Hobbyman2 wrote:https://courses.cit.cornell.edu/arch264 ... xample7.1/
Capacity of wood column calculator
Jonathan Ochshorn
© 2008-2014 Jonathan Ochshorn.
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Directions: Select wood species and grade (or enter values for modulus of elasticity, E, and allowable stress, Fc, after setting "Species" for "Other"), wet service conditions, duration of load factor (CD), and effective column height for both axes (unless braced at different points, both heights should be the same -- see Fig. 1). Select either the 2005 or 2012 National Design Specification (NDS) values for lumber sizes, and choose either nails or bolts for built-up columns (see the NDS for nail and bolt requirements). Revised values for Southern Pine (effective June 1, 2013) are included only when the 2012 NDS is selected. Press "update" button.
See additional explanations and examples in my text. The duration of load factor, CD, for common proportions of dead and live loads is 1.0. For other combined loads (e.g., snow and dead load), see text for further details.
Note that the size factor adjustment (CF) should not be included in the allowable stress value entered, as it is already included in the calculations for each column size. The combined values of allowable stress and size factor for Southern Pine have been accounted for.
The x-axis refers to the "strong" axis of bending, except in the case of 3-2x4's bolted together, where the y-axis is stronger (see Fig. 2a). Fig. 2b shows an example where different unbraced lengths apply to the two axes: sheathing nailed to the stud prevents buckling about the y-axis, but not the x-axis. In this case, one might model the column with an unbraced height of 8 feet about the x-axis, and 0 feet about the y-axis.
axes of buckling
Fig. 1. Wood compression element showing different unbraced lengths for x- and y-axesaxes of buckling
Fig. 2. a) definition of x- and y-axes for wood cross-sections; b) example of continuous bracing for y-axis
Update
Species
These values not used except for 'other' species
Dimension lumber
Fc (psi) =
1,700
Emin (psi) =
690,000
Emin (psi) Fc (psi) Column size Capacity (lb)
580,000
1100
2x4
636
2-2x4
2,911
Grade
3-2x4
8,820
2x6
998
2-2x6
4,559
3-2x6
13,716
2x8
1,315
2-2x8
5,988
3-2x8
17,869
Lumber dimensions:
2x10
1,676
2-2x10
7,610
3-2x10
22,499
2x12
2,039
2-2x12
9,255
Duration of load factor, Cd
3-2x12
27,363
4x4
7,497
4x6
11,723
4x8
15,368
4x10
19,485
Outdoors (wet service conditions)?
4x12
23,698
Beams and stringers
Fc (psi) =
1,100
Emin (psi) =
580,000
Column size Capacity (lb)
Unbraced height, KL (ft), x-axis
6x10
42,775
6x12
52,023
8x12
79,068
8.50
Posts and timbers
Unbraced height, KL (ft), y-axis Fc (psi) =
1,150
Emin (psi) =
580,000
Column size Capacity (lb)
6x6
26,137
8.50
6x8
34,454
8x8
52,866
For built-up columns:
8x10
67,450
10x10
91,529
10x12
111,319
12x12
139,048
Capacity calculation values for:
x-axis dimension = 5.5 in.
y-axis dimension = 3 in.
Cf or size factor = 1.1
Cm or wet service factor = 1
Cd or load duration factor = 1
See values of Fc above; F*c = Fc x Cf x Cm x Cd = 1870 psi
Values for x-axis buckling:
See values of E'min above. FcE = 0.822 x E'min / (le/d)^2 = 1649.1 psi.
For built-up columns only, the value of Kf = 1 for buckling about the x-axis.
Cp or stability factor includes Kf and equals: 0.646
Values for y-axis buckling:
See values of E'min above. FcE = 0.822 x E'min / (le/d)^2 = 490.64 psi.
For nailed built-up columns only, the value of Kf = 0.6 for buckling about the y-axis.
Cp or stability factor includes Kf and equals: 0.148
Capacity of 2-2x6 = F*c x minimum Cp x area = 1870 x 0.148 x 5.5 x 3 = 4559 lb.
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Disclaimer: This calculator is not intended to be used for the design of actual structures, but only for schematic (preliminary) understanding of structural design principles. For the design of an actual structure, a competent professional should be consulted.
First posted July 1, 2008 | Last updated March 28, 2014
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a 3.3 x 3.5 isnt the same as a 4x4 in a strength test. 