Sigma Xi, The Scientific Research Society

Engineering: The Twin Towers Author(s): Henry Petroski Source: American Scientist, Vol. 84, No. 4 (JULY-AUGUST 1996), pp. 322-326 Published by: Sigma Xi, The Scientific Research Society Stable URL: http://www.jstor.org/stable/29775699 . Accessed: 01/08/2013 20:53

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The Petronas Twin Towers

Henry Petroski

a For two decades, the 110-story Sears Tower The Federation ofMalaysia is southeast Asian stood as the tallest building in theworld. country of about 20million people, the vast major? in located Topping out at 1,454 feet above ground lev? ity of whom live West , just on el?almost as tall as a string of five football fields above the equator theMalay Peninsula, be? tween to to the would be long?the bundle of nine steel tubes Thailand the north and Singapore in federation in? standing just outside Chicago's Loop could be south. (As established 1963, the said to have cast a shadow over all other sky? cluded Singapore, but it seceded in 1965.) The two are to scrapers since its completion in 1974. New York's states of East Malaysia situated the east, World Trade Center, the 1,368- and 1,362-foot-tall across the South China Sea on Borneo, the third twin towers completed only a year earlier, held largest island in theworld. , the cap? a North the record as tallestbuildings foronly a brief time. ital ofMalaysia, is served by modern a Before that, theEmpire State Building, at 1,250 feet South Expressway that puts Singapore within di? tall even without itsbroadcasting towers?which, five-hour drive. The city's Subang Airport has like those of the Sears Tower, do not count as part rect flightsthroughout theworld and hourly flights arrive and of the building proper?held theworld height thatdepart forand fromSingapore, pas? a courses record forover four decades. Completed in 1931, sengers get bird's eye view of lush golf rubber trees?a of the that the Empire State then surpassed -year-old among sign changes in which has been , which at 1,046 feet tall had have been takingplace Malaysia, as a state been the firstto break themagical 1,000-footmark. described ''predominantly Malay Islamic Before then, theWoolworth building, a 792-foot with strongChinese and Indian influences." tallGothic cathedral of commerce paid for in cash A Vision of the Future by the profits from its namesake's chain of five was and ten-cent stores, had stood as the world's In the 1980s, theMalaysian economy based on as rubber and tin. tallest building for almost two decades. commodities such palm oil, with the rise of a headed ?so named since the 1880s,when However, government were and Prime Minister Chicago's 100-foot-tall buildings marvels by the strong-willed powerful Mahathir bin a medical of contemporary ?seem Mohammad, by training to assert itselfas a to have sprouted up in temporal and spatial clus? doctor,Malaysia began country on move. The minister is said to have ters,with Chicago and New York proving espe? the prime as the of cially hospitable to the form and its financing. "reinterpreted Islam allowing pursuit and the Throughout most of the 20th century, the sky? wealth and technical knowledge," gov? came to be articulat? scraper was considered a particularly American ernment's official objective native of the genre, growing with the economy and optimism ed, in Bahasa Melayu, the language as of cities such as Atlanta, Houston, Los Angeles ethnic Bumiputra population, Wawasan 2020? and Seattle. In the last decade of the century, or Vision 2020 in English, the country's accepted commerce however, the frontier of the has language of and industry. The vision moved across the Pacific Ocean to the Far East. has Malaysia transformed into a fully developed nation with man? Today, most of the tallest buildings in theworld industrialized by theyear 2020, as themain are being proposed for locations such Tokyo, ufacturing and construction becoming The Taiwan, Hong Kong and mainland China. And driving forces of the country's economy. are Centre is in a they are not only being proposed; they being Kuala Lumpur City project helping re? a built, with the tallest building in theworld big way tomake theMalaysian vision reality. Centre is a 100-acre devel? cently being topped out at 1,482 feet in Kuala Kuala Lumpur City on the site of a former the Se Lumpur, Malaysia. opment racetrack, as langor Turf Club, and is described among the real estate in the Henry Petroski is Aleksandar S. Vesic Professor of Civil largest development projects and world. As the result of an international Engineering and chairman of the Department of Civil competi? Box tion held in a master ideal Environmental Engineering at Duke University. Address: 1990, plan?"an city 90287, Durham, NC 27708-0287. within-a-city"?was defined by the U.S. firm of

