640 publications from this institution
A common feature of many steel building frames is the use of two bolts to anchor a baseplate welded to the column end to the concrete foundation. Such a connection is typically assumed to represent a ‘pinned’ connection, meaning that it is assumed for design purposes that the connection is incapable of transferring bending moment. However, virtually no experimental observations to support such a design assumption have been reported. The present paper presents experimental findings for column-base connection behaviour under axial load and bending moment. The influence of the soil is not considered in the present work.
"SYNOPSIS OF PAPER 7622. COMPUTER ANALYSIS OF REINFORCED CONCCRETE TANKS. ." Proceedings of the Institution of Civil Engineers, 55(3), pp. 672
In the search for the absolute minimum amount of reinforcement to be provided in a structure to support predefined loading, most attention has been given to problems for which the relationship between unit cost of material and stress relationships is simple—usually linear. Such an assumption is convenient and reasonably realistic when reinforcement percentages are low. However, for higher reinforcement percentages, and when, as in the case of cylindrical shells, there occur axial as well as radial loads, a more refined analysis procedure is desirable. This paper considers the optimal (absolute minimum reinforcement) strength design of closed cylindrical shells subject to uniform pressure and having rigid ends. Two cases are considered: the shell wall rigidly connected to the ends, and the shell wall hinged at the ends. For convenience, only internal pressure loading is considered in detail, although, using the theory given, results for external pressure cases can readily be obtained. It is assumed that buckling is not a critical factor in the design and that serviceability criteria can be met independently.
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)
No abstract is provided for this article.
The marine immersion corrosion of irons and steel under calcareous deposition (principally calcium carbonate) is known to be relatively low for shorter exposures (e.g., a few years). Herein the effect of calcareous deposition on corrosion is considered for exposures up to 1,300 y. The data are derived from archaeological steel and iron shipwrecks, cast iron cannons and cannonballs, and wrought iron anchors in locations where there was direct evidence, in and on the corrosion products, of calcareous deposition. Such deposition promotes formation of calcium and ferrous carbonate layers of low permeability on and within rusts. These tend to inhibit both early and long-term corrosion rates. The data show that up to about 200 y exposure corrosion losses as a function of time can be approximated closely by a linear function of time. Longer exposures follow a moderate power-law function, consistent with diffusion considerations. Comments are made about the likely interplay between calcareous deposition and microbiological corrosion.
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 piles being driven into the ground. 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 a pile hammer. The probable shape of force pulses produced during pile driving were obtained from observations by others and approximated by an equivalent trapezoidal force pulse. The differential equation of motion was solved for this force pulse using the Runge Kutta technique and for physical parameters corresponding to those of a slender steel pile which was observed whilst being driven. The resulting solution was found to agree well with observed pile behaviour during driving in that the magnitude of lateral displacements were very small. It is also shown that the magnitude of lateral displacements reduces as the mass of the pile hammer increases, due to inertial effects. In principle, the theory presented can be used to determine the maximum slenderness ratio for a cantilever pile so as to keep the lateral deflections within a prescribed value for a given pulse shape. (Author/TRRL)
Offshore structures are subject to poorly defined hazards such as storms, continued wave action, corrosion and ship impact, and are themselves not well defined in terms of their strength or resistance. Traditional design methods for offshore structures have, on the whole, worked well, but there are now moves to develop probabilistically-based design rules. This is a sound strategy since uncertainties in information can be rationally incorporated in the design and analysis process. The application of reliability theory extends, however, also to the sphere of analysis and decision making in the construction stages. The paper briefly reviews the essential concepts of structural reliability theory and then indicates the various ways in which it has been or can be applied in practical situations. This includes analysis for peak loading and for fatigue as well as other criteria. Some ongoing research areas will be noted.
No abstract is provided for this article.
In estimating the effect of a change in a random variable parameter on the (time-invariant) probability of structural failure estimated through Monte Carlo methods the usual approach is to carry out a duplicate simulation run for each parameter being varied. The associated computational cost may become prohibitive when many random variables are involved. Herein a procedure is proposed in which the numerical results from a Monte Carlo reliability estimation procedure are converted to a form that will allow the basic ideas of the first order reliability method to be employed. Using these allows sensitivity estimates of low computational cost to be made. Illustrative examples with sensitivities computed both by conventional Monte Carlo and the proposed procedure show good agreement over a range of probability distributions for the input random variables and for various complexities of the limit state function.
No abstract is provided for this article.
Accelerated low water corrosion of steel piling in sea water harbours in the UK, Europe and elsewhere has been shown recently to be the result primarily of water pollution. Elevated levels of dissolved inorganic nitrogen in sea and brackish waters are responsible for microbiologically influenced corrosion of steel piling below the low water tide level. This is demonstrated in field data from 13 Australian experimental sites, nine US naval sites and some severe sites in Australia, Norway, Japan and the UK. Localised perforation of sheet piling, often associated only with the webs of U and Z profile piles, is shown to be the result of centreline segregation, porosity and composition differences in steel profiles. These stem from the steelmaking process and are likely to be less severe for modern steels. The results explain most of the observations for actual steel piling in various harbours, both vertically and horizontally (i.e. for U and Z and other pile profile types).
