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The 1,100-foot Wilshire Grand Center in Los Angeles made history on Sept. 3 as the skyscraper officially became the tallest building west of the Mississippi River. It is arguably the most complicated high-rise ever constructed as architects worked tirelessly to design for one of the most earthquake-prone regions on Earth.

New skyscraper designed to roll with 'punch' of quakes


Leeanna McLean
Digital Reporter

Friday, September 23, 2016, 2:59 PM - The 1,100-foot Wilshire Grand Center in Los Angeles made history on Sept. 3 as the skyscraper officially became the tallest building west of the Mississippi River. It is arguably the most complicated high-rise ever constructed as architects worked tirelessly to design for one of the most earthquake-prone regions on Earth.

Once complete, the building will feature 400,000 square feet of office space, a 900-room hotel, restaurants and shops.

While the building's cigar box shape is optimal for a long and narrow modern look, it is vulnerable to the region's extreme conditions, CNN reports.


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"This was the most complicated and the highest seismic-demand project I have been involved in," engineer Leonard Joseph of Thornton Tomasetti told the news agency. "A long and narrow building in an earthquake is quite stiff and strong in the long direction, but more flexible in the crosswise direction, so that was the challenge here."

The tower is fitted with a concrete core and a steel frame connected by thirty outriggers (braces) at three different levels of the building.

Like many other cutting-edge skyscrapers, the Wilshire Grand is designed to actually roll during seismic events.


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"You don't want a building to be overly stiff because the more it fights the ground movement, the bigger the force developed inside the building," Joseph told CNN. "It should roll with the punch."

In Canada, Toronto's iconic CN tower was built to withstand an earthquake as strong as 8.5 on the Richter scale. It is also able to endure winds up to 400 km/h.

In the event of an earthquake, the Wilshire Grand's design allows for seven feet of sway without causing significant damage. The building would shift more at the top, according to Joseph. However, the engineer planned for a degree of damage as he believes the building would not emerge from a major quake completely unscathed.

"(We) accept the idea of damage at selected, pre-established locations such as coupling beams," Joseph told CNN. "There would be a whole bunch of cracking concrete at the end of these beams in an earthquake, but they hold together and don't drop on someone's head."

Before construction began, the design was tested with several earthquake simulations.

By using archived data, geotechnical engineer Martin Hudson modeled the effects of 11 different earthquakes on the tower.

"Several (simulations) represented earthquakes fairly close to the site, and we also looked at what happened with an earthquake on a larger fault such as San Andreas, 100 km from the site," Hudson told CNN. "The overall shaking from the two sequences is not vastly different but the characteristics are. The closer earthquake has higher frequency vibrations like a truck hitting the building, and the San Andreas earthquake is more of a long, rolling motion."

The top of the tower, including the spire, had to be redesigned due to the simulations. Inspired by the Eiffel Tower, the original plan was to build a "lacy" glass crown and spire, according to Joseph.

"But the Eiffel Tower does not have high seismic loads," he told CNN. "A thinner spire would have been lovely, but it would fail under earthquake loads."

Given rapid advances in technology, it is now possible to construct tall buildings in earthquake zones.

"The computational power available is extremely strong compared to five or ten years ago," structural engineer Grace Kang of the Pacific Earthquake Engineering Research Center told CNN. "This has enabled the profession to conduct more simulations (and) the database for ground motion records has increased tremendously."

The Wilshire Grand Center is expected to open in early 2017.

SOURCE: CNN

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