Finite element idealization of a cold-formed steel portal frame

A simple linear beam idealization of a cold-formed steel portal frame is presented in which beam elements are used to idealize the column and rafter members, and rotational spring elements are used to represent the rotational flexibility of the joints. In addition, the beam idealization takes into account the finite connection length of the joints. Deflections predicted using the beam idealization are shown to be comparable to deflections obtained from both a linear finite element shell idealization and full-scale laboratory tests. Using the beam idealization, deflections under rafter load are divided into three components: Deflection due to flexure of the column and rafter members, deflection due to bolt-hole elongation, and deflection due to in-plane bracket deformation. Of these deflection components, the deflection due to bolt-hole elongation is the most significant and cannot, therefore, be ignored. Using the beam idealization, engineers can analyze and design cold-formed steel portal frames, including making appropriate allowances for connection effects, without the need to resort to expensive finite element shell analysis.

Serviceability design of a cold-formed steel portal frame having semi-rigid joints

Details are given of a cold-formed steel portal framing system that uses simple bolted moment-connections for both the eaves and apex joints. However, such joints function as semi-rigid and, as a result, the design of the proposed system will be dominated by serviceability requirements. While serviceability is a mandatory design requirement, actual deflection limits for portal frames are not prescribed in many of the national standards. In this paper, a review of the design constraints that have an effect on deflection limits is discussed, and rational values appropriate for use with cold-formed steel portal frames are recommended. Adopting these deflection limits, it is shown through a design example how a cold-formed steel portal frame having semi-rigid eaves and apex joints can be a feasible alternative to rigid-jointed frames in appropriate circumstances.

Effects of elevated temperatures on bolted moment-connections between cold-formed steel members

Experimental investigations at ambient temperature into the behaviour of bolted moment-connections between cold-formed steel members have previously been described. Full-scale joint tests have demonstrated that the channel-sections being connected are susceptible to premature failure, the result of web buckling caused by the concentration of load transfer from the bolts. The results of tests on bolted lap joints have been used to propose design recommendations for the shear strength in bearing of the bolt-hole. For both types of test, the results of non-linear elasto-plastic finite element analyses have been shown to have good agreement. No consideration, however, has been given to the behaviour of such connections at elevated temperatures. This paper describes non-linear elasto-plastic finite element parametric studies into the effects of elevated temperatures on bolted moment-connections between cold-formed steel members. Two issues at elevated temperatures are investigated:

Design optimization of cold-formed steel portal frames taking into account the effect of building topology

Cold-formed steel portal frames are a popular form of construction for low-rise commercial, light industrial and agricultural buildings with spans of up to 20 m. In this article, a real-coded genetic algorithm is described that is used to minimize the cost of the main frame of such buildings. The key decision variables considered in this proposed algorithm consist of both the spacing and pitch of the frame as continuous variables, as well as the discrete section sizes.A routine taking the structural analysis and frame design for cold-formed steel sections is embedded into a genetic algorithm. The results show that the real-coded genetic algorithm handles effectively the mixture of design variables, with high robustness and consistency in achieving the optimum solution. All wind load combinations according to Australian code are considered in this research. Results for frames with knee braces are also included, for which the optimization achieved even larger savings in cost.

Cold-formed steel sections with web openings subjected to web crippling under two-flange loading conditions - part I: Tests and finite element analysis

The results of 82 web crippling tests are presented, with 20 tests conducted on channel sections without web openings and 62 tests conducted on channel sections with web openings. The tests consider both end-two-flange and interior-two-flange loading conditions. In the case of the tests with web openings, the hole was located directly under the concentrated load. The concentrated load was applied through bearing plates; the effect of different bearing lengths is investigated. In addition, the cases of both flanges fastened and unfastened to the support is considered. A non-linear elasto-plastic finite element model is described, and the results compared against the laboratory test results; a good agreement was obtained in terms of both strength and failure modes.

Cold-formed steel sections with web openings subjected to web crippling under two-flange loading conditions - Part II: Parametric study and proposed design equations

A parametric study of cold-formed steel sections with web openings subjected to web crippling was undertaken using finite element analysis, to investigate the effects of web holes and cross-section sizes on the web crippling strengths of channel sections subjected to web crippling under both interior-two-flange (ITF) and end-two-flange (ETF) loading conditions. In both loading conditions, the hole was centred beneath the bearing plate. It was demonstrated that the main factors influencing the web crippling strength are the ratio of the hole depth to the flat depth of the web, and the ratio of the length of bearing plates to the flat depth of the web. In this paper, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and finite element results.

The Cold War and British Debates over the Boycott of the 1980 Moscow Olympics

This article examines the debate precipitated by the Thatcher government's (unsuccessful) attempt to secure a British boycott of the 1980 Moscow Olympics in response to the Soviet invasion of Afghanistan. Aware that it faced a struggle to win over the autonomous British Olympic Association, but with Thatcher in particular keen to support the United States, the government's case that the invasion required a specific response in the form of a boycott was steadily overshadowed as the public debate increasingly focused on arguments over human rights and détente and the use of state power.

Cold, Hungry and Scared:Prison Films About the Troubles

The cinematic representations of the prison experience during the Northern Irish Troubles.

Anthelmintic drug residues in beef: UPLC-MS/MS method validation, European retail beef survey, and associated exposure and risk assessments

Anthelmintic drugs are widely used to control parasitic infections in cattle. The ProSafeBeef project addressed the need for data on the exposure of European consumers of beef to potentially harmful drug residues. A novel analytical method based on matrix solid-phase dispersive extraction and ultra-performance liquid chromatography-tandem mass spectrometry was validated for 37 anthelmintic drugs and metabolites in muscle (assay decision limits, CCa, = 0.15-10.2 µg kg -1). Seven European countries (France, Spain, Slovenia, Ireland, Italy, Belgium and Portugal) participated in a survey of retail beef purchased in local shops. Of 1061 beef samples analysed, 26 (2.45%) contained detectable residues of anthelmintic drugs (0.2-171 µg kg -1), none above its European Union maximum residue limit (MRL) or action level. Residues detected included closantel, levamisole, doramectin, eprinomectin, moxidectin, ivermectin, albendazole and rafoxanide. In a risk assessment applied to mean residue concentrations across all samples, observed residues accounted for less than 0.1% of the MRL for each compound. An exposure assessment based on the consumption of meat at the 99th percentile of consumption of adults in 14 European countries demonstrated that beef accounted for less than 0.02% of the acceptable daily intake for each compound in each country. This study is the first of its kind to apply such a risk-based approach to an extensive multi-residue survey of veterinary drug residues in food. It has demonstrated that the risk of exposure of the European consumer to anthelmintic drug residues in beef is negligible, indicating that regulation and monitoring is having the desired effect of limiting residues to non-hazardous concentrations. © 2012 Copyright Taylor and Francis Group, LLC.