Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
In the field of steel structures, steel grades serve as the “identity cards” of steel materials, functioning as specific symbols or codes used to precisely identify the type and performance characteristics of steel. Through a clever combination of letters and numbers, they comprehensively present key information such as the steel’s type, chemical composition, performance features, and intended applications. This greatly facilitates the rapid identification and appropriate selection of steel materials during production, design, and application processes.
Steel Grade Composition Rules
Steel grades follow a rigorous and standardized composition structure, typically consisting of the yield strength letter (Q) + yield strength value + quality grade (A/B/C/D/E) + deoxidation method (F, Z, TZ, usually optional).
Taking the common Q235B as an example: “Q” denotes yield strength, ‘235’ represents the yield strength value in MPa, “B” indicates quality grade, and the deoxidation method is omitted in this designation, defaulting to killed steel (Z) per standard.
Standard Requirements
Recommended steel grades for common applications are based on the “Steel Structure Design Code.” In steel structure design, the following grades should be prioritized: Q235, Q345, Q355, Q390, Q420, Q460, and Q345GJ. Among these, GJ denotes a specific designation for high-rise construction steel. This grade is specifically engineered for high-rise structural applications, offering superior strength, toughness, and weldability to better meet the structural safety requirements of tall buildings under complex loading conditions.
The quality grades of steel (A, B, C, D, E) primarily relate to the regional environmental conditions and production processes. It is important to clarify that the quality grade itself does not directly influence structural design. Structural design is primarily based on the strength values preceding the grades (e.g., Q235, Q345) to determine the dimensions, shape, and load-bearing capacity of structural members.
Typical Application Scenarios
National Stadium (Bird’s Nest)
The National Stadium (Bird’s Nest), as a globally renowned landmark, features a steel structure design that is both highly challenging and innovative. The project utilized approximately 48,000 tons of steel. For material selection, about 80% (plate thickness t < 34mm) employed Q345D grade steel, which offers excellent strength and toughness to meet the mechanical performance requirements of the Bird’s Nest’s complex spatial structure under various loads. The remaining 20% (t ≥ 34mm) utilized Q345GJ high-performance structural steel, whose superior properties provided reliable structural support for this large-scale public building. Additionally, 700 tons (column tops) employed 110mm-thick Q460E grade steel plates. This marks China’s first application of 460MPa high-strength, high-performance thick plates in construction engineering, demonstrating a technological breakthrough in the application of steel structural materials.
National Stadium
The steel roof structure of the National Stadium employs a single-curved, double-curved tension (prestressed) truss system. This unique structural form imposes stringent requirements on the performance of the steel materials. The upper chords of the steel roof truss utilize seamless steel pipes, while the lower chords employ rectangular steel pipes, both fabricated from Q345C steel. Q345C steel possesses excellent weldability and mechanical properties, ensuring the steel roof structure maintains stable performance under prestressing and when subjected to various loads.
National Centre for the Performing Arts
The shell structure of the National Centre for the Performing Arts is a semi-ellipsoid, with its steel structure project utilizing approximately 6,800 tons of steel. The primary material is Q345D grade steel. The strength and toughness of Q345D grade steel meet the mechanical requirements for the large-span, complex curved surface structure of the theatre shell. Additionally, its excellent weldability and workability facilitate the fabrication and installation of the shell’s steel structure.
