Structural Integrity

This is 99% Invisible. I’m Roman Mars.

William LeMessurier: I’m going to tell you a story first about how a building got designed, a very unusual building in New York, the Citicorp Tower.

Roman: When it was built in 1977, Citicorp Center was, at 59 stories, the 7th tallest building in the world.

Joel Werner: You know, I can still remember the first time I saw the Citicorp Center. As you exit the local subway station at Lexington and 53rd in Midtown, Manhattan you’re confronted by a sheer 915-foot building face shooting up right from your feet.

Roman: That’s reporter Joel Werner.

Joel: With its gleaming facade of glass and steel and striking 45-degree angle crown, Citicorp Center is truly one of the most spectacular skyscrapers on a skyline known for its spectacular skyscrapers. But really it’s the base of the building that takes your breath away. This massive 59 story skyscraper levitates midair, hovering 115 feet above the street corner.

Roman: At first glance, the building seems to violate the basic laws of physics.

Joel: When you look up, you look directly at the underside of the building corner. It overhangs the sidewalk. I mean we’d expect the column on even the grounds. Instead, there’s nothing, just thin air.

Roman: Of course the building isn’t really levitating. It’s propped up on stilts which join the building at the midpoint of each side. It does not look sturdy. But it’s got to be sturdy. It’s got to be safe for they wouldn’t have built it this way, right?

Joel: Yes, well that’s the secret about this building. It was literally a secret for nearly 2 decades after it was built. The Citicorp Center could very well have blown over in the wind.

William: But I wonder now was when was this building going to fall down?

Roman: The Architect of the Citigroup Center was Hugh Stubbins but most of the credit for this building is given to the Chief Structural Engineer, William LeMessurier.

William: You’ll laugh at me but I did conceive it on a napkin at a Greek restaurant in Cambridge.

Joel: LeMessurier passed away in 2007. This is him giving a talk at MIT in 1995.

William: The whole problem was to build a building on a site that has a church at one corner.

Joel: Saint Peter’s Lutheran Church.

William: Honey-old building but this is the lowest point of Victorian architecture.

Roman: I don’t think it was that bad.

Joel: Saint Peter sat at the corner of the lot. When the church sold their land to Citicorp, it was on the condition that they build a new church in the exact same location. Beyond that, the company was free to build their skyscraper around the church and in the airspace above it. So a plan was hatched to float the building over the church. Hence the stilts and because the church was in the corner of the lot, LeMessurier put the stilts in kind of a weird place.

William: You couldn’t have columns in the corners where they ought to be on a conventional building so they were moved to the middle.

Joel: Placing the columns at the midpoint of each side rather in the corners made the building less stable. So for additional support, LeMessurier designed a chevron bracing structure, essentially rows and rows of V’s, each 8 stories high pointing down the middle of each building face to where the supporting columns had been moved.

William: Actually the architect wanted to keep the building simple at its skin because there was so much drama going on at the bottom and at the top anyway. He said, “No, if we’re going to have any diagonals I don’t ever want to see them.”

Joel: So the chevron bracing structure was slipped under the skin of the building. It formed the Citicorp Center’s skeleton. Now, one of the amazing things about this chevron bracing structure is that it’s so lightweight that when the wind blows–

William: It’s more dynamically excitable than a building that weighed twice as much.

Joel: In other words, it moves with the wind.

Roman: Which most people find really unsettling.

Joel: Understandably, right? So, LeMessurier added something called a tuned mass damper.

William: The tuned mass damper is a mass of concrete which is 29 feet square and about 8 feet thick. It weighs 400 tons. It is floated on pressurized oil bearings.

Joel: The device sits at the very top of the building and acts to steady the oscillations. It offsets the wind gusts.

Roman: So to recap, we have a 59 story tower floating on 115-foot stilts.

Joel: Stilts which are not in the corner where you would expect them but rather in the middle of each side of the base.

Roman: With a skeleton of beams shaped like V’s which make it super light for a skyscraper.

Joel: And to stop it from swaying in the wind, there’s a 400-ton block of concrete on the roof, totally ingenious, really cutting edge design. And LeMessurier is a pro, so in accordance with the New York City building code, he runs all kinds of mathematical models to make sure the building is going to hold up.

Roman: And everything seemed just fine until, as LeMessurier tells it, he got a phone call.

William: June 1978, I’m in my office. I got a call from a student at some– I do not know the school. I wish he would call me for the past he never has. But anyway, he was a real student from New Jersey. I think he was an architectural student and his teacher had given him this building to study and report on because it’s unusual.

Joel: As LeMessurier tells it, these precocious college senior calls him up to ask how his building structure is going to cope with quartering winds.

Roman: An undergraduate student calling out the head of a world-renowned engineering firm on one of the most innovative skyscraper designs of its day.

