Eliminating Flex in Supporting Steel

Question:
I used 2-inch-wide, ½-inch-thick steel flat bar as supports for a raised concrete bartop, but it’s flexing too much. What should I have used?

Answer:
The use of flat steel barstock as a bartop support is common, mainly because thin steel (1/4 to ½ inch) is easy to hide under the countertop. Steel is strong, but strength is not the issue here, stiffness is. And the stiffness of steel depends on the shape and orientation. Flat steel barstock is too flexible to provide a secure, rigid support for a heavy concrete countertop.

A piece of steel flatbar oriented horizontally seems fairly stiff, but it really acts like a spring. So if use a series of steel bars fastened to the top of a pony wall as the supports for a raised concrete bartop, the steel bars behave structurally as a cantilever and the weight of the concrete bears on the steel. But any additional weight from someone leaning on the bartop will cause the steel bars to flex.

If you orient the same steel flatbar vertically, so it’s now 2 inches tall and ½ inch wide, that increases its stiffness by a factor of 64! You may think that increasing the width of the bar would have similar benefits, but actually increasing the bar’s width from 2 inches to 4 inches increases stiffness only by a factor of 2. So you can see that a vertical orientation is much stronger. This is just like floor joists or roof rafters. If you’ve ever seen a stick-framed house, you know that joists and rafters are oriented vertically.

If you simply can’t orient the bars vertically because of aesthetic concerns, using wider bars and/or increasing the number of bars will help. But that’s not nearly as effective as turning them on edge.

Another thing you can do to accommodate vertically oriented steel bars is design the bartop with a thick, dropped edge. The bartop will appear to be very thick, but in fact will be only 1 ½ or 2 inches thick, and the steel will be concealed behind the dropped edge.

I did this with a round bartop that extended 2 feet out, as shown in the photos. The steel in this case is square in cross section, and it is lagged to a stud in the wall behind the cabinet. The vertical sides of the steel provide stiffness, and lagging the steel to the stud prevents tipping.

A steel bar oriented vertically will support the weight of a countertop without flexing. A dropped edge conceals the steel without adding to the overall thickness of the countertop.