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Mixed-use high rise building in response to natural forces

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Mixed-use high rise building in response to natural forces

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Content MIXED-USE HIGH RISE BUILDING
IN RESPO N SE TO NATURAL FORCES
by
S asw ata K. Mitra
A T hesis P resented to the
FACULTY OF THE SCHOOL OF ARCHITECTURE
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
R equirem ents for the D egree
MASTER OF BUILDING SCIENCE
August 1993
Copyright 1993
Sasw ata K. Mitra
U N IV E R SITY O F S O U T H E R N C A L IF O R N IA
T H E G R A D U A T E S C H O O L
U N IV E R S IT Y PA R K
L O S A N G E L E S , C A L IF O R N IA 9 0 0 0 7
This thesis, written by
SA^W ATA K OMAFS- lyUTjCA
under the direction of h.\?f>.__..Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate School, in partial fulfillment of the
requirements for the degree of
;........
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S COMMITTEE
“La maison est une machine a habiter. “
- Le Corbusier
11
‘ .... it is a voice resonant and rich, ringing amidst the wealth and
joy of life. In utterance sublime and melodious, it prophesies a time
to come, and not so far away, when the wretched and the yearning ,
the sordid and the fierce, shall escape the bondage and the mania of
fixed ideas... Qualifying as it does in every technical regard, and
conforming to the mandatory items of the official program of
instructions, it goes freely in advance, and, with the steel frame as
the thesis, displays a high science of design such as the world up to
this day had neither known nor surmised. In its single solidarity of
concentrated intention, there is a revealed logic of a new order, the
logic of living things.... Rising from the earth in suspiration as of
the earth and as of the universal genius of man, it ascends in beauty
and serenity....until its lofty crest seems at one with the sky.’
- Louis H. Sullivan’s description o f Eliel Saarinen’s skyscraper
design entry fo r the Chicago Tribune’s One Hundred Thousand
Dollar Architectural Competition o f 1922.
ABSTRACT
The aim of this thesis is to: (1) research about tall buildings in general and their
structural systems in particular, (2) study the effects of lateral loads on different
structural configurations and modifications, (3) test the effect of introducing air
gaps in the structural configuration of a building in reducing wind pressures on its
surfaces, and (4) check if this procedure can decrease material usage by reducing
the lateral loading. It was found from wind tunnel tests that gaps did reduce the
wind pressures considerably. Furthermore, when the modified (with one gap)
configuration was tested with reduced wind loading, it was found to use less
structural material (after paying the premium for reduced number o f floors).
iv
KEYWORDS
BUILDING SYSTEMS
GAPS
H IG H -R ISE BUILDINGS
MIXED-USE BUILDINGS
MULTI-USE BUILDINGS
SKY GARDEN
STRUCTURAL SYSTEMS
TA LL BUILDINGS
WIND TUNNEL TESTING
v
ACKNOWLEDGMENTS
The single-most important person I acknowledge my thankfulness to is Dr. Goetz
Schierle, my principal advisor and Director of the Building Science program. He
not only gave me knowledge, understanding and guidance, but also, motivation and
perseverance. I am also humbly indebted to professors Pierre Koenig, Dimitry
Vergun and James Ambrose for all their help. My friends also aided me immensely
and I would like to thank them profusely. It has been an extremely stimulating and
gratifying experience to have worked on this thesis project and I have learnt about
'
many diverse aspects of building technology and construction. Finally, I would like
to remember one of the greatest structural engineers of high-rise buildings, the Late
r
j Fazlur M. Khan of SOM, who has been a wonderful source of inspiration. His
j work has specially stimulated my interest in this field. My heartfelt gratitude goes
out to all who made this possible. Thank you.
j Saswata Kumar Mitra.
j Los Angeles, California, U.S.A.
!
j August 1993.
l
CONTENTS
0.1 ABSTRACT
0.2 KEYWORDS
0.3 ACKNOWLEDGEMENTS
1 .0 RESEARCH
1.1 DEFINITION OF A TALL BUILDING
1.2 RAISON D’ETRE
1.3 EVOLUTION
1.4 MIXED-USE HIGH-RISE
1.5 STRUCTURAL SYSTEMS FOR TALL BUILDINGS
1.6 CASE STUDIES
2 .0 ANALYSIS OF FRAMING CONFIGURATIONS
2.1 INITIAL STRUCTURAL DESIGN
3 .0 TESTING
3.1 AIM AND INTRODUCTION
3.2 PROCEDURE
3.3 CALCULATIONS
3.4 RESULTS
3.5 CONCLUSIONS
4 .0 APPLICATION
4.1 AIM 66
5.2 ASSUMPTIONS AND METHODOLOGY 67
5.3 RESULTS 69
5.4 CONCLUSION 70
6 .0 REFERENCES
6.1 TEXT AND DIAGRAM REFERENCES AND BIBLIOGRAPHY 71
viii
DEFINITION OF A TALL BUILDING
How do we define a tall building ? An adjective like ‘tall’ is always used in a
relative sense. A building which is even five stories high may be defined as tall in
one place because it has elevators, while in another place it may not. Generally
speaking, a tall building may be defined as one whose design, construction or
operation have required special consideration(s) because o f its tallness. Thus, the
actual height is not important. Nor is its use or appearance.
Thus the definition of a tall building is dependant on a number of factors which may
be technological or aesthetic. For this purpose, it is important to identify the
function and the setting of the particular structure. Commercial buildings account
for more than 50% of the skyscrapers today. These include offices, stores and
public utility. Residential buildings make up a further one-third and they may be in
the form of apartments, hotels, hostels and dormitories. The rest are either
industrial (warehousing, manufacturing or processing), institutional (schools,
hospitals, laboratories, libraries, museums, etc.), for public assembly (theater,
auditorium, restaurant, etc.), for special purposes (parking deck, transport
interface, etc.), or, for multiple uses, which are combinations of those mentioned.
Where are these buildings located ? About half of the world’s tallest buildings are in
North America, including the tallest building in the world, the Sears Tower in
Chicago (1454 feet, architects - Skidmore, Owings and Merrill), built in 1974. This
compares with the 2 108-feet-tall Transmission Tower in Warsaw, Poland, built in
the same year as the Sears Tower, which is the tallest man-made structure of any
kind. The tallest building outside the United States of America is the Bank of China
1
building in Hong Kong (1040 feet, architects - 1 . M. Pei and Associates). The John
Hancock Center in Chicago is the tallest multi-use high-rise in the world with 100
floors of offices, apartments, parking and commercial areas. The tallest concrete
building in the world is the 75-storey, 946-feet tall 311 South Wacker Drive Office
Tower in Chicago, and there are only eleven buildings taller. The Empire State
Building (1250 feet, architects - Shreve, Lamb and Harmon) was the tallest for
more than thirty years from 1931, when it was built, until the Sears Tower came
up. Although the Hong Kong and Shanghai Banking Corporation headquarters
(architects - Foster Associates) in Hong Kong has only 43 floors it is supposed to
be the most expensive multi-storeyed building ever built —
i5 3 o
Fig. 1.1. Scale of the World’ s Tallest Buildings [Scheuller 1990]
Many supertail buildings have been and are being proposed. Architect Cesar Pelli
is designing a 125-story giant for Chicago, which may be built in the very near
future. Frank Lloyd Wright proposed the "mile high" Illinois Sky-City, which
would be a 528-storeyed steel cantilever housing 130,000 people! LeMessurier had
the idea for a building with 207 floors, having a trussed megaframe and an aspect
ratio of 12. He aptly named it the "Erewhon Center"! Architect Harry Weese and
engineer Charles Thornton introduced the concept of the "twisted shaft" for very tall
buildings. These structures worked similarly to some of the supertali guyed
transmission towers. They proposed a 210-storey structure, which has a 300-foot
square base which twists upwards to a 200-foot square top. There have been many
such "tall" proposals and as far as the design of these structures, only the sky is the
limit!
3
RAISON D’ETRE
W hy we have tall buildings
Today we see a proliferation of tall buildings in most cities of the developed and
not-so-developed countries. In countries where arable land is critical, like Japan,
agricultural land cannot be allowed to cede into agricultural areas. Thus, multi
storey development has to be resorted to accommodate in the land available. Also,
these developments help save costs and energy involved in transportation and urban
services.
We have also seen that people migrate to the cities for various reasons. Urban areas
usually provide many employment opportunities as also many services which are
not available in rural areas, especially in the developing world. Therefore, as the
population increases due to this, while the usable area remains more or less the
same, shorter buildings have to yield their place to taller ones.
