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Willis Tower

From Alfawiki
Willis Tower
Company typeOffice skyscraper
IndustryCommercial real estate
Founded1973; 53 years ago (1973)
Headquarters
Chicago
,
United States
Key people
Bruce Graham (architect), Fazlur Rahman Khan (structural engineer)
ProductsOffice space, observation deck (Skydeck)

Willis Tower Overview

The Willis Tower, widely still recognized by its former name Sears Tower, stands as a 110-story skyscraper reaching 1,451-foot (442.3 m) located in Chicago's Loop district in Illinois, USA. This iconic structure was designed by architect Bruce Graham and structural engineer Fazlur Rahman Khan of the renowned firm Skidmore, Owings & Merrill (SOM). Upon its completion in 1973, it claimed the title of the world's tallest building, maintaining this distinction for nearly a quarter-century. Today, it ranks as the third tallest building in the Western Hemisphere and holds the position of the 23rd tallest globally. The Skydeck observation area attracts over 1.7 million visitors annually, making it one of Chicago’s premier attractions.[1]

Situated on a block bordered by Franklin Street, Jackson Boulevard, Wacker Drive, and Adams Street, the design features nine square-shaped "tubes" arranged in a 3×3 grid pattern, with seven tubes stepping back at higher levels. While standard floor counting lists 108 stories, the building's management counts the main roof as floor 109 and includes a mechanical penthouse roof as floor 110.[2][3] The exterior is composed of black glass panels combined with anodized aluminum. At its base lies a retail area known as the Catalog. Initially, Sears occupied the lower half of the tower as its headquarters until 1994, while leasing out upper floors.

Originally known as the Sears Tower from its inception until 2009, the building adopted its current name following a naming rights agreement with the Willis Group. Despite this change, many locals continue to refer to it by its original name.[4] As of April 2018, United Airlines is the building’s largest occupant, leasing approximately 20 floors.[5][6][7] Other significant tenants include Willis Towers Watson, which lends its name to the building; law firms such as ArentFox Schiff and Seyfarth Shaw; and Morgan Stanley, which became the fourth-largest tenant in 2017.[7][8]

Site selection

Since 1906, Sears, Roebuck & Co. had maintained offices in a complex located on Chicago's west side. By 1966, these facilities no longer met the company's needs, prompting Sears leadership to initiate a search for a new headquarters location. By 1969, Sears had grown to become the world's largest retailer, employing approximately 350,000 people. Relocating the headquarters to a suburban area was deemed impractical due to the necessity of moving around 7,000 staff members. Consequently, Sears opted to centralize its numerous employees, previously scattered across various Chicago offices, into a single building situated on the western edge of Chicago's Loop.

The company enlisted its legal advisors, Arnstein, Gluck, Weitzenfeld & Minow (currently known as Saul Ewing LLP), to recommend potential sites. After consulting with governmental agencies and reviewing relevant regulations, the firm presented two alternatives. The first was located on Goose Island northwest of the Loop; however, this option was dismissed by Sears’s vice president of real estate, Matthew J. Stacom. The second choice was a two-block parcel within the Loop bordered by Franklin Street to the east, Jackson Boulevard to the south, Wacker Drive on the west, and Adams Street to the north. Although more centrally positioned, this site was relatively compact at approximately 55,000 square feet. Over the previous five years, Bernard Feinberg, Albert I. Rubenstein, and Philip Teinowitz had gathered most of this property but had been unable to secure an adjacent 74,000-square-foot lot owned by Greyhound Lines.

Feinberg, Rubenstein, and Teinowitz then acquired options on three neighboring lots with the condition that failure to purchase at least one within 90 days would result in forfeiture of all options. Ultimately, Sears completed acquisition of the Loop site in 1970. Following this purchase, Sears obtained authorization to close a block of Quincy Street that divided the property east-to-west. Legal representatives from Arnstein’s firm, led by Andrew Adsit, proceeded with purchasing individual parcels piece by piece. In total, Sears bought 15 buildings from about 100 different owners and compensated the City of Chicago $2.7 million (equivalent to an inflation-adjusted sum) for closing Quincy Street through that block.

Design process

Sears leadership projected that their new headquarters would require approximately 4.2 million square feet (390,000 m2), distributed across either 70 floors with 60,000 square feet (5,600 m2) per level or 60 floors with 70,000 square feet (6,500 m2) each. The company engaged the architectural firm Skidmore, Owings & Merrill (SOM) to create the tower’s design. SOM also took on the role of principal structural engineer, while Jaros, Baum & Bolles handled the mechanical, electrical, and plumbing engineering aspects.

Initially, Sears intended to relocate its merchandise division into the building and lease out any additional space until further expansion was necessary. While Sears executives favored expansive floor plates of at least 100,000 square feet (9,300 m2), SOM architects expressed concerns that such large areas might not appeal to smaller tenants. An alternative concept featured two separate towers connected by a skybridge, offering floor sizes of 50,000 square feet (4,600 m2) and 30,000 square feet (2,800 m2), respectively; however, this configuration proved impractical.

To attract a wider range of renters, some floors were designed with reduced footprints, which necessitated increasing the building’s overall height to satisfy Sears's total floor area requirements. Partners Bruce Graham and structural engineer Fazlur Rahman Khan of SOM proposed a design featuring 55,000-square-foot (5,100 m2) floor plates in the lower portion of the tower, combined with a series of setbacks that gradually reduced floor size toward the top—resulting in the iconic stepped profile. During the design phase, it is said that one architect arranged nine cigars vertically to illustrate the setbacks until both agreed on the final layout. This design allowed Sears to occupy the larger lower floors while providing more conventional office spaces above for leasing.

The firm Saphier, Lerner, Schindler was responsible for defining Sears's spatial needs and designing custom furnishings. They conducted an extensive year-long study to optimize the layout for 16 departments within the company.

