Improved design of drilled flange (DF) moment resisting connection for seismic regions

Reduced beam section (RBS) connection was developed as an authentic alternative for welded unreinforced flange connections to prevent the wide spread typical damage of the beam to column welded connections observed after the 1994 Northridge earthquake. Drilled flange (DF) connection, as the next generation of RBS connection, was developed to replace the former RBS connection, due to their easier construction. The present study aims to investigate the effects of different design parameters such as center-to-center distance of the drilled holes, drilled holes diameter, row number of the drilled holes and beam span-to-depth ratio on seismic performance of DF connection. For this purpose, experimentally validated detailed finite element models (FEMs) are used. Also, the cyclic responses of FEMs are utilized to validate the proposed closed-form equations for estimating the yield moment and plastic moment capacity of DF connection. The results indicate that placing the specified limits on the latter design parameters can reduce equivalent plastic strain and Rupture Index at CJP groove weld line of DF connection up to 100 and 154%, respectively. Furthermore, based on the analytical results, the proposed closed-form equations can predict the plastic moment capacity and the yield moment of DF connection with the maximum errors bound less than 8 and 9%, respectively. The results of this study provide the practical recommendations for DF connection seismic design.