99% Invisible - 99% Invisible-34- The Speed of Light for Building Pyramids

Episode Date: August 19, 2011

Last year, Steve Burrows CBE (Principle at the engineering consulting firm Arup) spent several weeks in Egypt studying the pyramids through the eyes of a modern day structural engineer. The result, which was presented in a documentary for the Discovery … Continue reading →

We get support from UC Davis, a globally ranked university, working to solve the world's most pressing problems in food, energy, health, education, and the environment. UC Davis researchers collaborate and innovate in California and around the globe to find transformational solutions. It's all part of the university's mission to promote quality of life for all living things. Find out more at 21stCentry.ucdavis.edu. This is 99% Invisible. I'm Roman Mars. Steve Burrows is a principal at an engineering consulting company called Arup. I'm Steve Burrows, CBE, and I'm a professional engineer.

And when he saw the great pyramid in Egypt for the first time, he reacted pretty much the way I imagine most people were here. When you actually go and see something that's somewhere in the region of 40 stories high that was built 4,000 years ago, you know you just have this incredible wow moment. But then that structural engineer brain kicks in. Every time you look at something you think, first of all, how did they do that?

Then I start thinking, how would I do that? In a recent article in Design Intelligence, he took those questions head on, as if a client gave him a brief to build something like the Great Pyramid today. We get these incredible challenges, where you're doing something that's never been done before. So one of the incredible facts for me was that the great pyramid stood as the tallest building in the world, for centuries. And as someone who, in the present day, is hired to engineers seemingly impossible structures,

Steve Rose thinks that the engineers of 2,600 BC really knew what was possible and made most of the major decisions as a present-day engineer would. So some of the things they knew were that if they built on the Giza Plateau, they could put stones that, to a certain pressure, and the ground didn't collapse beneath it. You can look at other pyramids and see the previous mistakes they were made. And they got to know what the ground capacity was, and I think that determined the size of the great pyramid. Because if you're going to build the tallest building in the world, how tall do you want it to be? Do you want it to be a mile?

Or just a bit taller than the last tallest building? You've got to make a decision. And I think the decision was made for them by the quality of the ground that they were building on. So that was number one. Secondly, they had to build it in the Pharaoh's lifetime. I'm pretty sure that somebody, you know, a contractor said, you know, with the best will in the world, we can only lay this number of stones a day, and I can only assemble this many men. And assembling men seems to be the right wording here because I totally missed

this historical revision. But the consensus now is that it was a rather privileged, well-treated class of Egyptians that built the pyramids, not slaves. That blew my mind, Cecil B. DeMille is going to be pissed. Twenty thousand men can only lay this many stones a day, and the Pharaoh typically lives thirty-five years, so that many men, times that many stones, that many stones times 35 years means it's going to be this high. So the ground can only hold so much mass without buckling, the workers can only build so much in a Pharaoh's lifetime. And finally the material had to be delivered to the site in time to build the thing.

And I would think, depending where the quarry was relative to the actual site, which was chosen for its known ground bearing capacity, and also height and visibility above Cairo. They also figured out that they could only get so many stones there. They only had so much material of the quality at the quarry. So Steve Bros. thinks that these practical engineering considerations determine the size of the pyramid. It's height, the number of stones, and ultimately, what we all marvel at thousands of years later.

It wasn't so much mystique as just practical necessity. Another practical consideration that led to the pyramid's longevity is material chemistry. There are other ancient buildings that I'm not held up as well as the pyramid. The buildings I saw had lasted thousands of years, and they hadn't all performed perfectly well. So it was pretty clear to me that the Egyptians had a pretty good understanding of the material

they were working with, but it wasn't 100% perfect. For example, the first large mud brick structures that I looked at had massive vertical cracks in them. And it was very clear to me that they were thermal cracks. What had happened is that they were used to building walls. But when a wall turns a corner, that point becomes very stiff. And because the temperature is very hugely between day and night, these materials, these walls, are expanding contract.

