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How Engineering EarthquakeResistant Buildings Could Save Lives Designed to Withstand the Next Big Shockwave Interview with Sinan Acikgoz, Structural Engineer

Spring 2018 | US: $10.99

architexture

team.

A intelligent, accessible publication focused on delivering unique content on architectural design being applied to modern day. With a commitment to the details, architexture delivers stunning photography coupled with intelligent articles to help inspire the future.

Editorial Team Alan Perez Robyn Marsh Joseph Maffeo Creative Abygayl Normal Sales Manager Kathryn Angel Printing Litho-craft Distribution Jason-Jasoff

architexture ¡ earthquakes

Contributers Mona Mor Pearl Ygirl Daniel Tennant Dallon Adams Robyn Marsh People Six Humanoid Seven Front Cover Left: Tall Cover Building | Photo by Person Someone Right: Damage done by the 1980 Mexico Earthquake | Photo by News Station 4

contents.

An Interview with Engineer Sinan Acikgoz

How Engineering Earthquake Resistant Buildings Can Save Lives

Designed to Withstand the Next Big Shockwave

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Inquiries Architexture Magazine 111 Federal Street Boston, MA 02110 Ph: 978.857.2251 F: 617.242.5862

Spring 2019 ¡ 3

letter from the editor.

ARCHITECTURE AS A CRITICAL LANGUAGE WITH WHICH TO FACE THE WORLD. Change of the more profound, epochal kind forms the subject of this month’s earthquakes, which considers frameworks for analyzing the awesome and still unfolding narrative of human cultural evolution. Armed with such rich insights, we might thus derive a more profound sense of how we really want to live and how to engage with society. Regular readers might be surprised to see the traditionally monochromatic pages spring into color as Dallon Adams shows us seven of the worlds largest and earthquake-resistant structures 12. Sinan Acikgoz will answer our questions about what earthquakes can do to buildings and how its theories relate to architecture 36. Designing for mother nature is becoming a more pressing matter as the world's population continues to grow.

How can we use architecture to be a less destructive people? Port au Prince said it best, "Earthquakes don't kill people. Buildings do."

Yet as a collective, conscious society, we are clearly still struggling to attain such holistic bliss. The fragility of the man-made world was brought into sharp realization by the impact of the recent earthquakes in Mexico City 46. We look into the history of the Shaken City and what they have done to prepare for the future of the city as they prepare for the next century of earthquakes.

Latterly, Kiremidjian received John Fritz Medal for her research in the field of probabilistic seismic risk assessment and for her leadership in the classroom, educating the next generation of earthquake engineers 51.

The Archi-Texture Team

architexture ¡ earthquakes

contents.

Engineer Spotlight: Anne Kiremidjian

A Shaken City 56 Among the Mountains

51

63 A Leaf on a Flat Surface

46

68 Indigenous Architecture in Our Cities

68 59 This month we got a letter sent to the editorial team. It was only a photo, no note. Thank you Daria Nepriakinha, this cracked us up.

59 Environmentally Conscious Industrial Complexes

71 Zombie Bunker: The Ultimate Earthquake Proof HomeBun 76 Inside is the New Outside: Architectural Interiors 78 Trusse Me On This

Spring 2019 ¡ 5

Designed to Withstand the Next Big

SHOCK

As our urban centers become more densely populated, Engineers are continuously looking to maximize this space by building upward rather than outward. As a result, we’ve seen massive skyscrapers sprout up in metropolitans around the world. As history has shown time and time again, a massive tremor in an ill-designed city center can have costly and, most importantly, deadly ramifications. This is why earthquake proof buildings, also known as earthquake resistant buildings, are becoming more common. But just because a building is sturdy doesn’t mean it can’t have style. We’ve collected the most amazing and gorgeous earthquake proof buildings from around the world.

architexture · earthquakes

Shanghai Tower (bottom left), Shanghai World Financial Center (top right), Jin Mao Tower (bottom right) | Photo by Alessio Lin

WAVE

by Dallon Adams

Taipei 101 Taipei, Taiwan

At 1,667 feet tall, Taipei 101 was the tallest building in the world when it was completed in 2004. While it may no longer hold claim to this engineering title, Taipei 101 still houses some of the most impressive seismic- and weather-resistant technologies ever designed. Taipei 101 uses a massive internal damper to control swaying and minimize the possibility of structural damage or failure, making it a very earthquake resistant building. The goal of such a damper isn’t so much as to prevent swaying in general, but to instead attempt to control this movement.

