5. STRUCTURAL DESIGN OF CONNECTIONS 5.5.2 Axially loaded screws For connections in softwood timber or LVL/GLVL with ε ≥ 15° of screws in accordance with EN 14592 with: • 6 mm ≤ d ≤ 12 mm • 0,6 ≤ d1 /d ≤ 0,75 where d is the outer thread diameter; and d1 is the inner thread diameter The characteristic withdrawal capacity should be taken as 32: F_(ax,ε,Rk)=(n_ef ∙ k_(ax )∙ f_(ax,90,k) ∙ d ∙ l (5.28) where k_ax={█(0,5+(0,5∙ε)/(45°) for 15°≤ε45°≤ε≤90°)┤ (5.29) k_β=1,5∙cos^2 β+sin^2 β (5.30) Fax,ε,Rk is the characteristic withdrawal capacity of the connection at an angle ε to the grain [N]; fax,90,k is the characteristic withdrawal strength perpendicular to the grain determined in accordance with EN 14592 for the associated density ρa [N/mm²]; nef is the effective number of screws, nef = n0,9 where n is the number of screws acting together in a connection; kax is a factor to consider the influence of the angle ε between screw axis and grain direction and the long-term behavior; lef is the penetration length of the threaded part [mm]; ρk is the characteristic density [kg/m³]; ρa is the associated density for fax,k [kg/m³]; kβ is a factor considering the influence of the angle β between the screw axis and the LVL’s wide face; ε is the angle between the screw axis and the grain direction, with ε ≥ 15°, see Figure 5.7; and β is the angle between the screw axis and the LVL’s wide face, with 0°≤ β ≤ 90°, see figure 5.7. Note: Failure modes in the steel or in the timber around the screw are brittle, i.e. with minimal ultimate deformation and therefore have a limited possibility for stress redistribution. For screws in LVL, the characteristic withdrawal parameter may be assumed as fax,90,k =15 N/mm², when ρa = 500 kg/m³ and screws 6 mm ≤ d ≤ 12 mm in softwood LVL/GLVL. The characteristic pull-through resistance of connections with axially loaded screws should be taken as: F_(ax,ε,Rk)=n_ef∙f_(head,k)∙d_h^2 (ρ_k/ρ_a )^0,8 (5.31) where Fax,ε,Rk is the characteristic pull-through capacity of the connection at an angle ε to the grain [N], with ε ≥ 30° fhead,k is the characteristic pull-through parameter of the screw determined in accordance with EN 14592 for the associated density ρa dh is the diameter of the screw head [mm] 5.5.3 Inclined screw connections Inclined screwing is an efficient way to connect LVL members together or to other types of timber members. Although the connections transfer shear forces, the fasteners are axially loaded. The instructions in this subsection are based on the Finnish Handbook RIL205-1:2017 for Eurocode 5, Chapter 8.7.4S 31. These rules concern the design of single shear connections according to Figure 5.11, where the screw inclination angle α should be between 30°…60° in regard to the shear plane. The screws are axially loaded. The head side timber member (t1) may be replaced with a steel plate if the screw head has a full bearing area on the steel plate for a Figure 5.12 (b) tension screw connection. The screws should be self-drilling and fully threaded or partly threaded with a smooth part diameter of ds ≤ 0.8d, where d is the outer thread diameter. Different or supplementary connection types and screw specifications differing from eurocode 5 may be used according to their ETA. Cross screw connection The cross screw connection is built up from symmetrical screw pairs, see Figure 5.12 (a), in which one screw is under compression and the other under tension. The characteristic load-carrying capacity of the cross screw connection is calculated by the equation: R_k=n_p^0,9 (R_(C,k)+R_(T,k) )cos ε (5.32) where np is the number of screw pairs in the joint; and α is the angle between screw axis and the shear plane (30° ≤ α ≤ 60°), see Figure 5.12 (a) The characteristic compression capacity of the screw is calculated by the equation: R_(C,k)=min{█(f_(ax,ε,1,k) d l_(g,1)@f_(ax (g,2)@0,8〖 f〗_(tens,k) )┤ (5.33) The characteristic withdrawal capacity of the screw is calculated by the equation: R_(T,k)=min{█(f_(ax,ε,1,k) d l_(g,1)+f_(head,k) ρ_a )^0,8@f_(ax,ε,2,k) d〖 l〗_(g,2)@f_(tens,k) )┤ (5.34) h,k =( C ∙ cos2 + sin2 ) ∙ (2,5 ∙ cos2 + sin2 ) N/mm2 C =�1 for LVL−P and GLVL−P min� ( −2) 3 or LVL−C and GLVL−C (5.23) ax,ε,Rk = ef ∙ ax ∙ ax,90,k ∙ ∙ ef β � k a�0,8 (5.24) ax =�0,5+0,5∙ 45° for 15° ≤ <45° 1 for 45° ≤ ≤90° (5.25) =1,5∙ cos2 +sin2 (5.26) ax,ε,Rk = ef ∙ head,k ∙ h2� k a�0,8 (5.27) Cross screw connection The cross screw connection is built up from symmetrical screw pairs, see which one screw is under compression and the other under