Application of line sampling simulation method to reliability benchmark problems

A procedure denoted as Line Sampling (LS) has been developed for estimating the reliability of static and dynamical systems. The efficiency and accuracy of the method is shown by application to the subset of the entire spectrum of the posed benchmark problems [Schuëller GI, Pradlwarter HJ, Koutsourelakis PS. Benchmark study on reliability estimation in higher dimensions of structural systems. In URL: http://www.uibk.ac.at/mechanik/Publications/benchmark.html. Institute of Engineering Mechanics, Leopold-Franzens University, Innsbruck, Austria, 2004], i.e. in particular linear systems with random properties. The notion of design point excitation for non-linear systems is discussed and its use extended for reliability estimations of conservative non-linear MDOF systems considering critical conditional excitation.For solving the hysteretic MDOF system with uncertain structural parameters subjected to general Gaussian excitation, however, the general applicable subset procedure [Au SK, Beck JL. Estimation of small failure probabilities in high dimensions by subset simulation. Probab Eng Mech 2001;16:263–277] has been used combined with Importance Sampling.     

General outlook of UNIPASS™ V5.0: A general-purpose probabilistic software system

This paper briefly describes many features, options and capabilities of UNIfied Probabilistic Assessment Software System, UNIPASS™ Version 5.0. This software is a PC-based Windows 32 compliant software engine that can be utilized independently, as a stand-alone tool, or integrated with deterministic software tools to perform complex probabilistic analysis. In the analysis, UNIPASS™ provides the basis for modeling uncertainties, defining variable probability distribution and probabilistic response models, computing probabilities, identifying most likely outcomes, and providing sensitivity measures, while the deterministic software tools may be integrated to provide the computational framework for constructing complex deterministic models. Combining a familiar Windows-based interface with a simple menu-driven system, UNIPASS™ integrates easily into most existing environments without a significant learning curve or additional hardware investment.     

Stochastic collocation-based nonlinear analysis of concrete bridges with uncertain parameters

This paper focuses on the stochastic response of concrete bridges considering uncertainty in bearing and abutment stiffness. A multi-span simply supported bridge with concrete girders is selected. A 3D-dimensional model is prepared, and nonlinear response history analyses are performed. For the numerical dynamic simulation, the non-sampling stochastic method based on generalized polynomial chaos (gPC) expansion is utilised. The uncertain parameters include the vertical and shear stiffness of bearings and the lateral stiffness of abutments are presented by the truncated gPC expansions. Furthermore, the system response such as base shear, acceleration, velocity and displacement in different columns is presented by gPC expansion with unknown deterministic coefficients. The stochastic Galerkin projection is employed to calculate a set of deterministic equations. A non-intrusive solution, as a set of collocation points, determines the unknown gPC coefficients of the system response and the results are compared with Monte Carlo simulations. The key advantage of spectral discretization is the combination of the mentioned method with the spatial discretization, e.g. finite element model. This study also emphasises the accuracy in results and time efficiency of the proposed non-sampling method for uncertainty quantification of stochastic systems comparing to sampling procedure (e.g. Monte Carlo simulation).     

A Monte Carlo method for thermal building simulation

A simplified Monte Carlo method for finding an approximation of the building inside temperature distribution is given. Present simulation techniques are either over-simplified and use only a deterministic method, or are highly complex stochastic models. The new method consists of a Monte Carlo approach to find typical input distributions, used in conjunction with a more traditional deterministic building thermal simulation model. The output distribution is obtained by estimating the output distribution from a carefully selected sample of input distributions.Radiation and temperature input data are simulated separately, and then the combined effect is found with a numerical convolution integral. Because the convolution integral is only strictly valid for independent variables, a verification study is also presented, using four different buildings and five different ventilation rates.Complete experimental verification of the method requires measuring the inside temperature distribution for 5 years, with five different ventilation rates for the same four buildings. This was out of the timeframe of this study. Therefore, the method was verified by comparison of results obtained with the new technique and comprehensive results obtained by simulating every day for the same period with historical weather data.The results show that the average predicted temperature error is 0.68 °C, with a standard deviation of 1.37 °C. The verification thus shows that by using the new Monte Carlo method a good approximation can be found for the inside temperature distribution by using only 4% of the days from the 5-year period.     

