Gresham College Lectures

The Future of Tall Buildings

May 09, 2023 Gresham College
Gresham College Lectures
The Future of Tall Buildings
Show Notes Transcript

This lecture will explore the technologies that make tall buildings possible. With the current climate crisis in mind, what is the carbon footprint of a building, and how can it be reduced?

Finally, the lecturer will present some recent projects by Foster + Partners, and set out his vision for the future of tall buildings, the new technologies that are improving them, and the benefits they offer to society.

A lecture by Roger Ridsdill Smith recorded on 27 April 2023 at Barnard's Inn Hall, London.

The transcript and downloadable versions of the lecture are available from the Gresham College website:

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So I'm gonna take a particular focus during this talk.The construction industry currently accounts for around 39% of the carbon dioxide emissions annually, and 28% of that is operational, and 11% is related to construction directly and tool buildings require a relatively larger amount of carbon in their construction than lower rise structures.My question is, how can we justify that?What's the future of tool buildings?Is it reasonable to construct any more tool buildings or should we consign them to construction history?I'm gonna talk through the history of, uh, tool buildings up to now, uh, particularly since their explosion at the end of the 19th century.And then I'll discuss the technology of tool building designs now, and then I'll come back to this question with some thoughts about the future.So, tool buildings through history have been limited by the possibilities of the structural techniques available.At the time.The pyramids in Egypt were the first man-made structures to break through the hundred meter height mark.The most famous were constructed in the 26th century BC and the largest of them, the Giza pyramid was 146 meters above ground level.More specific to the theme of towers, the Alexandria Lighthouse was built, uh, around 250 years BC and measured around 120 meters.So it's not until the cathedral construction period of the Middle Ages that these heights were surpassed.And even after all this time, the towers were not radically greater in height from those built more than 1600 years before.So Lincoln Cathedral built in the spire built in 1311 was reputedly 160 meters until it collapsed in 1548.And there are other sps, which followed around Europe around about the same period, all around about 150 meters high.So Cologne Cathedral was the tallest building in the world at 157 meters in 1880.And they're all built the same way.They're built out of load-bearing masonry stone blocks piled on top of one another to create walls.So they're heavy and their height is limited by three structural factors.The capacity of the stone wall to support itself, the capacity of the ground beneath it to support it, and then the stability of the entire structure against the loads acting on it, principally lateral loads.And then, of course, a further factor limiting the height of any buildings was the difficulty for anybody to go up them.Uh, so they were used for power or status or as a beacon, but not for economic reasons, because not very many people wanted to or needed to go that far up into the air.And there were two technical transformations in the 19th century, which transformed that.Elijah Otis is the sort of famously known inventor of the elevator.He demonstrated this as the sort of mythology of the invention.He demonstrated a new safety hoist at the exhibition of the industry of all nations in New York City in 1854.He was standing on his hoist, the single rope supporting it was cut, and the platform dropped a few centimeters and then stayed where it was.So he'd invented a safety mechanism.Plenty of people used hoist before that, but they didn't like the safety implications if they broke.And so popular history records, this is the beginning of the elevators, but the, the reality is more prosaic.Uh, lots of people around that period were coming up with and using and trying to, uh, invent elevators.Uh, Otis, the company was one of them.Elijah Otis was the entrepreneur who had this one, but many others were involved in it too.The main point is that during this period, there was a frenzy of activity to fulfill an economic need for people to go safely up buildings.And the second major innovation, uh, innovation of that period was the incorporation of structural steel into the load-bearing structure of buildings rather than only load-bearing stones.So the modern era of steel production steel had been around for a long time before this, but the modern era was invented with a by Henry Bessemer, really, or he evolved a process, the Bessemer process in 1855, which dropped the price of mild steel, significantly a factor of more than five, and enabled it to be produced more cheaply than raw time.And so that really transformed the possibilities of, of building.And those possibilities manifested themselves first in America and particularly in Chicago.And pretty soon afterwards, uh, round of very soon afterwards, New York.So instead of the buildings using load-bearing masonry walls, as had been the case up till then, they started to be constructed as a stone skeleton.So you'll notice that this gets called a skyscraper.It's 42 meters high.Uh, the, the particular focus is, and in fact this, this, um, this project, the home insurance building is, is known as being the first skyscraper.And that's really because of the change in its construction method.But there's a debate about that because you can see on the left those steels vertically pointing, just coming out of the top of the walls.But there was still load-bearing masonry in this, this skyscraper, uh, William LeBaron, Jenny, the architect, um, built in 1885, and then some other additions made.But if we look at others around the same period, you can see clearly the fact that there's a steel skeleton, a frame, and then the cladding is following on.So that's a transformation in building technology that instead of building with low bearing masonry walls, we're now building with a steel skeleton.And here's another one.The same period, the reliance building in Chicago, 62 meters, again, the steel frame and this time, uh, plate glass and ceramic cladding.So of course, those are the technological means, but there had to be a reason for that.And there were very strong economic drivers for that.Uh, in that period, Chicago and New York were growing extraordinarily fast, and land values were increasing very quickly.So in New York, land values doubled between 1840 and 1870, and at the same time, there was a big benefit and economic benefit in density and in staying close to the coast.So in 1816, it cost as much to transport goods 30 