Willis Tower (Formerly Sears Tower)

History of Willis Tower Architecture Skydeck Your Home's Value

The Willis Tower 233 South Wacker Drive, Chicago Illinois, 60606, formerly known as the Sears Tower, is a colossal skyscraper standing at 1,451 feet (442.3 meters) tall, located in the Loop community area of Chicago, Illinois, in the United States. This architectural marvel was designed by the renowned architect Bruce Graham and engineer Fazlur Rahman Khan from the firm Skidmore, Owings & Merrill (SOM) and was completed in 1973, claiming the title of the world's tallest building for almost a quarter of a century. It currently ranks as the third-tallest building in the Western Hemisphere and the 23rd-tallest in the world. The Skydeck observation deck, offering stunning panoramic views, attracts over 1.7 million visitors annually, making it a premier tourist attraction in Chicago.

The tower is situated within the boundaries of Franklin Street, Jackson Boulevard, Wacker Drive, and Adams Street. Its unique design features nine square "tubes" arranged in a 3x3 matrix, with seven of these tubes stepping back at higher floors. While the standard count is 108 stories, the building's owners consider the main roof as the 109th level and the mechanical penthouse roof as the 110th level. The exterior showcases an elegant combination of anodized aluminum and black glass, while the base hosts a retail complex known as the Catalog. Sears, a major retail company, originally occupied the lower portion of the tower until 1994 when it moved its headquarters, with the upper floors being leased to other businesses.

Originally named the Sears Tower, the building underwent a name change in 2009 when the naming rights were acquired by the Willis Group. However, many local residents still refer to it by its former name. In April 2018, the largest tenant in the building became United Airlines, occupying approximately 20 floors. Other prominent tenants include Willis Towers Watson, Schiff Hardin, Seyfarth Shaw, and Morgan Stanley, which became the fourth-largest tenant in 2017.

History and Planning:

Sears, Roebuck & Co., an established office complex occupant on Chicago's west side since 1906, recognized the need for new and larger facilities by 1966. With around 350,000 employees, Sears was the world's largest retailer at the time. Considering relocation, they opted to consolidate their employees into a single building located on the western edge of Chicago's Loop, thus avoiding the need to relocate 7,000 employees. Sears consulted with legal counsel Arnstein, Gluck, Weitzenfeld & Minow (now Saul Ewing LLP) and settled on two options. The first was the Goose Island area to the northwest, but this was rejected. The second, a two-block area within the Loop, became their choice, despite its relatively small size. The site was bounded by Franklin Street to the east, Jackson Boulevard to the south, Wacker Drive to the west, and Adams Street to the north. Bernard Feinberg, Albert I. Rubenstein, and Philip Teinowitz, who had been assembling the site for five years, eventually sold it to Sears in 1970. Sears purchased 15 buildings from 100 different owners and paid the city of Chicago $2.7 million to close down a block of Quincy Street.

Design Process:

Sears estimated that their new building would require approximately 4.2 million square feet of space, which could be divided into 70 stories with 60,000 square feet each or 60 stories with 70,000 square feet each. They entrusted the architectural and structural design to Skidmore, Owings & Merrill (SOM), with MEP engineering by Jaros, Baum & Bolles. Sears initially planned to occupy the lower floors and lease out the remaining space, but concerns arose about attracting smaller tenants to the large floor areas. To address this, the building's height was increased to accommodate Sears's needs while offering conventional office space on the upper levels. Architects Bruce Graham and Fazlur Rahman Khan proposed a tower with 55,000-square-foot floors in the lower section and a series of setbacks with gradually tapering floor plates, creating the iconic look of the tower. During the design process, a creative arrangement was agreed upon, inspired by stacking nine cigars vertically. This configuration allowed Sears to utilize the lower stories while making upper floors suitable for rent. Saphier, Lerner, Schindler were responsible for determining Sears's space requirements and designing furniture for the company. Their year-long study determined how to lay out 16 of the company's departments within the building.

As Sears continued to project growth, the tower's height increased accordingly. While Chicago's zoning laws theoretically allowed for a 300-story building with 13.5 million square feet of space on the site, potential tenants preferred lower heights. Additionally, the Federal Aviation Administration (FAA) placed height restrictions to protect air traffic, although they publicly denied imposing such a limit. Plans for the tower were officially announced on July 27, 1970, revealing a 1,450-foot-tall building containing 109 stories from Wacker Drive and 110 stories from Franklin Street, ultimately becoming the world's tallest building by roof height. However, New York City's World Trade Center Twin Towers, under construction at the time, would have taller antennas. Despite the tower's vast space, only about 3.7 million square feet are dedicated to offices out of its total 4.4 million square feet.

