Design of composite asymmetric cellular beams and beams with large web openings

The design of composite asymmetric cellular beams is not fully covered by existing guidance but is an area of important practical application. Asymmetry in the shape of the cross-section of cellular beams causes development of additional bending moments in the web-posts between closely placed openings. Furthermore, the development of local composite action influences the distribution of forces in the web-flange Tees. The design method presented in this paper takes account of high degrees of asymmetry in the cross-section and also the influence of elongated or rectangular openings.

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.

Pull-out forces in shear connectors in composite beams with large web openings

Composite beams with large web openings are often used, and their design is controlled by Vierendeel bending at the four corners of each opening, which is assisted by local composite action with the floor slab. Development of this Vierendeel bending resistance may be limited by pull-out failure of the shear connectors. In this paper, a non-linear elasto-plastic finite element model of a composite beam with web openings was used to investigate this mode of pull-out failure. A test was performed on a typical composite slab in which the shear connectors were subject to pure tension and the failure load was 67 kN, which is approximately 70% of the longitudinal shear resistance. The results of the finite element model are compared against those obtained using the established design theory, that does not limit the vertical pull-out resistance of the shear connectors. It is shown that the local bending resistance due to composite action should be reduced when limited by pull-out of the shear connectors. A parametric study investigated the effect of openings of 600 to 1200 mm length. A simple model is developed to establish the Vierendeel bending resistance, when limited by pull-out of the shear connectors.

Effect of web holes on web crippling strength of cold-formed steel channel sections under end-one-flange loading condition – Part I: Tests and finite element analysis

Web openings could be used in cold-formed steel beam members, such as wall studs or floor joints, to facilitate ease of services in buildings. In this paper, a combination of tests and non-linear finite element analyses is used to investigate the effect of such holes on web crippling under end-one-flange (EOF) loading condition; the cases of both flanges fastened and unfastened to the bearing plates are considered. The results of 74 web crippling tests are presented, with 22 tests conducted on channel sections without web openings and 52 tests conducted on channel sections with web openings. In the case of the tests with web openings, the hole was either located centred above the bearing plates or having a horizontal clear distance to the near edge of the bearing plates. A good agreement between the tests and finite element analyses was obtained in term of both strength and failure modes.

Effect of web holes on web crippling strength of cold-formed steel channel sections under end-one-flange loading condition - Part II: Parametric study and proposed design equations

A parametric study of cold-formed steel sections with web openings subjected to web crippling under end-one-flange (EOF) loading condition is undertaken, using finite element analysis, to investigate the effects of web holes and cross-section sizes. The holes are located either centred above the bearing plates or with a horizontal clear distance to the near edge of the bearing plates. It was demonstrated that the main factors influencing the web crippling strength are the ratio of the hole depth to the depth of the web, the ratio of the length of bearing plates to the flat depth of the web and the location of the holes as defined by the distance of the hole from the edge of the bearing plate divided by the flat depth of web. In this study, design recommendations in the form of web crippling strength reduction factor equations are proposed, which are conservative when compared with the experimental and finite element results.

Postbuckling behaviour of a blade-stiffened composite panel loaded in uniaxial compression

The postbuckling behaviour of a panel with blade-stiffeners incorporating tapered flanges was experimentally investigated. A new failure mechanism was identified for this particular type of stiffener. Failure was initiated by mid-plane delamination at the free edge of the postbuckled stiffener web at a node-line. This was consistent with an interlaminar shear stress failure and was calculated from strain gauge measurements using an approximate analysis based on lamination theory and incorporating edge effects. The critical shear stress was found to agree well with the shear strength obtained from a three-point bending test of the web laminate. 

Modified stiffened panel analysis methods for laser beam and friction stir welded aircraft panels

The introduction of advanced welding methods as an alternative joining process to riveting in the manufacture of primary aircraft structure has the potential to realize reductions in both manufacturing costs and structural weight. Current design and analysis methods for aircraft panels have been developed and validated for riveted fabrication. For welded panels, considering the buckling collapse design philosophy of aircraft stiffened panels, strength prediction methods considering welding process effects for both local-buckling and post-buckling behaviours must be developed and validated. This article reports on the work undertaken to develop analysis methods for the crippling failure of stiffened panels fabricated using laser beam and friction stir welding. The work assesses modifications to conventional analysis methods and finite-element analysis methods for strength prediction. The analysis work is validated experimentally with welded single stiffener crippling specimens. The experimental programme has demonstrated the potential static strength of laser beam and friction stir welded sheet-stiffener joints for post-buckling panel applications. The work undertaken has demonstrated that the crippling behaviour of welded stiffened panels may be analysed considering standard-buckling behaviour. However, stiffened panel buckling analysis procedures must be altered to account for the weld joint geometry and process altered material properties. © IMechE 2006.

A Novel Multimodal Interface for Improving Visually Impaired People's Web Accessibility

This paper introduces a novel interface designed to help blind and visually impaired people to explore and navigate on the Web. In contrast to traditionally used assistive tools, such as screen readers and magnifiers, the new interface employs a combination of both audio and haptic features to provide spatial and navigational information to users. The haptic features are presented via a low-cost force feedback mouse allowing blind people to interact with the Web, in a similar fashion to their sighted counterparts. The audio provides navigational and textual information through the use of non-speech sounds and synthesised speech. Interacting with the multimodal interface offers a novel experience to target users, especially to those with total blindness. A series of experiments have been conducted to ascertain the usability of the interface and compare its performance to that of a traditional screen reader. Results have shown the advantages that the new multimodal interface offers blind and visually impaired people. This includes the enhanced perception of the spatial layout of Web pages, and navigation towards elements on a page. Certain issues regarding the design of the haptic and audio features raised in the evaluation are discussed and presented in terms of recommendations for future work.