Capital Gate, Abu Dhabi - Megastructures: Leaning Tower of Abu Dhabi - UAE

 

dubai is famous for its audacious engineering projects but now its neighboring city abu dhabi could surpass them all this is capital gate the most inclined skyscraper on the planet

it defies gravity leaning at almost five  

times more than italy's leaning tower of  pisa to make it stand up it'll take some extraordinary engineering that could rewrite the skyscraper

rulebook

 on the edge of the persian gulf lies the shakedom of abu dhabi  it's the largest and richest of seven states that unified in 1971 to form the united arab emirates abu dhabi is undergoing one of the biggest makeovers of modern  times its ruler sheikh khalifa bin zayed al-nayan wants to join the city super league and he's spending over 200 billion  dollars to transform his capital into a

world-class business and tourist 

destination he's already spent a reputed three billion dollars creating the most expensive hotel ever built the emirates palace boasts 114 gold domes

and is the height of luxury where rooms 

cost up to twelve thousand dollars a night and that's not all he's built one of the largest and most opulent mosques on earth capable of accommodating forty  thousand worshipers the grand mosque boasts the largest carpet on the planet and the world's biggest gem encrusted chandelier but even these structures have not quenched his thirst for the extraordinary now the shake wants a building so spectacular it will instantly become an international symbol for abu dhabi

the man appointed with the task of 

delivering this architectural icon is the sheik's cousin his  highness sheikh sultan bin takhnun al-nayan architecturally it will be a unique building and positioning abaddabi as one of the cultural hubs around the world and architecture is part of that overall inspiration and art it's a tough challenge this is a land where extreme engineering is the norm neighboring emirate dubai has already built the world's tallest skyscraper the 828 meter high burj khalifa and an iconic luxury hotel the burj sultan signs up a team of architects and gives them a clear brief not to go bigger or taller but to challenge the rules of architecture for neil van der veen one of the concept architects it's a unique opportunity the spirit of times in the uae was that anything was possible really you could do anything we can do something in the architecture

that will represent that abu dhabi is 

right at the cutting edge the architects look for inspiration in 

abu dhabi's landscape 

they find it in the windswept dunes and the rolling waves of the persian gulf 

we took this idea of wind and water 

which are both dynamic fluid type of rhythms of nature and we said how can we capture those in time as a result you get a much smoother face

i was really 

very happy and when we first see it because such such building you can get the first impression from the first few seconds the team come up with an extraordinary design

a tower that spirals out of the ground 

to 160 meters  inspired by a desert whirlwind and the splash of a wave rising over the sand this gravity-defying skyscraper tilts almost five times more than italy's leaning tower of pisa no single angle of this tower is the same as another it's a structure guaranteed to amaze we really wanted this to happen they could see a vision suddenly they could

see something that would stand for them 

then there was no stopping us sheikh sultan wants the lower floors to become the most prestigious office address in abu dhabi with the top 18 levels

assigned as a five-star hotel fit for 

royalty but for maximum impact this landmark skyscraper

also needs a prestigious location 

the shake decides the tower will stand next to a monument of national importance the grandstand built by his uncle and founding father of the united arab emirates sheikh zayed it's used to this day for national celebrations this monument and the skyscraper will link abu dhabi's future with its past over the past 50 years this land has 

experienced extreme 

change like no the other of huge oil reserves in 1958 set the wheels of progress in motion abu dhabi's ruler sheikh zayed had a vision 

unify the shakedoms and secure their

financial future from western dominance 

he then set about using his black gold to create a city

that rose out of the desert 

today zyed's legacy is all around and now his son wants to leave one of his own to transform abu dhabi once again but this time to put it on the world map

sheikh khalifa plans a new two billion  dollar business district called the capital center situated

alongside the middle east's largest 

business hub the abu dhabi national exhibition center

it's the ideal location for an 

architectural icon and inspired by its location the new tower

is named capital gate 

now the idea must make the leap from the drawing board to the construction site the only problem is no one has ever attempted a skyscraper like this before