As Sears maintained optimistic forecasts for growth, plans for the tower’s height continued to escalate. Although Chicago’s zoning regulations were relatively permissive—allowing for a theoretical building up to 300 stories with 13.5 million square feet (1,250,000 m2)—most prospective tenants preferred not to occupy excessively tall office spaces. Moreover, the Federal Aviation Administration (FAA) imposed restrictions on building heights in the vicinity to safeguard air traffic operations. While FAA representatives publicly denied setting explicit height limits, any increase beyond a certain point would have required raising the area's minimum safe altitude by approximately 1,000 feet (300 m) for each additional foot of building height.

The tower’s plans were officially unveiled on July 27, 1970. The proposed structure would rise about 1,450-foot-tall (440 m), encompassing 109 stories as measured from Wacker Drive and 110 stories from Franklin Street. This design would establish Sears Tower as the tallest building worldwide by roof height, although New York City’s then-under-construction World Trade Center Twin Towers would surpass it in antenna height. The total floor area was planned at roughly 4.4 million square feet (410,000 m2), with approximately 3.7 million square feet (340,000 m2) allocated specifically for office use.

Initial Construction Phase

File:Sears Willis Tower.jpg
The Sears Tower (currently known as the Willis Tower) under construction in 1973

Foundation work began in August 1970, with contractors excavating the site to a depth of 50 feet (15 m) and removing approximately 180,000 cubic feet (5,100 m3) of soil.[9] By November of that year, Spencer, White & Prentis Inc. was engaged in digging a trench around the perimeter, which was 60 feet (18 m) deep and measured 20 by 216 feet (6.1 by 65.8 m). Within this trench, a slurry wall composed of concrete and reinforced steel was constructed.[10] Steel supports were installed to prevent the slurry wall from collapsing inward, while caissons were used to drill 201 holes into the ground. Additionally, a sewer located beneath Quincy Street—planned to be permanently closed for the tower's construction—was rerouted.[9]

The Diesel Construction Company served as the general contractor for the Sears Tower project.[11] On June 7, 1971, Sears, Roebuck & Co. chairman Gordon M. Metcalf ceremoniously placed the first steel beam.[12][13] The workforce comprised roughly 2,000 employees. To expedite progress, a concrete plant was established in the tower's basement, enabling crews to pour about one-third of a concrete floor daily. Two temporary kitchens were set up on-site for workers’ convenience, and communication systems including telephones and loudspeakers were installed on every level. Temporary generators capable of supplying up to 14,000 kilowatts (19,000 hp) were also implemented; during colder months, much of this power was dedicated to heating exposed steel beams on the lowest five floors.[14]

Broadcast Signal Dispute

By late 1971, concerns emerged among Chicagoland residents and broadcasters regarding potential interference with television signals caused by the new Sears Tower.[15][16] Estimates suggested that approximately 15 percent of Chicago’s population might experience blocked TV signals and another 20 percent could encounter "double images," primarily affecting areas northwest and southeast of downtown.[15][16] That same year, officials from Skokie, a suburb northwest of Chicago, threatened legal action seeking an injunction to halt further construction.[17][18] In response, Sears initiated research into solutions aimed at minimizing the building’s impact on broadcast transmissions. According to Variety magazine, the Sears Tower itself was not uniquely disruptive since several shorter towers within the Loop also caused signal interference.[19] Nevertheless, in February 1972, the Illinois Citizens' Committee for Broadcasting formally lodged a complaint with the Federal Communications Commission (FCC).[20]Cite error: The opening <ref> tag is malformed or has a bad name

The first lawsuit addressing these issues was filed by Lake County’s state attorney on March 17, 1972.[21][22] Shortly thereafter, on March 28, Skokie along with Northbrook and Deerfield filed a second suit in Cook County Circuit Court.[22][23] Sears moved to dismiss both lawsuits—which sought to limit the tower’s height to 67 stories—and explored installing antennas atop the building in April 1972.Cite error: The opening <ref> tag is malformed or has a bad name[23] Despite ongoing litigation delays, construction proceeded.[24] Later that month, Sears requested authorization to increase the tower’s height by 350 feet (110 m) and add a new antenna,[25][26] although eight out of ten Chicago television stations opposed this proposal.[27][28] On May 17, 1972, Chief Judge LaVerne Dickson of Lake County Circuit Court dismissed the suit, ruling that viewers did not possess a legal right to interference-free reception.[29] By then, construction had reached the 58th floor.[30] The Lake County attorney appealed to the Illinois Supreme Court.[30] On June 12, Judge Charles R. Barrett upheld prior decisions stating that plaintiffs had no entitlement to perfect television reception.[31]

Meanwhile, the FCC declined involvement in the height dispute citing lack of jurisdiction.[32] The FAA gave approval for antennas atop the tower in June 1972,Cite error: The opening <ref> tag is malformed or has a bad nameCite error: The opening <ref> tag is malformed or has a bad name and later that month the Illinois Supreme Court affirmed earlier rulings from Lake and Cook County courts.Cite error: The opening <ref> tag is malformed or has a bad name Construction was temporarily suspended in July due to a labor strike.Cite error: The opening <ref> tag is malformed or has a bad name In August, Sears officially announced plans for broadcast antennas on the roof and pledged $5 million (equivalent to $Template:Formatprice in Template:Inflation/year)Template:Inflation/fn toward relocating broadcast stations to the tower.[33][34] The United States Court of Appeals for the Seventh Circuit upheld the FCC’s decision in September,Cite error: The opening <ref> tag is malformed or has a bad name and later that year in November, the United States Supreme Court declined to hear an appeal against this ruling.[35][36]

