(0:00) I'd like to thank Carol for inviting me to do this. She asked me to talk about Burj Khalifa, and we talked about topics and decided to say what we learned. In this process of what we learned, the first question is: What did we know, and where do we go from that?

Before I go on, though, I want to point out that Carol wanted to dedicate this whole series to Les Robertson, and I think that's totally appropriate. I can speak for most of my colleagues of my generation that Les was a mentor to all of us. It was great to run into him and SawTeen somewhere in the world, have dinner, and hear the stories, which would teach us both about technology and ethics and about life topics. It was really quite a pleasure too, even though we were competitors, in a commercial sense, we were all friends and colleagues in a professional sense.

(1:13) Okay, now, Burj Khalifa. What have we learned? Let's start out with the concept of what did we know? I want to go through a couple of concepts that are fundamental to understanding what we're going to talk about.

First of all, when you see a giant tall building such as the Willis Tower, do not think of it as anything other than a giant beam coming out of the ground, cantilevering out of the ground. If you think of it as thousands of elements, such as these beams and spandrel beams and floor beams and columns and the like, it's too complicated. Our brains cannot deal with that complexity. Think of it as just a giant beam going out of the ground, and even more than that, as a cantilever beam. Believe it or not, the first structural theorist of the modern age, you might say, was Galileo. In 1638, he wrote this treatise on structural engineering. Sure enough, he has this cantilever beam, in this case of wood, cantilevering out of this remnant wall with a weight on the end, and he goes about the discussion of the properties. If you took a cantilever beam, such as what he drew, sticking out of the wall, but you turned it vertically. Tall buildings are cantilever beams coming out of the ground, in a very, very real sense – particularly the supertall, the ones that are really tall and slender. This is a very good analogy. Here on the left, you see this frame, which looks like a building. Next to it is something that actually looks like what people are used to seeing as a beam. If you look at the beam, it has different attributes, different parts, here, I drew an "I" beam.

(2:58) Okay. So you have these two horizontal plates we call flanges. Those take what we call the toppling force, or the overturning moment. If you were to stand up, spread your feet, and someone pushed on you laterally, one of your feet is going to have more force on it, and the other is going to start trying to lift off. So those legs and feet are like the flanges, but they're tied together through your body, which is the web. You have to have all these things, you have to have the flanges, and then you have to have the web. In a building, it could be arranged in many, many ways.

(3:39) Here I show a square to represent the core of the building, the perimeter of the building, or some part of the building. This very clear concept is used for the engineers and architects,. This drawing is from our archive. It’s an elevation of what was in the Sears Tower. On the right is actually a plot of the fundamental structural property of a thing called a moment of inertia and how it is approximated. If you get down to the bottom of the Sears Tower, my predecessors called it a bundled tube. To me, it's really kind of a big box beam with a bunch of webs. You can see how the wind is blowing in this direction. You have tensile forces at one extreme and compressive forces at the other and you have these four lines of frames to connect the two, much like you might see in just a simple beam.

(4:42) The second thing I want to go into is some terminology. That may not be as clear to people who are not involved in tall building design or construction. So here's a little terminology: pretend this is the floor plate of a tall building. You have this gray area which we call the lease span, that's the part you either rent or sell. That's where the office space, the hotel rooms, or the apartments are. Then inside that gray rectangle is this reddish thing that we call the core. Now, the core is the functional backbone of the building. But it doesn't have to always be in the middle. Here I show you this core that has a lot of components. There's two concepts here, there's the architectural core, and the structural core.

(5:35) Here you see the architectural core. There are various components. The blue stuff has a lot of the mechanical stuff in the vertical circulation for maintenance. Here, you see the stairs, there's a fan room in here, there's two freight elevators in here, a big one and a small one. So that's part of the core, the architectural core. Then you see these green zones, these are the passenger elevators, that take the tenants to their floors, this one happens to have four zones. If you're in an office building, you have to have restrooms, so that's what you see in yellow. Then you have all kinds of electrical conduit banks and plumbing banks that you have to find a home for and so you don't have a series of closets, that'll be a speaker and this is the architectural core.

(6:26) Now, because of the way these things lay out, you have opportunities for a structural core, if you choose to have one. Because the elevators generally only have doors on one side, they have a blank face on the other side. Same thing for stairs, they only have a door in limited places. So what one can often do is take those zones, and use them as places to put a very efficient structure. Here, I've drawn this in red. Those red elements could be concrete walls, or they could be, you know, steel bracing or the like, but they are opportunities for us to put in structural elements, which are kind of obtrusive, into the building. Of course they come in all kinds of configurations and Pete Weismantle next week is going to go into this in a deep dive and talk about various different cores you could have. Here, there's a linear core, split core, and you can have cores that are offset. That is not common, but you know, the Inland Steel building in Chicago, and  the Cheesegrater in London have an offset core. We've recently done an offset core project with Brian Lee, I did one in China quite recently. You're going to have big square cores, and so that there's a lot of finesse and design that goes into the core of a tall building.

