Experimental Research on Residual Clamping Force of Friction High-Strength Bolt after Corrosion Loss Simulated by Wire Cutting

Abstract

Clamping force is crucial for resisting slip loads in friction-type high-strength bolted (FHSB) connections, and following corrosion, it diminishes due to sectional reduction of the nuts and/or bolt heads. Evaluating clamping force loss (CFL) in corroded FHSBs is essential for steel bridge inspection and maintenance. The cutting methods currently employed to simulate corrosion encounter challenges including limited shapes, low efficiency, and poor accuracy, leading to significant data dispersion in experiments and diminished reliability of evaluation models. Furthermore, existing evaluation models fail to fully consider the influence of factors such as corrosion shape, size, thread specifications, corrosion location, and initial clamping force (ICF) on clamping force. Hence, this research proposed a novel wire-cutting simulation corrosion method (WCSCM) and conducted experiments on 80 specimens. Based on experimental results, five clamping force evaluation models were systematically established for corrosion shapes including thickness uniform corrosion, height uniform corrosion, height and thickness corrosion, eccentric corrosion, and trapezoid corrosion, and their fitting accuracy was compared and analyzed. Furthermore, the impact of thread specifications, corrosion location, and ICF on clamping force was discussed. Finally, procedures for measuring field corrosion bolt dimensions and methods for approximating corrosion shapes were proposed, followed by validation of the evaluation model’s effectiveness through on-site bridge testing. The findings showed that the WCSCM accurately reproduced the corrosion shapes and sizes of the nuts and/or bolt heads, with regression equation coefficients exceeding 0.97, notably higher than those of existing models. The CFL resulting from various corrosion shapes and sizes exhibited variation, indicating the necessity for distinct models tailored to each corrosion damage pattern of the nuts and/or bolt heads. The impact of thickness uniform corrosion on clamping force primarily correlated with ICF, with less influence from thread specification or corrosion location. The proposed models were able to achieve an accuracy level within ±20%, providing a basis for replacing corroded bolts on steel bridges.