Optimum arm geometry for ductile modular connectors

A cast modular connector (MC) has been developed for use as an energy dissipating detail in seismic-resistant bolted steel moment frames. The MC relies on a series of variable section elements (arms) to minimize plastic strain demand and a stiff end region joined by a base to virtually eliminate bolt prying forces and provide a hysteresis characteristic absent of degradation. The MC was developed through a comprehensive program that included heavy industry partner involvement, analytical research, and experimental verification. This 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. A MC prototype was cast on the basis of these recommendations. These prototypes were tested under monotonic and cyclic loading and exhibited remarkable ductility, far exceeding qualifying rotational capacities.