There are many factors to be considered for the construction of high-rise buildings
[Beedle 1984]. Their effect may be beneficial or detrimental according to the matter
in which they are dealt with. Some of these are:
Econom ics: In most developed countries and the large cities of others, a tall
building may be the lowest-cost solution in urban areas where land costs are high
and the infrastructural facilities are adequately available. They can fit in smoothly
with other high-rises and the large-scale business and organizational structures with
a large number of skilled and semi-skill labor. However, the case could be very
different where these conditions do not exist.
4
Social and Cultural factors: Several social and cultural problems are created due to
the residence in tall buildings. The habitants may not be able to adjust to the new
environment, particularly those with a rural background. Also several activities may
be restricted, like keeping pets, playing area for children, etc. They are seen as
places more suitable for singles or couples without little children, but may be
adopted with special care, for larger families.
Population D ensity: Higher construction may not imply higher density of
population, especially in areas where land area is not a limiting factor. However, in
cities like Singapore and Hong Kong, the extremely high population densities
necessitates high-rise construction. To maintain certain norms of light, open space,
etc., medium-rise development (8 to 14 stories) can create similar densities as high-
rise construction.
Transport and Communication: A large amount of traffic is generated by tall
buildings which can heavily burden the cities existing system. On the other hand,
they create concentrations of people. Therefore, if their development is
accompanied by one of an urban transportation system, the result can be an
economical one. Other communication media like the telephone system can be
developed in a similar manner.
Symbolism: High-rise buildings can symbolize social and economic power and
governmental authority. This has been seen since the early times, when the mayor's
house or church steeple was the tallest building in the town or village to represent
their power or prestige. The point that has to be kept in mind about this is that their
______________________ 5
\
is no conflict of interest between this motivation and the welfare of the inhabitants
of the area.
Fig. 1. 2. The Transamerica Tower in San Francisco has becom e the identifying
symbol of the bank and is represented in its corporate logo. [Bums 1985]
Energy Consumption: Tall buildings are deemed more energy efficient than low-rise
development of similar magnitude because the stacking of floors one above the
other reduces their net surface areas. This is seen clearly when the energy costs for
a high-rise is compared to a group of low-rise units covering the same area.
6
Material and Labor: Large volume production is required for tall buildings and most
of the materials used are manufactured in bulk. This reduces their unit cost
considerably. At the same time, skilled labor and material must be available for their
design and construction, otherwise, there may be adverse financial implications.
Safety: Usually tall buildings have higher building safety standards due to their
higher occupancy. However, the safety of one occupant may be jeopardized by
somebody else’ s negligence. For example, a fire on the first floor affects the
occupants on all the floors.
Aesthetic: Tall buildings have a marked influence on the architectural aesthetics of
an area. Their design must consider that aspect carefully. They can be important
elements of the city's skyline, so much so that, they can identify the city by them,
like the Empire State building symbolizes Manhattan. [Beedle 1984J
7
EVOLUTION
Man has always looked up to the sky and strived to reach higher and higher. A
higher position implies a better position and vice versa. Thus the instinct to build
taller was natural. The Ziggurat, which was built more than five thousand years
ago, shows us that even then, the people aspired to build as tall as possible with the
limited materials and construction technology at their disposal. The height of sixty
meters of that monument by Imhotep surely amazes us, considering the time frame,
although it must be noted that the manpower at his disposal was virtually unlimited.
Fig.1.3. The Ziggurat at Ur. [Kostov 1984]
The quest to reach for the skies is best illustrated by Gothic architecture. These
buildings reflect a philosophy which stresses greater height and taller spaces in all
aspects of the structure, both internally as well as externally. The structural system
is based on how to hold the parts together and how the forces may be resolved.
Structural elements like domes, vaults, arches, etc., are boldly and artistically
expressed and they all give a feeling of tallness, while at the same time are so
8
configured that they carry the loading from various parts of the building. A
conversation between Louis I. Kahn, the famous 20th century architect and an art
historian friend, evaluating a Gothic building, could describe the feeling to a certain
extent; the historian remarked,” How beautifully they are going up”, while Kahn
said, “How beautifully they are coming down.” [Gideon 1980] Even today, when
the sciences of architecture and engineering are distinguished from each other,
Gothic styles are often chosen for the facade of buildings.
iluaiJliiiijH
Fig. 1.4. Gothic Cathedral at Chartres - Section. [Kostov 1984]
It was during the age of the Industrial Revolution that we saw the advent of tall
buildings in the modem context. Chicago is generally considered as the birthplace
of skyscrapers. During the late 19th century, tall buildings were constructed at a
prolific rate in the Chicago ‘loop’ area. The reason for the proliferation of this
9
new kind of construction was mainly economic but certain technical inventions
made it possible.
Previously, most buildings had been constructed by the wall bearing system. As the
number of stories of the building increased the thickness of the bearing walls at the
lower levels increased correspondingly, until such a stage was reached that the
usable space at the lower floors of a tall building had dwindled considerably. The
skeletal construction system solved this ‘bottom-heavy’ problem. With this system
came a new method of structural calculation. Le Baron William Jenny of L’ecole
Polytechnique can be credited with pioneering work in this field at that time. He
designed the famed ten-storey Home life Insurance Company Building in Chicago,
thus heralding the skyscraper era.
However, taller buildings required a new system of vertical transportation. The
invention of the elevator by Elisha Otis in 1854, solved this problem. The first one
was installed in 1857, in the Haughwout Building in New York City, (architects -
D. Badger and J. P. Gaynore). After numerous modifications on the mechanism of
elevators for speed and safety, they remain the most efficient system of vertical
transportation in tall buildings to date.
Another problem which had to be solved was that the heavy load of the skyscraper
had to be borne by a relatively smaller area of the foundation.The solution lay in the
floating foundation system which had the capacity to transmit and distribute loads
evenly to low bearing soil. Although, this sort of system was not new, (it was
found in some cathedrals of the Medieval times), its application for tall structures
was an innovation. The pile foundation system was also another system which was
10
widely used. The area available for the foundation was restriced but piles could be
bored deep upto the bedrock was reached so their area was not dependent on the
quality of the soil immediately below the ground line.
There have been many other important contributing factors to this change. As the
skeletal structure was being used for most of the new skyscrapers steel became the
important construction material. By the middle of the 19th century, the process of
manufacture of steel was developed, notably by the Bessemer process. (Scheuller
1990). There was also the development of a method of fireproofing iron. These
inventions set about a rapid growth in the construction material industry. The 984-
feet Eiffel Tower designed in 1889 (structural designer - Gustav Eiffel), became
famous all over the world due to its elaborate structural framework, its great
structural form and the fact that people could be transported to its top in its double-
decker elevators.
Fig. 1.5. La Tourd’Eiffel, Paris. [Kostov 1984]
1 1
These technical innovations led to a novel concept of architectural design, too. The
elevators, staircase, sanitary block and the services shaft formed the core of the
building. Thus, we had the concept of the core, the body and the skin of the
building. The skeletal frame consisting of the columns and beams formed the skin
and bones of the building, while the body consisted of the bulk of the structure
with the usable space.
Meanwhile, by the beginning of the twentieth century, the focus of skyscrapers had
shifted from Chicago to New York, where buildings of unprecedented height were
being constructed in rapid succession. The 47-storied Singer Building (architect -
Ernest Flagg) was followed by the Woolworth Building (architect - Cass Gilbert),
which was 792 feet high and had 57 floors. It remained the tallest building in the
world till 1930, when it was surpassed by the 77-storied Chrysler Building
(architect - William Van Allen). However, the very next year, the world witnessed a
quantum leap in the field of high-rise construction by the inauguration of the 1250
feet high and 102-storied Empire State Building (architects - Shreve, Lamb and
Harmon), one of the few tall buildings, which , even today, receives worldwide
recognition. [Scheuller 1990]
Parallel to the development of these steel buildings was that of reinforced concrete
ones. John Aspdin had invented Portland cement in 1824, and since then the
process of manufacture of cement and precast concrete parts had progressed
considerably. The Ingalls Building (architects - Elzner and Anderson) in Cincinnati
is believed to be the first reinforced concrete skyscraper. It was 16 floors high.