tension. The carrying capacity of the cross screw connection is calculated by the equa k = p0,9( C,k + T,k)cos (5.28) Where is the number of screw pairs in the joint; and α is the angle between screw axis and the shear plane (30° ≤ 5.11 (a) The characteristic compression capacity of the screw is calculated by the C,k =min{ ax,ε,1,k g,1 ax,ε,2,k g,2 0,8 tens,k The characteristic withdrawal capacity of the screw is calculated by the e T,k =min{ ax,ε,1,k g,1 + head,k h2( a)0,8 ax,ε,2,k g,2 tens,k where fax,ε,1,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction fax,ε,2,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction d is the outer threaded diameter [mm]; lg,1 is the penetration length of the threaded part in the head sid Cross screw connection The cross screw connection is built up from symmetrical screw pairs, see which one screw is under compression and the other under tension. The carrying capacity of the cross screw connection is calculated by the equa k = p0,9( C,k + T,k)cos (5.28) Where np is the number of screw pairs in the joint; and α is the angle between screw axis and the shear plane (30° ≤ 5.11 (a) The characteristic compression capacity of the screw is calculated by the C,k =min{ ax,ε,1,k g,1 ax,ε,2,k g,2 0,8 tens,k The characteristic withdrawal capacity of the screw is calculated by the eq T,k =min{ ax,ε,1,k g,1 + head,k h2( a)0,8 ax,ε,2,k g,2 tens,k where fax,ε,1,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction fax,ε,2,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction d is the outer threaded diameter [mm]; Cross screw connection The cross screw connection is built up from symmetrical screw pairs, see which one screw is under compression and the other under tension. The carrying capacity of the cross screw connection is calculated by the equa k = p0,9( C,k + T,k)cos (5.28) Where np is the number of screw pairs in the joint; and α is the angle between screw axis and the shear plane (30° ≤ 5.11 (a) The characteristic compression capacity of the screw is calculated by the C,k =min{ ax,ε,1,k g,1 ax,ε,2,k g,2 0,8 tens,k The characteristic withdrawal capacity of the screw is calculated by the eq T,k =min{ ax,ε,1,k g,1 + head,k h2( a)0,8 ax,ε,2,k g,2 tens,k where fax,ε,1,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction fax,ε,2,k is the characteristic withdrawal strength parameter for a scre member of the connection at an angle ε to the grain direction 185 (255) ax,ε,Rk = ef ∙ ax ∙ ax,90,k ∙ ∙ ef β ( k a) 0,8 (5.28) where ax ={ 0,5+0,5∙ 45° for 15° ≤ < 45° 1 for 45° ≤ ≤ 90° (5.29) =1,5 ∙ cos2 +sin2 (5.30) Fax,ε,Rk is the characteristic withdrawal capacity of the connection at an angle ε to the grain [N]; fax,90,k is the characteristic withdrawal strength perpendicular to the grain determined in accordance with EN 14592 for the associated density ρa [N/mm²]; nef is the effective number of screws, nef = n 0,9 where n is the number of screws acting together in a connection; kax is a factor to consider the influence of the angle ε between screw axis and grain direction and the long-term behavior; lef is the penetration length of the threaded part [mm]; is the characteristic density [kg/m³]; is the associated density for fax,k [kg/m³]; kβ is a factor considering the influence of the angle β between the screw axis and the LVL’s wide face; ε is the angle between the screw axis and the grain direction, with ε ≥ 15°, see Figure 5.7; and β is the angle between the screw axis and the LVL’s wide face, with 0°≤ β ≤ 90°, see figure 5.7. Note: Failure modes in the steel or in the timber around the screw are brittle, i.e. with minimal ultimate deformation and therefore have a limited possibility for stress redistribution. For screws in LVL, the characteristic withdrawal parameter may be assumed as fax,90,k =15 N/mm², when ρa = 500 kg/m³ and screws 6 mm ≤ d ≤ 12 mm in softwood LVL/GLVL. The characteristic pull-through resistance of connections with axially loaded screws should be taken as: ax,ε,Rk = ef ∙ head,k ∙ h2( k a)0,8 (5.31) where Fax,ε,Rk is the characteristic pull-through capacity of the connection at an angle ε to the grain [N], with ε ≥ 30° fhead,k is the characteristic pull-through parameter of the screw determined in accordance with EN 14592 for the associated density ρa dh is the diameter of the screw head [mm] 5.5.3 Inclined screw connections Inclined screwing is an efficient way to connect LVL members together or to other types of 154 LVL Handbook Europe
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