4. STRUCTURAL DESIGN OF LVL STRUCTURES Table 4.3. Values of kdef for different LVL types in different service classes. Table 4.2. Values of kmod for LVL (the same values are used for structural timber, glulam and CLT and plywood). Service class Permanent Long-term Medium-term Short-term Instantaneous 1 0,60 0,70 0,80 0,90 1,10 2 0,60 0,70 0,80 0,90 1,10 3 0,50 0,55 0,65 0,70 0,90 LVL 04, Table 4.3 Product type Service class 1 Service class 2 Service class 3 LVL-P 0,60 0,80 2,00 LVL-C in edgewise loading 0,60 0,80 2,00 LVL-C in flatwise loading 0,80 1,00 2,50 ufin= uinst,G(1+kdef) + uinst,Q,1(1+ψ2,1 ∙ kdef) + uinst,Q,i(ψ0,i+ψ2,i ∙ kdef) (4.2) where ufin is the final deflection including creep deformation; uinst,G is the instantaneous deflection due to permanent actions; uinst,Q,1 is the instantaneous deflection due to the leading variable action; and uinst,Q,i is the instantaneous deflection due to accompanying variable actions. LVL-C has a higher kdef value when the loading causes deformation in the flatwise direction due to rolling shear deformation of the cross veneers similar to plywood. When LVL-C panel is used as a component of stressed-skin panels, the kdef value in the longitudinal direction of the element is the same as for LVL-P, because the loading causes mainly axial stresses on the panel. 4.1.6 Design resistance and stiffness Design resistance in ULS design is determined from the design values of the strength properties by modifying the characteristic properties with partial safety factor γM and modification factor kmod. f_d=(k_mod∙f_k)/γ_M (4.3) (EC5 2.17) where fk is the characteristic 5% value of a strength property; kmod is the modification factor that takes into account the duration of load and service class, see Table 4.2; and γM is the partial safety factor of the material. Mean values for stiffness properties are used in SLS design and are determined for short-term loading in service class 1 conditions. The influence of creep deformation is taken into account by the kdef factor. Characteristic 5% stiffness values are used for stability calculation in ULS design. 4.2 STRUCTURAL PROPERTIES OF LVL AND STRENGTH CLASSES The mechanical properties of structural LVL are determined according to the harmonized product standard EN 14374. The properties are assessed and their constancy of performance verified according to the AVCP system 1 of the EU construction product regulations. LVL suppliers declare their individual product properties in their Declaration of Performance (DoPs). In the future EN 14374 LVL product categories will be introduced but in the meanwhile LVL industry has decided to launch them as LVL strength classes. Information about the strength classes can be found from the Laminated Veneer Lumber (LVL) bulletin: New European strength classes 15, FprEN 14374 Annex B, and these are described in the following subsections 4.2.1 and 4.2.2. The bending and axial strength and stiffness properties of LVL-C with crossband veneers having different layups (i.e. veneer orientation) may be calculated from one set of tests according to FprEN 14374 Annex A by applying layup factors according to Annex C for thickness ranges specified in Annex A. LVL-C properties are defined with the assumption that the cross veneers are zero layers. fin = inst,G(1+ def)+ inst,Q,1�1+ 2,1 ∙ def�+ inst,Q,i� 0,i + 2,i ∙ def� (4.2) d = mod∙ k M (4.3) (EC5 2.17) (4.2) fin = inst,G(1+ def)+ inst,Q,1�1+ 2,1 ∙ def�+ inst,Q,i� 0,i + 2,i ∙ def� (4.2) d = mod∙ k M (4.3) (EC5 2.17) 116 LVL Handbook Europe
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