Since then, many remarkable R.C.C. buildings were constructed including those by
Auguste Perret (Rue Franklin Apartments, Paris), Frank Lloyd Wright (Unity
1 2
Temple, Oak Park, Illinois, Johnson Wax Tower, Racine, Wisconsin and Price
Tower, Bartlesville, Oklahoma) and Bertrand Goldberg (Marina Towers in
Chicago). [Schueller 1990]
As the population of cities started increasing, the limited urban area gave rise to the
construction of the skyscrapers, forming a densely populated area, usually referred
to as “downtown”. It also made better economic sense to build a tall building in
such areas because usually the land costs there were higher. By the beginning of the
1970s, efficient high-rise structural systems had been developed, whose application
produced the tallest buildings of the world to date.
Fig.1.7. Price Tower, Bartlesville. Plan and Section. [Arreger et al.1975]
1 3
MIXED-USE HIGH-RISE BUILDINGS
The Industrial Revolution and technological progress of the 19th and 20th century
caused a pattern of urban settlement in which the living and working spaces became
more and more separated in urban areas. The city center or ‘downtown’ became a
conglomeration of the offices and commercial establishments while the residential
areas were moved outside these urban areas. The city centers had noticeably taller
buildings which housed these offices although some cities did have high-rise
apartment complexes. However, the structures and construction of these types of
buildings were vastly different. Large-span structural systems were required for the
office buildings while the spans in the residential ones could be relatively shorter.
The former also required more complicated mechanical and electrical systems and
consequently greater floor-to-floor heights.
During the sixties, people started becoming concerned about energy utilization and
the urban quality of life. They started to question the sensibility of segregating the
working and living spaces in urban areas. Thus the concept of multi-use buildings
took birth. They started becoming popular due to their inherent advantages and
builders and developers became increasingly interested in such projects because of
their economic and marketing promise.
When choosing the structural system for a multi-use skyscraper, a number of points
have to be considered. [Khan, F. et al.1983] Some of the important ones are :
a) Floor-to-floor height, which is different for different functions.
b) Size of columns and spandrel beams, which may differ in office and apartment
buildings.
14
c) Optimum interior column spacing for each kind of use.
d) Exterior column spacing, which is dependent on the planning module.
e) Floor plans of the various levels.
f) Transfer levels and Mechanical levels
Considering the floor plans required for the various functions of a multi-use
building , structural considerations would warrant us to put the parking level at the
bottom since the column spacing is the least; the hotels and residential floors above
that, and the commercial and office space at the top because the spacing has to be
maximum. This is due to the fact that lower floor columns have to carry a much
greater load than the ones above them. However, considering rentability and
circulation office and commercial space comes above the parking and apartments are
located at the top. This gives the best accessibility to the commercial areas and the
best view to the residential areas. Thus, there is a pronounced clash in the
configurations for both considerations (Fig. 1.8).
O FF. A FT.
COMM. O F F .
A P T . COMM.
P A R K PARK
Fig. 1.8. Ideal Configuration for Rentability and Use (left) and Ideal for Structure (right).
[Khan et al.1983]
This problem was solved in one way by sloping the building pyramidally, as in the
John Hancock Center in Chicago. Thus, the floor area reduces with height so as to
suit the changing usage. The floor-to-floor height can also be reduced in the higher
____________________________________ 15
residential floors so that the floor slabs can directly be used as the ceiling of the
floor below, without the need for false ceilings as in the commercial areas
(Fig. 1.9).
PARK PARK
COMM.
Fig. 1.9. Preferred for Use and Rentability (left) and Preferred for Structure (right).
[Khan et al.1983]
The alternative solution is to study the relative importance of the different uses of
building and arrive at a optimum span, which can then be applied throughout the
structure. It has been found that 30ft x 30ft or 25ft x 25ft bays are easily adaptable
to parking, offices, commercial and residential spaces.
16
STRUCTURAL SYSTEMS FOR TALL BUILDINGS
According to the late Fazlur Khan (Principal Structural Engineer, Skidmore, Owing
and Merrill), the bending stresses due to lateral forces, in a tall structure, should not
exceed one-thkd the axial gravity stress. As the building gets taller, the lateral sway
of the building increases and thus the need to make it stiffer. This stiffness can be
increased by using more material. Thus, it is the endeavor of most structural
systems to minimize the effect of horizontal forces on it so that, correspondingly,
the amount of material used can also be minimized. The quantity of the structural
material used is measured in terms of weight per unit area (psf). The efficiency of a
system lies in its ability to reduce this figure and effectively resist all the forces it is
subjected to. As more and more efficient structural systems have been evolved, it
has been noticed that if the building is considered as a three-dimensional unit
instead of one being composed of rigid frames its efficacy to resist lateral forces is
considerably enhanced (Fig. 1.11).
The overall efficiency of the structural system of a high-rise building is dependent
on a number of other factors like its shape, aspect ratio, function, loading
conditions, etc. A reference could be made to Khan’s chart (Fig. 1.10), which
describes various structural systems and their applications for different heights.The
optimum solution for a building of a certain height may not be based on this chart as
many specific conditions may apply.
It is noticeable that the premium one has to pay to go taller, can be markedly
reduced by the use of a more appropriately efficient system. One can compare the
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cases of the 60-storied Chase Manhattan Bank, New York, built in 1963, which
has a rigid braced frame and which uses structural steel at 55 psf, to the 110-storied
World Trade Center, New York, built in 1972, which uses the framed tube concept
and 37 psf . In fact, the John Hancock Tower, Chicago, with 100 floors, has a
vertical trussed tube and uses only 29 pounds of steel per square foot. [Khan 1983]
40
MATERIAL FOR
LATERAL LOADS
Relative
ESiciency
Parameter 30
WaSs
C olum ns
Floor
Fiamlng
100 20 40 60
Number of Stories
Fig. 1.11. Fazlur Khan’s Structural Material Efficiency Graph. [Khan 1973]
The Polish engineers Kowalczyk, Kwiecinski, Lubinski and Pawloski also studied
the evolution of the structural systems of tall buildings through the years, especially
in Eastern Europe.They noted that 95% of the high-rise construction is in the form
of 16-to-25 storey apartment buildings and they use reinforced concrete as the
principal structural material. This is because in these countries, concrete is relatively
cheaper than steel, is easily manufactured, has good fire-resisting and
soundproofing qualities and there are well-developed assembly methods, especially
for precast elements, in those areas. However, when the building is taller steel
construction may be more suitable.
Concrete buildings with more than 25 floors have reinforced concrete skeleton
framing. Internal core systems are popular because they provide good fire-
2 0 !
Number of Storeys
70
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F r a m e S tru ctu res
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Fig. 1.12. Structural systems for high-rise buildings suggested by Kowalczyk et al. [Kowalczyk et al 1983]
resistance to the elevator and piping shafts, resist lateral forces without involving
the surrounding skeleton, and, can be constructed easily by slipforming or climb-
shuttering. Given in the chart (Fig. 1.12.) are some structural systems suggested by
Kowlczyk et al for buildings having 25 to 75 stories. [Kowalczyk 1983]
The tallness of a building can be expressed numerically in terms of its slenderness
ratio,(w) which is its total height divided by its minimum width (w=H/Bmin)- It is
clear that as the height of the buildings increase their slenderness ratios also tend to
go up. Usually most codes recommend that the index does not exceed 6,
particularly in areas where extreme lateral loading is expected. [Kowalczyk 1983]
WALL SYSTEMS
Before the introduction of the skeletal system, the load-bearing wall system was the
main support structure used for tall buildings. However, it had some serious
shortcomings. As the building got higher the walls became thicker and heavier, thus
restricting and reducing the plan outlay and making the structure vulnerable to
certain dynamic loads like seismic. A case in point is the 16-storied Monadnock
Building (architects - Burnham and Root) in Chicago, Illinois , which when built in
1891, had six-foot-thick walls at the ground level.
Fig. 1.13. Monadnock Building, Chicago. [Goldsmith 1985]
22
The design of the wall was based on the resultant thrust line being within the
middle-third (kern) of the wall’s cross-section to avoid tensile stress. Also, a
simple thumb-rule could be applied to its design, which stated that a minimum wall
thickness required was 12 inches with an increment of four inches for every storey
below the top. [Scheuller 1990]
Thin wall masonry construction was introduced after World War II and was quite
popular in Europe. This type of construction had drastically reduced the wall
thickness as its design was based on different principles. It treats the building as a
whole by making the walls and floors work together to resist and transfer the
lateral loads. The 23-storied Penn Circle Apartment Building in Pittsburg (architect
- Tasso Katselas) was built in 1967 and had brick bearing walls. Meanwhile, in
earthquake-prone areas like California, reinforced concrete beating walls were
being used to stand up to the seismic forces in those areas.
