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Characterizing structural resiliency after severe damage to a few load-carrying members is challenging. Engineers use various computational approaches to assess the vulnerability of structures and to evaluate the parameters that affect their response. Few of these approaches are capable of predicting the actual peak load-carrying capacity a damaged structure can withstand before experiencing total collapse, and practically none of them have been verified against actual test results. In this paper, experimental data from large-scale tests on steel–concrete composite floor systems under different column loss scenarios were used to develop and to validate a high-fidelity numerical modeling approach capable of predicting the response of the tests up to total collapse. This approach incorporates geometric and material nonlinearity, explicit modeling of steel and concrete failure, and contact modeling using LS-DYNA version R10.2.0. Nearly all specimen components were modeled using brick elements, including the concrete slab, steel members, bolts, and other connecting elements. The corrugated metal decking was represented with shell elements, and beam elements represent the reinforcing steel and shear studs. The predicted response and ultimate load–carrying capacity up to total collapse show good agreement with the results of the experimental tests. Validating the numerical models revealed the sensitivity of various modeling parameters and demonstrated the potential for inaccurate predictions of response when certain parameters were not correctly specified. The most important of these parameters are described in this manuscript. Lessons learned from the current study are helpful for understanding the mechanisms that have the greatest impact on collapse of composite floor systems, and these lessons can be used to gain insight on the collapse potential of other structures with different geometries or configurations. [ABSTRACT FROM AUTHOR]

The delamination of concrete from steel decking will reduce the strength and decrease the stiffness of the composite slab. Visual monitoring of delamination is typically not possible in many cases. A possible alternative is ultrasonic-based health monitoring. In this study, a novel damage index (DI) based on the absolute energy change (AEC) of the ultrasonic waves is adopted to quantify delamination damage in the composite floor. AEC-DI was constructed based on the decomposed signals provided by the wavelet transform. The monitoring process of the composite floor was conducted ultrasonically under flexural loading. An ultrasonic surface (Rayleigh) wave is employed for damage detection using gel-coupled piezoceramic sensors. The results revealed that the reliability and accuracy of AEC-DI in detecting composite floor separation is better than that of RMSD-DI. [ABSTRACT FROM AUTHOR]

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]

A new composite floor system was developed to reduce floor-to-floor height and to improve structural capacity and fire resistance as compared with existing encased composite floor systems. The proposed system is composed of asymmetric steel beams with web openings, a biaxial hollow concrete slab, and glass fiber-reinforced plastic (GFRP) plates. The shear resistance of the typical composite beams is commonly determined based on the shear strength of the steel web alone. However, for the proposed system, because the steel web has several circular openings, the concrete contribution to the shear resistance should be included in the design equation. In this paper, tests and finiteelement analyses were conducted to evaluate the contribution of the shear-resisting components in the proposed system. An asymmetric steel beam with web openings, inner concrete panels, and a biaxial hollow concrete slab within the effective width for shear were considered as shear-resisting components. Each component fully resisted the applied shear force, exceeding the expected value until failure, and the design equation suggested was suitable for predicting the shear strength of the proposed system. [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]

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]

Over the past decade, much research has focused on the behaviour of structures following the failure of a key structural component. Particular attention has been given to sudden column loss, though questions remain as to whether this event-independent scenario is relevant to actual extreme events such as explosion. Few studies have been conducted to assess the performance of floor slabs above a failed column, and the computational tools used have not been validated against experimental results. The research program presented in this paper investigates the adequacy of sudden column loss as an idealisation of local damage caused by realistic explosion events, and extends prior work by combining the development of accurate computational models with large-scale testing of a typical floor system in a prototypical steel-framed structure. The floor system consists of corrugated decking topped by a lightly reinforced concrete slab that is connected to the floor beams through shear studs. The design is consistent with typical building practices in the US. The first test has been completed, and subsequent tests are currently being planned. This paper addresses the importance of robustness design for localized damage and includes a detailed description regarding how the research program advances the current state of knowledge for assessing robustness of compositely constructed steel-framed buildings. [ABSTRACT FROM AUTHOR]