The compressive post-local bucking behaviour of thin plates using a semi-energy finite strip approach

A geometrically non-linear finite strip for the post-local-buckling analysis of geometrically perfect thin-walled prismatic structures under uniform end shortening is developed in this paper. The formulation of the aforementioned finite strip is based on the concept of the semi-energy approach. In this method, the out-of-plane displacement of the finite strip is the only displacement which is postulated by a deflected form. The postulated deflected form is substituted into von Kármán’s compatibility equation which is solved exactly to obtain the corresponding forms of the mid-plane stresses and displacements. The solution of von Kármán’s compatibility equation and the postulated out-of-plane deflected form are then used to evaluate the potential energy of the related finite strip. Finally, by invoking the principle of minimum potential energy, the equilibrium equations of the finite strip are derived. The developed finite strip is then applied to analyse the post-local-buckling behaviour of thin flat plates. The results are discussed in detail and compared with those available from published works, wherever possible. This has provided confidence in the validity and capability of the developed finite strip in handling the post-local-buckling problem of plate structures.     

Nonlinear buckling of microfabricated thin annular plates

Annular plate structures are commonly used in MEMS devices, particularly in pumps and valves. In MEMS applications, large nonlinear deflections are routinely achieved. In this paper, the nonlinear buckling of a thin elastic annular plate under a compressive radial force acting in the plane of the plate is considered. Although the critical loads at which buckling starts can be determined by solving a linear eigenvalue problem, the large deflection behavior of a buckled plate beyond the critical loads can be described by the nonlinear theory proposed by von Kármán. The buckling loads of the annular plate for various boundary conditions are calculated and the post-buckling behaviors are examined. Interestingly, the buckling of an annular plate exhibits a supercritical pitchfork bifurcation. Thus, the post-buckling behavior is stable and will not collapse catastrophically. Several design implications for microfabricated structures, in particular microvalves, are also given.     

Auto-parametric resonance in thin cylindrical shells using the slow fluctuation method

Internal auto-parametric instabilities in the non-linear vibrations of an undamped and unloaded cylindrical shell are studied. The focus is on the coupling between two modes that can combine to break the in–out symmetry and give an energetically favourable pattern of deformation. When the ratio of the natural frequencies is close to 2, internal resonance triggers significant energy transfer between the modes. This energy exchange has both regular and chaotic features, which were previously investigated by other methods of analysis in [J. Sound Vibrat. 227 (1999) 65; J. Sound Vibrat. 248 (2001) 395]. A Rayleigh-Ritz discretization of the von Kármán–Donnell equations is employed to derive the Hamiltonian equations in R⁴. A perturbation analysis using action-angle coordinates gives slow fluctuation equations that can be solved by quadrature in Jacobian elliptic functions: and, a simple analytical criterion for the parametric instability is presented. This analytical solution gives a good approximation to the regular motions, and provides a framework in which to examine the chaotic motions that are studied in [J. Sound Vibrat. 248 (2001) 395].     

Buckling of elastic cylindrical shells considering the effect of localized axisymmetric imperfections

The effect of localized axisymmetric initial imperfections on the critical load of elastic cylindrical shells subjected to axial compression is studied through analytical modeling. Some classical results regarding sensitivity of shell buckling strength with respect to distributed defects having axisymmetric or asymmetric forms are recalled. Special emphasis is placed after that on the more severe case of localized defects satisfying axial symmetry by displaying an analytical solution to the Von Kármán–Donnell shell equations under specific boundary conditions. The obtained results show that the critical load varies very much with the geometrical parameters of the localized defect. These variations are not monotonic in general. They indicate, however, a clear reduction of the shell critical load for some defects recognized as the most hazardous isolated ones. Reduction of the critical load is found to reach a level which is up to two times lower than that predicted by general distributed defects.     

Nonlinear thermomechanical post-buckling of circular FGM plate with geometric imperfection

Nonlinear thermomechanical post-buckling of an imperfect functionally graded material (FGM) circular plate, subjected to both mechanical load and transversely non-uniform temperature rise, is presented. The material properties of FGM plates are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Based on von Kármán's plate theory, equilibrium equations governing a large axi-symmetric deformation of the FGM circular plate under thermomechanical loads are derived. In the analysis, the geometric imperfections of the plate are taken into account. By using a shooting method the nonlinear ordinary differential equations with immovably clamped boundary conditions are solved numerically. Responses for the nonlinear thermomechanical post-buckling responses of the FGM plate are obtained. Numerical examples are presented that relate to the performances of perfect and imperfect, homogenous and graded plates. Characteristic curves of the post-buckling deformation of the imperfect FGM circular plate varying with thermal loads, imperfection parameters and volume fraction index are plotted. And then effects of the load parameters, materials constitution, and the geometric imperfection of the plate on the deformation are discussed in detail.     