Topping-out and completion

In November 1972, the Sears Tower claimed the title of Chicago's tallest structure,[37] overtaking the Standard Oil Building, which had held this distinction for just one month.[38] At that stage, approximately 1,600 laborers were engaged on the Sears project across three shifts; there had been one fatality during construction to that point.[11][37] The building’s finalization faced considerable delays caused by labor disputes and adverse weather conditions. Concrete placement had advanced to the 77th floor, while steel erection reached the 84th floor; completing the remaining steel framework was challenging due to strong winds at higher elevations.[37] Local broadcasters WTTW and WLS-TV planned to install provisional transmission antennas atop the tower once the steel skeleton was finished.[39] By February 1973, the superstructure had ascended to the 100th floor, surpassing the height of New York City's Empire State Building.[40]

The tower was officially topped out on May 3, 1973.[41] On the eve of this milestone, the Chicago Tribune editorial board remarked: "Step aside, New York. Starting tomorrow, when children envision towering buildings, their thoughts will shift from you and landmarks like the Empire State Building and World Trade Center."[42] However, the structural frame was not entirely finished as three to four floors remained incomplete.[43] Tragically, one week following the topping-out ceremony, a fire in an elevator shaft resulted in four worker fatalities.[43][44] Four days later, an unrelated accident caused a fifth worker to die after falling from the building.[45] Construction ceased once more in June due to another labor strike,[46][47] while Sears began relocating office furniture into the building during that same month.[48] The total expenditure for construction was approximately US$150 million,[49] (equivalent to $Template:Format price adjusted for inflation).Template:Inflation-fn Despite its vast scale, Sears officials indicated that the building lacked sufficient space to host their annual shareholder meetings; thus they continued leasing facilities elsewhere.[50]

Inauguration and Initial Period

During the weekend of September 9, 1973, the initial group of Sears personnel began relocating into the tower.[48][51] That same month, the building’s rooftop became home to Chicago’s first-ever flashing beacons.[52] With the tower’s debut, broadcasters located at Chicago’s second-tallest structure, the John Hancock Center, faced the decision of whether to move operations to the new Sears Tower.[53] Two television stations opted to transfer their facilities.[54] Meanwhile, six other broadcasters chose to remain at the John Hancock Center, referencing a study that indicated a relocation would yield only marginal advantages.[54][55] Late-1973 documents revealed that the Sears Tower generated significantly more signal interference than either Sears or the broadcasters had initially disclosed.[55] In February 1974, WLS-TV relocated its transmission to the Sears Tower,[56] followed by WTTW in March.[57]

By March of that year, approximately seventy-five percent of the building’s floors were leased; Sears had rented out upper levels to firms including Goldman Sachs, Northwest Industries, and Schiff Hardin.[58] In October 1974, a mobile sculpture crafted by Alexander Calder was unveiled in the lobby.[59][60] Despite optimistic forecasts for expansion by Sears, the company announced layoffs of around five hundred employees—roughly seven percent of its workforce of seven thousand stationed at the tower—in late 1974.[61] Beyond traditional competitors like Montgomery Ward, new retail powerhouses such as Kmart, Kohl's, and Walmart emerged. The surplus office space that developed during the 1980s resulted in lower-than-expected tenant occupancy rates for the tower, leaving it partially vacant for approximately ten years.

Renovation and relocation

File:6 102778 Sears Tower.jpg
The tower in 1978, shortly after completion

In February 1984, Sears declared plans to refurbish the building in order to boost foot traffic on its lower levels.[62][63] At that time, over half of the tower was occupied by approximately 6,500 Sears employees,[63][64] who were housed within the bottom 48 floors.[64] The remaining upper floors accommodated around 5,500 staff working for nearly 70 different firms.[63] The renovation included installing a four-story glass dome over the main entrance and transforming the first four floors into a retail atrium. Additionally, a visitor center for the building’s Skydeck was added.[62][63] These improvements, designed by SOM, reached completion by mid-1985.[64] Paul Gapp of the Chicago Tribune commented that SOM had "skillfully proportioned the new entrance to complement the building’s towering height," and noted that the updated atrium "alleviated the previously confined atmosphere just inside the Franklin entrance".[65]

In 1988, Sears announced intentions to sell the tower and relocate its merchandising division from the lower half of the premises.[66] The company aimed to generate at least $1 billion through this sale and offered several incentives to attract buyers, including a commitment to continue leasing the lower floors until new tenants were secured.[67] By July 1989, negotiations were underway with four major corporations interested in purchasing the building.[68] Challenges in finding a buyer arose partly because many potential tenants found the size of the lower floors excessive.[69] A near-sale to Canadian firm Olympia & York fell through in September 1989 due to disagreements over responsibility for property taxes.[70] Subsequently, in November 1989, Sears opted to refinance rather than sell the tower.[71] In 1990, Sears secured an $850 million mortgage loan from MetLife and AEW Capital Management, with MetLife holding the mortgage note; this loan was scheduled to mature in 2005.[72]

The law firm Keck, Mahin & Cate chose in 1990 to relocate to what would become 77 West Wacker Drive, declining Sears’ efforts to retain them.Cite error: The opening <ref> tag is malformed or has a bad name Two years later, Sears began moving its own operations out of the tower to a newly constructed campus in Hoffman Estates, Illinois, which was completed in 1995.[72] As the mortgage maturity approached, Sears renegotiated terms in 1994. The revised agreement relieved Sears of direct responsibility for the $850 million loan and reduced its ownership status to nominal only, while AEW and MetLife gained effective control. Under this arrangement, AEW and MetLife were entitled to assume formal ownership by 2003.[72] In 1997, Toronto-based TrizecHahn, then lessee of the CN Tower, purchased AEW’s stake for $110 million, taking on $4 million in liabilities along with a $734 million mortgage.Cite error: The opening <ref> tag is malformed or has a bad nameCite error: The opening <ref> tag is malformed or has a bad name

21st century

Trizec initially anticipated that the Sears Tower's value would rapidly climb to $1 billion. However, these expectations were not realized, as the building continued to struggle with vacancy and other challenges reminiscent of those experienced during Sears' tenure. Despite this, Trizec achieved moderate success in securing new tenants. In the aftermath of the September 11 attacks, two major occupants, Goldman Sachs and Merrill Lynch, promptly revealed plans to vacate approximately 300,000 ft2 of office space. By 2003, Trizec divested its ownership stake in the tower, selling it to MetLife for $9 million.

