Editing Willis Tower (section)

=== Form and facade ===
Each of the "tubes" is a column-free module measuring {{convert|75|by|75|ft}},<ref>{{cite web |date=September 2, 2007 |title=Sears Tower |url=http://www.tallestbuildingintheworld.com/building_id_5_Sears+Tower.php |url-status=dead |archive-url=https://web.archive.org/web/20090226193756/http://www.tallestbuildingintheworld.com/building_id_5_Sears+Tower.php |archive-date=February 26, 2009 |access-date=September 14, 2009 |work=TallestBuildingintheWorld.com}}</ref> which [[Setback (architecture)|set back]] at different stories.<ref name="PL p. 182" /> There are setbacks at the 50th, 66th, and 90th floors.<ref name="Drexler Menges 2009 p." /><ref name="Žaknić Smith Rice Council on Tall Buildings and Urban Habitat p.">{{cite book |last1=Žaknić |first1=Ivan |title=100 of the world's tallest buildings |last2=Smith |first2=Matthew |last3=Rice |first3=Dolores B. |author4=Council on Tall Buildings and Urban Habitat |date=1998 |publisher=Gingko Press |isbn=3-927258-60-1 |page=207 |oclc=40110184}}</ref><ref name="p148369539" /> The lowest 50 stories contain nine tubes and cover {{convert|52000|ft2}} each.<ref name="n108217158" /><ref name=":2" /><ref name="n109122999" /> The northwest and southeast tubes terminate at the 50th floor. The 51st through 66th floors each span {{convert|41420|ft2}}, above which the northeast and southwest tubes end. From the 67th to 90th floors, each story is shaped like a cross, covering {{convert|30170|ft2}}. The north, east, and south tubes end at the 90th floor; the remaining west and center tubes reach 108 floors, with an area of {{convert|12283|ft2}} on each of the top stories.<ref name="n108217158" />
[[File:FR khan sculputure at Sears tower.jpg|thumb|right|Sculpture honoring [[Fazlur Rahman Khan]], considered the father of tubular designs, at the Willis Tower. Khan is known for making important advancements in skyscraper engineering.]]
The Sears Tower was the first building to use this innovative design. It was both structurally efficient and economic: at 1,450 feet, it provided more space and rose higher than the [[Empire State Building]] and cost much less per unit area.<ref name="Lynn S.Beadle pays tribute to Khan">{{cite book |author=National Academy of Engineering |url=https://books.google.com/books?id=vD0rAAAAYAAJ |title=Memorial Tributes |publisher=National Academies |year=1979 |isbn=9780309034821 |id=NAP:14723}}</ref> The system would prove highly influential in skyscraper construction and has been used in most [[supertall]] buildings since, including the world's current tallest building, the [[Burj Khalifa]].<ref>{{cite news |title=Burj Dubai: The new pinnacle of vanity |newspaper=Telegraph |url=https://www.telegraph.co.uk/news/worldnews/middleeast/dubai/6934603/Burj-Dubai-The-new-pinnacle-of-vanity.html |url-status=live |url-access=subscription |access-date=February 25, 2014 |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/worldnews/middleeast/dubai/6934603/Burj-Dubai-The-new-pinnacle-of-vanity.html |archive-date=January 11, 2022}}{{cbignore}}</ref><ref>{{cite news |title=Top 10 world's tallest steel buildings |newspaper=Construction Week Online |date=September 27, 2010 |url=http://www.constructionweekonline.com/article-9180-top-10-worlds-tallest-steel-buildings/1/print/ |access-date=February 25, 2014 |publisher=Constructionweekonline.com}}</ref> In February 1982, two television antennas were added to the structure, increasing its total height to {{convert|1707|ft|m|1}}. The western antenna was later extended, bringing the overall height to {{convert|1729|ft|m|1}}<ref name="skyscraperCenter" /> on June 5, 2000, to improve reception of local [[NBC]] station [[WMAQ-TV]].

