Concrete filled steel tube

Concrete filled steel tube (CFST) is a construction technique used for columns, electricity transmitting towers, and, in the 21st century, skyscrapers and arch bridges (especially the ones with a very long span). CFST is a composite material similar to reinforced concrete, except that the steel reinforcement comes not in form of a rebar embedded into concrete, but as a steel tube outside of the concrete body.

The all-way compression experienced by the concrete core inside the tube increases its bearing capacity and deformability. The latter, even when the high-strength concrete, makes the failure modes to be "quasi-plastic", greatly increasing survivability of the construction in case of an earthquake.

The pipes used can be circular or rectangular in section and might contain further reinforcement inside, or the concrete can be sandwiched between two concentric tubes in a concrete-filled double skin steel tubular (CFDST) construction.