Systemic approach for the maintenance of complex structural systems

This article was downloaded by: [Universita Studi la Sapienza]
On: 05 October 2011, At: 04:08
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Structure and Infrastructure Engineering
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/nsie20
Systemic approach for the maintenance of complex
structural systems
Franco Bontempi
a
, Konstantinos Gkoumas
a
& Stefania Arangio
a
a
Department of Structural and Geotechnical Engineering, Faculty of Engineering, University
of Rome ‘La Sapienza’, Via Eudossiana, 18, 00184, Italy
Available online: 25 Jun 2008
To cite this article: Franco Bontempi, Konstantinos Gkoumas & Stefania Arangio (2008): Systemic approach for the
maintenance of complex structural systems, Structure and Infrastructure Engineering, 4:2, 77-94
To link to this article: http://dx.doi.org/10.1080/15732470601155235
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to
anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation that the contents
will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should
be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,
proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in
connection with or arising out of the use of this material.

Systemic approach for the maintenance
of complex structural systems
FRANCO BONTEMPI, KONSTANTINOS GKOUMAS and STEFANIA ARANGIO*
Department of Structural and Geotechnical Engineering, Faculty of Engineering, University of Rome ‘La Sapienza’,
Via Eudossiana, 18, 00184, Italy
(Received 20 January 2005; accepted in revised form 7 September 2006)
This paper deals with the general framework for the development and the maintenance of
complex structural systems. In the first part, starting with a semantic analysis of the term
‘structure’, the traditional approach to structural problem solving has been reconsidered.
Consequently, a systemic approach for the formulation of the different kinds of direct
and inverse problems has been framed, particularly with regards to structural design and
maintenance. The overall design phase is defined with the aid of the performance-based
design (PBD) philosophy, emphasizing the concepts of dependability and enlightening
the role of structural identification. The second part of the present work analyses
structural health monitoring (SHM) in the systemic way previously introduced. Finally,
the techniques related to the implementation of the monitoring process are introduced
and a synoptic overview of methods and instruments for structural health monitoring is
presented, with particular attention to the ones necessary for structural damage
identification.
Keywords: Structural systems; Systems engineering; Performance-based design; Depend-
ability; Structural health monitoring; Complexity
1. Introduction
The theoretical framework for the design of complex
structural systems should be based on a comprehensive
evaluation of all the performances. The aim of structural
engineering is not only to achieve an ideally good design
and a nominal construction, but also to assure, by means of
appropriate maintenance, the long term exploitation of the
system.
In this perspective, the procedures based on the concepts
of system engineering can be profitably applied. System
engineering is a robust approach to the creation, the design,
the realization and the operation of systems. Complex
structural systems should be designed using this innovative
approach; in fact, a structure is a real physical object
inserted in its environment in which a variety of factors
should be taken into consideration. The traditional
approaches are not able to consider the numerous
interrelated aspects (qualitative and quantitative) charac-
teristic of the system complexity.
Furthermore, the recent improvement in data measure-
ment and in elaboration technologies has created the
proper conditions to improve the decisional tool based on
the performance on site, leading to a new systemic design
philosophy based on the performances, the so-called
performance-based design (PBD).
Starting from the identification and the quantification of
system goals and requirements, once the performances are
fixed, a correct and robust design can be implemented.
When the design is complete, a verification phase must take
place to validate and to assess the design in accordance with
the specifications previously chosen. Under this premise,
dependability provision and assessment during the whole
life of the structure should be performed for the system and
*Corresponding author. Email: stefania.arangio@uniroma1.it
Structure and Infrastructure Engineering, Vol. 4, No. 2, April 2008, 77 – 94
Structure and Infrastructure Engineering
ISSN 1573-2479 print/ISSN 1744-8980 online ª 2008 Taylor & Francis
http://www.tandf.co.uk/journals
DOI: 10.1080/15732470601155235
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

its components. In this way, serviceability and safety can be
assured and the overall service life can be increased.
In this context, a structural health monitoring system
assumes an essential role and should be designed as an
integral part of the global structural project. In the
following, we will show that structural health monitoring
can be implemented according to two, often intertwined,
approaches: one low level approach which considers the
materials (or the basic components) that comprise the
structure, and one high level approach which considers
the structure (or the sub-structures within the structure) as
a whole.
2. The structural system as an extension of the concept
of the structure
2.1 Traditional approach to structural problem solving
There are different ways to introduce the concept of
‘structure’; a good definition is a device for channelling
loads that result from the use and/or presence of the
building to the ground (Schodek 1998). Traditionally, the
diverse problems related to the structures are classified as
direct and inverse, as shown in figure 1 (Arangio 2004).
A direct problem is an analysis problem; it consists of the
evaluation of the response of a structure immersed in the
so-called design environment, i.e. under assigned external
actions and other boundary conditions, and the agreement
with the fulfilment of all the design constrains, by using a
suitable model.
Inverse problems are, on the other hand, those for which
the structural response constitutes available known data.
Yet, with reference to figure 1 and according to the nature
of the other unknowns as shown in figure 2, the inverse
problems can be classified into:
Synthesis problems: given the actions and the constraints,
the structure is designed to obtain a specific structural
response;
Control problems: given a description for the structure and
the mandatory structural response, an appropriate action
to generate that response is searched;
Identification problems: given both the actions and the
structural response, the model is looked for.
2.2 The systemic framework for structural problems
Traditionally, the solution of the structural problems is
obtained from the input data by applying a set of rules or
equations that lead to the desired output. Nowadays, an
approach to the resolution of structural problems that is
strictly related to the application of general rules or
equations really seems to be both a restrictive and not
very effective one. In fact, the necessity to build more and
more complex structures emphasizes the presence and
correlation of numerous factors that contribute to deter-
mining its characteristics.
A global approach considers the structure as a real
physical object inserted in its environment where a variety
of factors should be taken into consideration. In this way, it
is possible to contemplate aspects associated both with the
intricacy and the uncertainties of the problem at hand.
Some of these aspects, and it is worth realizing that these
are the most important ones, belong to economics or
Figure 1. Direct and inverse problems in structural engineering.
78 F. Bontempi et al.
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