Biosphere reserves and the “Yucatán” syndrome: another look at the role of NGOs

After centuries of cultural and economic conquest of the Americas by European and Euro-American conquistadors, contemporary rhetoric in ex-colonial powers heralds the decline of material and ideological imperialism. Instead, it is purported that today's world is peopled by a great brotherhood, with the more affluent striving to relieve their less fortunate, underdeveloped kith. This conviction is inherent in organizations which dispense money, information, training, and other resources in the name of community development and endangered species and environmental conservation. What is rarely perceived – and practically never said – is that these “benevolent” foreign aid activities typically result in the concentration of resources and power in the hands of a few, the building of empires, and the compounding of already difficult situations, counter-productive to stated objectives. The Yucatán Peninsula is a classic case of persistent imperialism: the geographic name is a corruption of the Mayan “matan cub a than” (“I do not understand you”), while contemporary development and conservation programs habitually exhibit cultural ignorance and dominance. This paper explores a diverse literature on non-governmental organizations, reflects on likely consequences of cultural dominance, and implores professional anthropologists to be adventurous in propagating anthropological knowledge relevant to environmental protection.     

Biophilia as the invariant in human thinking: A case study — the town of Tábor

Aesthetic and symbolical relations of humans to nature were not properly considered either in theory or in practice of urban planning as it was carried out in our country in the 1970s and 1980s. The fact, that elements of nature within urban environment play an important role as they partly satisfy the biophila needs of man, i.e. his affinity with plants and animals, was generally neglected.The contribution describes the attitudes of inhabitants in the housing estate of the town of Tábor, South Bohemia to the urban environment they live in. Based on the empirical evidence, two conclusions can be arrived at. Absence of nature, at least in its symbolical form, proved to be the factor limiting the “pleasant existence” of the people living within housing estates. Low willingness of inhabitants to actively participate in the process of making their urban environment livable seems to remain one of the most crucial problems inherited from the former totalitarian regime.     

Etude de l'evolution de la qualite des eaux de riviere

In France, the creation of a “Ministère de l'Environnement et du Cadre de Vie” and “Agences Financieres de Bassin” has made it possible to obtain information on the water quality of rivers and on the measures necessary to improve water quality. Particularly in the Adour-Garonne Basin, much information is now available. The methodology needed to draw conclusions concerning the quality of the rivers and to show the effectiveness of control measures has been developed.This method has been tested in two catchments (Fig. 1): L'Adour (15,000 km²) and La Dordogne (24,000 km²). The steps that were necessary before this method could be used were: critical assessment of the available data; identification and measurements of pollution sources. This called for the collection of information, annual statistics for each sampling station and information concerning the value and importance of measured parameters.Detailed information is available from 1971 and 1976 and this is shown by maps and graphical representations of the variations in the value of different parameters (Fig. 2).Statistical analysis has also been carried out on the information available for the period 1971–1976.Two methods were used: analysis of the principal components, the method most used being shown by Figs 3 and 4 and the “STATIS” method developed recently which treats the whole data “At 3 indices” (Fig. 5).Research has been carried out on the causal relations between the water quality and the sources of pollution.A simple graphical method is proposed to explain the effect of a strongly preponderant pollutant source. It allows easy visualisation of the change in the relationship between two series of variables (Fig. 8).In general cases of several sources of pollution a simplified method using BOD exclusively has been developed. It consists in comparing the values measured in the river and the estimates obtained from inflows of various sources and those from upstream basins (Fig. 9).The application of this method has made it possible to distinguish local or general tendencies in reference to the intervention realised by the “Agence Financiere de Bassin”.Attention has been given to the variations obtained between laboratories and research information and the necessity to extend application of the statistical method to parameters other than BOD₅.Comparable action is being taken for the whole basin of the Rhone (French). The information obtained for “L'Adour and La Dordogne” has led to a study not only of the concentration of pollutants but two types of flow, with flow measurements and concentration being taken into account in order to eliminate hydraulic effects.     

