Static analysis of thin-walled structures using polynomial and exact solutions. Application to thin-walled pipes

A new finite element procedure for the static analysis of beam thin-walled structures of open or closed cross-section is presented. The method is a combined or mixed one, based on the superposition of beam and shell strains and displacements. An essential part of this work is the development of new shape functions (which are either ‘exact’, or polynomial) for the interpolation of the shell displacements.The above method is applied to the thin-walled curved pipe problem and compared to the von Karman approach. Excellent results are obtained, as well as a drastic reduction of the total number of nodal variables.     

Post-failure fracture angle of brittle pipes subjected to differential ground movements

Centrifuge testing of four glass pipe models has been used to measure the kinematics associated with cast iron pipe fracture and the relative rotation of the pipeline on either side of the fracture when fracture is induced by a normal ground fault. The model pipelines were fabricated at 1/30th scale using solid glass rod of semi-circular cross-section. After placing each model against the transparent sidewall of a test box, the pipe was buried and the tested at 30 g. Movements of the soil and the model pipe were monitored using particle image velocimetry, and analysis was used to examine both the curvature distributions before fracture, the fracture pattern (i.e. the fracture locations) expected for cast iron pipes passing across a normal ground fault, and the post-test rotations across the fractures. The depth of soil cover was observed not to make a significant difference to the amount of initial fracture angle for the range of covers investigated in this study (1.125–2.25 m in prototype scale). The fracture angle was shown to be well represented by the slope of the pipe displacements at the inflection point. The use of normalized peak curvature to estimate the fracture angle (rotation across the fracture) was demonstrated. The estimated magnitude of rotation after the pipe breaks can then be used to estimate the local stresses and strains that would develop in a polymer liner inserted within the cast iron pipeline before fracture initiates and which is therefore subjected to longitudinal bending stresses after the cast iron pipe fractures, values of ‘demand‘ that can then be evaluated against measurements of liner strength (i.e. its stress and/or strain limits). The initial angle of rotation directly across the fractures after they form is approximately the same regardless of when the pipe initially breaks, and regardless of the soil cover depth and soil density. However, the magnitude of the vertical ground displacement across the normal fault needed to induce fracture varies considerably for the different burial conditions that were considered, and the rotation angle increases steadily after fracture if the amount of vertical ground displacement continues to grow.     

Introduction of the leak-before-break (LBB) concept for cast iron water pipes on the basis of laboratory experiments

Failure of cast iron water mains in Australia is a common occurrence. Water utilities are seeking solutions to optimise the renewal and rehabilitation of ageing cast iron critical water mains (diameter ≥ 300 mm). Failure pressures of three large-diameter cast iron pipe specimens (600 mm in diameter) were tested. A large corrosion patch was machined onto each pipe section to initiate pipe failure. A large corrosion patch and significant reduction (>90%) of pipe wall thickness were needed to fail the tested pipe specimens. All three pipes under test exhibited leaking before bursting, indicating that the concept of leak-before-break (LBB) could be used for pipe failure prevention. In addition, LBB provides valuable information that could be added to the pipe asset database to make better management decisions on repair or replacement along with all other asset information. The study also found that small corrosion patches (<50 mm) with low remaining wall thickness may cause pipe leaks, but are less likely to cause major pipe bursts.     

Research needs for on-line pipeline replacement techniques

This paper presents suggested research needs associated with on-line pipeline replacement techniques, such as pipe bursting and pipe splitting. These research needs were compiled prior to, and then debated at, a workshop involving both academia and industry. The aim of the workshop was to assess whether the suggested needs were accurately stated, whether there were additions to make, and most importantly to attach a priority to the research needs. This was achieved by a process of debates and subsequent voting. The areas considered to be most important for research are highlighted in paper. It is concluded that although there has been extensive research into some of the more common types of on-line replacement techniques, for example pipe bursting, there is still a need for further research. The priority research identified from the workshop are in the areas of decision making tools, improved information on safe distances to adjacent utilities and techniques for minimising open excavation when disconnecting and reconnecting laterals.     

Continuous accountability for acceptable building performance

Complexities in building technology when not fully understood, have resulted in a less than favorable aggregate impact on the building's environment. A surprisingly high portion of U.S. non-industrial buildings do not provide satisfactory task environments. Developments in computer technology have infused new thought processes in the way we plan, design, build and operate our buildings. This paper proposes a social and technical use of Knowledge-based-systems (KBS) for continuous accountability to assure healthy buildings. Diagnostics, as an emerging discipline in building design and operation, is also discussed. A proposed framework for such accountability and the resulting ‘chain of custody’, that draws on the medical paradigm and associated diagnostic procedures is presented. It is suggested that KBS also be used for the development and interpretation of criteria for evaluating building performance from initial conception through design, construction and operation. Thus, KBS is expected to aid in the analysis of ‘virtual’ and ‘actual’ buildings that may be ‘sick’ or ‘healthy’. It is proposed that for a building to provide satisfactory performance over its life-time, the ‘life-cycle’ concept must be modified in terms of the roles, responsibilities, and configuration of the building team, and in terms of its costing procedures.     

