The problem for the World Trade Center was that regular steel:
Above 750 F, steel starts to lose its structural integrity, and at 1100 F, steel loses 50 percent of its strength.A new formula infuses steel with nanoscale copper particles, this formula could maintain structural integrity at temperatures up to 1000 degrees F.
There is new concrete reinforced with whisker-thin steel fibers and carbon nanotubes to increase strength. Those nanotubes, tested by MIT professor John E. Fernandez, give the concrete flexibility to prevent cracking, and when cracks do occur the nanotubes can bridge the divide and stop them from spreading. If those tiny tubes could be filled with a bonding agent, the concrete could also heal itself.
New York’s Freedom Tower will be built around a 3 ft. reinforced concrete core wall that will help transfer loads throughout the building. “This tower was designed to be redundant,” lead designer Jeffrey Holmes says. “If something happens to a column or a beam, there’s plenty of strength and robustness so the building can heal itself by transferring loads to other areas.”
There are also better emergency evacuation systems
Burj Dubai, meanwhile, has expanded its evacuation procedures with a “lifeboat” elevator mode that includes 10 high-speed shuttles, among them two fire service cars in the concrete core.
An Israeli company called Escape Rescue Systems suggests that building managers have collapsible escape cabins stored on the roof. The cabins, which could carry 150 people, would swing onto the side of the building and descend to the ground quickly