Case Study
Analysis of natural draught cooling towers
- Eigenvalue
analysis
- Wind loading analysis
- Seismic response assessment
 Bierrum International Ltd provided
the design and specialist construction equipment for the building of
two new cooling towers at the Trino Vercellese power plant in
northern Italy. Bierrum used LUSAS Civil & Structural to
help with its design of the 90m high structures for its client,
Italy’s largest power company, ENEL (Ente Nazionale per l’Energia
eLettrica).
The cooling towers, which were some
of the first to be built in Italy, include many state-of-the-art
features; including ‘dry’ cooling technology and the
incorporation of meridional support columns and a central chimney.
On coming into service in June 1998 it became ENEL’s first modern,
greenfield Gas Turbine and Combined-Cycle Plant. Bierrum were
responsible for the complete structural design of the towers, as
well as for the supply of all specialist construction equipment and
supervision.
Construction
Each cooling tower is supported on a
5.8 metre wide by 2.0 metre high conventional reinforced concrete
annular ring foundation. The foundations incorporate plinths for
each of the 36 pre-cast concrete support columns. As each column
weighed in excess of 90 tonnes sophisticated lifting and temporary
works schemes were designed to assist installation. The tower shells
were constructed using a patented climbing access and formwork
system that provided easy access to the working face and allowed a
1.5m lift of concrete to be constructed every working day.
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| Typical
mode shape |
Stress
contours from wind loading |
Modelling and
analysis
The tower shell, support columns and
ring foundation were all modelled. LUSAS command files (useful for
creating families of structures) were used to both create the two
thousand element model as well as assist in the processing of the
results. Loading on the structures included dead and wind loads,
temperature effects, earthquake loads and stresses due to the
settlement of the foundations. John Turner, Bierrum’s Chief
Engineer at the time and now of John Turner (Engineering
Consultants) Ltd. said: "we decided to use separate analyses
for short and long term loads, and for alternative foundation
stiffnesses, and we used the LUSAS eigenvalue facilities for
calculating the seismic response and for checking for global
buckling." In summary he said: "The deformed mesh and
stress contour plots produced by LUSAS proved invaluable in showing
how the structure was responding to the various loading
conditions."
"The
deformed mesh and stress contour plots produced by LUSAS proved
invaluable in showing how the structure was responding to the various
loading conditions."
John Turner (formerly
of Bierrum International Ltd)
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