Early Phase of Construction

The construction of what is now known as the Willis Tower, originally the Sears Tower, began in August 1970 with the groundwork. Contractors excavated the site to a depth of 50 feet (15 meters), removing 180,000 cubic feet (5,100 cubic meters) of soil in the process. In November of that year, Spencer, White & Prentis Inc. initiated the construction of a trench surrounding the site, measuring 60 feet (18 meters) deep and 20 by 216 feet (6.1 by 65.8 meters) in dimensions. Within this trench, a slurry wall made of concrete and reinforced steel was erected.

To prevent the slurry wall from collapsing inward, steel bracing was used, and 201 holes were drilled into the ground using caissons. Additionally, a sewer that ran beneath Quincy Street, which was to be permanently closed as part of the tower's construction, was rerouted.

The Diesel Construction Company served as the general contractor for the Sears Tower project. On June 7, 1971, Gordon M. Metcalf, chairman of Sears, Roebuck & Co., laid the building's first steel beam during a ceremonial event. Approximately 2,000 workers were employed for this massive construction project.

In order to expedite the construction process, a concrete plant was established in the building's basement. This allowed workers to pour one-third of a concrete floor every day. Temporary kitchens were set up on-site for the workers, and telephone and loudspeaker systems were installed on every floor to facilitate communication. Moreover, temporary generators capable of supplying up to 14,000 kilowatts (19,000 horsepower) simultaneously were installed. During the winter months, most of this electricity was utilized to heat the exposed steel beams on the lower five floors.

Broadcast Signal Controversy

By late 1971, concerns had arisen among local residents and broadcasters that the Sears Tower's construction would interfere with television broadcasts. It was estimated that the building would obstruct television signals for 15 percent of Chicago's population and create "double images" for an additional 20 percent, particularly affecting communities to the northwest and southeast. In response to these concerns, Sears initiated research to mitigate the tower's impact on broadcast signals.

Despite the tower itself not being the sole cause of interference, as other shorter towers in the Loop also affected broadcast signals, the Illinois Citizens' Committee for Broadcasting filed a formal complaint with the Federal Communications Commission (FCC) in February 1972.

Legal battles ensued, with lawsuits filed by state and local authorities. While the construction of the tower continued, Sears applied for permission to increase the building's height limit by 350 feet (110 meters) and install a new antenna in April 1972. However, this plan faced criticism from eight of Chicago's ten television stations.

In May 1972, Judge LaVerne Dickson, Chief of the Lake County Circuit Court, dismissed one of the lawsuits, stating that television viewers did not have the right to reception without interference. The Lake County attorney appealed to the Illinois Supreme Court, which ultimately affirmed the rulings of the Lake and Cook County circuit courts. Despite these legal challenges, construction on the tower progressed. However, it was briefly halted in July 1972 due to a labor strike. The following month, Sears announced plans to install broadcast antennas on the tower's roof and offered financial assistance to relocate broadcast stations to the Sears Tower.

In September 1972, the United States Court of Appeals for the Seventh Circuit upheld the FCC's decision regarding the tower's height, and the United States Supreme Court declined to hear an appeal of this decision in November 1972. Work was temporarily paused once more in June 1973 due to another labor strike.

Topping-Out and Completion

The Sears Tower achieved the status of Chicago's tallest building in November 1972, surpassing the Standard Oil Building, which had held that record for a month. At this point, the construction project employed 1,600 workers in three shifts, with one worker having tragically lost their life during the project up to that point. The construction had been delayed considerably due to labor strikes and adverse weather conditions. By February 1973, concrete work had reached the 77th floor, while the steel superstructure had reached the 84th floor. The remaining steelwork posed challenges due to high winds at greater heights.

On May 3, 1973, the Sears Tower was officially topped out, although technically it was not yet complete, with three to four stories still remaining to be built. Following this ceremony, four workers tragically lost their lives in a fire in an elevator shaft one week later. Another worker fell from the tower in an unrelated incident four days after that.