politics, i.e. to the social spheres (Blanchard 1997). The fact
that different points of view interact reciprocally implicates
that a substantial variation of any of these points may
eventually change the characteristics of the system as a
whole. Just these connections form one of the signs of
complexity and an approach that does not take into
account this reality may be short-sighted.
It is useful therefore to reconsider the previously given
definition of structure; a structure is better defined as ‘a
physical entity having a unitary character that can be
conceived of as an organization of positioned constituent
elements in space in which the character of the whole
dominates the interrelationship of the parts’ (Schodek
1998). This definition highlights that a modern approach
has to evolve from the idea of ‘structure’ as a simple device
for channelling loads, to the idea of a ‘structural system’ as
‘a set of interrelated components which interact with one
another in an organised fashion towards a common
purpose’ (NASA 1995). This systemic approach includes
a set of activities that lead and control the overall design,
implementation and integration of a complex set of
interacting components. It has been said that the notion
of structural systems is a ‘marriage of structural engineer-
ing and systems science’ (Skelton 2002).
From the operative point of view, the previous definition
of structural system points out some key concepts related to
the systemic approach, those of reductionism and integra-
tion (Sydenham 2004). Effectively, in the presence of
complex structural problems, the systemic approach applies
the widely used human thinking process where a large
complex topic is broken down into smaller parts. This
paradigm of problem solving is known as reductionism and
constitutes a basic thinking methodology of engineering; it
is the top-down process of forward engineering and it can
be represented graphically (as shown in the left hand side of
figure 3) by a pyramid, set up with various objects
positioned in a hierarchic manner. The peak of the pyramid
represents the goal (the whole structural problem), the
lower levels represent a description of fractional objects
(the sub-problems in which the problem can be divided),
and the base corresponds to basic details. As a result, a
project is intended and estimated with increasing levels of
detail one level at a time.
On the other hand, in those situations where the
details comprise a starting point, a bottom-up approach
is used for the integration of low-level objectives into more
complex, higher-level objectives (as shown in the right hand
side of figure 3). In common practice, however, real world
problems are unclear and lack not only of straightforward
solution process, but also a single point of view. In fact,
frequently in the structural domain, the goals and the
details are known, while uncertainties lie in the activities
that take place in the intermediate levels. These activities
are mostly based on experience and are carried out
through successive refinements. In this case, the strategy
(illustrated in the central part of figure 3) becomes a mixed
recipe of top-down and bottom-up procedures that may be
used alternately with the techniques of reverse-engineering.
In this way, one analyses iteratively a system in order
to identify its components and their interrelationships,
possibly creating alternative useful representations of the
system.
During the solution procedure, the various activities are
identified and conceptual models are generated and
compared with the real situation. Extreme differences are
then rectified in the conceptual model and the implementa-
tion is adjusted. The overall loop is then closed by
implementing the best available plan, with the process
being repeated until reasonable success is achieved. This
approach allows us to analyse the problem in a holistic
manner, working with the whole system rather than just
parts, but it requires an exact definition of the performance
Figure 2. Overview of data related to structural problems.
Maintenance of complex structural systems 79
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

requirements and of the analysis, modelling and grade of
complexity of the system.
2.3 Systemic approach to structural design
and optimization
Universally, demand for structural systems requires three
dominant aspects to be optimized. These are generally
described as the cost, time and performance factors (CPT).
Attempting to optimize all three factors simultaneously is a
very difficult task. However, the adoption of improved
systemic processes seems to significantly improve all three
at the same time. In fact, the objective of a systemic
approach is that the system is designed, built and operated
in the most cost-effective way possible. It means that a cost-
effective system must provide a particular kind of balance
between effectiveness and cost; the system must provide the
most effectiveness for the resources expended or, equiva-
lently, it must be the least expensive for the effectiveness it
provides.
This condition is a weak one, because there are usually
many designs that meet the constraints. Each possible
design can be represented as a point in the trade-off space
between effectiveness and cost. A graph, plotting the
maximum achievable effectiveness of available design with
current technology as a function of cost, would in general
yield a curved line such as the one shown in figure 4. The
curved line represents the envelope of the currently
available technology in terms of cost-effectiveness. In
addition, this curve shows the saturation effect that is
usually encountered as the highest levels of performances
are approached. Points above the line cannot be achieved
with currently available technology and they represent
currently unachievable designs, although some of these
points may be feasible in the future when further
technological advances will be made. Points inside the
envelope are feasible, but are dominated by designs whose
combined cost and effectiveness lie on the envelope.
Considering the starting point D0 for the design inside the
envelope, there are alternatives that reduce costs without
Figure 4. Uncertainty in the cost-effective solutions
(adapted from NASA (1995)).
Figure 3. Top-down and bottom-up approach to problem solving.
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

