Home
Tower Cranes: An Appreciation

Tower Cranes: An Appreciation

James S. Robbins

5 Mins
|
September 7, 2010

Editor's Note: The print version of this article is accompanied by two stunning panoramic photos of Dubai, by German photographer Josh von Staudach.

Tower cranes are ubiquitous here in Washington, D.C.  They often dominate the skyline, especially on the eastern side of town where the arc of development is pressing outward. Southeast Washington near the Navy Yard has seen a legion of cranes march though the neighborhood in recent years. Rubble-strewn lots and abandoned buildings have given way to glass-sheathed office towers and a new baseball stadium.

Where some see progress however, others see injustice. Homeless advocate Tom Howarth noted in an article in the Washington Post that to the poor and the homeless the tower cranes are “birds that eat poor people. Once those birds pass through your community, a lot of poor people are gone.” He decried the practice of allowing markets to determine real estate development, noting that in free markets “the poor are doomed.” He also decried the recent development of a neighborhood located between Mt. Vernon Square and Massachusetts Avenue, known as Northwest One, which he says is “best known for concentrated poverty and crime.” Today high rises speckle the area and construction is ongoing. But to Howarth the cranes are predatory emblems of an uncaring market overawing a defenseless and complicit government. As he says, “times change, cranes come and poor folks have to move.”

Yet it’s easy to keep the tower cranes from roosting in your city. “Have you seen any tower cranes in Lahore?” Pakistani economist Dr Abdus Samad asked in the Pakistan Daily Times. “I have asked this question many times,” Samad wrote, “and always received the same answer: ‘No!’”  Lahore is the second largest city in Pakistan, home to 6.3 million people. But rent control, a “commercialization fee” on any land used for office purposes (25 percent of the value of the land for a four-story building and a flat rate fee for every additional floor), and height restrictions have kept the tower cranes out of Lahore. In part these restrictions seek to preserve historic Mughal and colonial architecture. But it is unclear how this policy may have benefited the poor. Dr. Samad notes that Pakistan is “a poor country and needs to implement policies that will encourage our economic sectors to grow rapidly. … Imagine, our children have grown up without seeing a tower crane!” That’s a deprived childhood indeed.

DESIGNING PROGRESS

Most tower cranes are manufactured in Europe, where the design was born. A century ago most cranes were of the “derrick” type, in which the boom is hinged to a rotating base, with a cable running from the base up the boom and over a pulley its tip, the hook hanging down. The crane was named for Thomas Derrick, an Elizabethan-era executioner who adapted the design to make hangings easier. The cramped conditions in European cities made use of derrick cranes increasingly impractical, since they required open space to swing the boom. Also derrick cranes also faced practical height limits that began to tell as new technologies made possible ever higher structures.

One response to the challenges of modern cities was the gantry design, most prominently credited to Julius Wolff & Co. in 1908. Gantry cranes feature suspended beams with moving trolleys that can more easily range a worksite. But they tended to be heavy and take a long time to construct, and so became more commonly used at docks and shipyards, where they could be permanently installed.

The tower crane as we know it today was born from and helped to meet the formidable challenges and opportunities present in rebuilding war-torn Germany. In 1949 Hans Liebherr devised this crane, called the TK-10, based on a simple but inspired idea. He designed a vertical, bottom-slewing (rotating) mast topped by a horizontal jib (boom), with 360 degree rotation and the ability to pick up materiel and move it anywhere within reach of the jib. Since the crane could move on a central pivot above the worksite this gave the ability to work in confined spaces with more stability, more speed, and greater reach. That central insight is the genius of the design. The TK-10 was also easily transportable, and could be assembled quickly. Liebherr’s crane soon came not only to dominate but also to expand the market for cranes as new uses were found to exploit the flexibility of the design. Liebherr’s invention and sound business sense built one of the great fortunes of the world. Liebherr International AG is still a dominant force in this market.

Today tower cranes are manufactured by scores of companies. They come in different sizes, heights, and reach, and are designed for different functions at different building sites. Most today have a top-mounted slewing unit, rather than rotating at the base like the TK-10. Some are bolted to the ground on 200 ton concrete blocks, others self-erect on mobile pads weighted down with iron. Some stand atop the skyscrapers themselves, and rise with them. Hydraulic jacks on a “top climber” below the slewing unit push it twenty feet up and another section of mast is installed below. Over time the cranes have evolved to be able to bear heavier loads over a greater radius with tighter control, and be erected and taken down faster.

Tower cranes are the epicenter of the construction site. They get jobs done quickly, lifting, placing, and getting the hook back down speedily (and safely) to start the process over again. They are expensive to operate, but so efficient that the time savings more than makes up for the outlay. The cranes at work have a majesty that can be stirring, especially up close. Sometimes they seem to be moving in synch, and they are typically unlocked and allowed to “weather vane” in high winds. The poetry of the cranes has not gone unnoticed; in Helsinki in the late 1980s a group of Finnish art students were given permission at a construction site to choreograph the movements of seven tower cranes at night, lit with two floodlights and moving to the sound of ambient music. When snow fell during the performance it “seemed a magical sight” said one observer.

DYNAMIC DUBAI

Tower crane activity is a map of dynamism of the world market, in new economies and old. They are called the state bird of Nevada, given their ubiquity in Las Vegas. They are also called state birds in Florida, California, Texas, or wherever they flock. There are forests of cranes in Singapore, Taipei, and Beijing. Even Moscow, once a decaying hulk in the wake of the Soviet collapse, is now the most expensive city in the world to live in, home to 74 billionaires, and a permanent construction site.

But nowhere lays claim to as many tower cranes as the Emirate of Dubai, which hosts 15 to 24 percent of the world’s 125,000 or so active cranes. They are visible wherever one looks, scattered across the thirty mile urban strip slowly expanding between the desert and the sea. One estimate has it that there is one tower crane for every 44 inhabitants in Dubai. It is a fitting roost for the cranes, a country in which for the time being vision in urban planning is unfettered. The ruling Al Maktoum dynasty has overseen a phenomenal building boom, carving a modern city out of the desert, and pushing a series of man-made archipelagos into the Arabian Gulf.

Dubai is an architect’s dream, a tabula rasa in which imaginative designs are encouraged. Take for example the sail-shaped Burj al Arab hotel, the spiky, twisting spires in the Lagoons, the sleekly asymmetrical Pentominium or the tablet-shaped Index Tower. The Burj Dubai, currently nearing completion, will easily be the world’s tallest building at a projected 2,684 feet, almost twice the height of the Empire State building. Yet this is modest compared to the planned Nakheel Tower, the new Dubai capitol building, which will be over a kilometer high, house 55,000 people, have offices for 45,000 more. Dubai is an example of what can be achieved with vision, capitalization, and an encouraging government. (It may also be an example of the transitory benefits of what Aristotle called enlightened monarchy, which can quickly lead to despotism.) It is no wonder it is the tower crane capitol of the world.

The current global credit crunch will undoubtedly slow the march of the tower cranes, as projects are put on hold or cancelled. But as the world rights itself the cranes will come back. They thrive where people thrive. They are instruments for the realization of aspirations. Tower cranes mark the outposts of human frontiers; where they are present good things are happening.