phimeca-soft

This paper provides a presentation of phimeca software for reliability analysis. The completion of this software has been achieved thanks to years of experience at the French Institute for Advanced Mechanics and phimeca engineering company is developing the commercial version. First, inherent hypotheses of first/second order and conditional simulation methods are briefly stated and their implementation discussed. Algorithms combining the physical model under concern – defined through an explicit formula, a finite element code computation or a user-defined function – and a stochastic model of the input are then presented to the reader. A special attention is given to the graphical user interface GUI in this paper so as to comply with the objectives of this special issue of “Structural Reliability Software” and the use of the GUI is illustrated through a very basic example. To conclude, a significant industrial application is presented demonstrating the capabilities of the software in the context of a large finite element model and a non-linear material behaviour.     

Predicting performance of EPB TBMs by using a stochastic model implemented into a deterministic model

The current study is an attempt to address the stochastic nature of the rock excavation process by suggesting a stochastic performance prediction model implemented into a deterministic model developed for hard rock TBMs. Full-scale linear cutting experiments using constant cross-section and V-type of disc cutters are performed on two different limestone samples to provide the basic input required for the deterministic model used for estimation of instantaneous penetration rate, daily advance rate, thrust and torque requirements of TBMs. Stochastic estimation is performed by using a Monte Carlo simulation program by applying iterations to implement the probabilistic distribution of each model parameter and provide knowledge of a confidence level. Results of the suggested model are verified by measuring the field performance of two earth pressure balance (EPB) TBMs excavating competent rocks in semi-closed mode. The results indicate that the suggested model works well for prediction of instantaneous cutting/penetration rate for both TBMs and both types of disc cutters. However, an improvement on the model is required for estimation of cutterhead torque and thrust of EPB TBMs. The stochastic model implemented into the deterministic model results in almost similar predictions with the deterministic model in 50% (best guess) probability. However, the stochastic modeling provides a tool for exploring the full implications of linear cutting experiments and allows assessing the probability of occurrence and predicting variations of the TBM performance parameters, covering the uncertainties/risks.     

基于非侵入式随机有限元法的地下洞室可靠度分析

提出了地下洞室变形可靠度分析的非侵入式随机有限元法。介绍了随机多项式展开的基本原理,采用 GEOSLOPE 的 SIGMA/W 模块进行确定性有限元分析。提出了随机多项式展开与 SIGMA/W 模块接口方法及其流程图,从而实现了确定性有限元分析和随机分析一体化。最后研究了非侵入式随机有限元法在地下洞室变形可靠度分析中的应用。结果表明：非侵入式随机有限元法使得随机分析与确定性有限元分析互不耦合,其计算效率是传统的蒙特卡罗模拟方法无可比拟的,它是地下洞室变形可靠度问题分析一种有效的方法。采用二次衬砌支护是提高地下洞室可靠度有效的方法。此外,岩体变形模量的变异性对地下洞室变形可靠度有非常明显的影响,而岩体重度的变异性对可靠度基本上没有影响。因此,在地质勘查中要尽可能准确地确定岩体的变形模量,从而有效地提高地下洞室变形可靠度。     

Comparison of methods of including stochastic factors into deterministic models of indoor air quality

The paper discusses problems connected with the inclusion of stochastic factors in deterministic models of indoor air quality (IAQ). Three different methods are shortly presented: quasi-dynamic multizone modelling with generation of input data time series; multizone modelling based on the theory of stochastic differential equations: and Monte Carlo simulation with independent random generation of stochastic parameters. The described methods are compared using a computer simulation of carbon dioxide concentration in a simple two-compartment office. The comparison of simulation results shows that the way in which stochastic disturbances are included in the models does not have an important influence on mean value of predicted carbon dioxide concentration. At the same time, the analysis of standard deviations indicates that the method of disturbance generation and its later incorporation into the IAQ models have a great influence on the probability distribution of estimated concentrations. Finally, there is a discussion on the main advantages and disadvantages of each of the proposed methods.     

