Who makes steel for AI data centers

A data center is a steel frame holding up a roof over equipment that weighs a great deal. Structural steel makes the frame, rebar reinforces the concrete, and both are ordered in quantity early, on a schedule where late steel stops everything behind it. What AI has changed is the loading. Liquid-cooled racks are much heavier than the air- cooled racks that data center structural standards grew up around, mechanical equipment on the roof has grown, and overhead structure now carries cooling manifolds and busway as well as cable. The result is more steel per square metre than a conventional hall, plus foundation and slab work sized for point loads that would have been unusual a few years ago. The supply picture is mostly a domestic one — structural steel is heavy and freight- sensitive, so mills and fabricators serve regional markets — and the constraint is usually fabrication and erection capacity rather than raw mill output. What to look for is the split between the mills that make the steel and the fabricators who detail, cut and assemble it, since the fabricator is where schedules slip; whether a project uses modular or prefabricated steel assemblies, which shifts work off the critical path; and trade policy, which changes delivered price in ways that have nothing to do with mill capacity.