(7:58) A third concept I want to get out there at the very beginning, so you understand my presentation, is the dominance of the wind in tall buildings. This is very, very, very important. Here is a little animation on the left of the wind going past an object. When wind goes past an object, it goes past in a somewhat irregular manner, first to one side, and then the other. On the right, if you look closely here, here's a photograph of the John Hancock building in Chicago with a cloud going past the building. On the left, as you see those red and blue swirls – we call those vortices – so we call that vortex shedding. Here on the Hancock on the right you can actually see the vortex forming in this cloud and this incredible photograph that was done by a woman who is a professor at Northwestern University, she's an experienced scholar. Laurie Shannon took this amazing photograph of these vortexes being formed in the cloud. Every time that happens, you'll have a pressure differential from one side of your building to the other. What that does is it tends to rock the building back and forth and like a child on a swing. If the kids kick their feet, at the natural harmonics of the swing, they go very high. If you're trying to hold this person up this child, at that height, it would be a great effort, but they're able to get to that great height just by pulsing their feet at the natural frequency of the spring and they go higher, and higher, and higher.

(9:33) This happens on all scales, these vortices, you can see them in satellite photographs going around mountains, or at the scale of a lamppost. Here's a quite amazing photograph of people going down the highway. The wind is not blowing that fast, but here it was going at just the right speeds to excite the natural harmonics of these lampposts, and you can see it's quite dramatic. In fact, if a tall building were ever to fall over in a windstorm, it would probably fall over sideways. And because of that, we do a tremendous amount of wind tunnel studies. In fact, recently, SOM actually created a wind tunnel in the office, which we use for early processes, like our concept design competitions. Though, for the final design, we go to commercial wind tunnels to get the final data that we use for design.

So, I've gone through the terminology and the beam analogy, and the wind. Now, what were the structural concepts that were created in the 20th century? A very, very important one is this early building, which is the framed tube. This was developed by (Fazlur Khan, with) Myron Goldsmith, who was both an architect and an engineer. He studied under both Mies van der Rohe and Pierre Luigi Nervi.

(11:01) Where this giant building is a beam, we call it a tube, and instead of being a tube of solid faces, it has windows punched in it, but it still acts very much like a tube. You'll notice that this perimeter frame, which is showing the plan on the left, is what takes all the wind and in the middle, there's a core, but only an architectural core. There's no structural core, just some openings for stairs and elevators and this is very important. Just like how calculus was invented by both Newton and Leibniz at about the same time, Les Robertson and his team were working on the World Trade Center, and they came up with a very similar solution, but from a philosophically different approach. The Chestnut Dewitt was researched by Myron Goldsmith, Falzur Khan, Hal Iyengar, under the architectural guidance of Bruce Graham. This system was about taking the structure and making it the skin. This one – I’m just reading some of Les' notes – is more about taking the skin and making it the structure. They end up in very similar places, but from a different point of view. The World Trade Center had columns at every 40 inches, you know, every meter apart, with the windows, about half that – about 20 inch-wide windows. That gave Les and his team an opportunity to put in columns every meter around the perimeter and that was what he did.

(12:43) Of course, this tubular system was very highly used in the last century, once again, such as the bundle tube of the Willis Tower or the Sears Tower. Contemporaneously with the Chestnut Dewitt Building was this building, which we used to call the Brunswick Building, also here in Chicago. This had both a structural core and a perimeter tube, and conceptually, it was being developed the same time as the Chestnut Dewitt and perhaps earlier. This system was essentially a system that Scott Duncan described in his talk about the Guiyang project where it was basically a tube in a tube, which is still a very, very good structural system. There are no outriggers, you have two competent systems, you have the perimeter, which acts like a beam and the core which also acts like a beam.

(13:39) Another important invention of the last century was using steel and concrete in the same building. This is one of the very earliest ones in the late 60s. Here the inside is all steel and the perimeter was initially built with very small steel columns. You can see them in this construction photograph and later they were concrete encased to make a concrete frame. This is like a steel building with concrete on the outside and another thing that was an important innovation was the opposite of that, a steel building with concrete on the inside. Here's one of the earliest examples I've been able to find. It's in Denver, Colorado. It was done by my firm where you had a concrete core which acts like a series of "I" beams and C shaped beams coming out of the ground to resist the wind loads, and all the floor framing around is just simple, large span steel framing.

(14:42) Another innovation of the last century was of course the braced tower. Here's the diagram of the Hancock Building. Once again, all the load is taken on the perimeter and the inside structure is just there for gravity. I'm going to show you another version of that. If you want to tell a Chicago building from a New York building, look at how you turn the corner. That could be a whole discussion as to how to turn the corner in a tall building. But anyway, here is a tall braced tube. Les went on to do a tall braced building, where he actually had composite elements. He brought the concrete not only to the core or to the perimeter, but within the diagonal bracing itself.

(15:32) Another important concept from the last century is the core and outrigger. Here's the First Wisconsin Building from the late 60s, where you have a steel core with outriggers. I'll show you a little diagram later. If you just had the core, it's too slender, it would move a lot. In this old slide, we have a light blue line, how much it deflects. Then what you do is you use something like a hat truss and an outrigger truss, and you grab these perimeter columns that you'd need for gravity. It rights the building, like reaching out if you're skiing and you grab your ski poles to right your body. As an aside, Les put a hat truss on the top of the World Trade Center towers well when the antennas were added. Amazingly, I learned this only yesterday, from Tom Leslie, the professor at Iowa State University, that Nervi had done a core and outrigger building in concrete in Montreal in the very early 60s. These good ideas are floating in the ether for engineers to grab.

