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1. Introduction
For many years, dams have acted as major engineering works to
improve various sectors of our society or even introduce factors
in a region that make the location more appropriate for people to
remain in their places of origin.
Some of the main functions of dams include: flood control in areas
near rivers, water storage and irrigation in areas with long periods
of drought, containment of tailings from mining companies, recre-
ation, and power generation.
Since the beginning of the Industrial Revolution, society has in-
creasingly needed energy sources. As a result, the governments
of several countries began to invest heavily in building dams, be-
cause they can generate large amounts of energy depending on
the site where they are installed. Not only has the number of dams
increased but their size has also increased, as is the case of the
Itaipu concrete dam, built by Brazil in association with Paraguay.
The dam is the largest operating hydroelectric facility in terms of
annual generating capacity. The construction of this dam con-
sumed approximately 28 million tons of concrete [1]. The concrete
dam of Itaipu has maximum height of 196 meters from the crest to
the foundation, and is 7,919 meters long.
Currently, there is a major concern in conducting a detailed assess-
ment of the structural behavior of buildings. This is justified by the
fact that many structures that are built nowadays are much larger
than those built in the past, because they have an innovative struc-
tural arrangement or are even prone to exceptional actions, such as
those structures erected in countries with strong seismicity.
In structural engineering, dams are among the structures that have
been monitored for a long time and have a higher number of in-
stalled sensors - usually thousands, as is the case of the Tucuruí
dam, in northern Brazil, which has about 2,800 sensors [2].
According to the Centro da Memória da Eletricidade no Brasil (Bra-
zilian Center forElectric Power History) [3], the study of dam safety
began in the United States around the 1950›s with the dam safety
program of the Bureau of Reclamation, which established the rec-
ommendations on the matter after a review by the National Re-
search Council›s Report. Such recommendations include installing
field instruments that enable monitoring the structural behavior of
dams and prioritize inspection of dams in high-risk sites.
The first analyses related to dam engineering focused on the deter-
mination of displacements, strains and stresses. With the advent
of new sensors, it became possible to determine other structural
behaviors, such as: determination of natural frequencies and vibra-
tion modes, allowing the comparison of numerical results with the
measured data, which also allowed the online evolution of natural
frequencies and early detection of structural deterioration and ag-
ing processes [4].
Because of the size of large dams, which are among the largest
constructions in civil engineering, it became necessary to estab-
lish some methods to verify the safety conditions of this type of
construction, since collapse of these structures brings about huge
social, economic and environmental damages.
According to [5], the safety control of a dam comprises the envi-
ronmental safety control, the hydraulic and operating safety con-
trol, and structural safety control. The procedures for assessing the
safety of a dam along its life are called auscultation.
This paper uses predictive models based on multiple regression
and control charts to predict magnitudes measured by typical instru-
ments installed in concrete dams. Prediction models and control
charts can be used by auscultation team technicians and engineers
to assess structure behavior and to analyze the data measured,
since the measured values are susceptible to errors that may occur
during data collection or even due to instrument failure.
These new tools add a new parameter to be analyzed in relation
to the structural safety control of dams, which in some cases takes
into account only the comparison of the instrument-measured data
against warning values usually established in the dam design stage.
As an object of study, we considered the direct pendulum installed
on concrete block TA-2 of the Tucuruí Hydroelectric Power Plant,
which is used to measure the displacements of the block crest.
2. Background
Because large dams are constructions that require high economic
investments and play a key role in Brazil’s energy plan, it is ex-
pected that special care will be in place for the building and main-
tenance of such constructions. Brazilian Law No. 12.334 [6], dated
20 September, 2010, establishes the National Dam Safety Policy,
the goals of which, according to its article three, are as follows:
I - ensure compliance with dam safety standards in order to reduce
the possibility of accidents and the consequences thereof;
II - regulate the safety actions to be taken in the planning, design,
construction, first filling, operation, decommissioning, and fu-
ture uses of dams throughout the country;
III - the people in charge of the dams are to promote safety moni-
toring and follow-up;
IV - create conditions for extending dam controls by the govern-
ment, based on the supervision, guidance and correction of
safety actions;
V - collect information that supports governmental management of
dams;
VI - establish technical compliance that allows for evaluating the
adequacy of those parameters established by the Government;
VII - develop a culture of dam safety and risk management.
Therefore, auscultation plans are put into practice when the con-
structions begin and are followed up throughout dam’s life.
A considerable amount of research has been developed in Brazil
and Portugal to develop dam behavior prediction models, espe-
cially based on multiple regression models, thus contributing to
improving safety control procedures with direct reflex on the main-
tenance of said structures as well. Amongst such works, one can
mention the research carried out at LNEC - the National Labora-
tory of Civil Engineering, in Portugal, [7] and [8] as well as several
Brazilian contributions, such as those made by [9] and [10].
Based on well-adjusted behavior prediction models, the reading
of the instruments should be close to the value estimated; other-
wise, it is possible to investigate the cause of this discrepancy and,
if necessary, employ timely preventive actions. The auscultation
team may also count on the help of control charts, which allow for
easy viewing when the dam is undergoing a change in behavior.
3. Auscultation
According to [11], although instrumentation does not provide the
solution to all problems, when it is properly designed, installed
and read, it can not only assess the safety conditions of a project
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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
R. A. C. LOPES | E. P. SANTOS
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L. A. C. M. VELOSO