EWPAA Structural Plywood and LVL Design Manual - Engineered ...

I (neutral axis(NA)-stiffness= (bd 3 1 /12) + 2[(bd 3 2 /12) + (bd 2 x (y 1 ) 2 ] +0.03 x 2 [(bd x3 /12 + (2bd x x (y x ) 2 )I (neutral axis(NA)-strength= (bd 3 1 /12) + 2[ (bd 3 2 /12) + (bd 2 x (y 1 ) 2 ]Z (NA)= I (NA) strength / 0.5dFIGURE 6.3: Example of cross-banded LVL section properties for on flat bending, bending deflection and shear6.4 LVL – Design MethodologyLimit States Design to AS1720.1-1997The design capacity of structural LVL, designed in accordance with the limit states design format ofAS1720.1-1997, is achieved by modifying the characteristic strengths by a geometric section property,a material capacity factor Φ and in-service factors (k and j factors). Structural reliability is achieved throughthe use of these modified characteristic strength capacities and factored loads as detailed in AS/NZS 1170.0 :2002.Strength Limit State CapacityThe strength limit state condition is satisfied when the design capacity of the structural LVL exceeds thedesign load effects from the factored loads. That is:ΦR > S*where ΦR = design capacity of the LVL memberS* = design action effect, eg. bending moment, M*, shear force, V*, etc.and ΦR = k mod [f o '.X]g 19).where Φ = capacity factork mod = product of relevant modification factors (eg.k 1 , k 6 , k 7 , k 12 , k 19 ,fo'= appropriate characteristic strengthX = geometric section property.Serviceability Limit State CapacityThe serviceability limit state is achieved when in-service displacements are kept within acceptablelimits. Calculated bending deflections and shear deformations must be modified by in service modificationfactors (j 2 , j 3 and j 6 as appropriate). Guidance on serviceability limit states is given in Appendix C of AS/NZS1170.0 : 2002.6.5 Beam DesignFigure 6.4 defines the minor (y-y) and major (x-x) axes of bending referred to in establishing strength limitstates for beams.39