In the design and construction of high-strength bolt friction joints, an axial force reduction due to relaxation is known to occur. This reduction has been supplemented by tightening the bolts with an introduced axial force that is 10% higher than the design axial force. In this study, we focused on the residual axial force of frictional joints of high-strength bolts, and the extracted high-strength bolts from four steel bridges in service considering different bridge types, bolt types, and joint surface treatments to determine whether the residual axial force was maintained as designed. The results of the investigation showed that the residual axial forces from the four bridges were lower than the design values except for some.
