A three-step model for the performance-based numerical simulations of the fire response of steel-RC two-layered beam-like composite structures is presented and validated. The first step consists of the determination of the evolution of temperatures in the structure's surroundings. Moisture and the heat transfer through the RC layer and the conduction of heat over the steel layer are obtained in the second step. In concrete, the transfer of water vapour, dry air, and free water is discussed as well as the evaporation and liquefaction phenomena and the dehydration of concrete and its thermal and mechanical degradation. Within the framework of the third step, a geometrically and materially non-linear mechanical response of the structure is proposed accounting for interlayer slips and uplifts as well as for various material-related phenomena such as the material hardening/softening and creep. The governing equations are solved numerically. An efficient, novel strain-based finite element formulation is introduced for the mechanical analysis. Due to its generality and consideration of several different possible non-linear material, geometrical, and interlayer contact phenomena and their couplings the model can be of a use to a broader fire science community for exploring the impact of different physical parameters on the results of the addressed numerical simulations, thereby providing directions for further research. In the paper a case of such a study is also demonstrated exploring the contribution of the steel sheet and the flexibility of the interlayer connection of a standard trapezoidal steel-RC slab to its ultimate fire resistance. A reasonable contribution of the sheet is proved if the stiffness ratio between the integrated and the external tensile reinforcement of the RC plate is low provided that the contact connection is sufficiently stiff.
COBISS.SI-ID: 2076775
A new finite element model for steel–concrete side–plated beams exposed to mechanical and firelike thermal loading is presented. The moisture and heat transfer through concrete is considered to be independent on mechanical deformations. The hygro-thermo-mechanical analysis is performed in two separate steps starting with the moisture and heat transfer analysis and continuing with the mechanical stress– strain analysis. The finite element model of Davie, Pearce, and Bićanić was implemented for the moisture and heat transfer analysis in the concrete part of the beam. The Fourier equation of heat transfer for non-porous solids was applied in the steel part of the section. A novel, strain-based finite element formulation of the planar beam is proposed for the mechanical part of the fire analysis. Each of the two steps of the model is first verified by comparing the present numerical results with the experimental and numerical data available in the literature. The finite element formulations of both the hygrothermal and the mechanical steps of the analysis are found to be reliable and accurate. Finally, effects of the side reinforcing of a RC beam as one of the methods of structural retrofitting are explored in the case of a typical fire scenario and an important contribution of the side plates to the ultimate fire resistance of the beam is confirmed, particularly when higher levels of the service load are applied to the beam.
COBISS.SI-ID: 6309217
A new mathematical model and its analytical solution for the analysis of the stress-strain state of a linear elastic beam cracked in flexure and strengthened with plates on its lateral sides is presented. Both the longitudinal and the transversal interactions at the side plate/beam interfaceare considered. Linear behaviour of the contact connection is assumed. The method is based upon the linearised planar beam theory of Reissner. The weakening of the beam induced by the flexural crack is modelled conventionally as a rotational spring. The suitability of the theory is demonstrated in a case presentation involving the comparison between analytical results of the present beam (one-dimensional) model, the experiments and the numerical results of a full three-dimensional solid model created in the LUSAS finite element analysis software. An excellent agreement between the results is observed and the proposed formulation is found to be accurate and reliable. Finally, the solution is employed in an engineering analysis, discussing the effects of the material and the geometric properties of selected characteristic cases of the observed beams on the static and kinematic quantities, including the boundary conditions of the side plates, the longitudinal and the transversal stiffness of the connection, the size of the cracks, the span of the beam, and the length and the stiffness of the sideplates. For the cracked cantilever beam, a substantial effect of any of these parameters is found. In contrast, for the cracked two-span continuous beam, only the effect of the stiffness of the side plates and the effect of the length of the beam spans are noticeable. The present formulation was later on modified for use in our analyses of fire effect on structures.
COBISS.SI-ID: 6031457
A new finite element model for the analysis of the restrained curved reinforced-concrete (RC) beams simultaneously exposed to mechanical and extreme fire-like thermal loading is presented. The moisture and heat transfer through concrete is considered to be uncoupled with the deformation and the shape change of the beam. The hygro–thermo-mechanical analysis is performed in two separate steps, the first one starting with the coupled moisture and heat transfer analysis, and the next one continuing with the mechanical stress–strain analysis. A novel, strain-based finite element formulation of the curved planar beam has been developed for the mechanical part of the fire analysis. The unilateral soil–concrete beam contact is modelled with the set of discrete non-linear springs situated at nodes of the finite element mesh at the soil–beam contact. The model is verified by the numerical results of a full three-dimensional solid finite element model created in the LUSAS finite element analysis software and they are in good agreement with the present solution. In the subsequent parametric studies, the effects of material parameters of soil dictating the unilateral restraining forces to the beam, the load magnitude and the boundary conditions on the behaviour of the curved reinforced-concrete RC beam exposed to fire are investigated.
COBISS.SI-ID: 6877281
A new semi-analytical procedure is derived for the determination of buckling of the reinforced concrete column exposed to fire. The fire analysis is performed in three separate steps, of which the time development of temperatures in the fire compartment is performed first, followed by the coupled heat and moisture transfer analysis and, finally, by the mechanical analysis. A particular emphasis has been given to the critical buckling time and the remaining critical buckling load at a selected time. For this purpose, a parametric study has been performed by which the influence of different geometric parameters on the buckling load capacity of reinforced concrete columns has been assessed. The results of this study show that the load-carrying capacity of the column reduces significantly with the increasing time of fire exposure and the column slenderness. Moreover, the initial mechanical load has a small, although not negligible effect on the buckling load capacity.
COBISS.SI-ID: 6871137