(16:55) You can't talk about the last century without talking about Bill LeMessurier, a very, very clear thinker. There are several very important buildings that were not built, and this is one of them. The Bank of the Southwest where you had this, essentially, the entire inside transferred out to these large concrete columns at the outside to make a very stiff building. This composition was never realized. Another important building that was not realized was the Miglin Beitler Tower by Charlie Thornton and company working with Cesar Pelli. He had this large concrete core, which was the outrigger, and a very slender tower. It was 2,000 feet tall, which was at that time perceived to be the height limit for the US, certainly in Chicago, so it's a very, very slender tower.

(17:53)  Another system that was realized, many of the buildings that were shown in this project, including the one Dennis Poon is going to show later in this series, were core and outrigger systems. That's what's used for the Jin Mao Tower and Mark Sarkisian is going to speak about this later. Another important building, at least in my opinion, that was not built is Seven South Dearborn, which was called a stayed mass. At the very bottom, it was this large concrete core, about 60 feet square that went up, that was outriggered to the outside. For the top, kind of two thirds of the building, there was only the core. So this is kind of the extreme where you have only the core, and the floors are cantilevered off the core. An idea of some of this was done by Bill LeMessurier in the Singapore Treasury Building or, you could sa, Frank Lloyd Wright's Research Tower for Johnson Wax in Wisconsin, was of this ilk.

(19:00) Now, this was important, I think, for the structural system, but also for the wind engineering that we did on this. By the way, Les Robertson was the peer reviewer on this project. One of the things that we as engineers often like to do is have peer reviews, and in fact we paid for the peer review. We like to hire a smart engineer to come ask us annoying questions while it's still on paper. So I said that we'd be sure that we have the right thing. Les and Bill Faschen and SawTeen See are great peer reviewers who have helped us on many projects by coming in and asking annoying questions. But anyhow, this building, because there are no columns for the top part of the building, it works architecturally and structurally to expose the slots. Working with Adrian Smith these were opened up and we found a tremendous decrease in the forces of the building caused by the slots and the shape of the floor around it. So this was very important. And so that brings us to the 21st century and the Burj Khalifa.

(20:11) Now, the Burj Khalifa for us started, you might say, March 1, eighteen years ago in 2003. We had a meeting in New York City. Adrian Smith joined us with George Efstathiou, the manager from the New York office, Imad Ghantous, and myself. We met with some people from a place in the Middle East called Dubai. They wanted the world's tallest building, so they decided to have a very short two or three week idea competition, which we were fortunate to win. While we were getting ready for this competition, we talked in the office about this particular project, which we had just finished designing. It was under construction. It was this "Y" shaped building called Tower Palace III in Seoul, Korea. It’s 73 stories, but it was originally 92 stories, and it behaved very, very well.

(21:14) I remember talking to the team saying “this idea has got legs: we can go a lot higher.” And so, when we did our competition we came up with this scheme as our initial scheme in the spring of 2003. Actually this scheme didn't work, and I'll talk about that later, but this is where we started. Our initial scheme was only 518 meters tall. Dennis Poon's building, Taipei 101, was 508 meters, so we were ten meters taller. It was the world's tallest building. But as the design progressed we soon went to 725 meters, and then while the building was actually already under construction, we ended up at 828 meters. During the design process, the building grew by 310 meters. That's equal to the height of the Eiffel Tower. That was the change in height of the building during the design process. It was a big step. If you look at the evolution of the heights of buildings, using the Council on Tall Buildings and Urban Habitat’s measurement rules, if you go from the Empire State building to Taipei 101, it's a modest steady growth in the height of the world's tallest building. Then here comes the Burj, and it's over 60 percent taller than what came before.I want to talk a little about why that is.

(22:56) But first, how big is that? Okay, well, this is what it would look like in Chicago, or downtown in Manhattan, or if you prefer, Midtown, gives you an idea. If there's anybody from overseas, here's what it would look like in the City of London. Or you might say it really belongs to Canary Wharf, and that's probably true, that's what it looks like. You can put it in Paris, but I would never put it next to the Eiffel Tower. The Eiffel Tower is too important to be distracted by something else, but I think it would look kind of nice in La Defense. Okay, this is what it actually looks like at its home, which is in Dubai. What I'm going to do is kind of walk you through the building and give you a little tour of it.

(23:51) It's 828 meters which is 2,717 feet, a little bit more than a half mile, to give you an idea. It's a pretty good hike from bottom to top. In the tower itself is about 3 million square feet, which is a lot of square feet, but not that much. Sears Tower is 4.4 million square feet. Les Robertson's Twin Towers had 4 million square feet per tower. So it's big, but not that big. In the base is another 2 million square feet for a total of about 5 million square feet. In this part of the development it has a series of functions which I'm going to lead you through here. You can see them all together. At the very bottom it's primarily residential and, to go back for a second, it's all residential, either hotel or apartments, except for the pink: the pink is offices and so on. Here at the very bottom was Giorgio Armani's first hotel.

