Proposal for Codification of a DSM Design Approach for Cold-Formed Steel Short-to Intermediate Angle Columns

This paper presents a proposal for the codification of an efficient design approach for cold-formed steel short-to-intermediate equal-leg angle columns, consisting of a slight modification of a design approach developed by Dinis & Camotim (2015) and based on the Direct Strength Method (DSM). After (i) collecting the available experimental and numerical failure load data, comprising fixed-ended and pin-ended columns with several geometries (cross-section dimensions and length) and reported by various researchers, and (ii) briefly reviewing the mechanical reasoning behind the proposed procedures, the search for new/simpler expressions to provide the DSM design curves is addressed. Their merits are assessed through (i) the quality of the estimates of the available failure load data and (ii) the determination of the corresponding LRFD resistance factors. Concerning the latter, it is shown that the value recommended, for compression members, by the North American Specification (NAS) for the Design of Cold-Formed Steel Structural Members (AISI 2012), namely Φc =0.85, can also be adopted for angle columns

Proposal to Improve the DSM Design of Cold-Formed Steel Angle Columns: Need, Background, Quality Assessment and Illustration

This paper presents a proposal for the codification of an efficient design approach, based on the Direct Strength Method (DSM), for cold-formed steel equal-leg angle columns with short-to-intermediate lengths, i.e., those buckling in flexural-torsional modes. Initially, the available experimental failure load data, comprising fixed-ended and pin-ended (“cylindrical hinges”) columns with several geometries (cross-section dimensions and lengths) and tested by various researchers, are collected and used to show that the currently codified DSM design provisions are not able to handle adequately short-to- intermediate angle columns and that a specific DSM-based design approach is needed to estimate the failure loads of such columns. Then, the paper presents a brief overview of the structural reasoning behind the DSM-based design approach proposed by Dinis & Camotim (2015, 2016). Next, the quality (accuracy and reliability) of the failure load estimates obtained with this design approach is assessed through the comparison with the above experimental failure load data and also a fairly large number of numerical failure loads. This merit assessment includes the determination of the LRFD resistance factors concerning the failure-to-predicted load ratios -- it is shown that the value recommended, for compression members, by the North American Specification (AISI 2016), Φc=0.85, can also be adopted for short-to-intermediate angle columns designed with this DSM-based approach. Finally, the paper presents and discusses a few numerical examples, which illustrate the application of the proposed design approach and provide evidence of its advantages and benefits, when compared with the currently codified one

Patterns of alpha and beta diversity of epigean arthropods at contrasting land-uses of an oceanic island (Terceira, Azores)

"[…]. To study the effect of land-use change in biological communities it is necessary to understand how are the different components of diversity distributed in space. Diversity has long been separated into different components according to the phenomena that interest ecologists (Whittaker, 1960, 1972): i) local species richness, i.e., alpha (community) diversity that measures the species richness of a local assemblage; ii) beta diversity, the degree of difference between communities (Whittaker et al., 2001), that measures turnover of species between communities and; iii) gamma (regional) diversity, which can be considered an equivalent to alpha diversity on a larger scale, but reflects the allopatric distribution of related taxa. Alpha diversity, of which species richness is just the most visible measure, is perhaps the most studied aspect of diversity. However, probably more important than knowing how many species live in a site at a given time, it is to know what species are these. In islands, where the introduction of non-indigenous species is one of the major threats to indigenous species (Borges et al., 2006; Martín et al., 2008), especially endemics, this question is even more significant. Even if man-made habitats are species rich, they may be empty of species considered as conservation priority and abundant in exotic species (Cardoso et al. 2009a). […]" (da Introdução)Fundação para a Ciência e a Tecnologia, Portugal

On the Influence of Local-Distortional Interaction in the Behavior and Design of Cold-Formed Steel Web-Stiffened Lipped Channel Columns

This paper reports the results of a numerical (ABAQUS shell finite element analysis) investigation on the influence of local-distortional (L-D) interaction in the ultimate strength and design of cold-formed steel fixed-ended web-stiffened lipped channel columns -- hereafter termed “WSLC columns”. These results concern columns with various geometries and yield stresses, ensuring a wide variety of combined ratios between (i) the distortional and local critical buckling stresses, and (ii) the yield and the higher of the above buckling stresses. The objectives of this work are two-fold: (i) to acquire in-depth understanding on the mechanics underlying the L-D interaction in the WSLC columns analyzed, all selected to ensure that local buckling is triggered by the flanges, and also (ii) to provide a first contribution towards the efficient Direct Strength Method (DSM) design of these structural elements. The results presented and discussed concern the (i) post-buckling behavior (elastic and elastic-plastic), (ii) ultimate strength and (iii) failure mechanisms of the WSLC columns previously selected to undergo L-D interaction. Special attention is paid to comparing the ultimate strength erosions, due to L-D interaction, exhibited by the WSLC columns investigated here and the “plain cross-section” (i.e., without intermediate stiffeners) columns studied earlier by the authors (Martins et al. 2014a). Finally, the paper closes with some considerations about the impact of the findings reported in this work on the design of cold-formed steel columns undergoing different levels of L-D interaction

