Analysis of Temperature Distribution in Steel-Concrete Composite Beams with Concrete Hollow Core Slabs with Rectangular Openings Under Fire Conditions

Abstract The structural contribution of slab in steel–concrete composite beams depends on the interaction between materials. Despite providing procedures for temperature evolution and strength reduction in composite beams with solid slabs, NBR 14,323 does not include specific recommendations for systems that incorporate hollow-core slabs. Towards addressing that knowledge gap, this manuscript reports on a comprehensive parametric numerical investigation of temperature distribution in steel–concrete composite beams that incorporate hollow-core concrete slabs with rectangular openings. Building upon previous research, the study evaluates rectangular openings, expands the range of concrete densities to six classes (1,750-3,000 kg/m³), and increases the numerical database from 60 to 120 thermal models. The expanded database enables a systematic assessment of the combined influence of opening geometry and concrete density on the thermal response of hollow-core slabs and provides new temperature distribution tables suitable for future code development. According to the results, six tables show the temperature variation along the slab depth for densities ranging from 1,750 to 3,000 kg/m³, indicating hollow-core slabs consistently develop higher temperatures than those prescribed by NBR 14,323 for solid slabs of same density. The results also show opening geometry substantially affects the temperature distribution, with differences of up to 85.8 °C between rectangular and circular openings in function of slab layer and fire exposure time. Therefore, both internal geometry and concrete density should be considered for the development of future structural fire design provisions for hollow-core slab systems. The aforementioned tables provide a preliminary technical basis for assessments of the thermal behavior of hollow-core slabs with rectangular openings and may support future improvements to structural fire design provisions for steel–concrete composite beams.