During the four-month period between mid-December 1886 and mid-April 1887, in which Sullivan was thoroughly immersed in revising the overall design of the building’s exterior to gain the approval of a majority of the Board, Adler was hard at work planning its engineering and construction. As we have seen during this period, many of Chicago’s architects were still providing the services of what we now call the general contractor/construction manager, that is, responsible for the building’s actual construction. While Adler would be responsible for overseeing the contracts and construction of the building’s structure and exterior enclosure, Sullivan would serve the same role for the building’s interior fittings.
Peck and his supporters were in a hurry to get the project under construction if for no other reason than to send a message to the rest of the country that things had quieted down since the Haymarket Square bombing and the ongoing court case, and that business was getting back to normal so it was now quite safe to renew investment in the city’s real estate. Today, starting construction before the design of a building is completed is standard practice, but for such a large building as the Auditorium, to start construction before the design was finalized, however, at that time in history presented those responsible with a series of great risks. Adler knew he had a few months to play with as it would take that long to clear and excavate the site to the depth required for the building’s foundation that had begun on January 28, 1887. Nonetheless, at some point, if he was going to keep the project moving forward, the building’s final design and size would have to be frozen soon so that he could accurately design its footings so that their construction could start as soon as the excavation had been completed. This occurred immediately following Sullivan’s trip to New York to consult with Ware on February 12, with the entire office going into full production mode to produce the final design, layout, dimensions, and the over 200 hand-drawn drawings needed to assist the construction workers in their efforts.
Adler used these drawings to calculate the loads in every wall and column so that he could accurately size the required bearing area of each footing. Among the issues that Adler had to contend with were, 1.) the proximity to the lake and the corresponding high watertable and its hydrostatic pressure; 2.) the foundations of adjacent buildings, especially those of the Studebaker Building adjacent to the north (excavation had to be done in such a manner that the foundations of existing buildings didn’t move); and 3.) the desire to locate a basement below the stage as deep as possible to permit the usage of the latest stage equipment (that posed its own problem as the building’s own foundations immediately surrounding the stage would be at a much shallower elevation, and thereby, potentially could exert pressure on the stage’s foundation walls. Another unique foundation problem that Adler faced was the construction of the water-tight basement under the stage to house the stage’s hydraulic equipment. This required a space that was 18’ below the floor of the stage, a depth of 22’ below grade, which put this floor at an elevation that was seven feet below the mean level of Lake Michigan. The hydrostatic pressure of the ground water at such a level required a great amount of sheer weight to resist its potential uplift. Adler designed a three-foot thick “laminated floor built up of several layers of concrete, Trinidad asphalt, and asphalt-saturated felt, counterweighted by concrete and steel rails.” Wanting to keep the Ground Floor level with the sidewalk for commercial reasons and still have a basement under it with a ceiling height of ten to fourteen feet for “a boiler and machinery plant of nearly 2000 horse power, incidental to the lighting, heating, cooling, ventilating, elevator, kitchen and laundry apparatus of the building required for its suitable accommodation an area equal to fully two-thirds that of the entire building,” Adler was forced to push the foundations to a level seventeen feet below street grade, a depth heretofore never attempted as it was thought to be of questionable strength (thirteen feet had been the traditional limit up to this time).
Of particular concern to him was to get the foundation for the 16-story tower right. By this time the Board of Trade’s 303’ tower was beginning to show signs of distress as a direct result of Boyington’s naïve attempt to spread the tower’s concentrated weight over the entire building’s foundation raft, rather than isolating it on its own footing. The result of this decision was that the tower was settling at a greater rate than the rest of the building simply because it weighed much more than the body of the building. Even the six-foot thick raft foundation of stone, concrete, and timber that Boyington had placed under the entire building was not strong enough to resist this. Therefore, as the tower was settling at a faster rate, it was pulling the immediate material of the adjacent body with it, creating some very large cracks. (Eventually this would force the building owners to remove the tower completely, in order to preserve the rest of the building.) This Adler, obviously, was committed to avoiding, and so, he dedicated a foundation just for the tower that he knew would be more heavily loaded than the rest of the foundation. He sized it employing Baumann’s theory of isolated footings in an attempt to equalize the settlement of the tower and that of the rest of the building, and in so doing, hoped to eliminate the differential settlement that was tearing the Board of Trade apart.
Adler designed the tower’s foundation to be a five-foot thick raft or mat comprised of a series of layered materials. First, Adler placed two layers of water-saturated heavy timbers directly on the ground (they were saturated as a response to the presence of the ground water to minimize any chance of dry rot caused by an alternating cycle of being dry, then wet). On top of this were laid “three layers of criss-crossed steel rails and three layers of iron I-beams.” The whole was surrounded into a monolithic slab with concrete.
Because he was still going to use masonry stepped pyramidal foundations under the entire building (Root had only used the first rail-reinforced footings the previous winter and the jury was still out on how well these would perform over time), the tower’s foundation would be even more heavily-loaded, requiring a greater area of bearing to spread their loads at the same pressure as the other footings, with a corresponding increase in their height. This meant that the footings for the tower would have to be taller than those of the rest of the building, and therefore, would need to be even deeper than those of the rest of the building so that the extra height of these foundations didn’t extend into the floor of the tower’s vestibule. Adler placed these at eighteen feet below grade. Nonetheless, Adler still “hedged his bet” somewhat, in that he tied the tower’s foundation to the footings that were immediate adjacent to those of the tower with 15” deep steel beams that ran continuously through the tower’s entire foundation, hoping that any extra settlement of the tower would be resisted by and spread to the adjacent footings via these beams. Adler also understood that the tower would take longer to construct than the lower body of the building. This may seem obvious to you, but it presented a significant problem: because the tower weighed more, he had to make the tower footings so much larger than those of the rest of the building in order to have the same bearing pressure and resulting settlement, once construction had been completed. So far, so good… However, this meant that because the tower’s footings were larger, during the erection of the first ten stories, the pressure under the larger tower footings (and its settlement) would be less than that of the rest of the building (i.e., both the tower walls and the body walls were 10 stories high, thereby weighing the same; but the footings were larger under the tower, spreading the load over a greater area resulting in less settlement than the walls). When construction of the tower above the body began to impose more weight on its footings, the tower would continue to settle while the body did not and would tear apart the tower from the body, much like wha was happening in the Board of Trade. Adler, therefore, “preloaded” the tower footing with bricks and pig iron that equalled the weight of the six extra stories of the tower before the construction of the main block began, and then once construction of the tower above the body began, removed, floor by floor, an amount of dead wright from the footing that corresponding to the weight of the floor that was being constructed.
Morrison, Hugh, Louis Sullivan: Prophet of Modern Architecture. 1935. Reprint, New York: W.W. Norton, 1962.
Siry, Joseph M. The Chicago Auditorium Building. Chicago: University of Chicago Press, 2002.
Twombly, Robert. Louis Sullivan: His Life & Work, Chicago: University of Chicago Press, 1986.
Twombly, Robert and Narciso Menocal. Louis Sullivan: The Poetry of Architecture. New York: Norton, 2000.
(If you have any questions or suggestions, please feel free to eMail me at: firstname.lastname@example.org)