The statistical characteristics of corroded steel plate surfaces exposed to marine environments are of interest for assessing longer term structural safety and integrity using probabilistic methods. This requires information about the variability of corrosion loss and pitting over surfaces. The present paper reports on the observed statistical character of the surfaces of 10 large (1.2 m × 0.8 m × 3 mm thick) steel plates exposed in temperate climate marine immersion, tidal and splash zones for 2.5 years. For the analysis the plates were cut into smaller segments that were mechanically scanned to obtain digitised surface topographies. These were then analysed to estimate the correlation structure and the standard deviation of the surface topography. Considerable differences were found for these and for the mean corrosion loss between different exposure zones. For any one segment the surface topography was found to be highly statistically dependent, implying that smaller coupon sizes can provide adequate estimates of corrosion loss. From this it may be inferred that the deepest pits are not statistically independent as commonly assumed in extreme value statistical representations.
The present paper is concerned with estimating the reliability of underground pipelines subject to externally applied loading and to corrosion, either externally or internally, or both. This affects the strength of the pipeline in resisting the applied loads so that the reliability would be expected to decrease with time. Corrosion is a phenomenon about which there is a great deal of uncertainty. One way of allowing for this is through probabilistic modeling of the material loss as a nonlinear function of time. This approach is explored in the present paper, using a nonlinear function first postulated for atmospheric corrosion. This model is incorporated into expressions for stress resulting from externally applied loading and internal pressure to provide a limit state function expressing the boundary between survival and failure of the system. The probability of system failure is then evaluated using techniques developed for structural reliability analysis.
In the application of the first-order second moment (FOSM) method to problems also involing the finite element method, the gradients of the limit state function with respect to the basic random variables need to be calculated. In principle, these calculations can be from repeated or modified application of the probabilistic finite element routine. In practical problems, however, the number of basic random variables may be very large and therefore the computation of the gradients is often very expensive. This is particular true in the FOSM analysis since the required computation of the gradient vector at each iteration step in the optimization algorithm is proportional to the number of basic random variables. To reduce CPU time without affecting the accuracy, a new formulation which can be used for the gradients calculations is developed in this paper. A direct comparison with other methods suggests that the new formulation is able to reduce significantly the CPU time and storage space requirements in the calcalation.
Marine environments are well-known to be very corrosive for mild and low alloy steels. For reasons of economy, such steels are still the preferred materials for off-shore structures, ship hulls, sheet piling and harbour-side facilities. Despite some quite extensive, long-term experimental test programs, the prediction of the likely corrosion loss of material is still rather simplistic, even though the various factors that can influence marine corrosion are known. However, precise understanding of the mechanics of marine corrosion has been slow to develop and mathematical formulation has been largely neglected. This paper reviews the various factors of importance in marine corrosion, outlines previous models and describes on-going work aimed at developing a probabilistic phenomenological model for time-dependent material loss of mild and low alloy steels in immersion conditions.
This paper is concerned with developing an understanding of the transition between modes 1 and 2 of the bi-modal characteristic often observed for corrosion (mass) loss of many different alloys and in a variety of longer-term (years) exposure conditions. Corrosion losses and pit depth and size for carbon steels (0.01 wt%, 0.04 wt%, and 0.06 wt% C) immersed continuously in sheltered 20°C (av.) seawater, 30°C (constant) seawater, and 70°C (constant) distilled water environments are reported with observations at 14 d and 28 d intervals over 1.4 y. The data allow clear demonstration of bi-modal behavior and variability in mass loss much less than typical for unprotected environments. All cases showed significant development of pit depths and pit areas particularly later in mode 1, through the transition phase and into mode 2. Using established observations of pitting mechanisms, the development of pitting is interpreted as facilitating the reduction in pH at the corrosion interface that permits the cathodic reaction to change from oxygen reduction in mode 1 to hydrogen evolution in mode 2, consistent with longer-term predominantly anaerobic corrosion in the later part of the bi-modal model. The observations also shed some light on the relationship between pitting corrosion and what is conventionally referred to as uniform corrosion.
Reinforced concrete (RC) bridges deteriorate with time. This results in reduction of their resistance, and, consequently, of their reliability. Corrosion of embedded reinforcing steel is one of the main causes of deterioration. The paper presents a method for reliability assessment of RC slab bridges with corroded reinforcement. The method includes a traffic load model, a corrosion model, and a nonlinear finite element structural model. Two types of corrosion—general corrosion, including spalling and debond between concrete and the corroded reinforcement, and localized corrosion—are considered. Reliability is estimated in terms of the reliability index using the first-order reliability method. Uncertainties associated with material properties, geometry, loads, and corrosion parameters are taken into account. A sensitivity analysis of a simple span bridge is carried out to examine the influence of these uncertainties on the bridge reliability. Reliability assessment of a deteriorated three-span continuous bridge illustrates the application of the method.