This tuned mass damper weighs 728 tons and is suspended between the 87th and 92nd floors. During an earthquake or high winds, the pendulum counteracts the building’s movements. In 2005, during Typhoon Soudelor, Taipei 101 was blitzed with winds of 100 miles per hour and even a gust of 145 mph. However, the damper — which was engineered for a maximum wind speed of 135 mph — quite literally weathered the storm. You can watch the pendulum in motion during Typhoon Soudelor.

DAMPER SYSTEM IN TAIPEI 101 The damper consist of a steel sphere 18 feet across and weighing 728 ton. The ball can move 5 feet in any direction and reduce sways by 40 percent. There are two additional tuned mass dampers, each weighing 7 tons, installed at the tip of the spire provide additional protection.

architexture · earthquakes

Taipei 101 towering above the Taipei skyline.

Photo by Remi Yuan

91st floor deck

89th floor deck The damper sits between the 89th and 87th floors and has an indoor observation deck. The damper is another beautiful architectural element of Taipei 101.

Spring 2019 ¡ 9

Shanghai Tower Shanghai, China

Standing more than 2,000 feet high, the Shanghai Tower is the second tallest building on the planet. Unfortunately, Shanghai is located in a seismically active area and the site of the tower is composed primarily of soft, clay-heavy soil. To boost the foundation and make it more of an earthquake proof building, engineers incorporated 980 piles–some nearly 300 feet deep–secured within 2.15 million cubic feet of reinforced concrete.

Like Taipei 101, the Shanghai Tower also utilizes a tuned mass damper to control sway during an earthquake or high winds. Weighing in at 1,000 tons, the damper in the Shanghai Tower dwarfs the device used in Taipei 101 by more than 200 tons. As the building sways, the inertia of the weight counters this movement.

For optimal counterbalancing, a series of shock absorbers keep the pendulum from swinging too far or too quickly.

Shanghai Tower designed by Gensler ARCHITEXTURE ·16

DAMPER SYSTEM IN SHANGHAI TOWER The Shanghai Tower's 1,000-ton damping system, the device that boosts the stability of the country's highest building. The damper emphasizes the blend of form and function.

Transamerica Pyramid sitting above the iconic San Francisco skyline. Photo by Katy Raddatz

Transamerica Pyramid San Francisco, California

A study published in 2016, stated that current predictive earthquake models could be significantly underestimating the potential of the next massive tremor to strike the Bay Area. This future shock is currently forecasted to be at least as strong as the notorious 1994 6.7-magnitude Northridge quake and the Transamerica Pyramid—currently the tallest building in San Francisco—was deigned to withstand the inevitable Big One. The building itself sits on a 52-feet deep foundation of concrete and steel that was designed to move with the earth during a quake. The exterior is made of precast quartz aggregate, buttressed with reinforcing rods at four points on each level. During the 1989, the 6.9-magnitude Loma Prieta quake, the building shook for more than a minute and the top floor swayed from side-to-side nearly a foot, but the building sustained no structural damage.

A series of sensors installed in the frame of the building measure horizontal displacement and according to the U.S. Geological Survey, the Transamerica Pyramid could withstand an even larger seismic event. It may be a truly earthquake proof building.

Spring 2019 · 11

Mori Tower Tokyo, Japan

Japan sits in one of the most seismically active regions on the planet. Each year, the country experiences more than 100,000 earthquakes, according to the Seismology Society of Japan. After the catastrophic 1995 Great Hanshin earthquake—or Kobe earthquake as it is more commonly referred to as—the country mandated new engineering standards and sweeping retrofitting overhauls to prevent similar devastations in the future.

Mori Tower is one of the tallest buildings in Tokyo and per its official website, the tower was designed to be a“city to escape into’ rather than a city from which people run away.” To fulfill this ambitious goal, the Mori Tower features some of the most sophisticated motion-absorbing, earthquake resistant building technology ever implemented.

Like Taipei 101, Mori Tower uses damper engineering for seismic resistance.

