4. STRUCTURAL DESIGN OF LVL STRUCTURES In the case of rectangular cross sections: I_tor=k_1∙h∙b^3 (4.43) Table 4.9. Effective length as a ratio of the span (Modified from EC5 Table 6.1.). The equation (4.42) of σm,crit may be replaced by a simplified equation: σ_(m,crit)=(c ∙ b^2)/(h ∙ l_ef ) E_0,05 (4.45) where c is 0,58 for LVL 48 P and 0,67 for LVL 36 C; b is the beam thickness [mm]; and h is the beam height [mm]. Note: More advanced design instructions for LTB can be found from manufacturers’ technical documentation. 4.3.10 Notches The effects of stress concentrations at the notch shall be taken into account in the strength verification of members. The effect of stress concentrations may be disregarded in the following cases: • Tension or compression parallel to the grain • Bending with tensile stresses at the notch, if the taper is not steeper than 1:i = 1:10, that is i≥10, see Figure 4.20 a) • Bending with compressive stresses at the notch, see Figure 4.20 b) Figure 4.19. Installation of notched rafter beam. where k_1=1/3 (1-(0,63∙b)/h) (4.44) k1 = 0,14 as a accurate value for square cross sections, 0,12 based on approximate equation (4.44); k1 = 0,23, when h/b = 2; k1 = 0,28, when h/b = 4; k1 = 0,30, when h/b = 6; and k1 = 0,31, when h/b = 10 tor = 1 ∙ ℎ ∙ 3 (4.43) 1 =1 3�1−0,63∙ ℎ � m,crit = ∙ 2 ℎ ∙ ef 0,05 1 =1 3�1−0,63∙ ℎ � (4.44) m,crit = ∙ 2 ℎ ∙ ef 0,05 (4.45) LVL 04, Table 4.9 Beam type Loading type lef / l a Simply supported Constant moment 1,0 Uniformly distributed load 0,9 Concentrated force at the middle of the span 0,8 Cantilever Uniformly distributed load 0,5 Concentrated force at the middle of the span 0,8 a The ratio between the effective length lef and the span l is valid for a beam with torsionally restrained supports and loaded at the centre of the gravity. If the load is applied at the compression edge of the beam. lef should be increased by 2h and may be decreased by 0,5h for a load at the tension edge of the beam. When a beam is supported against lateral torsional buckling (LTB) from the compressive edge and the beam is loaded from the compressive side, the effective length lef in the design is the distance between the LTB supports a + 2h. When the beam is loaded from the tensile side, the effective length lef = a - 0,5h. When the compressive edge of the beam is loaded only with point loads at the locations of the LBT supports, the effective length lef = a 31. 130 LVL Handbook Europe
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