Syndicate ownership

In March 2004, MetLife declared its intention to transfer ownership of the building to a consortium of investors,[73] including New York-based individuals Joseph Chetrit, Joseph Moinian, Lloyd Goldman, Joseph Cayre, and Jeffrey Feil, alongside American Landmark Properties from Skokie, Illinois.Cite error: The opening <ref> tag is malformed or has a bad name The transaction was reported at $840 million, secured by an $825 million mortgage.Cite error: The opening <ref> tag is malformed or has a bad name Two years later, in February 2007, the owners refinanced with a $780 million loan from UBS,[74] which appraised the tower at $1.2 billion.[75]

File:Willis Tower night 2.jpg
The tower illuminated at night in 2009

Starting in 2007, plans were explored to develop a hotel on the north side of Jackson Boulevard—situated between Wacker Drive and Franklin Street—near the observation deck entrance and above the underground parking structure. The owners indicated that this second structure had been part of the original architectural concept. Nonetheless, the project was ultimately abandoned due to zoning restrictions that prohibited erecting a building of such height at that location.Cite error: The opening <ref> tag is malformed or has a bad name In February 2009, consideration was given to repainting the tower silver as part of a rebranding effort aimed at emphasizing its energy efficiency improvements; however, this proposal was later dropped. The repainting was projected to cost around $50 million.

Although Sears' naming rights expired in 2003, the skyscraper continued to be referred to as the Sears Tower for several years despite ownership changes. In March 2009, London-based insurance firm Willis Group Holdings secured leasing space within the building and acquired its naming rights.Cite error: The opening <ref> tag is malformed or has a bad nameCite error: The opening <ref> tag is malformed or has a bad name The official renaming to Willis Tower took place on July 16, 2009.[76][77] By 2011, discussions were underway among the owners about potentially selling part or all of their stake in the building to an investor.[78] The following year, United Airlines announced plans to relocate its corporate headquarters from 77 West Wacker Drive to Willis Tower.[5]

Blackstone ownership

In March 2015, the Willis Tower was listed for sale with an asking price of $1.5 billion. During that same month, the Blackstone Group acquired the skyscraper for approximately $1.3 billion, marking the highest transaction amount ever recorded for a property in the United States outside New York City. In January 2017, Blackstone revealed plans for a $500 million renovation project that included developing the Catalog, a six-story commercial structure that would replace the existing plaza on Jackson Boulevard and the entrance on Wacker Drive. The architectural firm Gensler was commissioned to design this overhaul. Enhancements featured a rooftop terrace atop the Catalog and a comprehensive upgrade of the building’s HVAC systems. Additionally, most elevators—except those serving the Skydeck—underwent modernization for the first time in the tower’s history; these new elevators operate faster and consume 35 percent less energy. The owners also incorporated artwork by artists such as Olafur Eliasson and Jacob Hashimoto throughout the building.

To finance these improvements, Blackstone secured a $1 billion loan in February 2017 from a consortium of banks including Goldman Sachs, replacing $750 million of maturing CMBS debt. Due to rising renovation expenses, Blackstone refinanced in 2018 with a new $1.3 billion loan provided by Deutsche Bank and Barclays. Early that year, the "Lunchbox" entrance on Wacker Drive was demolished to make way for the Catalog development. A steel globe sculpture adjacent to this entrance, originally installed in 2010 by the Poblocki Sign Company, was relocated to Elmhurst, Illinois. In June 2018, a 40,000-square-foot private club opened on the 66th and 67th floors, featuring tenant-exclusive venues such as the Craftsman restaurant and Frame lounge, alongside a public dining option called the East Room. Later that September, Urbanspace announced plans to operate a food hall within the building’s lower levels.

In 2020, insurance firm Aon proposed acquiring Willis Towers Watson, which had succeeded the Willis Group as owner of the tower, spurring speculation about yet another potential name change for the building. However, this merger was abandoned in 2021 after an antitrust lawsuit filed by the United States Department of Justice. The extensive renovation concluded in May 2022. At that time, although nearly 85 percent of Willis Tower’s space was leased, both tenant occupancy and visitor numbers had declined considerably since 2019, partly due to impacts from the COVID-19 pandemic in Chicago. In April 2023, The New York Times reported that Blackstone had written down its investment in Willis Tower by $119 million.

Incidents

In June 2006, the FBI apprehended seven individuals who faced charges related to a conspiracy aimed at demolishing the tower. Deputy FBI Director John Pistole characterized their scheme as "more aspirational than operational". The legal proceedings commenced in October 2007. Following three trials, five defendants were found guilty while two were acquitted. The group's purported ringleader, Narseal Batiste, received a prison sentence of thirteen and a half years. Due to concerns stemming from this threat, the building’s largest occupant at the time, Ernst & Young, relocated to North Wacker Drive in early 2009.

In May 2020, intense rainfall led to flooding across three basement levels, causing a power outage within the building. This disruption also affected numerous television and radio broadcasters, taking many stations off the air.

Architecture

File:Willis Tower tube structure.svg
Simplified floor plans illustrating the bundled tube design of Willis Tower

The Willis Tower’s design was crafted by architect Bruce Graham along with structural engineer Fazlur Rahman Khan from Skidmore, Owings and Merrill. Their concept involved nine square "tubes" arranged in a 3×3 grid, creating a square footprint with sides measuring 225-foot (69 m). The building offers approximately 3,810,000 sq ft (354,000 m2) of leasable space and was constructed to support a workforce of 16,500 employees.

