Nicholas T. Busque
260429206
EPSYS-330
Earthquakes & Earth Structure
April 9th, 2014
Abstract: Innovations in Structural Design in Earthquake Resistivity
The earth is continually changing; the tectonic plates are always in motion,
and massive faults crease the outer shell of the planet. This activity from the earth in
turn produces movements that cause the ground we stand on to move. Earthquakes
are often associated with destruction, and also seen associated with the collapse of
civil structures. However, despite the destructive nature of earthquakes,
engineering at its finest has proven capable of providing buildings that can
withstand rather impressive figures on the Richter scale. Even more impressive is
the different feats of engineering that went into developing the monuments, and
each sporting a different methodology in earthquake resistivity. Importantly, in this
piece the fantastic structures that were assessed for their resilience against
earthquakes reside in; the city of Dubai, United Arab Emirates; Yokohama City,
Japan, and the Torre Mayor in Mexico City.
Burj Khalifa is the world’s tallest building, and stands in its grandeur of 160
plus stories a massive 2720 feet tall. Ailing in the inspiring city of Dubai, this
structure design by architects Skidmore Owings & Merrill LLP offered more than
aesthetics in their three-pronged, Y-shaped plan-view. Each prong was equidistant,
and was perfectly symmetrical. However, progressively each floor after 7 stories
would retract horizontally reducing the reach of the shape’s arm. This in effect gave
a graduated spiral towards the top of the Burj Khalifa, each 7 or stories the diameter
of the building reduced towards its core. This design provided excellent structural
base support for the building, keeping it prone from tipping. This is also interesting
due to the foundation that was instilled for this colossal building to rest on. A 3.7
meter thick slab of raft or surface concrete slab was laid in the shape of the
buildings section cut, and this was on top of 192 concrete piles. These structures
reached 50 meters deep into the sand, all 1.5 meters in diameter. This foundation
design maximizes the capacity of the entire building, acting as an anchor and relying
on the raw strength of the building materials. This type of design prompted the need
for effective materials that prove best in strength to weight ratios.
Another quite interesting structural design in the Burj is its hexagonal core.
This geometry suited the shape of entire design quite well, and efficiently
distributes loads throughout the core without providing weak points. This promotes
high torsional rigidity, and minimizes lateral movements. With all the information
gathered about the engineering approach for the Burj Khalifa, it is quite clear that
the desired method of durability for this building was brute strength and shear
resistance. Every aspect demands the maximum and most efficient use of a
structural aspect to withstand given shocks or pressures. In theory, minimizing the
movement an incredibly tall building will experience, the less of a response
earthquake related energy transfer would effect motions that can lead to
subsequent collapse in the upper portions of the edifice.
From another side of the world, Yokohama City’s Landmark tower is a
massive structure for the country of Japan. The country’s tallest building measuring
up to 972 feet, this tower is a feat of engineering. Japan as a country experiences
massive amounts of earthquakes, and historically has dealt with numerous
disasters. These disasters can be attributed to the large amount of fault lines the
seemingly surround and split the country. This led to incredible developments in
civil engineering, and eventually produced one of the most unique approaches to
earthquake resistance.
As it so seemingly fits to start at the bottom of the structure, the Yokohama
Landmark tower sports an interestingly different base than most. In a rather
ingenious idea, the building was designed with roller supports at its base and sole
connection to the ground. This part of the design proves rather effective to deal with
lateral or horizontal movements that occur during an earthquake. Instead of relying
on the building to completely resist moving, the rollers actively engage movement
from the ground. This movement transfers very little energy to the building, and
minimizes the effect of oscillation.
Moving up the structure of the building, the choice of material all shared a
flexible characteristic, much different than methodology that was seen in Dubai.
Here instead of dealing with materials that need to resist deformation, the engineers
decided on materials that could experience a high amount of energy and deform
elastically. Benefits from this approach are seen through the initial effect of energy
transfer in the rollers. This absorption of initial movements in the rollers allows for
a choice of materials that can deal with multiple stimulations of movement, and
suffer very little damage. Brittle or strong materials in effect lose their durability
over time and exposure to forces. Flexible materials absorb some energy as opposed
to resisting it, and can experience deformation with the constraints of allowable
magnitudes. This simply meaning that if forces experienced do not induced what is
known as plastic or permanent deformation, its durability is resilient no matter how
many times shock is experienced well before fatigue sets in.
Lastly, a dual set of HMDs, or “hybrid mass damper” systems, offer another
interesting effect on the tower’s movements. These masses, each weighing 170 tons,
are supported on a multi-step pendulum. Based on computer responses to
movements, as well as natural ones, the masses act to passively counteract the
building’s response to earthquake movement. This helps reduce some vibrations
that can offer possible and unwarranted hazards to individuals in the building.
Overall, the approach taken in this building’s design offers excellent resilience in a
country that encounters an incredibly high amount of seismic activity.
Now let us journey to Mexico City, once again another area unfortunately
plagued by earthquakes. Here lies another one of the world’s giants, the Torre
Mayor. This structure stretches over 50 stories into the air, and is the first of the
world’s tallest buildings to implement fluid viscous dampers as a means to control
energy delivered from earthquakes. Taking this aspect along with the inevitably
sound structure design to support the building set sights high for maximum load
bearing on the Torre Mayor. Designed to withstand 9.0-magnitude quakes, the
shock absorbers implemented in this buildings design were in fact originally used to
brace structures against nuclear detonation.
With 98 of the fluid viscous dampers placed strategically on the ground floor
and several floors above, the effect of this design was tested shortly after the
buildings opening in 2003. A 7.6 magnitude earthquake struck near Mexico-city, and
as the soils of the city are much softer than surrounding areas, propagating
movement was amplified. However, many accounts from occupants from within the
building stated that the tremors felt much less than what actually occurred outside
of the building. The government of Mexico also authorized an inspection of the
newly opened Torre Mayor, and no damages were reported. The impact of the
combined efforts of 280-tonne short wall dampers and 570-tonne long wall
dampers is seen in the buildings resilience through a rather high magnitude
earthquake.