The research presented in this thesis focuses on the quantification of the effect of limited site investigations on the design and performance of pile foundations. Limited site investigation is one of the main causes of structural foundation failures. Over the last 30 years, most site investigations conducted for infrastructure projects have been dictated by minimum cost and time of completion, rather than meeting the need to appropriately characterise soil properties (Institution of Civil Engineers 1991; Jaksa et al. 2003). As a result, limited site investigations remain common, resulting in a higher risk of structural foundation failure, unforeseen additional construction, and/or repair costs. Also, limited site investigations can result in over-designing foundations, leading to increased and unnecessary cost (ASFE 1996). Based on the reliability examination method for site investigations introduced by Jaksa et al. (2003) and performed by Goldsworthy (2006), this research investigated the effect of limited site investigations on the design of pile foundations. This was achieved by generating three-dimensional random fields to obtain a virtual site consisting of soil properties at certain levels of variability, and by simulating various numbers of cone penetration tests (CPTs) and pile foundations on the generated site. Once the site and the CPTs were simulated, the cone tip resistance (qc) was profiled along the vertical and horizontal axes. The simulated qc profiles yielded by the CPTs were then used to compute axial pile load capacity termed the pile foundation design based on site investigations (SI). In parallel, the axial pile load capacity of the simulated pile foundation utilising the “true” cone tip resistance along the simulated pile was also determined. This is termed “the true” design, or the benchmark pile foundation design, and referred to as pile foundation design based on complete knowledge (CK). At the end of this process, the research compared the pile foundation designs based on SI and those based on CK. The reliability of the foundation design based on SI was analysed with a probabilistic approach, using the Monte Carlo technique. The results indicated that limited site investigations have a significant impact on the design of pile foundations. The results showed that minimum sampling efforts result in a high risk of over- or under-designing piles. More intensive sampling efforts, in contrast, led to a low risk of under- or over-design. The results also indicated that the levels of spatial variability of the soil are notable factors that affect the effectiveness of site investigations. These results will assist geotechnical engineers in planning a site investigation in a more rational manner with knowledge of the associated risks. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375097 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

The research presented in this thesis focuses on the quantification of the effect of limited site investigations on the design and performance of pile foundations. Limited site investigation is one of the main causes of structural foundation failures. Over the last 30 years, most site investigations conducted for infrastructure projects have been dictated by minimum cost and time of completion, rather than meeting the need to appropriately characterise soil properties (Institution of Civil Engineers 1991; Jaksa et al. 2003). As a result, limited site investigations remain common, resulting in a higher risk of structural foundation failure, unforeseen additional construction, and/or repair costs. Also, limited site investigations can result in over-designing foundations, leading to increased and unnecessary cost (ASFE 1996). Based on the reliability examination method for site investigations introduced by Jaksa et al. (2003) and performed by Goldsworthy (2006), this research investigated the effect of limited site investigations on the design of pile foundations. This was achieved by generating three-dimensional random fields to obtain a virtual site consisting of soil properties at certain levels of variability, and by simulating various numbers of cone penetration tests (CPTs) and pile foundations on the generated site. Once the site and the CPTs were simulated, the cone tip resistance (qc) was profiled along the vertical and horizontal axes. The simulated qc profiles yielded by the CPTs were then used to compute axial pile load capacity termed the pile foundation design based on site investigations (SI). In parallel, the axial pile load capacity of the simulated pile foundation utilising the “true” cone tip resistance along the simulated pile was also determined. This is termed “the true” design, or the benchmark pile foundation design, and referred to as pile foundation design based on complete knowledge (CK). At the end of this process, the research compared the pile foundation designs based on SI and those based on CK. The reliability of the foundation design based on SI was analysed with a probabilistic approach, using the Monte Carlo technique. The results indicated that limited site investigations have a significant impact on the design of pile foundations. The results showed that minimum sampling efforts result in a high risk of over- or under-designing piles. More intensive sampling efforts, in contrast, led to a low risk of under- or over-design. The results also indicated that the levels of spatial variability of the soil are notable factors that affect the effectiveness of site investigations. These results will assist geotechnical engineers in planning a site investigation in a more rational manner with knowledge of the associated risks. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375097 / Thesis (M.Eng.Sc.) - University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21752号 / 工博第4569号 / 新制||工||1712(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 西脇 眞二, 准教授 泉井 一浩, 教授 椹木 哲夫, 教授 松原 厚 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This thesis presents three novel contributions to the application as well as development of ranking and selection procedures. Ranking and selection is an important topic in the discrete event simulation literature concerned with the use of statistical approaches to select the best or set of best systems from a set of simulated alternatives. Ranking and selection is comprised of three different approaches: subset selection, indifference zone selection, and multiple comparisons. The methodology addressed in this thesis focuses primarily on the first two approaches: subset selection and indifference zone selection. Our first contribution regards the application of existing ranking and selection procedures to an important body of literature known as system reliability design. If we are capable of modeling a system via a network of arcs and nodes, then the difficult problem of determining the most reliable network configuration, given a set of design constraints, is an optimization problem that we refer to as the network reliability design problem. In this thesis, we first present a novel solution approach for one type of network reliability design optimization problem where total enumeration of the solution space is feasible and desirable. This approach focuses on improving the efficiency of the evaluation of system reliabilities as well as quantifying the probability of correctly selecting the true best design based on the estimation of the expected system reliabilities through the use of ranking and selection procedures, both of which are novel ideas in the system reliability design literature. Altogether, this method eliminates the guess work that was previously associated with this design problem and maintains significant runtime improvements over the existing methodology. Our second contribution regards the development of a new optimization framework for the network reliability design problem that is applicable to any topological and terminal configuration as well as solution sets of any sizes. This framework focuses on improving the efficiency of the evaluation and comparison of system reliabilities, while providing a more robust performance and user-friendly procedure in terms of the input parameter level selection. This is accomplished through the introduction of two novel statistical sampling procedures based on the concepts of ranking and selection: Sequential Selection of the Best Subset and Duplicate Generation. Altogether, this framework achieves the same convergence and solution quality as the baseline cross-entropy approach, but achieves runtime and sample size improvements on the order of 450% to 1500% over the example networks tested. Our final contribution regards the development and extension of the general ranking and selection literature with novel procedures for the problem concerned with the selection of the -best systems, where system means and variances are unknown and potentially unequal. We present three new ranking and selection procedures: a subset selection procedure, an indifference zone selection procedure, and a combined two stage subset selection and indifference zone selection procedure. All procedures are backed by proofs of the theoretical guarantees as well as empirical results on the probability of correct selection. We also investigate the effect of various parameters on each procedure's overall performance.

