Residual Clamping Force Assessment of Friction Type High-Strength Bolt in Steel Bridges

Firstly, nine high-strength bolted gusset plates with different degrees of corrosion are selected from the upstream and downstream box girders of the steel bridge. Three corrosion nuts are selected for each gusset plate, Each corrosion nut is measured three times and the average value of its residual thickness is taken. Then, according to the empirical formula of equivalent radius and residual clamping force obtained from manual cutting nut test, the collected residual thickness of nuts is substituted into the formula to obtain the residual clamping force of 27 corroded nuts and high-strength bolts. The results show that: (1) the nuts outside the measured bolt box are seriously corroded, the bolt head in the box is not corroded, and the nuts are exposed to the outside all year round; (2) The measured residual radius loss ratio of corroded nut is 60%, and the maximum clamping force loss ratio of high-strength bolt is 59.62%; (3) The bolts of upstream GSW1 are seriously rusted compared with downstream GSW2, and the loss of effective clamping force is greater, which is related to the perennial wind direction; (4) When the residual radius loss ratio is more than 36.11%, and the clamping force loss ratio is more than 20%, it can be considered to replace the bolts with serious corrosion.