BERKELEY — The building of the future will be able to keep standing even after a bomb blast knocks out first-floor supports, scientists say.
How far into the future? About two weeks, it turns out.
On Monday, University of California, Berkeley, professor Hassan Astaneh supervised the final test of the new technology, which uses cables embedded in the floors and encircling the building to act as emergency support if a supporting column is destroyed.
The collapse of the Alfred P. Murrah Federal Building, which killed 168 people and injured hundreds more, was caused by a bomb that destroyed a single supporting column.
The new technology – the same kind of engineering that keeps suspension bridges up – will be used at the new federal courthouse that is about to be constructed in Seattle. It also is expected to go into a new federal courthouse that will start going up in San Francisco in the next few years.
“This is our confirmation,” said Willie Hirano, a structural engineer with the Government Services Administration in Seattle who observed the test.
The design was originally developed by the structural and civil engineering firm of Skilling Ward Magnusson Barkshire of Seattle.
Scientists at Berkeley and Lawrence Livermore National Laboratory had run a number of tests and simulations. But the test Monday went further, taking the fortified floor to the limit.
First, a critical column supporting the floor, built about three feet off the ground, was taken away, leaving just the cables holding the floor up.
“Five, four, three, two, one!” called out professor Hassan Astaneh as thousands of pounds of pressure were slowly exerted on the floor.
For a few minutes, bolts snapped and steel girders groaned with the ominous sound effects of a disaster movie.
“Eighty thousand pounds on the floor ... 130,000 pounds on the floor,” Astaneh said as the concrete slab sagged with a thunderous rumbling.
“It’s holding – 190,000 pounds, it’s holding,” Astaneh said.
The test stopped at 190,000 pounds because that was how much pressure it took to force the test floor down to the real floor below.
The cables held and when the pressure was reversed the test floor slowly rose about 18 inches.
Better design can’t save people who are next to a bomb when it explodes.
An explosion creates 40,000 pounds of pressure per square foot; the worst storm in nature exerts 40 pounds per square foot, Astaneh said.
But the cable should save lives by preventing upper floors from collapsing and giving people room to escape, Astaneh said.
Cables could also make repair much simpler, allowing workers to jack up the floor and fix the bolts.
Putting cables into new construction such as the federal courthouse adds about $2 a square foot to the regular cost of $200 a square foot, Astaneh said. They also could be used in retrofitting, probably for about the same cost, he said.
“The next step is application,” he said.