Observations and classification of roof strata behaviour over longwall coal mining panels in India

A study has been made of a number of mechanized longwall panels in various coal mines in India, concentrating on the geology, physico-mechanical rock properties and the behaviour of the coal measure roof rocks during mining. The research has highlighted the splitting and caving characteristics of the strata rocks and enabled the development of a roof-rock classification system. Roof rocks are classified into six categories based on the: (a) mean weighted uniaxial compressive strength; (b) RQD; (c) (i) type of rocks, (ii) presence of cracks, fissile beds, splitting, etc., (iii) presence of water; and (d) thickness of bed layer. The behaviour of layers and composite layers in the immediate roof rock mass is also enumerated. Relations between the rock strength properties and values for the bulking factor of the failed rock are included. The concepts of a ‘weighting zone’ and ‘caving zone’ are proposed. The paper also clarifies the occurrence of different types of failure, such as periodic falls. All these findings should be helpful during calculation of the powered support capacity.     

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.     

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.     

Simplified model for numerical calculation of pull forces in static pipe-bursting operations

Trenchless pipe replacement, or pipe bursting, is defined as the replacement of an original pipe by fragmenting the existing conduit and simultaneously installing product pipe in its place. In the static method of pipe replacement, the original pipe fails in tension by radial forces developed from the cone-shaped bursting head geometry that are applied to the pipe wall from within the pipe, as it is pulled or pushed through the existing pipe. The fragmented pieces are pressed into the surrounding soil as it is being displaced, thus creating a cavity for the product pipe. This paper presents a simplified model to calculate the maximum pull force (a function of the friction, bursting, and soil compression shear forces) required to be overcome to complete a static pipe-bursting pull. Based on site-specific information, the model provides an initial avenue for contractors, engineers, and manufacturers in planning successful trenchless pipe replacement projects.     

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.     

Evaluation of an attempt to cultivate shrubs and trees on a heap of a potash mine

Starting at the end of November 1993, the Dr. Kahl GmbH has attempted to grow shrubs (Amorpha: Amorpha fructuosa and snow-berry: Symphoricarpos rivularis) and trees (poplar hybrid ‘University of Idaho’ Populus deltoides and Eleagnus angustifolia), on the heap of the potash mine Sondershausen/Harz (Free state of Thuringia). Patented water-saving planting method was used. A flexible planting container made of polyethylene was first filled with 50 g polyacrylamide (also called ‘hydrogel’) and after that with about 40 kg of a mixture of anhydrite (CaSO₄) — the mean soil of the heap — and dried sewage sludge, respectively, composted sewage sludge on top of the hydrogel. After placing the container into the ground, one-year-old seedlings of the shrubs or trees were planted into the containers. Five years after planting investigations on the plants and soil were started. The results until now show that, using the planting method, Amorpha, the poplar ‘University of Idaho’ and the Eleagnus are able to grow under the poor conditions of the heap.     

Simulation-based life cycle cost modeling and maintenance plan for water mains

Life cycle cost (LCC) is an essential approach to decide on alternative rehabilitation strategies for infrastructure systems, such as water mains. The research presented in this article identifies several rehabilitation methods for water mains, which are classified into three main categories: repair, renovation and replacement. A simulation-based LCC (SLCC) model is developed to compare different rehabilitation scenarios/alternatives for various types of water mains (i.e. cast iron, ductile iron, concrete, polyvinyl chloride and asbestos cement). Results show that ‘open trench’ and ‘slip lining’ are the most appropriate methods for the ‘repair’ and ‘renovation’ categories, respectively. However, the most suitable method for the ‘replacement’ category is ‘pipe bursting’ for pipe diameters less than 750 mm (<30″) and ‘open cut’ for pipe diameters greater than 750 mm (>30″). A rehabilitation plan is developed based on the SLCC results. This plan recommends repairing pipes using ‘open trench’ until the breakage rate reaches 0.5 breaks/km/year, then, replace the pipe beyond this threshold. Based on the designed SLCC model, web-based software is developed to determine the optimal rehabilitation scenarios. The developed model and software help academics and practitioners (e.g. municipal engineers) to predict the suitable new installation and/or rehabilitation programs as well as their corresponding costs.     

Predicting ground conditions ahead of the tunnel face by vector orientation analysis

Tunnel construction frequently makes use of radial displacements to monitor tunnel support performance, particularly in complex ground conditions. In recent years, absolute displacement monitoring methods have replaced the more traditional radial convergence measurements. It has been suggested by Schubert and Budil (1995) [The importance of longitudinal deformation in tunnel excavation. In: Fujii, T. (Ed.), Proceedings of the 8th ISRM Congress on Rock Mechanics, Tokyo, vol. 3. A.A. Balkema, Rotterdam, pp. 1411–1444.] that these near-face displacements could also be used to forecast the tunnel conditions ahead of the advancing tunnel face. This paper presents the results from a series of detailed three-dimensional analyses in varying ground conditions, which compares vertical (radial) displacements measured at the roof, vector orientations associated with these roof displacements and tunnel face displacements (extrusion). These numerical results suggest that in all cases vector orientation provided additional information not obtained from traditional radial displacements or face extrusion. If interpreted correctly the vector orientations could provide advanced warning of changing ground conditions in the vicinity of the tunnel face.     

