Technical properties

Fire stability

Wooden structures with a large cross-section remain highly stable in a fire. Despite its flammability, the penetration rate for burning glulam is slow at around 0.5–1 mm per minute. This low penetration rate is due in part to the insulating charcoal layer that forms on the surface of glulam products. Smoke development in a fire is moderate.

 
 

Glulam retains much of its load-bearing capacity even in a fire. The figure shows a glulam cross-section before a fire (left), after 30 minutes of burning (centre) and after 60 minutes of burning (right) in a four-side fire attack.

 
In Sweden, glulam is classified for fire safety in line with the building regulations issued by Boverket. When designing glulam structures for fire resistance, account must be taken of the dimensions of the glulam products and the design of the fixings. Some fixings survive a fire better than others. They are usually inset into the glulam, which provides protection against fire. In public buildings that demand high standards of fire safety, it is common to use dowel connectors with inset metal plates and glued-in rods. Läs mer i Limträhandbok Del 1 - 3.
 

Design values of material properties

The design values of the material properties are a crucial factor when drawing up glulam designs. Strength class GL30 states the characteristic bending strength value. GL stands for GluLam. In Sweden, glulam manufacturers are subject to ongoing control by an accredited certification body. The products are CE marked and the wood laminates are mechanically strength-graded.

Designs should also take into account the serviceability limit state (deflection) and the ultimate limit state (load-bearing capacity). Useful information on design values can be found in The Glulam Handbook Parts 1–3. The Glulam Handbook PThe glulam manufacturers are also happy to help with design specifications and dimensions. 

Cross-section data

When drawing up designs, components with the necessary cross-section data are chosen to establish the correct load-bearing capacity and deformations under the loads in question. Tables of cross-section data and information on dimensioning can be found in  The Glulam Handbook Parts 1–3

Simple designs can be made using computer software or diagrams in the handbook. Contact your nearest builders’ merchant or timber merchant, or Swedish Wood.