Question

using reference design values for No. 1 DF-L (Douglass Fir Larch) 10x10

use the format conversion factor to determine the nominal values for LRFD.

Fb=1200

Ft=825

Fv=170

Fc_perpendicular=625

Fc=1000

E=1600000

Emin=580,000

Answer 1

Ans) Given,

Bending stress = 1200 psi

Shear stress = 825 psi

F_v = 170 psi

Fc perpendicular = 625 psi

Fc = 1000psi

Modulus of Elasticity of Timber = 1600000 psi

Modulus of elasticity for stability (E_min) = 580000 psi

According to LRFD ,

_c (compression)= 0.90

_s (stability)=0.85

Format conversion factor (K_F) for compression = 2.16 / _c

= 2.40

K_F for stability = 1.5 / c

= 1.76

Also , = 0.80

So,Nominal crushing strength (F_n) = Fc x K_F x x c x Cm x Ct

where Cm and Ct are wet service factor and temperature factor respectively,

Assuming Cm = 0.90 and Ct =1 ,

Putting values ,

F_n= 1000 x 2.40 x 0.80 x 0.90 x 0.90 x 1

= 1555 psf

P = A x Fn

= 10 x10 x1555

= 155500 lbs

In Buckling ,

E^'_min = E_min x K_F x s x Cm x Ct

Putting values,

E'_min = 580000 x 1.76 x 0.85 x 0.9 x 1

= 780912 psi