Petronas Towers

Sigma Xi, The Scientific Research Society

Engineering: The Petronas 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 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp

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Engineering!

The

Twin

Petronas

Towers

Henry Petroski two decades, the 110-story Sears Tower stood as the tallest building in theworld. Topping out at 1,454 feet above ground lev? el?almost as tall as a string of five football fields would be long?the bundle of nine steel tubes standing just outside Chicago's Loop could be said to have cast a shadow over all other sky? scrapers since its completion in 1974.New York's World Trade Center, the 1,368- and 1,362-foot-tall twin towers completed only a year earlier, held the record as tallestbuildings foronly a brief time. Before that, theEmpire State Building, at 1,250 feet tall even without itsbroadcasting towers?which, like those of the Sears Tower, do not count as part theworld height of the building proper?held record forover four decades. Completed in 1931, the Empire State then surpassed the one-year-old Chrysler building, which at 1,046 feet tall had been the firsttobreak themagical 1,000-footmark. Before then, theWoolworth building, a 792-foot tallGothic cathedral of commerce paid for in cash by the profits from its namesake's chain of five and ten-cent stores, had stood as the world's tallest building foralmost two decades. Skyscrapers?so named since the 1880s,when 100-foot-tall buildings were marvels Chicago's

For

of

structural

contemporary

engineering?seem

to have sprouted up in temporal and spatial clus? ters,with Chicago and New York proving espe? cially hospitable to the form and its financing. Throughout most of the 20th century, the sky? scraper was considered a particularly American genre, growing with the economy and optimism of cities such as Atlanta, Houston, Los Angeles and Seattle. In the last decade of the century, however, the frontier of the skyscraper has moved across the Pacific Ocean to the Far East. Today, most of the tallest buildings in theworld are being proposed for locations such as Tokyo, Taiwan, Hong Kong and mainland China. And are being they are not only being proposed; they built, with the tallest building in theworld re? cently being topped out at 1,482 feet in Kuala Lumpur, Malaysia. is Aleksandar S. Vesic Professor of Civil Petroski and chairman of the Department of Civil and Engineering Environmental Engineering at Duke University. Address: Box

Henry

90287, Durham, NC

322

American

27708-0287.

Scientist, Volume

The Federation ofMalaysia is a southeast Asian country of about 20million people, thevast major? located just ity of whom live inWest Malaysia, above the equator on theMalay Peninsula, be? tween Thailand to thenorth and Singapore to the south. (As established in 1963, the federation in? cluded Singapore, but it seceded in 1965.) The two are situated to the east, states of East Malaysia across the South China Sea on Borneo, the third largest island in theworld. Kuala Lumpur, the cap? is served by a modern North ital ofMalaysia, South Expressway that puts Singapore within a five-hourdrive. The city's Subang Airport has di? rect flightsthroughout theworld and hourly flights thatdepart forand arrive fromSingapore, and pas? sengers get a bird's eye view of lush golf courses among rubber trees?a sign of the changes that have been takingplace inMalaysia, which has been described as ''predominantly aMalay Islamic state with strongChinese and Indian influences." A Vision of the Future In the 1980s, theMalaysian economy was based on commodities such as palm oil, rubber and tin. However,

with

the rise

of a

government

headed

by the strong-willed and powerful Prime Minister Mahathir bin Mohammad, by training a medical doctor,Malaysia began to assert itselfas a country on themove. The prime minister is said to have "reinterpreted Islam as allowing the pursuit of wealth and technical knowledge," and the gov? ernment's official objective came to be articulat? ed, in Bahasa Melayu, the native language of the ethnic Bumiputra population, asWawasan 2020? or Vision 2020 inEnglish, the country's accepted language of commerce and industry. The vision has Malaysia transformed into a fully developed industrialized nation by theyear 2020, with man? ufacturing and construction becoming themain driving forces of the country's economy. The Kuala Lumpur City Centre project is helping in a a reality. big way tomake theMalaysian vision Kuala Lumpur City Centre is a 100-acre devel? opment on the site of a former racetrack, the Se as among the langor Turf Club, and is described estate real development projects in the largest world. As the result of an international competi? ideal city tion held in 1990, a master plan?"an defined by the U.S. firm of within-a-city"?was

84

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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 thepublic, and a complex of 20 or so surrounding buildings thatwill contain office space, apart? ments, hotel rooms, recreational facilities, restau? rants,

shops,

banks,

a convention

center,

(L

a 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, source national oil and the company Malaysia's of the towers' name, and the government. As they have risen tobecome theworld's tallestbuildings, 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 thearchitectCesar 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 adopted a multipointed star pattern as a footprint forhis building design. His early scheme called for a 12-pointed star layout, but thiswas changed to a modified 8-pointed floorplan with intermediate arcswhen theprime minister observed that the for? mer geometrywas more Arabic thanMalaysian. Architecture and Engineering The final design of skyscrapers, especially those that are to be the tallest in theworld, does not evolve wholly froman architect's drawings. How a structurewill stand against the forces of nature? whether theground motion in an earthquake zone, thewind at hundreds of feet above the ground or theheat of the sun beating down on the ground? requires the insight and calculation of a structural engineer. (The exposed structureofChicago's John

Figure

2. Building

design

evolved

to incorporate

Islamic

gl!