miles inland as it did for those goods to cross the Atlantic.So there was a good reason to stay near other coast.So as quickly as tool buildings arrived, a philosophy of their construction and their design was developed.And this is a quote that I really love from Louis Sullivan, very famous architect, one of the pioneers of the modern movement, uh, and one of the most forward thinking architects of his generation.And he wrote a piece called The Tall Building, artistically considered in 1896, in which he said, whether it be the sweeping eagle in his flight or the open apple blossom, the toiling workhorse, the blithe swan, the branching oak, the winding stream at its base, the drifting clouds overall, the coursing sun form ever follows function.And this is the law.That's how people wrote about architecture in those days.And we all really bear in mind that that's a, that's, uh, uh, that's really a phrase that has lived on ever since then.But it's just interesting to see where it originally came from.And Louis Sullivan built some fantastic skyscrapers, but form hasn't always followed function in the evolution of skyscrapers or in fact, other buildings since then.And I'm not going to go through the whole history of skyscrapers, but suffice to say that that's not always the case.There's not always a, a, a clear identity of the, uh, skyscraper with its, with its function.And maybe the climate emergency is one way to recenter that, to measure the impact of departures from the most efficient structural response for a particular design.So, as I said, this is the skyline of Chicago in 1927, which I think has a lot of tall buildings in it.And this is the skyline of Manhattan in 1931.So there was a tipping point in these cities, and a huge amount of high-rise construction through a combination of technology and economic and political will.So I'm going to move on now to describe modern technology, the modern technology of, uh, of tool buildings.And I'm gonna show some examples from our work.So at Foster and Partners, we work in integrated teams.I'm the head of the structural team, and we work with the architects and other engineers and specialists inside the office on projects from the beginning of the process.So we've designed, uh, structures either at competition, winning, uh, competition, winning projects, or through to completion around the world.And I'm gonna show some of the principles of, uh, tour building construction with some of those as examples.These are the lu sail towers in Doha.They're designed by the practice and completed for the FIFA World Cup in 2022 in Qatar.And they're four towers arranged in two pairs, 257 meters and 300 meters tall.Uh, we build in the structural team, we build cardboard models.This is around about, um, a meter or so high.And the idea of these cardboard models is they show the structure alone.We remove the cladding so that we just see the skeleton of the building, because we want to make structures which are logical and efficient and don't need to be hidden or have have anything to cover them up.We want to see them and make them beautiful.So if I, if I focus on this tower, a tool building is a cantilever fixed at the base and subjected to both vertical and lateral loads.The vertical loads are primarily due to the building users, and the lateral loads are of course, due to wind and also earthquake.Earthquake loads, the shaking of the ground, which is mostly horizontal, a little bit vertical, but mostly horizontal loads.And those loads, those forces are carried down by the structure to the foundations.And the most common way to resist the lateral loads in modern buildings is by using the building's core.You can see this section, uh, uh, uh, tric section, and you can see the core in the middle there.So this is the part of the building which contains the vertical circulation, the stairs and the lifts.And also quite often the spaces that are needed to put the mechanical services into the building, but above a certain height of a building, somewhere between 150 and 250 meters.But there's no absolute rule.It depends on the building structure and the loads acting on it.The core isn't enough.The building's too tall for that.And at that point, we need to mobilize the outside of the building.We need to use the full width of the building to resist the lateral loads acting on it.And this is one method used quite often, which is to install trusses, which we call outriggers, which link the core to the outside columns in order to get the full stiffness and strength of the columns around the perimeter.So these are the loose sail towers under construction.And you can see on the right hand side the core, which is built in reinforced concrete coming out of the top of the, uh, towers, and then the floors and the columns following on.And this shows there's this same view.We're at the top of one of the towers looking across to another of its neighbors at the reinforced concrete core coming up the middle.And this also shows, you can see around the diagonals, the outrigger floor, which has a truss around the perimeter to equalize the loads going down the columns, uh, around the, uh, around the perimeter.And there are the, uh, towers viewed from the sea.So another tower now, uh, in, uh, New York, 4 25 Park Avenue.Uh, and this is, uh, as you can see in Manhattan, uh, just, just off to the, uh, the top of a Park Avenue quite near Central Park.And this is a competition that we won in 2012.Now, uh, tall buildings in Manhattan are required to fit within a tapering volume, which is defined in planning rules, and it gets thinner over the building height in order to allow light to penetrate down between the buildings to the streets at ground level.And as well as doing that, the client wanted to move the vertical circulation, the core of the building away to the side, rather than being in the middle, so that he'd get a whole floor plate, which was addressing directly Park Avenue, and the core would be pushed to the back, and those floor plates would be addressing the street.And they'd also, of course, get the views of, uh, central Park, uh, just off to the north.And this is the scheme that we came up with, once again, a cardboard model to show it three views of it.And it was conceived again, to be as minimal response as possible to the brief that we had.In this case,A single line of columns, which I've picked out in red, starts at the top of the building, and it bifurcates twice, it divides into two, and it also goes back to the core behind.So you can see at those two levels, those diagonals.And in doing that, in bifurcating at those levels, the columns connect with the core behind.You can see in the side elevation over to the right hand side that those diagonals are connecting back to the core.And what that does is the same thing as the outrigger was doing for Lu sail