In July 1973, Sears began moving furniture into the building, and by March 1974, three-quarters of the space in the tower was occupied. While Sears initially leased the upper stories to tenants such as Goldman Sachs, Northwest Industries, and Schiff Hardin, it became evident that the tower would not attract as many tenants as projected due to a surplus of office space in the 1980s. As a result, the tower remained partially vacant for a decade.

Renovation and Relocation

In February 1984, Sears announced plans to renovate the building, particularly focusing on the lower floors to attract visitors. At that time, more than half of the building was occupied by 6,500 Sears employees, spanning the lowest 48 stories. The remaining portion of the tower accommodated 5,500 employees from approximately 70 companies.

The renovation project, designed by SOM, involved covering the main entrance with a four-story glass dome and converting the first four stories into a shopping atrium. Additionally, a visitor center for the Skydeck observation area was constructed. These renovations were completed by mid-1985.

In 1988, Sears decided to sell the tower and relocate its merchandising division from the lower half of the building. Several potential buyers were considered, but challenges arose due to the large size of the lower stories, which made them unsuitable for many tenants.

In 1990, the law firm Keck, Mahin & Cate chose to move to 77 West Wacker Drive instead of staying in the Sears Tower. By 1995, Sears had begun moving its offices to a new campus in Hoffman Estates, Illinois.

Ownership Changes in the 21st Century

In March 2004, MetLife announced its intention to sell the building to a group of investors, including Joseph Chetrit, Joseph Moinian, Lloyd Goldman, Joseph Cayre, Jeffrey Feil, and American Landmark Properties. The sale was quoted at $840 million, with $825 million held as a mortgage. Subsequently, in February 2007, the owners secured a $780 million loan from UBS. At that time, UBS valued the tower at $1.2 billion. Throughout the 21st century, discussions took place regarding the possibility of constructing a hotel adjacent to the tower's north side. However, this plan was abandoned due to zoning restrictions. The naming rights to the building changed in March 2009 when London-based insurance broker Willis Group Holdings leased a portion of the tower and officially renamed it the Willis Tower on July 16, 2009. In 2011, the building's owners considered selling a partial ownership stake or the entire building to an investor. In the following year, United Airlines announced its corporate headquarters

Architectural Structure

The Willis Tower's architectural design involves a breakdown of its bundled tube structure, featuring simplified floor plans. This iconic skyscraper was conceived by architect Bruce Graham in collaboration with structural engineer Fazlur Rahman Khan, both of Skidmore, Owings and Merrill. Their innovative approach involved creating nine square "tubes," arranged in a 3x3 grid to form a square base with sides measuring 225 feet (69 meters). The total floor area of the building spans an impressive 3,787,200 square feet (351,800 square meters), designed to accommodate up to 16,500 employees.

Design and Facade

Each of these "tubes" represents a column-free module measuring 75 by 75 feet (23 by 23 meters), with setbacks at different levels. Notable setbacks occur at the 50th, 66th, and 90th floors. The lower 50 stories house nine tubes, each covering an area of 52,000 square feet (4,800 square meters). The northwest and southeast tubes conclude at the 50th floor, while the 51st through 66th floors span 41,420 square feet (3,848 square meters) each. From the 67th to the 90th floors, each level adopts a cross-shaped layout, covering 30,170 square feet (2,803 square meters). The north, east, and south tubes conclude at the 90th floor, while the remaining west and center tubes extend to 108 floors, each offering an area of 12,283 square feet (1,141.1 square meters) on the uppermost stories.

The Willis Tower is celebrated for being the pioneer of this groundbreaking tubular design, which not only maximized space but also proved to be cost-effective. Standing at a height of 1,450 feet, it surpassed the Empire State Building in height while being more economically efficient in terms of unit area. This design system greatly influenced the construction of supertall skyscrapers worldwide, including the Burj Khalifa, the current tallest building globally. Subsequently, in February 1982, the tower's height was increased to 1,707 feet with the addition of two television antennas, later extended to 1,729 feet in 2000 to enhance local NBC station WMAQ-TV reception.

The exterior structure of the Willis Tower features columns spaced at 15-foot intervals, supporting a facade crafted from anodized aluminum and black glass. Alcoa supplied 4 million pounds of aluminum sheeting for the building's facade. Notably, black bands are present on the tower's exterior around the 29th-32nd, 64th-65th, 88th-89th, and 104th-108th floors, serving as louvers to facilitate ventilation for the building's environmental systems while concealing its belted trusses. The majority of the facade comprises 16,000 rectangular windows, each measuring 5 by 8 feet and tinted with bronze.