However, rather than implementing a massive tuned damper Mori Tower uses 192 of fluid-filled shock absorbers. These semi-active dampers are filled with a thick oil, and as the tower begins to sway — as a result of tremor or high winds–this oil is sloshed in the opposite direction to counter and/or minimize this swaying.

MANY OF THE TALLEST BUILDINGS ARE EARTHQUAKE-PROOF A chart of the world's tallest buildings, many of which have mechanisms in place to prevent earthquake damage. Buildings Left to right: Burj Kahlifa, Taipei 101, Shanghai World Financial Center, International Commerce Center in Hong Kong, Petronas Towers, Nanjing Greenland Financial Complex, Willis Tower, Trump International Hotel & Tower, and Jin Mao Tower.

Mori Tower designed by Kohn Pedersen Fox and The Jerde Partnership.

New Wilshire Grand Center Los Angeles, California

Southern California is long overdue for a massive earthquake and this was known even prior to a newly identified fault in the area capable of creating a 7.4-magnitude earthquake. With this rather foreboding knowledge in mind, Los Angeles has some of the most expansive-seismic building regulations in the country. In fact, in 2015, more than 15,000 buildings were required to be retrofitted to meet these new guidelines.

As one could imagine, the tallest building in Los Angeles, the New Wilshire Grand tower, went through rather rigorous seismic modeling beforehand. During testing it was realized that an earthquake could create catastrophic whiplash on the top floors of the building. To counter this, the team implemented 30 outriggers along three sections of the building. Outriggers are braces that form triangles that extend from the center of the complex to the exterior columns of the building, allowing the facility to resist vertical and lateral forces.

To further buttress these outriggers, engineers incorporated a series of so-called buckling-restrained braces to each unit. These specialized braces can stretch and also compress without buckling. The building itself sits on a 17.5-foot concrete foundation and the seismic savvy skyscraper also utilizes a joint between the base and the tower that is capable of sustaining up to 1.5-feet of sway.

Wilshire Grand Center is the first major skyscraper to be built in Los Angeles in a quarter century.

TECHNOLOGY INCORPORATED A distinctive feature of the 73-story high building is its sail-shaped crown which is illuminated with programmable LED lighting at night.

Spring 2018 ¡ 13

Inside Sabiha Gokcen Airport the infrustructure is vital to damage from earthquakes.

Sabiha Gokcen Airport is the world's largest seismically isolated building, meaning the building moves side-to-side during an earthquake. The whole building moves as a single unit, preventing damage from uneven forces acting on the structure.

Sabiha Gökçen Airport Istanbul, Turkey

In 1999, a 7.4-magnitude earthquake hit Istanbul killing 17,000 people. Seeing as the city is situated near the Arabian, African, and Eurasian tectonic plates, another large quake is projected to happen within the next 30 years. With that in mind, engineers designed Istanbul’s Sabiha Gökçen Airport to be able to withstand the next inevitable seismic shock. The airport now claims the lofty and very specific title of the world’s largest seismically isolated building.

The two-million square foot complex sits above the ground on more than 300 seismic isolators. These individual bearings shift with the undulations of the earthquake, allowing the entire building to move as a single unit. This design diminishes the acceleration the building would experience during an earthquake by 80 percent.

architexture · earthquakes

Komatsu Seiren Nomi, Japan

The Strand Rod is a carbon fiber composite which is covered in both synthetic and inorganic fibers and finished with a thermoplastic resin.

Not all earthquake proof building designs utilize the most sophisticated dampers or seismic isolators to protect buildings during major seismic shifts. A Japanese textile firm, Komatsu Seiren, recently used high-tensile twine developed from carbon fiber to reinforce its facility in Nomi, Japan. Architects Kengo Kuma and Associates then attached more than 1,000 of these high-tensile rods to the roof of the facility. Inside the showroom, another “curtain” of nearly 3,000 additional rods add further structural reinforcement. Together these systems help minimize the horizontal forces exerted during an earthquake. ◊

FIRST OF ITS KIND The world’s first seismic reinforcement structure using a carbon fiber material designed by Kengo Kuma, a world renowned architect.

