Experimental Study on Shear and Flexural Performance of Section Steel Plug-In Composite Joint for Prestressed Centrifugal Concrete Hollow Square Piles

Prestressed centrifugal concrete hollow square piles often require on-site splicing, and the structural reliability of the pile connection largely governs the performance of the assembled pile. To address the limitations of conventional welded and mechanical joints, a section steel plug-in composite joint combining central grouted steel tube anchorage and peripheral end-plate welding was developed and experimentally evaluated. Flexural and shear tests were conducted on 12 full-scale specimens, including pile shaft specimens and joint specimens with cross-sectional side lengths of 400, 500, and 600 mm. The flexural and shear behavior of the jointed specimens was assessed in terms of bearing capacity, load–deflection response, crack development, and failure mode by comparison with the corresponding pile shafts. Under flexural loading, the pile shaft specimens mainly failed by fracture of prestressing steel bars at midspan, whereas the joint specimens failed near the loading point by prestressing steel fracture, indicating that the critical failure region shifted away from the joint core. The flexural capacities of the joint specimens reached about 92–97% of those of the corresponding pile shafts. Under shear loading, both pile shaft and joint specimens mainly exhibited diagonal compression failure in the flexural–shear region, while no obvious damage was observed in the joint core region. The shear capacities of the joint specimens were about 103–130% of those of the corresponding pile shafts. These results indicate that the proposed section steel plug-in composite joint can effectively maintain flexural resistance while enhancing shear performance. The central steel tube, hardened grout, anchorage reinforcement, and peripheral welds jointly contributed to the integrity and force transfer capacity of the connection, showing favorable potential for engineering application in prestressed centrifugal concrete hollow square pile splicing.