Overview
ISO 9087:1998 specifies a laboratory method to determine the nail and screw holding power in wood when the fastener is loaded axially (pull-out). The standard defines how to measure the maximum extraction force and how to express wood resistance as a specific resistance (force per unit penetration). It is published by ISO/TC 165 (Timber structures) and is widely used for evaluating fastener performance, quality control and comparative material characterization.
Key topics and technical requirements
- Principle: Measure the maximum axial force (Fmax) required to extract a nail or screw and calculate specific resistance s = Fmax / l (expressed in N/mm), where l is penetration depth.
- Apparatus: Accurate testing machine (load accuracy ±1%), axial extraction device, instruments for measuring nail/screw diameters (±0.1 mm) and linear dimensions (±1 mm), and moisture determination equipment per ISO 3130.
- Specimen preparation:
- Rectangular prism test pieces with dimensions as specified (or equivalent arrangement) to avoid splitting.
- Holes for screws drilled to allow hand insertion; hole diameter chosen to optimize screwing and extraction resistance.
- Nails/screws must be clean, undamaged and used only once; characteristics recorded in the test report.
- Procedure:
- Insert two nails or two screws in each of three grain directions (radial, tangential, along grain) per layout.
- Depth: nails two‑thirds of length (disregarding sharpened tip); screws at thread length (or two‑thirds threaded length when threaded up to head).
- Extract between 2 h and 3 h after insertion; extraction movement continuous and constant so extraction time is 1–2 minutes.
- Measure Fmax to ±1% and determine specimen moisture content after testing.
- Acceptance and calculation:
- Reject specimens with moisture content differing by more than 2% from the standardized value.
- Express specific resistance to 0.1 N/mm and report arithmetic means of paired determinations (note >10% discrepancies).
- Reporting: Includes sampling, specimen dimensions, moisture/density, fastener details (type, size, coating), results and statistical parameters, date and test laboratory.
Applications and users
ISO 9087:1998 is practical for:
- Timber product manufacturers and fastener suppliers (quality control, product development)
- Structural and civil engineers assessing connection performance
- Testing laboratories and research organizations studying wood-fastener behavior
- Building code authorities and certification bodies for comparative data on holding power
Keywords: ISO 9087:1998, nail holding power, screw holding power, wood testing, axial load extraction test, specific resistance, timber structures.
Related standards
- ISO 3129 - Sampling and general requirements for physical/mechanical wood tests
- ISO 3130 - Determination of moisture content
- ISO 3131 - Determination of density
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