A probabilistic examination of the ultimate strength of cold-formed steel elements

The statistical characteristics (mean and variance) of the ultimate strength of cold-formed steel plates in uniform compression and pure bending are calculated and compared to deterministic approximations. Three quantities: plate thickness, longitudinal flexural residual stress magnitude and first mode imperfection magnitude, are treated as random variables. Based on existing experimental data, appropriate probability distributions are determined for the three random variables. The ultimate strength calculations are performed numerically using the finite element method (FEM). The statistical characteristics are calculated using two methods: Monte Carlo simulation and Taylor series approximation. The results are compared to the deterministic design approach of the American Iron and Steel Institute (AISI) Specification for the design of cold-formed structural members.     

Project conceptualization using pragmatic methods

An important and difficult part of project management is the conceptualization stage – particularly when dealing with multiple powerful stakeholders and ‘messy’ situations. Pragmatism provides a way forward that makes central the ‘concepts’ being used to conceptualize the project (e.g. ‘timeliness’ or ‘sustainability’). This paper argues for a sequence of two approaches suggested in the literature that combine this pragmatism and soft systems thinking to conceptualize projects. These are Alexander’s ‘Synthesis’ [1] and Checkland’s ‘CATWOE’ [2]. The first identifies concepts or worldviews, the second uses these to draft a series of ‘what needs to be done’ statements. In the way of Pragmatic Systems Inquiry, these approaches suggested from the literature are then compared to a real case study: the LC-25 project.     

Global capital control and city hierarchies: an attempt to reposition Vienna in a world city network

This paper is devoted to foreign direct investments (FDIs), which have been allocated on a very low regional level. This makes it possible to first position Vienna within a global city system according to international capital flows and to analyze changes in this position. In addition to being a case study, this paper shall attempt to make a contribution to the conceptualisation of global cities as focal points of FDI-capital flows and the formation of a global city network by firm hierarchies. The dataset is used to analyze Vienna’s FDI-relations to other cities and makes it possible to examine spatial hierarchies based on uneven capital flows. As the data extend over a period of 17 years (from 1989 to 2005), the question can be posed whether geostrategic changes like the fall of the Iron Curtain and Austria becoming a member of the EU have led to new patterns of capital flows. It could be established that there is an ongoing degree of hierarchization within Vienna’s global city network and that the above mentioned changes in the “long decade of the 1990s” established Vienna as a gateway-bridge between the East and the West. On a global scale, however, Vienna’s city status was not raised in the process.     

轴向荷载作用下梁结构动力特性的随机分析

传统梁结构动力特性分析方法由于忽略结构参数的不确定性而不能满足实际工程设计需要,因此,将响应面法(RSM)、有限元法(FEM)和蒙特卡罗法各自的优点相结合,提出一种新的结构随机动力特性计算方法-混合分析法。该方法的最大特点是有效地利用响应面法(RSM)、有限元法(FEM)和蒙特卡罗法(MCS)各自的优点,并将其充分地结合起来。然后,运用该方法分析一简支梁自振频率的统计值。结果表明基于确定性模型的梁结构频率响应分析仅能给出频率响应的均值,忽略结构随机参数对频率响应的影响。为获得准确的频率响应值,有必要在今后的结构动力特性分析中考虑结构参数随机性的影响。最后,进行梁结构随机动力特性计算的敏感性因素分析,并指明影响梁结构动力特性的主要随机因素。     

