This code provides guidelines for the design and construction of laminated timber beams where the individual laminations are joined together using nails. It covers material selection for timber and nails, permissible stresses, design procedures for flexure and shear, and fabrication requirements to create structural timber elements.
Code of Practice for Design and Construction of Nailed Laminated Timber Beams
Quick Reference Values
Maximum moisture content for timber20%
Maximum difference in moisture content between laminations5%
Minimum nail spacing along the grain10d (d = nail diameter)
Minimum nail spacing across the grain5d (d = nail diameter)
Minimum end distance for nails10d (d = nail diameter)
Minimum edge distance for nails5d (d = nail diameter)
Minimum thickness of lamination20 mm
Key Formulas
V = n * p / s — Horizontal shear resistance per unit length of beam
s = n * p * I / (V * A * y) — Spacing of nails
Practical Notes
Ensuring the correct timber species and grade is crucial, as properties vary significantly. The code references IS 399 for timber classification.
Moisture content of all laminations at the time of fabrication must be controlled (below 20%) and be within a 5% range of each other to prevent issues from differential shrinkage.
The nailing pattern (size, spacing, edge/end distance) is critical for achieving the designed shear strength between laminations and must be strictly followed to prevent splitting.