SEVERAL CONSIDERATIONS ON HIGH STRENGTH BOLTED JOINTS TREATED WITH ZINC-RICH PAINT UNDER 15%-ADDITIONAL BOLT AXIAL FORCE

Abstract

 Friction type of high strength bolted joint treated with thick-type inorganic zinc-rich paint shows so large bolt axial force loss by relaxation that the bolt axial force often drops below the design axial force. One of the authors showed that safety and reliability of this type of joint can be improved by tightening the bolts under 15%-additional bolt axial force. However, the applicability of the proposed tightening method was verified with only the standard type specimens with 22mm main plate thickness. In addition, the proposed tightening method cannot be directly applied to the joints using torque-shear bolts. The purpose of this study is to evaluate the applicability of the proposed tightening method to the joints with thick main plates up to 75 mm and the joints using torque-shear bolts. In this study, bolt relaxation tests and slip tests were carried out with the specimens with thick plates. As a result, the characteristics of bolt axial force and slip coefficient of the joints were clarified. Based on the results, the applicability of the tightening method was verified for the joints with extremely thick plates. Furthermore, a new bolt-tightening method, in which the final tightening of the bolts is executed 24 hours after the temporary tightening, was proposed for the joints using torque-shear bolts.