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Improving Safety of Rebar Cages using Innovative Connectors
Civil and Environmental Engineering
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Prefabricated rebar cages are widely used in reinforced concrete constructions. These temporary structures are built by connecting longitudinal and transverse reinforcing bars (rebars), typically using tie-wires. Previous studies have identified tie-wire connections as the "weak links" in the rebar cage system, mainly responsible for failures in rebar cages at construction sites, resulting in injuries, fatalities, project delays, and increased construction costs. Consequently, this research explores the application of mechanical connectors for connecting rebars in a rebar cage. The research includes a comprehensive experimental and numerical investigation of the structural behavior of rebar cages, specifically those reinforced with mechanical connectors such as U-bolts and Cage Clamps. The overarching goal of the research is to promote the adoption of mechanical connectors as a viable solution to enhance the overall safety of rebar cages during different phases of construction.Through a series of experimental tests, the force-deformation response of mechanical connectors has been explored for crossbar connection in different degrees of freedom. The findings indicate that mechanical connectors offer significantly higher strength and stiffness compared to tie-wire connections. Subsequently, thirty-one experimental tests are performed on six full-scale underground pile-shaft rebar cages with tie-wires and mechanical connectors. The data obtained from the experiments are used to develop and calibrate detailed finite element models, demonstrating the effectiveness of mechanical connectors in enhancing the strength and stability of rebar cages. Building upon these experimental and numerical works, and through parametric studies and dimensional analysis, analytical models are developed to characterize the stiffness properties of a rebar cage as a function of its physical parameters. The derived stiffness properties are then used to create a simplified beam model for rebar cage analysis. The simplified model enables practitioners to analyze the deflection of rebar cages under on-site loading conditions without relying on complex and expensive finite element numerical models. Finally, in collaboration with rebar cage practitioners, a technical guideline and a best practice manual have been developed for the systematic analysis, design, fabrication, and handling of rebar cages using mechanical connectors. These documents provide a streamlined approach to decide about connector layouts, lifting process, and other rebar cage configurations, allowing for a practical process to design and fabricate rebar cages and ensure their stability and safety under common jobsite loading conditions.