322 American Scientist, Volume 84

This content downloaded from 132.206.27.24 on Thu, 1 Aug 2013 20:53:44 PM All use subject to JSTOR Terms and Conditions Klages, Carter, Vail & Associates of Cosa Mesa, California. It comprises a 50-acre park, which will include a lake,much ofwhich will be accessible to (L the public, and a complex of 20 or so surrounding buildings thatwill contain office space, apart? ments, hotel rooms, recreational facilities, restau? a convention a rants, shops, banks, center, civic center, a mosque and a plant to provide chilled water for cooling all these buildings in the sub? tropical climate. The firstphase of the $2 billion project includes the pair of buildings known as the Petronas Twin Towers, themselves costing ap? proximately $800 million, most of which was to be provided by Petroleum Nasional Berhad, gl! Set Sjjlsl Malaysia's national oil company and the source of the towers' name, and the government. As they have risen tobecome theworld's tallestbuildings, I^bsE Bis ^hbee?^ these striking towers have already become Kuala Lumpur's most significant landmark. Back in 1991, with themaster plan in hand, a separate internationaldesign competitionwas held to detenrtine exactlywhat kind of structurewould provide a significant focal point and monumental entrance toKuala Lumpur City Centre. The com? petitionwas won by the architectCesar Pelli & As? sociates ofNew Haven, Connecticut. According to Pelli, the client wanted a Malaysian image but could not say exactlywhat thatmeant. Existing tall buildings inKuala Lumpur were of theboxy inter? national style.With no indigenous structuralmod? els to inspire him, Pelli looked to Islamic art and a adopted multipointed star pattern as a footprint forhis building design. His early scheme called for a 12-pointed star layout, but thiswas changed to a Figure 1.World's tallest buildings, the are in Kuala modified 8-pointed floorplan with intermediate Lumpur City Centre, Kuala Lumpur, Malaysia. (Except where noted, arcswhen theprime minister observed that the for? photographs courtesy of Thornton-Tomasetti Engineers.) mer geometry was more Arabic thanMalaysian.

Architecture and Engineering Hancock Tower, for example, was the result of a The final design of skyscrapers, especially those collaboration between architectBruce Graham and are that to be the tallest in theworld, does not structuralengineer Fazlur Khan of thefirm of Skid evolve wholly from an architect's drawings. How a more, Owings and Merrill.) Pelli wished the "cos? structurewill stand against the forces of nature? mic pillars" in Kuala Lumpur to be joined by a a whether the ground motion in an earthquake zone, skybridge to form welcoming portal to Kuala thewind at hundreds of feet above the ground or Lumpur City Centre and tohave as few structural theheat of the sun beating down on the ground? columns as possible blocking the view outward requires the insight and calculation of a structural from the office floors. Such featureswere easy to engineer. (The exposed structure ofChicago's John render on the drawing board but no small task to

Figure 2. Building design evolved to incorporate Islamic themes. (Illustration courtesy of Cesar Pelli & Associates.)

1996 July-August 323

This content downloaded from 132.206.27.24 on Thu, 1 Aug 2013 20:53:44 PM All use subject to JSTOR Terms and Conditions realize in and steel. For theKuala Lumpur project, Pelli sought the structural expertise to ac? complish such objectives in the international engi? neering design firmof Thornton-Tomasetti Engi? neers, based inNew York City. Charles Thornton, chairman and principal in the firm,had longwant? ed to design the tallest building in theworld, and had indeed designed with Pelli a 125-storyMiglin rea? Beitler building forChicago that for financial sons did not come to fruition.He was thuswell on prepared towork again with Pelli the Petronas Twin Towers, equivalent inheight to 95 stories. The challenges associated with designing and building a skyscraper begin in the ground. If the foundation is not firm,the building will be suscep? tible to settling,which, in theworst case, can lead to are tilting and collapse. Underground conditions not often fullyknown, however, until extensive, al? beit usually still only sampling, exploration takes place, and thismay not proceed until the design is defined for to set the locations BARRCTTE enough engineers and of tests needed. As it turned out, the KENNYUli? types Kuala Lumpur master plan had sited the showcase buildings over an underground cliff.To found piles in the rock,which sloped very steeply and con? tained caverns, every pile locationwould have had to be surveyed before proceeding. Thus the loca? ELEVATIONNCUIPtJQ F0UNDATI0H8 tion of the towerswas moved about 200 feet to the southeast, where the fissured limestone 3. Foundation or barrettes, extend as generally Figure piles, deep was so that all could termi? as 400 feet. sufficientlydeep piles nate in the soil above the rock and therebyensure a more uniform foundation. This alluvial ground, known as Kenny Hill, is a weathered sandy shale that is considered relatively sound. The challenging foundation conditions necessitated drilling some more piles almost 400 feetdeep, than three times thedepth of the foundation beneath theSears Tow? er. Even then, the foundation of the buildings are as expected to settle as much three inches under theweight of the completed structure.

