One Shell Square, New Orleans, Louisana

In 1972, two years after designing the John Hancock Center and a year after campaigning rigorously for Bangladesh's independence during Muktijuddho, Fazlur Khan designed the 51-story One Shell Square in New Orleans, Louisiana by combining reinforced concrete and structural steel in a "composite tube". Standing at 697 feet (212 m) tall the One Shell Square is the tallest building in both the city of New Orleans and the state of Louisiana, and is taller than Louisiana's tallest peak, Driskill Mountain.

The building is primarily used for leaseable office space, with some retail space on the ground level. The design of the building is very similar to Houston's One Shell Plaza and Denver's Republic Plaza (Denver), both built by Skidmore, Owings and Merrill.

By designing structures based on structural principles with broad application he [Fazlur Rahman Khan] changed the way engineers and architects thought about high-rise design. The composite tube and the bundled tube, in particular, represented significant breakthroughs, paving the way to a multitude of new possibilities for structural design. Following the introduction of the composite structure (One Shell Square was completed in 1972), engineers were no longer forced to choose between concrete and steel when designing a tall building, but could mix these structural materials, instead.

Yasmin Sabina Khan

Sears Towers (later renamed Willis Tower), Chicago

In 1973 Fazlur Khan and Bruce Graham produced another "masterpiece" (as described by Time magazine) with the creation of the Sears Tower in Chicago. Using Fazlur Khan's "bundled tube" concept for the first time, the 110-story Sears Tower was created.

Expansion of world's largest retailer

In 1983 Richard Warren Sears, a railroad station agent, and Alvah Curtis Roebuck, a watchmaker, founded a mail order catalog called 'Sears, Roebuck & Company' which mainly catered to farmers. Julius Rosenwald took control in 1895 and greatly expanded its sales and profits. In the years that followed, the small company grew tremendously, becoming the largest mail order business in the world by 1906. In 1925 the company transitioned from the mail order business into regional stores and began opening local department stores. After the Second World War (1939 - 1945) Sears envisioned the rise of automobiles and advent of suburbs so they began building stores greatly on the fringe of cities. The business peaked in the 1950s and 1960s, far exceeding the competition and by 1969 Sears was the largest retailer in United States with a net income of $441 million. It had outgrown its headquarter 'The Great Works' on Homan Avenue, in the residential West Side of Chicago and also had offices leased throughout Chicago. Such was its phenomenal growth and domination the company decided to commission a new headquarter to accommodate future growth expectation. It was also in a very healthy financial position to fund the development of an impressive modern building.

In 1968 with over 7,000 employees scattered over 10 locations in Chicago, Sears chairman Gordon Metcalf decided to bring the company under one very large roof. Sears hired New York-based interior firm SLS Environetics to calculate how much space was required to cater for its present staff and their growth projection for the next 30 years. They would require vast amount of space not only because they were a big company but also because as the world's leading retailer they wanted to make a grand statement.

Being the largest retailer in the world, we thought we should have the largest headquarters in the world.

Gordon Metcalf, Chairman of Sears, after the completion of Sears Tower

Sears eventually selected Chicago Loop area as the location for its new headquarter since the area had good public transportation, access to all suburban railroads and bus network and thus was easily accessible for everyone. Sears found support for their project from Chicago's mayor Richard Daley who was keen on the commerce that Sears' headquarters would bring to the Chicago Loop area, which was partly undeveloped land.

Daley also lifted the height restriction on buildings through a zoning ordinance revision in 1955; the ordinance changed the maximum building height to sixteen times the area of the lot. The only remaining obstacle to build higher was the Federal Aviation Administration, which set the maximum building height for Chicago at 2000 ft. above sea level, or 1450 ft above ground. However, height did not initially concern Sears, as the original Tower design differed greatly from the final design.

Department of Civil and Environmental Engineering - Princeton University

SOM selected mainly due to the reputation of Bruce Graham and Fazlur Rahman Khan

Having decided to relocate and found the perfect location, now it was a matter of deciding what kind of building to put up. Sears chose Skidmore, Owings and Merrill (SOM) as their architectural designer. At the time SOM were the preeminent office builders for large corporations and had the most talented staff. The growing reputation of gurus Bruce Graham and Fazlur Rahman Khan was also a huge contributing factor in favouring SOM over others. Fazlur Khan had been the brainchild behind the revolutionary X-grid exterior of Chicago's John Hancock Center, then the world's third tallest building. The Hancock was tapered towards the top to provide for various tenant requirements, and since the Sears would contain an excess 2 million square feet compared to the initial space demand, it was fundamental that the new designers considered various tenants requirements similar to Hancock. The shape of the John Hancock Center was also similar to what they needed.

