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BRUNSWICK BUILDING HANCOCK CENTER SEARS TOWER ONE SHELL PLAZA TWO 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 1960’s 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.html


http://khan.princeton.edu/khanHancock.html

http://khan.princeton.edu/khanSears.html


http://khan.princeton.edu/khanOneShell.html

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


http://khan.princeton.edu/khanHancock.html


http://khan.princeton.edu/khanOneShell.html





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 building’s 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 9’4”. 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



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) a beam 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



construction.”7 These tests ensured the feasibility of the beam which was at the time the “world’s

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 building’s beam-column

framework by exposing the building’s bare concrete façade. 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 Khan’s 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.))