Joel: Quartering winds, the winds that caught the student’s attention, are those that hit the building on the corner, exerting pressure on 2 faces at once. LeMessurier’s calculations on the perpendicular winds, winds that hit the face of the building square on, seemed to be fine. But as the story goes, the student raised the alarm about Citicorp Center being particularly vulnerable at its corners.

Roman: It turns out LeMessurier had never run the numbers on what quartering winds would do to the building because normally buildings are strongest at their corners.

Joel: But this is no normal building. Remember what’s going on here. Supporting columns shifted to the midpoint of each building face, the chevron bracing skeleton, and the unusually light mass of the building. Taken alone, no one of these design quirks should have presented a problem. But as the student told LeMessurier taken together, they left Citicorp Center particularly vulnerable to wind striking the structure at its corners.

Roman: And when LeMessurier started to investigate the student’s claims, he realized that the root of the problem had to do with a change that had been made to the original plans. It had to do with how the chevron bracing structure was fastened together. LeMessurier’s plan originally called for the joints to be welded.

William: With full penetration welds.

Roman: But the contractor had suggested using bolts instead.

William: Bethlehem Steel actually designed beautiful bolts and connections for the forces that my people gave them.

Roman: It was a cost-saving measure. LeMessurier says that this change would have happened without his knowledge.

Joel: Given the wind load calculations LeMessurier’s team had supplied, welding these V’s together was overkill. Run the math and it looked like bolts would do just fine.

Roman: And bolts would have done just fine on pretty much any other building except Citicorp Center had an Achilles heel on each of its 4 corners.

Joel: LeMessurier could now see what no one else had.

Roman: No one except for that pesky student from New Jersey.

Joel: And as LeMessurier started looking into the student’s claims about these quartering winds, he realized the situation wasn’t just bad.

Roman: It was a disaster waiting to happen.

William: The return period to failure was 16 years, think about that.

Joel: Here’s what that means. LeMessurier calculated the quartering wind velocities required to topple Citicorp Center. He then matched these velocities to weather patterns to see how frequently on average, winds strong enough to blow the building over, occurred.

Roman: LeMessurier found that a storm strong enough to knock over the building hits New York City on average once every 55 years. But that’s only if the tuned mass damper is working.

Joel: The tuned mass damper needs power to run. And if you get a huge storm, LeMessurier realized, it’s not unlikely that the city could suffer a blackout.

Roman: LeMessurier ran the numbers again, this time imagining the damper without power.

William: It was even worse.

Roman: Without the damper, a storm strong enough to topple Citicorp Center hits New York on average once every 16 years.

Joel: To put this another way, for each year the building was standing there was about a 1 in 16 chance of a storm potent enough to take out the Citicorp Center.

Roman: This building is 915 feet high. If it failed it would topple sideways in the wind, crashing into other Manhattan skyscrapers. A whole slew of buildings from Midtown to Central Park would fall like dominoes.

William: This thing is in real trouble.

Roman: This brand new skyscraper was on the verge of catastrophic failure.

Joel: But the imminent disaster wasn’t the result of one glaring oversight. Rather, it was a sequence of minor issues. Let’s remember how we got here. This building was on stilts because they had to build over the church.

Roman: And stilts placed at the corners would have been just fine except the church was at the corner of the lot, so the stilts had to be in the middle of each face.

Joel: And that could have been A-OK except the offset stilts led LeMessurier to use an ultralight chevron bracing structure.

Roman: Which would have been perfectly adequate except in the end those chevron V’s were bolted, not welded together.

Joel: And even that could have been fine, except no one thought about how vulnerable this crazy design was to wind blowing at its corners.

Roman: No one except an anonymous college student.

Joel: LeMessurier went to Citicorp Chairman, Walter Wriston and told him they would need to open up the building and weld it back together.

William: He said, “How much it’s going to cost?” I don’t think it’s going to cost an awful lot, a million or 2? That’s nothing. Well, a building that cost 175 million and if it falls down–

Joel: From here, LeMessurier and his team worked with the Citicorp bigwigs to coordinate emergency repairs on the building. With the help of the NYPD, they worked out an evacuation plan spanning a 10 block radius. They had 2500 Red Cross volunteers on standby and 3 different weather services employed 24/7 to keep an eye on potential windstorms. They welded through the night and quit at daybreak just as the building occupants returned to work.

Roman: But all this happened in secret over 3 months without telling anyone who worked there.

Joel: Which is the part of the story I kind of have a problem with. I mean isn’t this situation serious enough to warrant informing the building’s tenants? My wife works in a skyscraper in Midtown, Manhattan and, it’s about informed consent. I’d want her to be able to make the judgment call about whether or not to go work in a faulty building, not to have it made for her.

