James' World 2

Click the link below the picture

.

The evacuation of a skyscraper in Midtown Manhattan and the surrounding area was ordered on Tuesday after the building showed signs of potential collapse that may have been caused by overload, experts say.

The Fire Department of the City of New York (FDNY) said in a statement on Tuesday that it received a call to the building just before 8 A.M. EDT. When the FDNY arrived at 235 East 42nd Street, near Grand Central Terminal, it found at least two steel columns buckling on the 21st and 22nd floors and sagging flooring between the 21st and 26th floors.

Buckling steel columns are a well-known issue among the engineering community, says Gregoy Deierlein, a professor of structural engineering at Stanford University. Deierlein wouldn’t speculate on what specifically may have caused the buckling in this case. But he says it’s not uncommon for columns to become damaged or weakened. That, in turn, can lead floors above the weak points to sag as the column bends, he says.

“Imagine if you’re standing on the floor and you look over—the portion of the floor supported by that column would have dropped a little bit, so it’s going to look like a sagging floor,” Deierlein says.

When buildings like this skyscraper are constructed, engineers erect columns designed to support not just the weight of the building itself but also a certain amount of “live load” per square foot. That extra load includes the people using the building and any other contents. Deierlein says that sometimes the live load limit can be exceeded during renovations because construction materials may be stockpiled inside a building while work is ongoing.

“That could be a very concentrated live load, which could be enough load to overcome the column strength,” he says. “Then the question is, is the column strength enough for what it should have been designed for? Or it could have been a combination of the column wasn’t quite strong enough for what it was designed for, and then you add a lot of load to it.”

While several stories were being added to the building as part of the renovation, Magued Iskaner, a professor in the civil, urban and environmental engineering department at the New York University Tandon School of Engineering, says he would be “very surprised” if this wasn’t taken into account during the planning stages.

“One of the most common reasons for increase of load is that the load gets transferred from one area of a building to a new area,” he adds. “All of these people could have done these things correctly, but the presumed capacity of a column is off simply because there was a latent defect that nobody knew about.”

The most likely point of failure for load-bearing infrastructure is at the joints which connect components, says Doug Holmes, an engineering professor at Boston University. Those connections are “where a significant amount of shearing forces are exerted—think a bolt shearing off—and in the buckling of columns. But, of course, if there is corrosion or wear or damage, any of the components along the load path can be a source of failure.”

The 37-story tower, which formerly served as the New York City headquarters of pharmaceutical giant Pfizer, is in the middle of a $75 million conversion from offices into a luxury apartment project, with some 1,600 units planned.

The conversion from offices to residential is a joint project by David Werner Real Estate Investments and MetroLoft. In a comment reported by the New York Times, MetroLoft said: “The safety of everyone at and surrounding the building is our number one priority.”

In an update sent to Scientific American on Wednesday, a MetroLoft spokesperson said a team had worked with the Department of Buildings (DOB) to stabilize the affected columns, and the DOB had confirmed the structure’s stability. They added that the issue had only affected 30 units and the building was at no time under threat of collapse.

“We are in the process of addressing the issue and will fully rebuild this portion of the building in tandem with ongoing construction,” the spokesperson said. “We remain on schedule, and this work will not delay delivery of the building as it is such a small portion of the project. We are working around the clock so that operations can resume and life in the area can return to normal.”

Gensler, the architecture firm leading the project, did not immediately reply to a request for comment.

Engineers from the DOB have also been deployed to the scene, and the FDNY is reportedly using drones to further examine the building.

The New York Times and other outlets report that emergency beams and other supporting structures are being installed in an effort take pressure off the affected columns. Deierlein says that these measures are needed in the short term—at least until the cause of the damage can be ascertained. But a permanent replacement of the columns “is not an easy thing in an existing building like this.”

.

.

.

Click the link below for the complete article:

.

__________________________________________