Innovative Concrete Designing the superstructure of the building pre? sented another set of challenges. Among the first decisions facing structural consultant Thornton and his associates at Ranhill Bersekutu inMalaysia was the choice between steel and concrete. Al? are though the tallest skyscrapers steel structures, thatmaterial was not readily available inMalaysia, on where prohibitively high tariffs imported steel make concrete the constructionmaterial of choice. Furthermore, steel buildings tend tobe more flexi? ble than concrete ones and sometimes have to be fittedwith mechanical devices known as tuned mass dampers to ameliorate the effects of vibra? on tions induced by thewind. Concrete structures, the other hand, although they tend tobe stifferand have qualities that damp out quickly any vibra? tions that do begin, often are bulkier-looking than steel. Since the architectwished the Petronas Tow? ers tobe slender-looking and have columns spaced rather far conventional concrete columns Figure 4. Digging machine prepared ground for founda? apart, tion barrettes. would have been too aesthetically broad and struc

American Scientist, Volume 84

This content downloaded from 132.206.27.24 on Thu, 1 Aug 2013 20:53:44 PM All use subject to JSTOR Terms and Conditions an rurally heavy. To overcome this objection, ex? tremely high-strength concrete was developed, with bearing capacities as much as three times that of concrete conventionally used inMalaysia, or elsewhere for thatmatter. Special concrete mixes, using local materials, were developed to produce compressive strengths as high as 10,000 pounds per square inch,with quality control provided by state-of-the-art computerized systems. Being made of high-strength concrete, the columns around the periphery of the towers could be smaller indiameter and lower inmass, thus re? ducing theirdead weight. Still, at the base of the towers, the columns are nearly eight feet indiame? ter.The towers are not purely concrete structures, however, and the floor beams spanning between each building's core and ring of columns aremade of steel.This was done to speed construction,mini? mize the floorheight and better accommodate such mechanical equipment as cooling ducts. The taper? ing at the top of thebuilding demanded some es? pecially trickystructural engineering, and itsgeom? etrynecessitated the installationof a wide variety of different-sizeglass panels. The record height of the towers is achieved through the pinnacles at their tops,which are part of the basic ardhitecture and structure proper, unlike the broadcast antennas after the facton such as the Em? were erected buildings Figure 5. Pinnacles atop towers jacked into place. pire State Building and the Sears Tower. (The offi? cial arbiter of skyscraper records, the Council on The towerswill also be connected to each other a a Tall Buildings and Urban Habitat, confirmed at an at the level of the sky lobbies by sky , 190 executive committeemeeting inApril that theSears foot-long steelwalkway thatnot onlywill facilitate Tower had indeed been surpassed as the tallest movement between and the other but serve as an building on Earth.) The pinnacles, with designs also will alternative escape route in the based on minarets rather than Gothic cathedral event of a fireor other emergency, such as occurred spires,were erected by jacking them skyward from when the terroristbombing forced the evacuation within theuppermost part of thehull of the towers. of one of the towers of theWorld Trade Center. But design was the result of detailed stud? the sky bridge's design presented additional and a ies including many options. The final design is unusual structuralproblems. Since the two towers scaled-up version of one originally proposed to can sway in thewind both in phase and out of as provide a more graceful tower top and, coinciden phase, as well twist in independent directions, tally,reach a record-breaking height. Thornton, an the sky bridge could not be attached rigidly be? avid sailor, likens the structural support for thepin? tween the vertical structures.Thus special bearing nacles to thatof themast of a sailboat. connections had tobe devised to allow foras much at Among what makes extremely tallbuildings vi? as 12 inches of horizontal movement each way able investments is the amount of usable, rentable or each end, as well as the twisting. Because such a saleable floor space they contain relative to their long, unsupported sky bridge would have tohave were to height. As buildings grow taller,more and more of been of very heavy construction if it not theirvolume must be devoted to to trans? sag in themiddle, a set of slender steel legswas de? port the tens of thousands of occupants up and signed to angle up from supports on each tower down. In thePetronas Towers, theusable floor space about 160 feetbelow to of the skybridge. ex? was increased considerably by theaddition of small? To prevent such slender struts from vibrating er 44-story structures, referred to as "bustles," to cessively in thewind, thus presenting thepotential each tower.With thebustles, which are tobe topped foruncontrollable motion or at least the accelerated mass were by prayer rooms for theMuslim occupants who will growth of fatigue cracks, tuned dampers be called to prayer twice each working day, each designed tobe installed inside the legs. (Eachmast? an tower has about 2million square feetof officespace. like pinnacle also has a damper in the form of The internal transportation system thatmoves peo? energy-absorbing, rubber-sheathed chain.) ple vertically in the towerswill include double-deck The Petronas Twin Towers and all the buildings express elevators to optimize the use of the shafts. planned for the will are as em? Passengers will transfer to and from double-deck be what known intelligent buildings, local elevators in sky lobbies about halfway up the ploying automatic controls and communications on and buildings, the 41st and 42nd floors. systems tominimize energy consumption

