CivilEngineeringBible.com CivilEngineeringBible.com

Solved Example: Design of Sawn Timber Column

Articles > Solved Example: Design of Sawn Timber Column

Question:

Design data:

Floor area supported by column:  A = 80 ft2

Unsupported length of column, L = 10 ft

Hinge support at top and bottom of column

Design load:

Floor live load: WL = 30 psf

Floor dead load: WD = 10 psf

Superimposed dead load: WSD = 5 psf

Timber: Southern pine, moisture less than 19%, used in normal room temperature.

 

Solution:

Refer to Design of Sawn Timber Columns and Compressive Members article for concepts.

1. Select southern pine, 4"x4" stud grade, d = 3.5 in

Actual cross section: Ac = 12.25 in2.

Allowable compressive stress parallel to grain: Fc = 975 psi

2. Calculate slenderness ratio: Ke = 1, Le =Ke´L = 10 ft, Le/d = 34 < 50

3. Calculate compressive stress with load duration factor

Load duration factor for dead load: CD = 0.9

Load duration factors for live load: CD = 1.0

Calculate Design load: P = [WD + WSD+ WL]´A = 3600 lb

Column compressive stress, fc=P/Ac = 293.8 psi

4. Calculate allowable stress without Cp.

CM=1, Ct=1, Cf=1

Fc* = Fc´CM´Ct´CF = 975 psi

5. Calculate elasticity modulus

E’=E´CM´Ct = 1.4´106 psi

6. Calculate FcE

KcE=0.3

FcE= KcE*E’/(Le/d)2= 357.3 psi

7. Calculate Cp

c = 0.8

C_p=frac{1+F_{cB}/F^*_c}{2c}-sqrt{[frac{1+F_{cB}/F^*_c}{2c}]^2-frac{F_{cB}/F^*_c}{c}}

Cp = 0.333

8. Calculate allowable compressive stress

F”c = Fc*´Cp = 324.8 psi               >          fc= 293.8 psi     O.K.


Read also:



Share:


Follow our official Facebook page (@civilengineeringbible) and Twitter page (@CivilEngBible) and do not miss the best civil engineering tools and articles!