decreasing any aspect of effectiveness (design point D1) or
that increase some aspects of the effectiveness without
decreasing others or without increasing costs (design
point D2). For these reasons, the projects represented by
the points on the envelope are called the cost-effective
solutions.
The process of finding the most cost-effective design is
additionally complicated by the influence of uncertainty. The
exact outcomes achieved by a particular system design
cannot be known in advance with certainty, so the cost and
the effectiveness of a design are better described by a
probability distribution than by a point. With reference to
figure 4, distributions resulting from a design which has little
uncertainty are dense and highly compact, as is shown for
concept A, while distributions associated with risky designs
may have significant probabilities of producing highly
undesirable outcomes, as is suggested by the presence of an
additional low effectiveness/high cost cloud for concept C.
Concept B represents an intermediate situation.
It is interesting to consider aspects of the structural
system cost as a function of the care of the design. In
figure 5, the overall ownership cost curve Ct is represented
as the sum of the design cost Cd, the maintenance cost Cm
and the operation cost Co. If greater effort is put into
obtaining a better and more robust design then, with an
obvious increment of the design cost, it is usually the case
that the maintenance cost will drop while the cost of
operation will not change markedly. The process of
minimizing the expected total cost is defined as life-cycle
optimization (Frangopol et al. 2001).
In order to apply the systemic approach to the design of
the structural system it is necessary to take into account the
design role within the phases of the system life-cycle. The
procedure starts with an interaction between the designer
and the customer to establish the needs, which then become
the key in the process; these needs are consequently used as
references and driving statements for carrying out a
requirements analysis. The next step is to break down
the task until its constituents become clear. This is the
requirement analysis step. A functional analysis with the
allocation of functions and collection of elements is then
developed. Consequently, potential solutions are synthe-
sized, by the aggregation of various parts previously
collected. If, after this step, the results are unsatisfactory,
then the loop has to be repeated. Iterations regarding the
requirements, the design and the validation may be
required for several loops. This whole process is called
the systems engineering process (SEP), or simply the egg
(see figure 6).
The whole structural design process can be reviewed
within this systemic view, particularly considering the
recent improvements in measurement and elaboration data
technologies. These have created the proper conditions to
advance the decisional tools through the enhancement of
the information related both to the structural performances
on site and to the measurement systems. The enormous
advantages that can be drawn by the results of these
measurements and the development of these technologies
have led to the birth of activities inside the domain of the
so-called performance-based structural engineering (Smith
2001, Silvestri 2002). In particular, the design of complex
structures may draw benefits from this new systemic design
philosophy based on the performances, with the possibility
of obtaining perfection of the design solution in the context
of the theory of excellence, a really comprehensive general-
ization of the re-engineering technique (Catallo et al. 2003).
Figure 5. Costs associated with optimization (adapted from Sydenham (2004)).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

The first five phases shown in figure 7 are traditionally
considered by the structural design procedure and lead to
the ‘as built’ construction. They are:
1) Formulation of the problem;
2) Synthesis of the solution;
3) Analysis of the proposed solution;
4) Evaluation of the solution performances;
5) Construction.
Difficulties associated with this kind of approach are
evident. The ‘as built’ structure could be different from
the ‘as designed’ one due to different factors such as
fabrication mistakes or unexpected conditions during the
construction phase, or can also be due to inappropriate
design assumptions. The latter could create doubts about
the accuracy of the analysis results leading to a predicted
behaviour that does not correspond to the real one. A way
to avoid these difficulties can be achieved using a
Figure 6. System engineering process (adapted from Sydenham (2004)).
Figure 7. Extended scheme for the design process (adapted from Smith (2001)).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

monitoring system. In this case, three further steps must be
added to the traditional design phases in figure 7:
6) Monitoring of the real construction;
7) Comparison between results from monitoring and
expected behaviour results;
8) Increase in the accuracy of expectation of the future
structural behaviour.
These three more steps are the starting point of a truly
systemic performance-based approach to structural engi-
neering, leading to the further additions of figure 8:
9) Reformulation. Development of advanced probabil-
istic methods for a more accurate description of the
required behaviour and of the required performance;
10) Weak Evaluation. This methodology assumes that the
analysis is exact and that all the actions are known
exactly from the probabilistic viewpoint;
11) Model improvement. The necessity connected to the
models improvement comes from experiences based
on monitoring, where expected and measured beha-
viours on ‘as built’ structures are directly compared;
12) Strong Evaluation. A third kind of evaluation, called
strong, becomes possible when the improvement (see
previous point) aims to assign more accurate values to
the parameters used and to define a more accurate
modelling hypothesis.
2.4 The concept of dependability and the need
for monitoring
For complex structural systems, or large scale projects
where there are significant dependencies between elements
or sub-systems, it is important to have a solid knowledge
both of how the system works as a whole, and also of how
the elements behave singularly. The goal is to achieve
established limits of the acceptable service and safety levels.
Therefore, it becomes important to define a global concept
that groups the attributes assumed to be relevant.
Dependability can be defined as the collective term used
to describe the availability performance and its influencing
factors. Hence, dependability is a more comprehensive
concept than reliability that, in the case of complex
structural systems, may include some or all of the following
attributes (Bentley 1993, Catallo 2005):
. Availability, as the degree to which the system is
operable;
. Serviceability, as the quality of being able to provide
good service;
. Safety, as the absence of dangerous situations with
possible catastrophic consequences on the users or on
the environment;
. Reliability, as the ability of the system to perform safety
and serviceability during time;
. Robustness, as the capability of not being damaged by
accidental loads, e.g. fire, explosions, aeroplane impact
or consequences of human error, to an extent dis-
proportionate to the severity of the triggering event (see
also Catallo 2005);
. Maintainability, as the ease and the speed by which any
activity related to the preservation and upgrade of the
structure can be carried out on the system or on its parts.
In a generic manner, one can presume that the occurrence
of negative events is highly correlated with the perceived
complexity of a system. This affirmation asks for a case to
Figure 8. Further phases in PBD (adapted from Smith (2001)).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