Bruce and Faz collaborated closely in the design of number of buildings throughout the 1960s, and eventually it lead to the design of the John Hancock, which is a very tall building. And there was this dynamic energy that existed between the two of them.

, Structural Engineer at SOM

It was only after SOM got involved that the building took its final form.

Cigarettes used to explain bundled tube concept

The studies by SLS Environetics concluded that their current space requirement was 2 million square feet and future space requirements was between 3.5 - 4 million square feet, with a floor area of 110,000 square feet per department. Seeking a cost-effective solution, Sears envisaged a large 40-story cube building as the potential solution. However, SOM conducted its own studies and concluded that the departments could save significant amounts of time by stacking two 55,000 square ft stories on top of one another. This would change the building into an 80-story tower, but only if SOM could make it cost-effective. And Sears and Bruce Graham both wanted something distinctive, not another 'Big John'. This required a new structural system.

The idea of using tube construction was starting to gain momentum in the architectural world, especially in light of its successful usage on the John Hancock Center. However, Sears Tower offered an even taller variation on the tube theme, consisting not of a single tube, as at the Hancock, but nine interlocked tubes. Fazlur Khan and his team came up with the bundled tube structural system that defined the Sears Tower.

Bundled tube constituted a whole new architectural vocabulary.

Fazlur Rahman Khan

The idea for Sears Tower was since this was such a large building the tube started to become inefficient because it [i.e. Sears Tower] was so wide and so deep. So the idea was why not take multiple tubes and put them together, bundle them. And so Sears Tower, if you look at the floor plan, is a series of 9 tubes 3x3 that are bundled together.

John Zils, Structural Engineer at SOM

Reflecting the enthusiasm created by the bundled tube, Architectural Record referred to it as "perhaps the most intriguing concept to evolve in the ultra-high skyscraper". This concept offered unprecedented flexibility in creating architectural space and new possibilities for architectural expression. At the same time, the modular, or bundled, tube provided remarkable structural stiffness: the structural steel weight of the 1,450-foot-tall Sears Tower is a low 33 lb. per sq. ft. of gross floor area - for comparison, that of the 1,250-foot-tall, skeleton frame, Empire State Building is over 42.

Yasmin Sabina Khan

Bruce Graham and Fazlur Khan would often meet outside of work to discuss different ideas for the project. Whilst having lunch one afternoon at the Chicago Club they hit on a design that would become the Sears Tower.

We were pursuing the idea of the bundled tube system and Faz was trying to discuss this to Bruce, and finally Bruce says 'I think I understand what you're saying'. Bruce was a smoker, so he took out his pack of cigarettes and took out a number of cigarettes and kind of held them in his hand and had them coming to different height and asked Faz if this in fact was his idea? This is what he was thinking the system might look like from an architectural standpoint, from a visual standpoint. And Faz said 'that's exactly right'.

John Zils

According to Fazlur Khan's bundled tube concept, nine 75-foot square continuous steel tubes (tied and placed on a 3x3 grid) would form the tower's 225 x 225-ft dimensions from grade and rise together. Two would drop off at the 50th floor and the remaining seven would rise to the 66th floor where two more would stop. The remaining five would continue to 90th floor where three more would stop. Finally, the last two would rise to the summit. Beyond giving the building its visual and physical strength, the bundled tube system had the added attraction of saving Sears $10 million as compared to pre-existing structural systems.

Several designs, one with 80,000-square-foot floors, another that included two towers-one for Sears and one to rent out-were proposed. Ultimately the decision was to go up and up and up. Khan and Graham finally submitted the "bundled tube"... It was a strong, resilient, remarkable design. The effect, it was quickly pointed out, was not unlike a massive, uneven stack of Sears catalogs.

Bill Brashler of Chicago Tribune

The building plan consists of 9 squares, each 75 feet across, placed in a three-by-three grid arrangement. Each square has 5 columns per side spaced 15 feet on centers, with adjacent squares sharing columns. As the columns rise up the building, each square in the plan forms a tube, which can be seen on the exterior of the building. These tubes are independently strong but are further strengthened by the interactions between each other through truss connections. While the tubes connect at each floor level with beams and floors trusses, several large trussed levels act as the main horizontal connectors in the buildings. These trussed levels, which also contain the mechanical systems for the building, appear as black horizontal bands on the façade. While the louvres covering the trussed levels mask the structural details, the purpose of these levels remains abundantly clear visually.

