Experimental and analytical investigation of bracket moment connection for precast concrete beam-to-composite column joints

In large industrial buildings, precast prestressed concrete beams and composite columns are appealing to achieve longer span and higher story height, with temporary supporting and scaffolding minimized. To facilitate field erection of moment connection between precast beams and composite columns, a bracket connection transferring beam loads to the column by connecting the beam to a composite bracket attached to the column has been developed. Since precast beams are lap-spliced and integrated with the bracket by concrete engagement at the interfaces, the connection performance depends on beam lap length and load transfer details (i.e., concrete shear keys). In this study, the seismic performance of precast prestressed concrete beam-to-composite column joints with the bracket connection was experimentally and analytically investigated. Cyclic loading tests were conducted on four full-scale specimens with different beam lap lengths and load transfer details. For the specimens with a longer beam lap length, the bracket connection successfully transferred the beam flexural strength to the column with the connection barely damaged. The governing failure mode was beam flexural yield occurring at the bracket end. However, for the specimen with a shorter beam lap length, relative slips at the interfaces of the beam and bracket occurred and thus the strength was governed by the bracket connection. Excellent ductility satisfying the acceptance limit of special moment frame in AISC 341 was achieved in all specimens. The load transfer at the bracket connection through concrete shear keys and other details were further investigated through finite element analysis. Design models to predict the connection strength were proposed and the validity of the models was verified through comparisons with the tests and analyses.