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Formulae for determining the elastic buckling loads of structural steel rectangular hollow sections (RHS) subjected to concentrated transverse forces are presented herein. The predicted elastic buckling load is bounded by a theoretical lower bound, where only the material within the bearing length is mobilised, and a practical upper bound, where the adjacent material is mobilised to its maximum extent. The lower bound is the elastic buckling load of a wide plate with a width equal to the bearing length and a length equal to the web depth, while the upper bound is determined from finite element (FE) analyses of various representative loading scenarios. The level of mobilisation of adjacent material is quantified by introducing a coefficient ζ that is calibrated through FE analyses in the commercial package ABAQUS, with the rotational stiffness afforded to the webs by the flanges also being captured. The four loading scenarios defined in the North American Specification (NAS) and Australian/New Zealand Standard (AS/NZS) for the design of cold-formed steel structures, namely the Interior-Two-Flange (ITF), End-Two-Flange (ETF), Interior-One-Flange (IOF) and End-One-Flange (EOF) loading conditions, alongside their transitional cases, are considered. Rectangular hollow sections with a broad spectrum of cross-sectional geometric proportions and bearing lengths encompassing the aforementioned loading conditions are considered. It is found that the developed formulae for predicting the elastic buckling loads under concentrated transverse forces provide accurate results that are typically within 5% of the numerical values. Hence, the developed formulae can be employed as a convenient alternative to numerical methods in advanced structural design methodologies, such as the Direct Strength Method (DSM) and the Continuous Strength Method (CSM).
The introduction of the coronary stent in 1986 was one of the most far-reaching changes in the practice of interventional cardiology since its inception in 1977. Despite all the benefits of the using a metallic drug eluting stent (DES), their limitations have generated interest towards biodegradable technology. These biodegradable stents, which are made of polymers or metal alloys with or without a drug coating, have the potential to scaffold the artery to allow natural healing to take place, and then biodegrade. The development of this technology has been slow, however several biodegradable stents have entered into clinical trials, with many more at the preclinical stage of development. Concurrently conventional metallic DES have tried to address their limitations; in particular they have sought to repair their damaged reputation following concerns over stent thrombosis. Accordingly, stents with a more biocompatible polymer and DES which are polymer-free have been developed, and are currently being evaluated in clinical trials. This article will review the status of biodegradable stents, and these newer DES, during this exciting period in interventional cardiology as technology strives to develop the ideal coronary stent.
The critical buckling characteristics of hydrostatically pressurized complete spherical shells filled with an elastic medium are demonstrated. A model based on small deflection thin shell theory, the equations of which are solved in conjunction with variational principles, is presented. In the exact formulation, axisymmetric and inextensional assumptions are not used initially and the elastic medium is modelled as a Winkler foundation, i.e., using uncoupled radial springs with a constant foundation modulus that is independent of wave numbers of shell buckling modes. Simplified approximations based on a Rayleigh-Ritz approach are also introduced for critical buckling pressure and mode number with a considerable degree of accuracy. Characteristic modal shapes are demonstrated for a wide range of material and geometric parameters. A phase diagram is established to obtain the requisite thickness to radius, and stiffness ratios for a desired mode profile. The present exact formulation can be readily extended to apply to more general cases of non-axisymmetric buckling problems.
A 54-year-old female presented with inferoposterior ST-segment elevation myocardial infarction. Coronary angiogram revealed total occlusion of the proximal left circumflex artery. Following a thrombus aspiration, without administration of glycoprotein IIb/IIIa inhibitor, direct stenting with a drug-eluting metallic stent was performed. After stent implantation, angiogram showed thrombolysis in myocardial infarction (TIMI) grade III flow, without any evidence of intraluminal defect …
Abstract The odd-even behaviour observed for liquid crystal dimers has been predicted to be a sensitive function of the geometry of the link joining the mesogenic groups to the flexible spacer. Here we report the synthesis of two cyanobiphenyl dimers with methylene links, together with a determination of their transitional properties. In particular we have probed their orientational order via the major and biaxial orientational order parameters of a solute molecule, anthracene-d 10, using NMR spectroscopy. For comparison we have also determined the corresponding quantities for the cyanobiphenyl dimers with ether links. The enhanced odd-even effect observed for the methylene linked dimers relative to those with ether links is in good accord with theory.