case evaluation, with regards to the type of structural
system under investigation and the level of performance
required.
There are a number of reasons for dependability
provision and assessment with regards to the maintenance
of structural systems:
. Ever-increasing requirements from users in terms of
quality;
. High performance expectation from the final product;
. Elevated interdependencies;
. Elevated costs due to low quality parts or sub-systems;
. Collateral administrative or financial issues (e.g. insur-
ances).
All these aspects can be summarized in one word: structural
complexity. It is clear that the dependability provision is
subjected to the function for which the structural system is
commended and the dependability of the system can be
addressed within certain ‘a priori’ imposed limits, often
obtained by heuristic judgement.
The threats for system dependability can be sub-divided
into:
. Failure;
. Error;
. Fault.
It is important to distinguish the meaning of these terms.
In the case of failure, the service that the system delivers
deviates from compliance with the system specifications
for a specified period of time. In the case of error, the
system is in an incorrect state, it may or may not cause
failure. On the other hand, a fault is a defect and
represents a potential cause of error, active or dormant.
The means for dependability assessment include (Avizienis
et al. 2004):
. Fault forecasting, concerning the estimation of the
presence, the creation and the consequences of faults;
. Fault prevention, aiming to prevent the occurrence or
the introduction of faults;
. Fault tolerance, as the ability of the system to continue
normal operation despite the presence of faults;
. Fault removal, aiming to reduce the number or the
severity of faults.
Beginning with the assessment of possible failures, local
or global, in the structural system, it is possible to
determine the effects of a failure in the global performances
with a failure modes and effect analysis (FMEA), while a
quantitative evaluation can be linked to these effects within
a failure modes and effect critical analysis (FMECA). These
are the bottom-up techniques.
Event trees pictorially represent the logical order in
which events in a system can occur (Stewart and Melchers
1997). They begin with an initiating event, and then the
consequences of the event are followed through a series of
possible paths. Each path is assigned a probability of
occurrence. Therefore, the probability of the various
possible outcomes can be calculated. Event tree analysis
is based on binary logic, in which an event has either
happened or not, or a component has failed or has not. It is
valuable to analyse the consequences arising from a failure
or undesired event.
Fault trees look like a complement to event trees. The
idea is to begin with a general conclusion (event) and, using
a top-down approach, to generate a logic model that
provides for both qualitative and quantitative evaluation of
the system reliability.
Failure tree analysis (FTA) is a top-down search method
that consists of the construction of the failure trees of the
events and the relative evaluation in terms of probability.
In a FTA, a logical analysis takes place that consists of the
construction of the trees and their transformation into
Boolean expressions. It should be noted that FTA is a
method for analysing causes of hazards to the system, not
for identifying them. Therefore, the top event must have
been foreseen and thus identified by means of other
techniques.
It is important to realize that regarding complexity, since
it is necessary to set a synthetic view by graphical language,
it is essential to abandon the pure equation-based descrip-
tion of the structure (Haimes 1998). Nowadays commercial
software is available to implement system analysis as above.
2.5 Structural identification
As previously stated, this structural identification process
finds structural characteristics, models or actions through
the measurement of the structural response. Traditionally,
structural identification was developed in the field of
mechanics and aeronautics, where experimental investiga-
tions can be conducted directly in the laboratory, mostly by
scale models of the structure under inquiry. Recently, the
implementation of structural identification techniques has
experienced a huge growth. An important task in this
process is the determination of the modal parameters. In
fact, dynamic properties represent an intrinsic character-
istic of the structure and therefore can represent its integrity
more accurately. As a consequence, they can be useful
during the testing of a new or rehabilitated structure or in
the structural health monitoring of an existing one.
Structural identification represents an appropriate way of
relating experimental results to analytic ones.
The identification of the mechanical properties of a
structural system can be extremely useful in structural
health monitoring or in diagnostic procedures. These allow
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

global assessment and appraisal of the potential occurrence
of damage phenomena. Structural identification is carried
out in the presence of damage states, or during the service
life of the structure. The way to deal with this problem is by
using theoretical models, corrected on the basis of
experimental results by model updating procedures. The
aim of model updating is to minimize the difference
between the calculated values of the theoretical model
and the experimental measurements of the dynamic
parameters of the structure. Structural damage may be
identified with a side by side comparison of the structural
model, both in intact and damaged conditions. In order to
achieve an exact evaluation of the structural system
performances, the structural identification, based on the
monitoring data, assumes a role of primary importance.
3. Implementation of the structural monitoring process
The maintenance process is firmly correlated to the
structural monitoring process. Recent progress in the field
of monitoring systems (the reduction of the price of
hardware, the development of more and more accurate
and reliable software, not to mention the decrease in size of
the equipment) form the premise of developing, construct-
ing, managing, recovering and dismantling the majority of
civil engineering systems on the basis of data measurement.
All these lead to an evolution of the concept of the
structural monitoring process, which is no longer intended
to be the passive exploration of deterioration or damaged
states originating by observing the structure. On the
contrary, the new approach is about the principle of
controlling the structural system in a proactive way, in
order to reveal the presence of any undesired fault and to
understand the causes of failure.
These days, structural (health) monitoring is an essential
tool for the verification of the effective accomplishment of
the expected performance and for updating the system reli-
ability (Papadimitriou et al. 2001). Therefore, the monitor-
ing process should be planned during the design phase.
3.1 Structural monitoring hierarchies
It is important to note that the planning of monitoring
processes is strictly related to the complexity of the
structure. In fact, the cost, as a parameter, has to be taken
into consideration. Three major implementations of the
monitoring process can be defined:
. Visual inspection;
. Monitoring ‘by event’;
. Continuous monitoring.
Visual inspections and monitoring by event concern the
main implementation for the overseeing of the structural
system, and they are organised as an integral part of the
structural management program. On the other hand,
continuous monitoring, as the name suggests, takes place
with the continuous (with respect to time) reading of data,
obtained from different instruments installed on the
structure. It is essential for the assessment, in real or
almost real time, of the integrity, reliability, durability and
safety of the structural system.
The process of monitoring by event differs from that of
continuous monitoring due to the fact that it is carried out
only for the time period strictly necessary for the
completion of the requested assessment. The instrumenta-
tion is required from the first phases of the project in order
to achieve a successful integration with the structure. In
some cases, wherever there can be expected continuous
variations of the global behaviour, or in the case of
aggressive environments, the installation may be of a
permanent type.
Nevertheless, the present situation suggests that struc-
tures are still designed in a conventional way. In these cases,
monitoring systems are employed merely on structural
systems with innovative or unique characteristics, like
complex infrastructural systems, long span bridges, dams,
and generally, critical structures or systems subjected to
significant accidental or environmental actions. In design,
the implementation of a permanent control system is rare.
This leads to the downgrading of the monitoring process to
a secondary role that typically has as a primary scope the
programming of visual inspections once degrading states or
structural damages are revealed from local and/or specific
measures in the course of an event monitoring process. Only
in the event of excessive damage is a continuous monitoring
system is scheduled, typically by means of temporarily
installed equipment on the structure, as a consequence of
the difficulty in identifying the origin of the damage itself.
A simple classification of situations includes two
categories: complex structural systems that can justify a
continuous monitoring system as a consequence of long
term cost reduction and serviceability, and ordinary
structures, for which such a system, for the added cost, is
not considered important. For the first class, structural
health monitoring incorporates all the implementations
previously mentioned. Parameters under observation are
those subjected to the variations caused by environmental
or accidental actions. Collected data is inserted into a
database, in order to be elaborated and transmitted. The
next step includes elaboration from skilled personnel,
aiming for the assessment of the structural behaviour. In
this way, numerical results can be integrated with normal
visual inspections, a process that allows further interven-
tion in case of malfunctions or structural damage. An
integration with numerical models leads to the verification
of the required performance, established during the design
phase.
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

