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Case Studies: |
Dynamic Identification of the Qutub Minar, New Delhi, India
The results
presented are
made available by research assistant
Luis Ramos, M.Sc. Department of Civil
Engineering, University of Minho, Portugal.
This work has been carried out with the support
of the European-Indian Economic Cross Cultural
Program, under contract ALA/95/23/2003/077-122,
“Improving the Seismic Resistance of Cultural
Heritage Buildings”.
The Qutub Minar is the highest monument of India
and on of the tallest stone masonry towers in
the world. An interior circular staircase, with
379 steps, communicates to the balconies, where
the muezzin called to the prayer. This minaret
is also symbolic, which glorifies the victory of
Islam against idolatry. The construction began
during the reign of Qutb-ud-din around 1202 but
only the first story of the tower was
constructed. The next ruler, Iltutmish, added
the next three stories. It was damaged by
lightning in 1326 and again in 1368. In 1503,
Sikandar Lodi carried out some restoration and
enlargement of the upper storeys.
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The minaret is circular in plan, with a base of
14.0 m diameter and it tapers to a diameter of
3.0 m at the top along a height of 72.5 m. The
stairway is spiral, around the central masonry
shaft, and is made by Delhi quartzite stone.
Each storey has a balcony, which is supported by
a system of stalactite bracketing, while the
uppermost storey finishes with a platform.
The tower is mainly composed by an external
shell built with a masonry wall with three
leaves and a cylindered central core. These two
elements are connected by the helicoidally
stairs and, locally and randomly, by 27 bracing
beams composed by stone units with an average
cross section of 0.4 ´ 0.4 m2.
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The modal identification was made under the
Euro-Indian Research Project Improving the
Seismic Resistance of Cultural Heritage
Buildings, contract ALA-95-23-2003-077-122,
with the main issue to study the seismic
resistance of the monument.
For the response, measurements of 20 points in
four levels of the structure were selected to
measure the accelerations caused by ambient
vibrations. The seven data series acquired at
100 Hz were then processed by a decimation of 5
(Nyquist frequency of 10 Hz), with segment
length of 516 points with 66.67% window overlap,
with 3 projection channels for the subspace
identification.
For the stochastic estimation of the models, 20
structural modes and 30 noise modes were
considered. Pairs of narrow frequencies could be
seen, with very close values for the first two
modes, as can be observed in the following
figure. This fact and the complexity of the
structure increase the difficulty on the
estimation of the first two modes.
Below
you can download AVI
movies of some of the modes. The modes
have been estimated with
the Principal Component
Stochastic Subspace Identification
estimator available in
the ARTeMIS Extractor
Pro version.
Hint: To get the
maximum out of the
downloaded AVI movie,
please set your AVI
movie player to "Repeat
Forever".
Related Information
The Masonry and Historical Constructions Group
of Department of Civil Engineering of the
University of Minho (www.civil.uminho.pt/masonry)
tries to act at all levels related to masonry
and historical constructions, including
inspection, advanced testing and modelling,
assessment and strengthening, and combining top
level research, specialized consultancy and
product development for the industry.
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