everyone realized that this is a 

a crazy structure to build and how are we going to build it to make capitalgate's gravity-defying design a reality it'll take some extraordinary 

engineering 

and the challenge begins on day one its top floors overhang its base by 33 meters

creating huge forces that want to rip 

the building's foundations out of the ground at the construction site project architect tony archibald is daunted by the task ahead it's my first join the job i've shown the drawings and i kind of did a double take and i wasn't quite sure that i got the correct the correct understanding of the project and really it took me a few moments before i realized what we're about to undertake keeping capital gait upright is a huge engineering challenge

there isn't just one solution to 

overcome the forces of gravity it will take a whole range of pioneering techniques but the task starts with the foundations deep underground on one side of the building the weight is going down into the ground on the other side it's been lifted out of the ground and that's that's due to the large overhang that we're having to deal with the solution requires almost 400 concrete piles that work in two different ways on the leaning side half of the piles push the overhang's forces into the ground on the opposite side the remaining piles anchor

deeper into the bedrock they resist the 

stretching forces trying to wrench the building out of the 

ground  

finally to evenly distribute capital gates forces into the piles a deep concrete slab reinforced with steel is laid on top what the foundation's uh taught us is that every single aspect of this building has to be custom engineered excavators dig out a colossal six thousand cubic meters of sand and over eight weeks hundreds of piles are driven into the ground we had an awful lot of piles to put in a very close proximity it was a real difficult challenge there can be no let up on this schedule shake soltan once capital gate complete by an impossibly tight deadline in less than two years time abu dhabi will host the world future energy summit over 3 000 delegates from 50 countries and the world's press will convene at the neighboring abu dhabi national exhibition  center it's the perfect opportunity to showcase capital gate and prove abu dhabi is at the forefront

of innovation 

and after setting we finished by 19 to accelerate to go but this gives the team just 24

months to design 

and build a unique skyscraper with the foundations finished building above ground can begin but because of the dramatic lean it will have to be constructed in a very different way to a conventional skyscraper we realized once we've done the foundations that this was going to be the first of many difficult problems a normal skyscraper requires a solid core to hold it upright the capital gates curves will just crack and topple a standard core engineers must discard conventional thinking and devise a way to defy gravity inspired by the nearby desert landscape and its wind-shaped dunes architects have designed a curved leaning tower but it'll take some audacious engineering to stop capital gate from falling over normal skyscrapers are built around a

slim vertical core 

which helps to channel the building's weight into the ground there's so much overhang on this building meant that a conventional core there was no way it was going to work

you just can't build a straight core 

it's just not strong enough capitalgate's design would cause a conventional core to bend dangerously the pull of the massive overhang wants to stretch the core on one side causing the concrete to tear apart you've got to service even though no it is it is actually 300. it's a maximum four levels structural engineer knows it's a serious problem that must

be solved 

when i saw this one i thought it's impossible it's not gonna work it's just some sketch somebody left it somewhere but i always think that the architect is easier for them to just draw something but it's not easy for us to fulfill or satisfy their needs the engineers develop two ground-breaking solutions the first part of their plan is to build the core with a curve bending in the opposite direction to the building's lean as the structure grows its weight pulls the core straight

in total it shifts 350 millimeters 

and the effect is significant the concrete that would have been

stretched by the overhangs pull 

will now be compressed and strengthened you build it bent and then as you add the slabs to the upper levels it pulls it back into vertical so basically that

whole 

vertical core is in tension and that gives it immense strength  the core grows four meters a week and construction manager les fairchild is in charge of building it this is probably the most complex core that i've come across it's built at an angle and effectively the core holds the whole building up the core is built using a technique called jump forming first a dense mesh of steel