tower, which is connecting and mobilizing the full width of the building to resist lateral loads, which in New York, particularly, which isn't seismic, uh, is particularly wind.So I'm going to show you what that means in terms of the forces acting, uh, on the building, and therefore the reacting forces inside the, uh, structure.On the left hand side, you can see a side elevation.And in red, those are the compression forces coming down the columns on the front, the gray is the, is the building core, and the red is the forces, the compression forces in the columns.And you can see them gradually increasing further down towards the bottom, and of course, splitting into every time they meet a, a bifurcation point.And then to the right hand side of the cardboard model, uh, you can see the overturning moment, and that's the bending moment which the building is having to resist when the wind blows to the side.So the wind's blowing, and the building, which is working as a cantilever, has to resist that load at the base.So you can see that line starting at zero at the top, up at 800 feet.That's where the 800 is, and gradually increasing.And the blue line shows the total moment, which has got to a maximum point at the bottom.And the red line shows the moment which is being resisted by the core.And what you can see is about halfway up, particularly at 400 feet, those diagonals are effectively splitting the load between the columns and the core.So they're work, they're working as an outrigger.So we found this a very exciting, um, graph because it was showing that our structure was working as we wanted it to, to divide the load between the core and the line of columns to make it efficient.And it's always interesting.We always find it encouraging that when we've done a competition scheme, that's what gets built.And you can see on the right hand side the construction of the tower going up.You can see those columns bifurcating.And this is the finished structure from the front.The first view that you saw was a photo montage from the competition and from the side.So again, to reiterate, we are looking for buildings that you could take the cladding off and the structure would look exactly the same as it looks from the outside.The final tower that I want to show of ours is in Shenzhen.It's under construction at the moment, and it's 388 meters high.So one of the tallest buildings that will be built in Shenzhen at the moment.It has some associated buildings around the, on the same site that we also are designing.So the stability for this building is provided by a combination of the core, the reinforced concrete core, which again, is off to the side again, in order to achieve big, usable floor plates.You can see that on the left, combined with external columns around the perimeter of the tower.And you can see those immediately over to the right, and those are linked to the core.So there's a connection once again with trusses, which we've brought out those five lines of trusses and perimeter and perimeter structure in order to make a combined system to resist the loads.And there's another part of the loads that need to be resisted in Shenzhen, which is true of a lot of the world, but just happens not to be true in the UK or, uh, or most of the east coast of the states, which is that it's seismic sig.It has significant seismicity, and that horizontal shaking load, uh, imparts an enormous amount of energy into the building.And so we've used a technology called buckling, restrained braces, which form part of those trusses and absorb the load.And our, our ability to analyze, uh, towers now has really advanced substantially, and we can now do what's called performance-based design, which means that we can analyze the behavior of the building under specific earthquake events.So this is a particular earthquake which has been modeled and then applied to the building, slightly exaggerated scale, but to, so we can investigate the behavior of the building under that load.And here the building is on site.You can see it on the right hand side, once again, the concrete core going up ahead and the, uh, perimeter columns you can see being built and the floors between, uh, uh, behind them.So I want to now move back to the original question that I asked.That's, that's a sort of a, a a, a brief, uh, synopsis of the technology that we use in our design approach to tool buildings, which is our design approach to, to all buildings, really, the original question, how does the technical capability that enables buildings like this to be built fit with a climate emergency and our need to reduce drastically, radically the production of greenhouse gases?And this is a debate which is ongoing in the construction community, and understandably, there are strongly held feelings about it.So this is, uh, really an emerging science, uh, which I'm going to give you some, some ideas about.I'm gonna start by doing some definitions, which I'm, which is useful that everybody has the same definitions to start with.So carbon dioxide equivalent is the measurement that we use to compare the global warming potential of different greenhouse gases.The table on the right shows different greenhouse gases, and you can see that carbon dioxide doesn't have the largest global warming potential, but it is the gas that's most heavily emitted, and it has a relatively long lifetime compared to other greenhouse gases.Most carbon dioxide emissions are the result of the combustion of fossil fuels, not all of them, and that's something I'll be touching on, but most of them through transport and through industrial processes, uh, which require high temperatures.So for example, 1500 degrees for the, for the fabrication, the manufacturer of steel or cement.Then two other definitions.First of all, we measure the whole life carbon footprint of a building.And that's a combination of the carbon produced during its construction, which is the embodied carbon and the carbon produced during its use, heating it, cooling it, lighting it, uh, and uh, and that's the operational carbon.So improvements in the operational carbon insulation, better power, better power usage in modern buildings has reduced operational carbon a lot.And what used to be not quite so seriously considered really 10, 15 years ago, embodied carbon maybe 20 years ago, has now become a much more substantial percentage of the overall carbon carbon footprint of a building.And there's a second factor that we should consider, uh, when we're thinking about buildings, and that's their users.And this is a measure, the household carbon footprint, which is the impact of the building users.So we are measuring here the greenhouse gas emissions required to, uh, produce and distribute and dispose of all household consumption over a year.And this is what economists use more often really than, uh, than