Postbuckling analysis of cross-ply laminated cylindrical shell panels under parabolic mechanical edge loading

Postbuckling equilibrium paths of simply supported cross-ply laminated cylindrical shell panels subjected to non-uniform (parabolic) inplane loads are traced in this paper. Love's shell theory with higher order shear deformation theory and von Kármán nonlinear strain–displacement relations are used in the mathematical formulation of the problem. In the first step, the plate membrane problem is solved to evaluate the stress distribution within the prebuckling range as the applied inplane edge load is non-uniform. The governing shell panel postbuckling equations are derived from the principle of minimum total potential energy using the above stress distributions. Adopting multi-term Galerkin's approximation, the governing equations are reduced into a set of non-linear algebraic equations. Newton–Raphson method in conjunction with Riks approach is employed to plot the postbuckling paths through limit points. Numerical results are presented for symmetric (0/90/0) crossply laminated cylindrical shell panels under parabolic inplane load, lateral distributed load and initial imperfections. Limit loads and snap-through behavior of shell panels are studied.     

Solution to the problem of axisymmetric and asymmetric dynamic instability of three-layered annular plates

This paper presents the solution to the dynamic stability problem of three-layered, annular plate loaded by compressive stress increasing in time. The solution enables the evaluation of the critical, dynamic loads corresponding to the various modes of plate buckling. The symmetrical cross-section structure of plate is described by the classical theory of sandwich plate with the broken line hypothesis, the nonlinear Kármán’s plate equations and linear physical relations. The solution is based on Bubnov–Galerkin method and finite difference method. The values of critical dynamic loads have been calculated by means of the stability criterion presented by (Volmir (1972) [1]). The comparison of values of critical dynamic and static loads is presented, using the dynamic ratio. The obtained results have been compared with those obtained for plate model built by means of finite element method. The calculations were carried out using the ABAQS system. The dynamic response of plate models examined by two methods is consistent.     

Toxicity, accumulation and elimination studies of α-hexachlorocyclohexane (α-HCH) with freshwater organisms of different trophic levels

A short- and long-term toxicity study with α-hexachlorocyclohexane (α-HCH) was carried out with freshwater organisms of different trophic levels (algae, crustaceae and fishes). In this study mortality, immobilization, growth, reproduction, histopathologic changes and enzyme activities were chosen as criteria.Furthermore accumulation and elimination processes were investigated in separate organisms as well as the uptake of α-HCH by one organism and through a food-chain.Finally a tentative method for deriving an “ecological limit” for χ-HCH in surface water is described.     

A continuum of organizations formed to carry out projects: Temporary and stationary organization forms

Projects are carried out by temporary organizations. These organizations can function independently or in cooperation with stationary organizations. To enable efficient project and program management, these differences in organization structure have to be considered. This paper therefore contrasts organizations formed to carry out activities at project sites based on forms of employment, work processes and resource networks used. Findings indicate that temporary organizations that are dominated by stationary “parent” organizations often rely on its abilities to secure access to crucial resources and to identify suitable work processes. “Pure” or virtually “pure” temporary organizations instead rely on their employees’ skills and contacts to develop suitable routines and gain access to resources.     

Search-based importance sampling

Importance sampling as a special technique in Monte Carlo probability integration has been shown to be a highly efficient and rather unrestricted method. Non-Gaussian and dependent random variables and nonlinear limit functions can be treated relatively easily and with reasonable rates of convergence. A major draw-back, however, is the need to identify so-called “interesting” or “important” regions for integration. Reference to first-order second-moment (FOSM) methods may help, as well as numerical maximization routines applied. Each involves certain difficulties. An alternative procedure, based on directing and correcting the importance sampling function as sampling is carried out, is presented herein. In particular it is possible to have a multi-modal sampling function.     

IHAS at Exeter 1982. First Scientific Assembly. Exeter, England, 19–30 July, 1982

This study contains the results so far of tests which have been carried out on samples of sedimented municipal effluent stabilized by means of simple preservation methods by the working party on “stabilization of samples” from the German Chemists Association's hydrochemistry team and evaluated with a view to providing recommendations on methods of preservation. It was assumed that the recurrent standard deviation of the test methods applied is less than ± 10%. Consequently a deviation in the measured concentrations by more than 10% in terms of the initial concentration after a given storage period of the preserved sample was to be regarded as a real change in the corresponding contents of the sample. Accordingly the datum “storage period of preserved sample” means that the samples must on no account be preserved for longer than the stated time, and that the actual storage period should, if appropriate, be shorter depending on the accuracy requirements.     

