|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Fri Feb 05, 2016 7:07 pm Post subject: New York is Home for the 1st and 100th Supertall Tower
|NEW YORK IS HOME TO THE 1ST AND 100TH SUPERTALL TOWER
By Kevin Wilcox
The reasons why developers build supertall towers hasn't changed much in 85 years, but how they are designed and built has advanced significantly.
The tall, slender tower at 432 Park Avenue in New York City is the 100th skyscraper to be considered as supertall, having a height of more than 300 m. The number of supertall towers across the world could double in just the next five years. Wikimedia Commons/Citizen 59
February 2, 2016—Eighty-five years and 0.8 mi separate the first supertall building in the world, New York's gleaming Chrysler Building, from the 100 th supertall—432 Park Avenue, a 1,396 ft residential tower completed late last year in New York City. The Council on Tall Buildings and Urban Habitat (CTBUH) defines a supertall building as one with a minimum height of 300 m, and the construction of such towers has been increasing at an ever-growing rate.
When the Chrysler Building—and the Empire State Building, which followed a year later—were completed, the heady fiscal excesses of the 1920s had already been crushed by the harsh realities of the Great Depression. Decades passed before another supertall tower would be constructed. But the number of supertall towers has doubled in the past five years, according to the CTBUH, and that number could conceivably double again in the next five years with approximately 142 more supertall projects under construction now.
"These supertall towers have always been symbolic," says Jason Gabel, the communications manager for the CTBUH. "They are often symbolic of a rise to prominence—whether that is by a company in America in the 1930s or a modern Chinese city that is trying to attract global commerce to that location. They are all making a statement. That is the overriding similarity."
Although the reasons for developing a supertall tower haven't changed a great deal since ground was broken for the Chrysler Building, how those buildings are developed has changed immensely. The advent of high-performance concrete, mass dampers, and mixed-use floor plans have made it much easier to put a supertall tower on sites that were formerly deemed ineligible to support such towers. By growing leaner as they have grown taller, the towers can also be woven into the urban fabric much more effectively, Gabel notes.
"Steel was the reigning king for decades in the tall building industry, [but] we have seen concrete and composite systems vastly overtake that, especially in the past two decades," Gabel says. He calls high-performance concrete "a major advancement."
"They have really gotten the chemistry down. It can provide high-strength, high stability, and high pumping performance, while experiencing minimal shrinkage," Gabel notes. "And it's relatively cost-effective when compared to other materials that are often used for supertall structures."
These advances in concrete have been developed in conjunction with advanced form work systems that can be installed at great heights yet require minimal support points. These innovations, complemented by the advent of various enclosed scaffolding systems, minimize the need for workers to slide along exposed beams at great heights.
Gabel points to building information modeling (BIM) systems as another key technology that the engineering and construction professions have employed to help build these complex structures at a pace not seen before. Projects that once required reams of technical drawings can now be represented in a digital 3-D model that easily identifies the costly conflicts between systems and components that were once discovered only during construction, causing costly delays and rework.
"BIM is able to paint a picture of the tower that nobody has been able to see before. You can now quantify and optimize various building systems holistically and with the input of numerous project stakeholders simultaneously." Gabel says. "This is especially important for supertall towers because, the bigger the building, the more BIM has the potential to help out a project. There are queries that can be run in the system that would've taken ages beforehand," Gabel says.
The building 432 Park Avenue was designed by Rafael Viñoly Architects and SLCE Architects, LLP, and its structural engineering was provided by WSP Cantor Seinuk, now known as WSP Parsons Brinckerhoff—all of New York City. Constructed by the U.S. branch of the Australian construction company Lend Lease, the building stands out among other supertall towers in several key ways, Gabel says. For one, it is extremely narrow for its height—15 ft tall for each 1 ft wide—proportions made possible by an emerging understanding of how to dissipate wind loads on supertall towers. Among the strategies used are open mechanical levels that are situated at strategic locations along the length of the tower to enable wind to pass through in key locations. The building also makes use of advances in dampening technology to minimize the effects of sway. "These dampers take a lot of technical consideration to execute properly, but once installed they can dramatically decrease sway during dramatic weather events," Gabel says. "We had people tour the building as part of our CTBUH 2015 New York Conference, during a pretty intense storm, so they were able to see the tuned mass dampers sway heavily—and they didn't feel the movement at all," Gabel says. This is important because 432 Park Avenue is a luxury residential tower and people are much more likely to notice and be troubled by building sway while lying in bed at night than when they are walking through a busy office building, for example.
While 432 Park Avenue embodies many of the trends affecting the world of supertall towers, and advances the form in others, it defies one other pronounced trend: many of the newest supertalls are sited in Asia or the Middle East and serve a mix of residential and commercial needs. "Overall, you are seeing a big change in the functions of these supertall towers," Gabel says. "They used to be all-office, which was often the sole function of iconic commercial districts of the past. While you still have office components in the supertalls going up, it's not just office anymore. It's mixed use. Ever more of these buildings are being built with residential, hotel, and commercial components," Gabel says.
And ever more are being built in China and the Middle East, where the buildings are used to draw attention to cities and business districts, placing those areas on the world financial and commercial stage. "There is a very deliberate set of actions that the Chinese government is taking to populate not only the country's largest centers, but also their midtier cities, and some cities that didn't even exist until recently, "Gabel says. "The thinking is, what better way to mark this new urban center then with a supertall centerpiece?" And because the government is a key stakeholder in the development of the projects, they continue to move forward in the face of economic weakness in China.
As the supertall tower becomes more commonplace, developers are turning to megatall tower projects, with a minimum height of a staggering 600 m, to make their marks. There are three megatall towers in the world, but four more are currently under construction.