Reconquering the city

Choosing a title for the 1900 campaign in favour of the cities of Europe and for improving the quality of life in them was a difficult task for the experts of the Council of Europe. Before arriving at the rather weak term ‘renaissance’, alternatives ranging from ‘renewal’ to ‘rehabilitation’ and even ‘reconquest’ of the city were considered. This last term seems to me, in spite of its military connotations, to grasp the problem well enough.     

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.     

Principles of diamond tool technology for sawing rock

In a rock sawing operation, a single diamond particle acting as a sliding indenter expends energy by generating compression in the rock in the form of a ‘stress epicentre’ through the action of confined crushing: this compression causes the rock fracture mechanism. It is not a cutting operation per se—indeed sharp diamond particles can be a liability. The sawing requirement is for a high strength, high heat resistance indentor, with a potential for displacement that is compatible with that of the rock. Currently used tests for rock strength do not indicate energy consumption, but the Shore and Brinell hardness tests are relevant. However, the consumed energy is predictable from a new index of rock strength, called Brook hardness, which has been specifically developed for sliding diamond indenters. The ‘stress epicentre’ is located with reference to the diamond indenter through a force vector which is stable for all circular sawing velocities, but it changes with frame sawing and drilling because they operate at about a tenth of the sawing velocity. The ‘stress epicentre’ is at the location of the crushed, compacted material under the indenter. Changes in the position of the stress epicentre can increase energy efficiency by as much as 100% and reduce the generation of vertical force by as much as 70%. Drilling tests using feed/revolution as the measure of penetration are used to simulate the variable velocity of frame saws by reducing the revolutions/minute. These tests reveal a previously unrecorded sawing mechanism that can improve the use of frame saws because strong granite can now be frame sawn with diamond. This improved potential should also apply to drill bits if they use feed per revolution as the means of penetration, instead of a static bit load. By measuring diamond by volume rather than by weight, and considering alternative options, accurate tool control can now be achieved, with every aspect being predictable. Optimisation of rock sawing operations has shown that performance can be increased by 100–200% with tools removing as much as 30 tonnes in saw cuts per carat of diamond consumed. Because some rock mechanics terms used in the paper may have different meanings in the rock sawing context, a glossary of terms with further explanations is included at the end of the paper.     

顶管破管一体化地下管道施工仿真模拟

文章的工程背景为天津自来水管道的更换工程,该项目采用静压破管法施工,采用球墨铸铁顶管直接安装顶推头,实现顶推破管一体化的新型施工工艺.文章通过ANSYS有限元仿真模拟软件来模拟地下静压破管的施工过程,对该过程中锥头及管道的应力、变形状况进行分析,计算出施工过程中管子端部的受力以及锥头所需的推力,并设计合适的锥头外形,从而为实际施工工艺的选取和顶推头的设计提供理论依据.     

Three-dimensional back-analysis of displacements in exploration adits — principles and application

Back-analysis from displacements has been attracting the interest of the rock engineering profession in recent years. It has been applied since its inception in the 1970’s because of its instinctive practical value to the designer. In this paper we discuss the principles and application of one feasible method, that of Three-dimensional displacement Back-Analysis (TBA), which is used to back analyze the modulus of elasticity (E) of the rock mass and the horizontal component (P) of rock stress mainly by means of displacements measured during the the excavation of an exploratory geological adit. An attempt is also being made to solve the problem of unique resolution of TBA.     

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.     

A semi-analytical model for local post-buckling analysis of stringer- and frame-stiffened cylindrical panels

A fast semi-analytical model for the post-buckling analysis of stiffened cylindrical panels is presented. The panel is comprised of a skin (shell) and stiffeners in both longitudinal (stringers) and circumferential direction (frames). Local buckling modes are considered where the skin may buckle within a bay and may induce rotation of the stiffeners. Stringers and frames are considered as structural elements and are thus not ‘smeared’ onto the skin. Large out-of-plane deflections and thus non-linear strain–displacement relations of skin and stiffeners are taken into account. The displacements of skin and stiffeners are approximated by trigonometric functions (Fourier series). First, a linear buckling eigenvalue analysis is carried out and some combination of buckling eigenmodes is chosen as imperfection. Then the load history is started and the Fourier coefficients are determined by minimizing the stiffened panel's energy at each load level. A curve-tracing algorithm, the Riks method, is used to solve the equations. The present model can be used to assess the post-buckling behavior of stiffened panels, for example, aircraft fuselage sections.