Roman: Their thinking was a contingency plan was in place and ready to be invoked as soon as a storm strong enough to blow the building down was in striking distance of New York except–

Joel: There was a giant storm racing up the East Coast, Hurricane Ella. LeMessurier says the powers that be were just hours away from calling in the evacuation. But the hurricane veered into the Atlantic before it hit New York and in the end, the public was never notified.

Roman: I know what you’re thinking. If only there was some kind of independent organization that serves the public’s right to know that might wonder why Citicorp Center was aglow with blow torches all night every night. Something like a newspaper, except–

Joel: The New York Times was on strike.

William: Not only did the New York Times go on strike but all the newspapers in New York went on strike until October, so we had a press blackout. And that was the greatest thing that ever happened.

Roman: So, word never got out and construction was finished.

Joel: And Citicorp Center has remained standing ever since, long enough to be renamed Citigroup Center and later 601 Lexington. The whole thing remained a secret for almost 20 years.

Roman: In the early 90s, writer Joe Morgenstern overheard the story being told at a party. He interviewed LeMessurier and broke the story in the New Yorker in 1995.

Joel: LeMessurier went on to tell the story publicly like he did at MIT which is how we have him talking about this. And, after the story got out, it was written up as a textbook case of good ethics in structural engineering. New York was spared a tremendous loss of life and the annihilation of its skyline all because Bill LeMessurier was humble enough to give time to the inquiry of an undergraduate student.

Roman: Thank goodness for this uppity college senior and his thesis and kudos to Bill LeMessurier who through his humility and heroism saves the day.

William: That’s really the end of the story.

Roman: Except–

William: Wait a minute, there are a couple of more things here.

Joel: Let’s take a step back and remember how this story starts.

William: I got a call from a student. It was a real student from New Jersey. I think he was an architectural student. His teacher had given him this building to study. I do not know the school. I wish he would call me.

Joel: The way LeMessurier tells it and how Joe Morgenstern told it in the New Yorker that a college student, the young hero of that story, was lost to history.

Roman: Okay wait for it. Wait for this moment. It’s a good one. Here it comes.

Diane: It would have been sometime in the early 90s. I remember being upstairs in my bedroom and had one of my sons, he was sort of hanging off me as I was trying to put him down to go to bed. And suddenly my husband who had been downstairs started yelling a little bit saying, “Diane, quick. Turn on the TV. Your thesis building is on TV.”

Joel: This is Diane Hartley.

Roman: As far as we can tell, she was the student in LeMessurier’s story.

Diane: And so, I was holding the baby with one arm, I fumbled for the remote and got to the channel, just in time to hear–

Man 1: This building could have killed tens of thousands of people.

Man 2: The extraordinary chain of events began with a phone call out of the blue from a student in New Jersey whose professor had told him to write a paper on the Citicorp Tower. William LeMessurier.

William: I explained to this student at the telephone call that he could tell his professor.

Diane: I was aghast. I’d nearly dropped my baby.

Joel: This was the first time Diane had ever heard of the emergency retrofits, the round the clock weather monitoring, the evacuation plans–

Roman: And the involvement of a student.

Joel: So, when she heard LeMessurier reference a student, a male student.

Diane: I, of course, assumed “Gosh, there was some guy studying the building as well. And wow, how could I miss this? Wow.” So it was pretty remarkable but I, of course, assumed at the time that there as another fellow who would have been a better researcher than I had been.

Joel: In fact, Diane never even considered that she might be the student in the story. That is until she went to a Princeton event honoring her thesis adviser, David Billington.

Diane: When I showed up at the event, David said, “Well, have you ever heard of the problems with the Citicorp Center?” And I said, “Yes, isn’t that pretty remarkable? I wonder who it was that discovered this problem.” And he said, “You know, Diane, there are very few engineering schools in New Jersey and quite frankly I know all of them. I know the heads of the programs of all of them and I’ve talked to all of them. There was no other student from New Jersey that was studying the building except for you. So it must have been you.”

David Billington: Yes, I don’t know of any other student.

Joel: This is David Billington, the thesis adviser.

David: Yes, my name is David Billington. That’s correct and I’m an engineer, spent 53 years at Princeton as a faculty member. I was Diane Hartley’s thesis adviser. She wrote the most outstanding thesis [chuckles] anybody, was very long, have you ever seen it? Two big volumes, yes anyway.

Joel: To hear Diane Hartley and David Billington tell the story, Diane wasn’t some in your face know it all.

Roman: Here is her version of the events.

Diane: So, I was 21 years old and I was a senior at Princeton University where I was studying architecture and urban planning. My thesis, I had selected the topic of the Citicorp Center in New York, which had only recently been completed and occupied.

Joel: She reached out to LeMessurier’s firm to get the calculations that they had run. And then she tried to replicate the math herself. To do the work again from the start and see if she got the same answers as LeMessurier’s engineers. David Billington, her adviser, asked her to ask LeMessurier’s firm about the quartering winds.