reinforcement is assembled 

a mold then closes around the steel to form the shape of the core the steel mesh is then filled with concrete then the mold or form can climb up the core wall for the process to start all over again jump form is a hydraulic platform once we've cast each four metre level we simply attach it to some runners and we jump it hydraulically up to the next level the core will be strengthened as it straightens but for the core to carry extreme loads the concrete must be reinforced using steel rods called rebar the rebar is installed during the day time but temperatures of up to 50 degrees celsius and concrete don't mix it dries too fast and could crack to set at the right speed the concrete has to be poured during the cool of the night as the core grows higher the liquid concrete has to be pumped over longer and longer distances so the consistency of every batch is first checked in a slump test to ensure it won't block the pipes when you first say coming out the wagon you can usually tell whether it's a tight mix or whether it's a loose mix and that's what we're testing for early in the slum test we simply make a cone lift the cone off and depending how much it reduces in height tells you exactly what the slump is when we just witnessed this 215

millimeters which is within the 

specification so that's good to go [Applause] whilst the truck drives to the pump fairchild needs to get onto the core he can take the stairs but 90 meters up is a long climb he knows a much faster way crane lift it's going fairly well and we've had a

nice continuous supply of concrete 

and we're now pumping it up to the upper levels of the building and the lads are just mentally working  away we actually work from one side to the other and meet the d players so they're doing everything right it's always exciting when we pour concrete it means it's another achievement really we're going up another level but building the core out of  alignment and packing it with rebar still isn't enough to stop gravity toppling capital gate

what we came up with is a 

post-tensioning solution where we introduced much more reinforcement into the core wall and then use the tensioning process basically that was done by introducing high tensile strands to the center of the walls when we released the designated height

we simply applied tension 

you're actually stretching the tendons that fall through the wall and we're actually pulling them tight and that's done by tensioning machine so effectively what you would have when the tension is complete when the load was applied to the core the core would stay intact and the additional reinforcement would prevent it from falling over to post tension the core 146 steel tendons are threaded vertically through the concrete each tendon is 20 meters long and runs through five floors of the building overlapping each other for maximum strength 

when the tendons are stretched the 

stress counteracts the pulling force created by the massive overhang stopping the concrete from tearing apart on-site the team are post-tensioning the 

core 

but no one has ever attempted this vertically in a skyscraper the long tendon is lifted to the top of the core the team used the steel tendon's weight to force it through a duct already cast through the core once the tendon is in position the team lock off both ends ready to tension its individual strands a pneumatic jack clamps around one strand at a time and stretches it it's equivalent to about five family cars pulling on one end of the rope with the steel tendon now stretched to the right 

stress level 

concrete pouring can continue upwards the quantity of cable that's been used

is approximately 120 

tons and 120 000 meters in length it's about 44 times the golden gate bridge

this process is repeated over and over 

and means the core should withstand the huge loads generated by capital gates extreme overhang but now an even greater challenge must be tackled

the building's twisting leaning design 

must somehow be turned from  theory into reality and once again it'll mean bending the rules of architecture to create abu dhabi's architectural icon capital gate needs an exterior curved leaning frame but once again the building's extreme tilt

creates a problem the shape of the 

building with this very pronounced overhang traditional  skyscraper building solutions just weren't going to work there's no way the building design

requires it to be thin to maximize floor 

space and allow for huge panoramic windows irfan ahmed is one of the engineers who has to find a solution for structural engineers always it's challenging to accept the architectural requirement you know they always once thinner and thinner and thinner

surprisingly the humble chicken could 

help with this engineering dilemma it is essentially a skin of structure around the outside of the building not unlike an egg egg can withstand huge loads because it evenly distributes forces down through its shell which means the shell can be thin

creating more space inside 

so it's very very thin it's very very strong if i try to crush this egg

you can see that it's actually amazingly 

resilient so let's see how resilient here i have 170 eggs

laid out and we're going to put load on 

top of these in the form of greaseblocks namely the truth so far so good each one of these blocks weighs 15 kilos so we've nearly got uh half the weight of a car on here now on our 170 eggs let's see how far we can push this that's 30 blocks and i think it's about to go it's going big time now this is the end these eggs eventually crack under the weight

