ISO 3545-2:1989

Overview

ISO 3545-2:1989, “Steel tubes and fittings - Symbols for use in specifications - Part 2: Square and rectangular hollow sections,” standardizes the most commonly used symbols and terminology for square and rectangular steel hollow sections. Its purpose is to facilitate clear, consistent specifications and technical communication in standards, drawings and product documentation. The document includes five illustrative figures that show the meaning of the defined symbols.

Key Topics and Requirements

• Symbol definitions for geometric and mechanical properties, including:
  • Cross-sectional dimensions: B (side length or shorter side), H (longer side)
  • Wall thickness (T) and cross-sectional area (A)
  • Corner radii: ri (inner), ro (outer), rm (mean), rcalc (used for calculations), rmax (maximum permitted)
  • Section properties: moment of inertia (Ix, Iy), section modulus (Wx, Wy), radius of gyration (i, ix, iy)
  • Plastic properties: plastic modulus (Z, Zx, Zy)
  • Torsional constants: torsional inertia (J) and torsional modulus (c)
• Tolerances and geometric imperfections - symbols for squareness, concavity/convexity, and twist are referenced; for tolerance systems the standard refers to ISO 5252:1977.
• Illustrative figures (figures 1–5) that clarify symbol placement and interpretation for specification texts and drawings.
• Note: For square hollow sections many criteria are equal for x and y axes; the standard indicates this where applicable.

Applications

ISO 3545-2 is practical for:

• Standards committees and writers creating product or test standards that reference square/rectangular hollow sections.
• Structural, mechanical and civil engineers specifying section properties in calculations, structural models and design documentation.
• Manufacturers and fabricators preparing datasheets, production drawings and quality control documentation.
• Procurement and inspection teams ensuring unambiguous ordering, acceptance criteria and conformity assessment.
• Software developers implementing CAD/CAM libraries or structural analysis tools that need consistent symbol sets for properties and drawing annotations.

Using ISO 3545-2 reduces misinterpretation in specifications, speeds communication between suppliers and users, and supports consistent reporting of section properties in technical documents and software.

Related Standards

• ISO 3545 (series): other parts cover circular cross-sections and fittings (e.g., parts for circular tubes and tubular fittings).
• ISO 5252:1977 - Steel tubes: Tolerance systems (referenced for tolerance symbols).