David: The quartering wind, I thought that was a problem and that it should be looked at.

Diane: So, I obtained calculations from the design engineer from LeMessurier’s office and I concluded the governing loading condition was the wind hitting the corner of the building.

Joel: But the math just wasn’t coming outright.

Diane: I was struggling with the calculations. I assumed of course that the engineer had done the right thing and any inconsistency that I might find would be my error. The building was standing.

Joel: After all, she was just a college senior and LeMessurier and his people were established, internationally renowned professional structural engineers.

Roman: Diane got back in touch with LeMessurier’s firm although she never talked with LeMessurier herself.

Diane: I never called LeMessurier. I never said these things that were documented in the various reports that have been published to date.

Joel: Diane did talk to a junior engineer, LeMessurier’s New York office named Joel Weinstein. She showed him her calculations.

Diane: But at the end of the day, no, I didn’t feel that I had put my finger on a major problem. I assumed I was wrong and wasn’t understanding things.

Roman: Even David Billington who told Diane to look into the quartering winds in the first place didn’t think there was any imminent threat.

David: I mean I don’t think either of us really were in a position to say at the time, “You got to do something, Bill, right away.” We didn’t have that feeling. I had a feeling that she should talk to the designers and find out whether this quartering wind had been considered and if so, what was the outcome.

Roman: But somehow Diane’s discovery got silently passed up the totem pole within LeMessurier’s firm.

David: Weinstein must have said, “Well, I better check with Bill.” That would have been the logical thing to do and he probably did that. I never heard that. You never heard it I guess.

Joel: We asked Joel Weinstein the engineer about meeting Diane and what happened afterward. But he says he has no memory of this either way, though he does acknowledge that if Diane remembers speaking to him, then it probably happened. That, in such a circumstance, he would have passed her message onto LeMessurier.

Roman: So it could be that’s why LeMessurier remembers speaking to a male student. He was conflating Diane Hartley the student with Joel Weinstein his own staffer.

Joel: Now, of course, it is possible that there was a male student.

Roman: A third man.

Joel: He somehow had the same data as Diane and actually did talk to LeMessurier on the phone.

Roman: But I find it really hard to believe that such a person didn’t come forward and claim the spotlight after the story broke.

Joel: Gender aside, Diane definitely doesn’t fit the image of the precocious student. She identified a problem without even recognizing the significance of what she had done for decades.

Diane: It’s not that I did something. It’s that perhaps my questions helped someone figure something out. Perhaps my questions were meant to be. I think if I had really realized that there was a problem and put my finger on it and raised it up the flagpole, I could pat myself on the back for having done something that was pretty remarkable. But at the end of the day, I feel like I was a bit player in a play that had a happy ending.

David: So yes, she deserves more credit than she’s gotten. [chuckles] You could tell her that, include that I think that that’s right. That’s I think the coda for this.

Roman: 99% Invisible was produced this week by Joel Werner and Sam Greenspan. With Katie Mingle, Avery Trufleman and me, Roman Mars. Special thanks to Michael Vardaro who wrote the AIA Trust white paper about Citicorp Center, Shamil Raghavan at the National Academy of Engineering for helping me track down archival audio of William LeMessurier and Allen Bellows of website Damn Interesting for talking to me about this about 2 years ago at this point. We are Project 91.7 local public radio KALW in San Francisco and produced at the offices of Arcsine, a beautiful architecture firm in beautiful downtown Oakland, California.



“Wild’n Cuz I’m Young” — Kid Cudi
“A Drifting Up”— Jon Hopkins
“Cobweb Collector”— Twink
“Aufbruch”; “Its Caption Was A Star”— The Octopus Project
“Panic Disorder”— Melodium
“Dome Nest”— OK Ikumi
“brass practice”— Lullatone
“Red Air”— OK Ikumi
“Grundlsee”; “Sunlight”— OK Ikumi
“Making Up Minds”; “Dome Nest”— OK Ikumi

  1. I’m having trouble visualizing the tower, could someone smarter than me post a “floorplan” that shows where all the supports are? It looks like there is something in the middle of the tower base?

