640 publications from this institution
Localized pipe wall damage accounts for many failures. Numerical modelling of pipes under increasing axial load and constant internal pressure when there is corrosion pits on the exterior surface of the pipe is reported herein. It is shown that for the assumed ideal elastic–plastic material the shape and volume of the plastic field depend on pit depth and its geometry. Pipe wall fracture around a pit can be associated with a critical plastic section. The results reported herein should be relevant for estimating of the risk of perforation and of loss of contents for steel pipes under different loading.
Improved understanding of the development with time of pitting and corrosion of the external surfaces of buried cast iron water pipes is crucial for the management of water supply distribution networks. The present study reports observations of surface topography of cast iron pipes exposed between 34 and 129 years in clay soils. Pit depths, surface areas and widths associated with deeper pits are reported, including as functions of exposure period. Pitting appears to progress in a step-wise manner as also earlier reported for the corrosion of steels. While there is a relation between pit depth and lateral size of pits through the amalgamation of pits to form plateaus into which new pits tend to form, the predominant progression of material loss through corrosion and pitting is into the metal rather than laterally. The practical implications of these observations are discussed.
The process of structural design has received very little attention from the research community despite its centralness in day to day structural engineering. Much of the research which has been done has been carried out in Australia over a number of years and with the cooperation of many structural engineers. The present paper reviews the reasons for being engaged in this relatively unusual research activity and provides an overview of the work to date. A review is given of the incidence and type of errors made in basic design tasks such as calculations, table look up and table interpolation, and how these errors relate to results obtained for more comprehensive tasks such as loading determination and member design. One of the outcomes of the work has been to suggest areas in certain current design codes which are prone to misinterpretation by practitioners. Preliminary results related to design computation checking and inspection are also reviewed. This work potentially has major implications for quality assurance programmes. (Author/TRRL)
"DISCUSSION. THE INFLUENCE OF CONTROL PROCESSES IN STRUCTURAL ENGINEERING.." Proceedings of the Institution of Civil Engineers, 67(2), pp. 551–552
No abstract is provided for this article.
Elementary monte-carlo sampling as a technique to artificially replicate an experimental program has been used successfully for relatively simple problems, provided the failure probability to be calculated is relatively large. The present paper reviews the elementary monte-carlo method and describes a little known, but improved approach known as importance sampling (a).
In the mathematical modelling of the ‘general’ corrosion of mild and low alloy steels and of some other metals oxygen diffusion through the corrosion products to the corroding surface controls the rate of corrosion at least during some period in the corrosion–time behaviour relationship. Under slightly different theoretical assumptions various early authors derived expressions for this phase. It was usually assumed the derived relationship applied from initial immersion. Only very limited laboratory support for the derived relationships exists. They have been applied to field data for atmospheric corrosion but with constants and exponents modified empirically. In the present paper the theory is reviewed and extended. It is argued that diffusion control cannot apply from first immersion and that this provides considerably greater freedom to mathematical modelling. Allowance is made for non-uniform corrosion product density and permeability and for loss of corrosion product. Recent detailed ‘at-sea’ experimental observations obtained on the Eastern Australian seaboard are applied to test the theory for mild steel. It is shown that the most likely competing mathematical relationships produce relatively similar results. The derived relationship is fitted to literature data to deduce its temperature dependence.
n-Dimensional integration by Monte Carlo directional importance sampling using analytical or numerical integration for each simulated direction is discussed. A suitable general class of sampling distributions is considered. The class is denoted as the class of mixed ūgm-centred standard Gaussian and D -truncated ūgm-centred standard Gaussian distributions, where ūgm is a position vector and is a pragmatically chosen subset of R n. The relative efficiency of different choices of the sampling distribution from the class is studied by way of examples for probability integration in particular. In addition, the same integrals are formulated in different variable representations by the substitution method before the directional Monte Carlo integration is carried out. Moreover, it is demonstrated how sensitivities of the integrals with respect to parameter variations or integration boundary variations can be obtained during the same Monte Carlo simulation primarily set up for obtaining the integral. The novelty compared with previous reports on the topic of integration in the standard Gaussian space is the demonstration that the combination of simulation and numerical integration can be applied for general integrals without any significant change of efficiency.
The long-term corrosion progression of steel reinforcement is important for estimating the life of reinforced concrete infrastructure. Reviews of field experience and results from recent controlled long-term experiments show that the development of reinforcement corrosion is much more complex than the classical empirical Tuutti model. A new, comprehensive model is proposed, referencing observations and inferences from many field and laboratory observations and built on the bi-modal model for the corrosion of steel. It includes the critical roles of air-voids in the concrete at the concrete-steel interface and the effect of long-term alkali leaching as accelerated by the presence of chlorides. Both are affected by compaction and concrete permeability. The role of chlorides in the early stages is confined to pitting within air-voids. These are critical for allowing initiation to occur, while their size influences the severity of early corrosion. Empirical data show that for seawater with an average water temperature in the range of 10–20 °C, the corresponding rate of long-term corrosion ra is in the range of 0.012–0.015 mm/y.
