Photo: Camara Porter/AdMedia/Sipa USA
The former Pfizer building, after last week’s fearful excitement, has settled down, literally. The Department of Buildings says it’s stable; temporary steel has shored up the floors above and below a pair of buckled columns; and you can once again walk down 42nd Street without fearing that the whole thing is about to come down on top of you. Now it’s time for whatever is called for to continue the project, a lot of which will involve figuring out what went wrong. Which is … what, exactly?
The obvious — though not necessarily correct — assumption is that a big and dumbass engineering error is at fault here, a miscalculation that the structural columns of the old building would be able to carry the new stories on top and couldn’t. But when I spoke with a couple of engineers about the project, they offered that such a flat-out design mistake is pretty unlikely. “Something was submitted that the city approved, right?” says Mohamad Saadeghvaziri, a civil-engineering professor at NJIT. “That something should — must have! — showed beefing up those columns. Now, the engineer forgot to do that? That’s crazy.” Dominick Pilla, a civil-engineering professor at NYU and founder of the firm DRPilla Consulting Engineers, added that there was likely an outside review on a project of this scale — “most vertical augmentations require a peer review” — and that it would have likely caught something so basic.
Instead, Saadeghvaziri and Pilla independently suggested (without, they took pains to admit, having seen actual plans or paperwork from the conversion) that we may be seeing the result of a sequencing mistake. Sometimes, as work is progressing on a building, interrelated tasks are overlapped. For example, maybe that column needed beefing up, but the contractor elected to start building floors on top and then do the reinforcement a short time later. You can’t say that such a move is inherently unsafe — don’t forget that, for example, those floors up above were raw space, and the columns holding them up are rated for apartments full of finishes and furniture and people, which provides some margin — but, obviously, it has to be done with close attention to the load rating. Pilla offers a hypothetical scenario where the engineers tell the contractor, “You guys built this thing all out of sequence. Hey, you better go back and do these columns because, as of Monday, they weren’t done yet, and you guys are on the sixth floor already.” That wouldn’t be an engineering error so much as a project-management one. “To say that the engineer neglected to check — that is a big leap,” says Pilla. He pauses, then adds with a little laugh. “I’m a design engineer, of course, so I’m speaking from that perspective.”
There is a third-party auditor, known as the special inspector, on every major construction site whose job it is to keep an eye on procedural glitches. For this job it was a firm called Domani, which, the New York Times is reporting, has been accused of cutting corners in the past; that implication of blame is speculative, at least for the moment, and guilt and penalties will surely be doled out after the investigations, including a preliminary criminal inquiry by the city.
In any case, construction will resume soon enough. (It is unlikely, judging by Berman’s statements, that he’ll take the building down and start over.) The first order of business, since last week, has been to ensure that the building has stopped moving. The tools to measure that today are incredibly fine and precise, involving sensors and lasers. As Saadeghvaziri put it to me, “You know, just as from space we can read a newspaper on the ground, we can monitor the movements to hundredths of millimeters.” In the meantime, photos show temporary shoring, in the form of heavy square steel tubes, propping up the floor above.
Next comes the analysis, to see where the building’s weight is being borne down to the ground. Structural loading is analogous to a liquid, explains Saadeghvaziri: “Take a hundred buckets of water and pour it at the top floor — it’ll find its way to the bottom.” Without the column that’s been lost, the remaining ones carry more of that flow, and may need extra reinforcement in addition to whatever they might have already been scheduled for. In the damaged section of the building, the crosswise beams that connected the buckled columns are also carrying new and unexpected stresses, since they’ve lost support. (Imagine reaching outward to grab a heavy bag that sits on a table, then having the table pulled out from under it. You might be able to hold it up at arm’s length, but not indefinitely.) Since the building was under conversion, its structure had likely already been analyzed, Pilla suggests, so it was probably fairly quick work to figure out which columns were now carrying the weight that had formerly been on the failed one. Then, he says, “you figure out that the columns need to be reinforced” and by how much. Often, that reinforcement takes the form of extra steel plates bolted to their sides. Some steel ties could perhaps also be placed between them as well to add stiffness, although that would not be an ideal choice because it would intrude on the interior space.
In photos of the building, you can see that the floors above the busted columns now droop a few inches. You might imagine that the next order of business is to jack them up so they’re level again, but that may not be so likely. “Easier said than done — you’ve got 18 floors above it,” explains Saadeghvaziri. Pilla, too, was skeptical: “From a structural standpoint, jacking that building back up is extremely problematic. What are you going to jack against? And what are you going to use to lift it up? You’ve got to take the load off from above and push the floor into place, and then do that all the way up. That doesn’t make much sense. You could do it, but it’s just an enormous amount of work.”
Instead, the solution may be to leave that drooping floor in place, repairing any damage to it but not moving it further. This choice may seem alarming on the surface, but you see it in old houses all the time. (A floor sags over the centuries, and when you renovate, you let it be rather than try to straighten it out, lest you crack all the plaster everywhere else.) Then you build a solid structure below to hold it firm, and then level off the surface so the floor doesn’t slope, and redo the façade so you don’t see it. (The developer, Nathan Berman, has said that the slab will be replaced, presumably because it’s cracked.) “If you just built a perfect, very stiff, very strong column under that sag,” Saadeghvaziri explains, it will carry whatever new structure is put on top of it safely. Pinna suggested a similar approach: “It looks like there’s like five or six floors that have sagged and sloped. So put columns in where needed, and then hopefully you have a working floor to ceiling height” — that is, nothing’s drooping so far that you’ve obviously lost some headroom — “and level everything. You might just look to level the floor from above and then put a dropped ceiling in to level it from underneath.” Whoever rents the affected apartments might never know that there was a near-disaster there, except that their ceilings are nine-and-a-half-feet high instead of ten.
You do have to wonder whether this has the potential to dampen the enthusiasm for residential conversions of office buildings. Saadeghvaziri hopes it won’t. “We’re all interested in recycling,” he says. “And as far as infrastructure, adaptive reuse is the best green design we could have. So I hope this failure is not used as an excuse for some ban on reuse. We want to provide housing, you know? But if we wanna fast-track it, you have to have checks and balances.”