    1. Joseph M. Johnson, Ph.D., P.E.

      As an engineer, I am always amazed at the extent to which architects will go to make excused for their art. Contrary to the statements at the end of the show, you cannot separate the structural problems from the architectural ones. If we were talking about some sort of abstract artwork, you may be able to make some sort of argument that, but for the fact that the building was endangering the lives of all its occupants and many of its neighbors, the artistry was amazing. BUT IT IS NOT AN ABSTRACT ARTWORK. It is a building with thousands of souls working and living in and around it. The Architect has an obligation first and foremost, not to his art, but to public safety.
      Also, I reject the characterization that this story had a happy ending. There was no loss of life, but that was due entirely to chance. But for a series of lucky accidents, there would still be a dangerous domino threating the skyline of Manhattan. As it turns out, Mr. LeMessurier could hide the fig leaf that a design change from his original plan reduced the safety margin and that restoring his welded chevrons made the building safe again. But, this was only a happy accident. Let’s be clear. Those responsible for the safety of this building didn’t even do the right calculations to be sure the building had sufficient safety margins. It was little more than luck that welding the bolted joints was a sufficient solution to the problem.

      In the case of the Citi Center Building, the architects chose an innovative design that required a structure that went against thousands of years of conventional wisdom with respect to the design of tall structures. Good on them, except, they failed to do the necessary calculations to be sure that the building was safe. This is a failure, pure & simple.

      99PI, now I am looking at you. Framing this story as anything but an epic fail is an epic fail on your part.

    2. Here’s the structural of the building:

      and here’s Google search results for “CIti corp center””

      As a former architecture student, I absolutely love this episode. And I lover 99% Invisible. I can’t share this episode enough.

      Good jobs guys and thank you.

    3. The chevron shaped steel frame – seen in the sketch above – is at the perimeter of the tower and the center of it is taken up by the elevator/service core – which also helps hold the building up.
      In between them is column-free office space.

  2. Mat Merten, PE

    I agree with Mr. Johnson above. Mr. LeMessurier did a upstanding job taking swift action to fix the problem, What he did should be praised in ethics courses. But his firm made a significant error which endangered lives. I can see how a non-engineer can frame this story as happy ending, but in my world people get fired for negligence like this.

    I would be curious to know if LeMessurier was penalized by the Engineering Board of NY for this calculational oversight.

    1. FormulaLes

      I disagree.

      A student alerted the engineer to a problem with the design. The engineer listened, then went to the client, admitted to the problem. The engineer then went to find a way to solve the problem. Whilst a solution was being found, steps and procedures were put in place to deal with the worse case scenario of a building collapse. In my mind this is an engineer acting ethically.

      It is important to understand that there was not a fundamental problem with the design of the structure, but rather during construction the connections for the diagonal beams were changed from welded to bolted, at the request of the contractor, and approved by the engineer. In hindsight that request should not have been approved, but that does not automatically imply negligence of the engineer.

      In my mind the engineer would have been negligent if they were acting outside their area of competence, which they were not. The engineer would also be negligent if they ignored recognised design standards, or if they didn’t follow proper checking and peer review processes.

      The other possible avenue of negligence would be if the engineer ignored the problem when it was brought to their attention, or tried to shift the blame onto someone else. The engineer however accepted responsibility for the problem and took actions to fix the problem.

      About the only thing to my mind that should have been handled differently was the removal of the secrecy surrounding the rectification work. But can you place the blame for that at the engineer? I am doubtful that the engineer would have had much control over the secrecy adopted.

    2. Joseph M. Johnson, Ph.D., P.E.

      “It is important to understand that there was not a fundamental problem with the design of the structure, but rather during construction the connections for the diagonal beams were changed from welded to bolted, at the request of the contractor, and approved by the engineer. In hindsight that request should not have been approved, but that does not automatically imply negligence of the engineer.”

      The fact that the building was safe “as designed” (welded) was due to little more than luck. Read the New Yorker Article. Mr. LeMessurier had not done the calculations for a wind from a corner. In normal designs this is not necessary (because in normal designs, the worst case loading is a perpendicular wind), but Mr. LeMessurier wasn’t doing a normal design was he? Because he was doing an unusual design, he (and all those around him) had an obligation to carefully explore the normal set of calculations and see if the normal assumptions apply (and to think of new cases as well).

      They did not do this. The first time he did the calculations (according to the New Yorker article) was in order to show this pesky student just how wrong they were.

      I repeat myself, but I cannot see this as anything but an epic failure of the architecture and engineering communities. This building was not safe by design. It was safe by accident.

      It should be told over the campfire or at conferences or wherever scary stories are told to young engineers and architects to keep them on the straight and narrow.

  3. Ric

    The TV Show “Numb3rs” > Season 1 > Episode 4 “Structural Corruption” retells a fictionalized version of this story, but it has a lot of facts right and real computer models of the quartering winds twisting that would happen. Worth a watch after hearing this episode.

  4. bread

    Just visited this place during my lunch break. It really is breathtaking. I spent a good 10 minutes just ogling. It’s a shame what folks take for granted. What an amazing structure.

