At 8 feet, it was the biggest object ever tested on the lab’s so-called shake table. (The table can hold 6,000 pounds.) The plan was to see if a steel reinforcing rod screwed through the middle would hold the limestone sections together.
Shortly before noon, a warning buzzer sounded. A blue emergency light began flashing, and the crowd of student bystanders put on their hard hats.
Lab manager Adrian Brugger announced that the quake was about to begin.
“And, start,” he said.
The metal table on which the pinnacle was bolted began to jerk back and forth, squeaking as it did. There was no rumbling. No falling debris. No one fleeing into the streets.
It lasted 30 seconds. Brugger turned from a bank of computer screens and said, “That’s it.” The room was silent. That was it? Yes, he said, that was it. Applause broke out.
On Wednesday morning, an “earthquake” similar to
the 5.8-magnitude quake that struck the Washington region in August 2011 was simulated in New York City.
But it was in a laboratory. There were no injuries, and the whole thing was sort of underwhelming.
The simulation was a success, though. The steel rod held the pieces of the test pinnacle firmly together. There was nary a crack in the stone or the mortar.
“Well, there you have it,” said Joe Alonso, the head stonemason at the cathedral, who had helped put the test together and was watching. “I’m glad what we didn’t see. We saw it on August 23, 2011. That was enough for me.”
“It’s not very interesting,” said George Deodatis, chair of Columbia’s department of civil engineering and engineering mechanics. “But this is how the earthquake occurred.”
He said the engineers thought about adding some low frequency noise to the test for effect. “But we’re not Hollywood,” he said. “We’re scientists.”
The real earthquake, on a Tuesday afternoon, rattled the 301-foot-tall Episcopal cathedral to the tips of its majestic towers. Huge stone finials, gargoyles and crockets shook loose and came crashing down.
The quake knocked off the top of the southwest pinnacle on the cathedral’s central tower, which fell onto the cathedral roof, and nearly knocked over the tops of three other pinnacles, which were within seconds of falling.
All loose or dislodged stone was subsequently removed from the structure, which sustained millions of dollars in damage. Full repairs are expected to take years.
The stones of the old pinnacles had only been held together with small dowels, Alonso said. As earthquake repairs proceeded on the English Gothic cathedral in Northwest Washington, experts realized they needed a better system of reinforcement.
The steel rod seemed to be the answer.
On Wednesday, Alonso, who has been immersed in the cathedral’s repairs since the quake, said he believed it worked.
“That rod that’s in there, the way we (screwed) it down, I would imagine that did what it was supposed to do,” he said. “Without that rod, if that was doweled together with those little bronze dowels . . . there’s no doubt this thing would have come apart just like they did in the quake.”
As for the simulation, Deodatis said it was difficult to replicate exactly what the cathedral — almost 100 miles from the quake’s epicenter near Mineral, Va. — experienced.
The Columbia engineers came up with a good estimate and then bumped the intensity up a notch. “It’s very close to what happened that day,” he said.
The test, which cost about $45,000, was about a year in the making, Alonso said.
It was largely arranged by longtime cathedral consultant Robert Mark, a professor emeritus of architecture and civil engineering at Princeton University and a Capitol Hill resident.
Mark and Deodatis were colleagues at Princeton.
Mark, who was also present, said an early plan had been to place a model of the entire cathedral on the shake table. But he realized a model would not generate the data they wanted.
“We decided it’s better to do it at full scale because we wanted to check how the stone and the mortar stood up,” he said.
To set up the test, Alonso ordered five pre-cut limestone pieces from the same quarry in Indiana that provided stone for the construction of the cathedral. He and other cathedral stonemasons then assembled them into a rough copy of the pinnacle section that fell.
Last month, the disassembled pieces were trucked to Columbia, and earlier this month Alonso and his men reassembled them in the Columbia laboratory and fastened them together with the rod.
“The intent was . . . to simulate as close as possible the finished and fully re-created pinnacle that’s going to go back up on the central tower,” said James W. Shepherd, the cathedral’s director of preservation and facilities.
The test piece won’t be used again in a new pinnacle, Alonso said, but the stone will be recycled.
The main test Wednesday was not the only earthquake in the lab. A lesser shake was delivered, as well as a more severe shake. The pinnacle structure was sound throughout.
After the tests, Alonso and Deodatis used magnifiers to examine the surface of the stone for cracks.
“It’s in perfect condition,” Deodatis said at one point. “You’re absolutely safe.”
He added later: “I would stand next to this during an earthquake.”
“You can’t get a better guarantee than that,” Mark said.