but they withstood over 450 kilos 

half the weight of a family car [Applause] yeah we used to have it all around the corner capital gate can't channel forces with eggshell but it can use the principle of how it works using a dire grid a dire grid is a giant mesh of steel that wraps around the core steel beams connect to a node or joint to form a cruciform section 720 uniquely shaped sections linked

together 

to form the thin but immensely strong diagram working together these cruciforms equally distribute the forces down the outside of the building the way it does that is by making a uniform  net so that the forces are very evenly distributed and that means that we can get away with

slender sections 

on site a team of 240 steel fabricators assemble the dire grid they've built the easier straight part of capital gate's base but now the structure is starting to lean making

installation even more challenging 

each cruciform weighing up to 16 tons has a unique geometry

and must be crane lifted at a precise 

angle if the dire grid is not assembled with millimeter  ccuracy

the mesh will not channel the loads and 

the structure could be weakened the engineers must  ommunicate closely with the expert steel fabricators they design and manufacture the dire 

grid 150 kilometers away 

in the neighboring emirates sharjah here cutting edge construction is the 

norm 

they've built one of malaysia's petronas towers and dubai's iconic skyscrapers the burj al-arab and the burj khalifa but capital gates revolutionary design pushes even these experts to the  limit on the planning floor project engineer p baskaran and his team need bespoke 3d software to tackle the building's highly complex dire grid the 3d modeling is done and any unforeseen criticalities will be very clearly identified in the 3d model each one of the 720  cruciforms is precision engineered not only to channel huge forces but to connect with millimeter accuracy to the neighboring cruciforms and the glass facade but to measure their exact angles the

team used some old-school technology 

chalk it might look unsophisticated but it's highly accurate ensuring all the elements will join together to keep up with construction the factory must produce 18 cruciforms every week constructing such a huge building and this critical building within the short span you know without working 24 hours it is

absolutely it's not going to happen  

as the skyscraper reaches new heights the long hours start to pay off this design pushes the dow grid technology to its absolute limit and in fact far beyond what's ever been achieved so far even in your dreams you're thinking about this project so once you see the structure coming up you forget all the long hours you spend and all the sleepless nights a colossus is fast emerging from the abu dhabi sands now this leaning tower must be glad  with a glass facade and as always with this gravity-defying structure it's going to require some revolutionary engineering glazing capital gates leaning curved frame is a major problem covering its unusual contours with curved glass will blow the budget so the skyscrapers curves must  somehow be clad using cost-effective flat glass panes fortunately ancient greek geometry can  help

because you've got a complex shape that 

is it's an organic shape it's a curved shape the only way to model that with straight lines is to use triangles triangular panes can pivot in three directions and  when joined together can cover complex geometric surfaces but because every angle of the building is unique it'll take 26 000 triangular panes to form the facade with so many glass triangles to cut the local glass factory springs into action each pane is scored by an automated diamond  cutter to an exact pattern the triangles are then sent along the production line the team is under constant pressure to deliver enough glass to the site after several weeks eight diamonds are in place

and another hundred standing by 

but the glass design is so unconventional it still has to pass a number of tests to prove it's up to the job because we've already started the glass installation the results of this test are absolutely key each panel is stacked one up on the other so if we had any kind of problem we would have had to unstack them which would have had disastrous  onsequences for the program this is no ordinary glass skin after all capital gate's core straightens as it grows the skyscraper will not stop moving until after completion normal glass facades can accommodate minute movements caused by wind and temperature changes but to stop the glass shattering and keep the building watertight the panels must be designed to shift by up to 20 millimeters the scale of that kind of movement is almost unheard of in in glazing systems it's a vast amount of movement with glass installation ongoing construction manager craig rooney needs 

to know the panels will perform 

we don't want to get to the top we've done it we've installed it we think we've done a great job and in all weeks the panels must be tested to the limit at a dubai laboratory a plane engine and many liters of water simulate worst-case scenario weather now the moment of truth any leaks could be a disaster and it's bad news the first time we got a full water test we had a leak the fact that we had a leak was was devastating to the whole team and very 