  5. Although not specifically highlighted, the engineers who take a look at Figure B-19 of the thesis (posted, above) will see the fundamental calculation error: calling out the distance from the column to the axis of rotation as ‘d/2’. With ‘d’ typically referring to the length of the diagonal of the floor plan, the correct distance should have been called out as ‘d/4’. This may well have resulted from applying the formula for calculating overturning moment in convention structures (i.e., with columns at the corners, or ‘d/2’ from the axis of rotation) rather than thinking through how the formula should be derived given the unique structure (i.e. twice the column section, but each located ‘d/4’ from the axis of rotation). This was my point of debate with LeMessurier’s project engineer, who asserted that the structure was ‘more efficient’ in ways that I failed to understand.

    1. roman

      Sam here, producer at 99% Invisible. I just found out that my mom worked at Citicorp Center from 1979-1981 and was there during the secret renovations! Thanks Diane!

  6. Juan Rivera, P.E.

    As a structural engineer myself, I was fascinated by this episode. In response to comment #11 above, the figure d/2 must be referring to half the distance between columns, as measured perpendicular to the axis or rotation shown. Moreover, what you say is true “With ‘d’ typically referring to the length of the diagonal of the floor plan”, then the distance from the corner to the building would be d/2. Thus, by the Pythagorean theorem, half the distance between the columns would be SQRT(d)/2, not d/4.

    1. Curious One

      Could you please post a figure showing how you came up with your answer? I’m no engineer, but I am curious. I proved (to myself at least) that the distance from a column to the axis of rotation shown is indeed d/4. If d is the diagonal, and the columns lie at the midpoint of each side, then line AB forms (with the top corner) a triangle similar (in the geometric sense) to the triangle formed by the horizontal diagonal and the top corner of the building. Because the diagonal is d, and the columns lie at the midpoint of a side, length AB is d/2. The distance from the midpoint of AB (which lies on the axis of rotation) to the column is half of d/2 = d/4. Could you please explain to this curious one WHY that is not so? Thanks in advance.

    2. Juan Rivera, P.E.

      In response to curious one: I guess the confusion comes from the fact that we are using different assumptions. I realize now you are assuming “d” is the diagonal across the floor plan of the building. That is why you get the correct value of d/4 as the distance between the column and the axis of rotation. I was usind “d” as the dimension of the building itself on the side. But in defense of the original engineer who drew the picture, I think he denoted “d” as the distance between the columns and not as a function of the building dimensions. Sorry for the confusion.

    3. Curious One

      Thank you for taking the time to respond to my question. Perhaps we should both defer to Ms. Hartley’s comment at #11 above for the proper interpretation of the figure, as she is presumably most familiar with the source material.

      However, I still have a small issue with your original comment. If we assume d is the length of a side, then the indicated distance is still not sqrt(d)/2. That is what caught my eye in your original post–I couldn’t understand where the ‘sqrt(d)’ term would come from. I couldn’t quite follow what you were saying well enough to try the math on my own, so I figured I’d ask you! Regardless, by the pythagorean theorem, if d is the length of a side of the building, the indicated length is d/2sqrt(2).

      Am I missing something else?

      Again, I appreciate you taking the time to reply. Thank you.

  7. Joseph M. Johnson, Ph.D., P.E.

    From the New Yorker Aritcle:
    “LeMessurier had long since established the strength of those braces in perpendicular winds–the only calculation required by New York City’s building code. Now, in the spirit of intellectual play, he wanted to see if they were just as strong in winds hitting from forty-five degrees. His new calculations surprised him.”

    Again, once more with FEELING, he had not even DONE a vital calculation to know his building was safe. He had turned an age old design practice on its head by putting the columns in the middle of the sides rather than at the corners. Okay this is fine, live outside the box all you want, you clever guy. BUT, then you don’t get to lean back in your chair collecting awards for your cleverness if you used shortcuts (such as “the worst case wind loading condition is when the wind hits a wall broadside”) that depend on living INSIDE the box. It was on him and all those around him to be 100% sure that living outside the box was safe in this case. Clearly, he didn’t do that.

    I think it is also important to remember that the bolt vs. weld on the chevrons is a complete red herring. If they had followed his design to the letter, it STILL would have been nothing but luck that kept the building from falling down. He didn’t KNOW it was safe until well after the building was standing atop the NYC skyline.

    Mr. LeMessusier deserves our scorn. Engineers and Architects alike should denounce him for having such ill regard for the public safety.

    1. Joseph M. Johnson, Ph.D., P.E.

      I just now realized that the title of the Episode is a pun. I propose a new, better title: Structural Failure

  8. Nevil Nayak

    I work at Citi and find “Episode 110: Structural Integrity” a great read. I’m sharing it on the internal blog. Thanks.

