Economical Weld Details and Design for Continuity and Doubler Plates in Steel Special Moment Frames

Abstract

For seismic design of steel special moment frames (SMFs) the current seismic provisions require the use of continuity plates when either the proportion between the beam flange width and column flange thickness is not met or a strength limit state is not satisfied. The provisions require that the weldments between these continuity plates and the column flanges be a complete joint penetration (CJP) groove weld. Full-scale testing of 10 moment frame connections was performed to investigate the design of continuity plates using fillet welds instead of CJP welds. Six of these frames were one-sided connections using the prequalified reduced beam section (RBS) connection. The remaining four were two-sided connections using the prequalified welded unreinforced flange-welded web (WUF-W) connection. While violating the current continuity plate requirements, all 10 connections surpassed the 0.04-rad story drift criterion required by the provisions for SMF connections. The testing has demonstrated that (1) the criteria governing when to use a continuity plate may be relaxed for RBS connections, (2) fillet welds sized to develop the tensile strength of the continuity plate may be used to fasten the continuity plate to the column flange, (3) the required continuity plate thickness may be determined based on a plastic interaction equation, and (4) the width-to-thickness ratio of continuity plates should be limited to prevent instability. It was also found that sizing the doubler plate welds for the shear flow determined from their elastic shear stiffness, as opposed to developing the shear strength of the doubler plate as required on the provisions, was adequate to fasten an elastic doubler plate to a column.