The bearing-wall system finds a good application in buildings where there are many
subdivisions of the space, like in apartment buildings, hotels and condominiums.
They could easily be placed from 12 to 20 feet apart without interfering with the
interior planning to a great extent. Thus it has been used frequently in such
buildings. Architect Bertrand Goldberg designed some interesting bearing-wall
supported multi-storied buildings like the 16-storey Hillard Housing center in
Chicago, Illinois, which had a flower-shaped plan, and the 10-storey St. Joseph’s
Hospital in Tacoma, Washington, which has an amoeba-shaped plan and innovative
elliptical windows. The latter’s bearing wall is supported by a number of
cylindrical columns with conical capitals that connect into arches. The famous
23
complex of the Unite d’Habitation in Marseilles, France, designed by Le Corbusier,
has 17 stories of reinforced concrete walls placed at an average of 13 -8 apart.
E 3
EEi.
Fig. 1.14. Unite d'Habitation, Marseilles. [Arregeret al 1975]
2 4
SKELETAL SYSTEMS
Before computers could be used for structural analysis, the skeletal system was the
most popular structural system. Through the emergence of the Chicago school, this
system received a fresh impetuous. Louis Sullivan and Mies van der Rohe were
two of the pioneers of this style, which is characterized by the simplicity of form.
Later, they provided inspiration to a generation of architects who believed that form
follows function and the simpler the form the better was its utility.
Building frames are basically either moment-resisting or hinged and braced. The
former usually consist of rectangular grids of horizontal beams and vertical
columns connected by rigid joints. Buildings with flat slabs can also be considered
as rigid-framed ones as the slabs could be treated as wide, shallow beams. This
system proved to be quite economical for buildings upto 30 stories high. Hinged
frames have the frame units connected by pinned joints so that only the shear and
axial forces are transferred. Braced frames may consist of either hinged or moment-
resisting frames with some form of lateral bracing like shear wall, diagonal
members, etc. However, when we distinguish between shear walls and bracing and
limit the use of linear elements as bracing members. Shear walls will be discussed
separately.
The 662-foot-high Chicago Civic Center (architects - C.F. Murphy & Associates
and Skidmore, Owings & Merrill) in Chicago, Illinois, has 87-foot-span girders to
form large bays for courtrooms. The rigid frame is stiffened by shear trusses in the
core area.
2 5
The 52-storey One Shell Plaza building in Houston, Texas (architects - Skidmore,
Owings & Merrill) has one-way 40-foot-span joist slabs between the core and
exterior columns and a two-way waffle slab at the comers.The Hartford Building in
Chicago (architects - Skidmore, Owings & Merrill) has 11.5 ft X 22 ft flat slabs.
They are connected to the columns by rounded haunch connections.
- '•H I,, " ‘" t..,.
mi.
; '’••iniuii.
•‘■Iis.litll,,,
Fig. 1.15. One Shell Plaza, Houston. [Colaco 1985]
26
CORE STRUCTURES
Due to the height of tall buildings, the lateral stabilizers like diagonal bracing or
shear walls, which may be required, could interfere with the space planning or the
facades. Since office buildings require large open spaces for maximum flexibility,
these stabilizers are located internally, enclosing the vertical transportation systems,
service ducts and other common service areas.
Cores should ideally be placed in such a manner that there is minimum eccentricity
with respect to natural forces, so as not to cause torsional stresses. In the case of
shear wall cores, the presence of penetrations can adversely affect its strength. They
should not be very large and should preferably be staggered.
The configurations of the cores may be in the form a single core (usually central) or
multiple cores (as in bridge-structures). They may also be used in combination with
other structural elements like moment-resisting frames, suspension systems, etc. In
these combinations, the cores act together with the peripheral elements to resist
lateral and vertical forces.
Cores with cantilevered floor framing usually carry all the vertical loading on the
building as they are transferred directly to it by the flooring structural system. The
St. Mark’s Tower in New York City (architect - Frank Lloyd Wright) has a 16-
storied core with cantilevered floor slabs. The plan is based on a rotated cross.The
Olivetti Towers in Frankfurt, Germany (architect - Egon Eiermann), uses the core
to collect the loading of the floors from a strong inverted concrete pyramid at the
base and not directly from the floor slabs.
27
The TV Center in Bratislava, Czechoslovakia, has 29 floors and two reinforced
concrete cores to take the wind loading.There are inclined R.C. walls at the comers
to transmit the torque. Apart from these elements the rest of the structure, including
the floor framing and perimeter columns, is made of steel, and takes the gravity
loading. [Kowalczyk et al.1983]
L F
Fig. 1.16. TV Center, Bratislava. Plan and Section. [Kowalczyk 1983]
The 23-storied Knights of Columbus building in New Haven, Connecticut
(architects - Kevin Roche, John Dinkeloo & Associates) is a typical example of a
structure which uses multiple cores. It has four cylindrical concrete towers at the
comers of a square and a central square one which houses the vertical transportation
system.There are massive steel girders that span from the central core to the corner
towers which carry the load of the floors.
28
B:+^^
7797
Fig. 1.17. Knights of Columbus, New Haven. [Schierle 1993]
Pier Luigi Nervi designed the famous Pirelli Building in Milan, Italy in 1959. It has
a couple of triangular cores at the two ends of the slender plan, which act together
with twin wall columns. These support a ribbed floor structure spanning 80 to 43
feet. The thickness of these massive wall columns reduce appreciably with the
building’s height. Thus in this we see a combination of the application of cores and
shear walls. [Arreger et al,1975]
29
29
BRACED FRAME SYSTEMS
Bracing is the most popular form in which lateral forces are resisted. Their
application is found on all kinds of buildings, especially on tall ones as these lateral
forces can be the governing factor in their structures’ design.Bracing can be in
various forms like linear elements with pinned or rigid connections, truss frames,
infill panels, different kinds of shear walls, etc. However, when we talk of braced
frame systems for tall buildings, we exclude the application of shear walls for
bracing.
Bracing can be seen in the exterior frame or internally to surround the core. Gustav
Eiffel designed the landmark Eiffel Tower for the 1889 Paris Exhibition, which is
essentially a wrought-iron braced structure. Built over a hundred years ago, its
height of 984 feet amazed the world.
There are basically two kinds of bracing - concentric and eccentric. Some of the
popular kinds of concentric bracing in use are the diagonal bracing, K-bracing, X-
bracing and lattice-bracing. These may be applied only in one floor or bay or may
span several of these. The use of each kind depends on the stiffness required and its
suitability for a particular place, e.g. X-bracing cannot be used in places large door
openings are required.
In concentrically braced frames, the structure acts like a vertical truss thus
eliminating bending of the columns. The loading is taken in the form of axial stress
in the members. Thus deflection due to lateral forces is considerably reduced using
relatively slender members. However, in seismic areas, normal bracing may cause
30
the structure to lose ductility in the case of a severe earthquake.Thus, sometimes a
back-up rigid frame is used.
Dr. Egor Popov of the University of California at Berkeley introduced the concept
of the eccentrically-braced frame for tall buildings in seismic zones, since the
conventional concentric bracing tends to make the structure too stiff and its ductility
may be decreased. In this case, the bracing member is connected to the beam at a
certain distance from the column-beam connection instead thus transmitting the axial
force, in shear and bending, along the beam, making the system more ductile.
ISUSL
Fig. 1.18. Concentric Bracing in the First Wisconsin Bank, Milwaukee and Eccentric
Bracing in the Century Tower (proposed), Tokyo. [Burns 1985]
3 1
Many times the bracing of a building is exposed to give a character to its facade.
The 42-storey First Wisconsin Center (architects - Skidmore, Owings & Merrill) in
Milwaukee has plainly expressed hat and belt trusses. The First International Office
Tower (architects - Hellmuth, Obata & Kassabaum Inc.) in Dallas, has huge cross
bracing members running across the four facades of its 56 stories. The IBM
Building (architects - Curtis and Davis) in Pittsburg, Pennsylvania, has a fine
meshing of diagonal bracing members which are boldly expressed in the facade.
Eccentric bracing is proposed for the Century Tower (architects - Foster Associates)
in the earthquake-prone Tokyo, Japan, and they are visible in its elevations.
3 2
SUSPENSION STRUCTURES
In the late sixties, the idea of the application of the suspension principle to carry
loads originated. The substitution of cables to carry the loads of the floors, for
columns reduced the amount of material considerably. It also allowed a column-free
space at the base since the floors were hung from the frame above.