alarming 

the diamonds connect to each other by a bespoke two-layer seal the flexible spongy seal allows the diamonds to move and keeps water out but if any water does seep through the outer seal

drainage tubes fitted at intervals let 

the water flow away the panel has failed the test water has flooded inside and penetrated the inner seal if it was a fundamental failure we're back to the drawing board so the cost and the budget and the program all will completely out the window the panel is examined answers are needed fast fortunately it's not a design failure they discover 

a drainage tube is only blocked with 

sand the problem resolved installation can step up a gear but as always with this audacious building one problem is solved and another is just around the corner

to give capitalgate's five-star hotel lobby the wow factor architects again plan to push the design to the extreme now they want to build an infinity pool and a restaurant hanging 100 meters above the ground 18 months into the build capitalgate's design is about to give a new slant on high-rise living the architects want a pool deck and restaurant suspended in the sky but it's an engineering headache there's so many requirements that architects have that really put us in so much trouble as

engineers 

but you want to make sure you have a safe structure the design calls for a two-story extension hanging without any visible support but the pool's water alone will weigh 150 tons

the structure's huge mass means it needs 

reinforcement we needed some supports from below otherwise there was no other solution i don't think you can have a cantilever that's huge on this building the design will only work if it's underpinned with 22 steel struts they will carry the loads back into the building but the struts must also look delicate to meet the architect's aesthetic 

demands 

on the construction site 90 meters up the pool and restaurant is taking shape all of its structural elements are in

position  

except one the team are raising its last six-ton floor beam it's taken many crane lifts but one of the highest suspended swimming pools in the world has made the leap from blueprint to

building 

see all those lines that you just throw them they're actually drawing the same thing for you but with a crane but the feeling is indescribable the structure's muscular struts and connections are also elegant the idea behind these these junctions is that they they behave like the insects that can walk on water they're sufficiently light but the surface tension keeps them above the water so these little brackets dissipate the forces from all that weight capital gait is fast becoming an abu 

dhabi landmark 

but the taller it gets the more the weight of its upper floors is a problem the skyscraper needs to go on a diet and this time the architects come up with a clever solution the building has lots of visual surprises and one of the most important ones of those is the internal atrium it's a kind of a light well that brings light from the sky deep inside the building and it extends over half the height of the building so it starts out very very small at the bottom and opens out in a big funnel this cavernous hull is good news for reducing weight and minimizes forces but the atrium is a double-edged sword the flaws are critical in transferring loads from the 

dire grid to the core 

a giant hole through 18 floors means these loads must find another pathway

it's a very very big hole in every 

single floor plate so our engineers really had their work cut out

you don't want to have an opening in 

your floor you want to have more concrete reinforced concrete to transfer these forces the forces need to flow away and the solution is pioneering an internal web of steel mirroring the external dire grid this is the first time we've ever heard of this being done the internal diagram is actually a fundamental part of the structure this funnel-shaped internal skeleton carries the forces of an 18-storey building down to its tapered base and into the core but the loads are extremely high for such a small area to stop the atrium punching through the core wall the concrete needs protection the answer six giant plates of steel that brace the connection to the core wall the connections are really a wonderful wonderful piece of  engineering they're eight meters high they span two floors and they connect back into the court

the atrium's near completion brings abu 

dhabi one step closer to achieving an iconic landmark

but as the sun goes down this isn't the 

only celebration underway on site the indian steel team are holding an annual blessing to the hindu

god lord vishwakama 

the protector of architects and engineers their livelihoods depend on staying  safe and although they use safety equipment and are highly skilled working with huge sections of steel at height is never risk-free we pay our respect to god and get the blessings from the guard

