The response of an initially curved cantilever strut with a lumped mass at the tip subject to arbitrary axial impact loads is described, as a model for the dynamic response of unrestrained piles during driving. The differential equation of motion defining the lateral movement of impact-loaded cantilever struts is derived. This equation includes the effect of inertial resistance to motion provided by both the strut self-mass and the mass of the pile hammer. The shape of force pulses produced during pile driving was approximated by an equivalent trapezoidal force pulse. The differential equation of motion was solved for this force pulse using the runge-kutta technique. The solution was found to agree with observed pile behaviour during driving. It is shown that the magnitude of lateral displacements reduces as the mass of the pile hammer increases, because of inertial effects. (Author/TRRL)
This paper presents an example of the way structural reliability may change with time, in this case due to the effect of low-cycle fatigue. This may be of interest for structures subject to the possibility of high overload during their design lives. Inelastic fracture mechanics theory is reviewed in the first part of the paper. This is followed by a discussion of distributions appropriate for use in a reliability analysis. Monte-Carlo simulation is then employed to show how, typically, the failure probability changes with the number of load applications to the structure, i.e., with time. (Author/TRRL)
No abstract is provided for this article.
The critical role of manganese sulphide (MnS) inclusions for the initiation of the short-term growth of pitting or localized corrosion of low carbon steels has long been recognized. Classical results show that pitting probability and pitting severity increases with increased sulphide concentration for low carbon steels as a result of magnesium sulphides acting as local cathodes for initiating pitting corrosion. However, the iron carbides (cementite) in steels can also act as local cathodes for initiation of pitting corrosion. Herein it is proposed that there is competition between pits for cathodic area and that this will determine the severity of pitting and general corrosion observed in extended exposures. Preliminary experimental data for immersion exposures of up to 56 days in natural seawater of three low carbon steels show, contrary to conventional wisdom, greater pit depths for the steels with lower S content. However, the pit depth results are consistent with lower C/S ratios. This is considered to support the concept of cathodic competition between C and S. It is proposed that this offers explanations for a number of other phenomena, including the thus far unexplained apparently higher reactivity of some MnS inclusions.
In the earlier papers in this series optimal fibre layouts have been given for a variety of domain shapes and boundary conditions. The general feature which most of these layouts possess is that the reinforcement fibres are parallel to one another within the various zones. In the present paper attention is focused on cases with non-parallel reinforcement. The most common occurrence of such cases is in slabs with a free edge meeting a supported edge at other than a right angle, and at obtuse corners. A number of results for skew slabs and corners are presented.
No abstract is provided for this article.
This paper considers essential theoretical concepts and data requirements for engineering structural reliability assessment suitable for the estimation of the safety and reliability of corroding ships, offshore structures and pipelines. Such infrastructure operates in a harsh environment. Allowance must be made for structural deterioration since protective measures such as paint coatings, galvanizing or cathodic protection may be ineffective. Reliability analysis requires accurate engineering models for the description and prediction of material corrosion loss and for the maximum depth of pitting. New probability-based models for both these forms of corrosion have been proposed recently and calibrated against a wide range of data. The effects of water velocity and of water pollution are reviewed and compared with recently reported field data for a corrosion at an offshore oil platform. The data interpreted according to the model show good correlation when allowance is made for the season of first immersion and the adverse effects of seawater velocity and of water pollution. An example is given to illustrate the application of reliability analysis to a pipeline subject to pitting corrosion. An important outcome is that good quality estimation of the longer-term probability of loss of structural integrity requires good modelling of the longer-term corrosion behaviour. This is usually associated with anaerobic corrosion. As a result, it cannot be extrapolated from data for short-term corrosion as this is associated with aerobic corrosion conditions.
Mathematical models for creep and shrinkage of concrete are used in the paper to present a whole-process analysis of creep and shrinkage effects in reinforced concrete structures, allowing in particular for various uncertainties. A simulation method is proposed to predict the time- dependent load effect due to creep and shrinkage under stochastic loads. It is shown through the formulation and by example that the method has the advantage that all the random variability can be included in the load effect at any point in time. Because of the uncertainties of concrete material properties and the applied loads, all parameters that describe the properties of the structures and the nature of load at any point in time are treated as random variables.
Keywords EQUILIBRIUM, DESIGN, TORSIONLESS, LOADS, GRILLAGES, HILLERBORG, SLABS, CONCENTRATED, COLUMNS, MECHANISMS, PAVEMENTS... Show All
The rate of immersion corrosion is known to increase with water velocity. This has been demonstrated in laboratory conditions under short-term exposures. There are very few field data or l...
