Some years ago, the Steel Quiz of Modern Steel Construction asked “Which of the following camber ordinates for a 30ft W16x26 beam are not recommended? a. ¼ in., b. ½ in., c. 1-1/2 in, d. 2 in, e. 5 in.”
The editors answered that “a, b, and e. Usually cambers of ¾ in. or less are avoided because the cost of cambering may exceed the potential savings in concrete. They are so small and the cambering process is not so exact to begin with. Choice e is an impractical, large camber that may cause unacceptable beam web buckling.”
These answers most likely are accurate regarding bending done by what are commonly called “cambering machines,” devices incorporating one or two hydraulic rams to press the steel sections at various points to induce a camber.
But these answers are not accurate regarding beam bending done by what are commonly called “section benders,” “angle rolls” or “beam benders.” These machines typically incorporate three or four rolls to induce a camber or curve a structural steel section beyond a camber.
For example, we can roll-curve or bend the beam cited above to a 41 in. mid-ordinate rise with no web buckling. Of course this is far beyond a camber, but our point is that web buckling is not a limiting factor for large cambers if the right machinery and processes are used. Furthermore, we recommend getting a quick roll-curving quote to determine if, in fact, cambers of ¾ in. or less would exceed the potential savings in concrete. Lastly, cambering can be done to exacting tolerances when the roll-curving method is used on specially designed section benders.