Set Sjjlsl

I^bsE Bis

^hbee?^

tallest buildings, the Petronas Towers are in Kuala City Centre, Kuala Lumpur, Malaysia. (Except where noted, courtesy of Thornton-Tomasetti photographs Engineers.) Figure

1.World's

Lumpur

Hancock Tower, for example, was the result of a collaboration between architectBruce Graham and structuralengineer Fazlur Khan of thefirmof Skid more, Owings and Merrill.) Pelli wished the "cos? mic pillars" in Kuala Lumpur to be joined by a a skybridge to form welcoming portal to Kuala Centre and tohave as few structural Lumpur City columns as possible blocking the view outward from the office floors. Such featureswere easy to render on the drawing board but no small task to

themes.

(Illustration

courtesy

of Cesar

Pelli & Associates.)

1996 July-August 323

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BARRCTTE KENNYUli?

NCUIPtJQ F0UNDATI0H8 ELEVATION Figure 3. Foundation as 400 feet.

Figure 4. Digging tion barrettes.

American

piles,

machine

Scientist, Volume

or barrettes,

prepared

extend

ground

as deep

for founda?

realize in concrete 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 tallestbuilding in theworld, and had indeed designed with Pelli a 125-storyMiglin Beitler building forChicago that for financial rea? sons did not come to fruition.He was thuswell on thePetronas prepared towork again with Pelli Twin Towers, equivalent inheight to 95 stories. The challenges associated with designing and building a skyscraper begin in the ground. If the foundation isnot firm,thebuilding 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 enough for engineers to set the locations and types of tests needed. As it turned out, the 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? tion of the towerswas moved about 200 feet to the southeast, where the generally fissured limestone was sufficientlydeep so that all piles could termi? 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 than three times piles almost 400 feetdeep, thedepth of the foundation beneath theSears Tow? er. Even then, the foundation of the buildings are as three inches under expected to settle as much 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? though the tallest skyscrapers are steel structures, thatmaterial was not readily available inMalaysia, where prohibitively high tariffson 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? tions induced by thewind. Concrete structures,on the other hand, although they tend tobe stifferand have qualities that damp out quickly any vibra? tions thatdo begin, often are bulkier-looking than steel. Since the architectwished the Petronas Tow? ers tobe slender-looking and have columns spaced rather far apart, conventional concrete columns would have been too aesthetically broad and struc

84

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an ex? rurally heavy. To overcome this objection, was concrete developed, tremely high-strength with bearing capacities asmuch as three times that of concrete conventionally used inMalaysia, or elsewhere for thatmatter. Special concretemixes, using localmaterials, 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 theperiphery 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 floorbeams 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 trickystructuralengineering, and itsgeom? etrynecessitated the installationof awide 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 erected after the facton such buildings as theEm? pire State Building and the Sears Tower. (The offi? cial arbiter of skyscraper records, theCouncil on Tall Buildings and Urban Habitat, confirmed at an executive committeemeeting inApril that theSears Tower had indeed been surpassed as the tallest building on Earth.) The pinnacles, with designs based on minarets rather than Gothic cathedral spires,were erected by jacking them skyward from within theuppermost part of thehull of the towers. The pinnacle design was the result of detailed stud? ies including many options. The final design is a scaled-up version of one originally proposed to provide a more graceful tower top and, coinciden tally,reach a record-breaking height. Thornton, an avid sailor, likens the structural support for thepin? nacles to thatof themast of a sailboat. Among what makes extremely tallbuildings vi? able investments is theamount ofusable, rentableor saleable floor space they contain relative to their more and more of height. As buildings grow taller, theirvolume must be devoted to elevators to trans? port the tens of thousands of occupants up and down. In thePetronas Towers, theusable floor space was increased considerably by theaddition of small? er 44-story structures, referred to as "bustles," to each tower.With thebustles,which are tobe topped by prayer rooms for theMuslim occupants who will be called to prayer twice each working day, each towerhas about 2million square feetof officespace. The internal transportation system thatmoves peo? ple vertically in the towerswill include double-deck express elevators to optimize the use of the shafts. Passengers will transfer to and fromdouble-deck local elevators in sky lobbies about halfway up the on the41st and 42nd floors. buildings,

Figure

5. Pinnacles

atop

towers were

jacked

into place.