3.2 Monitoring protracted in time
Another important aspect that should not be neglected is
the role of the various implementations of monitoring
(visual inspections, by event and continuous monitoring)
for the different phases of the structure lifespan: design,
construction, testing, service life, and dismissing, as shown
in figures 9 and 10 (Senaud 2004). In these flow-charts, for
every phase, two different paths can be noted; one is related
to ordinary structures, and the other is related to complex
structural systems. In this way it is possible to distinguish
the main differences in the monitoring process, relating it to
the complexity of the structures.
3.2.1 Monitoring during design. For the entire design phase,
the location site of the structure is monitored, mostly
implementing ‘by event’ techniques. Data collection aims to
gather geotechnical information, such as the stratigraphy,
the physical and mechanical characteristics of the soil and
the underground water table. Furthermore, during this
phase, the testing of the materials constituting the struc-
ture’s components and the scale models of the structure
usually takes place. The design of the monitoring system
advances with the design of the structure. Firstly, the
parameters to be monitored are selected. Subsequently there
are choices to be made regarding the sensors to be used,
their quantity and location, the method of data transmis-
sion, the lodging of the central data collecting units, the
location of the control and processing units, and finally, the
method of an eventual data transfer via the internet to other
remote locations for storage and further analysis.
3.2.2 Monitoring during construction. During the construc-
tion period, special care is to be taken for the provision of a
temporary monitoring system, as a substitute for the main
one, which is still in the preparation stage. This phase
should be watched closely in order to intervene in case of
errors. The geotechnical instrumentation, used in the
previous design period, should be maintained in the
proximity of the construction site, in order to check possible
subsidence. The realization of the monitoring system
proceeds side by side with the one of the construction and
the positioning of the various instruments and sensors
should take place as intended.
Figure 9. Structural monitoring during design, construction and final inspection (Senaud 2004).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

3.2.3 Monitoring during testing. During the testing period,
an important role is reserved both for visual inspections
and for by event monitoring techniques. In particular, both
destructive and non-destructive tests may take place, in
order to assess the mechanical properties of the materials,
the condition of the steel reinforcement, and other
characteristics. Additional load tests may take place, in
order to assess the global behaviour, the applied loads and
the resulting stresses. Continuous monitoring takes place as
soon as the sensors network is completed. The purpose is to
record displacements and deformations during the load
tests. This may be a further occasion to test the monitoring
system as well, calibrating the sensors and verifying their
accuracy. In the case where a permanent monitoring system
is not planned, there should be provision for a temporary
network of sensors to conduct the load tests.
3.2.4 Monitoring during service. During the service period,
the approach is fairly different if one refers to a simple
structure or to a complex structural system (see figure 10).
In the first case, visual inspections should be carried out,
integrated if necessary with by event monitoring. Contin-
uous monitoring is employed only in special cases.
Complex structural systems, on the other hand, necessitate
further attention. In these cases, visual inspections and
continuous monitoring are mutually integrated, and only in
Figure 10. Monitoring during service and dismissing (Senaud 2004).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

the case of discordance or necessity does by event
monitoring techniques take place.
The monitoring plant starts to work at the beginning of
the service period,. From that moment forward, data
gathering is initiated. This process should go on until the
end of the service period of the structural system,
preferably without interruptions. The data collection may
be continuous or at defined intervals. It is very important
not to confuse the significance of continuous monitoring
with that of the continuous gathering of data. In the first
case one means that the structure is monitored for its whole
lifespan and not only in the case of necessity. On the other
hand, continuous data gathering means that the sensors
measure continuously, time after time.
A significant difference in terms of accumulated data
exists between the continuous and the discontinuous data
collection. Nevertheless, in both cases a central facility is
necessary for the process of storage and elaboration of the
gathered data. This aims to reduce and transform a large
amount of data, difficult to manage data, into a quantity
easier to interpret and exploit. The information obtained
can be integrated with results from numerical analysis in
order to compare the effective and the evaluated perfor-
mances of the structure. In this way, it is possible to
improve the accuracy of the models as well.
3.2.5 Monitoring during dismissing. Every time a structure is
dismissed, the monitoring system has to be dismantled as
well. The sensors should remain active for as long as
possible, in order to monitor the effective maintenance of
safety. This final period, in the case of complex structures,
is of great importance, not only for safety reasons, but also
for the appropriate recovery of the construction site and the
eventual recycle of materials.
3.3 The individuality of the monitoring process
The use of new methods based on the concepts of PBD and
dependability, as well as the development of new techniques
and technologies correlated to the monitoring process,
allows the reliable assessment of structural behaviour. On
this basis, and with careful management based on knowl-
edge, further understanding of the design, construction and
degradation process may be gained, allowing for a further
increase of the safety level. This does not mean that all
structures shall be equipped with the maximum technology
available. In fact, the restriction in terms of cost is
important. Therefore, it is important to create a monitoring
process, specific for each structural system, and congruent
with the available resources and the complexity of the
system.
According to these concepts, it is necessary to review the
classification adopted in figures 9 and 10, in which the
structures are divided into two large categories: simple
structural systems and complex structural systems. In
reality, considering the specificity of the monitoring
process, this is an oversimplified classification that can be
improved. A more refined classification includes:
. Ordinary structures;
. Selected structures;
. Special structures;
. Strategic structures;
. Active structures;
. Smart structures.
The different classes are characterized by different levels of
complexity in terms of information technology, as schema-
tically shown in figure 11 by means of increasing size
circles.
The ordinary structures are those that do not need
permanent monitoring equipment. For these, the usual
monitoring consists of periodical visual inspections. The
selected structures are provided with sensors for load
tests in order to assess the compliance with the effective
performances. The special structures require periodical
planned controls through visual inspections and provi-
sional instruments (monitoring by event). The data
collected is useful for the calibration of the analytical
model developed in the design phase, and provides
information regarding the structural behaviour during the
service life. The other three classes require continuous
monitoring, which has to be planned from the design phase.
The strategic structures require a monitoring system for
assessing the structural behaviour over time. The active
structures, as the name suggests, are provided with an
active control of the structural behaviour that ensures the
fulfilment of performances. The smart structures represent
the maximum in terms of strategic management of complex
structural systems. Their advantage consists of the possi-
bility to modify the structural behaviour through feedback
actions. In this sense, it is possible to apply structural field
techniques from the artificial intelligence field, such as
artificial neural networks or genetic algorithms (e.g. Sgambi
(2005)).
With this in mind, a specific scheme is shown in figure 12
(Senaud 2004). The five life phases of the charts in figures 9
and 10 are considered in a single chart, and it has been
extruded to a third dimension, to take into account the
complexity. In this way, the various planes represent
different complexity levels (Z axis), while on the X and Y
axes, the phases of the lifespan of the structure and the
different implementations of the monitoring process are
represented.
The results obtained from different monitoring processes
may be used in the organisation of the project phases and
the maintenance activities, allowing for the complete
assessment of the structural behaviour and the prevention
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

