Results 1 - 10 of 1867
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[en] The increase of vibration problems in modern footbridges shows that footbridges should no longer be designed for static loads only. Not only natural frequencies but also damping properties and pedestrian loading determine the dynamic response of footbridges and design tools should consider all of these factors. Footbridge vibrations don’t cause usually structural problems, but if the vibration behaviour does not satisfy the comfort criteria, changes in the design or damping devices could be considered. The most popular external damping devices are viscous dampers and tuned mass dampers (TMD). The paper presents the basic principles of optimal TMD configuration and design procedure. The efficiency of TMD is demonstrated on the example of a footbridge prone to vibrations induced by pedestrians. It is shown that if the TMD is tuned quite precisely the reduction of accelerations can be very significant. (paper)
[en] An extensive experimental investigation of buckling of conical shells that are supported only along their lower edge and that are loaded by the weight of a liquid leads to diagrams and formulas which can be used directly in the design of such shells. The margin of safety to be applied, the influence of welding stresses and the limitations on the validity of the formulas for structures with different boundary conditions are discussed. (orig.)
[en] The rigid-plastic limit analysis of shells of revolution and circular plates submmited to loads rotationally symetric is studied. The finite element method is used. The von Mises criteria that is used in sandwich shells is adopted. This criteria reduces the limit analysis problem in the application of the nonlinear programming techniques. Some results on the lower and upper limits of the collapse load are presented. (E.G.)
[pt]Estuda-se a analise limite rigido-plastica de cascas de revolucao e placas circulares sujeitas a carregamento rotacionalmente simetrico. Discretiza-se a estrutura atraves do MEF. Adota-se o criterio de von Mises valido para 'casca sandwich', o que reduz o problema de analise limite na aplicacao de tecnicas de programacao nao-linear. Apresentam-se resultados de limites superiores e inferiores da carga de colapso. (E.G.)
[en] The effects of prehydrostatic loading on microstructural changes and tensile deformation behavior of nuclear-grade isotropic graphite have been examined. Scanning electron micrographs show that formation of microcracks associated with delamination between basal planes occurs under hydrostatic loading. Hydrostatic loading on specimens results in the decrease in tensile strength and increase in residual strain generated by the applied tensile stress at various levels, indicating that the graphite material is weakened by hydrostatic loading. A relationship between residual strain and applied tensile stress for graphite hydrostatically-loaded at several pressure levels can be approximately expressed as element of= (AP + B) sigmasup(n) over a wide range hydrostatic pressure, where element of, P and sigma denote residual strain, hydrostatic pressure and applied tensile stress, respectively; A, B and n are constant. The effects of prehydrostatic loading on the tensile stress-strain behavior of the graphite were examined in more detail. The ratio of stress after hydrostatic loading to that before hydrostatic loading on the stress-strain relationship remains almost unchanged irrespective of strain. (orig.)
[en] Screw turns are known to be deformed as a result of the contact pliability of the nut and screw surfaces. The load distribution over the turns is investigated when fine thread is employed, when compression nuts are replaced by tension–compression and tension nuts, when the roughness of the working surfaces is increased, and when the load on the screw is increased.
[en] To study the load time history variation in the frequency domain, both Fourier transformation and response spectra were considered. Normal approximation (Central Limit Theorem) is employed to derive statistics for various confidence levels. Correlation factors on responses from reduced case applications are presented for various confidence levels. It is concluded that normal approximation with response spectral approach is the better method for determining the correlation factor for a pre-established confidence level, and that sufficient reliability on the structural responses may be achieved when reduced case applications are considered. This paper discusses methods of establishing correlation factors required for the adjustment of structural responses to achieve in acceptable confidence level. (orig./HP)
[en] Testing of 6M specification packages, performed in response to concerns over the integrity of the clamp-ring closure, showed that the clamp-ring was unable to retain the top in thirty foot drop tests of packages having the maximum allowed weight (290 kg or 640 lb). To determine if the clamp-ring closure was adequate for packages with lower contents weight, a series of tests were performed on packages weighing 147 kg (325 lb) at a range of impact angles. The results showed that the standard clamp-ring closure was unable to retain the top in tests of standard 6M packages weighing 147 kg (325 lb). A test employing a plywood disk enhanced closure with impact at 6.5 degrees retained its top successfully
[en] Some considerations regarding ice load in risk-based dam safety analysis are presented for small concrete dams. The most significant physical mechanisms leading to ice thrust on dams (such as thermal expansion and water level fluctuations) are outlined. Published literature on dam ice loads to examine ice load magnitude-return period relationships, sliding and overstressing failure mechanisms and structural performance criteria to resist ice loads, are also reviewed. Related loading combinations for structural safety evaluations were determined regarding the issue of simultaneity of ice loads with other events such as earthquakes. Parametric analyses were conducted on a small gravity dam section, 3m high, and a taller dam, 17.9 m high, to demonstrate the ultimate ice load carrying capability as a function of dam geometry and shear and tensile strengths of construction joints. Since the failure mechanism of a dam subjected to excessive ice loads is not well known, a model test can be useful to assess the safety margin between crack initiation and failure of a component. 18 refs., 2 tabs., 7 figs
[en] The indentation technique by static and modulated loading modes on the indenter is described. For Cu and W the characteristics of hardness and plasticity at static and dynamic mode were determined. For these metals it is shown that the modulated loading mode leads to decrease of hardness and increase of the plasticity characteristic. The proposed technique can be used to study the mechanical behavior and evaluation of materials and parts operating under vibration conditions and alternate loading.
[en] Highlights: → A limit moment equation applicable to planar/non-planar flaw of 0 ≤ θ ≤ π found in wall thinned straight pipes was proposed. → An idea to rationally classify planar/non-planar flaw in wall thinned pipes was proposed. → The equation based on the experimental observation focused on the fracture mode. - Abstract: In this paper, a limit bending moment equation applicable to all types of planar and non-planar flaws in wall-thinned straight pipes under bending was proposed. A system to rationally classify the planar/non-planar flaws in wall-thinned pipes was suggested based on experimental observations focused on the fracture mode. The results demonstrate the importance of distinguishing between axial and circumferential long flaws in wall-thinned pipes.