Department of Civil and Environmental Engineering - Princeton University

On the Sears Tower, Khan's structural design saved $10 million by using the modular tube system, a variation of tubular design.

The modules have common interior columns that make up two diaphragms, trisecting the building in two directions to stiffen the structure. The weight of the $150-million, 110-story structure is 33 lb per sq ft. Khan estimates that conventional tubular design, without diaphragms, would have resulted in a steel frame weight of 60 to 70 lb per sq ft.

Richard M. Kielar, assistant editor of Engineering News-Record magazine

The bundled tube concept delivered column-free office space, created a lightweight framing system that did not put a financial premium on height and reduced the wind load on the upper stories. It very easily enabled the architect to create modulation of space as they went up. This allowed Sears to occupy the tower's lower half which gave them plenty of floor space to cater for their business needs while leasing out the upper half to tenants. And since dropping off the various tubes resulted in a smaller floor plan, the upper half became more prestigious and attractive on the leasing market as it gave more perimeter offices with their uninterrupted, unique view of the Chicago skyline.

Interesting facts:

  • 8th tallest building in the world; tallest in Western Hemisphere
  • You can see four states: Illinois, Indiana, Wisconsin and Michigan
  • Cost more than $175 million to build
  • 4.5 million gross square feet (418,064 gross square meters) of floor space, roughly equivalent to 101 football fields or 16 city blocks in Chicago
  • Weighs more than 222,500 tons
  • 76,000 tons of steel used to create it
  • Average six inch (152 millimeter) building sway from true center; designed to withstand up of to three feet
  • Approximately 25,000 daily visitors
  • Took 2,000 workers three years to build
  • Approximately 16,100 windows
  • 104 elevators moving 1,200 feet per minute
  • Two entrances
  • Broadcasting radio and television stations from the rooftop

Dear Yasmin,

Your dad took me to the Sears Tower under construction making me wear a hard hat during the tour as, I remember, required by the building code. I felt proud that the rising structure designed by my brother was going to be the tallest building in the world.

Love,
Uncle Zillur

Zillur Rahman Khan tells niece Yasmin about his first time visit to brother Fazlur's Sears (Willis) Tower

Flirting with world record

The bundled tubes concept as well as the ingenious use of setbacks or "step-backs" set the Sears Tower design apart from earlier skyscrapers. Breaking record was just an afterthought.

The decision to become the tallest building was not part of the initial program. But in trying to meet the space requirement of 3.5 - 4 million square feet the bundled tube concept resulted in a design that was pushing more and more upward and was just flirting with the world record. Bruce Graham went into a meeting with the seniors of Sears and informed them that they were close to breaking the world record. All concerned soon realized, however, that the best thing the Tower had going for it was its commanding size, even if that was not the original idea. This sparked joyful celebration in the boardroom. Now the world's largest retailer would create the world's tallest building.

I want into a meeting with most of the Sears' executives and the architects in which there were a number of cardboard models. And out of a bag, Bruce, who was a consummate salesman pulled out this walnut model and put it on the table and suggested that we were so close to the ultimate, so close to the world's tallest building that we should consider going for the brass ring and the Sears executives almost broke into applause. There were smiles all around the table.

Richard Halpern, Construction Project Executive

Few weeks later on 27 July 1970 Sears management publicly unveiled the model for the Sears Tower.

The public was pretty excited about it. I think most of the excitement came from the fact that we were one-up on New York.

Hal Iyengar, Senior Structural Engineer at SOM

The project started immediately.

Project fast tracked

Although Fazlur Khan had already estimated that the structure itself would save Sears a great deal of money, SOM continued to reduce costs for its client, as interest rates on the $175 million dollar project became higher and higher. In order to complete the project in a timely and economical manner, several new construction techniques were employed in order to fast track the construction.

The initial stages of design and construction went smoothly for the Sears Tower. As the design moved forward, Fazlur Khan was unable to spend his full time on the project, as he was a partner at SOM. Instead, the project team was composed of six to eight people at any time, with Hal Iyengar as the team leader. The structural drawings were fast tracked along with the construction schedule, taking only 3 months to complete, rather than 8 months. The project team worked overtime, using computer modeling in order to meet the deadline. Once the final design was completed, construction began with the foundations, and proceeded according to plan. Every 'big wig' in Chicago wanted a piece of the historical project. The top people of all the companies working on the project were assigned to the Sears project.

