Municipal Building was quite close to the surface underneath the southern part of the building, the bedrock dropped to a depth of about under the northern portion of the site, where it would be extremely difficult to dig caissons. A layer of sand was present to a depth of , while the average depth of the bedrock under the building was about . The contract for the foundations was the largest to be awarded for a single building in the United States, with being excavated at a cost of $1.5 million. The foundations incorporated of concrete for the piers, as well as 70,000 barrels of cement. The foundations also included 125 caissons extending to an average depth of . The maximum depth of the caissons was below grade, and for the northern part of the site, the Foundation Company built larger caissons resting on sand at a depth of . While the caissons under the southern two-thirds of the building carry , the larger caissons under the northern third of the building carry only . The Municipal Building's frame had of steel, which required 20 derricks to erect. The superstructure weighed a total of . The above-ground walls, and half of the beams in the superstructure, were carried by steel-plate girders at the first floor. The girders were connected to other steel beams, which distributed the building's entire weight to the caissons. Each of the first-floor girders were about deep and grouped in sets of two or three. The Municipal Building's largest girders, supporting the Chambers Street arch, were long and up to deep. Interior The floors were arranged so that the elevator banks and stairs were on the eastern side of the building, while the offices were concentrated along the western side and on the north and south wings. There were four staircase shafts that extended the height of the building. In addition, 33 elevators were provided in the initial construction, though this number was later expanded to 37. Of the original elevators, 32 were accessible from the lobby. Most of the elevators from the lobby traveled only to the 25th story, where a separate elevator connected the 25th through 37th floors. During the 1934 elevator replacements, eight of the elevator shafts were shortened to make way for office space. Because the basement is mostly taken up by the subway station, the mechanical equipment is located on the fourth