(24:53) This was the bottom of the building, and the floor plate looked like this. If you look at the floor plate and you walk through it, you would think maybe it's just a normal-sized building. If you go back to the World Trade Center, Yamasaki or Les or, I'm not sure who, they like a tight grid on the outside. So you have a column every meter, every 40 inches. The glass is sort of like 50 percent solid and 50 percent open. If you go to what we used to call the Amoco building, the Aon Center here in Chicago, it is also 50 percent open. You have five-foot columns, and then five-foot glass and five-foot a column. Then you go to the Sears Tower, or Willis Tower, you have 10 feet of glass, five-foot columns, ten feet of glass, but still a lot of capacity. This particular building, the rooms are 30 feet wide, and the columns are either two feet wide or less. There is a tremendous amount of exposure if you're going to go tall. So this particular system we developed, enables us to do that. I think that's a very, very important aspect of this.

Now, let's continue up the building. We had the serviced residences, branded by Armani above there, and we have more residential floors. The floor plates are stepping back as we move ourselves up, and then we have the yellow and the luxury residential. Now, the developer, Emaar – brilliant, by the way, one of the most hardworking people I've ever met in my life – is Mohamed Alabbar the chairman of Emaar. They were clever enough that, in 2004, whenever the building was getting started, they sold the blue, the brown, and the yellow in two nights. Whoever bought those units had to cough up 50 percent of the purchase price within six months. That went a long way to financing the construction of this tower.

(27:11) Above there, of course, the floor plates are getting smaller. We have the corporate suites, and the boutique offices. When the chairman came to us and said we want to turn this into office space, we were kind of imagining what we're used to, like office space you see in New York City, or Chicago, big office floors, 40 foot lease spans. We were saying, “are you sure?”, but these are boutique offices. It goes to what Dubai is to the world, particularly to the Middle East, just like Singapore is to Southeast Asia, or Switzerland is to Europe. At one time, it's the place where everyone went to do business in the Middle East, because there's a lot of countries near Dubai, where it's hard to get a visa, it's hard to go there. So if you're a prominent business person from anywhere in that region, it's quite likely that you have office space in Dubai. And if you want some really prestigious space, your office space is in the Burj Khalifa. So, that very small floor space, you can see the square footage there from 13,000 square feet down to 5,000 square feet. There was also an observation deck. As was mentioned the other day, Emaar is making so much money off the observation deck, they've converted many of these floors into additional observation floors to take up all the traffic that they're getting.

(28:41) Here's an idea of these floor plates as you get up towards the top. You also have to have a series of mechanical spaces, if you will. Even though as a building this is over a 160-story structure. But you can't deal with that in the mechanical systems and the like, the voltage dropping in transformers, the water pressures would be astronomical. So what you do is you break the building into a series of shorter buildings, you might say there's 1,2,3,4,5, buildings, mechanically, that are stacked on top of each other. And then you have these mechanical floors which are used to service those zones. Now you gotta get up and down in the building. Elevators are very, very important. You know, and, I'm sure Pete will talk more about this, here is the core of the Burj Khalifa. At the maximum number of shafts it has at any point is 19 and here they are. There's actually 54 elevators or lifts in the building, but a lot of them are shuttles that come and go, but they stay within this footprint as you go up the building. This is not common in New York, but many places in the world is: you'll have sky lobbies. So you'll have an express elevator take you from the ground up to a sky lobby, like a lobby in the sky, at that point you will get on your local elevator, that will take you to individual floors. I believe it takes around two minutes for the longest trip to get to a floor. You also have to have freight elevators; at the time, the highest the freight elevator could go was half a kilometer. So we have one of those. Later technology enables elevators to go even higher. This is post 9/11, so exiting is very important. Stairs that are hardened and protective, and also because it's a long way down, we have a series of refuge floors, you know, areas of refuge where one can get out of the stairwell, take a break, and then continue your journey down.

(30:54) Now let me get into what made this possible. Well, first of all, luck. The right client, in the right place, at the right time. But let's put that aside for the moment. Let's go through more of the technical reasons that made it possible. I touched on four things: structural systems, wind engineering, integration of systems, and construction technology. Now, I want to introduce another idea which is very central to the structure, which is issues of scale, the fourth concept. Let's go back to Galileo for a moment. Okay, it turns out if you have a bone, let's say a bone which is supported on one edge, and the forces on it are given by the weight of the bone and you hit your stress limit, if you make a bone three times as long, it has to be nine times as wide. Just do the math to find out his calculations were a bit off, but his answer was correct. So Galileo came with it, so 1638. Now, actually, in animals, it's not just a bending question. There's other things so there's, the scaling ratio is a bit different than what he had, but, still, it's there. And the other book I show here is very important. It's well known in architecture, On Growth and Form by D’Arcy Thompson. D’Arcy Thompson talks about the animal world and the plant world, from the point of view of physics. The reason things in nature look like they do is generally not a willful act, it's because they're reacting to the physics of their (environment). The same thing is true for buildings, so there's an issue about how much you can just take a normal thing, a normal species and scale it up. You know, you can take a small mammal and enlarge it into an elephant, at some point it just doesn't doesn't work.

(32:58) This applies to buildings. If you were to take the Sears Tower, but make it bigger, it scales up by the cube. The same thing for me: if I were twice as tall, I'd be twice as wide, I'd be twice as thick, and I would weigh eight times as much. If you were to scale the Sears Tower, the floor plates would be too big, you'd be too far from the window, you'd have so much real estate, you would never be able to sell it. And so you’ve got to use a different animal, a different species. That was the Burj Khalifa. Yes, it only scales by the square. If I were to make the Burj Khalifa twice as tall I'd have twice as many levels, and I don't have to make the legs longer. Maybe I have twice as long legs, so I might have four times the area but not eight times the area, that's great, but also tells you that the Burj Khalifa could only scale so much further before it also needs to be put on the shelf and a different creature develops.

