Experimental Study on Force Transmission of Squeeze Bolt in the Anti-Pull Support of Nuclear Containment

The construction of AP/CAP series third-generation advanced nuclear power plants in China adopts an open-top construction method to facilitate equipment hoisting and ensure the continuity of equipment and module installation and construction in severe weather. The temporary opening and closing of the roof guarantee the smooth progress of the open roof construction. During the entire construction process of the nuclear power plant, three climbs are required. To be reusable in the same site, the temporary roof must be removable. At the same time, the top cover may encounter a 17-level typhoon, and the huge uplift force generated by the typhoon must be resisted by the uplift support of the top cover and the containment. Extrusion bolts are the key force transmission members in the anti-pull support. The anti-pull support is screwed into the extruded bolt supported by the vertical steel plate, so that the force transmission member and the containment are squeezed, thereby generating static friction to provide pull resistance. The extruded bolt in the antipull support is similar to the traditional clamping bolt. The bolt force is related to the relative roughness of each contact surface, bolt diameter, and bolt structure, but there is no relevant theory to determine the relationship between the tightening torque and the squeezing force of the bolt in the process of force transmission.
Given the above problems, this paper researched the force transmission of squeeze bolts. First, according to the different roughness of different force transmission members and contact surfaces, the friction block contact test, sleeve-friction block contact test, and flathead bolt contact test were designed to verify the necessity of setting friction block and the sleeve, and the improved method of spherical end bolt was proposed. Then, by adopting fixed torque electric wrench for staged loading, a method of directly establishing the relationship between electric wrench gear and bolt pressing force was obtained. Finally, based on the two sets of test results of the friction block and the sleeve being completely restrained and the spherical end bolts in direct contact with the containment, a method to improve the bolt force transmission was further proposed, and the dynamic friction coefficient between the friction block and the containment was obtained indirectly.
The following conclusions could be drawn. 1) The arrangement of friction block and sleeve minimized the damage of the anti-pull bearing to the containment during installation and use. When designing the bolt force transmission member, the spherical end bolt needed to be designed as the ellipsoid which was in approximate point contact with the socket groove and did not need to consider the influence of the thickness of the threaded hole on the force transmission of the bolt. 2) The directly established relationship between the gear position of the electric torque wrench and the extrusion force was useful for the engineering application of the electric torque wrench. 3) The obtained dynamic friction coefficient between the friction block and the simulated containment could provide a reference for the determination of the anti-pull resistance of the anti-pull bearing.