# Study on the Load-Bearing Behavior of Underground Steel Structures with Pitting Corrosion Damage
## 3 Design of Simulated Pitting Damage Tests  
### Specimens with Prefabricated Pitting  
In order to study the influence of pitting corrosion on the bearing performance of steel structures, the I-steel samples with prefabricated pitting corrosion are taken as the research object in this paper. To enhance experimental operability and ensure result reproducibility, the research emphasis is placed on four representative patterns of pitting  
Figure 1: Random distribution pitting model.  
corrosion distribution. At present, the intersection of pitting corrosion pits has not been incorporated into the research scope. Considering that each member in the steel structure mainly bears tension, compression, and bending deformation, axial compression and three-point bending tests are carried out on the I-steel samples with prefabricated pitting damage of different distribution types. The effects of pitting defect types on the failure mode, bearing capacity, and deformation capacity of I-steel members are analyzed. Under realistic working conditions, the natural corrosion process typically requires a span of 10 years or even longer to form a hemispherical pitting defect with a diameter of 4 mm. Conventional corrosion methods pose challenges in obtaining an ideal test sample within a short time frame. Consequently, in this paper, a precision mechanical processing approach is employed. A 4 mm drill bit is utilized on a CNC horizontal boring machine to fabricate pitting defects. By accurately setting the cutting time to 0.4 s, the sizes of the machined pits can be guaranteed to exhibit a high degree of consistency. During the drilling operation, low cutting parameters (a spindle speed of 100 r/min and a feed rate of 0.05 mm/r) are adopted. This effectively maintains the temperature in the processing area within a relatively low range of 200 \({}^{\circ}\)C-300 \({}^{\circ}\)C, thereby avoiding the occurrence of work hardening. Moreover, the microstructure of the steel remains relatively unchanged, minimizing the interference of the processing method on the mechanical properties of the steel and providing reliable defect samples for subsequent research on load-bearing performance.  
Due to the obvious aggregation phenomenon of pitting in actual service steel structures [22], when establishing the random pitting model in this paper, the pitting area was first evenly divided into several small square areas, and three specific square areas were selected to randomly generate pitting pits in the square area. In this paper, the influence of pitting corrosion of four distribution modes on the bearing capacity of the steel structure, as shown in Figure 2 (The black dots represent prefabricated pitting damage), will be analyzed. In this paper, the prefabricated pitting sample in the simulated pitting damage test is based on the hemispherical pitting model with a radius of 4 mm, and a random position pitting model is generated. The specific distribution mode is shown in Figure 2, which is divided into four defect types: a horizontal row, vertical row, triangular row, and inclined row.