Greenways: multiplying and diversifying in the 21st century

Building on the legacy of historic greenway planning in the U.S., several new initiatives have been taking shape and gaining recognition in the past decade. One is ‘Green Infrastructure’ planning which is a ‘must have’ inter-connected system of green spaces. Another is ‘Smart Conservation’—the counterpoint of another planning initiative that preceded it known as ‘Smart Growth’. This is the establishment of critical green corridors that should be preserved and maintained for predominantly ecological functions, in advance of or in conjunction with new development. ‘New Urbanism’ has focused on bringing order and coherence to escalating ‘Edge Cities’ on the urban fringe, based on walkable, mixed-use towns, villages and neighborhoods with integrated open-space systems. Transit-Oriented Developments (TODs) are transportation plans for accommodating regional growth around clustered ‘pedestrian pockets’ linked by transit systems. Both New Urbanism and TODs have applied similar principles to ‘brown sites’ and declining city neighborhoods.All these initiatives are different aspects of the greenway movement, expressing its many possibilities, enriching its original concepts, enlarging its credibility—if need be—and emphasizing its importance for and relevance to current issues of sustainability and ‘green’ planning and design. The author, a teacher/practitioner, discusses recent U.S. greenway examples at site, metropolitan and regional scales for which he has been the principal planner/designer or a consultant, and compares New Urbanism and TOD methodologies and approaches to established greenway-planning practices and the premises of Smart Conservation.     

Performance-based design in earthquake engineering: a multi-disciplinary review

This paper reviews the contributions of research towards the development of the methodologies associated with Performance-Based Seismic Engineering (PBSE). Research undertaken in various related disciplines is reviewed, under the broad section headings of (i) Engineering Seismology and Geology (Seismic Activity Modelling), (ii) Engineering Seismology (Seismic Hazard Modelling), (iii) Soil Dynamics, (iv) System Dynamics, and (v) Mechanics of Materials (Concrete used as example). The sequence of the discussion is consistent with a typical seismic assessment procedure, which commences with seismic activity modelling in the ‘upstream’ end of the procedure and finishes with consideration of structural mechanics behaviour at the ‘downstream’ end. Each section provides an outline of historical research and development, leading to a review of the state-of-the-art approaches. Particular emphasis is given to the inter-linking of the disciplines, and the paper refers to such links as ‘Nodal Points’. An example of a nodal point is the definition of probabilistic seismic hazard coefficients that are used to define seismic hazard in terms of elastic response spectra, for example the response spectral accelerations at key periods of 0.3 and 1.0 s. Each of the Nodal Points associated with the various disciplines has been critically reviewed, and shortcomings have been identified. For example, the inability of a probabilistic approach to fully represent an earthquake event as a physical process is highlighted. Also, the importance of putting emphasis in future research on determining the Maximum Credible (or Considered) Earthquake, MCE, is emphasised.

The paper brings to light the fact that, although significant achievements have been made in each of the related disciplines and in the connection of the Nodal Points, there has been relatively little change in substance at the Nodal Points themselves. An important outcome of this multi-disciplinary review is the identification of some key limitations in current procedures. The source of these limitations was traced upstream, and thence to the Nodal Points that provide the inter-disciplinary links. This process has been referred to herein as Upstream Feedback. A review of the problems at these links sows the seeds for further development, which would not have been possible had all the recent contributions been confined within the individual disciplines. Such an Upstream Feedback process, enabling improvements to the multi-discipinary links, would be instrumental in enhancing the overall effectiveness of PBSE in the future.     

GBT formulation to analyse the buckling behaviour of thin-walled members with arbitrarily ‘branched’ open cross-sections

This paper presents the derivation, validates and illustrates the application of a Generalised Beam Theory (GBT) formulation developed to analyse the buckling behaviour of thin-walled members with arbitrarily ‘branched’ open cross-sections. Following a brief overview of the conventional GBT, one addresses in great detail the modifications that must be incorporated into its cross-section analysis procedure, in order to be able to handle the ‘branching’ points — they concern mostly issues related to (i) the choice of the appropriate ‘elementary warping functions’ and (ii) the determination of the ‘initial flexural shape functions’. The derived formulation is then employed to investigate the local-plate, distortional and global buckling behaviour of (i) simply supported and fixed asymmetric E-section columns and (ii) simply supported I-section beams with unequal stiffened flanges. For validation purposes, several GBT-based results are compared with ‘exact’ values, obtained by means of finite strip or shell finite element analyses.     

‘Management by projects’: the management approach for the future

The trend toward the project-oriented company, performing simultaneously a network of internal and external projects, creates the demand for the management approach ‘Management by Projects’. The specific feature of ‘management by projects’ is that the management of single projects, the management of the network of projects and the management of the relationships between the company and the single projects are considered. For the successful management of the project-oriented company, instruments of ‘Management by Projects’ are presented.     

