Research on the Mechanical Properties of Mechanically Connected Splices of Prestressing Screw Bars Under Monotonic and Cyclic Loads

The mechanical properties of screw-thread steel bars used for prestressing concrete and their threaded ribs’ bearing mechanism have not been quantitatively studied, in contrast to the extensive qualitative research on ordinary steel mechanical connection splices. A quantitative investigation was conducted under various design parameters and working conditions to examine the mechanical connection splices of screw-thread steel bars used for prestressing concrete. The splices’ connection performance and their threaded ribs’ bearing mechanism were also examined. Analyzing the force on the threads of the splices under monotonic tensile loading allowed for the theoretical computation of the axial force coefficients for threaded ribs. The validated revised three-dimensional numerical model of splices is based on the findings of the theoretical calculations. Afterwards, rigorous numerical simulations of monotonic tensile loading, repeated tensile and compressive loading with high stress, and repeated tensile and compressive loading with large strain were performed on 45 splices with varying nominal rebar diameters, coupler outer diameters and lengths, and thread rib spacings. The results show that rebar pullout and rebar fracture are the two main ways in which splices might fail. After cyclic loading, the splices’ ultimate bearing capacity changed by 0.83% to 2.81%, and their ductility changed by 2.13% to 4.75% compared to after monotonic tensile loading. Although the splice load-carrying capacity and plastic deformation capacity were reduced by 2.11%~7.48% and 3.98%~25.78%, respectively, when the thread rib spacing was increased from the specified value to 0.6~0.8 times the nominal diameter of the rebar, the splice connection performance was still able to meet the requirements for class I splices. Approximately half of the splices’ load-bearing capability is provided by the 1–2 turns of threads close to the coupler ends; after cyclic loading, their stress rises by between 4.52% and 12.63% relative to monotonic tension. Stresses in all threaded ribs of the splices are increased by 5.49% to 27.76% as the distance between the threaded ribs increases to 1.0 and 1.2 times the nominal diameter of the rebar, which reduces the splice’s load-bearing capacity.