A framework is proposed that combines separately developed multidisciplinary optimization, multi-objective optimization, and joint probability assessment methods together but in a decoupled way, to solve joint probabilistic constraint, multi-objective, multidisciplinary optimization problems that are representative of realistic conceptual design problems of design alternative generation and selection. The intent here is to find the Weak Pareto Frontier (WPF) solutions that include additional compromised solutions besides the ones identified by a conventional Pareto frontier. This framework starts with constructing fast and accurate surrogate models of different disciplinary analyses. A new hybrid method is formed that consists of the second order Response Surface Methodology (RSM) and the Support Vector Regression (SVR) method. The three parameters needed by SVR to be pre-specified are automatically selected using a modified information criterion based on model fitting error, predicting error, and model complexity information. The model predicting error is estimated inexpensively with a new method called Random Cross Validation. This modified information criterion is also used to select the best surrogate model for a given problem out of the RSM, SVR, and the hybrid methods. A new neighborhood search method based on Monte Carlo simulation is proposed to find valid designs that satisfy the deterministic constraints and are consistent for the coupling variables featured in a multidisciplinary design problem, and at the same time decouple the three loops required by the multidisciplinary, multi-objective, and probabilistic features. Two schemes have been developed. One scheme finds the WPF by finding a large enough number of valid design solutions such that some WPF solutions are included in those valid solutions. Another scheme finds the WPF by directly finding the WPF of each consistent design zone. Then the probabilities of the PCs are estimated, and the WPF and corresponding design solutions are found. Various examples demonstrate the feasibility of this framework.

The presented paper deals with a theoretical analysis of the ultimate limit state. The results of experimental research carried out at the Institute of Metal and Timber Structures headed by Assoc. Prof. Karmazinová and Professor Melcher were applied. The geometrically and materially nonlinear solution based on the Timošenko’s solution is verified by the FEM model in the computer programme system ANSYS. The random influence of initial imperfections is taken into consideration. The FEM model also includes the influence of residual stress. In the parametric study, the influence of residual stress on the cross-section plastification is researched into, its influence on the load carrying capacity limit is, together with the influence of other imperfections, the subject of the stochastic analysis, applying the Latin Hypercube Sampling (LHS). Further on, the study proves a direct effect of the concrete part of the cross-section (combination of materials steel-concrete) on the decrease of load carrying capacity limit of the beam caused by influence of the residual stress of steel. With regard to the importance of time dependent phenomena of the concrete creep for the load carrying capacity, the studies given in the Ph.D. thesis are oriented in this respect. The parametric studies of the influence of the concrete creep having applied the Standard Eurocode 2 provide both a comparison of load carrying capacity limits when using common and high-strength concrete types, and also the variability of load carrying capacities. It follows from the comparison of the statistical analysis outputs according to the design reliability conditions of the Standard EN1990 and of the approach of Eurocode 4 that the Eurocode 4 can be recommended for dimensioning of this member type. According to the studies which we carried out, the design in compliance with Eurocode 4 can be evaluated as the reliable one. A larger set of experimental data is necessary to determine the economy.