Hollow Structural Section (HSS) is a type of steel with a hollow cross-section, typically used in construction, machinery manufacturing, and engineering structures. The cross-section of hollow structural sections can be square, rectangular, circular, or elliptical, with square tubes, rectangular tubes, and circular tubes being the most common. Due to its hollow nature, HSS can maintain high strength while effectively reducing weight, making it an ideal choice for lightweight structures. Today, we will mainly discuss square and rectangular tubes.