And when it contracts, the masonry will always break next to the stiff point. So every time there was a corner, I found a huge vertical crack, so they clearly didn't understand the thermal performance of mud bricks. And that problem is exacerbated by the fact that they laid these mud bricks on a mortar bed, so they effectively have two materials for building. So they do use mud brick and mortar. And by putting these different materials together, they thermally move at different amounts, and they had cracked.

So somebody must have said, well, if we'd only use one material, lay the bricks dry, would they have performed better? And the answer is yes. And the pyramids are exactly that. So there is only one material that's used. That means that the pyramids, they get very hot in the day and very cold at night. But the material throughout the pyramid is consistent.

And so it didn't crack, because they moved together, they effectively breathe. And because they breathe to account for the changes in temperature, they're able to last a long time without cracking and breaking up. So this prompted bros to think about modern buildings, where we put so many materials together all the time. Steel and glass and aluminium and concrete and cementitious materials and plasterboard. And I started walking round modern buildings and looking at where all the cracks were. And every crack is at the joint

between different materials. And I started to think maybe we could think about this a little bit more. And if we did, we could actually make buildings last longer just by thinking harder about those joints, which presently we solved by putting, you know, dewy material in the joint to try and take up that thermal movement. But if we just detail them better in the first place, they would last longer.

And I think, you know, the longer buildings last the more sustainable they are, the longer their life and the less materials we use in the long run. Longevity is probably the most basic route to sustainability and the pyramids are the poster children for longevity. You know there's an old Arab saying, man fears time, time fears the pyramids. In addition to chemistry, adhering to basic principles of physics keeps your building around for millennia with little or no maintenance. A pyramid is a nice, stable shape.

And I think they will have learned that. But it isn't as simple as the way I was thinking about it. If they had a bucket of sand, and they poured it on the floor, then it actually naturally makes a pyramid shape. So intuitively, they know that that is a stable thing to do. But actually, one of the interesting things is that the gradient of the sides of the pyramid is not determined like sand by its natural angle of repose. You can actually make it whatever you want to make it, but you can see from the prior pyramids, from the step pyramid and the bent pyramid, the pyramids that preceded the great pyramid, that they were sort of going a little bit steeper, but they never really got above 50 degrees, because I think somebody felt that

there's a sort of a maximum angle about which we should never exceed. So again empirically derived knowledge sets the agenda. If you put these things together, how much stone you can get, the bearing pressure that you can put on the ground, and the angle, you know, it determines the height of the building, and I'm pretty sure the simple mathematics and the work between the architect, engineering contractor, gave a practical limit to what could be built. This exercise in using engineering principles to augment the archaeological data may give us an insight into why the great pyramid is both the oldest and the largest pyramid of Giza, because people probably thought it was the limit of everything. It's the biggest bearing capacity. It's as steep as they could go, and it's as many stones as can be laid in a lifetime. You can't do any bigger than that. It's the speed of light if you like for building pyramids.

I know it's no revelation that the pyramids are well designed. I'm not an idiot, but learning about these practical considerations from Steve Bros. just made me appreciate their majesty in a new way. These structures are not otherworldly. You don't need to come up with crazy theories to explain them. They are the product of smart architects and designers and engineers and skilled workers who apply knowledge that was gained over time and passed down over generations. And through that perfectly understandable and repeatable process, they discovered their limit.

Don't get me wrong, I don't ever want to see the tallest building we could possibly build, but I might like to see the one designed with enough durability and flexibility to last for 4,000 years. 99% invisible was produced by me Roman Mars with support from Lunar, making a difference with creativity. It's a project of KALW-91.7 local public radio in San Francisco, the American Institute of Architects in San Francisco, and the Center for Architecture and Design. To find out more, go to the it's 99%invisible.org. ونسر حيوية ونضعت بفذك لو تنسان ونساك وتريني بنسجفك

وشتأل عزاب معك والأدن ويفكر أرجعتني في الوقت الدنيات جيني معاك وردخائم Мецгинема, урдоха и мари.