Spring 2019 · 15

Engineering Earthquake-Proof Buildings to Save Lives

by William Harris

architexture ¡ earthquakes

MORE THAN A MILLION PEOPLE HAVE DIED IN EARTHQUAKES in the last two decades. Seismic rumbling between the Earth’s tectonic plates puts some of the world’s most densely-populated countries at particular risk. Yet for the most part, earthquakes themselves do not pose the greatest risk: Collapsing buildings do. While buildings are generally designed to withstand vertical loads–the weight of their contents and inhabitants–they have not traditionally been built to withstand the side-to-side swaying that a tremor can bring.

San Francisco, CA is prone to Earthquakes, so many buildings are fit with stabalizing materials.

Photo by Chris Leipelt.

Spring 2019 · 17

Light walls and partitions and thin concrete floors can help. So can what are called shear walls, a system of panels and braces that effectively channel a side-to-side force downward into the building’s foundations. The giant concrete columns at the centre of modern skyscrapers do exactly that. There’s also a bit of simple physics known to the architects of ancient Japanese pagodas. These were built with a giant central pole called a shinbashira, which acted as a tremendously heavy pendulum. Seismic shuffling of the pagoda’s main structure transfers into the gentle swaying of the shinbashira. Since it was built in the early 7th century, the enormous Horyu-Ji Temple in Japan has survived dozens of big earthquakes. Modern builders have taken note: Taiwan’s Taipei 101 and the Citicorp Center in New York use hundreds of tonnes of concrete or steel to do the same job.

All this has the potential to make newer buildings safer. But as much of the infrastructure damage in Nepal has shown, it is also very important to apply this hardwon engineering knowledge and retro-fit older buildings as well. Let's look at how.

Built-In Damage Prevention During an earthquake, the energy released by the movement of huge segments of the Earth’s crust generate powerful forces that spread across hundreds of kilometers. When the base of a building shakes or lurches from the force of an earthquake, the difference between the top and bottom of the building can introduce new stress and strain onto the materials that support the structure, causing them to rupture.

Over the past few decades, new designs and materials have meant that buildings in earthquake zones and elsewhere have become better engineered to withstand the forces involved during a quake, but they are far from infallible. Researchers are developing novel techniques to ensure that future structures are even better equipped to avoid collapse. In fact, they may be able to predict or even prevent earthquakes before they happen. But before we get there, we need to understand how our current structures work (and don’t work).

JAPANESE PAGODA Japanese pagoda in Sensō-ji, Taitō-ku, Japan. The pagoda is built with a giant central pole called a shinbashira. This acts like a heavy pendulum that combat against earthquakes. Photo by Yu Kato

architexture · earthquakes

Looking up at the Transamerica Pyramid. Concrete can be a brittle material unless reinforced with rebar. Photo by Thoki Tafeni.

Andrew Whittaker, a professor of civil engineering at the University of Buffalo, notes that a building during an earthquake is like a person standing on a plank supported on a roller. If someone moves the roller, the base can no longer support the upper weight, which could cause the person to fall. In general, the taller the building, the stronger the difference in forces between the bottom and the top, increasing the likelihood that the material could break.

That’s why many cities in earthquake zones had restrictions on how many stories a building could have, according to Thomas Heaton, a professor of geophysics and civil engineering at the California Institute of Technology.

Of course, some materials are better at handling this changing energy than others. Wood works surprisingly well, “Wood is, in a sense, ideal in that it’s extremely light-

Inside a wooden structure in Helsinki, Finland. Photo by Kuvio Architectural Photography.

weight compared to its structural stiffness and strength,” Heaton tells Futurism. Concrete is typically a brittle material, but when it’s reinforced with steel rebar, it becomes much more elastic when shaken side to side. Others fare far worse: adobe clay buildings (millions of which were destroyed during the 2015 Nepal quake) and masonry (those made of brick or stone and held together by mortar).

The design of the structure, too, can concentrate or dissipate energy from an earthquake. Engineered wood, such as laminated wood, makes up the frame of the house. The

Wood is ideal, in that it's extremely lightweight compared to its structural stiffness and strength.

Spring 2019 · 19

The Zombie Bunker House

by KWK Promes is the type of building that would do the best in an earthquake.

beams are supported with sheer walls, which are designed to collapse under pressure from an earthquake, and are connected with metal bracings that loosen during shaking.

