The construction industry has a few ideas for taking cost out of wind turbine and wind transmission-tower foundations with the simplest of components: reinforcing bar. For instance, most rebar in foundations is a grade 60, meaning it has a tensile strength of 60 ksi (60,000 psi break strength). But boosting the steel strength to 97 ksi allows using less of it in concrete structures so it improves the flow of concrete.
The latter problem arises when the required amount of 60-ksi steel produces a dense cage of bar so closely positioned that concrete poured into the center of the cage flows poorly, if at all, through the bars. Inspections often find gaps and occlusions in the final foundation. The higher strength steel allows using less of it to meet structural requirements and produces a cage with much wider gaps between bars.
Stressteel Regional Manager Jim Close says the real savings are not in the cost difference of the rebars. “It comes in weight saving, which means the rebar cage can be lowered into foundation holes for most wind turbines and wind transmission towers using a smaller, and less-expensive-to-rent crane,” he says. “In addition, because the bars are threaded, a simple junction can join two bars into a longer unit. No welding is needed.” WPE
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