This report describes survey results obtained for detailed design tasks such as number manipulation (micro-tasks) as well as survey results for three realistically based macro tasks. The former have already been reported on earlier; the present report adds some new results. The macro-tasks were (a) design criteria determination; (b) loading calculation; and (c) typical member design. Only for the second task were the number of responses sufficiently large to obtain interesting results. However, the other two tasks provided useful insights and also clues for future research. The work reported herein can be considered to be a first step in obtaining better data on human error types and human error rates in design processes. For the abstracts of parts II and III see TRIS nos 394166 and 394167. (Author/TRRL)
Corrosion of steels in deep, cold, low oxygen sea waters over many decades often is attributed to microbiologically influenced corrosion (MIC). Herein it is argued that the available evidence does not support this proposition since (a) the few available in-situ deep sea field observations are consistent with long-term corrosion under abiotic conditions and (b) independent environmental studies indicate dissolved inorganic nitrogen, a necessary nutrient for MIC, is likely negligible or very low in deep sea waters. On that basis it is proposed that the rusticles observed on some shipwrecks, such as the Titanic, largely are the result of formation of ferrous hydroxides from ferrous ions released, very slowly, from the oxidation of magnetite rusts to maghemite. Direct evidence for this proposition is not available in-situ but is consistent with field observations and laboratory results.
Understanding the mechanisms of environmental stress corrosion is very important for assessing the durability and damage tolerance predictions of composites using glass as the main reinforcement. A mechanistic model describing these mechanisms for unidirectional GFRP in tension is described. The model is based both on the chemical behaviour of glass, and in particular that of glass flaws, and on more recent models of stress corrosion. These were combined with fracture mechanics, the shear lag theory, and a probability model for flaw size. The results are very encouraging. The model shows that it is possible to obtain mechanisms of GFRP breakdown, which corresponds to observed experimental behaviour.
No abstract is provided for this article.
Practical experience and experimental observations suggest that corrosion-affected concrete structures deteriorate at different rates as measured by strength and serviceability, with the latter deteriorating faster. Corrosion-induced problems related to structural serviceability also incur substantial costs in their reinstatement. It is therefore imperative to have a thorough assessment for the serviceability of these structures and to predict accurately the time for the reinstatement. Th current paper presents an application of time-dependent reliability methods to serviceability assessment of corrosion-affected concrete structures. Two approaches are employed to quantify the probability of serviceability failure owing to corrosion-induced concrete cracking and to determine the time for the structure to be unserviceable and hence requiring reinstatement. It is found that Monte Carlo simulation can be used to estimate the probability of serviceability failure with reasonable accuracy. It is also found that corrosion-induced concrete cracking can be modelled as a stochastic process. The application presented herein can serve as a guide for structural engineers and asset managers in making decisions with regard to the serviceability of corrosion-affected concrete structures. Timely intervention has the potential to prolong the service life of the structures.
Major structural systems are composed of many members and connections, each with individual properties. When the member properties and the loadings applied to the structure are specified in statistical terms, the determination of structural system reliability becomes a problem of multi-fold integration. Since direct integration is feasible only for extremely simple structures, several alternative approaches to the problem have been suggested; either through simplifying the integration process itself or through simplified reliability theory. These approaches are discussed in the context of use of computer programs and computer usage.
For many practical applications of system analysis by Monte Carlo simulation, an important piece of information is the sensitivity of the outcome to input information. One matter of interest is the sensitivity of the outcome of the variables controlling it, that is the gradients with respect to the (usually implicit) performance function. Typically, analytical first (and higher) derivatives are not available and the usual numerical approach requires major computational effort. The present paper proposes estimation of gradients using a simplified (linear) response surface, which is a function of the random variables, and which is constructed after the Monte Carlo simulation has been performed. It uses all, or a subset of, the simulation run outcomes. No extra simulation runs are required. There are few restrictions on the form of the performance function and the gradients are estimated at small computational cost. The present paper is restricted to normal random variables.
Accelerated low water corrosion (ALWC) is the term given to unusually high levels of corrosion immediately below the low water level in seawater exposures of steel piling. It has been associated wi...
For structural systems, calculation of the structural failure probability requires the determination of all the failure modes contributing significantly to the overall failure probability. For large systems it is not practical to enumerate fully all modes. The paper will present a procedure, termed the truncated enumeration method, which has been shown to be derivable rigorously from exhaustive enumeration when truncation of solution possibilities, not significant for the reliability assessment, is imposed. The method has been able to reproduce independently all known solutions obtained by others, but usually in a more systematic manner. The relationship of this method to other system reliability calculation techniques will be discussed, some limitations noted and some calculation results presented. (Author/TRRL)
This paper presents a nonlinear limit state model for the analysis of underground pipelines, stressed both in the circumferential and the longitudinal directions. The effects of internal fluid pressure, external soil and traffic loads, temperature and longitudinal pipe bending etc., are considered. A nonlinear corrosion model is used to represent the loss of pipe wall thickness with time. To allow for the uncertainties of the design variables, a reliability analysis technique has been adopted; this also allows calculation of the relative contribution of the random variables and the sensitivity of the reliability index or failure probability. Results obtained for typical pipelines are presented.