Every contractor was the top executive or chief operating officer of the organisation. If we wanted to get something done, we could get it done.

Richard Halpern, Construction Project Executive

The skeleton of the building was put up by the ironworkers. Most of these were from Chicago. However, ironworkers came from all over the country as they wanted to "have the bragging right" to say they worked in the tallest building in the world. To speed up the work and become more efficient, the columns and griders were wielded together offsite at the fabrication lab and transported on specially modified trucks. Once onsite, the tree units were directly lifted off the countless number of trucks - sometime as much as 100 truckload per day - and erected immediately as there was no storage on the site. This allowed the ironworkers to erect the building at an astonishing rate of two floors a week.

Every piece was numbered and floated on the truck at the right time so that it'd be next piece to go up on the building. It had to take a lot of coordination between the fabricators, shipping, and truckers to make it all run smooth. Everything had to stay in line.

Richard Gumber, crane operator for the last grid to go up on Sears Tower

The exercise was no more than putting together a whole series of tinker toys.

Hal Iyengar, Senior Structural Engineer at SOM

As the building climbed, workers found themselves fighting the force of mother nature in the struggle to claim a share of the sky, with the weather at the top drastically different from that of the ground. And though tight security practises were maintained throughout the project, unfortunately, a total of 6 people had died on the project, including one iron worker. Nevertheless, sharp planning and exemplary resourcefulness kept the project on the fast track.

We needed the cooperation of the unions who'd work on a staggered-start staggered-stop staggered-lunch. We needed the cooperation of the men who were willing to take meals off of carts that we brought up into the building. We had our own medical staff and first aid officers throughout the building, and other methodologies that was utilised kept the building on target from timing standing point of view. Otherwise, if it'd taken another day to build a floor you could see what the difference would've been with regards to the overall schedule.

Richard Halpern

Last grider goes up

Fittingly, on an abnormally cold and windy day on 3 May 1973 the building was ceremoniously topped off. Several thousand employees gathered outside the soaring Sears Tower to witness the historical moment. And just like the building, the topping off ceremony was grand. It was proudly attended by Mayor Richard J. Daley, all top Sears' executives, some politicians, and celebrities.

Strong winds threatened to delay the topping off of the building. It was feared the heavy beam would break some windows on its way to the top.

But the strong, cold winds seemed to die down just long enough for the lifting as dignitaries below stretched their necks upward and a chorus of hard hat electrical workers sang these lyrics:

"She towers so high
"Just scraping the sky
"She's The Tallest Rock."

She is indeed the tallest rock as she pierces the clouds 1,454 feet [nowadays over 1,700 feet] above Wacker Drive at Jackson Boulevard. A frame of 76,000 tons of steel encloses 4.5 million feet of floor space.

Richard Sears could never have dreamed of such an edifice bearing his name when he brought his fledgling mail-order business to Chicago in 1887.

Yet there she stood in the clear but cold sky yesterday as a monument to what is now the world's largest retailer - Sears Roebuck & Co. - and man's ability to reach higher and higher in search of a place to work and live.

Chicago Tribune (4 May 1973)

Ceremonial speeches where given by a handful of people. Amongst these were Mayor Daley and Cardinal Cody who blessed the building.

I want to thank them [Sears] for staying in Chicago when so many are leaving. Sears Roebuck, a name that means everything to the people of America, has no equal in the business world of Chicago.

Mayor Richard J. Daley

We ask that each time we look at this tower, may we be reminded of our unit.

Cardinal Cody

But it was not the dignitaries who took centre stage but the final beam (or grider) which would complete the mammoth structure. Weighing 2,500 pound, the beam was painted white and signed by 12,000 Sears employees, construction workers and Chicagoans. It was hoisted more than a quarter mile into the sky and made its final journey to the 110th floor. With that the skeleton of Sears Tower was now complete and stood up triumphantly.

I happen to be running the engine that day and when it got to 76th floor I figured I'm in control so I put the break on and stopped it, went out there and took a picture of the beam, got back in the cabin and raised it up again!

