ISO 16598:2015 - Timber structures - Structural classification for sawn timber
Overview
ISO 16598:2015 provides a basic international framework for establishing structural classes for sawn timber. It standardizes how timber populations (combinations of species, region and grade) are characterized for structural use by defining the primary and derived properties, methods for evaluating characteristic values, and rules for allocating timber to structural classes. The document is a template intended to harmonize approaches between regions - it does not supply final design values, adjustment factors, or cover durability or fire resistance.
Key technical topics and requirements
- Primary properties: Defines which structural properties are used to set class criteria:
- Bending strength (modulus of rupture) - characteristic at the 5th percentile with specified confidence (typical confidence cited: 75%).
- Bending stiffness (modulus of elasticity) - reported as mean and 5th percentile levels.
- Density - mean and 5th percentile values (small clear specimen testing is the typical basis).
- Testing basis:
- Full-size specimen testing is the preferred basis for bending or tension properties.
- Small clear specimens may be used only as an exception and must not be directly combined with full-size results without documented calibration.
- Derived properties: Established by standardized correlations to primary properties or by corroborative testing where needed.
- Class boundaries: Strength class intervals should be set at no less than 2 MPa.
- Allocation and normalization:
- A timber population qualifies for a class if characteristic values meet or exceed tabulated class values.
- Normalization of characteristic values is permitted to account for documented differences in sampling, testing methods, and dispersion - ensuring consistent safety levels across classes.
- Reporting and annexes: Includes normative data references and informative annexes (A: data, B: example class table, C: commentary).
Practical applications and intended users
ISO 16598:2015 is aimed at professionals and organizations involved in structural timber specification and standardization:
- Structural engineers and designers specifying sawn timber for buildings and bridges
- National standards bodies and code committees harmonizing grading and design values
- Timber producers and grading organizations establishing marketing groups or grades
- Testing laboratories and researchers validating property relationships and calibration between small-clear and full-size testing
- Regulators and procurement bodies needing a consistent framework for timber class interchangeability
Related standards
- ISO 12122-1 & ISO 12122-2 - Determination of characteristic values for timber (basic requirements and sawn timber)
- ISO 13910 - Approaches for density evaluation (referenced for density testing methodology)
Keywords: ISO 16598:2015, structural classification, sawn timber, timber structures, characteristic values, primary properties, derived properties, grading, design values, timber population.
