Timber Design
Basic Formulas
fb=McI
Horizontal Shear Stress
fv=VQIb
Formula for Spacing of Bolts and Nails
s=RIVQ=Rq
Notching of Beams Formulas
Fv=3V2bd′(dd′)
Beams notched at points of support on the tension side
Fv=3V2An(dd′n)
Beams notched at point of support on the compression side
V=23Fvb[d−e(d−d′)d′]
Allowable Bending Stress
Cs=√Ledb2
Short Unbraced Beam (Cs ≤ 10)
F′b=Fb
Intermediate Unbraced Column (10 < Cs ≤ Ck)
F′b=Fb[1−13(CsCk)4]
Ck=0.811√EFb
Long Unbraced Beam For (Ck < Cs < 50)
F′b=0.438ECs2
Allowable Compression at an Angle to Grain
Pn=Psin2ϕ+Qcos2ϕ
Hankinson's Formula
Pn=PQPsin2θ+Qcos2θ
Allowable Compressive Stress for Columns
F′c=Fc
Intermediate column (11 < Le/d < K)
F′c=Fc[1−13(Le/dK)4]
K=0.671√EFc
Long column (Le/d ≥ K)
F′c=0.30E(Le/d)2
Combined Flexure and Axial Stress
ftFt+fbFb≤1.0
fb−ftF′b≤1.0
Flexure and Axial Compression
fcF′c+fbF′b−Jfc≤1.0
J=Le/d−11K−11
K=0.671√EFc
Wind Load for the Design of Purlins
P=0.0000473v2
Wind pressure normal to the roof (Duchemins Formula)
Pn=2Psinθ1+sin2θ