Laminated wood

Material characteristics

Glulam is one of the most interesting structural materials because it enhances the constitutive capacities of wood as it is obtained by gluing slats parallel to their grain, obtaining a high degree of resistance. The slats, selected by sight and with special scanners that identify any defects, have a uniform thickness and are obtained from fresh roundwood selected by mechanical resistance class and artificially dried. The greatest lengths are achieved through finger jointing, the various layers are planed and glued with a continuously controlled process in order to guarantee the load-bearing capacity of the finished element. 

Glulam is made in a prefabricated manner and, compared to traditional structures, guarantees: speed of installation, lower environmental impact, economic savings. It is an industrial product, obtained by hot gluing under pressure wooden boards usable for structural use, stabilized for their hygrometric characteristics. In this way, thanks to the intersection of the lamellae with opposing grains, a composite material with high mechanical resistance is obtained which allows for greater uniformity of the resistance of the beam. Furthermore, while normal beams tend to have a square, circular or rectangular section with a poor ratio between the sides, laminated beams are, instead, capable of developing a section with a rectangular shape that is higher than it is wide which allows for greater resistance and to overcome larger spans.

Glued laminated wood improves the characteristics of the natural product, any physical defects, thus managing to cover even large spans, exceeding the limit of the length of tree trunks, it also retains the qualities of the basic material but lends itself to wider uses, therefore allowing to reach lengths of up to 50 m, to be bent, tapered, joined and combined in a very broad way.
For the production of lamellas, wood from conifers (spruce, fir, pine and larch) or broadleaf trees (beech, ash, oak) is used. An even more advanced system is the XLAM system, cross-laminated timber panels (CLT, Cross Laminated Timber). This system combines the technology of lamellas with that of compensation obtained from layers of boards glued orthogonally to those below.

Technical performance

Glulam also achieves excellent fire resistance because a carbonized layer forms on the external surface which slows down combustion and prevents further combustion in depth; the beams do not collapse suddenly. Through calculations, the combustion speed can be verified and, in relation to this, the duration of static resistance.
Wood allows for good breathability of the structure which improves the environmental comfort of the rooms and also allows for an excellent level of thermal and acoustic insulation, thanks to the sound-absorbing properties of the material.
The specific weight of laminated wood is 1/5 compared to that of reinforced concrete, to which are added the elastic performances, which allow greater flexibility of the structures, and make it an excellent solution in areas at risk of earthquakes.
One cannot overlook the undoubted aesthetic result of wooden structures and the wide choice of finishes and flexibility in the shapes and curves that can be created, while maintaining solidity and resistance.
Another aspect that cannot be overlooked is sustainability, representing a material that respects environmental criteria being a material coming from renewable resources. Sustainability, already respected for the best thermal and acoustic insulation characteristics, is summarized with lightness, structural efficiency, fire resistance and durability.
Low energy requirements are also guaranteed thanks to the management costs of the finished work, the lower production of carbon dioxide and other polluting substances, necessary for the production process and installation.

A look at the regulations

The technical standards that can be used for the design of laminated wood structures are the standards: UNI 90504 “Analytical procedure for evaluating the fire resistance of wooden construction elements” and UNI ENV 1995-1-2 “Eurocode 5 – design of wooden structures. Part 1-2 structural design against fire”. The EN 14080 standard, which allows obtaining the CE marking, regulates all the phases of product production: selection of the boards, formation of the joints, types and characteristics of the adhesives, tests to be carried out on the individual lamellae and on the final product. With the PEFC and FSC certifications, certification of the origin of the raw material is obtained and attestation of the correct use of forest resources, for the environmental protection to be guaranteed, based on international protocols, for future generations.
Glulam is widely used to create floors and roofs in combination with load-bearing masonry structures, to build roofs in combination with reinforced concrete structures and lends itself in a virtuous combination with steel and glass.

Wooden floors have excellent acoustic performance and are able to control vibrations with excellent static performance, with extraordinary results also in the field of floor recovery because the reinforcement of wooden floors with new beams allows to increase the resistance of the structure ensuring the necessary safety levels in addition to the existing structure, without replacing it, as also suggested by the NTC 2018 (the new Technical Standards for Construction referred to in the Ministerial Decree of 17.01.2018): "For historic buildings, in the consolidation of wooden floors, light diaphragms, of non-negligible rigidity, made dry, such as those obtained with double planking, are generally preferable" and for roofs "As regards roofs, in masonry buildings it is generally advisable to operate by maintaining the wooden roofs so as not to increase the masses in the highest part of the building".
The bending strength class is indicated by the acronym GL and varies in relation to the type of wood species and the way in which the lamellae are inserted with the annual growth rings facing in the same direction or in opposite directions. The UNI EN 1194:2000 standard specifies the system of strength classes of glued laminated coniferous wood for structural uses, with the characteristic values.
The NTC 2018 also introduced innovations to guarantee the prefabricated product and the training of plant managers of processing centers and structural wood producers.

A look at history

Glulam, particularly appreciated for its beams that can take on considerable shapes and lengths, can also be used for multi-storey buildings and its resistance to time is also improved by the engineering process of the material that takes on compact shapes and is less susceptible to attack by pathogens. The construction of centuries-old multi-storey wooden buildings such as Japanese pagodas, made exclusively of wood, dispels any doubts regarding the durability of the material, provided that it is a quality original material and is properly installed.
The buildings constructed after the 1783 earthquake in Calabria, and built with a masonry structure with wooden frames, had already been thought of as the best solution for resisting earthquakes, since the elasticity of the wood is capable of absorbing seismic action, the presence of the masonry provides resistance and rigidity, while the wooden frame ensures ductility to the panel. The 1783 earthquake had caused the Bourbons to issue a regulation which, based on the studies of Giovanni Vivenzio, proposed the system of the barracked house, built with a double wooden frame inserted into the load-bearing masonry. Laboratory tests, which reproduced the masonry panels with the same wooden frame, demonstrated the effectiveness of this construction method. The scientific articles relating to these tests are collected in the document H.Ea.RT (Historical Earthquake-Resistant Timber Frames in the Mediterranean Area).