The perimeter of the Willis Tower contains columns that are spaced {{convert|15|ft}} apart on their centers. The [[facade]] is made of anodized aluminum and black glass.<ref name="Drexler Menges 2009 p." /><ref name="Žaknić Smith Rice Council on Tall Buildings and Urban Habitat p." /> [[Alcoa]] manufactured {{convert|4|e6lb}} of aluminum sheeting for the building's facade.<ref>{{Cite news |date=August 9, 1971 |title=Alcoa to Supply Sears Tower Aluminum Sheet |pages=68 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109143707/alcoa-to-supply-sears-tower-aluminum/ |access-date=September 7, 2022}}</ref> Black bands appear on the tower around the 29th–32nd, 64th–65th, 88th–89th, and 104th–108th floors. These elements are louvers to ventilate the building's environmental support systems and obscure its [[truss|belted trusses]].<ref name=":3">''The Times-News'', February 15, 1975</ref> The rest of the facade is made of 16,000 rectangular windows.<ref name="p170442312">{{Cite news |last=Nagelberg |first=Alvin |date=June 24, 1973 |title=Going up:: a fantastic elevator voyage The Sears Tower Almanac 14 Sears Escalators link the 33d and 34th floors |page=I14 |work=Chicago Tribune |id={{proQuest|170442312}}}}</ref><ref name="p148412303">{{cite news |date=June 2, 1973 |title=Sears Tower Now Tallest In Nation |page=E12 |work=The Washington Post, Times Herald |issn=0190-8286 |id={{ProQuest|148412303}}}}</ref> all of which measure {{convert|5|by|8|ft}} and are tinted with bronze.<ref name="p148412303" />

Outside the building, there was originally a {{convert|80000|ft2|adj=on}} plaza made of pink granite.<ref name="p170442312" /> In the late 2010s, a three-level wing was built along the western and southern sides of the tower replacing the plaza. The [[roof garden]] above the annex spans {{convert|30000|ft2}}.<ref name="architecturalrecord.com" /><ref name="Chicago YIMBY 2020">{{cite web |date=October 22, 2020 |title=Final Touches Remain for Catalog, Willis Tower's New Podium in The Loop |url=https://chicagoyimby.com/2020/10/final-touches-remain-for-catalog-willis-towers-new-podium-in-the-loop.html |access-date=September 7, 2022 |website=Chicago YIMBY}}</ref> The annex contains a facade of black steel and aluminum, similar to in the original building.<ref name="architecturalrecord.com" /> The Jackson Boulevard facade of the annex contains an artwork by Olafur Eliasson, entitled ''Atmospheric wave wall''.<ref name="Willis Tower Art of the Neighborhood New">{{cite web |title=Art of the Neighborhood New |url=https://www.willistower.com/artoftheneighborhood |access-date=September 7, 2022 |website=Willis Tower}}</ref><ref name="Nast 2021">{{cite web |last=Li |first=Jennifer S. |date=January 13, 2021 |title=Olafur Eliasson's New Chicago Art Installation Captures Shifting Sunlight and a Changing Climate |url=https://www.architecturaldigest.com/story/olafur-eliassons-chicago-new-art-installation-captures-shifting-sunlight-and-a-changing-climate |access-date=September 7, 2022 |website=Architectural Digest}}</ref> The work, measuring {{convert|30|by|60|ft}} across,<ref name="Willis Tower Art of the Neighborhood New" /> comprises almost 2,000 blue-and-green steel tiles, which are decorated with hexagonal motifs.<ref name="Nast 2021" /><ref name="juliana neira I designboom 2021">{{cite web |last=Neira |first=Juliana |date=January 20, 2021 |title=Olafur Eliasson Installs 1,963 Dynamic Metal Tiles at Chicago's Willis Tower |url=https://www.designboom.com/art/olafur-eliasson-atmospheric-wave-wall-willis-tower-chicago-01-21-2021/ |access-date=September 7, 2022 |website=designboom}}</ref> The wall is backlit at night.<ref name="Willis Tower Art of the Neighborhood New" /><ref name="Nast 2021" />