Overview
ISO 12579:2007 - "Timber structures - Glued laminated timber - Method of test for shear strength of glue lines" - specifies a production quality‑control test method for measuring the shear strength of glue lines in glued laminated timber (glulam). It is designed to be used alongside ISO 12578 (component performance and production requirements) and applied to production batches to verify adhesive performance and structural integrity of glulam members.
Key Topics and Requirements
- Purpose and principle: Apply a shear stress at the glue line until failure; record ultimate load and estimate wood‑failure percentage.
- Test specimens:
- Standard: rectangular‑prism specimen with nominal shear‑plane dimensions b × t = 50 mm × 50 mm (actual dimensions measured).
- Alternatives: stepped rectangular‑prism, cylindrical (typically 25 mm diameter), or saw‑kerfed specimens. Alternative results must be correlated to standard specimens via regression (minimum 20 paired tests).
- Sampling: take specimens from specified positions across cross‑section (top, center, bottom thirds); sampling rate per ISO 12578.
- For wide glulam members, cut multiple specimens per specified width table.
- Apparatus and accuracy:
- Calibrated testing machine capable of applying compressive shear; load measurement accuracy better than ±5%.
- Shearing fixture that applies shear in the glue plane; specimens clamped so glue line is within 1 mm of sheared plane.
- Test procedure and environment:
- Test in conditions typical of production; moisture content should match production conditions.
- Measure sheared area dimensions to 0.5 mm accuracy.
- Loading rate so failure occurs after at least 20 s.
- Estimate wood‑failure percentage to the nearest 5%.
- Calculation and reporting:
- Shear strength fu = F / A (ultimate load divided by sheared area).
- Test report must include date, product description, specimen identification/location, timber species, adhesive type, specimen dimensions, ultimate load and shear strength, regression equation (if applicable), wood‑failure percentage, and tester signature.
Applications and Users
- Primary use: production quality control for manufacturers of glued laminated timber (glulam).
- Secondary users: structural and timber engineers, testing laboratories, certification bodies, and procurement/compliance teams verifying adhesive bond performance in structural members.
- Practical applications: batch acceptance testing, process control in pressing/adhesive application, verifying glue line quality for load‑bearing glulam used in buildings, bridges, and engineered timber structures.
Related Standards
- ISO 12578 - Timber structures - Glued laminated timber - Component performance and production requirements (referenced normative document for sampling frequency and pass/fail criteria).
Keywords: ISO 12579, glued laminated timber, glulam, shear strength test, glue line, quality control, test specimen, wood‑failure percentage.
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