The whole house is securely fastened to the foundation to prevent it from slipping off during a quake. Many modern skyscrapers do surprisingly well in earthquakes because the force exerted by strong winds demand that they are built to be flexible. Older structures can be retrofitted to be equipped with today’s safer techniques, but that’s sometimes more expensive than simply building something new.

The structures that would do best in an earthquake would be windowless, concrete entities, the kind of thing that most architects would deem hideous. “When I look at structures that people think are beautiful, open airy things full of windows, I just see crushed human bodies waiting to happen,” Heaton says.

Some newer, more sophisticated structures are built with a technique called base isolation. Rubbery devices are installed near the foundation of the building to absorb the energy from an earthquake, preventing it from dissipating throughout the frame. “You can think about it as something like a shock absorber in a motor vehicle scaled up

The structures that would do best in an earthquake would be windowless, concrete entities.

to a building level,” Whittaker says. Base isolation is still expensive, so it’s primarily employed in buildings that are used by large numbers of people or those that would be important in an emergency, such as hospitals and airports.

Base isolation is a technique developed to prevent or minimise damage to buildings during an earthquake. It has been used in New Zealand, as well as in India, Japan, Italy and the USA. Chris Gannon and Dr Bill Robinson of Robinson Seismic explain the base isolation principle.

A fixed-base building (built directly on the ground) will move with an earthquake’s motion and can sustain extensive damage.

When a building is built away (isolated) from the

architexture · earthquakes

ground, resting on flexible bearings or pads known as base isolators, it will only move a little or not at all during an earthquake The isolators work in a similar way to car suspension, which allows a car to travel over rough ground without those riding in the car getting thrown around.

Base isolation technology can make medium-rise masonry (stone or brick) or reinforced concrete structures capable of withstanding earthquakes, protecting them and their occupants from major damage or injury. It is not suitable for all types of structures and is designed for hard soil, not soft.

A fixed base building will move with an earthquake’s motion and can sustain extensive damage as a result. When a building is built away (isolated) from the ground, resting on flexible bearings or pads known as base isolators, it will only move a little or not at all during an earthquake.

Rubber is a key component in base isolators. Using old tires is a sustainable option.

How are Base Isolators Constructed?

Lead rubber bearings are at the core of the base isolator and after time return to their original state.

Lead rubber bearings were developed as base isolators in the 1970s. They consist of three basic components–a lead plug, rubber and steel, which are generally placed in layers.

The rubber provides flexibility through its ability to move but return to its original position. At the end of an earthquake, if a building hasn’t returned to its original position, the rubber bearings will slowly bring it back. This might take months, but it will return to its original position.

Lead was chosen because of its plastic property–while it may deform with the movement of the earthquake, it will revert to its original shape, and it is capable of deforming many times without losing strength. During an earthquake, the kinetic energy of the earthquake is absorbed into heat energy as the lead is deformed.

Using layers of steel with the rubber between means the bearing can move in a horizontal direction but is stiff in a vertical direction. These sort of inventions are how archeticts will combat the problem of earthquakes. ◊

Base isolators work similarly to the suspension on a car. They're made out of lead, rubber, and steal.

Spring 2019 · 21

are

earthquake-proof

Taipei 101 in Taiwan Photo by Jack Brind

architexture · earthquakes

buildings possible?

an interview with Sinan Acikgoz PhD Student in the structures group at Cambridge University Department of Engineering is working on new ways to make buildings resistant to earthquakes.

He showed Ginny Smith how to better protect buildings against damage.

Interview by Ginny Smith Spring 2019 ¡ 23

Sinan Well, there's a very important saying

which I think belongs to Nicholas Ambraseys who was a very big important man in our field. Port au Prince he said, "Earthquakes don't kill people. Buildings do." I think this lies at heart of the issue that we all live in buildings. We all need civil structures to actually sustain our society and we need to protect them from earthquakes.

Earthquakes happen over hundreds of years. They don't stop and our Earth is going to keep on giving us shakes here and there. So, we need to be prepared for these important events. They're very costly when they happen even when we actually manage to stop buildings from collapsing, stop that occurring during earthquakes. They can be very costly and they can be– if that happens on a regular basis, that can be very damaging economically.

