First, the scaffolding industry is undergoing a “material revolution.”
The phasing out of traditional scaffolding is accelerating: modular scaffolding is being explicitly banned, leading to a surge in the market share of modular scaffolding. Material compliance has become a strict requirement: the configuration of Q355B for uprights, Q235 for horizontal bars, and Q195 for diagonal braces has become an “entry ticket,” requiring material suppliers to upgrade accordingly.
Second, Material Classification: Not “Differentiation,” but Scientific Proportioning
1. Mechanical Roles of the Three Core Components
(1) The upright’s load-bearing characteristic is vertical compression (main load-bearing), requiring Q355B material, with high-strength compressive strength and a yield strength ≥355MPa.
(2) The horizontal bar’s load-bearing characteristic is horizontal tensile strength (connection stability), requiring Q235 material, with superior comprehensive performance and high welding strength.
(3) The diagonal bar’s load-bearing characteristic is shear support (auxiliary stability), requiring Q195 material, prioritizing economic efficiency and meeting auxiliary requirements.
Q355B (formerly Q345): Low-alloy high-strength steel, containing manganese, silicon, etc., improving strength while maintaining toughness, -20℃ low-temperature impact energy ≥34J (Grade B requirement).
Q235: An “all-rounder” among carbon structural steels, with a carbon content of 0.12%-0.20%, balancing strength and weldability.
Q195: Low-carbon steel (carbon content ≤0.12%), good plasticity but low strength, suitable for non-main load-bearing components.
Third, why must Q355B be used for uprights?
1. Ultimate bearing capacity test (verified by JGJ231-2010 standard)
Type B upright group (4 poles): Ultimate bearing capacity 396.3kN → 99.1kN per pole (≈10.1 tons)
Type Z heavy-duty upright group (4 poles): Ultimate bearing capacity 546.0kN → 136.5kN per pole (≈13.9 tons)
Key parameter calculation:
Stability coefficient φ: reflects the relationship between slenderness ratio and material strength
Type B upright φ=0.350 (calculated length l₀=1910mm)
Type Z upright φ=0.516 (thickened pipe wall design)
Safety redundancy: The experimental value exceeds the design value by more than 2 times, meeting the safety factor requirements of GB 51210.
2. What happens if the material is downgraded?
Assuming the uprights are replaced with Q235, the yield strength decreases by 34% (355→235MPa), the theoretical load-bearing capacity decreases to approximately 65kN, failing to meet the requirements of JG/T 503 standard, and the risk of scaffold collapse increases dramatically.
Fourth, 3 practical suggestions for building materials practitioners:
(1) Procurement pitfall avoidance guide:
Require suppliers to provide steel material specifications + third-party testing reports, focusing on verifying the C, Si, and Mn content and impact energy of Q355B.
Beware of “inferior quality”: Some manufacturers use galvanized Q235 steel pipes to impersonate Q355B (this can be identified through spectral detection).
(2) Engineering selection strategy:
Conventional building construction: Type B uprights (Φ48×3.2mm) meet the design value of 47.6kN.
Bridges/heavy-duty factories: Prioritize Type Z uprights (Φ60×3.2mm), with a load-bearing capacity of 88.9kN.
(3) Cost optimization direction:
Q195 steel can be used for diagonal braces and connectors, reducing the total steel cost by 20%-30%.
Avoid the misconception of “using only high-strength steel”—scientific grading is necessary to balance safety and efficiency.
Post time: Dec-11-2025