frames that the reliability of the system is sensitive mainly to correlation between the member strengths within the one member or between related members. However this sensitivity varies with the dominant collapse mode for the frame.
This chapter describes field observations for the corrosion of mooring chains used for offshore operations with FPSOs (Floating Production, Storage, and Offloading vessels) as used increasingly in the oil and gas industry. Field experience in tropical seawaters has shown some chains to develop severe localized corrosion (or pitting) after only eight years' exposure, much more than typical. It is shown that microbiologically influenced corrosion (MIC) was involved, attributed to nutrient pollution even though FPSOs were far removed from shore-based human and environmental influences.