Ginny Are there some buildings that are

more susceptible to earthquakes than others? I mean, I imagine the sort of really tall skyscrapers you see are probably more dangerous than old fashioned, sort of lower houses.

S I'm not so sure because it's a complex

issue in the sense that when you make a structure which is small, compact, stiff, that structure will end up attracting more load.

Actually, the structures you mentioned, the skyscrapers, they're all engineering structures. It's actually quite rare that you would find them in places where there's recurrent danger of earthquakes. So, there will be building regulations which would actually limit the number of stories or suggest that there should be technologies in place to actually prevent these buildings from moving a lot.

So actually, certain buildings are certainly more susceptible to earthquakes.

For instance, masonry buildings would be one example and a recent earthquake that

architexture ¡ earthquakes

happened in Christchurch for example was a good example of this where the earthquake hit at a city centre and city centre was full of beautiful old masonry buildings.

You must've all seen the Christchurch Cathedral after the earthquake and it was in shambles. So certainly, there are structures which are more susceptible and these are generally structures which are not engineered to withstand earthquakes with modern science techniques.

G So, what can you do to make a building

more resistant to earthquakes? Do you build one that won't move when the earthquake happens, it'll just stay nice and still so everyone inside is safe?

S That ideally would be great because if we had something that's rigid, if the ground moves, if you've got something that's sitting on a ground and it's completely rigid, the accelerations in that building will not exceed that of the ground. Whereas if you've got a flexible structure, I imagine a very tall skyscraper as you've given an example, that building actually will

Left: Christchurch Cathedral in New Zealand after the earthquake.

Below: Christchurch Cathedral in 1955, before the major earthquake.

amplify its motion at the top stories, you will get a lot of sway. And the strategies that we can do is actually, we can design our buildings to be completely elastic during an earthquake which is, the earthquake will happen just like you move a rubber band, you pull it back, you leave it and then it comes back to its own original state. So, we would ideally like to do that. We would ideally like to have a building which doesn't get damaged, but that's just far too expensive. So, what we do instead is we try to decouple the structure from the motion of the ground during an earthquake. So, that would be called base isolation.

That's one strategy and the second strategy is what is really commonly adopted today. You let the building get damaged during an earthquake, which is quite counterintuitive to people because one would hope that an earthquake-resistant building is damage proof. But what happens is this damage that occurs in a building is actually what saves the building. So, this is another strategy, but what earthquake engineers want right now, what is our biggest challenge is, actually making structures which are safe during an earthquake and which do not get damaged.

It's actually a really big challenge.

G Now, I've never actually been in an earthquake, so I'm finding it quite difficult to kind of imagine what happens to buildings during one. Dave, you've got something over there that's going to show us a bit more about how it would actually look if you were in an earthquake - a very, very small earthquake.

Dave Basically, what I've got here is a platform which acts

like the ground which if I turn it on, wobbles. It's basically like an earthquake. I can change the speed of that wobble.

And so, at the moment, it's wobbling quite slowly and the building is behaving fairly stiffly and it's just moving with the ground, and you're probably happy in that building.

But if I change the speed a bit faster... As you see now Ginny, the building is starting to bend.

Millennium Bridge in London Photo by Toa Heftiba

When the Millennium Bridge was opened, it was meant to be this huge thing and as soon as people marched over it, it started shaking.

G It's buckling under–the thing is, it's no longer shaking just in line with the Earth moving. It's sort of bending in the sections in the towers.

D So basically, buildings can have a natural speed at

which they want to vibrate. And if it's a very strong speed which is resonance of the building, that the building wants

Spring 2019 ¡ 25

Queenstown, New Zealand sits nestled in between mountains resulting from centuries of seismic activity. Photo by Toa Heftiba

have the same resonance though? Can you predict at what sort of frequency it's going to be shaking about?

S Well, this is actually a field where

to vibrate at, and if the earthquake happens to hit that, the vibrations get bigger and bigger, and bigger, and you get into real trouble. So, I imagine designing buildings to avoid the resonance being anywhere near an earthquake speed is very, very important to them.

S This is something that's quite important

that we try to actually take care of in our research. So, the concept of base isolation that we just discussed is essentially actually just this. So, there's a frequency range during an earthquake which the ground will move and you want to move away from that frequency. You want your structure to be away from that frequency so that the motion doesn't build up. So, the typical example of a resonance is, if you're pushing somebody when they're in a swing, so the motion will just build up, build up, build up, and that will be too dangerous.