Local perspectives in conservation politics: the case of the Ría Lagartos Biosphere Reserve, Yucatán, México

Local perspectives are presented on the conflicts and contradictions in the Ría Lagartos Biosphere Reserve, one of 10 priority reserve areas in México that receive financing from the World Bank and other development and conservation institutions. There are four villages into the reserve, whose total population ranges from 800 to 2500 inhabitants. At this reserve, decision-makers and administrators have focused on biological conservation, failing to understand the social and political relations of the local people, which are strongly affected by globalization and modern conservation policy. Modern conservation is a western discourse on nature, is a kind of “licence to conserve”, analogous to an automobile driver's licence. Conservation in Ría Lagartos means prohibition to the local population hence conflicts frequently arise between them and both local and federal authorities. However, there is an urgent need to move forward and recognise the diversity of discourses on nature that give rise to different kinds of knowledge and practices of conservation variously called popular, traditional, indigenous, and folk. This paper discusses the institutionalization of conservation in a natural protected area (biosphere reserve) in the northwest of Yucatán Peninsula. The researcher initially established rapport with the communities of this region more than 10 years ago, working on various ethnographic research projects from then to the present. This long-term relationship has (1) deepened the level of trust, (2) contributed substantially to the background knowledge critical for identifying local factors of importance, and (3) provided information necessary for the proper wording of questions in the local parlance. The research reported here continued to use the same ethnographic approach used in the former research projects, an ethnographic method including participant observation and informal interviews in homes, work places, local stores, and other places normally frequented by the local consultants. The research reported in this article was done from August 1996 to July 1997 in the three communities of the Biosphere Reserve of Ría Lagartos: Río Lagartos, San Felipe and Las Coloradas.     

Computational study on aerodynamic mitigation of wind-induced, large-amplitude vibrations of stay cables with strakes

Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Kármán vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10⁵. Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.     

Seismic vulnerability of monumental buildings

Monumental buildings are by definition unique buildings that cannot be reduced to any standard structural scheme: this makes it difficult to evaluate their seismic reliability, because—in addition to the many uncertainties that are common to all existing (and in particular “old”) buildings—no statistics on the behaviour of similar buildings can be available. To overcome this problem, the macroelement approach has been proposed a few years ago and since then repeatedly used to analyse and compare the seismic response of monumental buildings: the structural organism is considered as the assemblage of few components (e.g. the whole façade of a church) whose behaviour is typical of the behaviour of analogous macroelements in other buildings, and whose possible collapse mechanisms can be identified. In these studies, quasi-static loads have been used, as indeed common in many analyses of the seismic behaviour of masonry structures. This paper accepts these simplifying assumptions, and shows how—assuming appropriate probabilistic properties of the relevant quantities and a “logical diagram” describing the relation between collapse of macroelements and whole building—the probability of collapse and damage of each macroelement and of the whole building under given horizontal loads can be assessed. The procedure is formulated in detail with special reference to churches, and illustrated on two example cases. The same procedure can be used as the basis of a statistical extrapolation aimed at evaluating the probability distributions of collapse and damage among monumental buildings that are similar with regard to both the macroelement typologies and the logical diagram.     

The capital budgeting evaluation practices (2004) of building contractors in Hong Kong

This paper reports the investigation results of capital budgeting evaluation practices of Hong Kong building contractors. The survey aims to identify the popularity of various techniques for capital budgeting evaluation and to measure the changes of the practices longitudinally by comparing the results of the current study (2004) with those of the similar surveys conducted in 1994 and 1999. The current survey results revealed that the “formal financial evaluation” was the most popular technique for capital budget evaluation. The “payback period” was the mostly used investment appraisal technique. For risk appraisal techniques, “shortening payback period” occupied the first position. The “planning programming” remained as the most popular management science technique. Moreover, a comparison of the practices of large contracting firms was carried out to view the changes over the last 10 years. The results showed that the practice of capital budget evaluation was emphasized. The popularity of employing investment appraisal and risk analysis techniques was dropping. In addition, the capital budgeting evaluation techniques examined were fitted into a discriminant function analysis (DFA), which allowed contracting firms to be classified in accordance with their predominant characteristics in the practices. The classification result was 89.1% of all cases were correctly classified.