Experimental Research on Pre-Tension and Bearing Capacity of a New Type of Removable One-Sided Bolts

In order to assemble and disassemble steel members with closed-sections conveniently, a new type of detachable one-sided bolts was designed. This type of bolts mainly consists of a screw, a sleeve, a split spacer and a nut, and can be tightened in various ways. First of all, the pre-tension measurement and time-variation effect tests were conducted to study the pre-tension force. At the same time, the loss of pre-tension of the new bolt over time under different application sequences was also studied. And the applicable application methods were analyzed in the light of the actual situation. Then the load-displacement curves of bolted connections under shear and tensile loads were obtained by shear and tensile tests of single bolted connections. The force conditions and damage modes of single bolts under the two loads were analyzed, and the effects of different application sequences on the shear and tensile load capacities of bolted connections were investigated. Furthermore, the calculation method of tensile and shear bearing capacity of the new bolted connection was proposed based on the relevant codes and based on the test results. Finally, the bearing capacity of the new type of bolts was compared with that of different bolts in the relevant studies to assess the level of bearing capacity of the new type of bolts. The results showed that the maximum pre-tension relaxation of the bolts within 72 hours was 3.6%. It was recommended to use the screwing method where the sleeve was screwed first and then the screw (PB type), and the proportion of the torque applied first to the sleeve was more than 50%, which ensured that more than 60% of the pre-tensioning force was achieved. The method of application only affects the shear and tensile bearing capacity of the bolts in the case of friction-type connections, not in the case of compression-type connections. Split spacers played a controlling role in the forces on the bolted connection, the number of breaks in the split spacer under ultimate loads determined the damage mode in the shear model of the unilateral bolted connection, and the tensile bearing capacity depended on the shear cross-sectional area of the bolted split spacer. The shear and tensile ultimate bearing capacity obtained from the test matched well with the theoretical values obtained through the proposed bearing capacity calculation method, and the maximum error was within 11%, which proved that the bearing capacity calculation method possessed high accuracy. Compared with the same grade of one-sided bolts, the ultimate shear bearing capacity of frictional connection was similar, the ultimate shear bearing capacity of compressive connection was obviously superior, and the ultimate tensile bearing capacity of compressive connection was slightly lower.