the, uh, the carbon definitions that is more in the, uh, uh, engineering and architectural world of whole life carbon.So here is an estimate of the household carbon footprints of residents.And this actually is from a study of 31,500 zip codes across the states, across America.And they haven't measured all of those individual users.Of course, they're using, um, national survey data to predict consumption.So they're taking various measures, various factors, and predicting, uh, the average household's consumption.And there's a recognizable pattern.The densest areas, New York City, Philadelphia, Baltimore, the cities have the lowest household carbon footprints, and they're in green in the diagram.The suburbs, which surround them, have the highest household carbon footprints, and they're in red.This is something that you can see online.You can go and, uh, look across the whole of the states, but to hone in just closer in on New York, you can see exactly the same phenomenon, but just in more detail.And the primary reason for the difference between suburb and city center is the reduction in private transport.So transportation, carbon footprints are around 50% higher in large suburbs compared with large principle cities, while the total carbon footprint is around 25% higher.And this is the same information from that study expressed on graphs.So, uh, each yellow triangle is one of those 31,500 zip codes.You can see a, a lot of variation across them.The red, uh, series of dots is the line that is the average of those points, and you can see that.Uh, and so that's the household carbon footprint up on the right hand side.So round about 50 tons, 50 tons of carbon per year per household.Uh, so the states, by the way, I've, I use the states because they're incredibly good at gathering, um, statistical data and publishing it.Uh, these results hold true for other countries like the uk maybe slightly lower carbon footprints, but not substantial and considerably more than other countries.And you can see on the bottom axis, population density.So that's a logarithmic scale because the changes are so enormous from a rural area of the left hand side, very, very low density of people to dense cities, more than 10,000 people in a square mile.The center of New York is round about 25,000 people a square mile.But of course, those are very dense cities, and you can see on both graphs, both the one which hones in on the cities and for the overall zip codes around the country, that as the density reaches a critical value, the carbon footprint for those, for those households drops away and gradually reduces.So another study, then the same effect, but a completely separate study.Uh, this one is, uh, professor Edward Glazer of Harvard, who's looked at the difference across the same metropolitan area.So he's looked, in fact, at many cities, and the results come out to be similar.I've selected a few of them, four of them.And the way to interpret this graph, or to read this graph is that the zero point is the, is the point of the household carbon footprint in the center of that city.So on the bottom left at the bottom, that zero point is the center of New York.And then the difference between the center and the suburb is represented by that vertical bar.So the average carbon use, the household carbon footprint in the suburbs of New York is six and a half tons higher than in the city center.And you can see that that difference is due to three factors, the emissions from driving, the emissions from heating, uh, uh, and the emissions from electricity.So heating is largely, uh, natural gas in the states, in the northern states, and electricity is quite a lot due to cooling.So you can see that the, the, uh, cities in the south use more electricity because they're using more cooling air conditioning, and the cities in the north use more gas for heating, but all of them use more transport than in the city center.And a final study just to show that other countries have the same phenomenon.This was a, the same question, uh, studied in Australia by Colin Beat in Port Peter Newman for 4,000 living spaces across detached highrise and low rise, uh, um, housing in Sydney, Australia.And you'll see that in fact, there's a slight variation in their operational carbon.They haven't, hasn't taken into account in embodied carbon.But once you add transport on, once again, transport is the defining feature.Private transport in low density areas is the driver of their high carbon footprint.And the final study I want to show is one that we carried out ourselves, the sustainability group in foster and partners led by Chris Trot.And that was a study which combined operational energy as well as embodied carbon.And it did a comparison for two projects.One project is a tool tower in a dense city, 60 story tower in a dense city with very good public transport connections.And the other project is a three to five story building development in a low density area, primarily used by public, uh, by private transport.So if we first of all, look at the results for the building itself, so that's the whole life carbon, uh, without the pub, without the transport consideration.And you can see some interesting things in this graph.First of all, you can see that structure, of course, is higher for a tall building.There's more embodied energy, of course, there is in the, uh, structure of a tool building than there is in a low rise.But interestingly, it's not the largest of the embodied energies.In fact, this is projected over a 60 year lifespan of a building.That's a point that we can also discuss.But the, the point is that actually refitting those buildings.So the fit out of a building that is all the finishes that you put into it, and then stripping those out and doing the same thing several times over the building life has a huge effect on its embodied carbon.And we have a, in this study of Chris Trot and his team assumed a 10 year period between each refit.When you think about that for people's houses and offices, that's sort of a kind of a reasonable average.That's not particularly high.People do fitouts more often than that.And I should say these graphs also include for future electrification, both of the material production and of transport.So they're not just, uh, a snapshot taken today.So if we look at the side, you can see that the tool building does have a higher embodied energy, and in fact, a whole life carbon than the lowrise building, 43% higher in this study.However, the story changes significantly when we incorporate transport, so that once again, the private transport for the lowrise development changes the story and the overall carbon footprint in that low rise development is higher.So tool buildings enable urban density at which pub, at which point public transport becomes economically viable.And local travel distances become