  9. Fabula Raza

    On the surface, this story seems a stuffy piece of esoteric academic and scientific history. However, I’m fascinated by the amount of baggage that was stuffed into it. Besides the obvious form versus function debate, there are embedded points made on gender discrimination and if you don’t fear the bends of deep sea exploration, I’m sure finance and nationalism play a crucial part in this tragic comedy. Back in WW2, the Japanese used to fly planes in US warships, 13 years ago Muslims flew jetliners into trade center. My point is that through overt hostility or subtle negligence, New Yorkers should be adamant about this nearly averted disaster.

    But everything’s been resolved for now so I’d imagine there’s nothing to worry about and no need to be nervous anymore. The tuned mass damper point is important. I’m too lazy to look closely, but the calculations being discussed are taking into account a functioning tmd or in the event of power failure?

    I’m having a hard time determining what is being said on account of what is being said (no, not necessarily how, you read that right braniac).

  10. Bob

    I saw the original episode and even though not an engineer was appalled that a joint change from wield to bolt was granted without consulting the original designer. Further that cornering winds were not considered when even a non-engineer can see that cornering winds would put enormous strain on the building with the non-standard mid stilts.

  11. Chasalz

    A frightening expose to say the least. I wonder how many other architectural flaws there are hidden around the city just waiting for disaster to occur. Having worked across the street at 399 Park Ave. also Citibank, and occasionally in Citicorp Center, one never knows that one’s life could be in so much danger.

  12. jschmidt

    The Tacoma Washington bridge of the 50s comes to mind. That design didn’t plan on the winds and the resonance they can setup. Good catch by the student and kudos for the architect for not letting his ego get in the way. When I received a D in Statics and dynamics in college, I knew civil engineering was not for me.Great story.

  13. Oaklandguy

    On rare occasions, I have to park the car and listen carefully to a story on the radio. Yesterday was one of those occasions.

    My life’s story includes an engineering design that failed. The failure didn’t kill any humans, but did cause a major penalty to the client. I did my best to prevent the failure, but I was unable to do so.

    The project was the main wastewater treatment plant for a large city. I was a staff engineer for a corporation that was consultant to the city. I was assigned to review the basic design calculations for the project. The design was by one of the most brilliant engineers in the world, within that particular specialty. However, I spotted serious gaps in the project as designed. I argued with that brilliant engineer for some 8 hours over the course of a week. My superiors refused to take me sufficiently seriously, the plant was built the way they wanted, and the plant was unable to clean the wastewater enough to meet the requirements. Eventually, an additional process was added to the treatment plant so that it could produce water that was good enough to discharge. This retrofit cost many millions of dollars – I don’t know how many – and I suppose some fish died, although not any humans. The retrofit was paid for by taxpayers and/or the city’s customers. As for me, I was fired for “poor engineering judgement” long before the plant was actually built. Forces of ego contributed mightily to the failure.

    So when I heard the Citicorp Center story yesterday, I did indeed need to stop, write down some details, and learn more.

    — Oaklandguy, Apr. 18, 2014

  14. I love how almost every episode makes me want to visit the blog to see what’s being talked about. The stories stand on their own, but the site is a great bonus feature. Thanks for the amazing work.

  15. Very familiar with this story and building, and was excited to hear about the recent update!

    I worked across the street from Citicorp for 14 years (@ 909 3rd), and wasn’t worried as was mentioned in the podcast that it could “topple sideways in the wind …” Oh no. I worked across the street diagonally, which I thought was the way the building would have fallen.

    And thanks for using my picture in the blog. Glad to contribute here.

  16. Nice episode, classic 99pi. But my one takeaway was a wish that Diane Hartley not only got credit for the insight she had versus some bland, half-forgotten story of a male architect (because they’re all male), but also that she felt she had more right to be *right*! Kudos to her professor for seeing her impact.

  17. John Schinker

    What happened to the church? Looking at Google Streetview, it seems like the church is gone.

  18. Joseph M. Johnson, Ph.D., P.E.

    Question for the readers of this page,

    Doesn’t anyone else think it is cowardly on the part of Roman, Sam & the rest of the 99PI folk not to take an explicit stand on this issue?

    Roman often talks about architecture in the grandest terms. They should have taken a side on this very important issue.

    Even if they were not courageous enough to speak in their own voice, where was the voice denouncing Mr. LeMessurie for his obvious failing in this affair. Surely they could have found some engineer to be somewhat critical of the fact that he failed to do a fundamental calculation necessary to ascertain the safety of his design until after his building would have toppled had the wind not been favorable to him and to point out that in such a case it is shameful for him to hide behind his claim that repairs that added the necessary margin of safety was little more than returning the building to his original design? Surely they could have found this voice. But they didn’t because they didn’t look for this voice and thereby they took a definite side in the matter. The wrong side.

    Roman & the 99PI show takes sides all the time. They took sides in this case by not presenting any voice (easily found, do not say otherwise) deservedly denouncing Mr. LeMessurier’s colossal mistake. They have done a disservice not only to their listening audience but to engineers & architects worldwide.

