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This paper presents experimental investigations on the thermal and mechanical behavior of composite floors subjected to ISO standard fire. Four 5.2 m×3.7 m composite slabs are tested with different combinations of the presence of one unprotected secondary beam, direction of ribs, and location of the reinforcement. The experimental results show that the highest temperature in the reinforcements occurs during the cooling phase (30–50 °C increment after 10-min cooling). The temperature at the unexposed side of the slabs is below 100 °C up to 100-min heating, compared to the predicted fire resistance close to 90 mins from EC4. For the slabs without secondary beams, the cracks first occur around the boundaries of the slab, while for the slabs supported by one unprotected secondary beam, concrete cracks first occur on the top of the slab above the beam due to the negative bending moment, and later on develop around boundaries. Debonding is observed between the steel deck and concrete slab. The secondary beam significantly impacts the deformation shape of tested slabs. Although a large deflection, 1/20 of the span length, is reached in the tests, the composite slabs can still provide sufficient load-bearing capacity due to membrane action. The occurrence of tensile membrane action is confirmed by the measured tensile stress in the reinforcement and compressive stress in the concrete. A comparison between measured and predicted fire resistance of the slabs indicates that EC4 calculations might be used for the composite slabs beyond the specified geometry limit, and the prediction is conservative. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of two compartment fire experiments performed on the 9.1 m × 6.1 m composite floors using a full-scale two-story steel gravity frame to study the influence of slab reinforcement on the overall structural integrity. The floor specimens were designed to achieve a 2-h fire rating but had dissimilar slab reinforcement. The Test #1 specimen had steel wire reinforcement of 60 mm2/m width as the minimum permitted in the United States practice whereas the Test #2 specimen was reinforced with deformed steel bars (230 mm2/m) determined by incorporating tensile membrane action. The Test #1 specimen exhibited mid-panel slab integrity failure before reaching the specified fire rating period. However, the Test #2 specimen exhibited much smaller concrete cracks until it was heated up to 131 min and retained the post-fire residual strength at least two times greater than the design demand at ambient temperature. This unique large-scale testing demonstrated that the appropriate slab reinforcement scheme can delay the vertical deflection of the heated composite floor and maintain the structural integrity at large vertical displacements over a longer duration of fire exposure. • The influence of slab reinforcement on the structural integrity of steel-concrete composite floors under fire was evaluated. • Compartment fire experiments were conducted on the composite floor assemblies located in a full-scale two-story steel gravity frame. • Slab reinforcement of larger area and ductility can maintain the structural integrity of the slab for longer period of fire. • The enhanced slab reinforcement significantly delayed the increase in the vertical displacement of the composite floor. [ABSTRACT FROM AUTHOR]

Large-scale tests and accidental fires have demonstrated that the composite steel-framed buildings have significant load-bearing capacities and are more resilient to fire conditions compared to fire resistance tests performed on the isolated elements. Understanding the beneficial effect of the tensile membrane action will enable minimization of the amount of fire protection measures, which will increase the competitiveness of the use of steel–concrete composite floors in buildings. The fire resilience of floors is dependent on the connection behavior since the failure of the connection might lead to partial collapse of the interior beams. This paper presents a numerical investigation on the performance of a composite steel-framed floor system and the beam-to-beam shear connection at elevated temperatures. The paper also investigates the effect of the interior beams on the concrete slab in terms of vertical deflection, composite action and stress levels in the steel reinforcement. The results show that the single plate shear connection buckles and excessively deforms during the early phases of the fire. The out-of-plane distortion of the plate causes bolts to load in the tension. The connection reaches its rotational and axial capacity during the cooling phase of the fire resulting the bolts to fail with combined shear and tension. [ABSTRACT FROM AUTHOR]

According to full-scale fire tests, it is noticed that tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into the influence of vertical supports on the tensile membrane actions of the floor slabs. In this paper, the performances of a generic three dimensional 45 m×45 m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumes the connections behave as pinned or rigid for simplicity, two robust 2-node connection element models developed by the authors are used to model the behaviour of end-plate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is taken into consideration. The load-transfer mechanisms of composite floor when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed to enhance the fire resistance of composite buildings. [ABSTRACT FROM AUTHOR]