Citicorp Center | NYC skyscraper saved by a student’s question

0:00 this isn't almost failure that was caught an undergraduate student she asked a question to a daring structural engineer and he realized that he made a mistake a mistake so big that could cost 200,000 people their lives my name is Tyler lay I'm an engineering professor and I teach my students making mistakes as human we're all gonna do it sometimes these mistakes can have a big impact we're talking about the Citicorp Center which is in Manhattan New York it's built in 1977 1.3 million square feet was built for about in today's dollars about 880 million is it an

0:46 iconic structure on the New York skyline the architect was Hugh Stubbins jr. and the engineer one of the greatest of his time William will measure one of the challenges with this structure is it was to be built on the site of st. Peters of Allen to Cole Lutheran Church which was built in 1905 and the congregation at st. Peters didn't want to move I love their church and they love the spot so if they're talking with them they said guess what let you keep your spot and we'll build you a new church they were excited about that the church happen to be located right where the major column of the

1:34 structure was supposed to be so bill Stebbins came to the measure and said can we change the structural system so the original plant had four columns for major columns in the corners of the building and one major column in the center well a measure said what if we just slide the columns what if we just moved them over to have our new point well this is what it looked like this is the side view if I was to cut the building right here and start to look at it this is what the original structure looked like major columns on the sides and then these light floor systems or beams here in the center with the new one there was gonna be a new challenge how are we going to support these edges how

2:21 are we gonna keep them from deflecting too much so we came up with a pretty cool idea pine trees what do you I mean well he said I've seen pine trees and they kind of look like this they have branches that go up ever so often support the structure like that here's another view you can see these these diagonal members help hold up these beams one of the things that control tall building design is the wind in New York City they get hurricanes they get pretty high winds there it's a big deal there's a lot of concern and called drift of buildings

3:08 moving in and out and possibly hitting one another here's an image the city Corp Center with a look with the wind load on it and you can see when it does that and it wants to deflect to the side then this sides gonna be in tension it's gonna want to be pulled up and this sides gonna be in compression it's gonna be want to be pushed down and that means when I design for these diagonal members on this face they're gonna look something like this but what the measure figured out was the gravity load the weight of the people and the office furniture and everything else was so high that it was more than the wind load so on his calculations this is much

3:57 larger than this and so he didn't really have to design for these members to be in tension or to be pulled they're all designed to be overall in compression so if I look at this connection they just used very simple bolts to hold them together and then an undergraduate student named Diane Hartley at Princeton was doing her undergraduate thesis under David bellington amazing amazing professor of structural engineering and she was actually studying the Citicorp Center and she couldn't quite figure out how the structural system worked she actually called up the measures company and asked

4:44 questions it said when I analyze a structure like this it seems to make sense but if I analyze for a diagonal wind structure looks like it may fail it actually may fail and only a 70 mile-per-hour wind holy cow the measure had never thought about this load case he spent a lot of time thinking about it and then he realized he needed to get some help so the measure went first contacted his insurance company contacted the lawyers contacted Citicorp contacted the architect and said we have a problem I've made a mistake he was very

5:32 forthcoming about it said we've got to get this fixed he even came with them with an idea for a repair that's one tip if you ever make a mistake bring the solution with you to make the fix they ended up taking that bolt of connection and welding it they needed a lot of welders they hired every welder they could find in a hundred mile radius of New York City and they made all the repairs at night over a three-month period and they didn't tell anyone in the building what was going on now when people that knew that were public officials were the mayor the building commissioner and the head of the welders union why did they need the head of the

6:18 welders union because I needed to get somebody to convince those welders to work only at night to make the repairs they would actually pull back parts of the structure exposing them fix everything welded up put it back and not let anyone know what was going on I did it over about a three-month period and this story was not made public for about twenty years so what did the measure do right he admitted his mistake he let other people know about it he told others about the problem and he didn't create a hysteria kept everything under control nice and calm he assembled a great team to make the repairs and they went

7:03 flawlessly but what did the measure do wrong there's many people have criticized the measure and they say that he should have told the public if you would have worked in that building what you've wanted to know would you've wanted to know that your life was in danger because if that building goes and falls over from a wind load it's gonna take out other buildings around it people asked me it could have killed 200,000 people and a 70 mile-per-hour wind happens often that's kind of scary he didn't report what had happened for over 20 years he kept it a secret I'm sure he wasn't proud of what he did but he needs to let other people know so that they

7:50 don't make the same mistake and the biggest mistake of all is that he didn't have other people check his work not well enough I like to say mistakes you can't live with them you can't live without them if you have a job where you do things for other people especially do things for the public on a large scale it can't afford mistakes hey thank you so much for watching this I love making these videos and leave me a comment below did what measure do the right thing what do you think Thanks take care bye