Seismic behavior and failure modes analysis of lapping-connection between CFRST-columns and RC-beams

A novel developed lapping connection between concrete-filled rectangular steel tubular (CFRST) columns and reinforced concrete (RC) beams was introduced in this paper. In this new connection system, the longitudinal reinforcements of RC beams were interrupted so the steel tubular column can be continuous in the joint zone. The longitudinal reinforcements were lapped with the steel brackets, which were welded with the steel tubular column, to effectively transfer the moments and shear forces and reduce welding operation on site. The seismic performance of this newly connection was investigated through combination of theoretical research, experimental tests and finite element model analysis. Design methods of each part of the connection were proposed. Moreover, four beam-column connection specimens were tested under combined constant axial compression and cyclic loading. Based on the experimental results, the failure modes, hysteretic response, skeletal curve and ductility were discussed. The connection demonstrated favorable seismic performance in the tests and the capacity of connection characterized as beam bending failure mode was consistent with the theoretical results. A finite element model was developed and validated by a comparison with experimental results. The relative effects of the beam-column strength ratio kM on failure modes of the joints were conducted. Three typical failure modes which were beam bending failure mode, bending-shear mixed failure mode and joint shear failure mode as well as the discriminant kMD between different failure modes were determined. Theoretical results well agreed with the analytical results under joint shear failure mode, and bending failure mode with relatively inferior kM. [Display omitted] •A new type of lapping connection between CFRST column and RC beam is put forward.•The seismic performance including the failure mode, hysteretic response, and ductility of this connection is discussed.•A sophisticated FE model was established and validated to study the mechanical properties of this new type of connection.•Three failure modes and corresponding design methods are given based on experimental, numerical and theoretical analysis.