Laminated timber is a structural wood product made from strips of wood glued together. It is made up of at least four strips or sheets of sawn goods, maximum 45 mm thick, with the grain direction running along the length of the laminated timber product. The Finnish Glulam Association recommends that the strength class for glued laminated timber is GL 30c in accordance with Standard SFS-EN 14080.
Laminated timber is used for load-bearing structures, in both the horizontal and vertical directions, which are either left visible, or clad. As well as buildings, laminated timber is used in, e.g., load-bearing bridge construction.
Laminated timber is usually planed all round and is available in various finishes and pressure-impregnated. The most common cross-section dimensions are shown in the accompanying table, but laminated timber is also available to special dimensions.
Most common cross-section dimensions for laminated timber
Maximum height of laminated timber is approx. 2 metres and maximum length approx. 30 metres. Maximum dimensions vary according to manufacturer. The strips or sheets from which laminated timber is made are normally 45 mm maximum thickness for straight beams and 33 mm maximum thickness for curved structures.
Laminated timber beams have good fire resistance and do not bend under the effect of heat. Charring speed for laminated timber is approx. 0.6 mm/min. Charred depth after one hour in a normalfire is approx. 36 mm. Steel parts embedded in laminated timber are also fire protected for an equivalent period.
The properties of laminated timber are defined according to Finnish Standard SFS-EN 14080 and the manufacture of laminated timber according to SFS-EN 386. Laminated timber fulfilling these standards can be used in GL strength class according to SFS-EN 1194.
Slit GLT. Standard dimensions
*Only special orders
Glued timber is a wood product which does not fulfil the laminated timber standards, but is made by gluing two or more items of sawn goods together. Such products are used, as they are, in loadbearing construction and as blanks for various wood products such as window frames, laminated logs, etc. Strength-graded and ready finished glued timber products, etc. are available.
New Nordic handbook on laminated timber
The laminated timber handbook, which has been overhauled to comply with the Eurocodes and adapted for Finland, has been published. The book is an Internet publication in three parts which can be downloaded at puuinfo.fi.
Part 1 gives basic information about the properties and manufacture of laminated timber and its use in building.
Part 2 introduces in detail, the basics of designing laminated structures and their joints.
Part 3 presents, in condensed form, the equations, values and design methods used in dimensioning. The ways in which the methods are used are illustrated with examples.
This is a very useful handbook for designers, officials and construction firms, and can be used extensively for teaching at various levels in the construction field.