Editing Willis Tower (section)

=== Structural and mechanical features ===
The interior includes {{convert|74000|ST|LT t}} of steel, {{convert|4|e6lb}} of aluminum, and {{convert|101|acre|ft2 m2}} of concrete flooring.<ref name="p148412303" /><ref name="p133809828" /> The building contains diagonal columns only on the two stories immediately below each of the setbacks, thus reducing shear stress.<ref name="Žaknić Smith Rice Council on Tall Buildings and Urban Habitat p." /> The interior of the building could not contain diagonal beams, since these would have obstructed the connections between each of the "tubes". Therefore, the columns and the horizontal beams on each story are connected by rigid joints.<ref name="Drexler Menges 2009 p." /> The superstructure was designed to withstand wind gusts of {{convert|130|mph}}, which on average would occur once every hundred years.<ref name="p511514170" /> According to the ''Chicago Tribune'', the top of the building would be able to bend by as much as {{convert|7|in}}, returning to its normal position within 7.2 seconds.<ref name="p170442312" />

The Willis Tower's basement extends {{Convert|50|ft}} deep, resting on a {{convert|5|ft|m|-thick|adj=mid}} concrete slab. The ground directly beneath the building was largely made of clay; the underlying layer of limestone was as much as {{Convert|100|ft}} beneath ground level.<ref name="p169075911" /> As a result, the foundation was excavated using 201 [[Caisson (engineering)|caissons]],<ref name="p169075911" /><ref name="p1521729590" /> of which 114 reached the underlying limestone.<ref name="p1521729590" /> The caissons created holes that measured up to {{convert|10|ft}} across. Some holes at the northwestern and northeastern corners of the site filled up with groundwater and had to be drained. Workers next placed steel tubes into the holes, then poured concrete around the tubes.<ref name="p169075911" />

During the Sears Tower's construction, SOM and Chicago government officials considered adding "smoke free and fire free" areas to the building, as well as a complete sprinkler system serving all floors. Neither of these features had previously been used in a structure in Chicago.<ref name="n109143307">{{Cite news |last=Zahour |first=Frank |date=January 3, 1971 |title=City Planners Consider Pioneer Ideas for Including Fire Safety in Sears Tower |pages=34 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109143307/city-planners-consider-pioneer-ideas/ |access-date=September 7, 2022}}</ref> Even though regulations did not require a fire sprinkler system, the building was equipped with one from the beginning. There are around 40,000 sprinkler heads in the building, installed at a cost of $4 million.<ref name=":3" /> When it was completed, the Sears Tower was heated electrically, unlike older structures that used gas heating.<ref name="n109146209">{{Cite news |last=Nagelberg |first=Alvin |date=January 27, 1971 |title=Sears Tower Goes Electric; Standard Turns to Gas |pages=53 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109146209/sears-tower-goes-electric-standard/ |access-date=September 7, 2022}}</ref> It included 145,000 light fixtures and a cooling system capable of 17,000 tons of refrigeration.<ref name="p133809828" /><ref name="p148369539" /> Furthermore, the tower contained fire-suppression and communications systems for emergency use, which were powered by diesel generators.<ref name="p511514170" /><ref name="n109180857">{{Cite news |date=March 11, 1973 |title=Sears Tower betters code |pages=551 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109180857/sears-tower-betters-code/ |access-date=September 8, 2022}}</ref> If there was a fire in one section of the building, the building's smoke-detection system would close off the fresh-air intake openings in that section, discharging smoke outdoors.<ref name="p511514170" />

Fifteen above-ground stories, as well as three of the basement levels, contain mechanical equipment. Above the Skydeck on the 103rd floor is a seven-story mechanical penthouse.<ref name="p148369539" />

==== Elevators and escalators ====
The Sears Tower was planned with 103 elevators,<ref name="p511514170" /><ref name="p170442312" /> including 14 [[double-deck elevator]]s.<ref name="p511514170" /><ref name="p169950437">{{Cite news |date=October 11, 1970 |title=Sears Tower: What the Pedestrian Will See |page=C1 |work=Chicago Tribune |id={{proQuest|169950437}}}}</ref> The office stories are served by 97 elevator cabs; due to the presence of the double-deck elevators, these occupy 83 shafts.<ref name="Ori Brinson 2018" /> As designed, one bank of single-deck elevators connected the lobby to the lowest 28 stories.<ref name="p169950437" /> Banks of double-deck elevators traveled to "sky lobbies" at the 33rd/34th and 66th/67th floors, where passengers could transfer to local elevators. The 34th through 103rd stories were served by local elevators that operated from the sky lobbies.<ref name="p511514170" /><ref name="p169950437" /> Two elevators also ran directly from the lobby to the Skydeck on the 103rd floor.<ref name="n109146093">{{Cite news |last=Nagelberg |first=Alvin |date=April 11, 1971 |title=Glass Elevators Give Hotel Lift |pages=49 |work=Chicago Tribune |url=https://www.newspapers.com/clip/109146093/glass-elevators-give-hotel-liftalvin/ |access-date=September 7, 2022}}</ref> {{As of|2018}}, the elevators carried 5.8 million passengers per year.<ref name="Koziarz 20182" /><ref name="Ori Brinson 2018" />

Six of the elevators are used for freight.<ref name="p170442312" /> One of the freight elevators served all stories, traveling to a height of {{convert|1440|ft}}.<ref name="n109146093" /> During a fire or another emergency, this elevator would be reserved for the [[Chicago Fire Department]]. Other elevators would be controlled from the 33rd floor. During a fire, elevators would be dispatched to the affected floors to assist with evacuation.<ref name="p511514170" />

The building also had 16 escalators, including a set of double-height escalators that traveled from the main lobby to the lower mezzanine.<ref name="p169950437" /> Another set of escalators connects the 33rd and 34th stories.<ref name="p170442312" />