CATHEDRAL
experts say, some of that same technology will likely be used to return the 13th-century cathedral to a place that last year drew 12 million visitors.
One way to start, the experts said, will be to bring in other drones to survey locations inside the vast cathedral that are too dangerous or damaged for engineers to reach.
Jerry Hajjar, a civil engineering professor at Northeastern University, said drones can be equipped with sensors — such as small cameras and laser scanners — that will allow engineers to document fire damage and create highly accurate three-dimensional visions of specific locations inside the church.
Hajjar said other sensors may be able to peer inside the church’s walls like an X-ray and estimate the mineralogical properties and the degree of stress the structure is under. But the documentation effort could prove more difficult than it sounds, Hajjar said, noting that the higher a drone must rise, the lower the battery life and the amount of time it can stay in the air.
Another method for testing the cathedral’s integrity could involve robots, Hajjar said, pointing out that research is already underway for using climbing robots to inspect and repair steel bridges.
“The value of using robots became very apparent after the Fukushima disaster,” Hajjar said.
A popular video game could provide a source of digital information about the Notre Dame. In a 2014 article in the Verge, Caroline Miousse — an artist who worked on the video game Assassin’s Creed — said she devoted two years to creating a model of the church that captured the inside and outside of the building.
Once engineers have a clearer sense of the church’s structural integrity, experts said, they’ll be able to design a suitable roof. They’ll have to decide whether to rebuild the roof framing with timber. If they don’t opt for a structurally engineered wood, which could reduce the roof ’s weight and offer artistic freedom, engineers could choose toworkwith steel.
Though it would depart from the church’s original wooden roof, steel would allow engineers to use less material and be even lighter than wood, according to Gary Howes, COO of The Durable Group, a consortium of historic restoration companies.
Replacing what was lost may not be the biggest challenge, Howes said. Instead, he said, it will be marrying the old and the new, offering the building’s worldwide admirers a window in the past that includes upgrades and meets modern building codes.
“This project is going to be more about emotion than structure,” he said. “Everybody wants that cathedral to look like it has always looked, theway they remember it.”
Fortunately, Howes added, France has an advantage over the rest of the world.
“Some of the best craftsmen in the world are located in France,” he said. “Whether it’s restoration or even contemporary work, they haven’t lost the historic trades like we did here in the U.S. Each year, we go there to learn from them.”
James Shepherd, director of preservation and facilities at Washington National Cathedral, where damage from a 2011 earthquake is still unrepaired, said the immediate days after an event like Monday’s fire will be a critical time for the Notre Dame.
“They’ll need expertise there to make sure that they’re sorting through the rubble and pulling out things that are salvageable or not,” Shepherd said. “You’re talking about things that might be 700 or 800 years old that they’re trying to pull out that might be partially burned or partially damaged bywater.”