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

The polar moment of area (I p ) of each of the nail rings with respect to the nail groupcentroid may then be calculated by substituting appropriate values of , d and w v into thefollowing equation.Ipwhere: s⎡ 3322 w vd⎛ d ⎞ ⎛ ⎞= ⎢ + + ⎜⎟ + w vd⎜⎟s ⎢⎣12 12 ⎝ 2 ⎠ ⎝ 2 ⎠= nail spacing along the grain.2⎤⎥⎥⎦(10.11)The polar moment (I p ) for the joint group will then be the sum of the polar moments of theindividual rings of nails.10.4 Plywood / LVL Gusseted Joints – MethodologyThe steps involved in the design of a plywood / LVL gusseted joint, (for the nomenclaturerefer Figues 10.2 and 10.3) are as follows:i. Determine the portal frame moments, shears and axial forces from a rigid frameanalysis. Obtain a preliminary size of the column / rafter by application of theflexure formula:Z = M/f bFor portals spans to about 20m, assume a member breadth of b = 60 to 100mmii.iii.Determine the length of the gusset which should be 1.5 to 2 times depth of thecolumn / rafter.Determine the effective depth h for a mitred internal knee or ridge gusset or d efor an internal or external haunch gusset at the critical stress line.h = 2D orL − Dde=+ D or⎛ D ⎞1 + ⎜1− ⎟tan∝⎝ 2L ⎠de= L − ywhere ∝ = roof slopeDepth ofRafter Pitch in degreesrafter/5 10 15 20column d e (mm) de (mm) de (mm) de(mm)D (mm) L=1.5D L=2D L=1.5D L=2D L=1.5D L=2D L=1.5D L=2D200 295 390 290 380 285 370 280 360300 445 585 435 565 430 550 425 540400 590 776 580 755 570 735 565 715600 885 1165 870 1130 855 1100 845 1075800 1180 1555 1160 1510 1140 1470 1130 14301000 1475 1940 1450 1885 1425 1835 1405 17901200 1770 2330 1740 2260 1710 2200 1685 2145TABLE 10.1: Effective depths (d e ) for internal haunch gussetsiv.Determine a preliminary thickness for the plywood or LVL gusset. The thicknessof parallel plies (t) required each side of the joint is:6M* pt ≥2(Φk' 219 g19)fbdewhere: M* p = design in-plane moment on jointφ = capacity factor for plywood / LVLk 1k= duration of load strength modification factor= moisture condition strength modification factor19129