This study presents a novel concept and a guide for developing the next generation of fracture prediction models for corroded metallic pipelines. Based on this new concept, the first 3D burst capacity models are developed herein. These models combine simplicity and accuracy through the use of a new parameter, volume of the defect, to measure the burst pressure of corroded pipes with localized defects of complex morphology. The past 50 years has seen the development of numerous 2D burst capacity models, which have focused only on the longitudinal-section area of the corrosion defect and have become increasingly more complicated and less practical in an attempt to increase their relatively low accuracy and stability. Unlike these earlier models, the 3D models presented herein do not require definition of the exact defect profile; despite this, they are significantly more accurate and more stable than the well-known conventional models. Thus, they can significantly reduce the life-cycle costs of pipelines through eliminating or substantially reducing the unnecessary repair or replacement of corroded pipelines. The 3D models have been developed from two sets of computational models that were validated against full-scale burst capacity tests on API-5L pipes with localized complex-shaped defects. In addition, high-speed imaging of the fracture was used to determine the location of ductile crack initiation and the corresponding internal pressure.
In determining the force effects due to wave action on offshore structures it is conventional to use an equivalent linearisation to convert wave velocities to forces via Morison's equation. Different linearisations have been suggested. However, it is not, a priori, clear which is appropriate when structural fatigue is to be estimated. A (theoretical) criterion is introduced herein and examined in relation to a simple offshore structure.
In practice engineers and others need tools for predicting the amount of corrosion, and in particular the likely depth of corrosion pitting, for the safe management of steel infrastructure exposed to marine environments. Such corrosion may include the effect of microbiological influences. Much interest is in predicting, preferably accurately and quantitatively, the likely corrosion in the future. This requires mathematical models based on scientific principles and calibrated to relevant data. A model for longer term corrosion is reviewed briefly and the potential influence of bacteria and other microbiological species considered for exposures in marine environments. It relates availability of critical nutrients corrosion severity. This has shown good correlation for longer term (years) marine corrosion of steels and also for so-called accelerated low water corrosion of coastal structures such as sheet piling. The internal corrosion of water injection pipelines is considered and recent results reviewed.
This paper presents aspects of an attempt to begin to understand the nature and characteristics of human error in structural engineering design processes, and the effect human error may have on structural reliability. In simplest terms, this will be exhibited by the sensitivity of the structural reliability assessment to changes in human error and human variability input. Apart from any intrinsic value such as an assessment may have, it is the necessary first step in the wider context of attempting rationally to set appropriate reliability ensuring measures.
The sustainability of Royal Australian Navy (RAN) ships is affected by structural deterioration, including corrosion, which results in material loss through the oxidation of exposed steel. Deterioration through corrosion is one of the determining factors in developing the operational planning and economic aspects of structural maintenance management. The extent of corrosion depends on many environmental parameters making it difficult to predict efficient repair strategies using periodical time based maintenance. With this consideration, and the fact that the RAN owns an increasingly ageing fleet, new and innovative ways are required to effectively manage a ship. Presently there is no simulation tool available to the RAN that allows ship corrosion to be predicted. Tools such as these have been developed empirically for some commercial ships, however the corrosion loss models exhibit a high variability. By taking into consideration the operational parameters of the vessel a greater accuracy in modelling corrosion can be achieved.
This report deals with a preliminary investigation into human error rates incurred in three relatively simple structural design tasks. The tasks were (i) table look up, (ii) multiplication of two or three numbers on an electronic pocket calculator, and (iii) ranking exercise. Error rates and frequency distributions for the three tasks are reported (a).
This paper reviews recent developments in the prediction of the likely future corrosion losses and of the maximum pit depth for steels exposed to marine environments. A robust mathematical model based on corrosion science principles and calibrated for immersion conditions to an extensive range of literature and new data is described. The model has provided explanations for the effects of steel composition, water velocity, depth of immersion and seawater salinity and also has facilitated new interpretations of data for long-term pitting corrosion. This paper briefly overviews these developments and refers to some typical applications, including marine corrosion of ship ballast tanks, corrosion of sheet piling in harbours and corrosion of offshore platform mooring chains.
An overview of current practices and recent advances in corrosion assessment and management for ships and offshore structures is provided 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.
