Engineering Structures 25 (2003) 667–680 www.elsevier.com/locate/engstruct Ductile details for welded unreinforced moment connections subject to inelastic cyclic loading James M. Ricles * , Changshi Mao, Le-Wu Lu, John W. Fisher Dept. of Civil and Environmental Engineering, Lehigh University, 117 ATLSS Drive, Bethlehem, PA, 18015-4729, USA Abstract The results of a 3-D finite element study of welded unreinforced flange beam-to-column moment connections in steel special moment resisting frames are presented. Computer models of connection subassemblies were developed using the general-purpose nonlinear finite element program abaqus. Several issues were addressed in the study: (1) geometry and size of the weld access hole; (2) benefit of a welded beam web; (3) control of inelastic panel zone deformations; and (4) effectiveness of continuity plates in reducing local demand on the connection. The analytical results provided information related to basic performance and the effects that these connection parameters have on inelastic cyclic performance, thereby furthering the current understanding of welded moment connection behavior under seismic loading conditions and leading to improved design criteria. Based on the results of the analytical study, recommendations for the seismic design of connections are given. The incorporation of the recommendations into an experimental test program showed good connection ductility in the test specimens.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Beam web attachment; Connection; Continuity plates; Cyclic tests; Ductility; Finite element analysis; Fracture; Inelastic rotation; Panel zone; Plastic strain; Weld access hole; Welded 1. Introduction Numerous welded beam-to-column moment connec- tions in steel moment resisting frames (MRFs) failed during the 1994 Northridge Earthquake [1]. The failures raised many questions regarding the validity of design and construction procedures used at the time for these connections. Since the earthquake, several extensive analytical and experimental studies have been conducted to investigate the various aspects believed to be associa- ted with the failure observed in the pre-Northridge con- nection and to improve connection performance [2–9]. This paper presents the results of recent research con- ducted under Phase 2 of the SAC Steel Project that focused on the seismic resistance of welded unreinforced flange moment connections with improved details for special MRFs. The improvements in the connection detail include the use of notch tough electrodes, properly contoured and sized weld access holes, beam web full penetration welds, sufficient column panel zone strength, and column continuity plates with adequate thickness. * Corresponding author. Fax.: +1-610-758-5553. 0141-0296/03/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0141-0296(02)00176-1 Numerous weld access hole fractures have been reported in post-Northridge earthquake inspections and in laboratory tests, where conventional access hole con- figurations were employed in the connections. Previous finite element analysis [6] has shown that small access holes result in less strain concentration around the holes. However, the reduced hole diameter restricts access dur- ing welding, which tends to increase the size of the weld defects resulting from incomplete fusion at the root of the flange groove weld. For the beam lower flange the critical location of major defects often occurs near the access hole, where fracture may initiate. Additional stud- ies are therefore needed to further examine the effect of the size and geometry of the weld access hole on the fracture potential of the material near the hole. The typical shear tab of a pre-Northridge moment con- nection is welded to the column flange as well as bolted to the beam web. The shear tab is designed to resist the beam shear force, with the welded beam flanges resisting the beam bending moment. Previous experimental stud- ies [5,10] have shown that web supplemental fillet welds, which are provided along three edges of the shear tab, and full penetration groove welds between the beam web and column face enhance the strength, ductility and