we do that for the safety of all our 

workers and for the proper completion of the job every trade of workers we take the basic tools they are using on site that has to be just kept in front of god and the workers they feel themselves that they are in safe hands the tools are now blessed and the steel team's morale is high but the glass installers lifting diamonds to over a height of 100 meters are getting the wrong kind of lift from abu dhabi's highly unpredictable wind if the wind is too strong then you can feel this in your hands when you hold this diamond spy rope i always get nervous if i see the panel starting turning and this makes me always a little bit afraid when i see diamonds going up and starting leafing mayer has to act quickly or this four-ton diamond could smash into  the building not for the first time lifting glass is delayed by changeable weather at this rate mayer won't install the remaining 107 panels in time but abu dhabi's wind isn't the only problem the capital gate team face a last minute design request comes in from the shakes office that could have serious implications with just six months to go to completion the capital gate team should be on the

home straight 

but those plans may have to be put on hold i had a telephone call um saying that we had to put a helipad on the roof which i i didn't think was a joke but i i was astounded that we  got this at such a late point in the project integrating what will be abu dhabi's highest helipad atop one of the world's most daring skyscrapers at first seems a simple request but it actually poses two serious problems it'll create new forces that must be absorbed by the already strained core

and unpredictable wind flows that can 

cause potentially lethal flying conditions you get a thing called windshear tipping the whole helicopter onto its side and this is a very real and very dangerous risk these rapid wind changes known as wind shear can affect the lift on helicopter blades aircraft can be blown off course or literally fall out of the sky there is no way that we could  have any margin of error on the safety the only way we could predict what the windshield would be like on the top of the building was to model it in a wind tunnel in london england a scale model of capital gait is put through its paces in a high-tech wind tunnel just as the team fear within  seconds wind shear conditions appear air currents are flowing over the top of the building

but then separate from the surface 

spiraling inward to form a realm of turbulence wind engineer leighton aurelius knows the consequences could be serious if the pilots lose controlling this random ball of energy here they may in fact end up crashing onto the heli deck or even 

worse 

onto the tower itself so that can i'm sure that can occur but that's not all the wind tunnel test

reveals 

wind impacting the helipad is also creating huge suction forces we're talking about very large forces here wanting to pull the helipad off the top of the building something in the realm of several large trucks or big rigs trying to pull this helipad away to make the helipad safe aurelius and his team have to go against conventional thinking we didn't think that lowering the helipad was actually going to be the optimum design but we see reduced loading on the helipad as well as safer conditions for the pilots to land in lowering the heli deck to just two meters above the roof  dramatically decreases the wind shear threat and means capitalgate's core will withstand the additional loads we're relieved frankly the tests have actually confirmed now that we can actually have it in our original design position which is very low which will mean that the profile on the

skyline is exactly where we want it 

but it'll take another five months to just draw up the helipads  blueprints and a crane must be left behind to build it now with only weeks to go until zero hour

the team are installing one of the last 

glass panels it's a moment that once seemed a long way off in my office i have a plan of all the diamonds we have to install and in the beginning it looked like  i'm in jail and i'm marking the wall with marks for each day and so in the first time i felt i never will finish this project just 10 months since the first diamond was fitted the facade now shimmers in the sun capitalgate's internal fit out will take  another year only then will its five-star hotel and 

abu dhabi's most unusual office address 

be open for business but against the odds the team have 

created one of the most extraordinary 

megastructures on the planet gate twists and spirals out of  the  ground soaring to a full 162 meters it's taken nearly 6 million man hours to construct and its overhang is spectacular you see the building and you stand underneath the underhanger it's

extremely impressive it's a fantastic 

feat of engineering if you always open here in eternity but 

it's probably been the 

quickest two years of my life it's been an amazing journey and we've learned so much and actually i think we've demonstrated that some things that looked impossible or even ridiculous were actually possible and abu dhabi's past will soon be physically linked to its future by a wave of steel that'll rise over the grandstand and splash up the skyscrapers mirrored glass abu dhabi is a fascinating part of the world to be at the moment it says to people we  can step outside of the box we don't have to follow the rules with the 2010 world future energy summit just weeks away shake sultan can be sure capitalgate will show the world what abu dhabi is capable of this building is really iconic it catches the spirit of abu dhabi and will be part of 

the 

postcard image of the team have achieved what some thought was impossible a leaning tower that claims the world

record for the most

inclined skyscraper on earth

you