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

Using the theory of parallel axes and parallel ply theory, the calculation is as follows:I neutral axis (NA) – stiffness, parallel to face grain per width bwhereI(NA)⎡ 1⎢⎣12⎤⎥⎦⎡ 1⎢⎣1232323= 2 bd1 + A1(y1)+ 2 x 0.03 bd2+ A 2(y2) + bd3A1.5.1A 1 = d 1 bA2 = d 2 b0.03 = factor for plies running at right angles to span for I used in stiffnesscomputations only.⎤⎥⎦112I (NA)-strength, parallel to face grain per width b⎡ 1⎢⎣12⎤⎥⎦112323= 2 bd1 + A1(y1)+ bd3A1.5.2Neglecting cross-directional veneers as required by AS/NZS 2269 –Z(NA) parallel to face grainI ( NA)strength parallel=y 1where y 1 is the distance from neutral axis (NA) which is the centre-line of balanced plywood to the outside ofthe farthest veneer which is parallel to the span (see FIGURE A5.1 ).Face Grain Perpendicular to the SpanAn illustration and section of face grain perpendicular to the span is shown in FIGURE A5.2 (AS 1720.1-1997).The calculation is as follows:FIGURE A5.2: Face grain perpendicular to spanI(NA) – stiffness, perpendicular to face grain per width bI(NA)⎡ 1⎢⎣12⎤⎥⎦⎡ 1⎢⎣1232323= 2 x 0.03 bd1 + A1(y1)+ 2 bd2+ A 2(y2 ) + 0.03 bd3A1.5.3⎤⎥⎦112Again, the 0.03 factor is used for those veneers at right angles to span.I(NA) – strength, perpendicular to face grain per width b⎡ 1= 2 ⎢ bd⎣12322 + A 2(y2 )⎤⎥⎦35