640 publications from this institution
The role of human error in the effective implementation and use of structural engineering projects is reviewed and shown to be underestimated in conventional treatments of probabilistic structural design. Both suitable organization and control are required for project success. The concept of maximizing total expected socioeconomic utility is employed to derive criteria for selecting the levels of control required on the various tasks constituting the construction and use sequence of a structural engineering project. These criteria are applied to a hypothetical example using both the limited experimental evidence available and hypothesized data. Areas in which data are lacking and more research is required are given (a).
No abstract is provided for this article.
Achieving and predicting long-term durability for reinforced concrete structures particularly in marine environments remains a matter of much interest. Recent research findings based on observations from actual bridge performance and specially conducted long-term experiments for a wide variety of concretes indicate that chloride concentrations are involved only indirectly in initiating reinforcement corrosion and in serious active corrosion. For high quality concretes the critical aspect for long-term durability is the loss of concrete alkalinity, i.e. the acid neutralising capacity of the concrete, principally imparted by its cement content. Alkalinity is reduced, normally very slowly, by the rate of dissolution of calcium hydroxide. However, it is increased by chlorides. It is also increased by a greater internal surface area available for dissolution, such as in poor quality, porous, concretes. Only when the concrete pH drops sufficiently, to a level set by chemical thermodynamic conditions, will large-scale reinforcement corrosion be possible. Importantly, cracking of concrete cover through to the reinforcing bars is likely to cause accelerated localised loss of alkalinity, and thus severe very localised corrosion. Several examples of this are given, drawn from practical reinforced concrete structures. These observations have serious implications for serviceability inspections and for predicting remaining structural life.
This paper reports a systematic study of longer-term marine atmospheric and immersion corrosion losses for mild steel alloyed with small to moderate amounts (0, 2, 4, 6 and 8% by weight) of aluminium. Such steel coupons were exposed for up to 3 years in temperate sea water and also just below the mud-line, and for up to one year at two severe atmospheric marine locations. Compared with the coupons without aluminium, higher aluminium content reduced corrosion loss in immersed conditions from 10.5% after one year to 2.8% after 3 years. Below the mud-line corrosion losses showed a similar trend but were more varied. In the marine atmosphere, the reduction in corrosion loss for increased aluminium content ranged from 58 to 81% after one-year exposure. The results show that aluminium alloying above about 4% has limited additional benefit for corrosion in any of the marine exposure environments.
The quantification of mass loss, surface topography, depth of pitting, and localized corrosion for steels subject to marine corrosion requires the removal of rusts, preferably without causing additional mass loss, pitting, or other damage. Conventional procedures using inhibited hydrochloric acid or Clarke's solution are shown to remove short-term marine rusts but also to cause new corrosion including pitting and related rust products. Both increase with longer exposure to the cleaning solutions. Water washing with soft water left calcareous materials on the metal surface. Ultrasonic removal did not cause additional corrosion but was effective only for very light rusts. Although relatively slow, electrolytic cleaning (electrolysis) produced clean surfaces without new corrosion.
The work of previous investigators in the field of absolute optimal design of laterally loaded fibre reinforced plates is briefly reviewed and a further approach to the problem is outlined. This further approach suggests that the problem is essentially one-dimensional and consists in determining the optimum load carrying (load-path) directions at all points in the plate. Optimal fibre layouts for square, rectangular and triangular plates with both simply supported and clamped edges are given and some errors in previous work are noted.
Safety in structural engineering is an enduring issue with a long history. Extensive rules have been developed for its management, mainly for use at the design and construction stages, but are these sufficient? Increasingly, ageing, existing structures must be assessed for continued safety. Structures are part of much larger infrastructure systems and their failure may have significant system consequences. Emerging thinking suggests that for the realistic assessment of the safety of major structures, and hence the risks involved in their failure, structural engineers will need to adopt a broad risk management perspective. This will mean the adaptation of tools and techniques drawn from risk management for other potentially hazardous facilities and used in conjunction with the well‐developed techniques unique to structural reliability analysis. Major structural engineering projects may be categorized as being ‘low‐probability—high‐consequence’ types of risk. This implies that philosophies and practices for such types of risk already developed for hazardous facilities in other industries ought to be adaptable to major structural engineering projects. It is argued that such risks have relevance also for acts of war, sabotage and terrorism, provided their assessment involves appropriate inputs. Difficult societal decision processes are involved, including the management of post‐failure scenarios.
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.
The corrosion of steels in clay soils is of interest for buried steel infrastructure. To obtain better information about the early corrosion effects, mild steel coupons were exposed for 3, 6 and 13 months in finely graded clay soil at different moisture contents and with different degrees of compression to simulate compaction. It was found that the maximum corrosion mass loss and pit depths occurred at a soil moisture content of 17–18 wt-% for all exposures and levels of compaction, corresponding to around 0.65 degree of saturation. These values are broadly consistent with earlier findings for non-clay soils. For exposures of 3 months corrosion was predominantly localised but subsequently became more uniform. This was shown to be consistent with good compaction of the soil against the steel surface. Poorly compacted lumpy clays, however, showed larger areas of localised corrosion and relatively greater corrosion mass loss and deeper pitting.