Form and facade

The building's "tubes" consist of column-free units each measuring 75 by 75 feet (23 by 23 m),[79] which step back at various floors.[80] Specifically, setbacks occur at the 50th, 66th, and 90th levels.[60][81] The lowest section, encompassing the first 50 floors, includes nine tubes with each covering approximately 52,000 square feet (4,800 m2).[82][83][84] At the 50th floor, the northwest and southeast tubes conclude. Floors 51 through 66 span roughly 41,420 square feet (3,848 m2), where the northeast and southwest tubes end. Between the 67th and 90th floors, the floor plan takes a cross shape with an area of about 30,170 square feet (2,803 m2). The north, east, and south tubes terminate at floor 90; meanwhile, the west and central tubes extend up to the full height of 108 stories, with the uppermost floors covering around 12,283 square feet (1,141.1 m2) each.[82]

File:FR khan sculputure at Sears tower.jpg
A sculpture honoring Fazlur Rahman Khan, regarded as the pioneer of tubular structural designs, located at Willis Tower. Khan made significant contributions to skyscraper engineering advancements.

This pioneering tubular design was first implemented in the Sears Tower. It combined structural efficiency with cost-effectiveness: standing at 1,450 feet, it offered more usable space and surpassed the height of the Empire State Building while costing significantly less per square foot.[85] This structural system has since become highly influential in skyscraper construction and has been adopted in most supertall structures worldwide, including the current tallest building, the Burj Khalifa.[86][87] In February 1982, two television antennas were installed atop the structure, increasing its height to 1,707 feet (520.3 m). Subsequently, on June 5, 2000, the western antenna was extended further to reach a total height of 1,729 feet (527.0 m), enhancing signal reception for local NBC affiliate WMAQ-TV.[2]

Columns spaced at 15 feet (4.6 m) intervals run along the perimeter of Willis Tower. Its exterior facade consists of anodized aluminum paired with black glass.[60][81] The aluminum sheeting used for cladding—totaling approximately four million pounds—was produced by Alcoa.[88] Distinct black bands encircle the tower between floors 29–32, 64–65, 88–89, and 104–108; these are louvers designed to ventilate mechanical systems and conceal the building's belt trusses.[89] The remainder of the facade is composed of roughly sixteen thousand rectangular bronze-tinted windows,[90][91] each measuring 5 by 8 feet (1.5 by 2.4 m).[91]

Originally surrounding the tower was an 80,000 square feet (7,400 m2) plaza paved with pink granite.[90] However, during the late 2010s, this plaza was replaced by a three-story annex extending along the western and southern facades. The rooftop garden atop this addition covers an area of approximately 30,000 square feet (2,800 m2).[92][93] The annex’s exterior continues the theme of black steel combined with aluminum cladding consistent with the original structure.[92] On its Jackson Boulevard side is an art installation by Olafur Eliasson titled Atmospheric wave wall.[94][95] This artwork spans roughly 30 by 60 feet (9.1 by 18.3 m)[94] and features nearly two thousand blue-green steel tiles adorned with hexagonal patterns.[95][96] The installation is illuminated from behind during nighttime hours.[94][95]

Structural and Mechanical Characteristics

The building's interior framework comprises approximately 74,000 short tons of steel, 4 million pounds of aluminum, and concrete flooring covering about 101 acres (or 409,000 square meters). Diagonal columns are present solely on the two floors directly beneath each setback, a design choice that helps minimize shear forces. Due to the need to maintain unobstructed connections between the building's "tubes," diagonal beams were not incorporated inside; instead, the vertical columns and horizontal beams on every floor are joined with rigid connections. The superstructure is engineered to endure wind gusts reaching speeds of up to 130 miles per hour, an event statistically expected once every century. According to the Chicago Tribune, the tower's pinnacle can flex up to 7 inches and will return to its original position within approximately 7.2 seconds.

The Willis Tower’s foundation plunges about 50 feet underground, supported by a concrete slab roughly 5 feet thick. The subsurface soil primarily consists of clay, with a limestone bedrock located as deep as 100 feet below ground level. To establish a stable base, construction involved excavating 201 caissons, of which 114 extended down to the limestone layer. These caissons created holes measuring up to 10 feet in diameter; some located at the northwestern and northeastern corners accumulated groundwater and required drainage. Steel tubes were then inserted into these excavations before being encased in concrete.

During the Sears Tower's development, SOM architects and Chicago officials explored innovative safety features such as designated "smoke free and fire free" zones and installing a comprehensive sprinkler system throughout all floors—both unprecedented in Chicago buildings at that time. Although fire sprinkler systems were not mandated by regulations, one was installed from the outset, comprising approximately 40,000 sprinkler heads at an investment of $4 million. Upon completion, the tower utilized electric heating rather than the gas heating typical of older buildings. It also featured around 145,000 light fixtures and a refrigeration system with a capacity of 17,000 tons. Additionally, emergency fire-suppression and communication systems powered by diesel generators were integrated into the design. In case of fire in any section, the smoke-detection system would automatically shut off fresh-air intakes in that area to vent smoke outside.

Mechanical equipment is housed within fifteen stories above ground as well as three basement levels. Above the Skydeck on the 103rd floor lies a mechanical penthouse spanning seven stories.

Elevators and escalators

The Sears Tower was originally designed to include 103 elevators, among which were 14 double-deck elevators. Out of these, 97 elevator cabs service the office floors, utilizing 83 shafts due to the incorporation of double-deck systems. The design featured a bank of single-deck elevators providing access from the lobby to the lower 28 floors. Meanwhile, double-deck elevators connected the lobby to "sky lobbies" located on the 33rd/34th and 66th/67th levels, where passengers could switch to local elevators that serve floors 34 through 103. Additionally, two elevators offered direct travel from the lobby to the Skydeck on the 103rd floor. As of 2018, these elevators accommodated approximately 5.8 million riders annually.

Freight transportation within the building is managed by six dedicated elevators, one of which services all levels up to a height of 1440 feet. In emergency situations such as fires, this particular freight elevator is reserved exclusively for use by the Chicago Fire Department. Elevator operations during emergencies are coordinated from the 33rd floor, with specific elevators dispatched to affected floors to facilitate evacuation.

