Shear performance and design of detachable single-nut embedded bolts considering the in-hole installation position

This study investigates the shear performance and design method of single-nut embedded bolts (SNEBs), a detachable shear connector for prefabricated steel-concrete composite structures, with emphasis on the in-hole installation position of the bolt shank. Push-out tests were conducted to compare SNEBs and welded studs, and validated finite element models were developed to examine the effects of SNEB diameter, hole diameter, pretension force, concrete type, and in-hole bolt position. The results show that SNEB-connected specimens exhibited a four-stage load-slip response, including friction, slipping, bearing, and failure stages. The hole diameter governed the slip range before bolt-hole contact, while pretension mainly affected the initial slip resistance. Increasing SNEB diameter improved shear resistance and bearing-stage stiffness, but larger-diameter SNEBs in NC slabs could not fully mobilize bolt shear capacity because local concrete crushing became dominant. The in-hole bolt position controlled the bolt-hole contact sequence, causing asynchronous engagement, irregular load-slip curves, and shear capacity reductions of up to 26%. The same position-controlled curve patterns were observed for 8, 16, 20, and 24 mm SNEBs. A design method was proposed by considering both bolt-controlled and concrete-controlled resistances, with the ultimate resistance taken as the smaller value. Bolt-position and group-effect reduction factors were further introduced, providing a practical design approach for SNEB connectors considering installation tolerance.