Israel: metropolitan integration or ‘fractured regions’? An alternative perspective

This paper proposes an alternative account of the high degree of power centrality in Israel, by arguing that the territorial ‘fracturing’ of Israel's main social and ethnic groups has prevented the emergence of effective pressure for regional devolution. Israel's character as a settler and settling state, and its central project of Judaising contested territories, enabled the Israeli ‘ethnocracy’ and its (mainly Ashkenazi) elites to create a political geography of ‘fractured ethnic and social regions’. This was achieved by dispersing minorities and legitimising segregation and inequality, all in the name of the ‘national interest’.The Israeli political landscape is therefore organised as ‘fractured regions’, each representing a distinct and interconnected, yet geographically dispersed, set of localities. The logic of dispersal and segregation, in turn, has also influenced patterns of development and residential separation within Israel's main urban areas. Thus ethnic and social fragmentation and conflict, and not a putative process of national or metropolitan integration, can explain much of Israel's highly centralised power structure.     

The importance of ‘process’ in Rethinking Project Management: The story of a UK Government-funded research network

This paper tells the story of a UK Government-funded research network called Rethinking Project Management, funded by the Engineering and Physical Sciences Research Council between 2004 and 2006. The story is significant because of the considerable attention given to the process of the Network, both the inquiry process of ‘rethinking’ project management, and the broader social process in which the rethinking activity was carried out. In telling this story, the lead organisers explain how the inquiry process was organised as a learning system to enable the Network to ‘learn’ its way to relevant directions for future research, and secondly, how the broader social process was organised and facilitated to create a context for effective interaction between the people involved. A significant challenge in managing the research programme was how to engage the participants in purposeful inquiry, which would serve not only the primary aims of the Network, but would also yield new and interesting insights for the people involved. This paper seeks to explain how the lead organisers addressed this challenge, through a detailed and reflective discussion of how the research programme was organised and facilitated to achieve the Network’s primary aims. In summary, the principal aim in telling this story is to highlight the importance of process in collaborative research activity involving academics and practitioners, in order that other researchers might draw on the experience of this Network.     

Modeling error analysis of shear predicting models for RC beams

Analyses of the modeling error associated with several commonly referred models for predicting shear capacity of reinforced concrete beams were carried out using a database containing results of test beams that was established based on test specimens found in the literature. The database contains a total of 1146 test beams, each has sufficient information for calculating the shear capacity using the shear predicting model in the design code suggested by the American Concrete Institute (ACI), the simplified method recommended by the Canadian Standard Association (CSA), the modified compression field theory, the shear friction method and Zsutty’s method.Statistics of the modeling error suggest that the performance of the shear predicting model in the ACI code and the CSA simplified method is similar but significantly biased and associated with large coefficients of variation of the modeling error. Overall, Zsutty’s method may be considered to be the best predicting model among the models included in this study. However, for beams with stirrups, use of the modified compression field theory provides less biased prediction with less scatter. This is followed by Zsutty’s method and by one of the shear friction models.     

考虑轨道不平顺全概率分布的车桥随机分析方法

轨道不平顺是车桥耦合系统最主要的激励之一,其高维的随机性导致车桥耦合确定性计算模型不能精确反映实际系统动力响应的离散性。为了完整地反映实际线路中的轨道不平顺信息,文章建立一种适用于车桥耦合随机系统分析的轨道不平顺随机场模型,模型在包含了轨道谱概率、幅值、波长、相位等信息的基础之上,尽可能地减少了参数数量,通过与实测数据对比,该模型的有效性得以验证。此外,将该轨道不平顺随机场模型作为三维车 线 桥耦合时变计算模型的激励源,引入概率密度演化方法,对该耦合系统动力指标的统计特性及动力可靠度进行分析。结果表明,该轨道不平顺随机分析模型产生的空间序列较好地表征了平稳随机过程的谱表达;概率密度演化方法相对于蒙特卡洛方法有着更高的计算效率;不同的动力指标有着不同的均值、均方差、可靠度特征。