Editing Willis Tower (section)

==== Design process ====
Sears executives estimated that their new building would need about {{convert|4.2|e6ft2|m2}}, split into 70 stories with {{convert|60000|ft2}} each or 60 stories with {{convert|70000|ft2}} each.<ref name="p511528132" /> Sears commissioned architecture firm [[Skidmore, Owings & Merrill]] (SOM) to design the tower.<ref name="n108217158">{{Cite news |last=Nagelberg |first=Alvin |date=August 2, 1970 |title=Sears Tower: New Heights of Design: Will Blend Advanced Concepts |pages=97 |work=Chicago Tribune |url=https://www.newspapers.com/clip/108217158/sears-tower-new-heights-of-design/ |access-date=August 24, 2022}}</ref>  SOM was also the lead structural engineer, and [[Jaros, Baum & Bolles]] provided MEP engineering.<ref name="skyscraperCenter" />

Sears planned to move its merchandise group into the building initially, renting out the remaining space to other tenants until needed. Sears executives were accustomed to large floor areas of at least {{convert|100000|ft2}}, but SOM architects raised concerns that the large floors would be unattractive to smaller tenants. A subsequent proposal called for two buildings connected by a footbridge, which would respectively contain {{convert|50000|ft2}} and {{convert|30000|ft2}} on each floor, but this was also infeasible.<ref name="n108217158" />

Some floors were designed with smaller footprints to attract prospective lessees, so the building's height was increased to meet Sears's floor-area requirements.<ref name="n108217158" /> Architect [[Bruce Graham]] and structural engineer [[Fazlur Rahman Khan]], both of whom were partners with SOM, proposed a tower with {{convert|55000|sqft|m2|adj=on}} floors in the lower part of the building, as well as a series of [[Setback (architecture)|setback]]s with gradually tapering floor plates, giving the tower its distinctive look.<ref name=":2" /> During the design process, one of the architects reportedly pulled out nine cigars and staggered them vertically until the pair both agreed to the arrangement.<ref name=":2">{{Cite web|date=March 8, 2008|title=The Tallest Skyscraper - TIME|url=http://www.time.com/time/magazine/article/0,9171,907406,00.html|archive-url=https://web.archive.org/web/20080308034107/http://www.time.com/time/magazine/article/0,9171,907406,00.html|url-status=dead|archive-date=March 8, 2008|access-date=September 12, 2022}}</ref><ref name="PL p. 182">{{harvnb|Pridmore|Larson|2018|ps=.|p=182}}</ref> This allowed Sears to occupy the large lower stories, while providing more conventional office space that could be rented out on the upper stories.<ref name="n109122999">{{Cite news |date=August 30, 1970 |title=Tower Will Withstand High Wind |pages=97 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109122999/tower-will-withstand-high-wind/ |access-date=September 7, 2022}}</ref>  The firm of Saphier, Lerner, Schindler was responsible for determining Sears's space requirements and designing furniture for the company.<ref name="nyt-1970-10-18" /><ref name="p169878110" /> It conducted a year-long study to determine how 16 of the company's departments should be laid out within the building.<ref name="p169878110">{{Cite news |last=Nagelberg |first=Alvin |date=September 20, 1970 |title=Building Sears Tower--A Real "Inside" Job |page=C16 |work=Chicago Tribune |id={{proQuest|169878110}}}}</ref>

As Sears continued to offer optimistic growth projections, the height of the proposed tower also increased.<ref name="n108217158" /> Under Chicago's relatively lax [[zoning]] laws, the site could theoretically accommodate a 300-story building with {{convert|13.5|e6ft2}}.<ref name="nyt-1970-10-18" /> In practice, most potential tenants did not want excessively high offices.<ref name="nyt-1970-10-18" /> Additionally, the [[Federal Aviation Administration]] (FAA) restricted the height of structures in the area to protect air traffic.<ref name="nyt-1970-10-18" /><ref name="n108217158" /> FAA officials publicly denied that they had imposed a height limit;<ref name="p133622903">{{cite news |last=Martin |first=Paul R. |date=January 20, 1971 |title=A Rising Competition: It's Hard to Say Which Is Tallest Building: Trade Center and Sears Building Vie but Won't Admit It; Should a TV Tower Count? |page=1 |work=[[The Wall Street Journal]] |issn=0099-9660 |id={{ProQuest|133622903}}}}</ref> however, the area's [[minimum safe altitude]] would need to be raised by {{convert|1000|ft}} if the building was just {{convert|1|ft}} taller.<ref name="p1521729590">{{Cite news |last=Arthur |first=Art |date=July 1, 1971 |title=Sears Is Now Tallest |page=A13 |work=The Austin Statesman |id={{ProQuest|1521729590}}}}</ref> Plans for the tower were announced on July 27, 1970. The {{convert|1450|ft|4=-tall|adj=mid}} building would contain 109 stories as measured from Wacker Drive and 110 stories as measured from Franklin Street.<ref name="n108217480" /><ref name="nyt-1970-07-282">{{Cite news |date=July 28, 1970 |title=New Sears Building in Chicago Planned as the World's Tallest |language=en-US |work=The New York Times |url=https://www.nytimes.com/1970/07/28/archives/new-sears-building-in-chicago-planned-as-the-worlds-tallest.html |access-date=September 7, 2022 |issn=0362-4331}}</ref> This would make Sears's new tower the tallest in the world, as measured by roof height, although New York City's under-construction [[Twin Towers (New York City)|World Trade Center Twin Towers]] would have a taller antenna.<ref name="p133622903" /> Although the Sears Tower would contain {{convert|4.4|e6ft2}} of space, only about {{convert|3.7|e6ft2}} would be used as offices.<ref name="nyt-1970-07-282" />