    Joe J.

    P.S. I get that this building is amazing to behold. It is stunning. I gasped when I first looked at the pictures of it from a Google image search. I want this to be a great building. And, it is. Now. By the grace of God and not much else. It should have been great by design from before it was built. It was not and, as such, we should hold those responsible up as examples of the dangers of being blinded by pride in our own cleverness. JJ

    1. Mat Merten, PE

      I do not know what Mr. Mars’s background is, but I doubt he is a licensed engineer. And as such I do not expect him to see the world through our lens. I don’t expect him or many others to see this as an engineering failure (which was 100% owned up to). Mr. Mars is a wonderful story teller and most people will view this story as Mr. Mars does. Let “them” have it their way and let the engineers keep doing our thing in the background.

      No I don’t think it is “cowardly”. I think they are looking at this through their lens and we through ours.

      PS – wonder if the state board punished Mr. LeMessurier?

    2. Joseph M. Johnson, Ph.D., P.E.

      Yes, perhaps you are right. The Engineering Culture, in general, and that of Professional Engineers, in particular, has at its core the idea that every engineer has a duty to the public first and foremost — even above duty to their paying clients. The public cannot judge if a boiler will blow up, if an appliance will electrocute them, if a dam will burst or if a bridge will fall. We are in a position of trust, and even more so that doctors, we must not let the public down.

      And yet, I am quite disappointed in Roman and the 99PI gang as I feel they have a duty to the public as well.

      I feel strongly that they should have found a Professional Engineer (or actually almost ANY engineer based on those I work with and around) to condemn this clear lack of due diligence on the part of Mr. LeMessurier.

      Joe J.

  19. Great listening to this story, heard about this once before, but never got the full explanation. I hate to do it but I am going to:

    Guess he only LeMessurier’d once.

  20. I created an album on my Flickr site of scans of the original engineering and design drawings for Citicorp Center.

    They further illustrate the design innovations and almost tragic human error of planning only for perpendicular wind loads.

    The illustrations come from two books published about the Stubbins firm published decades ago and long before the public was notified of the engineering issues.

    Flickr Album:


  21. Oh, man, that was an fantastic story-telling for an incredibly well produced episode. Congrats Roman, his producers and everyone involved. Fascinating story.

  22. Josh

    Hi Roman / Sam,

    This was I think your best episode so far this year. It’s a great story, but it left me very unfulfilled. How could such a serious and seemingly simple mistake be made in engineering? How common are such mistakes? Also your story makes LeMessurier sound like a hero, but I think the ethical issues are not at all that clear cut, for example see this analysis:

    You did an episode before about the ethics of building prisons. I think this is well-worthy of a follow-up episode examining these issues, rather than just resting on the happy luck stemming from the random questions of a student.

  23. Irene LeMessurier

    To Mr. Johnson, I would like to point out that you do not know all the facts. The New Yorker article did not get all the facts straight. I think its wise not to believe everything you read. There is a reason you are not finding others to agree with your condemnation of my father.

  24. A fascinating story, and one that I was familiar with since I was heavily involved in the wind-tunnel model testing of that building in Canada in the early 1970s. Those tests were carried out in 1973-4 (not in 1978 as implied by the BBC story..) and reported by the University of Western Ontario to Le Messurier & Associates in 1975 (with preliminary results issued in 1974). In the tests the wind direction was varied every ten degrees, and the structural response of the building to ‘quartering’ winds could have been determined from them. However, apparently the New York Building Code of the time was used instead; that Code assumed that wind only blew at right angles to a wall of a building. The wind-tunnel tests also studied and reported on the wind forces across the wind – an important consideration for very tall buildings.

    While the late Bill LeMessurier is to be commended on his integrity in revealing the errors in the building design and structure, there was some obligation for him to read a report commissioned by his own company at the time it was issued, rather than using an outdated building code for such an important structure. Also even without reading that report, it should have been obvious that hurricane winds could blow in any direction with respect to the walls of any building in Manhattan.

    The 1973-4 wind tunnel testing also studied in detail the performance of the ‘tuned mass damper’ (400 tonnes of concrete at the top of the building) which I understand has performed successfully over the life of the building in reducing the wind-induced vibration in non-hurricane winds.

  25. Lucas

    I work on a corporate campus that has a number of TV screens to display messages and occasionally, quotes from our founder. I realized recently that this building is the background for one of the quotes:

    “We like individuals who are broad minded enough to respect the other person’s point of view regardless of his personal convictions.”

    I wish I could fulfill whichever designer created that image by telling them that I’m finally understanding this deep cut.

  26. Curious

    Why do they say that there was a 1/16 chance the building would come down each year; doesn’t that assume a 100 percent chance that a blackout would render there tuned mass damper inoperable every year?

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