Abstract: To address the low construction efficiency of existing prefabricated underground stations, the authors propose a column-supported, two-story, two-span assembled rectangular frame structure that utilizes steel-to-sleeve connections with overflowed grout technology. The structure comprises single-sided composite sidewalls, a cast-in-place bottom slab, prefabricated middle slabs, composite top slabs, and prefabricated concrete columns. The longitudinal reinforcement of the sidewalls employs steel-to-sleeve connections with overflowed grout. Meanwhile, the reinforcements of the prefabricated columns on the upper and lower floors use sleeve connections and are bolted to the bottom slab. A three-dimensional solid finite element model of the underground station was developed using a finite element modeling approach. This model accurately represents the characteristics of the prefabricated components and rebar connections. Through pushover analysis, the authors examine how the presence of embedment depth of longitudinal reinforcement extending from the middle and top prefabricated slabs into the sides of the longitudinal beams affects the mechanical performance of the prefabricated underground station. The obtained results are compared with those of a traditional cast-in-place structure. The analysis yields the following findings: (1) The prefabricated and cast-in-place underground stations exhibit a mixed hinge failure mode, with plastic hinges initially appearing at the ends of the middle columns. The load-displacement curve can be divided into four stages: elastic, yield, peak, and ultimate. (2) At a burial depth of 3 m, the overall lateral stiffness of the prefabricated structure, without extended reinforcement at the longitudinal beam sides of the middle and top slabs, is 4.2% lower than that of the structure with extended reinforcement. However, the presence of extended reinforcement has minimal effect on the peak load-bearing capacity and ductility of the prefabricated structure, with differences of <4%. Furthermore, the differences in peak load-bearing capacity and ductility between the prefabricated and cast-in-place stations are <6%. (3) At a burial depth of 10 m, the differences in load-bearing capacity, ductility, and stiffness between the prefabricated and cast-in-place structures are <7%. Compared to the structure at a 3 m depth, the structure at a 10-m depth exhibits increases of 10.5%－12.7% in load-bearing capacity and 31.8%－46.3% in stiffness, but a decrease of 14.5%－18.7% in ductility. Overall, the proposed prefabricated underground station structure with columns demonstrates favorable mechanical performance. The extension of longitudinal reinforcement from the middle and top slabs into the longitudinal beam sides has limited impact on the overall structural behavior.

Key words: prefabricated column-supported underground station, steel-to-sleeve connection with overflowed grout, integral structure, pushover analysis, finite element analysis, bearing capacity, displacement ductility