Failure Modes and Flexural Ductility of Steel Moment Connections

1 Associate Research Fellow,Center for Research on Earthquake Engineering (NCREE), Chinese Taiwan 2 Professor, Dept. of Civil Engineering, Taiwan University, Taipei, Chinese Taiwan 3 Assistant Professor, Dept. of Civil and Environmental Engineering, University of Kaohsiung, Kaohsiung, Chinese Taiwan Email: [email protected] ABSTRACT : Ductility is the main attribute of steel moment connections and the failure modes control it. This study reanalyzes the results of 66 past experiments in Taiwan, comparing connection ductility across failure modes. In reference to FEMA 1995, the failure mode and root cause identification was firstly made for each specimen. 56 of the specimens were found to fail for the main three modes. In details, 43% of the connections failed for flange-HAZ (Heat Affected Zone) fracture, 27% failed for flange-weld fracture, and 16% failed for flange buckling. Following that, the connection ductility of the 56 specimens was reanalyzed and compared in detail. The plastic rotation, at which a connection reaches its maximum moment strength, was used as the main measure of connection ductility. Flange-HAZ fracture gave an average of 1.98%, and flange-weld fracture and flange buckling changed it to 2.47% and 2.95%, respectively. Furthermore, equivalent monotonic ductility was used as another measure, assessing the connection ductility without the effect of loading history. Flange-HAZ fracture gave an average of 11.32, and flange-weld fracture and flange buckling changed it to 11.56 and 11.81, respectively. Finally, a numerical example was given to illustrate that the obtained results have important implications for making a strategy for the performance assessment and earthquake retrofitting of steel moment frames.