(34:14) This is a chart that Faz Khan started and that we keep adding to. You can look at these as building systems, but you might look at them as species of buildings, separate animals. Some of them evolved from other animals on the list, others species were just created out of whole cloth. One of the wonderful things about design is nature, let's say things evolve through evolution, or create through evolution. In our world, we're only limited by physics and creativity. And so we can create whole new animals and whole new species just by stepping back and looking at this in first principles. Another thing that's part of SOM's philosophy is we're very much into structural architecture. Which is if you take the skin off the building, does the architecture go away? Or is it the same? Here, you see a series of buildings where we only model the structure, every floor, all the interior structure, and the perimeter structure, but we hope that the architecture is still there.

(35:24) Now, let me talk about the structure of the Burj Khalifa. It's primarily a concrete building with a transition to steel towards the top, and it's on a raft, or mat. With about slightly less than 200 piles that are five feet in diameter that go down to 150 feet into a soft rock. It is made of some fairly simple components: some walls, some slabs, and a few columns – and if I were doing it again, I'd get rid of the columns. Lessons learned. Part of it, as I remember one time I gave a lecture, I was criticized for not being more unusual in my systems. And I remember thinking to myself – I didn't say this to the questioner – I actually want the building to get built. If you're going to try to get a contractor to build the world's tallest building, using systems they've never used, your chances of success are gonna go way down. So we wanted to use systems that were readily available – I think we only had seven separate companies tender for the project – and that people would recognize they could build. Then the issue was how to do height.

So this is the structural system. This is the species that we created for this building. We call it the buttressed core, and we gave it a name pretty late in the game. What you want to do is you want to let ideas flow and stuff, then at a certain point, try to describe what it is you're doing. This is true of design of almost any type. If it takes a lot of words to describe what you're doing, maybe you're not there yet. So at some point we came to the conclusion that it is a buttressed core. We have this hexagonal core in the middle, that is there to take the twisting to keep the building from twisting, but it's too slender to go to great heights. It could never handle the wind loads by itself, so we buttress it, with the walls coming off. So, this is a very different system than what we started with when we started with the system from Tower Palace Three.

(37:28) I knew that this was a new system that we ended up creating, and it was very, very successful. The way it worked when we started is, say that the wind is blowing against these two wings, that this third wing is like a buttress. That resists the force much like this man here, this is resisting wind with his umbrella, his front leg is, let's call that the core, and his back leg is the buttress. This is the system for the Burj Khalifa. Another thing this man is doing is he's using his weight to help resist the wind. This is very important for the design of tall buildings. It is what we call managing gravity. Plus that, we were able to, as I'll talk about later, reduce the wind forces tremendously.

(38:58) This is the bottom of the Burj Khalifa. If you walked up to this as a job site, and someone asked you how tall the building is, you would probably not say I think it's 160 stories plus. No, he'd probably say it's five stories, but because of the way we were able to control the wind and the gravity, we had no tension, even in a storm that happens once every 1700 years. Now wind, as we've said, is very dominant in tall buildings, and was a very dominant concern in the Burj Khalifa, so we do a whole lot of wind tunnel tests. We have these things which are very lightweight, like this is more like balsa wood that we have with the base that takes readings. We also have these things called aeroelastic tests, where there's instruments on the inside there and there's a structural element that takes readings so you get an idea of the forces. This kind of model moves in the wind where the first one doesn't. We did some things with a smoke test and cladding test to figure out what the pressures are on the skin. We also did a test to figure out if we were having problems with the scale of our wind tunnel models. This was a fairly large model for a wind tunnel test. This is done up in Ottawa, Canada in a 30 foot tall wind tunnel. Just to the left there is Peter Irwin, who led the wind engineering on this project. All the while we are tuning the building like a musical instrument, we're playing with not only the periods but the motions. If someone wants to shake this way, we'll make it move in a different direction. This is very important.

(40:00) Now let me go back to where we started. This is what we had, and we knew the wind was very critical, so the minute we won the competition we went into the wind tunnel. And guess what? The results were really bad. It moved too much and the forces were too big. So after a brief moment of panic, we kind of remembered The Hitchhiker's Guide to the Galaxy where it says: “DON’T PANIC.” So we put that aside and started engineering the problem, and the architectural and engineering team worked together and we started to reshape the building and also retune the building for the harmonics. Remember how this child has kicked their feet in uniform. What if we make the building so that the vortices are coming off at all different kinds of rates and then we look at how we tuned the building and relate to what we're getting.

(41:02) Instead of this child having two feet kicking in unison, the child has like 27 feet that are kicking with different rates, and the swing goes nowhere the forces are none. What we discovered was that there were essentially six directions. The wind coming into the nose, and then the wind coming in between two of the wings. Into the nose was pretty benign: there was a vortex, but it formed downstream from the building; when the wind came into the legs, the vortex would form and then hit the third leg. And so we did all this reshaping. We did many things. The setbacks – the building used to go counterclockwise – now they go clockwise. We actually rotated the entire building 120 degrees because of predominant wind direction, and in the process the forces went way down.

