## 4 Analysis of Old Hanger Test Detection
### Comprehensive Evaluation and Analysis  
Special tests of the whole bridge hanger indicated that, after 15 years of operation, all 64 hangers had varying degrees of illness, particularly anchor head corrosion, water seepage, and anticorrosion grease aging. The JTG/T H21-2011 Standard for Evaluation of Technical Condition of Highway Bridges [20] classifies hanger component disease levels from light to heavy, with grade 1 being the lightest. As shown in Figure 19, 23.4% of the anchor head threads of all 64 hangers on the bridge have corrosion extending to the nut, where the oxide skin is partially peeled off or can be scraped off, and a few rust pits exist on the surface (the disease grade is 3); 48.4% of anchor heads have water seepage, 37.5% of which have serious water accumulation or excess water vapor, and the air is humid (disease level 3); 56.3% of anticorrosion grease has different degrees of aging, 43.8% of which show serious volatilization, large caking, and mildew.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Testing Items** &
\begin{tabular}{c} **Standard** \\ **Requirements [18]** \\ \end{tabular} & **Test Results (KJ/m2)** & **Single-Item Judgment** \\ \hline PE sheath & & 1 & 23 \\ impact strength & \(\geq\)50 KJ/m2 & 2 & 21 \\  & & 3 & 26 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The impact strength test results of PE sheath.  
Figure 19: Statistics of service life of hangers: (**a**) anchor head thread corrosion assessment results, (**b**) anchor head water penetration assessment results, and (**c**) preservation grease aging assessment results.  
Figure 18: Impact test schematic.  
In the old hanger test results, the hanger as a whole and the tensile mechanical properties of a single steel wire are not significantly weakened, but the single steel wire torsion resistance and galvanized layer of copper sulfate-resistant performance are significantly weakened and cannot meet the use requirements. The extensibility and impact resistance of PE sheath material decline with age, making it unsuitable for hanger steel-wire sealing and protection. After a complete inspection, bridge hanger illness is mostly caused by non-stress faults. The major cause is the natural environment's erosion, age, and a faulty original structure. Timely maintenance treatment is needed since these illnesses would reduce building durability and service life.  
According to a statistical analysis of tied-arch bridge-hanger replacement instances [23], a tiny portion of them are due to substantial damage from car contact or seismic stress, which compromises bridge safety. Most hangers are damaged by natural corrosion and traffic stresses, resulting in hanger steel-wire corrosion and fatigue fracture, anchor head corrosion and water buildup, and a decline in anchoring effectiveness. Figure 20 presents 86 example bridges, showing that hangers last 3-23 years, averaging 14 years. The hanger's service life is much shorter than the bridge's designed service life, with 44.2% lasing between 10 and 15 years, 19.8% between 15 and 20 years, and 18.8% over 20 years. This report describes a 15-year-old bridge whose hangers have outlasted comparable bridges. Given the bridge's construction, the hanger disease detection and mechanical properties obtained from comprehensive analysis test results suggest that seriously diseased hangers should be replaced as soon as possible to ensure bridge safety.