The present paper describes a new analytical method for the prediction of temperature in longitudinal reinforcement bars of slim floor beams subjected to fire. This method is based on the isotherms of EN 1992-1-2 Annex A developed for concrete beams and slabs and is consequently applicable only to slim floor beams subjected to standard ISO fire curve. In addition to vertical heat fluxes, this method also considers 2D temperature field induced by the hot part of the beam web and by the lateral heating in case of long span composite flooring systems. An adaptation is proposed for reinforcement bars when situated close to the beam web. This new method leads to very good temperature predictions for R60, R90 and R120 fire resistance requirements. For less severe requirements, the reinforcement usually remains below 400°C and the resistance of hot-rolled reinforcement bars is not reduced for this range of temperatures. The better predictions of the sagging bending moment of the section under ISO fire by use of this new method have also been demonstrated within the present paper.
a b s t r a c tRecent full-scale experimental tests performed on steel and composite structures have demonstrated that the presence of tensile forces in axially-restrained beams during the cooling phase of a fire could lead to bolt failures. In order to understand this observation and design structures that are not prone to such a failure mode, it is essential to have a deep knowledge of the material behaviour of all the components, including bolts, during both the heating and cooling phase.In the present article, the test set-ups and the results of the tensile and shear tests performed at the Centro Sviluppo Materiali (Italy) on Grade 8.8 bolts under heating-cooling cycles are described.Then, material laws are defined for characterising the mechanical behaviour of Grade 8.8 bolts under heating and cooling phases. These laws account for the non-reversibility of the mechanical properties of Grade 8.8 bolts.
For composite cellular beams, additional deflections occur due to the loss of bending and shear stiffness at the opening positions and also due to slip in the shear connectors caused by partial shear connection. Design formulae are presented for the additional deflection of composite beams with cut circular openings or for cut and re-welded cellular beams as a function of the proportionate depth of the openings. The simplified formulae are calibrated against finite element results for both cellular and solid web beams and also against measured deflections of a 15.3m composite cellular beam test. This additional deflection is presented as a function of flexural and shear terms that are a function of the span: depth ratio. For modelling of cellular beams to determine deflections, the circular opening may be represented by an equivalent rectangular opening of length equal to 0.7 x opening diameter.
This paper presents the basis for the design of steel and composite beams with large web openings. The main design requirements are the transfer of shear by Vierendeel bending and the control of web buckling next to and between the openings. Cellular beams with regular circular openings are a common example of highly perforated beams and their flange areas are often highly asymmetric. For these beams, web-post moments may be generated to develop the full shear resistance of the cross-section. Tests on beams with circular, elongated circular and rectangular openings are presented which are used to verify the design methodology. In addition, the openings cause local displacements due
to shear and bending, which add to the overall deflection of perforated beams. Simplified formulae are presented to determine the additional deflection relative to the equivalent solid-web beams
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