Shrinkage-Induced Response of Composite Steel–Concrete Slabs: A State-of-the-Art Review

Composite steel–concrete slab is a floor typology widely used for building applications. Their design is usually governed by serviceability limit state requirements associated with the time-dependent response of the concrete. In this context, this paper presents a state-of-the-art review of research carried out to date on the long-term behavior of composite steel–concrete slabs. The particularity of this time-dependent response relies on the fact that the concrete cannot dry from the underside of the slab due to the presence of the profiled sheeting while it can dry from its upper surface. In the first part of the paper, a review of the work carried out on the identification of the time-dependent response of the concrete is presented by considering the peculiarities that occur due to the non-symmetric drying condition related to composite slabs. Particular attention is given to shrinkage effects and to the occurrence and influence of the non-uniform shrinkage gradient that develops in this form of construction over time. This is followed by the description and discussion of the experimental work performed on both simply-supported and continuous static configurations of composite slabs. In particular, the work published to date is summarized while highlighting the key parameters of the test samples and of the testing protocols adopted in the experiments. In the last part of the paper, available theoretical and design models proposed for the predictions of the shrinkage-induced behavior of composite slabs are presented and discussed.

A Proposal to Improve the Effectiveness of the Deflection Control Method Provided by Eurocodes for Concrete, Timber, and Composite Slabs

Limited deflection of structural members represents an important requirement to guarantee proper functionality and appearance of building and infrastructures. According to Eurocodes, this requirement is ensured by limiting the maximum deflection of horizontal structural members to a fraction of their span. However, each Eurocode provides different maximum deflection limits, which are independent of the type of superstructures considered. Thus, the respect of these limits may not always guarantee the integrity of certain superstructures. In this paper, the reliability of the Eurocode deflection control methods, in guaranteeing the integrity of the superstructures, is assessed and discussed. First, different types of horizontal member, namely rib and clay (hollow) pot, composite steel–concrete, and timber beam slabs are designed to respect the deflection limit enforced by the Eurocodes. Then, the maximum curvature developed by these members is compared with the ultimate (limit) curvatures of various superstructures (e.g., ceramic and stone tile floorings). The results obtained show that the approach adopted by Eurocode 2 may provide non-conservative results, but also that the rules proposed by Eurocodes 4 and 5, albeit more reliable, do not always guarantee the integrity of the superstructure. Based on these results, an alternative method, based on the curvature control, is proposed and its advantages and limitations critically discussed. This method appears simpler and more reliable than the method currently adopted by the Eurocodes.

Experimental Study on the Behavior of Steel–Concrete Composite Decks with Different Shear Span-to-Depth Ratios

This paper presents the results of an experimental study on the mechanical behaviors of steel‒concrete composite decks with different shear span-to-depth ratios. Herein, four composite decks categorized into two types with shear span-to-depth ratios of 2.5 and 4.6 are designed for an experimental program. The decks then undergo the four-point bending tests until failure to investigate the structural responses, such as the load, displacement, crack mechanism, and failure mode. Conventional section analysis is used to derive the flexural strength of composite decks in comparison with the test results. Additionally, the ductility of the composite decks is assessed based on the displacement indices. The analysis results demonstrate that the stiffness and capacity of the composite deck increase with the decrease in the shear span length. However, the ductility of the composite slabs increases with the shear span length. The flexural strengths predicted by section analysis overestimate the actual test results. The shear span-to-depth ratio affects the crack mechanism of the composite decks.

Bending performance of cross-laminated timber-concrete composite slabs according to the composite method

Bending strength tests were conducted of cross-laminated timber (CLT)-concrete composite slabs according to the shear connection method and carbon fiber reinforced plastic (CFRP) reinforcement. The bending strength of the composite slab that was shear-connected with an epoxy adhesive was 17% higher than that of a composite slab that was shear-connected with a self-tapping screw. In addition, the CLT-concrete slip of the former composite slab was also measured as 20% lower than the latter under the same load, showing a behavior close to that of a full composite. Both shear connection methods generated a failure in a low load-deformation section when there was a defect in the outermost tensile laminae of the CLT. In contrast, the CFRP reinforcement in the tension part of the composite slab suppressed the failure at the defect in the outermost tensile laminae. This reinforcement effect increased the reliability of the bending performance of the composite slab by preventing the failure of the composite slab while in a constant failure mode. Furthermore, the slip of the composite slab decreased 49% after its reinforcement with CFRP, showing a behavior close to that of a full composite.