of future deterioration or damage, thus reducing the risk
of conducting onerous interventions on the structural
system.
4. Structural health monitoring techniques
A structural health monitoring system should be able to
monitor the various loads to which the structure is
subjected to (e.g. Gkoumas 2004), such as natural
(ambient), anthropic and entropic loads, as well as the
consequent structural response to these loads and the
change in the state variables (as shown in figure 13 in the
case of a long span bridge). Over a longer period of time,
the entropic actions (decay of the materials) that influence
the structural behaviour should be assessed.
Most significant environmental loads involve tempera-
ture, wind, earthquake, rain, snow and, in the case of off-
shore structures, wave loads. In designing a structural
monitoring system, it is convenient to differentiate ‘slow’
environmental loads (such as temperature or humidity)
from those that vary rapidly (such as wind or earthquake).
Anthropic loads, in the case of bridges for example, consist
of pedestrian, highway or railway loading. In particular,
railway loading can be considered deterministic while, in
the case of highway loading, the knowledge of the
representative spectrum of vehicle configurations and traffic
patterns, together with a provision for the projected
increased loads, is essential both for reliability and fatigue
analysis.
Structural response monitoring can be implemented
generally with two often intertwined approaches: one
considers the materials that comprise the structure, while
the other considers the structure (or the sub-systems of the
structure) as a whole. In the first case, the monitoring
techniques are used to enquire about the local properties of
the materials (concrete, steel, wood, composite materials) in
order to evaluate their performance under different types of
loads, temperature variations, ageing etc. In the second
case, the structure is observed as a whole, with general
techniques, from a global, geometric point of view.
Dynamic characteristics of the structure may be used in
order to determine if damage is present in the structure, to
determine its approximate geometric location, to assess its
extension, and eventually, to predict the remaining service
life of the structure (Rytter 1993).
The basic premise of vibration-based damage detection is
that the damage will alter the stiffness, mass or energy
dissipation properties of a system, which, in turn, will alter
the measured dynamic response of the system (Farrar et al.
2001). Global methods, in contrast with local ones, do not
Figure 11. Relationship between classification of structures and characteristics of the monitoring process: sensors, quantity of
measurements, and feedback.
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

require either direct access to the structural elements or the
knowledge of their prior state.
The choice of monitoring method relies, apart from the
discretion of the project manager, on various parameters,
typically the:
. Typology and complexity of the structure under inquiry;
. Age of the structure;
. Condition of the structure;
. Available resources.
Most importantly of all is a case by case evaluation that
considers both the objectives to accomplish, and the
relevancy of the structural system under investigation.
4.1 Local structural health monitoring techniques
For the purposes of local structural health monitoring,
there is the need for sensors to sample the local state of the
materials of the structural elements. The parameters under
investigation are related to the physical, chemical and
Figure 13. Principal monitoring issues for a long span bridge.
Figure 12. The individuality of the monitoring process (Senaud 2004).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

