Local-plate and Distortional Post-buckling Behavior of Cold-formed Steel Lipped Channel Columns with Intermediate Stiffeners

This paper reports the results of an investigation concerning the local-plate and distortional post-buckling behavior of cold-formed steel lipped channel columns with web and flange intermediate stiffeners. They have all been obtained through geometrically non-linear analyses based on a recently developed and implemented Generalized Beam Theory (GBT) formulation that incorporates (i) conventional (shear undeformable), (ii) shear (non-linear warping) and (iii) transverse extension deformation modes. These results, some of which are compared with values yielded by shell finite element analyses performed in the code ABAQUS (mostly for validation purposes), provide the evolution, along a given local-plate or distortional post-buckling equilibrium path, of the column deformed configuration and relevant displacement profiles and/or stress diagrams. In order to assess the influence of the member end support conditions, one also compares the distortional post-buckling behaviors of columns having pinned/free-to-warp and fixed/warping-prevented end sections. Taking full advantage of the GBT unique modal features, all the above results are discussed in great detail and it becomes possible to unveil, explain and/or shed some new light on several interesting and scarcely known behavioral aspects. In particular, one is able to provide very clear and structurally meaningful explanations for the qualitative differences existing between the local-plate and distortional post-buckling behavior of lipped channel columns with and without intermediate stiffeners

GBT-based Distortional Buckling Formulae for Thin-walled Channel Columns and Beams

After a brief outline of the Generalized Beam Theory (GBT) fundamentals and linear stability analysis procedure, the main concepts and steps involved in the derivation of GBT -based fully analytical formulae are described and discussed. Such formulae provide distortional bifurcation stress estimates in cold-formed steel channel columns and beams with arbitrary sloping single-lip edge stiffeners and pinned/free-to-warp or fixed/warping-free end sections. The application of the proposed formulae is illustrated in detail and, in order to assess their accuracy and validity, results concerning several specific channel columns and beams are presented. In particular, the GBT-based analytical estimates are compared with exact numerical results and, whenever possible, also with values yielded by the formulae developed by Lau & Hancock, Hancock and Schafer

DSM for Web Crippling under Two-Flange Conditions

This paper summarizes recent investigations on the development of Direct Strength Method (DSM) for the design of cold-formed steel beams under two-flange (TF) loading against web crippling failure. Recently, the authors proposed a new approach to predict the web crippling failure load of cold-formed steel beams under External Two Flange (ETF) and Internal Two Flange (ITF) loadings using DSM. Firstly, existing experimental test data are summarized and then the accuracy of North-American Specification (AISI 2012) and Eurocode 3 (CEN 2006) provisions is briefly assessed. In order to obtain additional information on the web crippling behavior of each test specimen, non-linear numerical results are obtained. Since the calibration of the DSM-based formula involves the previous calculation of (i) elastic buckling load and (ii) plastic load, two procedures are presented. Buckling loads are determined using the GBTWEB software, intentionally developed for this purpose, while plastic loads are calculated using analytical expressions based on yield-line models. By adopting a non-linear regression, the coefficients of DSM-based formulae are determined using a set of 128 (ETF) and 130 (ITF) test results and the corresponding estimates of buckling and plastic loads. The DSM-based formulas for ETF and ITF web crippling design are successfully proposed and the resistance factors (LRFD) obtained are φ=0.81 (ETF) and φ=0.75 (ITF)

Mechanical properties of phenine nanotubes

Phenine Nanotubes (PhNT) are cylinder-shaped molecules synthetized from 1,3,5-trisubstituted benzene ring building blocks that can form tubular segments of different sizes. Small nanotube segments have been recently synthetized, and efforts are being made to increase the nanotubes’ length by adding more “phenine” units. To the authors’ best knowledge, a complete characterization of the mechanical properties of these nanotubes has not yet been accomplished. In this work, Reax and AIREBO forcefields were used to model armchair and zigzag PhNTs and Molecular Dynamics simulations were employed to determine their mechanical properties for tensile, compressive, bending and twisting loadings. It was found that PhNTs have a much lower Young’s modulus (about 30%) and tensile strengths (about 45%) than carbon nanotubes (CNTs), but can endure longer tensile strains without breaking apart. Although possessing a lower bending and twisting stiffness than CNTs, PhNT have highly flexible sidewalls due to their superior porosity, and therefore can withstand higher angles of twist and angles of bend without breaking bonds. This extra flexibility; extended porosity; possibility for heteroatom doping and reasonable strength, make PhNTs very promising candidates for a wide range of applications, such as sensing, ionic transistors or molecular sieving. Finally, a brief study on the application of elastic continuum shell formulas to predict the critical stress (compression), critical moment (bending) and critical torque (twisting) is also presented

Gossip-based service monitoring platform for wireless edge cloud computing

Edge cloud computing proposes to support shared services, by using the infrastructure at the network's edge. An important problem is the monitoring and management of services across the edge environment. Therefore, dissemination and gathering of data is not straightforward, differing from the classic cloud infrastructure. In this paper, we consider the environment of community networks for edge cloud computing, in which the monitoring of cloud services is required. We propose a monitoring platform to collect near real-time data about the services offered in the community network using a gossip-enabled network. We analyze and apply this gossip-enabled network to perform service discovery and information sharing, enabling data dissemination among the community. We implemented our solution as a prototype and used it for collecting service monitoring data from the real operational community network cloud, as a feasible deployment of our solution. By means of emulation and simulation we analyze in different scenarios, the behavior of the gossip overlay solution, and obtain average results regarding information propagation and consistency needs, i.e. in high latency situations, data convergence occurs within minutes.Peer ReviewedPostprint (author's final draft

Wetting of cholesteric liquid crystals

We investigate theoretically the wetting properties of cholesteric liquid crystals at a planar substrate. If the properties of substrate and of the interface are such that the cholesteric layers are not distorted the wetting properties are similar to those of a nematic liquid crystal. If, on the other hand, the anchoring conditions force the distortion of the liquid crystal layers the wetting properties are altered, the free cholesteric-isotropic interface is non-planar and there is a layer of topological defects close to the substrate. These deformations can either promote or hinder the wetting of the substrate by a cholesteric, depending on the properties of the cholesteric liquid crystal

Pattern-induced anchoring transitions in nematic liquid crystals

In this paper we revisit the problem of a nematic liquid crystal in contact with patterned substrates. The substrate is modelled as a periodic array of parallel infinite grooves of well-defined cross section sculpted on a chemically homogeneous substrate which favors local homeotropic anchoring of the nematic. We consider three cases: a sawtooth, a crenellated and a sinusoidal substrate. We analyse this problem within the modified Frank-Oseen formalism. We argue that, for substrate periodicities much larger than the extrapolation length, the existence of different nematic textures with distinct far-field orientations, as well as the anchoring transitions between them, are associated with the presence of topological defects either on or close to the substrate. For the sawtooth and sinusoidal case, we observe a homeotropic to planar anchoring transition as the substrate roughness is increased. On the other hand, a homeotropic to oblique anchoring transition is observed for crenellated substrates. In this case, the anchoring phase diagram shows a complex dependence on the substrate roughness and substrate anchoring strength.Comment: 36 pages, 15 figures, revised version submitted to Journal of Physics: Condensed Matte