The building also housed a total of 16 escalators, including a distinctive set of double-height escalators running from the main lobby down to the lower mezzanine. Another pair of escalators connects the 33rd and 34th floors.

Base

File:Base of the Willis Tower (2021).jpg
Bottom of the tower

Upon completion, the primary entrance was situated on Wacker Drive to the west side. A plaza extended along the south side, rising gently towards Franklin Street on the east. Since Franklin Street's elevation is approximately 6 feet lower than that of Wacker Drive, entrances on Franklin actually lead below the plaza level into the building’s lower mezzanine. Beneath ground level lie three basement floors encompassing roughly 400,000 square feet. These subterranean levels include a cafeteria with seating for 1,200 patrons, retail spaces, service areas, and a loading dock capable of accommodating up to 17 trucks. There is also a parking garage in the basement with space for about 150 vehicles.

As of 2022, the building’s base occupies approximately 463,000 square feet and features two tenant lobbies. Most tenants enter through entrances on Wacker Drive and Franklin Street, while visitors heading to retail shops, restaurants, or the Skydeck observation deck typically use the southern entrance on Jackson Boulevard. The Wacker Drive lobby showcases In the Heart of this Infinite Particle of Galactic Dust, an art installation created in 2019 by Jacob Hashimoto consisting of more than 7,000 rice-paper and resin disks suspended from the ceiling. To recognize Fazlur Khan’s pivotal role in skyscraper engineering design, the Structural Engineers Association of Illinois commissioned a sculpture honoring him for display in this lobby.

The commercial area occupying the building’s lowest floors is called the Catalog—a nod to Sears’ historic mail-order catalogs. This six-story retail complex contains numerous dining establishments and extends across three basement levels as well as into a three-story annex located south and west of the tower. The annex’s roof features a curved skylight made up of 240 glass panes; its northern portion is supported by black columns reminiscent of those found in the original tower structure. The Catalog includes architectural details inspired by Chicago’s urban landscape, such as handrails and stair landings reflecting local design elements. On its third floor, this complex houses a coworking space spanning approximately 30,000 square feet operated by Convene.

Skydeck

File:Willis tower skyboxes (1).jpg
Four transparent-bottom skyboxes attached to the west side of Willis Tower on the 103rd floor
File:Willis Tower glass box.jpg
Glass balcony featured at the Skydeck

The observation platform of Willis Tower, known as the Skydeck, began welcoming visitors on June 22, 1974. Situated on the 103rd floor, at an elevation of 1,353 feet (412.4 m) above street level, it stands as the tallest observation deck within the United States and ranks among Chicago’s most iconic attractions. Visitors have the opportunity to observe the building’s movement caused by wind and enjoy expansive views stretching across Illinois’ plains and over Lake Michigan to neighboring states such as Indiana, Michigan, and Wisconsin on clear days. Elevators transport guests to the summit in roughly one minute, during which they can perceive atmospheric pressure changes. Approximately 1.7 million people visit this site annually as of 2018. The venue also hosts an event space located on the 99th floor.

In January 2009, a significant upgrade of the Skydeck commenced, introducing retractable glass balconies that protrude about 4 feet (1.2 m) from the 103rd-floor exterior, overlooking South Wacker Drive. These fully transparent boxes, commonly referred to as "The Ledge," provide visitors with a view directly down to the street below. Designed to hold up to 5 short tons (4.5 metric tons), these glass extensions opened for public access on July 2, 2009. On May 29, 2014, one of these laminated glass floors developed a crack while occupied by guests; fortunately, no injuries occurred. The same glass panel experienced another fracture on June 12, 2019. A fifth glass ledge was introduced in May 2022 along the west facade facing South Wacker Drive.

File:WillisTowerPanorama01.jpg
Panoramic view of Chicago’s skyline from Willis Tower Skydeck

Height

File:Dubai-CN-Sears-towers.svg
Height comparison featuring (from left to right) Burj Khalifa, Dubai; CN Tower, Toronto; Willis Tower, Chicago

Upon its completion, the Sears Tower held the title of the tallest building worldwide, though it was not the tallest structure overall. The CN Tower in Toronto exceeded its height by approximately 350 feet (106.7 m).[97] However, the Council on Tall Buildings and Urban Habitat (CTBUH) does not classify the CN Tower as a building because it lacks continuous floors from ground level.Cite error: The opening <ref> tag is malformed or has a bad name The Willis Tower remains the third tallest building across both the Americas and the Western Hemisphere, ranking behind One World Trade Center and Central Park Tower in New York City. Its pinnacle reaches 1,729 feet (527.0 m), making it the third-tallest freestanding structure in the Americas.[2] Globally, it ranks as the 16th tallest freestanding structure by pinnacle height.

When completed in 1998, Kuala Lumpur's Petronas Twin Towers claimed the world’s tallest building status with a height of 1,482.6 feet (451.9 m), including their ornamental spires. This claim was contested by Chicago residents who pointed out that Sears Tower’s highest occupied floor was situated above those of the Petronas Towers.[98] This debate led to the establishment of four distinct "tallest building" categories. Within these, Petronas was recognized as tallest based on architectural height, which includes spires but excludes antennas.[98][99] In 2004, Taiwan’s Taipei 101 surpassed Petronas in spire height and also exceeded Sears Tower in roof height and highest occupied floor, claiming three of the four categories. Suggestions were made for Sears Tower to add decorative elements to reclaim its status over Taipei 101, but this never came to fruition.Cite error: The opening <ref> tag is malformed or has a bad nameCite error: The opening <ref> tag is malformed or has a bad name On August 12, 2007, developers announced that Dubai's Burj Khalifa had overtaken Willis Tower in every height measurement.Cite error: The opening <ref> tag is malformed or has a bad name After its completion, One World Trade Center in New York City surpassed Willis Tower in both structural and pinnacle heights; however, it did not exceed Willis Tower’s roof height, observation deck elevation, or highest occupied floor.Cite error: The opening <ref> tag is malformed or has a bad name