These structures usually have a big central tower with giant cantilevered trusses at
the top from which are supported the cable ‘columns’ holding up the floors. Thus
there is pure tension in these columns and the load is transferred indirectly to the
ground through the hanger at the top and the core tower. Since slenderness
considerations do not have to be taken into account in the design of these tensile
columns their cross-sections are much smaller compared to their compressive
counterparts. High-strength steels can be used to further enhance their efficiency.
This can help in creating an open facade for the building and give it the feeling of
lightness of space.
The suspension system, however, may make the structure too flexible and cause
large deformations. Thus, the stiffness of the core and the lack of rigidity of the
cables have to be carefully balanced in their design. Apart from the typical steel
tensile members which can be used for columns in this application prestressed
concrete tension columns can also be used. The prestressed steel could provide the
requisite high tensile strength while the concrete provided rigidity.
The system is well expressed in the 20-storied BMW Building (architect - Karl
Schwanzer) in Munich, Germany. It has four hangers at the center supported from
the post-tensioned bracket cross, which is cantilevered from the central concrete
__________ 3 3
core. These hangers support the clover-leaf-shaped floors at the center of the circle.
Besides the main prestressed concrete tensile columns, there are secondary columns
along the perimeter of the drums.
Another famous application of the suspension structure is the Federal Reserve Bank
Building (architects - Gunnar Birkerts & Associates) in Minneapolis, Minnesota. It
is a bridge-type of structure with two suspended catenaries along the two larger
facades. These are supported by four comer piers and a gigantic 30-foot-deep truss
which hold the piers together. The parabolic suspension cables are made up of four-
inch-thick cables, of which there are eight at the supports and two at the midspan.
The columns above the catenary are supported in compression, while at the bottom,
there are plate hangers which are in tension.
m in i ittfi;
iH w asag u ra
Fig. 1.19. Federal Reserve Bank, Minneapolis. [Burns 1985]
3 4
TUBE STRUCTURES
Beyond a certain height, two-dimensional frames and rigid inner cores are not
sufficient to efficiently resist the lateral forces incident on the building. In such
cases, the outer perimeter structural members may be more closely spaced so that
they cause the building to act like a hollow cantilevered tube. The columns and
spandrel beams spanning between them are closely meshed together to form the
exterior walls, which are rigidly connected to each other, and internally, are
spanned by stiff horizontal floor systems.
Spacing the columns close together gives the appearance of a peiforated tube to the
building. The spaces between the subsequent beams and columns are severely
restricted so that the glazing can be directly fixed in them, thus eliminating the need
of curtain walls. Lateral rigidity can be considerably enhanced by deepening the
spandrel beams. This can be done uniformly at each floor, throughout the height of
the building or only at certain levels (like the service floors) in the form of belt
trusses. The same effect could be achieved by introducing diagonal members as
bracing giving rise to the braced tube.
Some of the tallest buildings in the world are tubular structures. The 110-storey
World Trade Center twin towers (architects - Minoru Yamasaki & Associates) in
New York, are 1368-feet high framed tubes with 208-foot sides. The peripheral
columns are square boxes of 14-inch sides placed at 3 1/3 feet on center. The
spandrel beams are 4 1/3 feet deep. The famous example of a braced tube is the
pyramidal John Hancock Center (architects - Skidmore, Owings & Merrill) in
Chicago, which has its diagonal bracing clearly exposed in its facade. It was one of
35
the pioneering multi-use high-rise structures with 100 floors of commercial,
residential and parking spaces.
The Allied Bank Tower (architects - Skidmore, Owings & Merrill) in Houston has a
plan of two quarter circles forming two bundled tubes 970 feet high. It is
additionally stiffened by braced shear walls, outriggers and belt trusses. The 1484
feet high Sears Tower [details in case-study] in Chicago is the pioneering example
of the bundled, tube concept, envisaged by Fazlur Khan. It is composed of nine
square tubes of 75-foot sides with the tubes being terminated sequentially as the
height increases. Two of them reach the maximum height of 1454 feet, the highest
level reached by a habitable building on this planet.
Fig. 1.20. Allied Bank, Houston, Plans and Axonometrics. [Schierle 1993]
3 6
CASE STUDY #1
SEARS TOW ER
C hicago, Illinois, U.S.A.
Architects & Structural Engineers - Skidmore, Owings & Merrill
The 110 - story Sears Tower is the tallest building in the world, rising to 1454 feet
(443 meters ) above ground level. In terms of area coverage it ranks second only to
the Pentagon, with 4.4 million square feet. The site is an entire block with an area
of 129,000 square feet and is bound on the four sides by Wacker Drive ( in the
front) and Jackson, Franklin and Adams Streets. About 16,500 people work in the
building every day. Construction on the building started in August 1970 and the
first Sears employees moved into the finished and fitted building in September,
1973.
The skyscraper rises to its total height through a series of setbacks. The base of the
building consists of nine 75 ft X 75 ft column - free square forming a big square
with 225 feet sides. At the fiftieth floor, the northwest and southeast squares end
creating the first stepback. At the sixty-sixth floor the north east and the southwest
square are terminated and the cruciform shape thus created continues till the
ninetieth floor, when only the center and north squares go on till the top.
Fig. 1.21. Development of the Plan : Ground to 110th floor (left to right)
37
For purposes of resisting wind loads, the structure is considered to be a tube or
vertical cantilever fixed at the ground. Application of this concept to the particular
space criteria and the need to create a higher efficiency for the cantilever tube
resulted in the formation of a “modular tube” or “bundled tube” system. The nine
75 feet squares of varying heights correspond to a megamodular area. Together
they form the bundled tube of 225 feet square. The perforated walls of the tubes
have columns at 15 feet centers and deep beams at each floor, which act together to
resist wind. The beam - column connections are welded. Trussed levels, consisting
of diagonal members between columns, are provided at three intermediate
mechanical levels - two at the setback levels of the 66th and 90th floors and one
from the 29th to the 31st floors. The structural system provides interior- framed
tube lines which connect the opposing facade frames at two intermediate points
between the ends of the building, thereby reducing the effect of shear lag.
Due to the improved efficiency of the bundled tube framing in the resistance of
lateral forces, the unit amount of steel utilized was only 33 pounds per square foot.
The wind sway is about 0.3 inches per floor for the design wind pressure and the
fundamental period is 7.6 seconds.
Fig. 1.22. Reduction of Shear Lag without (left) and with (right)
Intermediate Framed Tube Lines
38
The columns and beams were built -up from plates and are typically 39 and 42
inches deep. The column flanges are 24 in. x 4 in. in cross-section at the bottom
and 12 in. x 3/4 in. at the top, and for the beams they are 16 in. x 2 3/4 in. at the
bottom and 10 in. x 1 in. at the top. Totally 76,000 tons of Structural steel was
used. All the columns have four inches of Thermofiber insulation behind aluminium
cladding.Fabrication and erection was based on a shop fabricated modular unit
consisting of a two-story column with shop attached half-length beam on either
side. These modules were then field bolted ( for shear only ) at the midspan of the
beam.
Fig. 1.23. Plans showing Core (left) and Framing (right)
The floor system at each floor consists of one-way trusses of 75 ft. spans at 15 ft.
centers. They are connected directly to columns by high-strength friction bolts ( for
shear only ). Their spanning is alternated every six floors to equalize the gravity
loading on the columns. The trusses are 40 inches deep and let the service ducts and
pipes pass through them. The floor slab has 2 1/2 inches of lightweight concrete
poured over a cellular metal deck system which spans between the the trusses.
39
w est
Cr.tcaco Loop
Milwaukee
Fig. 1.24. Sears Tower, Chicago. [Council on Tall Buildings 1982]
CASE STUDY #2
PEN N ZO IL PLACE
H ouston, Texas, U. S. A.
A rchitect - Philip Johnson
S tructural Engineers - Ellisor Engineers, Inc.
This is the largest office complex on a single block in Houston. It consists of two
trapezoidal towers, each rising vertically up to the 31st floor. Above that level one
side slopes at 45 degrees to meet the other side. Totally there are 38 floors in each
part and the height reached is 523 feet. The trapezoidal floor plan is 120 feet wide
and the maximum length is 250 feet. Each floor has approximately 20,000 square
feet of rentable floor area.
Fig. 1.25. Plans showing Core and Framing and Isometric. [Schierie 1993]
41
The principal structural system consists of a combination system of a steel frame
and concrete bracing elements. It utilizes concrete shear walls in the core and a
welded steel frame in the perimeter. Due to torsional considerations three extra
welded steel lines were required at the tapering end of the trapezoidal plan. The
sloped top of the building incorporates a rigid ‘A’-frame, which acts like a hat
truss, drastically reducing the overturning moment on the shear walls by engaging
the exterior columns on the parallel sides. The concrete shear walls were
constructed by 'slip-forming' to save erection time.
