Design of moment end-plate connections for seismic loading

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Virginia Tech


Analytical and experimental research into the seismic response of four-bolt extended moment end-plate connections was conducted. Full-scale connections, ranging in size from moderate to large, were designed, fabricated and tested under cyclic loading until connection failure was observed. The design procedures for minimum end-plate thickness were developed from yield-line theory with prying forces included in the bolt tension forces. Stiffened end-plates, four-bolt wide connections and shimmed end-plate connections were valiations of the four-bolt connection tested. A325 and A490 bolts with internal strain gauges were employed to record and analyze bolt tension forces. Test results demonstrate that the design approach is satisfactory, but several aspects of connection response not previously observed nor reported were encountered. When weld access holes were present in an extended end-plate connection, excessive 3-D stresses developed in the hole region, causing a brittle fracture of the beam flange. In the absence of weld access holes, ductile failure occurred, evidenced by local buckling of the beam flanges and plastic hinge formation. These two responses or failures were exhibited by all connection sizes. The use of end-plate stifieners appeared to provide sufficient stress reduction, as ductile failures were observed in all stiffened, extended end-plate connection tests with weld access holes. Grade 50 steel, four-bolt end-plate connections with built-up beam sections were also tested and demonstrated that inadequate weld strength exists in the beam web-toflange welds. Prior to fracture in these welds, the connections responded in a ductile manner with local beam flange buckling. In conjunction with the full-scale testing, finite element models were created for several connection sizes. When actual material properties of the steel and bolts were modeled, an excellent correlation of test data and the model was noted. When weld access holes were introduced in the models, an increase of flange strain in the hole region was noted. Although not conclusive nor comprehensive for every connection configuration, the four-bolt design appears satisfactory to survive seismic activity. Further research should provide answers to other configurations and eventually provide an acceptable alternative beam-to-column connection for high seismic areas.