The Structural Systems oF Tall Buildings - Tall Buildings: Structural Systems and Aerodynamic Form - page 14

Taking as a basis the columns, beams, shear trusses (braces), shear walls, and
outriggers that are the elements of the main vertical and horizontal structural systems,
buildings can be categorised as being reinforced concrete buildings where these
elements are made of reinforced concrete, or as steel buildings where these elements
are made of steel. We can define composite buildings as: those in which some struc-
tural elements are made of reinforced concrete and other structural elements are
made of steel; and/or those in which some structural elements are made of both struc-
tural steel and concrete together. Floor slabs are usually made of reinforced concrete
or are composite. Thus, it is general practice to use concrete/reinforced concrete in
slabs. Generally, the floor slabs in steel buildings are composite, and in reinforced
concrete and composite buildings they are reinforced concrete or composite.
Normally, composite floor slabs are formed by applying metal deck (trapezoidal steel
plate) with concrete/reinforced concrete topping. Composite floor slabs commonly
support structural steel or steel trusses. According to the Council on Tall Buildings
and Urban Habitat, in classifying tall buildings based on the materials used in their
structural systems, the main vertical and horizontal structural elements but also the
floor systems are taken into account.
The use of steel as a material for a structural system attracted attention in 1885
with the construction of the 55 m high Home Insurance Building (Chicago) ( Figure1.2 )
and of the 300 m high Eiffel Tower (Paris) in 1889. By the end of the 1990s all the
buildings achieving the title of “the world's tallest building” used steel structural
systems due to the superiority of structural steel in its strength to weight ratio, the ease
with which it can be transported, installed and assembled on-site, the wide range in
the choice of strength and cross-sections of the elements, and advances in fire and
corrosion resistance. The 442 m high Willis Tower (Chicago, 1974) ( Figure 3.73 ), with
a steel structural system, held the title of “the world's tallest building” from 1974 to
1998.
Reinforced concrete is formed by strengthening concrete with steel bars. The
discovery of reinforced concrete greatly increased the importance and use of concrete
in the construction industry. Architects and structural engineers used reinforced
concrete to produce unusual and aesthetic building forms, thanks to its ability to be
cast in any form, and to its much greater natural resistance to fire, compared with
steel. In addition, compared with a steel building, a reinforced concrete building
is naturally better at dampening wind induced building sway, which is one of the
problems frequently encountered in tall buildings and is perceived by the building
occupants. With the advances in technology, the increase in strength and developments
in concrete pumping technology - the ability to pump it to high levels - reinforced
concrete can now be used in all structural systems for tall buildings. The 16-storey,
65 m high Ingalls Building, built by Elzner and Anderson in Cincinnati in 1903, was
the first skyscraper with a reinforced concrete structural system ( Figure 3.1 ). In 1998
the Petronas Twin Towers , 452 m high and with a reinforced concrete structural system
( Figure 3.31 ), took the title of “the world's tallest building” from the Willis Tower,
which has a steel structural system. The Petronas Twin Towers were the first reinforced
concrete buildings that gained the title of the world's tallest.
While composite structural systems, consisting of steel and reinforced concrete
together, were only rarely seen in supertall buildings before 1970 (Chrysler Building