Deformation Capacity of Steel Beam-to-Column Connections Evaluated Based on Strain Histories

The plastic deformation capacity of beam-to-column connections strongly affects the seismic capacity of steel moment frames in seismic design. Ductile fractures that occur after adequate plastic deformation and crack propagation are one of the most typical steel component failure modes during earthquakes. For most structural steels, the strain-life relationship can be expressed using a Manson–Coffin-type equation. The current study focuses on whether there is a similar Manson–Coffin relationship between the average flange strain amplitude at the critical cross-section and the number of loading cycles until fracture. Shop welded beam-to-column connections made of 400 N/mm2 class structural steel are tested under cyclic loading histories in this study. Moreover, cyclic in-plane beam analysis is conducted using an experimental database of 10 beam-to-column connections that are loaded until ductile fractures occur to obtain the strain histories at the beam-end flanges. Based on the strain histories, it is found that, similar to the material level, there is a Manson-Coffin relationship between the average flange strain amplitude at the critical cross-section and the number of loading cycles until fracture. The current study provides a possible solution for the damage evaluation of steel beam-to-column connections based on strain amplitudes through analysis and a limited number of experiments.