Seismic behavior of full-scale precast assembly frame joints of special-shaped columns

The utilization of precast reinforced concrete frames is widespread in the construction industry. However, among all components of the frame structure, the joint is considered the most vulnerable and critical during horizontal seismic activity. This study aims to investigate the seismic performance of the joints of an I-shaped assembled monolithic column, a T-shaped assembled monolithic column and a T-shaped fully precast assembly column. This investigation studies the failure mode, crack pattern, strain curve, load-displacement curves, characteristic point and ductility, load-bearing and deformation capacity, strength and stiffness degradation, and energy dissipation capacity of the joints. The findings reveal that the I-shaped column frame joint experiences shear failure, while the T-shaped column frame joint fails at the ends of the beams. Stiffness degradation of column frame joints with the same cross-section is found to be similar. The assembled monolithic beam-column joint displays significant vertical interface cracking after prefabrication and casting, with a gradual decrease observed in the skeleton curve. In contrast, the T-shaped fully precast assembly column frame joint shows weak plastic deformation capacity at the beam hinges, leading to significant angle slip during bending failure and a severe pinching phenomenon in the hysteresis curve. Furthermore, the T-shaped column flange, compared to the Ishaped column section, increases the joint height and substantially enhances its shear bearing capacity, albeit at the expense of weakened bending bearing deformation capacity. This study develops an assembly connection method suitable for the special-shaped precast column-frame structural system.