By the end of the 20th century, the race to build the world's tallest
skyscraper grinded to a halt. Each new contender was only slightly
taller than the one before, and architects were running out of ways
to top their previous efforts. But in 2004 construction began
on a new building in Dubai, promising a revolutionary design
that would dwarf the competition. In 2009, the 828-meter Burj Khalifa
was complete, surpassing the previous
record-holder by over 60%. So what innovations allowed
for such a huge leap in height? For most of architectural history,
heavy building materials made it difficult for tall buildings
to support their own weight. To compensate, taller structures had
wider, thicker masonry at the base, making them substantially more expensive. The arrival of industrial steel
in the early 20th century helped buildings shed weight,
and stretch to new heights. But steel frames required intensive
labor to produce, often under poor working conditions. And when they were finished, these three dimensional grids took up huge
amounts of space inside buildings. Tall steel skyscrapers also had
larger, less dense surfaces, making them vulnerable to strong winds. Architects designed various
countermeasures to prevent swaying and structural damage, but to increase height further, engineers would have to completely rethink
how tall buildings were designed. Enter the father of modern skyscrapers:
Fazlur Rahman Khan. This Bangladeshi-American engineer
believed tall structures should bear their weight where they were
widest and most stable— on the outside. He proposed swapping an internal grid
of steel beams for a steel and concrete exoskeleton that would make buildings
more resilient to wind while using far less heavy materials. Khan developed this idea into what
he called tubular designs. These buildings had exterior steel frames
that were braced with concrete and connected to horizontal floor beams. Tubular frames proved superior
at absorbing and transferring the force of wind to a building's
foundation. And since the exterior walls could
bear the bulk of the load, internal supporting columns could
be removed to maximize space. Following the 1960s, tubular design
became the industry standard. This new philosophy allowed
for the construction of taller, sturdier skyscrapers, including many of the record holders
for world’s tallest building. But planning the Burj Khalifa would
take one more innovation. In 2004, the late Fazlur Khan’s
longtime employers, Skidmore, Owings & Merrill, completed
the Tower Palace III in South Korea. This building took Khan's exoskeleton
design one step further, with a central column supported
by three protruding wings. Each wing’s weight carries the other two, while the heavy concrete core acts
as a support beam, that also houses the building’s elevators
and mechanical infrastructure. This design, called the buttressed core, allowed the entire structure to work
as a single load-bearing unit, supporting the building’s 73 stories. SOM was confident the buttressed core
could support a much taller building, and they were determined to see how high
they could go with their next project. As only the second building
to use this design, the Burj Khalifa spans
an unprecedented 163 floors. To battle the monumental
vertical and lateral forces, the design strategically places
the strongest, load-bearing areas where the wind is also most powerful. Additionally, the Y-shaped layout
was specifically calibrated to minimize local wind forces. Every several floors,
one of the wings recedes slightly, forming a series of setbacks
in a clockwise pattern. This spiral shape disperses air currents, transforming 240 kilometer per hour
winds into harmless gusts. Considering its height and unique design, the Burj Khalifa was completed
in a staggeringly short five year period. However, this pace came
at a great human cost. The workforce consisted mostly
of South Asian migrants, who regularly endured shifts
over 12 hours long for a daily wage of roughly $10. Those who tried to quit or return home
had their paychecks and passports withheld by the project’s construction company. These abusive conditions led
to multiple protests, in addition to at least one suicide,
and one fatal accident reported on site. In the years following
the tower’s completion, the United Arab Emirates fell
under harsh scrutiny for failing to enforce worker
protection laws. Hopefully, future projects
will prioritize the individuals behind these engineering marvels
over the buildings themselves.