(41:49) This is our first test, on the left the red lines 100 year storm and if you go over to the 100 year storm after two reshapings the forces had gone way, way down. Because of that the building went up and up and up in height. We started with the one on the left, the intermediate one is the one here is also a red one. The black one here says the final scheme: that's what we actually built, but because we were trying to confuse the competition we went in the wind tunnel with this one tower which is much taller than we intended to build. Larry Novak and I and the senior engineers, we treated this like a science fair experiment to see what we could do. Then we got our results and guess what, the forces went down even more.

(42:38) So here on the left you see the initial scheme with the base moments, which kind of forces, the accelerations, how much does it move. After we reshaped it, even as the building grew so much, it went down, and this final scheme was 310 meters taller than the scheme on the left. But it had less force and moved substantially less. The one we tested was even better, but it had higher mode shades and we were already over 40 stories in the air. And so there was a hotspot down low so we weren't able to accommodate this change, but it gives you an idea how architecture and engineering working together can achieve amazing things.

(43:22) These buildings are Swiss watches. This core was an amazing amount of work. One of your future speakers, Ahmad Abdelrazaq, whom you may think of as a contractor, but he's actually a brilliant structural designer. He and Pete Weismantle both worked on this project during the design. Pete would propose a core and then Ahmad would study it and counter- propose. They went back and forth and took a long time and some serious negotiations to come up with a core that worked both architecturally and structurally. This thing is tighter than a drum. If you got to over 160 floors you do not want to waste much space and this essentially has zero wasted space. Every piece of space we could capture for a use was done. There's so much going on in these buildings. Here's the layout of all the shafts we need to do and then the holes we have to put in the structure.

(44:27) A little bit about the mechanical electrical stuff. This building is a giant lightning rod for the whole city of Dubai, if you will. And so the engineers were led by Luke Leung, they created a Faraday cage, and they used the skin of the building and grounded it to the structure and into the ground so it acts like a giant Faraday cage, so lightning would never come into the building. One of the other things that our MEP team recognized is that you're going through a different climate. I've been in Dubai in July where it was hot and humid at the base and you can feel that the climate changed – we’d go up on the outside of the building in a hoist – and when you got up to 160, it was pleasant. From very hot and humid to pleasant, right in the same place in the world. The only difference is elevation. So Luke Leung and his team took advantage of this "better air" if you will, or more efficient air in the design of mechanical systems.

We didn't have the opportunity to have a contractor on board when we did the design, so we made our best guess. I think we got it pretty right. We've designed this building for reuse of formwork. There's formwork on this building that was reused over 160 times.

(45:49) We use this incredible material that we still call it concrete but you should really have a new name. This stuff is very strong and very stiff and very workable. In fact, in the 18 years since we started working concrete – well, you know we're running out of adjectives to (describe it). So we're now talking about ultra high performance concrete which is twice as strong as what we used on the Burj Khalifa. Just to note, we specified a high but available, strength concrete for our project for the Burj Dubai (later the Burj Khalifa) and the contractor delivered material which was generally about 25% stronger than what we specified. Ahmad and his team figured out how to pump concrete. Ahmad left our firm and went to Samsung, who was originally the builder of this and they figured out how to pump concrete 2,000 feet in the air (600 meters). I thought, how can you figure that out? Well, they ran pipe back and forth across the desert floor until they got pressure losses that equaled pumping concrete vertically 600 meters and looked at what came out the other end was still concrete or not.

(47:04) So the foundations were put in and then it sat there for a while. Now I want you to look at this slide and look around you. It's all empty and deserted and it sat there for a while the owner Emaar negotiated a contract and the eventual winner was a consortium led by Arabtec, BESIX, and Samsung. It was led by Samsung, and then they showed up on the site in 2005 and we're off to the races. These are vertical factories. The forms jack themselves up and the concrete is pumped; you had to pick up the rebar. Eventually it got skinned. And then the spire: it was too tall to put the spire on top, so we built the spire inside the building and hoisted it out the top. Here we have the spire coming out of the building and of course there's a light bulb out there. You might have seen the photographs of Tom Cruise sitting up there at the very top of the building. It does get hit by lightning quite a bit. I've been there, but it does no damage. It's really quite interesting to watch.

(48:15) They finished the building, they washed the windows and it looks beautiful. The way it catches the light is amazing. It's really a hexagon that has six sides no more than one sixth of the buildings ever directly in the sun and all that sparkle is daylight not going into the building. And there you have it at the base. In January 2010, we had the opening ceremony. They announced the new name of the building: it went from Burj Dubai to Burj Khalifa, and they announced the height (828 meters). They had an incredible firework show. This is like a Hugh Ferriss drawing of the lights in the smoke and the like. It has been open as the world's tallest operating building for over 11 years.

Now, I will be quickly talking about developments in the buttressed core after Burj Khalifa. After that job, while the Burj was being built, the team went to some other proposal competitions. One of the things we did here (in the Las Vegas proposal), we got rid of all the setbacks, we had a gentle taper, we moved the stairs to the end of the corridor to act like a hammerhead. Las Vegas has terrible soils, so these were actually steel boxes. Steel shear walls filled with concrete, which has been really been brought to the fore by Ron Klemenic and Jon Magnusson in the last few years as a seismic application. We were doing this just to get rid of the weight.

