Experimental and Numerical Characterization of Ultralow-Cycle Fatigue Behavior of Steel Castings

Abstract

Steel castings have been increasingly used in building construction to enhance the seismic resistance of structures. Such castings are designed as yielding fuses that dissipate energy through large inelastic deformations, while the rest of the structure remains mainly elastic. Typically, the governing ultimate limit state of these yielding fuses is their ultralow-cycle fatigue (ULCF) life. This paper presents tests and finite-element analyses of small-scale coupons and full-scale tests of a variety of cast steel yielding connectors—devices that dissipate seismic energy through the inelastic deformation of cast steel triangular yielding fingers. This paper presents results of modeling improvements over previous numerical models of yielding connectors, an optimized material calibration procedure using an automated optimization algorithm and a device-specific ULCF model calibration process, the use of the stress-weighted damage model for fracture prediction that considers the Lode parameter along with the stress triaxiality, and an improved bolt friction model. These enhanced analyses provided good predictions of the onset of failure in full-scale steel castings across various specimen sizes and loading histories.