tensional states of the materials. For strain or crack
monitoring, it is necessary to adopt strain gauges or fibre
optics. In the first case, the sensing takes place by
measuring physical quantities, mostly by means of the
variation of the electricity that passes through them. Fibre
optics, on the other hand, represent the evolution of
sensing. The basis of their operation is the total internal
reflection of light rays travelling through tiny optical fibres.
Fibre optic sensors can be classified as extrinsic or
intrinsic ones. In an extrinsic sensor, the sensing takes place
in a region outside the fibre. The fibre itself essentially
serves as a conduit for the efficient transmission of light to
the sensing region. In an intrinsic sensor, one or more of the
physical properties of the fibre undergo a change, in this
way leading to the desired evaluation. For structural health
monitoring purposes, various types of sensors have been
presented. Some of them are still in a research state, while
others, such as those based on the Fabry-Perot inter-
ferometer, low coherence interferometry or fibre Bragg
gratings, have been installed and tested in a variety of
structures. The sensors may be embedded or may be
externally mounted on the structural element. The advan-
tages of implementing fibre optic sensors over classic strain
gauges consists of the absence of electromagnetic inter-
ferences, the smaller size, the higher temperature
capability, the greater multiplexing potential, and the
demodulation to longer distances and the greater resistance
to corrosion (Schultz et al. 1998). Most significant
disadvantages include the higher cost and the sometimes
limited accuracy.
For the detection and localization of failures in high
strength steel wire, strand or cable, acoustic, ultrasonic or
magnetic resonance methods can be applied. Other than
corrosion, high resistance steel, like the one used in
prestressed concrete for reinforcement in post-tensioned
structures or in supporting elements in cable-stayed or
suspension bridges, is subjected to degradation due to the
considerable tension applied, i.e. fatigue and hydrogen
embrittlement phenomena. These actions are the predomi-
nant cause of ductility loss, with the potential consequence
that the deficiency may be of a fragile type. The latest
technology sensors, like those based on acoustic wave
emission, allow for continuous, non-destructive monitor-
ing, combined with the liable determination of the exact
time and location of the failure. The registration and the
evaluation of the acoustic events take place in real time,
while a data processing unit is responsible for their
automatic filtration, under prefixed criteria.
For corrosion monitoring, embedded sensors are neces-
sary. In recent years, several monitoring systems have been
implemented in major infrastructure projects (Sørensen
et al. 2004), based on sensors capable of deducing the
corrosion risk of the steel reinforcement inside the concrete
structural elements. These sensors indicate the depth of the
critical chloride content and the depth of the carbonation
front initiating corrosion. Thus, the time to corrosion can
be determined, enabling the owners of the structures to
initiate preventive protection measures before cracks and
spalling occur. The most common type of sensors is those
embedded inside the fresh concrete during the construction.
The basic measuring principle is to place electrodes at
different depths related to the concrete surface, and to
measure the onset of corrosion of these electrodes one by
one. The measuring electrodes are made of steel, with a
similar composition as the reinforcing steel, to ensure that
they will start to corrode themselves at the same time as a
bar situated at the same depth. Measurements take place
manually, typically every six months or less. A similar
sensor that can be inserted at a later stage is used to
monitor corrosion on existing structures. Studies have
shown that its performance is in accordance with that of the
embedded sensors (Baessler et al. 2000).
4.2 Global structural health monitoring techniques
For the purposes of global (or geometric) structural health
monitoring, there is the necessity to obtain measurements of
the acceleration, the velocity and the displacement of the
structural elements, on a regular basis and with an elevated
sampling rate. Topographic techniques used in the past
(mostly during the testing period) provide highly accurate
results, but are not always appropriate for an efficient
implementation, fundamentally because of their low sam-
pling level and their limitations in three-dimensional
motion. Global monitoring techniques embrace vibration-
based structural damage detection, during which the
alteration of the stiffness, the mass or the energy dissipation
properties of the system (and consequently the alteration of
its measured dynamic response) is expected. Detection
methods, using changes in modal parameters to identify
damage, can be implemented with two distinct approaches
(Lauwagie et al. 2002). The first approach, which is called
‘the response-based approach’, compares modal parameters
of the undamaged structure with the modal parameters
obtained on the same structure in a damaged condition. The
presence and severity of the damage can be assessed by
evaluating the changes in natural frequencies and damping
ratios. The second approach, ‘the model-based approach’,
aims to find a set of model parameters of a mathematical
model, in most cases a finite element (FE) model, of the
considered structure, in order to have an optimal correla-
tion between the experimentally measured and numerically
calculated modal parameters. Damage can then be assessed
by investigating the model parameters obtained.
The premise of vibration-based structural health mon-
itoring is very promising, even though sometimes it is
difficult to accomplish since damage is typically a
local phenomenon and may not significantly influence the
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