(49:56) Then we also competed for the Kingdom Tower. This was one of our structural systems where we got rid of all the columns and all the setbacks. So we put the stairs at the end. And so this building had no setbacks, it was basically just a wall-only system that went up. And it was a tremendously efficient way to do it. This was our proposal for a one kilometer building. And this is what the floor plate looks as you transfer to the top. And so this is the development of the post- Burj buttressed core scheme.

(50:40) I want to quickly talk about a fifth idea, which is why buildings don't get built. This is a diagram the Council on Tall Buildings put out shortly after Burj opened. This was the 20 tallest buildings scheduled to be built about that time. One by one, many of them were cancelled, or put on hold and eventually canceled. In fact, only seven of them were built. And we knew this was happening, particularly when these really big ones were canceled. I didn't worry too much about that kind of stuff. But I would note what they were and I would wonder why they were canceled. A lot of times a lot of money was spent. The foundations were put in, sometimes it was just bad luck. Some of those were good, very good schemes with bad luck. Some of them, in my opinion, were dead on arrival, they were never going to happen. They had no clear structural idea. Or they're way too complicated, too difficult to construct, too slow to construct, inefficient use of material, and just too big. So if you want to do one, you have to have a clear structural idea, rational systems, proper scaling, understand scale and proportion. It needs to be efficient; minimize your carbon; you have to design for both wind and gravity; and make it simple to build and fast to build. The longer it takes to build a building, the more things can go wrong, the more chances of some financial or political things going to shut you down. So as my boss Hal Iyengar used to say, always have at least one idea of how you're going to build your project.

(52:27) Let’s close out with the idea “Why supertall?”. This is one of the core questions Carol's been asking quite a bit. Let me compare the 20th century. These are the buildings that are saved over 200 meters, around 50 stories, that were built in the last century. We are in the supertall era. If you look at the tallest building built every year, almost every year, there's a building that would fit Carol's definition of supertall,“taller than the Empire State Building.” Just look at SOM's own work, at this red line. Here are some of the buildings we think are going to be done in the next few years. Every one at the right of that red line would fit into Carol's show. Then “why super tall?” It's to plant the flag. Everyone knows where Dubai is now. I didn't when I started. Remember that hunk of desert I showed you in those earlier slides? Look at the city that's around it. Now it's quite amazing. Emaar has made an incredible thing. They have this incredible fountain with music and lights, and every day of the year there's thousands of people at the base of the Burj Khalifa to see the fountains and hear the music and see the light show. They use all of this to an incredible advantage to create a huge economic engine. This employs thousands and thousands of people. That is the result of this tall building. So with that, Carol, thank you.

CAROL WILLIS

(54:19) Thank you, Bill. A fantastic presentation. We are rather long on our time, but maybe we can spend another 5 or 10 minutes on an issue that pulls Les Robertson and the World Trade Center back into the discussion. One would normally think in broad decades or eras and say that the year 2000 would have marked some kind of 21st century type. But it was really 2001, that changed the idea of the skyscraper, because of 9/11. Now we are coming to the 20th anniversary of that tragic event that so many people at the time saw as the death of the skyscraper – which was much predicted in the press among critics. Yet it wasn't just that. It wasn't just the kind of popular conception or the media treatment, but people also believed that, psychologically, no one would want to occupy an office or an apartment in a very tall building. Or that no banker would lend money for projects. That, of course, is always necessary: the financial piece has to be in place for these projects to be constructible. It's not just the physics and it's you know, it's not the overall size, it's also the size of the loan that's necessary in order to make these buildings happen.

(58:03) So what you clearly demonstrated in the graphs and images is the volume of construction that happens now in the 21st century, which has only really accelerated since about 2010, I guess. Although you made clear to us that this is an evolution from not just early in the 21st century, but in the problem-solving of engineering that goes back through the 1990s, with great height through the 1980s, with a change in the relationship with the core and the facade, and indeed back to the 1960s, especially with innovations in concrete. I don't know if you have any more general comments on that history? And how conscious were you of that evolution? You said some things surprised you. Some, I know from our earlier discussion, you needed to pin down the date in order to understand what was the relationship of invention, within even partners in your firm, and other professional competitors? So do you want to comment on that historical evolution?

BILL BAKER  

(59:21) Sure. Like many of you know, I drove from Chicago to New York to help out after 9/11. So I was at Ground Zero, I think, the following Sunday or Monday. I also thought my career as a tall building engineer was over, because there weren't going to be any more. And that certainly was not true. Later I was on the FEMA investigation along with SawTeen See, Les' collaborator and partner, in trying to figure out what was going on and Jon Magnusson and others. We were colleagues from different firms trying  to assess the situation, and it did go further. But what's also interesting is Les was there kind of at the beginning to today. He was in his 30s when he was working on the World Trade Center, as was Fazlur Khan, and I think Bill LeMessurier was like two years older, and Fazlur Khan was one year younger than Les. So these young engineers were almost starting from scratch. There's this huge hiatus from the Empire State Building. So you had the Great Depression, World War II, a decade of recovery, more than a decade of recovery from World War II before the tall building started to really come back. In that timeframe, all those who would have been their mentors or predecessors were gone. They weren't in practice. So they were kind of starting over: first principles. They happen to have a new device out there, which was called the computer. Pretty crude by what we have today, but well employed by these people to do these very fundamental studies.

