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Seismic analysis of liquefied
natural gas tanks |
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Principia has extensive experience in
the civil design of storage tanks for liquefied natural gas
(LNG). Among many other projects, Principia has had full responsibility
for the civil design of 2 tanks in Dahej (India), 2 in Ras Laffan
(Qatar) and 2 in Barcelona (Spain); for these design activities
Principia counted on the collaboration of Esteyco
or Carlos Fernández
Casado. Principia has evaluated the seismic hazard at those
and many other tank sites, both in Spain (Barcelona, Sagunto,
Cartagena, Huelva, Ferrol, Bilbao and Las Palmas) and abroad
(Egypt, India, Qatar, Mexico, Peru, etc).
  Among
the requirements imposed, the dynamic response of the tank must
be evaluated in the course of the various design seismic motions
(OBE and SSE earthquakes), taking into account the corresponding
specifications: strength capacity, stability, integrity, containment
function, freeboard requirements, etc.
The photograph shows one of the Dahej tanks during construction;
it has a capacity of 150,000 m³ and is supported on 578
piles. The finite element model is one of several developped
for analysing the dynamic response of the tank.
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Vibration analysis of a footbridge in Bilbao |
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 New
techniques and materials have allowed a progressive lengthening
of bridge spans, for both traffic and pedestrians. Coupled with
slender geometries, this leads to vibration frequencies that
are low, close to the walking frequency of pedestrians. As a
result, pedestrians may be induced to synchronise their steps
with the vibrations of the footbridge, giving rise to a resonant
excitation and excessive motions. Not long after the present
project, London's Millenium Bridge became the most famous exponent
of these problems.
Principia has studied vibrations and dynamic amplification during
the design phase of a number of footbridges. One of them is
the 150 m Pedro Arrupe Footbridge in Bilbao. The studies were
based on a finite element model, generated to determine the
natural modes and frequencies, as well as the dynamic amplification
for the excitation caused by pedestrians. The project included
the design of four TMD devices (Tuned Mass Dampers) to limit
the expected vibration levels.
The actual footbridge is shown in the photograph. The figures
provide the expected motion levels with and without TMD's, as
well as the model employed in the calculations.
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Roof of the Reina Sofia
Museum |
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The wind too can be the trigger of excessive
vibrations. Many types of structures are sensitive to these
problems, one of them being cantilevered roofs with large
dimensions. The effects can worsen if the structural frequencies
are low and remain within the high energy region of the spectrum.
In support of the structural project by Esteyco
and an architectural design by Jean Nouvel, Principia carried
out the dynamic characterisation of the enlargement of the
National Museum and Arts Centre Reina Sofía (MNCARS)
in Madrid. In particular, the modes and frequencies of vibration
were determined for the roof of the museum extension.
The pictures present a virtual image of the roof, as well
as one of the finite element models used for supporting the
necessary dynamic calculations.
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