Damage control mechanism and seismic performance of a steel moment connection with replaceable low-yield-point steel double T-stub fuses

Abstract

To achieve a damage-controllable and earthquake-resilient steel frame with more feasible and simple dissipative devices, an innovative steel moment-resisting connection with bolted ductile double T-stub fuses is developed in this work. These T-stubs with appropriate free deformation length in the stems, made of Low-Yield-Point (LYP) steels instead of ordinary steels, simultaneously behave as connectors, bearing elements, and replaceable dissipative fuses that benefit from the inherent excellent ductility, dissipation capacity, and fatigue performance of the LYP materials. The cyclic responses of the connections with LYP T-stubs subjected to different weakening strategies are explored and compared via extensive nonlinear numerical parametric analyses. Subsequently, the influences of the free deformation length and the weakened degree of the T-stub stem on the seismic performance and the structural fuse effect are evaluated. Finally, optimal design suggestions for this connection are proposed, which provide a reference for engineering applications. Analytical results demonstrate that properly designed LYP T-stubs with various weakened parameters can act as structural fuses by dissipating more than 90% of the system energy and concentrating most of the plasticity and damage, which effectively protect the main structural members from damage while being subjected to seismic excitations. Besides, due to low yield strengths, to achieve an identical weakened degree, the T-stubs made of LYP steels are stockier than the ones made of traditional or high-strength steels. This feature is able to avoid serious local buckling of stem plates and significant strength degradation, thus is conducive to the improvement of the ductility. By comprehensively considering the construction advantages, ductility, dissipation capacity, structural fuse performance, and material efficiency, LYP T-stub with a relatively thin stem is a more promising solution. The method of increasing the free deformation length of the stem effectively controls the damage within the LYP T-stubs, adequately improves the effect of structural fuses, and further lowers the required weakened degree; thus, the protection of primary frame members is achieved without excessively reducing the strength of the connection. Nevertheless, the T-stub fuses with overly-large free deformation lengths and thin stem plates tend to buckle substantially, resulting in significant strength deterioration that adversely decreases the ductility of the connections. As a result, an optimal solution with a satisfactory weakened degree and an appropriate free deformation length (αd = 0.8 and le = 1.0 bts) is suggested as a good compromise among the material efficiency, dissipation and ductility capacities, and structural fuse performance.