5. STRUCTURAL DESIGN OF CONNECTIONS where fax,ε,1,k is the characteristic withdrawal strength parameter for a screw at the head side member of the connection at an angle ε to the grain direction [N/mm2]; fax,ε,2,k is the characteristic withdrawal strength parameter for a screw at the pointside member of the connection at an angle ε to the grain direction [N/mm2]; d is the outer threaded diameter [mm]; lg,1 is the penetration length of the threaded part in the head side member [mm]; lg,2 is the penetration length of the threaded part in the pointside member [mm]; ftens,k is the characteristic tensile capacity of the screw determined in accordance with EN 14592 [N]; fhead is the characteristic pull-through parameter of the screw for the associated density ρa [N/mm2]; dh is the head diameter [mm]; ρk is the characteristic density of LVL [kg/m3]; and ρa is the associated density for fhead,k [kg/m3]. When the screwing direction in the beam is ε = 90° to the grain direction (even though the angle β is inclined between the edge face and the wide face), it is not allowed to add the tension capacity of the head to the withdrawal capacity of the treaded part in the beam. Therefore the characteristic withdrawal capacity RT,k of the screw is calculated by the equation: R_(T,k)=min{█(max(f_(ax,90,1,k) d l_(g,1) ; f_(h (5.35) The withdrawal strength fax,ε,k is determined by testing according to EN 14592 and EN 1382 or it can be determined at angle ε to the grain as follows: f_(ax,ε,k)=〖k_ax ∙ f〗_(ax,90,k)/(1,5 cos^2 β + s (5.36) 32 where ε is the angle between the screw axis and the grain direction, ε ≥ 15°, see Figure 5.12; β is the angle between the screw axis and the LVL’s wide face, with 0°≤ β ≤ 90°, see Figure 5.7 kax in according to the equation (5.29) ρk is the characteristic density of LVL [kg/m3]; ρa is the associated density for fax,k [kg/m3]; and fax,90,k is the characteristic withdrawal strength parameter for a screw perpendicular to the grain direction [N/mm2]. It is determined by testing according to EN 14592 and EN 1382 or for screws in LVL, it may be assumed as fax,90,k =15 N/mm² for ρa = 500 kg/m³ and screws 6 mm≤ d ≤ 12 mm in softwood LVL/GLVL 32. Tension screwed connection In a joint consisting of only screws in tension, contact between the wood members is required. Tension screw connection Figure 5.12. Inclined screwed connections (A) cross screw connection (B) tension screw connection should not be used in conditions where wood drying could cause a gap of over 0.2d. The gap is determined from the wood shrinkage at a thickness of the LVL members in the screw length (L ∙ sin α) 31. The characteristic load-carrying capacity of the tension screw connection, see Figure 5.12 (b), is calculated by the equation: Rk = n0,9 R T,k (cos ε + μ ∙ sin ε) (5.37) where n is the number of screws in the connection; RT,k is the characteristic withdrawal capacity, see (5.35); α is the angle between screw axis and the shear plane (30° ≤ α ≤ 60°), see Figure 5.12 (b); and μ is the kinetic friction coefficient between the members, the following values may be used: 0.26 for untreated LVL edgewise or LVL to timber or timber-to-timber connections 0.30 for steel-to-timber connections 0.40 for untreated LVL flatwise connections C,k =min� ax,ε,1,k g,1 ax,ε,2,k g,2 0,8 tens,k (5.29) T,k =min� ax,ε,1,k g,1 + head,k h2� a�0,8 ax,ε,2,k g,2 tens,k (5.30) T,k =min⎨⎩⎧max� ax,90,1,k g,1 ; head,k h2� k a�0,8� ax,ε,2,k g,2 tens,k (5.31) ax,ε,k = ax ∙ ax,90,k 1,5 cos2 + sin2 � k a�0,8 (5.32) 32 A B 188 (255) T,k = min {max ( ax,90,1,k g,1 ; head,k h2( k a)0,8) ax,ε,2,k g,2 tens,k (5.35) The withdrawal strength fax,ε,k is determined by testing according to EN 14592 and EN 1382 or it can be determined at angle ε to the grain as follows: ax,ε,k = ax ∙ ax,90,k 1,5 cos2 + sin2 ( k a) 0,8 (5.36) 32 where ε is the angle between the screw axis and the grain direction, ε ≥ 15°, see Figure 5.11; β is the angle between the screw axis and the LVL’s wide face, with 0°≤ β ≤ 90°, see Figure 5.7 kax in according to the equation (5.29) ρk is the characteristic density of LVL [kg/m3]; ρa is the associated density for fax,k [kg/m3]; and fax,90,k is the characteristic withdrawal strength parameter for a screw perpendicular to the grain direction [N/mm2]. It is determined by testing according to EN 14592 and EN 1382 or for screws in LVL, it may be assumed as fax,90,k =15 N/mm² for ρa = 500 kg/m³ and screws 6 mm≤ d ≤ 12 mm in softwood LVL/GLVL 32. Tension screwed connection In a joint consisting of only screws in tension, contact between the wood members is required. Tension screw connection should not be used in conditions where wood drying could cause a gap of over 0.2d. The gap is determined from the wood shrinkage at a thickness of the LVL members in the screw length (L∙sin α) 31. The characteristic load-carrying capacity of the tension screw connection, see Figure 5.11 (b), is calculated by the equation: = (cos + ∙ sin ) LVL Handbook Europe 155
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