# Bending Behavior of Corroded H-Shaped Steel Beam in Underground Environment
## 1 Introduction  
Steel structures are extensively used owing to their high strength, good plasticity and toughness, ease of manufacturing, and short construction period [1]. H-shaped steel, angle steel, and channel steel are common steel products that are widely used in many engineering fields, such as civil engineering, coal mining, and petrochemical and oil refining [2; 3; 4; 5]. However, these steel products are unavoidably corroded by the environment during use [6; 7; 8; 9]. Hence, the mechanical performance of steel, including the yield stress, tensile strength, and elongation, degrades as a result of corrosion [10; 11; 12; 13; 14; 15; 16]. The bearing capacity of steel beams or steel columns also degrades as a result of corrosion. Therefore, evaluating the residual bearing capacity and elucidating the laws governing the degradation caused by the corrosion of steel structures is very important for safety appraisal. Various studies have investigated the mechanical properties of rusted steel. [PERSON] et al. [17] investigated the mechanical properties of steel corroded in a neutral salt spray environment. They found that the strength and elongation of the corroded steel showed an obvious linear degradation trend when the mass loss ratio beyond 4%. [PERSON] et al. [18] studied the mechanical properties of steel corroded in a real marine environment. The results show that the yield strength and ultimate strength of corroded steel decrease nonlinearly with the increase in volume loss rate (quadratic polynomial relationship). [PERSON] et al. [10] investigated the effect of pits size on the mechanical properties of steel. They used a method of mechanical drilling to make pits and found that the strength and ductility of the corroded steel decreased significantly with the depth and density of corrosionpit increasing. [PERSON] et al. [19] studied the relationship between surface morphology and mechanical properties of corroded steel and established a mode to assess the mechanical properties corroded steel. There are also some studies to investigate the bearing capacity of corroded steel members. [PERSON] and [PERSON] [20; 21; 22] investigated the law governing the degradation of the bearing capacity of H-shaped steel beams corroded in a marine environment. They reported that the failure modes and bearing capacity of H-shaped steel members were affected significantly by the distribution and size of etch pits. [PERSON] et al. [23; 24] and [PERSON] et al. [25; 26] investigated steel bridges in inland cities and reported that the majority of steel beams were partially corroded at the supports and most severely corroded at the webs and stiffeners. They thought the plate thickness was an important factor affecting the mechanical behavior of H-shaped steel beams after corrosion. Therefore, they investigated the effect of corrosion on steel members through a way to reduce the thickness of flange and web. [PERSON] et al. [27] investigated the ultimate bending moment of a severely corroded box girder through a series of nonlinear finite element analysis. The results showed that the stress-strain relationship was also a significate factor affecting the flexural performance of the box girder besides the residual thickness. Based on the above-mentioned studies, it is concluded that the corrosion morphology, residual thickness, and corrosion part, which are closely related to the corrosive environment, are the main factors affecting the residual bearing capacity of steel members. However, existing research has rarely considered the underground environment of coal mining operations. In China, H-shaped steel beams are often used as support in coal mining tunnels. Because of the harshness of underground environment in coal mine [28], the H-shaped steel beams are seriously corroded. It is worth thinking about how rusty the H-beam should be before being replaced, because the corrosion degree and replacement frequency have great influence on safety and cost.