The towerswill also be connected to each other at the level of the sky lobbies by a skybridge, a 190 foot-long steelwalkway thatnot onlywill facilitate movement between one tower and the other but also will serve as an alternative escape route in the event of a fireor other emergency, such as occurred when the terroristbombing forced the evacuation of one of the towers of theWorld Trade Center. But the sky bridge's design presented additional and unusual structuralproblems. Since the two towers can sway in thewind both in phase and out of phase, as well as twist in independent directions, the sky bridge could not be attached rigidly be? tween thevertical structures.Thus special bearing connections had tobe devised to allow forasmuch as 12 inches of horizontal movement each way at each end, as well as the twisting. Because such a long, unsupported sky bridge would have tohave been of very heavy construction if itwere not to sag in themiddle, a set of slender steel legswas de? signed to angle up from supports on each tower about 160 feetbelow to the center of the skybridge. To prevent such slender struts from vibrating ex? cessively in thewind, thuspresenting thepotential foruncontrollable motion or at least the accelerated growth of fatigue cracks, tunedmass dampers were designed tobe installed inside the legs. (Eachmast? like pinnacle also has a damper in the form of an energy-absorbing, rubber-sheathed chain.) The Petronas Twin Towers and all thebuildings planned for the Kuala Lumpur City Centre will be what are known as intelligent buildings, em? ploying automatic controls and communications systems tominimize energy consumption and 1996

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July-August 325

connects the towers, must accommodate at Figure 6. Sky Bridge (left), which up to 12 inches of horizontal movement each end. Tuned mass dampers in unwanted vibrations the at left cour? (right) prevent supporting legs. (Photograph tesy of Cesar Pelli & Associates.)

the comfort of occupants and the con? of use. The concept of an intelligent building dates from the 1980s,when costs associ? ated with installing and retrofittingenvironmental and communications systems were escalating. There also came tobe recognized clear advantages in incorporating networking capabilities into a new building, rather than providing tenantswith a structural shell that they themselves have to wire. In the Petronas Twin Towers, each floor or pair of floorshas itsown local area network forair conditioning and lighting, as well as a general purpose controller forunspecified futureuse.

maximize venience

Technology Transfer the record-breaking Although height of the Petronas Twin Towers will be theirmost imme? diately visible and talked-about feature, that no? toriety is likely to be short-lived, since taller buildings already are being planned for Shang? hai, China, and Melbourne, Australia. Among the more long-range benefits of the Petronas Twin Towers to theMalaysian economy is the considerable amount of technology transfer that has accompanied their design and construction, with the direction and input of the prime minis? ter. For example, the development of the high strength concrete used in the towers has in four years doubled the strength of concrete now pro? duced inMalaysia. This means thatbuildings can be built in less time and for lessmoney. Another by-product of the Twin Towers project has been the establishment of new local industries. The Twin Towers required about a million and a half square feetof stainless steel cladding and glass, in the form of 32,000 windows, to form a so-called curtainwall. This was the largest such job thatHar? mon Contract, theMinnesota-based participant in the cladding contract consortium, had ever tackled, 326

American

Scientist, Volume

and towin the job,Harmon prepared an 800-page bid tomeet theMalaysian expectation thatpropos? als be both educational and business instruments. Furthermore, as a condition of receiving such a large contract, theAmerican specialistwas required to set up shops inMalaysia to fabricate the compo? nents of the curtain wall and thereby introduce a new industry to the country. The experience gained by local engineers and contractors indesigning and building theworld's tallest buildings has prepared themwell to com? plete the rest of Kuala Lumpur City Centre by the year 2020. By demanding local participation in the project, theMalaysian government, led by its strong-willed prime minister, has ensured that the Petronas Twin Towers project will leave a legacy thatwill serve the local economy and so? ciety long after taller buildings are erected else? where in theworld. Acknowledgment I am grateful to Charles H. Thornton for his February 1996 lecture at Duke University on the Petronas Twin Towers, and to Leonard M. Joseph, vice president of Thornton-Tomasetti Engineers, for his comments on themanuscript for thiscolumn. Bibliography

E. A. 1996. A boom in malaysia reaches sky. The New York Times, (February 2): Cl, C3.

Gargan,

for the

cracks height ceiling as P., et al. 1996. Malaysia into future. Engineering News-Record, (January 15): 36-54.

Reina,

it

catapults

R. 1994. Twins. Civil Engineering, Malaysia's (July): 63-65. Robison, R. 1995. The twin towers of Kuala Lumpur. IEEE

Robison,

Spectrum, (October): 44-47. C. H., et al. 1960. concrete for High-strength high-rise towers. American Society of Civil Engineers Structures Congress XIV, Chicago, Illinois, April 15-18.

Thornton,

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