7. DURABILITY 7.1 SERVICE LIFE OF WOODEN BUILDINGS AND LVL STRUCTURES Buildings are normally designed for a 50-year service life. When structural LVL is produced and tested according to its harmonized product standard EN14374, the durability of the adhesive bonding strength and the mechanical properties meet the requirements of the design service life. However, the structural protection of the building shall be designed, executed and maintained so that the structures remain in service class 1 or 2 conditions. In remarkable buildings, the design service life is 100 years. This can be achieved with the same means as the default 50-year service life, but an increased safety factor for the design values of eventual climatic loads (wind and snow load) shall be used in the structural design. The safety factor is defined in national regulations, e.g. in Finland the design values of eventual climatic loads must be increased by factor 1,2 when the expected service life is above 100 years. The report 100 years’ service life of wood in service class 1 and 2 – dry and moderately humid conditions, Viitanen, VTT-R-04689-14 41 summarizes that to achieve a 100-year service life the following should be ensured: use of dry and CEmarked wood material; use of correct glue type and glue class for engineering components; good detailing and design; good execution and protection against weathering, take into account the effect of natural loading; proper maintenance and provision of a maintenance manual for users; and guarantee proper conditions for materials in the building throughout its service life. 7.2 DURABILITY CLASSIFICATIONS OF STRUCTURAL LVL PRODUCTS 7.2.1 Durability of adhesive bonding strength of structural LVL The adhesive and glue bond used for structural laminated veneer lumber (LVL) is suitable for service classes 1, 2 and 3 according to EN 1995-1-1:2004 (Eurocode 5). This is verified in a cleavage test defined in EN 14374:2004, Annex B. The test procedure for LVL specimens is as follows: • Immersion for at least 4h in boiling water • Drying in a ventilated oven for at least 16h at 60°C • Immersion for at least 4h in boiling water again • Cooling in room temperature water for at least 2h. • After the boiling & drying cycles, the samples are cleaved at least at one glue line close to the middle of the thickness and the apparent cohesive wood failure percentage is determined according to EN 314-1. • For each tested glue line the apparent cohesive wood failure percentage shall be at least 70%. Adhesive type I (full exposure to the weather) according to EN 301 or EN 15425 (polyurethane adhesives) shall be used for structurally glued products are made from structural LVL components. 7.2.2 Biological durability of softwood LVL LVL veneers always contain some sapwood. According to EN 350 sapwood is regarded as not durable unless otherwise proven by test data. The biological durability class of softwood LVL is therefore DC 5 (Not durable) according to this classification. 7.2.3 Structural LVL’s suitability for different use classes and service classes Structural LVL products can be used in service classes 1 and 2 as defined in Eurocode 5, which corresponds to the use classes 1 and 2 as defined in EN 335. Structural LVL products should not be used in service class 3 without additional protective treatment. Structurally glued products made from LVL components are not suitable for service class 3. Figure 7.2. Roof overhangs and high foundation level are practical means of structural wood protection to keep wooden structures in service class 2 (use class 2) or dryer conditions. Note: Assignment of structures to service classes may be given in the National Annex to EN1995-1-1 for each country. LVL Handbook Europe 169
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