New connection system for circular tubed reinforced concrete columns and steel beams

A new connection system for circular tubed reinforced concrete (TRC) columns and steel beams is proposed, where crossing diaphragms are introduced to withstand the moment at beam ends and interior diaphragms are added to withstand the shear at the interfaces between beam and joint. Interior diaphragms are more convenient for placement of curtain walls and architecturally desirable. The joint tube is used to improve the joint strength and the holes through the interior diaphragms are pre-drilled at the locations where the longitudinal reinforcing steel bars in column pass through. This relatively new configuration represents a diaphragm-through connection between circular TRC column and steel beam. In this study, the quasi-static reversed cyclic loading test was performed on five one-third scaled specimens and the feasibility of proposed connection was verified. A finite element model was then developed and validated with the experimental results, where the peak lateral load was accurately obtained. Furthermore, a shear-resistance model for the connections is suggested, from which theoretical formulas for predicting the shear resistance of connection are established.