Prior to the year 2000, Willis Tower did not hold the record for tallest building by pinnacle height. From 1969 until 1978, this distinction belonged to the John Hancock Center, whose antenna extended to 1,500 feet (457.2 m), standing 49 feet (14.9 m) taller than Sears Tower’s original height. One World Trade Center later claimed this record when a 359-foot (109.4-meter) antenna was added, raising its total height to 1,728 feet (526.7 m). In 1982, two antennas were installed on Willis Tower, increasing its total height to 1,707 feet (520.3 m), surpassing John Hancock Center but still shorter than One World Trade Center. Nevertheless, an extension of Willis Tower’s western antenna in June 2000 brought its pinnacle height to 1,729 feet (527.0 m), allowing it to narrowly claim the tallest building by pinnacle height title.

The lowest point of Willis Tower lies 43 feet (13 m) below Franklin Street’s elevation.Cite error: The opening <ref> tag is malformed or has a bad name

Climbing

File:View down from the Sears-Willis Tower Skydeck.jpg
Perspective of the tower's exterior wall from the Skydeck

On May 25, 1981, Dan Goodwin achieved the first successful external climb of the tower, outfitted in a custom-made Spider-Man costume. Employing suction cups, camming tools, and sky hooks, he ascended despite multiple interventions by the Chicago Fire Department. After a seven-hour effort, Goodwin was apprehended upon reaching the summit and subsequently faced trespassing charges. He explained that his climb aimed to highlight deficiencies in high-rise rescue and firefighting capabilities. Following extensive questioning by Chicago’s District Attorney and Fire Commissioner, Goodwin was released from custody.

In August 1999, French urban climber Alain "Spiderman" Robert scaled the building’s glass and steel façade using only his hands and feet. Nearing the top, dense fog created slippery conditions over the final 20 stories, complicating his ascent.

Since 2009, the Willis Tower has annually hosted SkyRise Chicago, recognized as the world’s tallest indoor stair climb. This charity event supports the Shirley Ryan AbilityLab and allows participants to legally ascend the tower’s 103-story staircase.

Naming rights

File:Willis Tower.jpg
West-facing exterior and main entrance

Although Sears sold the tower in 1994 and fully vacated it by 1995, it retained naming rights until 2003. Attempts by new owners to rename the building through agreements with CDW Corp in 2005 and the U.S. Olympic Committee in 2008 were unsuccessful. In 2009, British insurance firm Willis Group Holdings leased over 140,000 square feet (13,000 m2) across three floors. A representative from Willis confirmed that naming rights were acquired at no additional cost as part of lease negotiations. Consequently, on July 16, 2009, the building was officially renamed Willis Tower. These naming rights were secured for a duration of 15 years. When Aon acquired Willis Towers Watson in 2020, it maintained control of the naming rights agreement, which remains valid until March 2025.

The Chicago Tribune humorously noted that the new name evoked the catchphrase "What you talkin' 'bout, Willis?" from the sitcom Diff'rent Strokes. The publication also regarded the renaming as ill-advised given Chicago’s strong attachment to tradition and civic pride—highlighting local discontent similar to reactions following the change from Marshall Field's to Macy's. This sentiment was echoed in a July 16, 2009 CNN report where many Chicago residents expressed reluctance toward adopting the Willis Tower name. Additionally, an October 2010 issue of Chicago magazine included the skyscraper among Chicago’s top 40 architectural landmarks but deliberately referred to it as the "Sears Tower," ignoring its official renaming. Furthermore, Time magazine ranked this corporate rebranding among the top ten worst name changes due to unfavorable media coverage and petitions opposing it. Discussion about the name persisted into 2013 when columnist Eric Zorn remarked in the Chicago Tribune that despite four years since its rechristening as Willis Tower, public usage of the new name had yet to gain widespread acceptance.

Floor layouts

Level Function
110 Penthouse Roof Area
109 Roof with Mechanical Penthouse Structure
106-108 Mechanical Facilities
104-105 Communications and Mechanical Equipment
103 Skydeck Observation Deck
100-102 Communications Infrastructure
99 Secondary Skydeck and Dining Area
90-98 Office Spaces
88-89 Mechanical Systems
68-87 Office Areas
66-67 Sky Lobby Levels
64-65 Mechanical Zones
35-63 Office Floors
33-34 Sky Lobby Levels
29-32 Mechanical Floors
3-28 Office Levels
2 Restaurant and Upper Lobby Area
1 Main Lobby, Retail Shops, and Dining Venues
LL3-LL1 Lower Lobby, Skydeck Entry, Retail Outlets, and Restaurants

Broadcasting

File:Antenna of Willis Tower, Chicago, IL.jpg
Antennas atop the tower

Numerous broadcast transmitters are installed at the Willis Tower's summit. The following listings are organized by antenna height descending from the peak. When multiple stations share the same elevation on a mast, this signifies a shared antenna system utilizing a diplexer. Given the tower’s exceptional altitude, FM broadcasters (all classified as class B) operate with restricted power levels.

