Simulating column splice fracture and post-fracture response for seismic assessment of steel moment frames

Mitigating fracture in welded column splices is an important challenge for the safety of existing steel moment-resisting frames. While models to predict splice fracture have recently been developed, suitable approaches are not available to simulate the response of frames after splice fracture. Motivated by this, a two-dimensional displacement-based fiber element construct, termed the Splice Fracture Element (SFE), is presented. The SFE includes numerous features: (1) representation of the loss of strength in any fiber at a critical stress determined from fracture mechanics, (2) the ability to simulate the loss of shear strength of the cross-section when the entire section is severed – a phenomenon not readily simulated in conventional fiber elements, and (3) the ability to track the kinematics of the severed parts of the column to represent transfer of compressive stresses on contact. This formulation is implemented into an open-source software (OpenSees) and applied to conduct Nonlinear Response History Analysis (NLRHA) of two demonstration problems, including a 1-story frame and a 20-story frame. Benchmark simulations that do not simulate splice fracture or represent it without the loss of shear strength are also conducted. The results indicate that the SFE element can successfully simulate the key phenomena associated with splice fracture and post-fracture response.