1996 July-August 325

This content downloaded from 132.206.27.24 on Thu, 1 Aug 2013 20:53:44 PM All use subject to JSTOR Terms and Conditions 6. Figure Sky Bridge (left), which connects the towers, must accommodate up to 12 inches of horizontal movement at each end. Tuned mass dampers (right) prevent unwanted vibrations in the supporting legs. (Photograph at left cour? tesy of Cesar Pelli & Associates.)

maximize the comfort of con? occupants and the and towin the job,Harmon prepared an 800-page use. an venience of The concept of intelligent bid tomeet theMalaysian expectation thatpropos? building dates from the 1980s, when costs associ? als be both educational and business instruments. ated with and as a installing retrofittingenvironmental Furthermore, condition of receiving such a and communications were systems escalating. large contract, theAmerican specialistwas required came to There also be recognized clear advantages to set up shops inMalaysia to fabricate the compo? in a incorporating networking capabilities into nents of the curtain wall and thereby introduce a new building, rather than providing tenantswith new industry to the country. a structural shell that they themselves have to The experience gained by local engineers and wire. In or the Petronas Twin Towers, each floor contractors in designing and building theworld's own area pair of floorshas its local network forair tallest buildings has prepared themwell to com? and as as a conditioning lighting, well general plete the rest of Kuala Lumpur City Centre by use. purpose controller forunspecified future the year 2020. By demanding local participation in the project, theMalaysian government, led by Technology Transfer its strong-willed prime minister, has ensured that Although the record-breaking height of the the Petronas Twin Towers project will leave a Petronas Twin Towers will be theirmost imme? legacy thatwill serve the local economy and so? no? diately visible and talked-about feature, that ciety long after taller buildings are erected else? toriety is likely to be short-lived, since taller where in theworld. are buildings already being planned for Shang? hai, China, and Melbourne, Australia. Among Acknowledgment more the long-range benefits of the Petronas I am grateful to Charles H. Thornton for his Twin to Towers theMalaysian economy is the February 1996 lecture at Duke University on the amount considerable of technology transfer that Petronas Twin Towers, and to Leonard M. Joseph, has accompanied their design and construction, vice president of Thornton-Tomasetti Engineers, for with the on direction and input of the prime minis? his comments themanuscript for this column. ter. For example, the development of the high strength concrete used in the towers has in four Bibliography doubled of concrete now E. in years the strength pro? Gargan, A. 1996. A boom malaysia reaches for the The New York C3. duced inMalaysia. This means thatbuildings can sky. Times, (February 2): Cl, et al. as be built in less time and for lessmoney. Reina, P., 1996. Malaysia cracks height ceiling it Another of the Twin Towers catapults into future. Engineering News-Record, by-product project 36-54. has been the establishment of new local industries. (January 15): R. Robison, 1994. Malaysia's Twins. , The Twin Towers required about a million and a (July): 63-65. half square feetof stainless steel and cladding glass, Robison, R. 1995. The twin towers of Kuala IEEE in the form of 32,000 windows, to form a so-called Lumpur. Spectrum, (October): 44-47. curtainwall. This was the such thatHar? largest job C. et al. Thornton, H., 1960. High-strength concrete for mon Contract, theMinnesota-based in participant high-rise towers. American Society of Civil Engineers the contract ever Structures cladding consortium, had tackled, Congress XIV, Chicago, Illinois, April 15-18.

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