Alternative Fastening Mechanism for Shear Connectors with Cold-Formed Steel Shapes Involved in Composite Sections

Abstract

Over the past few decades, the use of steel-concrete composite sections has increased globally, to take advantage of compression strength in concrete and tensile strength in steel, ensuring its connection by employing stress transfer elements denominated shear connectors. The main connection systems, endorsed by the current design codes, are used by applying welding as a fastening mechanism to fix connectors and any alternative system must be validated through an experimental program. However, this thermal procedure produces a concentration of residual stresses during the cooling process and the risk of perforation in Cold-Formed Steel sections (CFS), affecting the behavior efficiency of the composite sections. In this research, self-drilling screws are proposed as an alternative mechanical system for connectors fastening. The system efficiency was initially compared to the powder-actuated nails mechanism, validating their advantages of installation and structural behavior. An experimental program was carried out to validate the capacity and performance of the system, through screw shear tests and full-scale beam tests. Therefore, it was possible to characterize the local behavior in the fastening mechanism and the overall behavior in the composite system. According to results, self-drilling screws are a viable alternative to use as a fastening mechanism in shear connectors for CFS and concrete composite sections. The composite system developed full capacity, even in inelastic range, without disconnection between materials. Self-drilling screws remained fixed on steel shapes without mechanical damage, allowing greater deformations than displacements under service conditions. 134 of the composite section is based on the concrete slab to withstand compression stresses and on the steel shape to withstand tensile stresses.Assembly of composite sections implies the attachment of stress transfer elements between materials, called shear connectors. These components can control possible uplifts and relative displacements on the connection interface. Moreover, the strain state is also modified due to the inclusion of shear connectors, thus a two-materials system becomes a composite system.This system was initially proposed for bridges, and due to its good structural performance, its uses were expanded to flooring systems in buildings (Lakkavalli and Liu 2006).Recently, within technologies with better structural efficiency, Cold-Formed Steel (CFS) sections have increased their structural applications in medium and small buildings (Hossain 2005), becoming a competitive alternative concerning Hot-Rolled Steel (HRS) sections, which are heavier but commonly used in conventional infrastructure (Hancock 2003).The main advantages of CFS are versatility in the generation of different cross-sections, the possibility of using it in long spans, ease in industrial production, high strength-to-weight ratio and speed in packaging, transport and assembly (Yu and LaBooube 2010). Moreover, these sections are considered as an alternative to...

Behavior of CSC-Type Shear Connectors under Pry-Out Shear Test: Analytical Study

“…Interaction between different elements was modeled by using both frictionless and frictional contacts to represent the behavior of the surfaces in the specimen components, avoiding free sliding and focusing on the mechanical restriction generated within the concrete slab. The value for the friction coefficient was assumed to be 0.80 between fasteners and shear connectors, and fasteners and steel section, due to the high connection evidenced in previous experimental tests [20] (Fig 6b).…”

“…In this research, an analytical study is carried out and a new typology of shear connectors is proposed, called CSC (confined shear connectors) [19]. Self-drilling screws are simulated as a fixing mechanism for the connectors, thus avoiding the disadvantages of welding, such as residual stresses or perforations in steel plates due to burns [20]. Numerical models were developed using the finite element method (FEM) in ANSYS software.…”