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

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