shorter.So walking and cycling becomes possible.And the benefits of density and working in close, close proximity are substantial for the economy of a country.I know that we often see this in a different way.We often think about the value of our houses or the cost of living in a city, but it's worth bearing in mind that the earnings, the productivity of a city is systematically higher than the productivity of low-rise areas.So in the United States, workers who live in big cities earn about 30% more than workers who don't.And the productivity of cities with over a million residents is more than 50% higher on average than, uh, the, uh, the productivity of areas in smaller metropolitan areas.So my point is, of course, we often think about that in terms of the cost of living, but the productivity of cities is higher.The amount of, uh, the amount, the contribution to the economy is higher<affirmative>.And this gap is true in, in, in both in, in developed countries and less developed countries.So really, my point here is there's no reason for it to cost more to live in a city.There's no absolute reason for it to cost more to live in a city than a suburb.That is because of policy decisions.That's because of the supply of new development in the cities, and the relatively low cost of private transport compared to public transport when you consider the subsidies made to private transport.And this, this slide really to show that it's worth considering that all countries are at different points of their urbanization, and that every city started life as a field.So I want to, I want to draw some conclusions together from that, from that study, and really look to the future.And it's easy in my view to come up with lots of thoughts about the future, but I want to focus on a couple.And really, my focus is going to be on things which I think are perhaps in this general discussion about the future of construction.They don't get as much notice as I think they should.Wherever possible, we should be using existing structures rather than taking down structures, uh, and building nuance.That, of course, is going to reduce our embodied energy.And where it's not practical, where we have to take a structure down, then we should recycle and reuse the materials that we remove.And that, that's, that's an, uh, evolving science.But we also need to make buildings that last.So a, a city street can last 500 or a thousand years while a building might be pulled down, let's say, uh, sometimes after 50 years, sometimes less, sometimes after 20 years.And our philosophy needs to change.We need to think of buildings as vertical streets.So the functions inside them can change, but the structure can remain.Now, I want to talk about the correlation for materials between embodied carbon and the embodied energy of their construct, uh, of their, uh, manufacturer.Uh, we need to focus on low carbon materials.We want to try to use, though we should use those as much as we possibly can.And as you can see, uh, since fossil fuels constitute the majority of energy used in material production, it's not that surprising that the embodied, uh, carbon of the, uh, of the fat manufacturer of those materials is correlated, is closely correlated.So at the top you can see steel, stainless steel, very high embodied carbon, very high embodied energy.And at the bottom concrete, which of course gets understandably a bad press, and I'm gonna focus on it, but actually has per kilo a relatively low amount of embodied carbon.So I want to focus on concrete, and that's gonna be, as I say, something which I think is, is maybe an area which isn't always focused on as much as it should be.Concrete is strong, durable, fire resistant and cost effective, but it is incredibly heavily used.And you can see at the bottom of this graph, cement project products and cementitious products are by far the most heavily consumed in the world, dwarfing the other materials, and that's use is accelerating exponentially.So cement related products, their use around the world is dramatically accelerating.And just a word on concrete.Concrete is made of cement and fine aggregates.Sand course aggregates about this big, about 20 10, 20 millimeters in diameter, water and air, and then reinforcement when it's reinforced, although a lot of concrete products aren't reinforced.And if I look at the graph on the right hand side, when I compare the volumetric constituents of concrete to the embodied carbon constituents, you can see that 90% of the embodied carbon of concrete is due to the manufacturer of cement.And there are two sources of carbon emissions from the manufacturer of cement.The first is the energy in burning the fossil fuels, currently fossil fuels largely, uh, to heat limestone up to 1500 degrees in order to create lime, to drive carbon dioxide away from calcium carbonate to create Lyme calcium cao.The second is that is also the carbon dioxide released in that chemical reaction itself.So there's an addition, additional and very significant element of cement carbon, which is due to the chemical reaction itself.So this huge worldwide production of cement means that it alone accounts for 8% of the world's total annual carbon dioxide emissions.And it's astonishing to consider that this universal material has not really changed substantially since it was patented.It was called ordinary Portland cement.And the word Portland came from the idea that it looked a bit like Portland stone by Joseph Aston in 1827, and then refined a little bit by his son William in the 1840s.The principle codes in the uk, the Euro codes, the American codes, are all based on this cement type ordinary Portland cement.But there are two currently additional me, uh, additional cementitious materials, which are used to mix into that cement, which have various properties, but one of which is you can consider that you've lowered the embodied carbon of your cement by mixing them in.One of them is pulverized fly ash, and the other one, which is com, a waste product from coal combustion.And the second one is blast furnace slag, which is the waste product from iron and steel production.So both very high energy processes, but we can consider, or we do consider in the way we count that though the energy, the carbon due to the, that process is already counted in the production of the primary process that they're, that they were used for.So their waste products, they're treated as waste products, and we should use them wherever we can.But as this graph shows, the availability of them is limited and it's dwindling, of course, course, because we are making fewer and fewer, we're burning fewer and fewer, we're trying to burn fewer and fewer fossil fuels.So we want to have fewer and fewer of them, and they're fully utilized.That is, it's a sort of scenario of if you don't use these products in your cement