4. STRUCTURAL DESIGN OF LVL STRUCTURES The effective contact area perpendicular to the grain, Aef, should be determined taking into account an effective contact length parallel to the grain, where the actual contact length, l, at each side is increased. Eurocode 5 does not include the parameters kc,90 and Aef for LVL in different orientations. The value of kc,90 should be taken as 1,0 for LVL in the edgewise loading direction. For LVL in the flatwise loading direction, kc,90 = 1,4 maybe used, when the distance ℓ1 ≥ 2h 15. The contact length and width may be increased according to the Table 4.7, but not more than a, ℓ or ℓ1/2, see Figure 4.12. LVL suppliers also have their own tailored instructions that may give more favourable design results. The increased contact length and factor kc,90 are less favourable for LVL in edgewise direction, than in the flatwise direction or compared to other wood products have, due to the failure behaviour of the products. LVL in the flatwise direction, solid wood and glulam have ductile behaviour under compression perpendicular to the grain. LVL has high strength values in the edgewise direction fc,90,edge,k = 6–9 N/mm2. However, it breaks in a more brittle manner, see Figure 4.13. Figure 4.14 shows a calculation example for an LVL beam supported on an LVL sole plate. Figure 4.12. (a) Compression Fc,90 of a sole plate (b) Compression Fc,90 of beam on supports (EC5 Figure 6.2). Table 4.7. kc,90-values and increase of the actual contact length for the design of compression strength perpendicular to the grain of LVL 15. 1 1 1 Figure 4.13. Example of LVL-C specimens in compression perpendicular to grain testing. In the flatwise direction LVL-C exhibits a ductile behaviour. In the edgewise direction orientation LVL-C is much stronger and stiffer, but undergoes more brittle failure due to buckling of the veneers. LVL 04, Table 4.7 Loading direction kc,90-values Increase of the actual contact lengtha [mm] Edgewise compression strength fc,90,edge,k 1,0 15 Flatwise compression strength fc,90,flat,k 1,4 — parallel to the grain of the surface veneers 30 — perpendicular to the grain of the surface veneers 15 a One-sided or two-sided increase of the actual contact length, but not more than a, l or l 1/2 according to EN 1995-1-1. 0 5 10 15 20 25 30 35 40 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 Load F [kN] Deformation [mm] Compression perpendicular to grain testing of LVL-C in edgewise and flatwise directions LVL-C edgewise LVL-C flatwise 124 LVL Handbook Europe
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