(61:23) If you look back at that chart I showed about construction last century, there were not that many really tall buildings, and every one mattered. Every tall building was known by everybody else. The Council on Tall Buildings and Urban Habitat always kind of thought it was kind of like an encounter group. You have all these engineers trying to figure out what they're doing, and they need somebody to talk to as they're trying to do these things. And so, the Council on Tall Buildings has shifted a bit, but it started out highly technical, mainly structural engineers talking to each other, sharing war stories. And what's interesting is what you always hear, what's written in the papers and what you hear in the bar – they're not always the same. I remember having a scotch with Bill LeMessurier hearing some good stories. So a lot was going on, but these people were very dedicated, and they realized that they were doing something very big, very special.

(62:36) In the process they created a toolkit of many many ideas and concepts. Coming into this century, we have those, and we also have the opportunity to create new ones. By going back to first principles, to the physics of the problem, you can come up with new solutions. They don't have to be a core and outrigger one more time. There are ways to do the new things by going back to first principles. We've learned to understand the importance of wind, you know, in the day of Les Robertson's early career, or Fazlur Khan, you know, you did the wind tunnel, and a lot of times you wouldn't get the results until your drawings were half done already. You hope that you didn't have a problem. Nowadays, we're going to use our wind tunnel in the office for competitions. We almost never do a tall building competition without doing a wind tunnel test to compare various shapes. That's very different in computational powers. A whole topic could be on seismic, a lot of work from the 20th century is more wind focused. Wind is always dominant for a building but seismic is also extremely important. So I think there's a lot of room for creativity, and seismic solutions for tall buildings. For me, can they lead to new architecture? Can buildings look different, because they are different? Because they're expressive of a new technology?

CAROL WILLIS 

(64:11) I think we'll talk about seismic a bit with Mark Sarkisian, who has specialized in that as well with SOM. Let me ask you one more question to sort of get you on the record on a topic that I know you care very much about, but you didn't talk very much about tonight and that is sustainability and the relationship of tall buildings to the question: Why do we go this tall in the climate crisis? With the obvious issues of climate sustainability, inequality and all of the other kinds of political angles, as well as real angles on the prudence of tall buildings?

BILL BAKER 

(65:01) Well, let me break this down into two categories, the supertalls. Those are icon makers, placemakers, and economy generators. For the tall building in general though, number one, we should all report on embodied carbon in everything we design. That we should try to do these with the least resources possible and try to be more clever. For me, the analogy is when Sears moved out of the Sears Tower, you know, the Sears Tower is 100 acres of office space on one city block within walking distance of all kinds of suburban trains. You take a CTA they had almost no parking because everybody came by mass transit. They moved to the suburbs. So, in the suburbs you have your office space, but you realize that your parking spot is probably larger than your office. There, the average area needed for a car spot is around 300 square feet, and my office is not 300 square feet, okay? So your car has more room than you do. Maybe it's not high rise, but sometimes it is. And then you have to drive to work. In America, you're taking all this land that could be for growing things, either agriculturally or just wildlife, and taking it out of service. I think it's a question of density more than height, perhaps. But sustainable, livable density, I think it's essential to our future. So I think we have to take it very seriously. We’ve got to do our best, but I think fundamentally, tall buildings and density are necessary.

CAROL WILLIS 

(66:54) That is certainly a refrain that you hear often from the Skyscraper Museum. I wonder if you think that in the same way that there is a social reason for buildings, and there's a physical reason for buildings to stand up. Can engineering solve problems of sustainability, through technology, through better design, so that we would get the win-win of density plus an engineering solution, which gives us a more sustainable building fabric?

BILL BAKER 

(67:30) You know, I talked a little bit about what we do in our MEP group here. There's a lot out there, it's coming fast. There's operational carbon, and then there's embodied carbon. AIA 2030 has goals, and structural engineers have a goal of zero embodied carbon in the future, and I think we're gonna get there. But it would be, particularly in places like England, or the UK, where there's legislation pushing that. Also in Europe. So, yeah, we can. It's going to come through the technologies like Adrian Smith talked about: using the skin to generate electricity; using much less energy on the inside of the buildings. In tall buildings we've done studies where you capture the stack effect. The Burj Khalifa, you go to a different climate, there's much cooler air up there. Can you snorkel it down and use it in your building? And so I think that there are clever ideas you want to do. Wind turbines, a lot of people do work on wind turbines. They haven't been as successful as we might like. But there's also that out there so I think it has to be our goal. And the more smart people we have doing tall buildings the sooner we'll get there.

CAROL WILLIS 

(69:03) Well, I think we could talk to you all night, so we'll invite you back for yet another lecture at another time for the Skyscraper Museum and bracket the 20 years of relationship that we've had taking advantage of your great knowledge. So we thank you for that, and we thank you for this evening. We invite everybody to come back next week when Peter Weismantle will talk about “Core Values” and really drill down into the concept of the concrete core so that we can begin to understand every aspect of the nuts and bolts – and not steel nuts and bolts – of the 21st century supertall typology. We couldn't have had a better person to have started off the series. So thank you Bill, and bye everybody. See you next time.