Experimental and analytical investigation on precast concrete-encased concrete-filled steel tube column-to-column dry connections under axial tension

Precast technologies featuring rapid construction and reduced on-site manpower have been gaining widespread adoption in the construction industry, particularly in reinforced concrete (RC) structures and composite steel–concrete structures over the past few decades, due to rising labour cost. However, to date, no workable precast connections have been developed for concrete-encased concrete-filled steel tube (CECFST) columns, which are increasingly used in ultra high-rise buildings and large-span bridges owing to its superior structural performance and excellent fire resistance. In this regard, to promote applications of CECFST columns in countries with increasing labour cost, this study develops two innovative precast CECFST column-to-column dry connections (PCDCs), through which the construction of CECFST structures would minimise heavy on-site work, such as welding or grouting of joints, formwork, and propping systems. Ten laboratory tests including four component tests and six column-to-column connection tests, were conducted to investigate tensile performance of the developed PCDCs. Key test results of all the ten specimens, such as load versus deformation relationships and failure modes, showed that the PCDCs had excellent tensile resistance and ductility. Furthermore, this paper carried out a series of theoretical analyses to quantify the ductility and tensile strength of the PCDCs through proposed load transfer mechanisms and component-based models. The design method of the PCDCs was presented by a simple flowchart and a worked example. With excellent structural performance, the PCDCs developed in this paper demonstrated huge potential to replace conventional cast-in-place (CIP) connections of CECFST columns.