Wind tunnel testing was carried out for the design of the aluminium and glass
facade and the structural system. These indicated that maximum torsion induced by
the buildings shape did not exceed that caused by the simple application of the
specified wind pressure applied uniformly across any one facade at a time.
A stub-girder system used for the floor framing which enables the air-conditioning
ducts to be carried through the built-up girder systems. Their increased depths also
)
saved on the amount of steel used compared to the conventional systems (to the
extent of 2.5 lb / sq.ft.). The concept of this girder is very similar to a vierendeel
one.
The foundation system used was a mat one. The bearing soil of the site consisted
of stiff clay. When compared to a pile foundation, the mat one proved more
economic. It is comprised of a reinforced concrete mat which projects
approximately 10 feet beyond the projected floor plan of the buildings.lt is 8 1/2
feet thick under the core and 6 1/4 feet thick under the peripheral columns.
Fig. 1.26. Pennzoil Building, Houston. [Colaco 1985]
CASE STUDY #3
FIR ST BANK TOW ER
T oronto, C anada.
A rchitects : Bregman and Harnann
S tructural Consultants : M.S. Yolles & Partners Ltd.
The First Bank Tower is the tallest building in Canada and is second only to the
Bank of China in Hong Kong, in terms terms of heights of buildings outside the
USA. It comprises of 72 floors out of which 66 are office floors. The height above
the street level is 935 feet with its foundations a further 47 feet below. The basic
plan is roughly a square measuring 191 feet by 181 feet. At the corners, smaller
squares are chamfered off. The typical floor-to-floor height is 12’-8”.
39'-O
2t v r 62 rrn
L F R A M E D T U B E \& O T Y R
Fig. 1.27. Plans showing Floor Framing. [Beaufait 1974]
The basic structural system of the building is a steel trussed tube. Closely spaced
columns and deep spandrel beams form the rigid frame. Since the wind loading was
______________ 4 4
the primary concern with respect to lateral forces, this system was chosen to tesist it
by using the total width of the building. Thus the interior framing had to take only
the gravity loads. The tube system also ensured that the framing on all the floors
was identical since they were unaffected by the varying lateral loading.
The columns of the tube are made out of 4 1/2 “ thick plates placed at ten feet on
center typically. The spandrel beams are like stiffener plates between them which
also serve as a vapour barrier and back-up for fixing the cladding material.
Meanwhile, the core columns are made up of plates up to six inches thick and are
designed to carry loads up to 19,000 kips at the foundation level.
The floor diaphragm serves the vital function of transferring the wind forces to the
side walls of the tube and to provide lateral support to the columns. The framing
consists of 21” deep purlins that run from the the core to the perimeter tube. These
| support a 2” thick metal deck on which is 3 1/2” of light weight concrete. [Beaufait
Fig. 1.28. First Bank tower, Toronto. [Beaufait 1974]
4 5
ANALYSIS OF FRAMING CONFIGURATIONS
IN ITIA L STRUCTURAL DESIGN
My ultimate goal was to design an efficient structural system for a building having
approximately thirty to fifty floors and subject it to certain tests. I had decided that
this building of mixed-usage, housing offices, commercial areas, apartments and
parking. Appropriate floors would be used as service floors. The residential floors
would be located above the office and commercial floors and the parking was
proposed entirely below ground level. The floor-to-floor height for the office floors
was taken as 14 feet and for the apartment floors 10 feet. The area of the floors at
the residential levels was roughly half of that of the office floors.
For the first step in finding an effective structural system for the high-rise building,
I took an example of a simple 30-storied building with a simple moment-resisting
steel frame. It had a square plan 75ft x 75ft with 9 bays of 25ft x 25ft. The floor-to-
floor height was taken as 14ft. A severe wind force corresponding to 100 mph was
applied. The live load at each floor was taken as 50 psf and the dead load as 100
psf.
I calculated the approximate sizes of the main members of the steel frame using the
portal method. Approximations were made at various stages of the procedure. The
building was assumed to be divided into four vertical zones and I basically used
four different column sizes for these four zones while I had one single section for
the beams for all the floors.
The building skeleton which I got from the above procedure, was taken as the basic
configuration for my further experiments. I analyzed it using the 2-D structural
______________________________ 4 6
analysis package FrameMac© and found the maximum deflection of the structure
under the influence of the same loading. This set of results was taken as the control.
(Figures 2.1 and 2.2) [FrameMac V1.12 User’s Manual]
Then I applied various modifications to this configuration and in each case I noted
the change in maximum deflection, keeping the loading constant. Some of the
modifications I tried were belt trusses, hat trusses and core bracing. The different
configurations and their resulting deflections are given in Figs. 2.2 and 2.3.
8 0 p s f
? 6 p s f
69psf
5 8 p s f
SECTION
7Sfl
25ft 25ft 25ft
L 76ft ,
I e*
2
ee
PLAN
Fig. 2.1. Structure and wind loading used for analysis.
S i l i ^ S i S l
12.64”
S I M P L E M O M E N T - R E S I S T I N G F R A M E
C O N T R O L C A S E
| X | X T X |
es
SEZ1 pxqxiX j
s :
12.62” 12.62” 12.35”
WITH B E LT AND H A T T R U S S E S
Fig. 2.2. Maximum deflections in control and modified c a ses.
12.31’
48
9.85”
10.04
9.88
W ITH CO RE B R A C IN G AND H A T T R U S S E S
10.08
9.58
9.94
9.80
10.05
W ITH CO RE BRACING AN D H A T AND B E L T T R U S S E S
Fig. 2.3. Maximum deflections in modified cases.
49
AIM AND INTRODUCTION
The aim of test was to study whether and to what degree, introducing gap(s)
between the floors of a high-rise building and massing it in a particular manner will
help to dissipate the wind pressure on it
Wind forces affect high-rise structures in a number of ways, and are an important
loading consideration in their design. It causes a response not only in the direction
of the wind but also perpendicular to it. Wind may also generate torsion due to the
different high and low pressure zones created.
The lateral loading on a building due to wind has a steady component (constant
mean velocity) and a dynamic component (varying gust velocity). The steady
component causes the structure to deflect in the direction of the wind while the
gusts cause it to vibrate. Usually, as we go higher, the wind velocity increases.
This is because frictional drag on the earth’s surface reduces the velocity. Also, it is
generally seen that the velocity is less in crowded urban areas as compared to open
ones, as there are more encumbrances to slow it down in the former.
As a wind stream hits a building it is deflected and then rejoins the original flow
pattern. More pressure is exerted on the windward side and suction is caused
along the sides and the back (leeward side). A descending wind movement is
caused along the front, thus producing a vortex at the ground level. Also, as the
wind passes the top and sides of the building, eddies and vortices are formed. The
latter produce circular up-drafts and suction streams, which create low pressure
areas on the sides. This pulls the building in the cross-wind direction. This
50
phenomenon is called ‘vortex shedding’ and can cause large movements of the
structure in the cross-wind direction.
What I wanted to find out from my experiments, is whether and to what degree, the
introduction of gaps in the body of the structure would help in reducing the wind
pressure on it I also wanted to check if the orientation of the masses of the building
made a difference in the wind pressures.
W IN D W IND
W IND
CONTROL W ITH 1 G A P W ITH 2 GAPS
Fig. 3.1. Different testing c a ses.
PR O C ED U R E
The height for the hypothetical building case assumed was thirty stories and its plan
square. An aspect ratio of approximately 1 : 6 was assumed. The wind pressures
generated on the surface of the building was monitored by building a scale model
and subjecting it to proportional wind ( corresponding to that in the actual case) in
the wind tunnel.
As the control, the building was first tested without any gaps whatsoever. Then,
different cases were tested with gaps of different sizes being introduced at different
levels of the structure. The orientation of the massing of the building was also
changed with respect to the wind direction, to study its effect on the wind pressures
generated. The results of the different cases were compared to that of the control
case and appropriate conclusions were drawn.
