Seismic Behavior of Bolted Connections and Energy-Dissipated Connections for Concrete-Filled Steel Columns and H-Beams

Abstract

The structural system of steel beams and Concrete-Filled Tubular (CFT) columns has the characteristics of high strength, ductility, load bearing capacity and fast construction. However, the behavior of beam-to-column connections is so complicated that it is not widely applied in practice. For the beam-to-column connection of this structural system, this study developed two detailed design methods, which are bolted connection and pre-stressed energy-dissipated connection. This study first established a series of mechanics theoretical models for these beam-to-column connections. Then a series of structural seismic-resistant tests was performed to verify the seismic resistance of these connections. The first topic of the study is “Seismic Behavior of Bolted Connections for CFT Columns and H-Beams”. Traditional beam-to-column connection was fully penetrating welded by backing bars on jobsites. This connection method usually produces voids between backing bar and column flange. When beam end is loaded, the voids will result in stress concentration, grow into column plate and tear the welding zone apart. Because of the weakness of welding zone, the beam-to-column connection failed before the strength and ductility of beam, column and panel zone were fully developed. In this paper, a new design of bolted beam-to-column connections for CFT is proposed. A mechanical model is established and a series of cyclic loading experiments have been conducted to verify it. The experimental results and theoretical results are very close, which demonstrates that the bolted connections have superior seismic resistance in stiffness, strength, ductility and energy dissipation mechanism. The second topic of the study is “Earthquake-resistant Behavior for Connections of Pre-stressed Steel Beams and CFT Columns with X-shaped Dampers”. The bolted beam-to-column connection design mentioned above have full hysteretic loops and advantages as high stiffness, strength, and good energy dissipation ability, but the moment-resistant structure will have residual displacement after an earthquake. Therefore, Pre-stressed structural system and energy-dissipated element concept were applied in the study. This study proposed a detail design which used X-shaped dampers as energy dissipation elements for pre-stressed steel beam and CFT column connection. The structural system is expected to retain self-centering ability after an earthquake since the X-shaped dampers are energy dissipation elements that can protect the major structural elements from damage. This study established mechanics models for this beam-to-column connection. A series of tests was performed to prove the seismic behavior of the connection. The experimental results showed that the beam-to-column connection not only can absorb most seismic energy through the X-shaped dampers, but also can be repaired fast and easily after earthquake. Besides, this study verified that the proposed beam-to-column connection has superior stiffness, strength, ductility, energy dissipation and self-centering ability. For the two design methods, the theoretical equations derived from beam-to-column connection mechanics model established in this study was proven realistic by experiments, so the equations and experimental results proposed in this study are worth referencing.