Data from a variety of field exposure programs is used to quantify the effect of concentration of dissolved inorganic nitrogen (DIN) on long-term seawater immersion corrosion loss of structural steels. A linear correlation model that asymptotes the long-term part of the previously proposed bi-modal corrosion loss model is used. It allows for average seawater temperature. Model parameters and their variability are determined and reported. The model permits prediction of long-term corrosion loss in nutrient polluted waters of known average temperature. An example shows that anthropological pollution of seawater potentially is a major hazard for corrosion of steel infrastructure.
SUMMARY: The corrosion of ferrous water mains is a signific ant problem for the Australian Water Industry. A significant proportion of Australia’s a geing water infrastructure is composed of cast iron and steel cement lined pipes, which are prone to co rrosion on the external surfaces that are in contac t with soil. Internal corrosion is not a significant issue for cement-lined pipes. For the water industr y to manage these ageing assets effectively, quantitativ e predictions of the damage likely to result from long-term corrosion are highly desirable. Many of t he fundamental corrosion mechanisms are known and there is considerable practical experience on t he corrosion of buried iron. However, the predictio n of the long-term corrosion losses, of pit depths an d pitting extent are not well developed, including understanding and prediction of the quantitative in fluences of external soil conditions. In this paper the basic mechanisms involved in the corrosion of ferro us metals in contact with soil are reviewed and the likely effects of various influencing factors such as soil moisture content, soil type and soil water chemistry on long-term corrosion are described. The review has found that long-term corrosion is controlled by diffusion processes and is a function of soil moisture content, soil density, and soil w ater quality. The review is followed by an outline of an approach to modelling long-term corrosion of cast iron pipes. It involves developing a realistic mode l for the prediction of pipe corrosion in soil and its calibration to field and historical data. Both the modelling approach and field data collection requirements are outlined.
Atmospheric corrosion of structural steels in the coastal zone is of significant economic performance, impacting on off-shore, port and harbour and industrial structures as well as ships, tanks and pipelines. However, despite much understanding of the fundamentals of the corrosion process, the tools available to structural engineers for predicting the initiation and the progression of corrosion are not sophisticated. This paper will outline the current situation and describe current efforts to develop predictive models for corrosion loss and for maximum pit depth for steels exposed to tidal, splash and coastal zone exposures. The models are based on the analysis of world-wide data and on corrosion science fundamentals. They also include recently developed understanding and research findings that demonstrate the critical role of bacteria in the overall corrosion process. The involvement of bacteria both in very short-term corrosion and in long-term corrosion has been demonstrated through detailed investigations of steels exposed in natural environments rather than in the laboratory. Bacterial culturing techniques, widely used in the offshore oil industry for example, are known not to be very reliable and for this reason the research has turned to the use DNA analysis to confirm the presence and numbers of bacteria involved and to allow their identification. The paper will give examples of the surfaces of steel exposed to sterile and to natural sea waters to demonstrate the importance of bacterial activity. This has important implications for the prediction of likely corrosion in polluted atmospheres and marine exposure conditions.
No abstract is provided for this article.
A recent study has shown that in marine conditions micro-pitting in mild steel is present very early after first immersion and that macro-pitting usually does not become significant until ...
Corrosion of water injection pipelines (WIP) in the oil and gas industry is a major issue involving potential premature life time predictions and unpredicted costs like periodic biocide treatment and pipeline pigging. This paper presents a part of a larger project concerned with improving understanding of the influence of bacterial activity on corrosion, as distinct from abiotic corrosion, in oil and gas transport systems for better management of pipeline systems. Observations are made concerning life time as a function of microbiologically influenced corrosion (MIC) risk and relationships between MIC, bacterial numbers and types, and water quality. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).
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)
The corrosion of steel reinforcement bars in reinforced concrete structures exposed to severe marine environments usually is attributed to the aggressive nature of chloride ions. In some cases in practice corrosion has been observed to commence already within a few years of exposure even with considerable concrete cover to the reinforcement and apparently high quality concretes. However, there are a number of other cases in practice for which corrosion initiation took much longer, even in cases with quite modest concrete cover and modest concrete quality. Many of these structures show satisfactory long-term structural performance, despite having high levels of localized chloride concentrations at the reinforcement. This disparity was noted already more than 50 years ago, but appears still not fully explained. This paper presents a systematic overview of cases reported in the engineering and corrosion literature and considers possible reasons for these differences. Consistent with observations by others, the data show that concretes made from blast furnace cements have better corrosion durability properties. The data also strongly suggest that concretes made with limestone or non-reactive dolomite aggregates or sufficiently high levels of other forms of calcium carbonates have favourable reinforcement corrosion properties. Both corrosion initiation and the onset of significant damage are delayed. Some possible reasons for this are explored briefly.
No abstract is provided for this article.
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