Exterior Renovations

Originally, the building featured an 80,000-square-foot plaza made of pink granite. However, in the late 2010s, a three-level wing was constructed along the western and southern sides of the tower, replacing the plaza. This new addition includes a roof garden spanning 30,000 square feet. The annex's facade maintains a consistent aesthetic with the original structure, featuring black steel and aluminum. The Jackson Boulevard facade of the annex boasts an artwork titled "Atmospheric Wave Wall" by Olafur Eliasson, measuring 30 by 60 feet and comprised of nearly 2,000 blue-and-green steel tiles adorned with hexagonal motifs, which are backlit at night.

Structural and Mechanical Aspects

Internally, the Willis Tower incorporates 74,000 short tons of steel, 4 million pounds of aluminum, and 101 acres of concrete flooring. Notably, diagonal columns are only present on the two stories immediately below each of the setbacks to minimize shear stress. The absence of diagonal beams allowed for unobstructed connections between the "tubes," with columns and horizontal beams on each level connected by rigid joints. The superstructure is engineered to withstand wind gusts of up to 130 miles per hour, a rare event occurring once every century on average. Additionally, the building's top is designed to flex by up to 7 inches, returning to its original position within 7.2 seconds.

The foundation of the Willis Tower extends 50 feet deep and rests on a 5-foot-thick concrete slab. Given the clay composition of the ground directly beneath the building, caissons were employed during excavation, with 201 of them reaching the underlying limestone layer, situated as much as 100 feet below ground level. These caissons created holes measuring up to 10 feet across, which were later filled with steel tubes and concrete.

Safety and Mechanical Systems

During construction, considerations were made to enhance safety, including the incorporation of fire sprinkler systems on all floors, an unusual feature at the time. Approximately 40,000 sprinkler heads were installed at a cost of $4 million. The building also featured an electrical heating system, in contrast to older structures relying on gas heating. Other features included 145,000 light fixtures and a robust cooling system capable of 17,000 tons of refrigeration. Emergency systems, including fire suppression and communication systems, were powered by diesel generators. In the event of a fire, the smoke-detection system would close off fresh-air intake openings on the affected floor, expelling smoke outdoors.

Mechanical Infrastructure

Fifteen above-ground stories, along with three basement levels, house mechanical equipment. Above the renowned Skydeck on the 103rd floor, a seven-story mechanical penthouse is situated.

Elevators and Escalators

The Willis Tower was equipped with an extensive elevator and escalator system. A total of 103 elevators were planned, including 14 double-deck elevators. Of these, 97 elevator cabs served the office stories, utilizing 83 shafts due to the presence of double-deck elevators. Single-deck elevators connected the lobby to the lowest 28 stories, while double-deck elevators served "sky lobbies" at the 33rd/34th and 66th/67th floors, allowing passengers to transfer to local elevators. Local elevators served the 34th through 103rd floors. Additionally, two elevators provided direct access from the lobby to the Skydeck on the 103rd floor. As of 2018, these elevators transported approximately 5.8 million passengers annually.

Six of the elevators were designated for freight use, with one of them reaching a height of 1,440 feet and reserved for the Chicago Fire Department during emergencies. In case of fire or other emergencies, the remaining elevators could be controlled from the 33rd floor and dispatched to assist with evacuation. The building also featured 16 escalators, including double-height escalators connecting the main lobby to the lower mezzanine and a set of escalators between the 33rd and 34th stories.

Interior Layout

The base of the Willis Tower, as of 2022, covers 463,000 square feet and features two tenant lobbies. Tenants primarily enter from Wacker Drive and Franklin Street, while visitors to the Skydeck observation deck and other facilities utilize the southern entrance on Jackson Boulevard. Notably,

Willis Tower Skydeck

The Willis Tower's Skydeck, situated on the 103rd floor and soaring 1,353 feet (412.4 meters) above the ground, welcomed its first visitors on June 22, 1974. It stands as the highest observation deck in the United States and is one of Chicago's most iconic tourist destinations. Tourists can not only admire breathtaking views but also feel the building sway in the wind, gazing far across the Illinois plains and Lake Michigan, encompassing Indiana, Michigan, and Wisconsin on clear days. The high-speed elevators whisk visitors to the top in just under a minute, providing a unique experience of changing air pressure during the ascent. As of 2018, approximately 1.7 million tourists visit the Skydeck annually. Additionally, the 99th floor hosts an event venue.

