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Alternative Weld Details and Design for Continuity Plates and Doubler Plates for Applications in Special Moment Frames


Steel Special Moment Frames (SMF) are regularly used as seismic force-resisting systems due to their excellent ductility and wide accommodation of building floor plans and heights. The current AISC Seismic Provisions require the use of reinforcing continuity plates and dictate their size based on a set of rules conservatively inferred from experimental testing. These rules often result in the unnecessary reinforcement of columns and usually require costly complete-joint-penetration (CJP) groove welds to fasten the reinforcing plates. Full-scale testing of 10 moment frames was performed to investigate the design of these continuity plates and their weldments. Six of these frames were exterior connections utilizing the prequalified Reduced Beam Section (RBS) connection, while the remaining four were interior connections utilizing 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 requirement of SMF according to the prequalification criteria of the AISC Seismic Provisions. Experimental testing was also performed to measure, for the first time, the in situ residual stresses of a continuity plate. Detailed parametric finite element modelling and modern fracture mechanics using the Cyclic Void Growth Model for ductile fracture prediction was used to develop an amended set of limit states of reinforced columns. These amended limit states, in conjunction with a newly proposed width-to-thickness requirement, permit the design of column reinforcement based on a rational plastic approach. A fillet weld design that capacity protects the weldments based on a von Mises yield surface is included in this new plastic design method. This new experimentally verified design basis for fillet weldments of continuity plates results in significant fabrication savings. It was also found that sizing the doubler plate weldments for the average developed shear flow according to the relative doubler plate stiffness was adequate to fasten the doubler plate. This results in significant savings over current requirements which currently require welds to develop the shear strength of the doubler plate.

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