The hypothetical building tested in the wind tunnel was a thirty-storey multi-use
high-rise one. The floor-to-floor height for the top 15 floors (residential) was 10
feet, while that for the bottom 15 (commercial) was 14 feet. The plan was a square
with 100 feet sides. All air gaps introduced were 30 feet high. The cylindrical core
continued.The model was made of plexiglass to a scale representing 100 feet by 1.5
inches. The Aspect Ratio for the control case was 1: 6
The wind pressure in the wind tunnel without the model was recorded at 0.19
inches of water column and with the model as 0.21 inches. Real-life turbulent wind
flow was attempted to be simulated by letting the air pass over a similar scale model
of a group of buildings of different sizes, before it reached the test model.
52
i
The pressure was tapped at the 4th (1,5,9 and 13), 11th (2,6,10 and 14), 19th
(3,7,11 and 15) and 26th (4,8,12 and 16) floors. Four cases were taken with 5 sets
of readings for each case. The pressure was measured on the front, side and back
faces of the building when it faces the wind squarely. Then it was placed in such a
manner that its sides are at 45 degrees to the wind direction. In this case two
readings were taken : front 45 and back 45.
The four configurations were: Case A, which is the control configuration and has
no gaps ; Case B, which has a gap between the 15th and 16th floors ; Case C,
which has a gap between the 23rd and 24th floors ; and, Case D, which has two
gaps between the 15th and 16th floors and the 23rd and 24th floors. The pressure
was monitored at the four levels for each of the five cases in each of these
configurations.The pressures were measured using pitot tubes and an analog
manometer, in terms of inches of water column, after caliberadng its ‘zero mark’.
.WIND
FRONT 45
W IN D
FRONT
BACK 45°
Fig. 3.2. Different c a ses of wind direction relative to building.
5 3
CALCULATIONS
The air velocity for the scaled wind tunnel testing is calculated thus:
Air velocity = 1096.2 x V ( Pv / D )
where, Pv = Velocity Pressure in inches o f water
D = Air Density in lb per cu.ft.
[ Air Density, D = 1.325 x Pb /T
where,
PB = Barometric Pressure in inches o f Mercury
T = Absolute Temperature ( F + 460) in Kelvin ]
Example
Data:
T = 73 F = 73 + 460 = 533 K
PB =29.9”
Therefore,
D = 1.325 x 29.91533
= 0.0743 Iblcuft
Thus, A ir Velocity for 0.21 inches o f water column is
Air Velocity = 1096.2 x V( 0.21 / 0.0743 )
= 1842.91 ft / min.
= (1842.91 x 60 ') / 5280f t
= 20.94 mph
54
r
RESULTS
The pressures which were measured for the different cases are given in the
following chart. The pressures at the different levels were compared to those in the
control case and their relative values were also tabulated ( see chart) as percentages
of the values in the control configuration.
It is noticed that the pressures in the cases with gaps are less than in those for the
control case. This reduction varies from 29% to 0%. In no case is a value in the
cases with gaps more than its corresponding value in the configuration without
gaps.
5 5____ |
EXPERIMENT NO.: /
DATE: Dec. 6, 1990
BAROMETER: 29.9" Hg
RELATIVE HUMIDITY: 22%
SUBJECT: H1GH-RISE-A
TIME - START: 15:30 END: 16:15
TEMPERATURE: 73 F
STATIC PRESS.:wf M = 0.21 w/o M -0.19
W IN D
CONFIGURATION A - Without Gap
POSITION FRONT SIDE
BACK
FRONT 45° BACK
1
0.09
0.34 0.30 0.15
0.30
2
0.05 0.35
0.30
0.14 0.30
3
0.03 0.31
0.30 0.16 0.31
4
0.02 0.30
0.29
0.12
0.30
All the PRESSURES are in IN C H ES OF W ATER CO LU M N .
56
EXPERIMENT NO.: 2
DATE: Dec. 6, 1990
BAROMETER: 29.9" Hg
RELATIVE HUMIDITY : 22%
C l
SUBJECT: HIGH-RISE-B
TIME - START: 16:30 END: 17:15
TEMPERATURE: 73 F
STATIC PRESS.:wt M = 0.21wlo M=0.19
uwiiiw
W IND
CONFIGURATION B - With I Gap in the Middle
POSITION FRONT SIDE BACK FRONT 45° BACK 45
1
0.08 0.32 0.27 0.10 0.28
2
0.04 0.33 0.27 0.09 0.27
3 0.01 0.28 0.28 0.10 0.28
4 0.02 0.27 0.29 0.11 0.29
All the PRESSURES are in IN C H ES O F W A TER CO LU M N .
5 7
EXPERIMENT NO.: 3
DATE: Dec. 6, 1990
BAROMETER: 2P.9” Hg
RELATIVE HUMIDITY: 2 2 %
SUBJECT: H1GH-RISE-C
TIME - START: 17:30 END: 18 :1 5
TEMPERATURE: 73 F
STATIC PRESS.: w/M = 0.21 w/o M=0.19
4
JH
W IND
CONFIGURATION C - With I Gap at the Top
POSITION FRONT
SIDE BACK
FRONT 45°
BACK
1
0.08
0.30
0.28
0.10
0.26
2
0.04 0.28 0.25
0.09
0.27
3
0.02 0.29
0.27
0.08
0.29
4
0.01 0.29
0.21
0.07
0.28
All the PRESSURES are in IN CH ES OF W ATER CO LU M N .
5 8
EXPERIMENT NO.: 4
DATE: Dec. 6, 1990
BAROMETER: 29.9” - Hg
RELATIVE HUMIDITY: 22%
El
SUBJECT: HlGH-RISE-D
TIME - START: 18:30 END: 19 :1 5
TEMPERATURE: 73 F
STATIC PRESS.: w! M = 0.21 w/o M=0.19
M -
W IN D
CONFIGURATION D - With 2 Gaps
POSITION FRONT SIDE BACK FRONT 45° BACK 45
1 0.08 0.30 0.26 0.10 0.28
2
0.04 0.30 0.26 0.09 0.24
3 0.01 0.28 0.28 0.09 0.30
4 0.01 0.28 0.28 0.08 0.29
All the PRESSURES are in IN CH ES O F W A TER COLUM N.
5 9
1
1
FRONT SIDE BACK FRONT 45° BACK 45° COMMENTS
A1 100% 100% 100% 100% 100% CONTROL CONFIGURATION - A
! A2
100% 100% 100% 100% 100%
1 A3 100% 100% 100% 100% 100% NO gaps between floors
A4 100% 100% 100% 100% 100%
B1 89% 94% 90% 67% 93% CONFIGURATION - B
B2 80% 94% 90% 64% 90%
B3 33% 90% 93% 63% 90% Gap between thel5th & 16th floors
! B4 100% 90% 100% 92% 97%
C1
C2
89% 88% 93% 67% 87% CONFIGURATION - C
80% 80% 83% 64% 90%
C3 66% 94% 90% 50% 94% Gap between the 23rd & 24th floors
C4 50% 97% 72% ' ' 58% 93%
D1 89% 88% 87% 66% 93% CONFIGURATION - D
D2 80% 86% 87% 64% 80% Gaps between the 15th & 16th
D3 33%. 90% 93% 56% 97% and 23rd and 24th floors
D4 50% 93% 97% 66% 97%
Os
All comparisons are with the corresponding control configuration
i ’ ‘
Table'3.1. Wind pressures for different configurations.
FRONT SIDE BACK FRONT 45° BACK 45° COMMENTS
A1 100% 100% 100% 100% 100% CONTROL CONFIGURATION - A
A2 100% 100% 100% 100% 100%
A3 100% 100% 100% 100% 100% NO gaps between floors
A4 100% 100% 100% • 100% 100%
B1 89% 94% 90% 67% 93% CONFIGURATION - B
B2 80% 94% 90% 64% 90%
B3 33% 90% 93% 63% 90% Gap between the 15 th & 16th floors
B4 100% 90% 100% 92% 97%
Cl
C2
89%
80%
88%
80%
93% 67% 87% CONFIGURATION - C
83% : 64% 90%
C3 66% 94% 90% 50% 94% Gap between the 23rd & 24th floors
C4 50% 97% 72% ' 58% 93%
D1 89% 88% 87% : 66% 93% CONFIGURATION - D
D2 80% 86% 87% 64% 80% Gaps between the 15th & 16th
D3 33% 90% 93% 56% 97% and 23rd and 24th floors
D4 50% 93% 97% 66% 97%
1
O x
All comparisons are with the corresponding control configuration i »
Table 3.2. Comparisons of wind pressures of different configurations with control case.
PRESSURE I N INCHES O F WATER
WIND PRESSURE COMPARISON
FRONT/BACK 90*
0.4
0.38
0.34
0.32
0 . 3 -
0.28
0.26
0.24
0.22
2
4
CONFIGURATION POSITION
A — B C - a - D
Fig. 3.3. Wind pressure comparison for Front/Back 90°!
