Steel gets stronger when it gets colder. This isn't a gimmick — it's a well-documented property of body-centered cubic metals. A36 structural steel at room temperature has a yield strength around 250 MPa. Cool it to liquid nitrogen temperatures (77 K, or −196 °C) and that climbs to roughly 450–500 MPa. Austenitic stainless steels do even better: 304 SS jumps from ~215 MPa yield at room temp to over 700 MPa at 77 K, and its ultimate tensile strength can exceed 1500 MPa. So what if we ran cryogenic plumbing through skyscraper columns to double their load capacity?

The seductive math. A typical 50-story tower has core columns sized for ~30 MN axial loads. If yield strength doubles, you could halve the steel cross-section, or keep the section and double the building height. For a 200,000 m² high-rise using ~15,000 tonnes of structural steel at ~$1,200/tonne, halving steel saves ~$9 million in material alone. Tempting.

Now the heat leak problem. Concrete and air around the column are at ~293 K. A bare steel column at 77 K with a surface area of, say, 400 m² per floor would conduct heat ferociously. With even a high-performance multilayer vacuum insulation (MLI) jacket — say k_eff ≈ 0.0005 W/m·K at 5 cm thickness — heat leak is:

Q = (k × A × ΔT) / t
Q = (0.0005 × 400 × 216) / 0.05 ≈ 864 W per floor

Over 50 floors: ~43 kW of continuous cooling load. Liquid nitrogen's latent heat of vaporization is 199 kJ/kg, so you'd boil off:

43,000 W ÷ 199,000 J/kg ≈ 0.22 kg/s ≈ 19 tonnes per day

At industrial LN₂ prices (~$0.15/kg delivered), that's ~$2,800/day, or $1 million per year just to keep the columns cold. Recondensing on-site with cryocoolers? A Stirling cryocooler at 77 K has a Carnot efficiency of maybe 15%; ideal Carnot COP at that ΔT is 77/(293−77) = 0.36, so real COP ≈ 0.05. You'd need ~860 kW of electrical input continuously. Goodbye, savings.

The structural nightmares. Thermal contraction of steel from 293 K to 77 K is about 0.3%. A 200 m column shrinks by 60 cm. Every beam-to-column connection becomes a thermal expansion joint capable of moving 6 mm per floor. Differential contraction between cooled columns and warm floor slabs would tear conventional moment connections apart. You'd need sliding bearings everywhere, sacrificing the lateral stiffness that makes a moment frame work in the first place.

And the human factor. A cryogenic leak in an occupied building displaces oxygen — LN₂ expands 700× when it vaporizes. A single 200-liter spill releases 140 m³ of nitrogen gas, enough to asphyxiate occupants in a stairwell. The 2006 Texas A&M nitrogen incident killed a researcher from a far smaller release.

Where it almost makes sense. Cryogenic strengthening is real and used: LNG storage tanks exploit the 9% nickel steel's improved toughness at −162 °C, and some aerospace tankage uses cold-strengthened austenitics. But these are incidentally cold — the cryogen is the cargo, not a structural service fluid.

For buildings, the energy-in-perpetuity to maintain strength dwarfs the one-time material savings within ~9 years, and that's before insurance underwriters laugh you out of the room.