Evaluation of drilled flange connections with combined arrangements of holes and notches

The reduced beam section (RBS) connections are used to improve the seismic behavior of rigid connections. The brittle failure and lateral-torsional buckling are the drawbacks of these connections. Drilled flange connections (DFC) are one of the novel configurations of RBS connections. This form of the reduction in beam section can reduce the probability of local buckling, however, the tearing of the beam flange between the drilled holes are the drawbacks of these connections. By implementation proper arrangements of holes and notches, more uniform strain distribution may be made in welds and drilled flanges. The experimental studies were conducted on a welded unreinforced flange (WUF) connection and suggested a sample of drilled flange connection with combined circular holes and notches (CDFC). The results of experimental studies were used to validate the analytical models. To evaluate the seismic performance of different arrangements of the flange drilling, various analytical models were prepared and their behavioral indexes were compared. Results of the analytical studies revealed that by applying the proper drilling pattern, the potential brittle failure, and local buckling of the drilled zone of DFC connections would be reduced. Among the studied arrangements (i.e., WUF, RBS, DFCs with inclined, parallel and combined notches and holes drilling patterns), CDFC with combined notches and holes drilling patterns performed better than the other connections, and Remarkable reductions of damage indexes were observed in connection. By implementing this pattern, the equivalent plastic strain would be reduced up to 71.1% in groove welds comparing to the conventional RBS connections.