Numerical analysis of temperature in concrete hollow-core slabs with circular openings used in steel–concrete composite beams

For the design of steel–concrete composite beams, it is essential to account for the interaction between the steel beam and the concrete slab, particularly by determining the slab’s contribution to the overall structural strength. The evolution of temperature and the corresponding strength reduction are defined by NBR 14323 (ABNT, 2013) for composite beams with solid concrete slabs. However, no design recommendations currently exist for steel–concrete composite beams connected to hollow core concrete slabs. To address this gap, the present study determined the temperature distribution along the height of hollow core slabs with circular openings through numerical analysis. For this purpose, thermal models were developed and calibrated in Abaqus to simulate the behavior of hollow core slabs under fire conditions. A parametric analysis was subsequently conducted using 60 thermal models, varying key parameters such as slab thickness, concrete density, and the dimensions and spacing of the openings. Based on the results, tables were developed presenting temperature values along the height of hollow core concrete slabs with light, normal, and heavy densities for four different fire durations (30, 60, 90, and 120 min). When comparing the values found for hollow core slabs with those from the NBR 14323 (ABNT, 2013) table for solid concrete slabs of normal density, it was observed that the values obtained in this study are higher than those specified in the standard. This discrepancy demonstrates that the use of code-based temperatures for hollow core slabs may result in non-conservative design assumptions, as the reduction in material strength is directly dependent on the temperature attained within the structural element. Moreover, the difference in temperatures can be attributed to the greater massiveness of the solid slab compared to the hollow core slab of the same thickness. For future research, it is recommended that a similar study be carried out with a larger number of models to improve the statistical reliability of the results. Additionally, the use of a more refined mesh is advised to allow for the generation of temperature distribution tables with thinner slices, thereby enhancing the precision of the thermal analysis. Moreover, applying an additional thermal load to the bottom surface of the openings is suggested to improve the accuracy of the numerical results.