Buy Tickets for Willis Tower Skydeck

In January 2009, a significant renovation of the Skydeck commenced, featuring the installation of retractable glass balconies extending about 4 feet (1.2 meters) from the 103rd-floor facade, offering an exhilarating view of South Wacker Drive below. These all-glass boxes, affectionately known as "The Ledge," opened to the public on July 2, 2009. An incident occurred on May 29, 2014, when the laminated glass flooring of one of the boxes cracked with visitors inside, but fortunately, there were no injuries. A similar incident took place on June 12, 2019, involving the same box. In May 2022, a fifth glass ledge was introduced on the west side, providing yet another stunning vantage point overlooking South Wacker Drive.

When the Sears Tower was initially completed, it held the title of the world's tallest building, although Toronto's CN Tower surpassed it in height by approximately 350 feet (106.7 meters). However, the Council on Tall Buildings and Urban Habitat (CTBUH) did not categorize the CN Tower as a building due to the absence of floors from the ground up. To this day, the Willis Tower remains the third tallest building in the Americas and the Western Hemisphere, following One World Trade Center and Central Park Tower in New York City. It stands as the third-tallest freestanding structure in the Americas, with a pinnacle height of 1,729 feet (527 meters), ranking as the 16th-tallest freestanding structure globally based on pinnacle height.

In 1998, when the Petronas Twin Towers in Kuala Lumpur, Malaysia, were completed, they claimed the title of the world's tallest building, measuring 1,482.6 feet (451.9 meters) in height, including decorative spires. This sparked a debate among Chicagoans, asserting that the Sears Tower's top floor was higher than that of the Petronas Towers. Consequently, four categories of "tallest building" were established. Taipei 101 in Taiwan subsequently claimed the record in three of the four categories in 2004, surpassing the Petronas Twin Towers in spire height and the Sears Tower in roof height and highest occupied floor. Suggestions were made to add cosmetic enhancements atop the Sears Tower to surpass Taipei 101, but this proposal was not realized. On August 12, 2007, the Burj Khalifa in Dubai reportedly surpassed the Sears Tower in all height categories. One World Trade Center in New York City also exceeded the Willis Tower in structural and pinnacle heights upon its completion, albeit not in roof height, observation deck elevation, or highest occupied floor.

Until 2000, the Sears Tower did not hold the record for the tallest building by pinnacle height. From 1969 to 1978, the John Hancock Center (175 East Delaware Entrance For Residential) claimed this record, with its antenna reaching a height of 1,500 feet (457.2 meters), surpassing the original height of the Sears Tower by 49 feet (14.9 meters). One World Trade Center eventually surpassed it in pinnacle height with the addition of a 359-foot (109.4-meter) antenna, bringing its total height to 1,727 feet (526.4 meters). In 1982, two antennas were installed, increasing its height to 1,707 feet (520.3 meters), surpassing the John Hancock Center but still trailing One World Trade Center. However, a further extension of the western antenna in June 2000 brought the Sears Tower's height to 1,729 feet (527 meters), allowing it to claim the title of the tallest building by pinnacle height. It's worth noting that the lowest level of the Willis Tower is situated 43 feet (13 meters) below the elevation of Franklin Street.

In a notable event on May 25, 1981, Dan Goodwin, dressed in a homemade Spider-Man suit equipped with suction cups, camming devices, and sky hooks, successfully made the first outside ascent of the tower. Despite several attempts by the Chicago Fire Department to stop him, he reached the top after a seven-hour climb and was subsequently arrested and charged with trespassing. Goodwin's climb aimed to draw attention to the shortcomings in high-rise rescue and firefighting techniques. Following a thorough interrogation by Chicago's District Attorney and Fire Commissioner, Goodwin was officially released from custody.

In August 1999, French urban climber Alain "Spiderman" Robert scaled the building's exterior glass and steel wall all the way to the top, using only his bare hands and feet. His daring ascent was complicated by thick fog near the end of the climb, making the last 20 stories of the building's glass and steel exterior slippery. Since 2009, the Willis Tower has annually hosted SkyRise Chicago, the world's tallest indoor stair climb, as a charity event benefiting Shirley Ryan AbilityLab. Participants are allowed to climb the Willis Tower's 103-story staircase legally as part of this event.

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