There are two basic types of braces
- Horizontal Braces – Braces that run horizontal between columns
- Diagonal Bracing – Braces that run at an angle between columns
It is possibly an over simplification but horizontal bracing is generally used to resist compression forces in the column and diagonal bracing is generally used to add stability to the structure by resisting twisting.
The goal of designing a structure is to find the optimum mix of
- Column material, size and shape
- Brace material, size, shape and spacing
Ideally, columns should be braced at their critical length. The critical length of a column is the length at which the column will no longer buckle (or bend) no matter how much weight is placed on it. A column at its critical length will fail by crushing. One way to determine if you have braced a structure correctly is to watch the structure as it is tested. If you see the columns buckling (or bending) right before the structure fails then you have not properly braced the structure for the particular columns you have chosen. Well built structures should not “explode” but should simply crush.
There is one other thing you should keep in mind about bracing a structure. Imagine that a 6″ column section will support 25 pounds. The Law of squares tells us that a 3″ section of the same column will support 100 pounds (invert 1/2 to get 2 – square 2 to get 4 and multiply 4 x 25=100). How much weight will the column support if you stack the 3″ piece on top of the 6″ piece thus creating a 9″ column.
If you said it will support 125 pounds then you guessed wrong. A column is only as strong as its weakest section so this column would only support 25 pounds since the 6″ section of column would fail at 25 pounds.