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    BRUNSWICK BUILDINGHANCOCK CENTERSEARS TOWERONE SHELL PLAZATWO SHELL PLAZA

    MAJOR WORKS

    BRUNSWICK BUILDING

    Chicago Illinois, 1965, 474ft, Reinforced Concrete

    Introduction

    The Brunswick Building (Figure 1) was commissioned in 19611 and completed in 19652, and became

    the tallest reinforced concrete structure of its time. At the time it was being built, Chicago was

    undergoing rapid inner-city development, fuelled by the urgent need for more office space. This was

    an after-effect of the Depression, which had seen a halt in new developments between 1945 and

    1955 within downtown Chicago, also known as the Loop. Things were made worse by a height

    restriction imposed on new developments in the 1940s.3 1955 saw the election of a new mayor,

    Richard J. Daley, who realized the need to revitalize the inner-city, and commissioned a

    development plan that included providing support and financial incentive for construction planning4.

    Over 1 million square feet of office space was added in downtown Chicago in 1958.5

    The 1960s was also a time of growing consciousness of the value of open, street-level plazas, and

    integration of high rises with the street level and surroundings. With this in mind, it was of great

    Fig. 1: Brunswick Building: loads in theclosely spaced perimeter columns are

    transferred through the transfer beam to the

    widely spaced columns at ground level

    http://khan.princeton.edu/khanBrunswick.htmlhttp://khan.princeton.edu/khanBrunswick.htmlhttp://khan.princeton.edu/khanHancock.htmlhttp://khan.princeton.edu/khanSears.htmlhttp://khan.princeton.edu/khanSears.htmlhttp://khan.princeton.edu/khanOneShell.htmlhttp://khan.princeton.edu/khanTwoShell.htmlhttp://khan.princeton.edu/khanTwoShell.htmlhttp://khan.princeton.edu/khanHancock.htmlhttp://khan.princeton.edu/khanSears.htmlhttp://khan.princeton.edu/khanOneShell.htmlhttp://khan.princeton.edu/khanTwoShell.htmlhttp://khan.princeton.edu/khanBrunswick.html
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    importance to develop structural systems that could allow for taller building construction. If buildings

    were made taller, then the same floor area could be created on a smaller footprint, and thus allow for

    these plazas to be built. The purpose of these open spaces was to allow relief for the pedestrian

    from the narrow canyons created by the tall buildings. For the Brunswick Building, chief design

    architect Bruce Graham and senior designer Myron Goldsmith hoped to open up a 51-foot-wideplaza containing reflecting pools, trees, and public art, but none of this was realized as the

    orientation prevented sunlight from entering the space. Twenty years later, a sculpture by Picasso

    was placed in the plaza between the Brunswick Building and the Daley Civic Center.

    Forces and Form

    The structural system of Brunswick Building consists of a concrete shear wall core surrounded by an

    outer concrete frame of columns and spandrels.6 At first, Khan did not consider that the outer frame

    would contribute significantly to the lateral stiffness of the building needed to take wind loads. But as

    he investigated the structural framework in more detail, he started to suspect that the close spacing

    of the columns could influence the buildings structural behavior. Together with other engineers, he

    carried out a careful approximate analysis of the two structural systems at play: (1) the shear wall

    core, and (2) the outer frame with a column spacing of 94. They discovered that subjected to lateral

    wind loading the frame combined with the shear wall core gives the structure a greater stiffness than

    previously than just one system (shear wall or rigid frame) acting alone.

    Fig. 2: This elevation of the lower part of the Brunswick structure shows the transfer of loads from

    closely spaced columns above to widely spaced columns below through a transfer wall beam

    One of the main features of the Brunswick Building is the 24 ft deep transfer wall beam near the

    ground level. Figure 2, shows how the transfer wall beam directs gravity loads from the closely

    spaced columns above to widely spaced columns at the ground. To study the effect of the depth of

    this transfer wall beam, we performed two analyses for a 2 bay equivalent system: one using the

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    actual transfer wall beam dimensions, and another with the depth of the transfer beam as one tenth

    of the actual beam depth. Representations of the axial forces through the members are shown in

    elevation in Figures 3(a) and (b).

    Fig. 3 a & b: Axial forces in the perimeter columns with (a) a full size transfer (24.1 ft depth), and (b) abeam with a depth 1/10 of the full size beam (2.41 ft depth)

    In the full size 24 ft beam analysis (Fig. 3(a)) the total gravity force is divided almost equally among

    the thirteencolumns above the transfer beam (all axial forces in the columns have the same

    magnitude expressed in the diagram by identical line thicknesses). Below the beam, the force is then

    divided among the three base columns, with the central column carrying more of the load than the

    two outer columns. This is not the case for the one tenth depth transfer beam. Fig. 3(b) shows the

    distribution of forces above the girder as having more force carried by the columns closest to the

    base columns and less force carried by the columns in the center of the spans between the base

    columns. The columns directly above the base columns see a gradual increase in axial force as they

    near the transfer beam (shown in figure 3b by increasing line thicknesses), while the other columns

    see a decrease in axial force. An arch-like effect appears as the forces gradually move towards the

    stiff column supports at the base. This shows that the depth of the transfer beam has a significant

    effect on the way in which the forces in the closely spaced columns above the wall beam distribute

    to the widely spaced columns below.

    Before beginning construction, Khan made sure that all possible loading conditions on the tall

    building were evaluated and produced a number of charts that predicted its behavior, all made

    possible through physical experimentation coupled with creative analytical thinking. For example,

    Khan worked with several professors on the transfer wall beam testing at the Structural Research

    Laboratory at the University of Illinois preceding construction. Some concerns had been raised

    regarding heat of hydration, an unusually small span-depth ratio, and nonconventional deep beam

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    construction.7 These tests ensured the feasibility of the beam which was at the time the worlds

    largest concrete girder;8 as a result, concerns were mitigated, as lab tests revealed a safety factor of

    3.0, yielding in flexure, minimal effect on horizontal construction joints, and appropriate

    reinforcement was made with confirmation.9

    Conclusion

    The Brunswick Building represents one of the first uses of reinforced concrete in modern tall

    buildings. The lack of an external glass curtain wall accentuates the buildings beam-column

    framework by exposing the buildings bare concrete faade. The massive transfer wall beam

    transfers the forces from the closely spaced columns above to the widely spaced columns below. In

    future designs such as Two Shell Plazaand Marine Midland Bank (Figure 4), Khan makes this

    transfer of forces in a more fluent, gradual way.

    The Brunswick Building marks the beginning of a series of Khans reinforced concrete

    structures.10 Over the 45 years that the building has been in existence, the Brunswick Building has

    stood the test of time. This was the first project for which Fazlur Khan was the project manager. His

    meticulous attention to detail and exploration of engineering innovations were just beginning and a

    sign of more to come.

    Fig. 4: Marine Midland Bank inRochester, NY with its structural

    undulating facade (photo by J. Wayman

    Williams Jr.))

    http://khan.princeton.edu/khanTwoShell.htmlhttp://khan.princeton.edu/khanTwoShell.html