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.
In this paper, the problem of fatigue crack propagation and ultimate fracture of a structure or mechanical component under random loading is addressed. The problem is formulated by combining the first passage failure model with stochastic models of crack propagation. The developed solution, based on the ensemble up-crossing rate approximation, requires a single mean crack growth computation, significantly speeds life-time analysis and allows consideration of non-destructive inspections. * Corresponding author. Tel.: +61 0438 461 725; Fax: +61 2 4021 6991; E-mail: andre.beck@studentmail.edu.au
A transcript of a discussion on the non-structural engineering aspects of buildings. The discussion also focuses on the special needs which are important for the construction and maintenance of heritage buildings.
The performance evaluation of many practical systems can be handled only through computationally intensive Monte Carlo simulation. Although a number of specialist techniques have been proposed, in general, estimation of the sensitivity of the outcome to changes in parameters involves duplicate simulations and finite differences for each parameter of interest. An approximate technique for gradient sensitivity estimation was outlined previously. It is appropriate when the performance function is uni-modal and relatively smooth in the region of interest. It generates all gradients simultaneously by converting Monte Carlo simulation run outcomes to an approximate analytic problem defined by a simplified response surface. The gradients then follow immediately. No extra simulation runs are required. Herein that approach is extended to non-Normal random variables and to the estimation of parameter sensitivities for random variable means and standard deviations. Some illustrative examples are given with comparisons to sensitivities computed by conventional Monte Carlo. The influence of constraint function(s) defining the admissible solution region is also considered.
A number of alternatives are available for the design of slab structures. The resulting structures have a greater or lesser degree of anisotropy of reinforcement, which in some cases may be quite extreme. The available experimental evidence is reviewed in order to clarify the role of such anisotropy.
Solving some integro-differential equation we find the Laplace transformation of the first passage time for Filtered Poisson Process generated by pulses with uniform or exponential distributions. Also, the martingale technique is applied for approximations of expectations accuracy is veryfying with the help of Monte-Carlo simulations.
Methods for determining the deflections at service loads in plastically designed structures are presented. A number of approaches to calculating these deflections are considered, since the usual method of performing a completely separate elastic analysis of the plastically designed structure is generally very cumbersome unless a computer is available. The alternative methods considered are: (a) direct estimation from plastic bending moment distribution; (B) correction approach; (C) exact calculation using a newly developed theorem; and (D) an approximate procedure using estimates of the bending moment diagrams for use in the unit dummy load method. Several examples are worked to illustrate the methods. It is shown that method (C) is a powerful direct and accurate technique for most simple structures (A). (TRRL)
Data for long-term marine immersion and half-tide corrosion loss and pitting of chromium-bearing and stainless steels is systematically re-examined and re-interpreted to show that it is consistent with the model previously proposed for mild and low-alloy steel corrosion. Early corrosion of chromium-bearing steels is well known to be influenced by bacterial activity in the biofilm adjacent to the metal surface. However, the effect appears short-lived and typically the corrosion rate declines, presumably due to the buildup of corrosion products, either on the surface or within pits. The data considered herein show that after some two to four years of exposure there is usually a considerable increase in the instantaneous corrosion rate both for weight loss and for pitting. This is interpreted in terms of the previously proposed model for the corrosion of steels as the result of bacterial activity but now located primarily within pits and crevices. This interpretation implies that the early and the later corrosion processes involve different mechanisms and that corrosion loss and pit depth data are not all from the same homogeneous population. As a result, the prediction of long-term corrosion from short-term laboratory or field observations is of doubtful validity. This has important implications for the prediction of the effective life of chromium-bearing and stainless steels in infrastructure applications.
The non-linear phenomenological model previously proposed for the ‘general’ corrosion loss of mild and low alloy steels under fully aerated ‘at-sea’ near-surface immersion conditions is applied to provide a new interpretation of literature data for copper-bearing steels. The data is examined to extract the parameters required for the model as a function of average seawater temperature. On the basis of the expectation of consistency, the data is then used to calibrate the parameters. All are generally consistent with the parameters derived earlier for mild and low alloy steels. The calibrated parameters are used to predict a consolidated plot of expected corrosion loss–time–temperature for copper-bearing steels. This compares favourably with a similar plot derived earlier from observed data alone.
No abstract is provided for this article.
Much concern exists about the apparently short durability of reinforced concrete structures in marine environments. However, there are many examples of structures that have survived for long periods of time with little evidence of reinforcement corrosion. Some of these were made with seawater as mixing water. Others had very little concrete cover. Detailed examination has revealed that reinforced concrete structures made with fine or coarse aggregate consisting of calcium carbonates such as limestone or seashells or with non-reactive dolomite have extended times to commencement of corrosion initiation and to active corrosion. The reasons for this are explored herein. In addition it is shown that some structures can have serious localized reinforcement corrosion without obvious exterior signs such as concrete cracking and delamination. This requires urgent research.
Some maritime structures may be exposed to higher temperature freshwaters and these can cause significant corrosion. Data obtained in a realistic experiment in which mild steel coupons were exposed for up to two years to hard freshwater at temperatures in the range 50-60°C are described and interpreted relative to the corrosion loss model earlier shown to be applicable to both seawater and fresh water corrosion. The model is reviewed briefly. It considers cathodic oxygen depolarization in the early stages of corrosion and the development of anoxic conditions that could permit the involvement of bacteria in the corrosion process. It is shown also that corrosion loss data for the hard tap water from Teddington, UK at 70ºC is consistent with the corrosion loss model. The trends derived from these data permit improved estimates to be made of the effect of water temperature on the longer-term corrosion loss of mild steels in both hard fresh waters and seawaters.
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 presents an overview of the considerable differences in the time taken before the commencement of reinforcement corrosion for real concrete structures exposed to various marine environments. Usually the disparity is attributed to differences in the rate at which chlorides can reach the reinforcement. However, actual field data do not consistently support this notion. Cases exist where the chloride contents are well above the normally accepted threshold level without obvious exterior evidence of corrosion. Based on recently reported observations for many identical elements exposed for some 65 years to the North Sea it is proposed that a high level of calcium carbonate in the concrete may be beneficial for long term durability, provided this is not compromised by poor workmanship, porous aggregates and alkali aggregate reactions. The hypothesis is discussed in terms of the current conventional wisdom for the corrosion of reinforcing steel in concrete structures.
No abstract is provided for this article.
No abstract is provided for this article.
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)
No abstract is provided for this article.
