5. STRUCTURAL DESIGN OF CONNECTIONS Wood failure should be checked for at tension-loaded member ends for connection force components that are parallel to the grain. There are two types of timber failure mode: block shear and plug shear. • Block shear needs to be checked for bolt and dowel connections and for screw connections when the centre member is screwed from both sides and the screws are overlapping. • Plug shear failure mode must be checked for steel-to-timber connections with surface fasteners (nails, screws, nail plates and shear plates). Plug shear must be checked also for external lamellas in cases where the dowels are shorter than the overall thickness of the members in the connection. For LVL-C wide face bolt and dowel connections, both block and plug shear failure modes must be checked. • Block and plug shear capacities are not checked for connections where all fasteners are in a single row parallel to the grain (n2 = 1). • If the timber member t1 has fasteners from opposite sides and the effective thickness tef ≥ 0.5t1, the block shear capacity of steel-to-timber connections should also be checked. • Block shear need not to be checked for bolt and dowel connections when: • the member thicknesses are t1 ≥ 4d, ts ≥ 5d (inner member) • there are max. 4 fasteners in a row parallel to the grain, and • the distance perpendicular to grain between bolts a2 ≥ 5d or between dowels a2 ≥ 4d., see Figure 5.11. The characteristic plug shear capacity is calculated using the equation: F_(ps,k)=L_(net,t)∙(t_ef∙f_(t,0,k)+(a_3+(n_1-1)∙a_ (5.7) where L_(net,t)=(n_2-1)∙(a_2-D) (5.8) t_ef=R_k/(d∙f_(h,0,k) ) (5.9) fh,0,k is the embedment strength according to subsection 5.5.1 or 5.6; n1 is the number of fasteners in rows parallel to the grain; n2 is the number of fastener rows perpendicular to the grain; a1 is the fastener spacing parallel to the grain; a2 is the fastener spacing perpendicular to the grain; a3 is the fastener end distance; D is the hole diameter; ft,0,k is the tension strength of the timber member: 35 N/mm2 for LVL 48 P and 19 N/mm2 for LVL 36 C; fv,0,k is the shear strength of the timber member: fv,0,flat,k is 2.3 N/mm2 for LVL 48 P and 1.3 N/mm2 for LVL 36 C in flatwise connections; Rk is the characteristic load-carrying capacity per shear plane per fastener; and d is the fastener diameter. Figure 5.11. A) Block shear failure mode B) Plug shear failure mode 31 A B 5.3.3 Block shear and plug shear failure modes at multiple dowel-type steel-totimber connections Block shear and plug shear failure modes shall be checked for steel-to-timber connections and tension-loaded member ends of double or multiple shear plane timber-to-timber connections. The wood failure capacity of the joint area can be calculated according to the method presented in the Finnish Handbook for EC5: RIL 205-1-2009, Section 8.2.4S 31. In addition, the effective number of fasteners, nef, according to Section 5.3.2 are taken into account to prevent splitting and row shear failure mode. This method cannot be used for edgewise LVL connections. o there are max 4 fasteners in a row parallel to the grain, an o the distance perpendicular to grain between bolts a2 ≥ 5d 4d., see Figure 5.10. Figure 5.10. a) Block shear failure mode b) Plug shear failure mode block shear failure 190320, Kuva_118_2 plug shear failure 190314 The characteristic plug shear capacity is calculated using the equatio ps,k = net,t ∙ ( ef ∙ t,0,k +( 3 +( 1 −1) ∙ 1 ∙ v,0,k ) ) net,t =( 2 −1) ∙ ( 2 − ) ef = k ∙ h,0,k o o the distance perpendicular to grain between bolts a2 ≥ 5d 4d., see Figure 5.10. Figure 5.10. a) Block shear failure mode b) Plug shear failure mode block shear failure 190320, Kuva_118_2 plug shear failure 190314 The characteristic plug shear capacity is calculated using the equatio ps,k = net,t ∙ ( ef ∙ t,0,k +( 3 +( 1 −1) ∙ 1 ∙ v,0,k)) where net,t =( 2 −1) ∙ ( 2 − ) ef = k ∙ h,0,k LVL Handbook Europe 151
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