mix, somebody else can use them in theirs.There's, there's not an unlimited supply of them, but there is another product or there is another approach.And that's an emerging technology, which is instead of using, or in fact as well as using those two cementitious materials, we can also use limestone before it's been calculated, before it's been turned to lime, uh, as is before, it's been heated in small amounts as well as calcium clay.So that's clay with particular constituents.It's not any clay.It needs to, there are particular elements of clay which have to be present in there, but still there is a huge supply of that all over the world.And if we use these elements, we can reduce potentially our carbon content of concrete by up to, or, or even in some cases over 40%.So that's a huge reduction.And in my view, we must focus on these materials reductions as well as recycling and reuse.And I don't think this gets as much attention as it deserves.I'm going to finish by focusing on a final example of our, uh, of our, uh, design process and one of the tool towers that we've been working on where, uh, the structural team worked on the competition to show what I hope that you've seen in some of our other projects, this focus on lean building design, which reflects the forces acting on them and the constraints of their location.So as I said earlier, we need to reflect, we need to reflect resource scarcity in our designs, and as a result of that, make our designs as efficient as a possible.This is the headquarters on the right hand side, the headquarters for JP Morgan in New York City.And it's a competition that we won in 2017, and it's on Park Avenue, slightly further along from 4 25 Park Avenue.And this is a planned view.On the left is the plan view of Park Avenue, and on the right is the plan view of the basement underneath Park Avenue, where you can see lots and lots of railway lines directly underneath the site.And those railway lines are going into Grand Central Station, which is further south on Park Avenue.So as you can imagine, that's an interesting particular constraint for a building.And we were told during the competition that we were given a specific response to where the column should go down into the ground level in order to respond to that constraint.All teams were given that, but we came up with another option.We came up with another solution where we gathered our columns into what we call fans.We gather them together to points at the ground level.You can see the model on the right hand side.There are three points on each of the facades, the north and the south facade, where those fans come together.And then the cutaway view on the left-hand side shows the columns inside the building where we've gathered together the columns into two points.And once again, uh, we've, uh, we've taken the loads down specific locations.This is the analysis of that building.You can see the model analysis on the left-hand side and the arrow showing that we're analyzing for wind loads across the building.That's the, that's the narrowest access of the site, 140 foot wide or 1400 foot tall building.So quite a slender building.And then beside that left hand view, you can see a section two, uh, a section and a view, uh, showing the structure.You can see on the first section the outriggers, which are mobilizing the core, where you can see all of those diagonal lines.That's the central core, which is built out of steel.And then the trusses go across and mobilize the outside columns.And then on the right-hand view, you can see the red and yellow, uh, forces.Yellow is tension and red is compression.And you can see the bracing, which is present on the east and west facades, which is contributing to the strength and stiffness of the building.So some people have said to us, are those decorative, uh, cross bracing?No, we don't do decorative cross bracing.We do cross bracing.And this bracing is adding substantial amounts of stiffness and strength to the tower and reducing the steel tonnage.And once again, it's always interesting to compare the competition photo montage that we did.Here's a view from the ground level.Looking at those fan columns, you can see two things.You can see the fans on the side facades, you can also see that big inverted V, which is linking the cross bracing and bringing it down to the ground.That's the view that we had at competition stage.And this is what's being built on site.Uh, that was a view from a few months back.And you can see exactly the same thing.The fans, the, the gathered steel columns on the side and the beginning of that brace on the top,The building in addition to this, will be a hundred percent powered by renewable energy sourced from a New York hydroelectric plant.And there was an existing building on the site, a lower building, and 97% of the building materials, all of the building materials finishes included, as well as the structure from that, uh, taking down that building were recycled or reused or upcycled.And to my original point, and in fact, one of the, um, one of the researchers, professor Glaser said when he was researching buildings, he said, the only reason you should be allowed to take down a building is if you put a tool one in its place.And to my original point, this building doubles the density of the previous building on the site.So I hope I've shown in this talk that tall buildings come through a combination of technical innovation and societal need, and a tipping point occurred around the second half of the 19th century during a period of rapid growth.And in my view, we're at a tipping point now with regards to our climate, and we need to build efficiently and reuse and recycle wherever we can and minimize the carbon in our construction.And we must consider buildings in parallel with their environment and with wider society.So increased density results in overall lower carbon emissions for, for the same system, for the same societal system, and it creates cities for people to live in and to thrive in.Thank you.Thank you very much indeed, Roger.Um, I get the privilege of having questions sent in from outside on the worldwide electric web.Um, and we'll then take a few questions from the audience.So the, the first one is, is interesting because it's about the concept that cities are all going upwards and people are living in them as well as working in them.But there is a, a socio question about whether that functions in the same way as a horizontal street.You have no gardens, you sometimes can't get out, um, from the living environment.How, how does your perception of how cities look and are built, constructed structurally deal with that social question?You mean by that?That if people want to live in a different way, they want to have gardens and, um, well, the, the the Cities are, are, are going up.Yes.And people are moving into them and living, take, look, take the area around, um, uh, the elephant and castle or, or out towards, um, the American embassy mm-hmm.