So, what we try to do in a base isolated building is actually, put something very soft underneath the structure so that its frequency will just go very low, and actually, this will decrease the loads that is acting on a structure.

G I remember the wibbly wobbly bridge in

London. When it first opened the Millennium Bridge, it was meant to be this huge thing and as soon as people marched over it, it started shaking. That was because people were marching in the same resonance. Do all earthquakes architexture ¡ earthquakes

there's a lot of research as well. We try to characterize earthquakes, but you cannot really specifically guess what specific earthquake is going to be like. So, we need to actually design it for a specific range of frequencies, specific range of large range of frequencies and be very conservative about how we do it. So, what happened with the Millennium Bridge was a very interesting example because the lateral frequency of the bridge actually really matched what the frequency of the people would be walking which is roughly about 1 hertz. So, this is a very specific example. With buildings, interestingly, the frequency actually falls in the range where the earthquakes would be most damaging. So especially, for short stocky structures, this is a big, big danger that we have. My personal research about earthquake engineering actually works on the structures which are rocking and these rocking structures are slightly different because we let them separate from the ground during an earthquake. So, the common strategy is, you would just tie down the structure to the ground and you would not let it separate so it would eat up all the energy of the earthquake. Whereas if you let a structure separate from the ground, it will actually take the earthquake energy and there's actually a setup there which we're going to be demonstrating with...

G So, Dave's model is about the height of

my hand, but this one's a little bit larger. So, what are we going to be showing with this model Sinan?

S So, this is a 3-storey shear frame which is a normal building frame. It's bare. It

So, I want to be in a rocking building rather than a wibbly wobbly one? doesn't have all the other non-structural components. But what would happen is, let's say there's an earthquake and if the building is fixed to the ground, it will start to shake and the building will actually start to take all the load. It will start to vibrate.

But what we propose is, instead of, and this idea is not actually our proposal. It has been around for a long, long time. Actually, if you let the building separate from the ground during an earthquake, it will just...

If you push a structure like this and hold it from the base, you can see that the columns are all taking all the load and that's actually quite heavy on the columns because we have to design them for bigger forces. But if the structure is rocking and if you push it, what will happen is, it will take the load, but the load will be actually translated into movements. This movement is actually causing the structure to have less load because it's more flexible and it's easy, ready to move and the concept of resonance that Dave mentioned. So, if you move something really far away, this has got a very big motion.

G I'm sorry Sinan. So, when you pushed it

and held it down to the ground, I could see that the columns were bending. But to me, literally walking the building, tipping half an edge off the ground and sort of letting it tilt backwards, if I was in this building, I'd rather have the columns bend. Is that the wrong way of thinking about it, just looking at this tilting at a 45-degree angle here?

S Well personally, I've never been to one

of these things. I would like to be and it's so much easier working on paper. But the

interesting thing about these is normally, in practice, what would happen is, instead of this fiddly little bits that we have here which restrain the structure, which restrain the shear frame down, we would have big steel members, steel tendons, which will run through the structure and hold it down. So actually, we would be allowing only very small motions. In terms of percentage, it would be only 1% of the height of the total building. So very, very small movements, we would allow and you would probably not be able to tell the difference in between a structure which is rocking and which is not. The interesting thing probably is that when you're in a structure which is rocking, yes, you would feel the low frequency motion of the structure going from the left to the right. You would feel this, but there would be actually less acceleration of the stories doing this fiddly motion. So, you would actually decrease loads on the structure and that's sort of the interesting thing because that causes the loads to be less. We can design the structures to be more economical and more resilient actually during an earthquake because they don't get damaged.

Left: The Transamerica Pyramid in San Fransisco, CA is one of the most earthquake resistant buildings in the seismic area. Photo by Eduardo Santos Above: The Hagia Sophia in Istanbul, Turkey has gone under development to prevent damage in the earthquake-prone area. Photo by Daniel Burka

We can design the structures to be more economical and more resilient actually during an earthquake because they don't get damaged.

