There are many activities to show how engineers know how to choose the structural material and shape, solid or hollow of a column or beam. We will next calculate one example to spark your interest in this fascinating store of knowledge. To demonstrate how doubling the thickness of a column affects (this is amazing) its load bearing capacity, draw the cross section of two columns. One is a 2x4, and the other is a 4x4(in.) wooden column.
Using the formula above for finding I, compare the moment of inertia of each.
I = (4)(2)3 / 12 which equals 2.67 in. 4
I = (4)(4)3 / 12 which equals 21.3 in.4
Therefore, we see that the 4x4 is _____ times stiffer than the 2x4. (8 times! 21.3 / 2.67 = 7.977…)
You can demonstrate further how a hollow 4x4 will support three times the weight of a solid 2x2.
More activities can be found on such internet sites as http:/polymorph.net/engineer.htm