PRESSURE I N INCHES O F WATER
WIND PRESSURE COMPARISON
SIDE 90*
0.35
0.34
0.33
0.32
0.31
0.3
0.29
0.28
0.27
1 3
2 4
CONFIGURATION POSITION
ON
A - h— B C D
Fig. 3.4. Wind pressure comparison for Side 90°.
O n
z
2
Z)
0 .4 8 -
_j
O
o
0 . 4 6 -
< r
L U
<
0 . 44 -
<:
u_
O
0.42
C O
U U
I
0.4
o
z
M M
0.38
z
L U
C C
0.36
3
C O
C O
0.34
L U
C C
C L
WIND PRESSURE COMPARISON
FRONT/BACK 45*
CONFIGURATION POSITION
Fig. 3.5. Wind pressure comparison for Front/Back 45°
C O N C LU SIO N S
After the pressure was monitored for the different cases and compared to the-control
case, it was apparent that introducing gaps in the building configuration
m ark e d ly (upto 29%) reduces the wind p ressure in cid en t on the
different surfaces of the building. Also, vortex shedding and suction
forces a re responsible fo r m uch higher w ind p ressu re s on th e
building faces than direct wind action.
Thus, gaps in the building configuration can be an asset not only aesthetically and
functionally ( as to separate different uses, as in this case ), but also in terms of
reducing the lateral forces acting on its structure.
65____
A PPLIC A TIO N OF TEST RESULTS
AIM
After testing the building in the wind tunnel with and without air gaps between the >
floors, the conclusion was drawn that these gaps did reduce the wind pressure
incident on the building’s surface. However, one had to consider the fact that a
premium was being paid in terms of the floor(s) reduced due to the gap(s). What
was important to study was to see if we could actually save some structural material
(in this case steel) by introducing these gaps. That was the reason which prompted
me to take the same 30-storey simple moment-resisting steel frame building and
subject it to both these conditions and see if the material used was less or more.
6 6
ASSUM PTIONS AND M ETHODOLOGY
The 30-storey moment-resisting steel frame designed previously was taken as the
control case. The floor-to-floor height was taken as 14 feet and the plan was 75 ft x
75 ft with 25ft x 25ft bays. As simulated in the wind tunnel, a uniform wind
pressure was assumed to act throughout the height of the building, which in this
case was taken as 80 psf corresponding to a wind speed of 100 mph.
After loading the frame for the wind pressure, it was statically analyzed using
Elm24©. [Elm V2.4 User’s Manual] The maximum deflection was noted and the
the sections of the members were adjusted until the deflection was just under
permissible limits. When this was achieved, the total weight of steel used was
computed by multiplying the various lengths of the members used by their
respective weights per linear foot. This gave the total amount of steel used for the
building frame, without gaps.
Then a gap was simulated equalling twice the floor-to-floor height, i.e. 28 feet.
Thus we basically had a building with 31 floors instead of 30. However* this
building had reduced wind pressure incident on it. Studying the wind tunnel test
results it was seen that the pressure is reduced by about 12% on an average. Thus
this new configuration was subjected to only 88% of the lateral pressure of the
previous case.
This case was once again analyzed using Elm24 and the maximum deflection noted.
The sections of the members were then adjusted and manipulated until the
maximum deflection equalled that for the first building case. Then, once again, the
6 7
This value of steel used was then compared to that of the previous case to find out
the increase or decrease in the amount of material used. The percentage of increase
or reduction was also noted.
WIND
80psf
WIND
70.4psf
(88%)
WITHOUT GAP WITH GAP
Fig. 4.1. Configurations without (left) and with (right) gaps.
6 8
_________
R E SU L T S
It was computed that the total amount of steel used for the first case was
13,596,000 lbs. while it was 11,993,320 lbs. for the latter case. Thus, there is a
reduction in the amount of steel used by about 11.78%, when the gap
is introduced (taking into account the extra floor of framing which is requited).
The steel usage for both corresponded to the same maximum deflection of 2.01
feet.
69
CONCLUSION
It is very interesting to note that, although the premium of having an extra
floor has to be paid to introduce the gap in the building
configuration, the reduced wind pressure incident on it actually
decreases the required steel quantity for the structural frame. Thus the
introduction of such air gaps may not only be functionally and aesthetically
beneficial but also help in saving structural material costs. This saving could be
substantial in a large sized building.
7 0
REFERENCES and BIBLIOGRAPHY
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Beaufait, F.W. (ed.) 1974. Proceedings of the Symposium on Tall
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Dept., Vanderbilt University
Beedle, L. (ed.) 1980. Monograph on Planning and Design of Tall
Buildings. ASCE
Beedle, L. (ed.). 1983. Developments in Tall Buildings. Hutchinson Ross
Publishing Co.
Beedle, L. and Falconer, D. 1984. Classification of Tall Building
Systems. Lehigh University.
Bums, J.G. (ed.). 1985. The Engineering Aesthetics of Tall
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Colaco, J.P. 1985. Aesthetics of High-Rise Building Structures. ASC E.
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Cowan, H. and Wilson, F. 1981. Structural Systems. V < ?n Nostrand Reinhold
Co.
Engels, H. 1977. Structure Systems. Deutsche Verlags-Anstalt.
Fletcher, Bannister. 1975 . A History of Architecture. The Athlone Press.
Gideon, S. 1980. Space, Time and Architecture. Harvard University Press.
Goldberger, P. 1982. The Skyscraper. Alfred A. Knopf.
Goldsmith, M.1985. Effect of Scale on Tall Buildings. ASCE.
Halprin, L. 1963. Cities.Tan Nostrand Reinhold Co.
Hambidge, J. 1967. Elements of Dynamic Symmetry - Dover Publications.
Hart, F. 1978. Multi-storey Buildings in Steel. John Wiley & Sons
Health, T. F. 1971. Aesthetics of Tall Buildings. Lehigh University. ^ ^
Howard, S. H. 1966. Structure - An Architect’s Approach. McGraw-Hill.
Huxtable, A.L. 1984. The Tall Building Artistically Considered. Pantheon
Books
Jencks, Charles. 1980. Skyscrapers - Skyprickers - Skycities. Rizzoli
International Publications
Johnson, P. 1979. Philip Johnson / John Burgee Architects. Random
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Khan, F. R. Future of High-Rise structures. Progressive Architecture,
October, 1972
Khan, F. R. and El Nimeiri, M. M. 1983. Structural Systems for Multi-Use
High-Rise Buildings. Hutchinson Ross Publishing Co.
Komendant, A. 1975. Eighteen Years with Architect Louis I. Kahn.
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Kostov, S. 1984. The History of Architecture. Oxford University Press.
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Ross Publishing Company.
Lamela, A. 1973. Town Planning and Vertical Architecture, The
Problem Raised Thereby and The Necessity of a New Outlook.
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Lin, T. Y. 1988. Structural Concepts and Systems for Engineers and
Architects.Van Nostrand Reinhold Co.
Messier, N. 1986. The Art Deco Skyscraper in New York. Peter Lang
Publishing.
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of Cities. University o f Hawaii.
Popov E. P., Takanashi, C. and Roeder, C. W. 1976 . Structural Steel
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Prak, N. S. 1977. Visual Perception of the Built Environment. Delft
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Saliga, P. A. (ed.). 1990. The Sky’s the Limit. Rizzoli Publications.
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Scheuller, W. 1990. Vertical Building Structure.Van Nostrand Reinhold Co.
72
: :_____________________________________________________ — ,
Schierle, G.G. 1993. Synergy of Form and Structure.USC Lecture Notes.
Scuri, P. 1990. Late-Twentieth-Century Skyscrapers. Van Nostrand
Reinhold Co.
Skidmore, Owings and Merrill. 1974. Architecture of Skidmore, Owings
and Merrill, 1963-1973. The Architectural Book Publishing Co.
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McGraw-Hill.
Tiggerman, S. 1980. Chicago Tribune Tower Competition and Late
Entries. Rizzoli International Publications.
-. 1986. FrameMac Version 1.12 User’s Manual. Compuneering, Inc.
-. 1989. Elm Version 2.4 User’s Manual. Fujistu America, Inc.
73
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Asset Metadata

Creator Mitra, Saswata Kumar (author)

Core Title Mixed-use high rise building in response to natural forces

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Degree Conferral Date 1993-08

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag engineering, architectural,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c17-784488

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