Spring 2019 ¡ 27

G So, by allowing it to tip from one side to

another, imperceptively if I was inside this building, you're putting it under less stress and that means in a big earthquake, it might get less damaged, right?

S Exactly, that's the case because as I said,

the current methodology that we have, we allow buildings to get damaged. This is not good for the long term because after an earthquake, there are millions and millions of dollars of damage. This is very bad for the economy and we want our structures to be safe.

G So basically, you're saying,

I'm wrong. I want to be in a rocking building rather than sort of the wibbly wobbly one.

How can you be sure if you're allowing it to sort of tilt to one side and then come back down again that it will come down in exactly the same place?

S So, that's a very important part of the research that we do. What we want to do is we want to restrain these structures. So, we don't let them fiddle about. As you can see from this model, when it actually rocks, it starts to walk off from its foundations which is quite architexture ¡ earthquakes

We actually have the technology to withstand earthquakes, but it sometimes boils down to actually having the regulations. dangerous. So, we want to keep it in place and the way we do it is, as I said, we would have large tendons which run through the structure. We would have other restrainers, other energy "dissipaters" which would dissipate the earthquake energy coming

from the ground and these would actually restrain the movements. So, that's one thing that we would engineer.

G Who's got any questions for Sinan?

Venud Hi. I'm Venud and I'm from

Cambridge, but I'm originally from India.

While growing up, I did experience a couple of earthquakes and the major one was the 2001 in West India. That was 7.7 magnitude I think and there was a lot of destruction and loss of life and property, but the main thing was, the capital near my city, there wasn't much destruction, but there were 50 multi-story buildings collapsed because there was absolutely no earthquake planning there. One of the major local rumors was that few buildings collapsed because they had a big swimming It can take decades to recover from the damage caused by an earthquake. Residential areas are devasted for longer. Photo

by Sunyu Kim

Jakarta is another place that is continually devastated by earthquakes, the concrete buildings can be greatly damaged during earthquakes. Photo

by Dan Johnson

Teran, Iran is a place constantly stricken with earthquakes, few of the structures have features to prevent collapse. Photo by Mahdiar Mahmoodi

pool on the top. Was there any truth to that or does that affect if you really have a big water body on the top of a building?

S Well, this is very interesting question.

I would imagine, this might not exactly be true because it's actually at the top. So probably, what happened was, if there was collapse especially was probably related to lower stories. In most of these cases, in recent earthquakes in Haiti for instance where there was massive damage, one of the things that earthquake engineers realize is, during these earthquakes, we are not currently learning sometimes many new things because we actually have the technology to withstand the earthquake, but it sometimes boils down to actually having the regulation, doing it properly.

This is a very big problem and especially in the developing world where an earthquake can still actually cause very big damage whereas in developed nations

for instance when the recent earthquake happened in New Zealand, life safety was actually reduced to a minimum. This is quite an achievement in terms of what we've done, but in that case, the economical damage was just beyond control. So, we have to manage both of these ends and that's a very big task I think which extends beyond earthquake engineers, goes to policy makers, and beyond.

G Okay, I've got another question you spoke

about partially destructive structures can you give an example of what that is?

again, going back to this Christchurch example. Many buildings after the earthquake were conventionally designed, which is just structures which are fixed to their ground which don't uplift as in the example that I've illustrated which don't have a base isolation at the bottom. So, these buildings just get damaged and when I say damaged, this is all control damage.

So, what would happen is, first, the beams would get damaged and then slowly, they would migrate to the columns because we designed beams to be weak so that they can dissipate the earthquake energy because they're not as essential as the columns. So, they get damaged first and then the damage would migrate to the columns.

In the meanwhile, the building is supposed to stay intact. But in terms of damage when I mean damage, you would see cracks on the building, you would see big cracks on the column and beam interfaces. This is all stuff you would expect. On top of it, after an earthquake, if it has gotten to this level of damage that it cannot be repaired which is very common because if you imagine a reinforced concrete building again, it's got steel bars running through it. So, how are you going to be actually removing those steels which have yielded completely during the earthquake without taking the column out and without replacing the whole structure. So, it becomes a very difficult issue. It is actually very common way of designing structures and it will just happen to any ordinary structure that you can imagine. â—Š

S So, when I say partially destructive

structures, imagine just ordinary reinforced concrete frame which is currently designed,

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