A cast modular connector (MC) has been developed for use in seismic-resistant steel moment frames. The MC is a field bolted beam flange connection intended to serve as the frame's special energy-dissipating detail. The connector is specifically configured for optimal seismic performance through a casting process. The MC possesses inherent ductility through variable-section arms that minimize plastic strain demand and a reliable yet economical fastening method through a base end-region that virtually eliminates prying forces on bolts.The dissertation presents three journal papers. The first paper describes the portion of the analytical research focused on establishing the optimum geometry for the energy dissipating arm elements. Key parameters were evaluated through parametric studies using nonlinear (material and geometry) finite element analysis and supported by basic theoretical models. The outcome was a set of optimum geometric ratios covering width reduction, length to thickness, aspect ratio, and fillet radius.The second paper describes the development process of the isolated connector rather than full-connection behavior. Designs were alternately evaluated for structural performance and castability through the electronic exchange of solid model files with steel foundry industry partners. The analytical results indicate the potential for excellent ductility and energy dissipation characteristics in the MC Beta prototype.The third paper focuses on the prototyping and experimental verification of the MC Beta prototype. Steel foundry industry partners cast the MC Beta prototype at approximately half-scale. The scaled MC Beta prototype was tested in isolated fashion under monotonic and cyclic loading. The experimental results confirmed the performance of the analytically-based designs. The MC Beta prototype exhibited exceptional performance in terms of stable energy dissipation, far exceeding qualifying rotational ductility capacities. In direct comparisons to a WT section of similar stiffness and strength, the MC Beta prototype possessed greatly enhanced ductility and energy dissipation characteristics.With the MC Beta prototype developed and experimentally verified under isolated conditions, an experimental verification of beam-to-column joints containing the scaled MCs were performed using accepted testing protocols. The preliminary test results indicate that the connection exceeded qualifying rotational ductility capacities and showed promise as a special energy-dissipating detail in seismic-resistant steel moment frames.
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