1.
1.1.
Introduction to High Rise Structures & Case Study
When does a Building become a High-rise?
● Height of which a building is considered tall is relative.
● NBC 2016 Part 4 Fire and Life Safety 2.25 describes High Rise Building as “All buildings 15 m or above in height shall be
considered as high rise buildings.”
● The Karnataka Fire Force Ordinance, 2023: “A high rise building” means a building of 21 meters or above in height irrespective
of its occupancy as defined in the National Building Code 2016.
● In Germany, consensus has been reached for the purpose of certain safety (fire protection) - “High rises are buildings in which the
floor of at least one occupied room is more than 22 m above the natural or a prescribed ground level.”
● Other countries also have building laws that define buildings exceeding specified heights, which can vary between 13 m to 50 m,
as high rises.
● Skyscrapers.com have chosen a building height of 35 m or 12 stories as a benchmark.
1.2.
What are the special features of high-rise structures? In terms of external
loading
In comparison to shorter buildings,
● Higher Vertical Loads i.e., Dead Load, Live Load & Snow Load
● Higher Lateral Loads i.e., Wind Load and Seismic Load.
Behavior of high-rise structural system under lateral loading is comparable to a cantilever fixed
into the subsoil. Horizontal loads are not constant over the height, but increases over the
height. Thus the moment towards the base increases more rapidly.
Absorption of horizontal loads and the ability to transmit the resulting moment into the foundation
is a primary task in the structural design of tall buildings.
With coupling of forces, the moment can be effectively
transferred.
However, this causes tensile stresses in the vertical
elements, which can only be tolerated in exceptional
cases in reinforced concrete construction.
Therefore an attempt is made to distribute the dead
loads (mainly flooring) in such a way that tensile
stresses resulting from horizontal loads are continually
compresses or overcompensated.
Thus the system of horizontal load removal, affects the
distribution of and transfer of vertical loads.
In terms of ensuring structural integrity, we should
validate elements such as building’s spatial rigidity
and load-bearing.
1.3 What is the historical background of the structure of High Rise Buildings?
Evolution of High Rises is closely linked to the urban development of Chicago.
Following the devastating fire of 1871, during which a large part of the city was
destroyed, new buildings in the reconstruction effort became increasingly higher.
Technical Innovations in building services, elevators, and motivation by prestige of
tall buildings as an expression of economic growth.
First generation of high rises consisted of steel frames. Steel columns and girders
were joined together to form rigid frames. Additional bracing with steel trusses, or infilled
non-load bearing masonry helped in absorption of wind loads.
However primary rigidity was provided by a grid of closely spaced steel columns, 6 to 9
m apart, bound together with beams to form a frame.
In 1885, first high rise to use steel skeleton was the Home Insurance Building in
Chicago, with a height of 55 m.
● Use of first rolled I-beams
● A high degree of fire safety with fire walls of masonry,
● Safe and Rapid Occupant Transportation System.
In parallel, more conventional massive building techniques
with load bearing masonry were still popular.
● In 1892 this traditional approach was used in Chicago’s Monadnock Building (Burnham & Root)
● It is a masonry building with 16 stories and a perforated facade.
● Load-bearing exterior walls increase to a thickness of almost 2 m at the ground floor.
Capabilities of this building tech. had reached its limits, and this construction style was not continued
thereafter.
● Further technical developments seemed to remove all limits to ever taller building.
● Highpoint of first generation of high rises was New York’s Woolworth Building (Cass Gilbert), finished in
1913.
● With its steel skeleton frame, hidden behind the gothic facade, this building reached a height of 235
m (55 stories).
● As a highly mechanized building with high speed elevators, full air-conditioning, electric lighting and
telephone systems, the Woolworth Building remained the world’s tallest building for 16 years.
After the first world war the resulting economic
depression brought an interruption to these development.
However, at 1920s the construction of high rise buildings
was resumed, culminating at the beginning of the 1930s
with New York’s Chrysler Building (313 m) and the
Empire State Building (383 m).
Empire State Building was tallest building in the world for
over 40 years.
Both had use steel skeleton framing system.
Engineers such as Fazlur Khan (SOM, Chicago),
William Le Messuirier (Boston) and Leslie E
Robertson (NY) developed new structures by attempting
to increase the efficiency of high rises and
simultaneously designing new load-bearing systems
required by new architecture.
To this end, so called tubes were developed - lateral
loads could be resisted by rigid tubes located on the
exterior. Thus internal space could be free of shear walls and lateral
reinforcement elements.
Buildings such as World Trade Center (NY), John Hancock Center and the Sears
Towers (Chicago) were constructed of steel in this fashion, with outer tube
structures also determining the building’s appearance.