Publicação
New developments on the bending resistance in composite slabs with steel deck under fire
| Resumo: | Composite steel/concrete slabs can be considered a union of a reinforced concrete layer located above a profiled steel sheet which may or may not be reinforced by steel bars. This configuration allows lightness in the structure, whereas the negative mesh located on the top side of the slab needs to resist only against the concrete shrinkage; the profiled steel deck with the reinforcement bars is responsible for resisting the sagging moments. The main objective of this work is to investigate the fire effect on the bending resistance of the composite slab with steel deck, comparing the behavior of Normal Weight Concrete (NWC) and Light Weight Concrete (LWC) when submitted to standard fire. The Eurocode 1994 1-2 is responsible for providing the guidelines for structural design of composite slabs under fire conditions. This standard presents a simplified calculation model to determine the slab sagging moment. However, it neglects some important effects occurring during a fire situation, such as the air-gap effect and the influence of the concrete layer h1. In order to optimize the calculation model presented by Eurocode 1994 1-2, a parametric study was performed using trapezoidal and re-entrant steel decks geometries. This study comprises two trapezoidal models (Confraplus 60 and Polydeck 59s) and two reentrant models (Multideck 50 and Bondek) with different thicknesses for h1. This analysis consists of a non-linear transient thermal analysis using the finite element method, performed on two different software: ANSYS and MATLAB. Based on the average temperature of each component, new coefficients and calculation proposal for annex D of Eurocode 1994-1.2 are presented, and the slabs reduction load-bearing capacity is determined. By analyzing the results provided by this study, it was possible to conclude that Eurocode 1994-1.2 simplified calculation method produces a lower temperature field than the parametric curves and the New Calculation Proposal, thus confirming the current analytical method produces unsafe results. A comparison of the estimated temperatures between the New Proposal and the temperatures of Eurocode 1994-1.2 showed an average variation of 6% for composite slabs with trapezoidal profiles and 10% for composite slabs with re-entrant profiles, and this effect is intensified for the initial fire resistance classes, which can reach up to 40%. The variation in temperatures also leads to variations in the reduction of the resistant capacity of the slabs; when comparing the two analytical models, the variation is around 3% to 20% for most fire resistance classes and can reach up to 50% for the initial rating times of 30 min and 45 min. |
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| Autores principais: | Silveira, Matheus Bez da |
| Assunto: | Composite slabs Normal weight concrete Lightweight concrete Numerical model |
| Ano: | 2022 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Instituto Politécnico de Bragança |
| Idioma: | inglês |
| Origem: | Biblioteca Digital do IPB |
| Resumo: | Composite steel/concrete slabs can be considered a union of a reinforced concrete layer located above a profiled steel sheet which may or may not be reinforced by steel bars. This configuration allows lightness in the structure, whereas the negative mesh located on the top side of the slab needs to resist only against the concrete shrinkage; the profiled steel deck with the reinforcement bars is responsible for resisting the sagging moments. The main objective of this work is to investigate the fire effect on the bending resistance of the composite slab with steel deck, comparing the behavior of Normal Weight Concrete (NWC) and Light Weight Concrete (LWC) when submitted to standard fire. The Eurocode 1994 1-2 is responsible for providing the guidelines for structural design of composite slabs under fire conditions. This standard presents a simplified calculation model to determine the slab sagging moment. However, it neglects some important effects occurring during a fire situation, such as the air-gap effect and the influence of the concrete layer h1. In order to optimize the calculation model presented by Eurocode 1994 1-2, a parametric study was performed using trapezoidal and re-entrant steel decks geometries. This study comprises two trapezoidal models (Confraplus 60 and Polydeck 59s) and two reentrant models (Multideck 50 and Bondek) with different thicknesses for h1. This analysis consists of a non-linear transient thermal analysis using the finite element method, performed on two different software: ANSYS and MATLAB. Based on the average temperature of each component, new coefficients and calculation proposal for annex D of Eurocode 1994-1.2 are presented, and the slabs reduction load-bearing capacity is determined. By analyzing the results provided by this study, it was possible to conclude that Eurocode 1994-1.2 simplified calculation method produces a lower temperature field than the parametric curves and the New Calculation Proposal, thus confirming the current analytical method produces unsafe results. A comparison of the estimated temperatures between the New Proposal and the temperatures of Eurocode 1994-1.2 showed an average variation of 6% for composite slabs with trapezoidal profiles and 10% for composite slabs with re-entrant profiles, and this effect is intensified for the initial fire resistance classes, which can reach up to 40%. The variation in temperatures also leads to variations in the reduction of the resistant capacity of the slabs; when comparing the two analytical models, the variation is around 3% to 20% for most fire resistance classes and can reach up to 50% for the initial rating times of 30 min and 45 min. |
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