Axial Compressive Behavior of Through-Beam Connections between Concrete-Filled Steel Tubular Columns and Reinforced Concrete Beams

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Abstract
This paper investigates the axial compressive behavior of a through-beam connection between concrete-filled steel tubular (CFST) columns and reinforced concrete (RC) beams. In this connection system, the steel tube is completely curtailed at the corresponding beam location, with the longitudinal steel reinforcing bars for the beam remaining continuous through the connection region. A strengthening ring beam is used to enlarge the connection zone in order to compensate for the possible decrease of the axial load-carrying capacity as a result of the discontinuity of the steel tube that encases the column. Two series of axial compressive tests on 32 beam-column specimens are reported. The first series of tests, including 5 full-scale connection specimens with CFST columns, show that with proper design, the axial load-carrying capacity of the connection can be higher than that of the CFST column. The feasibility of this type of connection is verified. The second series of tests, including 27 specimens with only the connection zone, evaluate the ultimate strength of the connection. It is shown that the height and the area ratio of the reinforcement in the ring beam have significant influence on the axial load-carrying capacity of the connection zone. Taking into consideration the confinement produced by multiple layers of ring bars and the effect of local compression, a formula for predicting the ultimate axial compressive strength of this connection is proposed. The accuracy of the proposed formula is validated through comparisons of the theoretical and experimental results.
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