Application of ductile fracture modelling in the assessment of steel structures

The “improved Jia (IJIA)” ductile fracture assessment (DFA) approach is applied to universal column (UC) steel members subjected to cyclic axial loading. The IJIA method is first validated and then used to develop fracture curves based on (i) standard Manson-Coffin (SMC) approach and (ii) cumulative inelastic deformation approach (CID). For variable amplitude loading, fracture initiation is predicted directly from the DFA and fracture curves. The application of DFA is further presented through (i) evaluating the effect of mean-strain offset on fracture capacity of steel member under constant-amplitude deformations by applying DFA approach to UC specimens, and (ii) developing a decision-making methodology to obtain the remaining earthquake life. An example is provided for remaining earthquake life assessment of a four-story eccentrically braced frame (EBF) building with link yielding. The DFA damage estimates were 0.85–1.33 of the values obtained from 16 UC specimen tests with an average estimate of 1.015 times that observed. For the analytical methods, average fracture occurred at 0.87 times that predicted by the SMC approach and 1.12 times that for the CID method. Additionally, an offset mean displacement had similar or better performance than when the testing was conducted with no offset. For the EBF example considered, 21 % of the earthquake life was estimated to be used according to the direct DFA method and it was recommended that the link should be retained, according to the assumptions made. • IJIA method predicted ductile fracture of UC columns within −15 % to 33 % error, suitable for ductile fracture assessment. • CID-based fracture curves showed better accuracy and consistency than standard Manson-Coffin approach. • Post-earthquake DFA enabled damage assessment of EBFs, supporting retain-or-replace structural decisions.