<affirmative>, they're, they're going up very, very, very vertically mm-hmm.<affirmative> and the living space seems small and the construction is unbelievably challenging and beautiful, but do people want to live in it when it's done, or are you responding to a commercial step?So I think I've had two responses to that.The first one is there's more than one need that people at different stages of their lives want to live in different ways, right?From their youth, uh, through to having children to retiring.In other words, we don't have to make one type of apartment for everybody.And the second one is, I think there's an implication in what you're asking, that people have more choice than, in my view, they have, I think that people's decisions are very much dictated, uh, by affordability in places like London.Certainly mine was, ours was.And, uh, really, you know, living in London, living in, uh, European cities has become incredibly expensive.So I would question really the point you are making that, yes, more buildings are getting built in the city center, but the fact remains that it's incredibly expensive to live in, in London.And that wasn't always the case.You know, in previous periods of London and other cities, people came to those cities in order because of economic hardship.They came to to, to get a job, uh, and, and, and work there because of economic hardship.So now the fact that it's, it's almost a luxury to be able to live in London, I think is, is something, which is one of the things I think we should discuss as a society.So, um, my second question is more structural.I hope when you look at the diagram, particularly of two 70 Park Avenue, yes.Everything comes down to a point.Yes.And it looks to the uninitiated like a single point of failure potential.Mm-hmm.<affirmative>, the, the, all the load is being transferred Yes.Through three or four points to the ground.Yes.Um, and it just looks fundamentally worrying for the innocent Well, so it isn't a single point of value.There are several points, and those points are designed for, uh, various different methods of, of things being removed, say it like that.So it, it has been taken into account the idea that the building doesn't, uh, need to stand, uh, can withstand different events where elements can be removed.So no, it's not a single point of failure.Okay.Open the question four, sir.The front here.Oh, hello.Um, you mentioned earlier about the buildings, the whole buildings, they have to get narrower as they get, get bigger.Is there a height where they have to start getting narrower?He example the walkie toki?Okay, so, uh, good question, because actually the, uh, the planning requirements vary from city to city.And I was referring particularly to, uh, New York, which has a very specific and quite pr uh, prescriptive method of calculating how tall your building can be compared to how wide it can be.And there are, it's quite a kind of complex rules, series of rules, but basically it's all really about trying to see the sky from the street.And so, in answer to your question, in New York, the height is limited by how much you set in.You can go quite high as long as you set in a long way.What you're really trying to do is, uh, is, is is allow a view of the sky from the street.The walkie-talkie is part of, uh, the London planning system, which is, which is entirely different.There are protective views of St.Paul's Cathedral from various points.And the, the tour buildings are have to say, have a discussion with relation to those, uh, with relation to those views that, but there are plenty of other planning.There's a, there's a whole planning process of course, but that's one of the most particular London planning rules.New York, uh, uh, and Chicago, for instance, is known as the, uh, city of Architecture.Can you tell me about September 11?You know, uh, huge concrete building.Yes.Like the World Trade Center?Yes.Just collapsed like a house of cards.Mm-hmm.<affirmative>, what went wrong there?So the twin towers are, are actually, there was a, they were actually a steel frame system.They had an external steel frame around the perimeter, the external perimeter.Uh, and that frame was impacted by this absolutely huge fuel load, which came into them, a, a really enormous amount of heat delivered into steel rather than concrete.And, uh, you know, there, there you could then also talk about the fact that most buildings have a reinforced concrete core, which has its own level of robustness.Uh, and the twin house was a very different structure from that one.So I guess my summary would be, it was a quite a particular structure with a very, of course, incredibly, uh, unique load with an enormous fuel load delivered into it, which, which meant for resulted in incredibly high temperatures, a around the, uh, around the tower.Next question.There's one right at the back, I think in fact, two at the back.While we are, while you're over there,I've been cycling through London for the last 35 years or so, and I've seen a lot of changes in that time.And as I cycle down nine El Lane towards Vox Hall Bridge, I see a horrible monstrosity before me.And all you are doing is promising more and more dehumanization the same ghastly 1984, although that's behind us now, what we've got in front of us, God only knows you are promising and providing a hideous future for mankind.That's what I've got to say.And I'm glad I'm 80, not 20 <laugh>.I'm sorry.I live there.You live there.Well, here, I mean, you know, it's interesting.I'm a cyclist too, actually.Uh, but you know, I think these, these are opinions are entirely valid, but they of course have an effect on other people.So, you know, I would, I would say our decisions, people here, maybe some of us already live in London.We are, we are taking decisions which affect other people who either don't or can't afford to.So I totally respect your, uh, point of view about the aesthetics of, uh, what you see as developments.Um, but I just think we have to be aware that when we take decisions about what we, what we like and don't like, it, it isn't a free decision.It still affects the rest of society.My question follows on from what the Lady of the Left says.Yes.Apart from planning laws or laws, is there any upper limit to the height of a, a building can be built?Okay.And also the second, the second question is, is how when you get a tall building, a len, a tall, slender building, how far down to the foundations do you have to go?What are the foundations made of?Yes, very good.Uh, and yes, that is a good interpretation of that question point taken.So how, first, first point, how tall can buildings go technically go?They can go much taller than they are now.Uh, so in terms of