At least two structural columns buckled and failed in a 37-story office tower in Midtown Manhattan on Tuesday, prompting evacuations of nearby streets and buildings. While city officials asserted that the tower was in no danger of collapsing completely, outside engineers said further failures in the structure could not be ruled out.
A pair of columns that failed completely were part of the tower’s existing structure. A New York Times review of images and videos from inside the building has found that several floors were added atop these columns.
City officials said in a news conference on Tuesday that the building was continuing to move, while they simultaneously assured the city that the building would not suffer “total collapse.” “The way this building is constructed, it’s a steel-frame building,” John Esposito, a chief in the Fire Department in New York, said at the afternoon news conference. “So, it would not be a total collapse. It would be more of a localized collapse.” Still, he said, “that remains our concern, that it’s moved.”
Engineers said that the movement itself was cause for concern. In a properly designed steel building, they said, loads should redistribute quickly to surviving structural supports if columns failed.
Joe DiPompeo, a former president of the Structural Engineering Institute at the American Society of Civil Engineers, said that if the structure had been overloaded, he would expect any movement “to happen very quickly,” rather than gradually.
“Generally when a column buckles, it’s a sudden failure,” Mr. DiPompeo said. He said that a full collapse remained unlikely given the redundancies built into the building codes.
Engineers often refer to the most dangerous possibility as a progressive collapse, a process in which structures near the initial failure become overstressed and also fail, potentially bringing down the building if the sequence continues. While unlikely, it cannot be ruled out, Mr. DiPompeo said.
Footage recorded from inside the building shows at least two structural columns appear to have failed completely, Mr. DiPompeo said. Other nonstructural, interior walls — or at least the metal “studs” that were in place to hold them up — also appear to have deformed.
“The only way that really happens is if the floor above them dropped. It looks like the floor above could have dropped a foot or two, which is obviously not a good situation,” Mr. DiPompeo said.
The 37-story building is in the process of being converted from office space into residential units. Four new floors and a large vertical portion were added onto the existing building in recent months. The vertical portion consists of a stack of over a dozen new floors cantilevered out over the existing building below.
Engineers said that there was nothing inherently wrong with adding residential floors or the cantilevered section above the columns that failed, as long as the original structure and the modifications had properly accounted for the added weight and wind loads.
“The cantilever alone doesn’t change anything,” Mr. DiPompeo said, but it does put additional load on the columns underneath — a factor that should have been reflected in the design.
Nathan Berman, managing principal and founder of MetroLoft, the developer overseeing the conversion, said on Tuesday that “this incident is nothing more than a typical construction mishap.”
He said two columns near the northwest corner of the tower had bent under the weight of additions to the building above, most likely because those columns had not been properly reinforced, though he said an investigation would determine the cause. The rest of the columns, he said, “picked up the weight.” He estimated the affected floors above the failed columns had sagged by a maximum of four inches.
Mr. Berman said that he expected the problems to be fixed and the project to be completed with, at most, a slight delay.
On Tuesday evening, installation of temporary shoring was set to begin shortly, in order to help stabilize the 20th and 21st floors of the building.
