Problem 5.17

 

5-1/8 x 28.5 24F-1.8E Douglas Fir, 32' span, D+S, uniform load over simple span, supported against buckling

 

Cross Section

 

area = 146.1 in.2 ✓

centroid = 14.25 in.

Ix = bh3/12 = 5.125 x 28.53 / 12 = 9887 in.4 ✓

Sx = I / centroid = 693.8 in.3 ✓

 

 

Adjusted Design Values

 

NDS Supplement table 5A

CV = (21/L)1/x (12/d)1/x (5.125/b)1/x = (21/32)1/10 (12/28.5)1/10 (5.125/5.125)1/10 = 0.8793 ≤ 1.0

Cfu = 1

CM = 1

NDS section 2.3

CD = 1.15 (S)

Ct = 1

NDS section 3.3

CL = 1 (supported against buckling)

NDS section 3.7

CP = 1 (not a column)

NDS section 3.10.4

Cb = 1 (not enough info)

NDS section 5.3

Cc = 1 (not curved)

 

Property Reference Design
Values (psi)
(Table 5A)		 Adjustment Factors (Table 5.3.1) Adjusted Design
Values (psi)
CD CM Ct CL CV Cfu Cc CP Cb
bending stress F+bx
F-bx		  2400
1450		  1.15 1 1 1 0.8793 1 1     2427
1466
tension stress parallel to grain Ft  1100  1.15 1 1             1265
shear stress parallel to grain Fvx  265  1.15 1 1             305
compression stress perpendicular to grain Fc⊥x  650   1 1           1 650
compression stress parallel to grain Fc  1600  1.15 1 1         1   1840
radial tension Frt  --  1.15 1 1             --
modulus of elasticity (or MOE) Ex  1,800,000   1 1             1,800,000
modulus of elasticity for stability calculations Ex min  930,000   1 1             930,000
modulus of elasticity Eaxial 1,700,000   1 1             1,700,000

 

 

Adjusted Design Values for MC > 16%

 

NDS Supplement table 5A

CM = 0.8 for Fb and Ft, 0.875 for Fv, 0.53 for Fc⊥, 0.73 for Fc, 0.833 for E and Emin

 

Property Reference Design
Values (psi)
(Table 5A)		 Adjustment Factors (Table 5.3.1) Adjusted Design
Values (psi)
CD CM Ct CL CV Cfu Cc CP Cb
bending stress F+bx
F-bx		  2400
1450		  1.15 0.8 1 1 0.8793 1 1     1942
1173
tension stress parallel to grain Ft  1100  1.15 0.8 1             1012
shear stress parallel to grain Fvx  265  1.15 0.875 1             267
compression stress perpendicular to grain Fc⊥x  650   0.53 1           1 345
compression stress parallel to grain Fc  1600  1.15 0.73 1         1   1343
radial tension Frt  --  1.15 1 1             --
modulus of elasticity (or MOE) Ex  1,800,000   0.833 1             1,500,000
modulus of elasticity for stability calculations Ex min  930,000   0.833 1             775,000
modulus of elasticity Eaxial 1,700,000   0.833 1             1,420,000