Study on the degradation of axial tensile performance of corroded bolts in steel bridges

As crucial connecting components in steel bridge structures, high-strength bolts are susceptible to corrosion from environmental factors such as corrosive agents in the air and rain during long-term service. This corrosion can reduce their load-bearing capacity, thereby threatening the safety of the entire structure. Most studies assess the degree of corrosion through mass loss, but lack a comprehensive quantitative analysis of its impact on mechanical performance. This study investigates the axial tensile performance degradation of corroded bolts based on fractal characteristics of the corroded surface and tensile mechanical performance experiments. By analyzing the fractal dimensions of corroded surfaces, which ranged between 2.026 and 2.053 for more severely damaged threads, a strong correlation was established between surface corrosion and tensile performance degradation. Bolts were classified into three categories based on fractal dimension, which quantitatively reflected the degradation of bolt tensile performance. finding that the ultimate tensile strength and load-bearing capacity decreased by 2.5–6.8 % and 1.25–5.5 %, respectively. Notably, the load at 75 % displacement dropped from 390 kN to 340 kN, a reduction of over 15 %.Finite Element Method (FEM) was used to simulate the bolt tensile process, and experimental data were used to fit damage-plastic constitutive models for bolts with different corrosion levels. The Void Growth Model (VGM) fracture criterion was employed to simulate bolt tensile fracture, predicting the axial tensile performance degradation of bolts with varying corrosion levels, and established a correction formula to quantify the impact of fractal dimension on the ultimate tensile strength of corroded bolts.This study provides a new approach for assessing corrosion impact and predicting the axial tensile performance of bolts in service.