their, uh, the ability for a buil building to go taller, the materials have the strength and the predictability and our analysis methods have moved on substantially.Of course, the forces go up exponentially, so you're designing for larger forces, uh, but they can go higher.And you'll be aware there are towers which have been designed.The Burge, uh, in Dubai is around 800 meters.There are towers of which have been designed taller than 800 meters.Uh, and they can technically go much higher.And you are right with your second question, or at least the implications of your second question, what are the foundations?That really depends a lot on the ground conditions.So in some countries, the ground or some cities, the ground conditions are very poor.So for example, San Francisco has pretty poor ground conditions and foundations for towers need to go down over 200 feet to find a, uh, to find a firm ground, which is incredible when you think about it, huh?How, how Down 200 feet.But how tall Is the building?The, the building might be 300 meters, so sorry to go and feet, so 130 meters down to hold up a building, 300 meters high, for example.So a long way down, whereas in New York, New York has amazingly good ground, uh, at the south of Manhattan and in, uh, and just south of Central Park.And that's why when you look at a profile of New York, you'll see that you've got tool buildings in a particular area just south of Central Park.Then the Skyland goes down because the, the, this incredibly good rock gets lower.And then at the south end, the rock comes back up again.So when you stand at Central Park, this rock comes out of the ground.It's amazingly resistant rock.So towers in New York, uh, not all towers, it depends on how tall they get, can be founded on pads.They can be founded on top of the rock or just into the rock.So it really very much depends on the ground conditions.Is a, is a, is a, is the short answer to that.How Do you do it on London clay?So London clay is a pretty good founding, uh, material.Uh, it's nowhere near as good as a rock.It's still a clay.Um, so you found on piles for tool buildings and you use, uh, shallow foundations as much as you can for other buildings, uh, because shallow foundations are less intrusive and quite often less expensive.So, um, chap with the beard, therefore be waiting a long time.Uh, just, I'd be interested to get your thoughts on where I, I fully accept that increased density has a lot of advantages, but where you already have lower density housing with established public transit, whether it's London, France, or it's the London or Paris.Uh, I'm from Chicago, so I, uh, know that that what that is.But is have you looked at or do you have any thoughts on are you better off building higher density outside of where you already have some of those, uh, situations and and increase the use of public transit or as part of the development or, uh, like you were, uh, kind of saying you did it in New York where you removed the, uh, existing and Yes.Okay.So understood.You know, your, your question, I interpret your question as saying if you have an existing development, how do you deal with working that existing development?And of course, Paris is a very interesting example, very dense city, uh, not particularly tall.Uh, and, and of course with understandably quite a lot of, uh, nervousness when people want to try and, uh, think about building tour buildings there.So I'm going to give you one version of this, but this is a far longer discussion in my view.There are some, there are some areas where it's quite easily decided because you are in an area which is low density, which really is a developing either neighborhood or city.And you know, we've talked, um, uh, inside the, you know, with colleagues of mine or the sustainability colleagues Chris Trot about when you have nodes, which are well served by public transportation, they can have low density around them, perhaps parks, but you've built up height around those transport nodes.I think that what you're talking about is almost a, that you can get onto the politics of should you be building in a particular city.And I think that, I think it is understandable that people have nervous reactions to that.Really what I'm trying to, and I I almost don't wanna get too much into the politics so much as to say we have to be, I want to bring to everybody's attention the reality.Yeah.The reality of the carbon footprint.So we may then have to take nuanced decisions about which parts of which cities we want to preserve for entirely valid reasons.I've lived in Paris, I can see lots of good reasons to, uh, not want to, uh, you know, to, to develop all of it, but we have to, I, I'm just trying to bring the information for evaluating those decisions.I mean, what's not to like about that skyline <laugh>.So, I mean, that's great, but I guess my concern is y your creme de la creme, you can build fantastic, uh, you know, fantastic architects.You do the math destruction engineers as a lease holder affected by fire safety.How do you ensure the quality build on these buildings?You only have to look what's happened since grandfa.I mean, it's been disastrous for hundreds of thousands of people buying these units in Highrise, in fact, not just highrise, lowrise buildings.Mm-hmm.So you can build fantastic buildings, but the qu when it comes down to money developers, value engineering.We've got these major issues.So how, what's your thoughts?How, how do you ensure quality builds?Well, you are touching on a particular issue, which is the cladding issues that have happened after Greenfield Tower.Uh, terrible tragedy that happened about 400 meters from where we live.And, uh, absolutely awful.And, uh, I, you know, I sympathize with lease holders who are in this incredibly difficult situation with regards to the cladding on their building.There's no other way to put it.They've got, uh, this very dangerous, very difficult situation with a, with a cladding, um, that I almost don't wanna kind of cut across a whole story as you, as you're aware of trying to sort that out.There are reports the building industry is changing and incorporating changes.Uh, there was a, um, uh, uh, Dan Judith Harris did a report, and that's being basically being incorporated into the way that we carry out and take responsibility for buildings at various stages.Uh, but I really, I guess my main theme is I do agree with you.I think that we do need to look after the quality of the buildings and that particular issue, that very specific issue that you are referring to is, is a really, really difficult one, a really difficult one.It seems to me that we could go on asking questions all night, and I'm terribly sorry to have to bring it to a close.It's, so thank you so much, Roger, for giving us a fantastic lecture, and please thank him in the usual way.Thank.