The processing of steel pipes generally falls into two categories — cold forming and hot processing — depending on whether the product is manufactured as a seamless pipe or a straight-seam pipe.
Based on these two primary manufacturing routes — cold-formed straight-seam pipes and hot-processed seamless pipes — the structural behavior and dimensional accuracy of steel tubes can vary significantly. In practical structural applications, designers therefore need a tubular section that offers consistent geometry, predictable mechanical performance, and reliable connection behavior. Circular Hollow Section (CHS) steel members meet these requirements effectively and are widely adopted in space frames, truss systems, and other load-bearing steel structures where uniform stress distribution and efficient node detailing are critical.
Section Requirements
For round steel pipes, the ratio of outer diameter to wall thickness must not exceed 100 (235/fy). The diameter–thickness ratio must meet the specified limits for both compression and bending members, with compression and bending components required to satisfy at least the S2 classification. In addition, slenderness ratios must remain within code limits: compression members may not exceed a slenderness ratio of 150, while tension members must remain below 400.
Coherent Node Requirements
- The main pipe’s external diameter must be equal to or larger than that of the branch pipe, and its wall thickness may not be thinner. At the point of connection, the branch pipe must not protrude into the cavity of the main pipe.
- The angle between the axes of the main and branch pipes must not be less than 30°.
- Eccentric connections between the branch pipe and main pipe should be avoided when possible.
- Branch pipe ends must be cut using an automatic pipe-cutting machine. For branch pipes with a wall thickness under 6 mm, beveling is not required.
- The weld connecting the branch pipe and the main pipe must satisfy the requirements of Article 13.2.2 when lap joints are used. The weld must be continuous around the full circumference, forming a smooth transition. Acceptable welding methods include full-circumference fillet welds or a combination of butt welds and fillet welds. When the angle between the branch and main pipe walls is 120° or greater, butt welding or beveled fillet welding is recommended. Fillet weld throat thickness must not exceed twice the branch pipe wall thickness. Lap-joint branch pipes may not be beveled, and the weld around the perimeter should equal twice the branch pipe wall thickness.
- The spacing between welds of adjacent branch pipes on the surface of the main pipe must not be less than the sum of the wall thicknesses of the two branch pipes.
Conclusion
In practice, achieving reliable performance from Circular Hollow Section steel members depends not only on sound design principles but also on precise fabrication, accurate cutting, and consistent welding quality at every node. From section proportion control to joint detailing and on-site execution, each step directly influences the structural safety and long-term durability of the system. Yunjoin focuses on providing engineered steel structure solutions with strict control over CHS member processing and connection quality, supporting designers and contractors with stable, standardized components that meet demanding structural and construction requirements.