A spatial scale assessment of habitat effects on arthropod communities of an oceanic island

Copyright © 2009 Elsevier Masson SAS. All rights reserved.Most habitats in the Azores have undergone substantial land-use changes and anthropogenic disturbance during the last six centuries. In this study we assessed how the richness, abundance and composition of arthropod communities change with: (1) habitat type and (2) the surrounding land-use at different spatial scales. The research was conducted in Terceira Island, Azores. In eighty-one sites of four different habitat types (natural and exotic forests, semi-natural and intensively managed pastures), epigaeic arthropods were captured with pitfall traps and classified as endemic, native or introduced. The land-use surrounding each site was characterized within a radius ranging from 100 to 5000 m. Non-parametric tests were used to identify differences in species richness, abundance and composition between habitat types at different spatial scales. Endemic and native species were more abundant in natural forests, while introduced species were more abundant in intensively managed pastures. Natural forests and intensively managed pastures influenced arthropod species richness and composition at all spatial scales. Exotic forests and semi-natural pastures, however, influenced the composition of arthropod communities at larger scales, promoting the connectivity of endemic and native species populations. Local species richness, abundance and composition of arthropod communities are mostly determined by the presence of nearby natural forests and/or intensively managed pastures. However, semi-natural pastures and exotic forests seem to play an important role as corridors between natural forests for both endemic and native species. Furthermore, exotic forests may serve as a refuge for some native species

Helicobacter pylori in both the sinuses and the stomach

Background: The role played by Helicobacter pylori in the sinuses, and its association with the same organism’s gastric infection, are still unclear. Methods: In order to compare H.pylori colonization patterns in the nose and stomach we conducted a cohort analysis of 14 patients, eligible for sinus surgery due to chronic medically refractory rhinosinusitis, who were tested for simultaneous presence of H. pylori, by histology, culture and polymerase chain reaction, in pathologic sinus tissue collected during surgery and in gastric mucosa obtained through gastroduodenal endoscopy. Results: H. pylori DNA was found in the sinus mucosa of 15.4% of patients with chronic rhinosinusitis, and all of them showed concurrent H. pylori stomach infection. Sinus colonization was not found without simultaneous gastric colonization, although most patients with gastric infection did not have the bacterial DNA in their sinuses. H. pylori’s presence in the nose was not associated with local inflammatory status, and no cultures could be obtained from any of the sinus tissue samples, including those positive for H. pylori DNA. Conclusions: Only H. pylori DNA, and not the culturable active form of the microorganism, could be found in the sinus mucosa of some patients with H. pylori gastric infection. We could not find evidence, however, that the bacterium’s presence in the nose contributes to local mucosal inflammation.info:eu-repo/semantics/publishedVersio

Vibration behavior of thin-walled steel members subjected to uniform bending.

This article reports the results of an investigation on the effects of internal moments on the vibration behavior of thin-walled steel members. The analyses are based on the Generalized Beam Theory (GBT), a thin-walled bar theory accounting for crosssection in-plane deformations ? its main distinctive feature is the representation of the member deformed configuration by means of a linear combination of cross-section deformation modes, multiplied by their longitudinal amplitude functions. The study concerns a simply supported T-section (with unequal flanges) members exhibiting a wide range of lengths and subjected to uniform internal moment diagrams ? their magnitudes are specified as percentages of the corresponding critical buckling values. After providing a brief overview of the main concepts and procedures involved in performing a GBT-based structural analysis, the vibration behavior of load-free and loaded T-section members is addressed ? the influence of the applied loadings is assessed in terms of (i) the fundamental frequency difference and (ii) the change in the corresponding vibration mode shape. For validation purposes, some GBT results are compared with values yielded by shell finite element analysis performed in the code ABAQUS (Simulia, 2008)

On the Direct Strength Design of Cold-Formed Steel Columns Falling in Local-Distortional Interactive Modes

This paper present and discusses proposals for the codification of efficient design approaches for cold-formed steel columns affected by local-distortional (L-D) interaction. These proposals, based on the Direct Strength Method (DSM), were developed, calibrated and validated on the basis of experimental and numerical (shell finite element) failure load data concerning columns with several cross-section shapes and obtained from investigations carried out by various researchers. Three types of L-D interaction are taken into account, namely “true L-D interaction”, “secondary local bifurcation L-D interaction” and “secondary distortional bifurcation L-D interaction”. Moreover, previously available DSM-based design approaches to handle column L-D interactive failures are reviewed and their merits are assessed and compared with those exhibited by the present proposals. The paper also presents reliability assessments of the failure load predictions provided by the available and proposed DSM-based design approaches, following the procedure prescribed by the current version of the North American Specification (NAS) for the Design of Cold-Formed Steel Structures (AISI 2012)