Ductile Fracture Initiation in Braces of Concentrically Braced Frames

Braces in concentrically braced frame system dissipate majority of the seismic energy imparted to the structure through inelastic cyclic axial deformations. During the inelastic cyclic deformations, the braces might initiate fracture prematurely   if the selection of the brace geometry is not decided properly. Hence, the main objective of the study is to couple the continuum-level study with micro-mechanical fracture model to decipher the localized mechanism behind the origin of brace fracture initiation phenomenon. Monotonic and cyclic notched bar test results available in the literature have been used to calibrate the numerical model for capturing the inelastic cyclic material response. The calibrated numerical model has then been used to model the braces across a wide range of brace geometries, using which the stress and strain histories for cyclic loading have been evaluated. The evaluated stress and strain histories with the help of micro-mechanical fracture model have been used to capture the ductile fracture initiation of braces. From the obtained results, it has been observed that the slenderness ratio and width to thickness ratio have a strong influence over the initiation of ductile fracture in braces.