Rising High with
GPS Network
by Agnes Zeiner
The Burj Dubai is the highest-rise building under
construction in the world. When completed in
2008 it will be the world’s tallest building, nearly
twice the size of New York’s Empire State Building and higher than the current title holder, the
Taipei Financial Center (Taipei 101) in Taiwan. The
final height is being kept secret. Not a secret on
the other hand, is the unique monitoring system
Leica Geosystems developed together with the
Chief Surveyor of Burj Dubai.
In recent years there has been considerable interest in the construction of super high-rise buildings,
primarily in the Far East. These buildings are subject
to strong external tilt effects caused, among other
things, by wind pressures, unilateral thermal effects
through exposure to sunlight, and unilateral loads.
12 | Reporter
Such effects are a particular challenge during the
construction phase of a high-rise building, in as much
as the high-rise building under construction is also
subject to tilt effects and will at least temporarily
lose its – usually exactly vertical – alignment.
The Burj Dubai in Dubai, UAE, will rise to a height of
over 800 m when completed in 2008. In addition to
being very tall it is also quite slim and it is anticipated
that there will be movement of the building at upper
levels due to wind loads, crane loads, construction
sequence and other factors. The self-climbing formwork system for the building is complex due to the
shape of the structure and requires a large number
of control points – currently over 240 are installed.
Douglas Hayes, Chief Surveyor in Burj Dubai Tower,
and Joel van Cranenbroeck, Business Development
Director at Leica Geosystems, developed a complete-
ly new procedure to provide reliable coordinated
points at the top of Burj Dubai using GPS observations combined with a network of precision inclination sensors.
At the beginning of construction, six permanent
benchmarks were established and precisely surveyed around the site. “From ground to about Level
20 resection was possible from the external control
marks, which are located about 100 to 150 m from
the base of the tower. Observation redundancy was
possible and very high quality results were achieved”,
says Douglas Hayes. But above Level 20 this system
was not applicable anymore due to obstruction from
the upper decks of the formwork system and poor
visibility.
“The movement of the structure creates several
problems for precise surveys. Theoretically, at any
particular instant in time you need to know exactly
how much the design centre line of the building is
offset from the actual vertical axis and at that same
instant you need to know the precise coordinates of
the instrument. However, a ‘mean’ position for both
elements taken over a short time period can provide
a suitable solution”, says Douglas Hayes. A complex
combination of GPS antenna/receivers, Total Stations,
Continuously Operating GPS Reference Stations Leica
GRX1200 Pro plus Leica GPS Spider and Leica Geo
Office Software, together with Leica Nivel220 dualaxis precise clinometers, accurately determines and
analyzes displacement of the tower alignment from
the vertical axis.
A dynamic model of the building has been developed and from this it has been possible to derive
values at any given level for the effect of construction sequence, building design and solar effects. This
‘smallest GPS network for the tallest building in the
world’ can be used for tower monitoring both during
construction and after completion of the structure”,
summarizes Douglas Hayes: “If the Nivel200 Network is integrated with other monitoring information it will provide a complete system of structural
monitoring.”
The “Vertical Cities”
Concept
“The challenge taken on by the vertical conquest of
space is not to beat height records but to redefine
dignified life in large communities. Authentic social
commitment lies in developing an innovative model
of vertical construction that unites revolutionary
technological concepts capable of exceeding the
500 m height limit and the new bio-ecological models
of town planning and architecture in a new philosophy of life,” say the Spanish architects Javier Pioz and
Maria Rosa Cervera.
Overpopulation, obsolete urban models with all their
rising problems, and the non-acceptance of the common 500 m limit led them to develop their “Vertical Cities Concept”, based on the consideration that
nature shows us how to build structures (Bionic Architecture). Their thesis: In massive nuclei and where
land is scarce “Vertical Cities” allow the ecological
expansion of cities. For Pioz and Cervera, buildings
up to 1,228 m high (equivalent to 300 floors) with
100,000 inhabitants are the future – for mankind
as well as for the environment: “Nature has all the
answers; in time man will learn all the questions.”
The Global Magazine of Leica Geosystems | 13