|Software for Operational
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,
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
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 storey's.
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 times 0.4 m2.
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
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
Hint: To get the maximum out of the downloaded
AVI movie, please set your AVI movie player to
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.