It is obtained by gluing two or more sheets of wood in a direction parallel to the blade axis. The sheets are obtained by glueing together, by serrated joints, pieces of sawn wood with a thickness between 6 and 45 mm.
Glued laminated wood structures are especially suitable for:
– Lights from 30 to 70 m in buildings for public, commercial or sports use.
– Moderate lights from 8 to 14 m in small and medium constructions
(usually prefabricated elements)
– Reduced self-weight cover structure.
– Structures that require resistance against certain chemical agents, such as salt stores to remove snow – ice from roads.
– When intended a special aesthetic aspect.
– There is a need for structures with high fire stability.
– Structures in situations of difficult maintenance.
Examples of applications:
– normal: churches, gyms, sports centers, swimming pools, shopping malls, hangars, factories, wineries, bridges, etc.;
– individuals: in aggressive and corrosive environments, in which other materials are limited to use: indoor pools, chemical plants, livestock-use vessels, aggressive industrial environments, buildings on the sea coast, etc.
The unit elements are sawn wooden boards with which, by juxtaposition by glued serrated joint, each sheet is constituted, which, by gluing of their faces, give rise to the piece, in a constructive logic similar to the
of masonry and stonework.
The most commonly used species in Europe is the Picea abies, which is commercially known as spruce, red spruce, spruce or false fir for use classes 1 and 2. And secondly wild pine, mainly when in-depth treatment is required for use classes 3.2 and 4.
In Spain Eucalyptus (Eucalyptus globulus), Oak (Quercus robur and Q. petraea), Chestnut (Castanea sativa) are also used; and to a lesser extent the Fresno (Fraxinus excelsior), the Hague (Fagus sylvatica) and the Iroko (Chlorophora excelsa, Chlorophora regia). Actions are currently being taken for inclusion in the standard.
– Quality or sturdy class of wood
The wood used in the sheets shall be classified according to UNEEN 14081-1.
– Moisture content
The moisture content of each sheet should be in the range of 6% to 15%, unless the adhesive manufacturer requires a narrower margin. The variation in the moisture content of the sheets within a part shall not be greater than 5 %.
They are obtained by joining the classified wooden pieces by serrated wooden joint.
The most commonly used today, depending on service class 1, 2 or 3, are:
– Melamine-Urea-Formaldehyde (MUF).
– Resorcin-Phenol-Formaldehyde (RPF).
– Polyurethane (PU.
If protective products are applied prior to sheet gluing, it should be documented that the specifications for the combination of adhesive and protective product are met.
DIMENSIONS PARTS AND CHARACTERISTICS OF THE SHEETS
As it is a product manufactured ex profeso its dimensions are not standardized, although they can be supplied without problems if the market so requires.
The range of widths depends on the width of the sheet, the most common are: 80, 100, 110, 130, 140, 160, 180, 200 and 220 mm (being the maximum of 280 mm).
It is a function of the thick sheet used. In the standard indicates a maximum allowed sheet thickness of 45 mm for service class 1 and 2; and 35 mm (< 41 mm) para la clase de servicio 3.
– Orientation of the pictures
All pictures should have the heart to the same side, with the exception of parts intended for class of service 3 in which the extreme pictures on each side should have the heart facing outwards.
It shall be as close as possible to the mean humidity of hygroscopic balance corresponding to the location of the work:
– 12% for service classes 1 and 2.
– 18% for class of service 3.
They are defined in UNE-EN 1194, which distinguishes 8 resilient classes, which are set out in the following tables (*):
– 4 when the composition is homogeneous (all sheets are of the same resistant class).
– 4 when combined (extreme sheets are of a superior sturdy class).
(*) in the latest drafts of UNE-EN 14080 these values are slightly modified.
We must not forget in this topic the importance of the constructive design of the structure that avoids unnecessary exposure to the weather and the possibility of water retention. Proper design can reduce the risk of deterioration.
In practice there are no durability problems in parts located in use classes 1 (indoor) and 2 (indoor and under cover without direct exposure to rainwater), virtually any species is suitable. In usage class 3.1 and especially at 3.2, 4 and 5
requires a kind of increased natural durability or a protective chemical treatment.
Usually coniferous species in structures do not have sufficient natural durability (almost always incorporate part of albura that is not durable) and therefore, for use in use classes 3.1, 3.2, 4 and 5 require treatment. For the choice of the appropriate type of treatment you can consult the Basic Structural Safety Document – Wood and the standard UNE EN 335-2 that defines the types of use.
The most commonly used species in Europe is the fir tree (Picea abies L. Karst), which is not impregnable, so its use is limited to the classes of use 1 and 2. Wild pine (Pinus sylvestris L.), is the most commonly used species for use class 3, as it can be treated in depth.
You can choose a species with sufficient natural durability for the class of use corresponding to the structure, or apply the appropriate protection treatment provided that the wood is sufficiently impregnable before obtaining the sheets and gluing them between yes (it is the most common practice), or apply the treatment to the piece of glued laminated wood.
Reaction to fire
Its type of fire reaction, according to UNE-EN 14080, is D-s2-d0 provided that it complies with its:
– Minimum mean density is equal to or greater than 380 kg/m3 .
– Minimum total thickness of the part is equal to or greater than 40 mm.
If the manufacturer defines a different type of fire reaction, he/she must provide the corresponding test and classification report in accordance with UNE-EN 13501-1.
The fire resistance of the structure involving glued laminated wood shall be calculated in accordance with the Fire Safety DB or in accordance with UNE-EN1995-1-2. The wood-dependent parameter is the rate of carbonization, which takes the effective values of: 0.5 to 0.7 mm/min in sawn wood of leafy and glued laminated wood.
Issuance of formaldehyde
In accordance with UNE-EN 14080, if the adhesive used in the manufacture of laminated wood contains formaldehyde it must be classified according to UNEEN 717-1 in the following emission classes E1 or E2.
By not reacting with the environment or with oxidizing or reducing agents, it becomes a suitable material for use in aggressive and corrosive environments, in which metals are limited in their applications.
Surface finish – Maintenance in outdoor applications
Like any other wood product placed outside they should receive finishes that protect the wood from infrared (heating) and ultraviolet (oxidation) rays.
MANUFACTURE, STORAGE AND TRANSPORT
Equipment, environmental manufacturing conditions, manufacturing process, and self-control must be carried out in accordance with the specifications of UNE-EN 386 or UNE-EN 14080 which will replace soon the previous one. It is common for the
manufacturer is voluntarily subjected to external control by a renowned body.
Storage, transport and assembly
It is recommended to apply a sealant, primer or coat them before they leave the factory.
During storage, transport and assembly, the parts shall be subjected to tensions higher than intended.
Glued laminated wood elements stored in construction shall be adequately protected from the weather. If possible it is recommended to cover them to avoid the action of rain and sun. They should be stored on crawls to avoid contact with the soil and on properly drained soils.
Once placed it is not convenient to exceed the one month period without the protection of coverage.
Fendas – Delaminations
Drying phenomena usually appear, due to variation in environmental conditions. On very particular occasions, delaminations may appear that are more psyer steepes caused mainly by poor manufacture.