Richard Gumber, crane operator for the last grid to go up on Sears Tower

Three months later, Sears would begin moving its employees into what became known as a "vertical city", 15,000 people working, shopping and dining inside one building.

Tallest building in the world for quarter of a century

Epitomising Bruce Graham's and Fazlur Khan's technical prowess, and standing 1,450 feet (443 meters) high - 1,730 feet (520 meters) high if you include the twin antennae - the Sears Tower officially became the tallest building in the world. It brought the prestigious title back to Chicago from New York, where the Empire State Building had held it for 40 years and the World Trade Center had grabbed it briefly in 1972 (before Sears took over in 1973).

The 1,450 feet height was a limit set by the Federal Aviation Administration, nevertheless the Sears Tower was still 100 feet higher than the previous record holder the World Trade Center and 200 feet taller than the Empire State Building.

If someone told us to design a building twice as high, we could do it.

Bruce Graham

It reigned as the world's tallest building for the next 25 years until the completion of the 88-story Petronas (Twin) Tower spires in Kuala Lumpur, Malaysia in 1998 which surpassed the Sears Tower by 29 feet. In 2010, the 160-story Burj Khalifa in Dubai, United Arab Emirates, became the tallest man-made structure in the world, at 2,716 feet (828 metres). And not surprisingly, the Burj Khalifa is another of SOM's creation with Adrian Smith taking Bruce Graham's role as Chief Architect, and Bill Baker taking Fazlur Khan's role as Chief Structural Engineer.

Burj Khalifa is the work of the grand old Chicago architectural firm of Skidmore Owings and Merrill, world leaders in design of supertall buildings. SOM, as it is known, has drunk very deeply of Wright's intoxicating brew of techno-mysticism and physical daring. But, touchingly and significantly, Fazlur Khan, SOM's engineering genius whose experiments ultimately made Burj Khalifa possible, was born not in a big Western city but in Bhandarikandi, Shibchur Upazila near Dhaka.

The Telegraph (UK)

Though the Sears Tower may have lost the tallest tag to other buildings around the world, it still remains the tallest building in United States, over 40 years after its creation.

Sears Tower...a building whose exterior profiles are a bold, vital and exciting departure from orthodox mediocrity. A finely engineered piece of sculpture, even if its interior is largely nondescript in the big-corporation manner.

Paul Gapp, Chicago Tribune architecture critic (1974)

Deterioration

Sears Tower was built to last. Initially it won critical praise for its strong skyline profile and refreshing, groundbreaking approach to architecture. But as time passed, Sears did not meet its growth expectations. Moving away from the horizontal layout of The Great Works headquarter, many Sears employees became disillusioned with life inside the vertical city. Some floors were so large that some employees never had an opportunity to look out of the window.

Sears workers used to brag about the fact that each light in the massive West Side complex was turned off at night in the spirit of corporate loyalty, but now a computer turned off the lights.

Instead of the sound of children at play after school, a voice came over the intercom speakers at four o’clock every day to tell you if it was raining outside, because it was often impossible to tell from inside the upright city.

Donald R. Katz, author of "The Big Store: Inside the Crisis and Revolution at Sears"

And though the area around Sears Tower was booming, the retailer themselves were not. Eventually by 1980s K-Mart and Walmart became bigger than Sears. In 1988, with revenue decreasing continuously, Sears Tower was put in the market for sale for $1 billion. Two years later, Sears retailer moved out of the tower and in 1992 moved into a complex in the Chicago suburbs, Hoffman Estates. No longer the world's largest retailer, Sears reinvested the assets from the sale of the tower to fuel the faltering business.

Following the takeover the tower underwent a series of renovation work to make it more attractive in the leasing market. Security was also upgraded especially after the New York attacks on 11 September 2001 (i.e. 9/11).

On 16 July 2009 Sears Tower was renamed to Willis Tower when British global insurance broker Willis Group Holdings moved into the Chicago landmark and became the largest tenant of the tower. The name change will stand for the duration of their ten year lease.

Nevertheless, the Sears (Willis) Tower still remains a powerful symbol of Chicago and its most famous landmark. And as the tallest building in North America, it's an unmissable and breathtaking sight.

The Willis Tower has been a part of the Chicago skyline for nearly 40 years. The exterior building material shows very little aging, a sign of its durable construction. Not only has the skyscraper become an integral part of Chicago's skyline, many of its details have allowed it to remain an effective and modern symbol of downtown Chicago.

Department of Civil and Environmental Engineering - Princeton University