A basic study on the evaluation of residual axial force of high strength bolts for steel bridges constructed in the same environment at different ages

Abstract

JIS 1186 on high strength bolts for friction joint was enacted in 1964 and thereafter, high strength bolts rapidly replaced the conventional rivets in steel bridges. This paper focuses on the residual axial force, although the slip coefficient of the joint surface and the bolt axial force are the two major factors that determine the bearing capacity of a high-strength bolt friction joint, a typical joining method for steel bridges. In the design and construction of high-strength bolt friction joints, it is known that there is an axial force reduction due to relaxation and it is believed that the bolts are tightened with an introduced axial force that is +10% greater than the design axial force to compensate for this reduction. There have been many studies on the aging of bridges, however most of them were conducted using specimens under well-controlled conditions, hence there have been few studies on bridges in service. Therefore, in this study, the specifications of high strength bolts of different types and the friction surface treatment of the connection were different. According to the construction age, high strength bolts were extracted from two in-service two way steel bridges subjected to live loads, temperature changes, and environmental effects under the same environment and bridge type to ascertain whether the residual axial forces of the two bridges were maintained according to the design specifications.As a result of the investigation, it was found that the residual axial forces of the two bridges were almost all below the design values, except for a few. This decrease in axial force can be attributed; to the influence of the management of the tightening force at the time of construction, the structural type, the bolt type, the friction joint surface treatment, etc.