For the simple structural system examined in the example, it is evident that the use of the approximate plastic elastic (hardening) model leads to a particularly simple systems reliability problem of the parallel type. This can be solved by noting that the elastic subsystem must, by definition, fail last, and that only rigid plastic limit states can be invoked earlier. Hence the problem reduces to an ideal plastic parallel system reliability problem, for which standard techniques, such as fosm, can be applied. Where the plastic subsystem involves more than one limit state, the intersection with the elastic hardening subsystem limit state may be less easy to find, and an equivalent linearization in fosm may be required. This is presently under investigation.
The adequate, long-term performance of reinforced concrete infrastructure depends greatly on being able to resist deterioration mechanisms such as reinforcement corrosion. The main mechanisms for this are described and critically reviewed in the light of properly-analyzed experience for, and behavior of, actual reinforced concrete structures. Recent research has shown that, for structures in the marine environment, the role of chlorides lies mainly in the reduction of the alkalinity of the protective, high-pH concrete, rather than in the direct attack on the reinforcement steel.
In this paper, a multitangent-plane surface method is suggested for calculating the reliability of complex structures of which the limit-state surfaces are not known explicitly. In this approach, multiple tangent planes are used to approximate the actual limit-state surface. Also radial importance sampling is used in conjunction with probabilistic finite-element (PFE) analysis. Numerical results suggest that the new method can be used to improve the accuracy of solutions obtained from first-order second moment (FOSM) analysis and also require considerably less CPU time when compared with Monte Carlo simulation (MCS) analysis. This method is only suitable for the case of a nonlinear concave or convex limit-state surface.
The future of regulation for integrated risk assessments and core applications are the main theme in a book which gives important insights into the trends that have developed within chemical, process and nuclear plants.
No abstract is provided for this article.
No abstract is provided for this article.
Considerable progress has been made in the theory of structural reliability in the last 15-20 years, particularly in relation to the analytical treatment of information. Much of this has gone relatively unnoticed by the engineering profession, even though the potential for structural reliability assessments in certain practical problems is now significant. Structural reliability theory has been applied, of course, to structural design code calibration, but has a much wider potential. Particularly in the offshore industry and in large projects it is being used where risk must be specifically considered and where to do so may yield considerable design and construction cost savings. In this paper the basic concepts of structural reliability theory will be reviewed and related to the standard and type of information usually available in engineering studies. An overview will also be given of the various calculation techniques now available.
Carbon steel pipelines are widely used for injection of sea and other waters into oil and gas wells so as to increase the rate of recovery, particularly from mature fields. Internal corrosion usually is mild. However, cases of very aggressive channelling corrosion along the bottom of the pipeline have been observed. Practical experience and anecdotal observations have attributed this to microbiologically influenced corrosion even though extensive use is made of preventative measures including biocides, oxygen scavengers, corrosion and scale inhibitors, and pipeline pigging. Interpretation of data and observations for five water injection pipelines, made available by industry, indicate that microbiologically influenced corrosion may play a part in causing channelling corrosion but that the most likely cause is under-deposit corrosion under pipe debris that settles during periods of pipeline shut-downs and low water velocity.
While it has been reportedly recognized that most casualties of marine structures including total losses have involved corrosion degradation, corrosion is one of the most important factors influencing safety and integrity of aging structures. Corrosion wastage also causes significant issues in terms of health, the environment, and financial expenditure. While the loss of a total system typically causes great concern, maintenance and repair of damaged structures is costly to society and the environment in general and important to the economic viability of the enterprises involved in particular. It is thus essential to develop advanced technologies that can allow for the proper assessment and management of corrosion. An overview of some recent developments in corrosion assessment and management for steel ships and offshore structures is addressed in the present paper. Relevant corrosion mechanisms, corrosion wastage models, design considerations (design corrosion-margin values), and preventive measures with the emphasis on marine structures are presented.
For the reliability assessment of structures which may fail in one of several failure modes, bounds on the probability of failure of the structure have been developed. It is well known that even the best of these bounds are dependent on the correlation between the failure modes and that this correlation is, in turn, dependent on the correlation between member properties. Relatively little appears to be known about the importance of member property correlation effects in reliability analysis, nor about the actual values of correlation coefficients. Before attempts are made to increase our knowledge of member correlation, the importance of correlation effects in structural reliability calculations should be assessed. A simple study of the sensitivity of structural reliability assessments to variations in correlation coefficients for parallel structures is described. It is demonstrated that the structural reliability for the structure considered is sensitive mainly to correlation between different locations within the same member or related members. (TRRL)
1. Introduction . The optimum design of plane reinforced concrete slabs frequently requires consideration of deflected shapes for the slab such that through every point there is at least one principal curvature (κ 1 ) direction on the deflected surface which is a constant curvature direction. The most interesting cases are those where only one principal direction has this property.
No abstract is provided for this article.
Keywords NEWCASTLE UNIVERSITY STRUCTURES, SYSTEMS, STRUCTURAL, RELIABILITY, LOADS, STOCHASTIC, FORMULATION, APPLIED, MODELLING, RIGID PLASTIC, INTEGRAL, MEMBERS, STRENGTH, ASSESSMENT, CONCRETE, REINFORCED, FRAMES, FOUR STOREY... Show All
Water-injection, oil production and water-supply pipelines are prone to pitting corrosion that may have a serious effect on their longer-term serviceability and sustainability. Typically, observed pit-depth data are handled for a reliability analysis using an extreme value distribution such as Gumbel. Available data do not always fit such monomodal probability distributions well, particularly in the most extreme pit-depth region, irrespective of the type of pipeline. Examples of this are presented, the reasons for this phenomenon are discussed and a rationale is presented for the otherwise entirely empirical use of the ‘domain of attraction’ in extreme value applications. This permits a more rational estimation of the probability of pipe-wall perforation, which is necessary for asset management and for system-sustainability decisions.
Burst capacity models and Finite Element Methods (FEM) are the most common methodologies to assess the remaining strength of corroded oil and gas pipelines. These methodologies are shown as potentially excessively conservative or to present considerable scatter in their predictions, in part because they idealize the actual shape of complex pitting by simple approximations. The new approach introduced herein employs improved Finite Element modelling of isolated complex-shaped pit geometries, uses volume loss in the burst capacity models for the first time and is validated against several existing test results. In addition, the present study assesses the accuracy of FEM–based predictions based on the simplified pit geometries and also the precision of well-known burst capacity models. A burst capacity model is proposed herein which is practical, easy to use, more accurate and more stable than all earlier well-known models.