Radio broadcasters

East Mast
  • Height: 482 m:
    • WLIT FM 93.9 MHz primary transmitter, 4.0 kW, AMFM ownership
    • WCHI FM 95.5 backup transmitter, 3.1 kW, AMFM ownership
  • Height: 480 m: WBMX FM 104.3 primary, 4.1 kW, CBS Radio
  • Height: 476 m: WTMX FM 101.9 primary, 4.2 kW, Hubbard Broadcasting
  • Height: 474 m: WBBM FM 96.3 primary, 4.2 kW, CBS Radio
  • Height: 472 m:
    • WKSC FM 103.5 primary, 4.3 kW, AMFM ownership
    • WGCI FM 107.5 primary, 3.7 kW, AMFM ownership
  • Height: 470 m: WFMT FM 98.7, power output of 6.0 kW
  • Height: 468 m: WLS FM 94.7 primary transmitter, at 4.4 kW
  • FCC database query for reference

valign=top|

West Mast
  • Heights: 460 & 451 m:
    • Backup transmitters for WFMT FM 98.7
  • Height: 443 m:
    • Backup transmitters for WBBM-FM FM 96.3 and WBMX FM 104.3
  • W264BF (simulcasting WHLP) at frequency of 100.7 MHz with a power of 2 W operated by Calvary Chapel of Costa Mesa
  • Allocation table includes WLIT, WLS, WBBM, WTMX, WBMX, WCFS
  • FCC database query for reference

The tower also hosts NOAA Weather Radio station KWO39, broadcasting at frequency 162.550 MHz. Managed by the Chicago office of the National Weather Service, this station incorporates Specific Area Message Encoding (SAME) technology to activate alert sirens on compatible weather radios in case of imminent emergencies.

Television stations

East mast
  • Height: 515 m:
    • WLS-TV channel 7 analog, 55 kW, ABC Owned Television Stations (Analog transmission ceased on June 12, 2009; currently digital-only.)
    • WLS-TV channel 7 permanent digital, 4.75 kW
  • Height: 510 m:
    • WCPX-TV channel 43 digital, 200 kW, Ion Media Networks
    • WCPX-TV channel 38 analog, 3630 kW, Ion Media Networks (Analog transmission ended June 12, 2009; digital-only now.)
    • WJYS channel 36 digital, 145 kW, Oxford Media Group
    • WCIU-TV channel 27 digital, 15.1 kW, Weigel Broadcasting
  • Height: 509 m:
    • WXFT-TV channel 59 temporary digital, 200 kW, Univision Communications
    • WXFT-TV channel 50 permanent digital, 230 kW, Univision Communications
  • Height: 498 m:
    • WTTW channel 11 analog, 60.3 kW, Window To the World Communications (Analog service discontinued June 12, 2009; now exclusively digital.)
    • WBBM-TV channel 12 digital, 8 kW, CBS Television Stations
  • Height: 480 m:
    • WFLD channel 31 digital backup, 475 kW, Fox Television Stations
    • WPWR-TV channel 51 digital backup, 508 kW, Fox Television Stations
  • Height: 478 m: WGN-TV channel 19 digital backup, 310/229 kW, Tribune Broadcasting
  • Height: 474 m:
    • WTTW channel 47 digital backup, 150 kW, Window To the World Communications
    • WLS-TV channel 52 digital backup, 220 kW, ABC Owned Television Stations
  • Height: unknown: WESV-LD channel 40 digital, 37.2 kW, Trinity Christian Center of Santa Ana
  • FCC query[100]
West mast
  • Height: 523 m: WPWR-TV channel 51 digital, power output of 1000 kW, Fox Television Stations
  • Height: 514 m: WLS-TV channel 52 temporary digital transmission at 153.6 kW, ABC Owned Television Stations
  • Height: 508 m: WMAQ-TV channel 29 digital broadcast with power of 350 kW, NBC Owned Television Stations
  • Height: 494 m:
    • WMAQ-TV channel 5 analog at 20 kW (Analog broadcasts ended June 12, 2009; now solely digital.)
    • WPWR-TV channel 50 analog at maximum power of 5000 kW (Analog discontinued June 12, 2009; currently only digital.)
    • WXFT-TV channel 60 analog at full power of 5000 kW (Analog service ceased June 12,2009; now exclusively digital.)
  • Height: 475 m: WFLD channel 31 digital with power levels of either 690 or up to1000 kW, Fox Television Stations
  • Height:473 m:WCIU-TVchannel26 analog at full power of5000 kW(Analog transmission ended June12,2009;digital only currently.)
  • Height:472 m:
    • WCIU-TV channel27 digital at power output of590 kW,weigel broadcasting
    • WSNS-TVchannel44 analog broadcast at5000 kW,NBC owned television stations(analog discontinued june12th2009;digital only)
    • WSNS-TV channel45 digital with power between467 and665 kW,NBC owned television stations
  • Height:465 m:WTTWchannel47 digital broadcast at300 kW window to the world communications
  • Height:455 m:WJYSchannel36 digital transmission at50 kW oxford media group
  • Height:453 m:WGN-TVchannel19 digital broadcast at645 kW tribune broadcasting
  • Height unknown:
  • FCC query[101]

Cultural portrayals

This structure has been featured in a variety of movies and TV programs set in Chicago. For instance, in Ferris Bueller's Day Off, the characters visit its observation deck. During a 2006 Chicago episode of Late Night with Conan O'Brien, a character named The Sears Tower Dressed In Sears Clothing was introduced. Additionally, the building appears in History Channel's Life After People, where it, alongside other man-made landmarks, deteriorates and collapses approximately two centuries after humanity disappears.

In the 2008 movie The Dark Knight, the building is depicted as part of Gotham City. It also features prominently in several scenes from the 2011 film Transformers: Dark of the Moon. Furthermore, the 2013 movie Man of Steel uses the tower as the setting for the offices of the Daily Planet.

Position in Chicago's skyline

Template:Chicago skyline

See also

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Sources

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External links

File:Commons-logo.svg
Wikimedia Commons has media related to Willis Tower.Template:Preview warning
Template:S-achTemplate:S-breakTemplate:S-breakTemplate:S-breakTemplate:S-break
Preceded by Tallest building worldwide
1,450 ft
1973–1998 		Succeeded by
World's tallest architectural element
1,450 ft
1973–1998

Template:S-break

Building with greatest number of floors
108 floors
2001–2007 		Succeeded by
Highest rooftop in the world
1,450 ft
1973–2003 		Succeeded by
Tallest U.S. building
1,450 ft
1973–2013 		Succeeded by
Preceded by Chicago’s tallest building
1,450 ft
1973–present 		Incumbent

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