lower-frequency global response of structures that is
normally measured during vibration tests (Farrar and Sohn
2000).
Accelerometers are the reference instruments for global
structural monitoring and particularly for vibration-based
monitoring. They are available in a variety of ranges
commercially. A first classification is between active and
passive ones. An active accelerometer (e.g. a piezoelectric)
gives an output without the need for an external power
supply, while a passive accelerometer changes only its
electric properties (e.g. capacitance) and requires an
external electrical power. In applications, the choice of
active or passive types of accelerometers is important, since
active sensors cannot measure static or dc mode operations
(Eren 1999). Accelerometers record the global behaviour of
the structure even in the presence of cracks or fractures.
Accelerometers based on MEMS (Microelectromechani-
cal systems) have recently been developed. MEMS are
devices and machines fabricated using techniques generally
used in microelectronics, often to integrate mechanical or
hydraulic functions, etc. with electrical functions. A typical
MEMS device combines a sensor with logic to perform a
monitoring function. One of the advantages of MEMS is
that they can be produced in high quantities, achieving
economy of scale. MEMS accelerometers can be separated
into two categories: capacitive and piezoresistive ones. Even
if both types use an internal seismic in order to perceive the
acceleration, their difference lies in the mechanism used to
correlate the movement of the mass to the acceleration.
Capacitive accelerometers directly measure the acceleration,
using balanced differential capacitors formed by capacitive
plates that are etched into the perimeters of both the seismic
mass and the substrate. On the other hand, traditional
piezoresistive accelerometers are generally used for out-of-
plane acceleration with a proof mass connected to a short
flexure upon which a piezoresistive material has been
implanted (Lynch et al. 2003).
Capacitive MEMS accelerometers have experienced a
superior commercial success with respect to piezoresistive
ones, this is due to the significant further reduction in their
manufacturing costs. In addition, some problems asso-
ciated with the temperature influence on the piezoresistive
materials led to the use of special shells or compensation
circuits, with a further increase in cost. In spite of this, new
researches aim to demonstrate the feasibility of cheap
piezoresistive MEMS accelerometers.
An accelerometer with a planar cantilevered proof mass
was fabricated upon a silicon die using deep reactive ion
etching (DRIE) techniques, in which the cantilever is a
single short flexure that is slender in the in-plane direction
limiting the out-of plane response of the proof mass
(Partridge et al. 2000). Oblique ion implantation was used
for the formation of piezoresistors upon the side walls of
the cantilevering element where a region of highly focused
strain existed. Over the full dynamic range, the acceler-
ometer was found to exhibit nearly constant sensitivity,
resulting in a linear transfer function of the sensor. During
a structural monitoring validation test (Lynch et al. 2003),
the frequencies of the calculated modes were found to be
within 3% of those calculated by the theoretical model. The
frequency response function from the high performance
piezoresistive accelerometer was noisier than those calcu-
lated by the capacitive accelerometers. This was expected
because of the dominance at low frequencies of a particular
type of noise inherent to the accelerometer’s design.
Global Positioning System (GPS) technology represents
the ultimate variety of global structural monitoring
techniques. The GPS is based on measuring the transit
time of radio signals emitted by orbiting satellites.
Displacements obtained with the GPS can be continuous,
automatic and conducted under diverse weather conditions.
The improvement of GPS technology in recent years,
combined with the continuous diminution in price of GPS
hardware and the automation of the structural monitoring
process, makes this method a valid alternative, especially if
considered in combination with other sensors (e.g. tilt-
meters, accelerometers, etc.). A broad review of the
challenges involving the implementation of GPS technol-
ogy is provided by Rizos (2001).
Positioning with GPS can be performed by either point
positioning or differential positioning. The point position-
ing technique employs one GPS receiver that simulta-
neously tracks four or more GPS satellites in order to
determine its own coordinates in a three-dimensional
Cartesian coordinate system and an associated ellipsoid
(WGS 84). The differential positioning technique consists
of determining the position of one (rover) receiver (located
at the point of interest), with respect to a fixed (reference)
one. The latter technique permits a higher positioning
accuracy, thus, it is the one used for structural monitoring
purposes.
Furthermore, differential positioning GPS can be applied
in two distinctive modes: real time or post-processing.
In real time differential GPS (RTDGPS), the compensa-
tion between stations (receivers) takes place during the
measurements. A base station computes, formats and
transmits corrections usually through some sort of data
link (e.g. VHF radio or cellular telephone) with each new
GPS observation. The roving unit requires some sort of
data link receiving equipment to collect the transmitted
GPS corrections and get them into the GPS receiver so they
can be applied to its current observations. The accuracy
observed in structural monitoring applications is of the
order of 1 cm horizontally and 2 cm vertically.
In post-processed differential GPS, the base and the
roving receivers have no active data link between them.
Instead, each one records the satellite observations that will
allow differential correction at a later time. Differential
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

correction software is used to combine and process the data
collected from these receivers. This technique is adequate
for the monitoring of structures that experience slow
displacements and require an elevated accuracy (2 to
4 cm horizontally and 6 to 8 cm vertically).
The principal problem in using GPS monitoring techni-
ques for structural monitoring comes from the presence of
errors in the measurements. Principal causes include phase
ambiguity (the phase measurements delivered are biased by
the same phase), multipath (interference caused by reflected
GPS signals arriving at the receiver as a result of nearby
structures or other reflective surfaces) and, sometimes,
troposphere delay (the propagation delay of the GPS signal
caused by the non-ionized or neutral atmosphere). There
have been various attempts to mitigate these errors, with
more or less success. For this reason, their integration with
other monitoring devices such as accelerometers has been
suggested (Roberts et al. 2000).
For very complex structural systems, such as long span
cable stayed or suspension bridges, the trend is to
implement GPS technology as a part of a broad monitoring
system, consisting of further sub-systems, each with an
elevated number of sensors (Wong et al. 2001). This is the
way to achieve continuity and redundancy in the measure-
ments and, at the same time, to guarantee the maximum
dependability of the structural system.
5. Conclusions
The development of new approaches in structural engineer-
ing based on performance-based design, system engineering
and structural health monitoring, combined with the use of
new technologies and new software allows the behaviour of
complex structural systems to be correctly assessed with a
lower degree of uncertainty.
In this study, it has been shown that the design of a
complex structural system involves several general aspects,
and therefore, their consideration and optimization need to
be organised and synthesized by implementing a perfor-
mance approach, which is opposite to the prescriptive
approach. The whole process should be organised within a
system engineering ‘modus operandi’ in an organic and
hierarchic way, in order to guarantee established depend-
ability levels.
Furthermore, the principal phases of the structural
health monitoring process are exposed in concise state-
ments, with regard to the maintenance of complex
structural systems. It has been shown that for correct
implementation of the monitoring process, the monitoring
process should be contingent to the structure’s complexity
and should be suitably planned for every phase of the
structure’s life. The use of latest generation GPS and fibre
optic technologies, integrated with additional sensors
installed on the structural system, allows a more
precise and reliable knowledge if the systemic approach is
adopted.
Acknowledgements
This study is closely based on different theses, submitted in
the academic year 2004/2005 at the Department of
Structural and Geotechnical Engineering of the Faculty
of Engineering, University of Rome ‘La Sapienza’, by S.
Arangio, K. Gkoumas, G. Senaud, L. Catallo and L.
Sgambi, with F. Bontempi as advisor. Furthermore, the
financial support of the University of Rome ‘La Sapienza’,
COFIN 2002/2004 and Stretto di Messina S.p.A. is
acknowledged. Nevertheless, the opinions and the results
presented here are the responsibility of the authors and
cannot be assumed to reflect the ones of the University of
Rome ‘La Sapienza’ or Stretto di Messina S.p.A. Finally,
the considerations of the anonymous reviewers are
appreciated.
References
Arangio, S., Risoluzione di problemi strutturali diretti ed inversi mediante
tecniche euristiche. Graduate thesis (in Italian), Department of
Structural and Geotechnical Engineering, School of Engineering,
University of Rome ‘La Sapienza’, 2004.
Avizienis, I., Laprie, J.C. and Randell, B., Dependability and its threats: a
taxonomy, in 18th IFIP World Computer Congress, Toulouse (France),
Building the Information Society, 2004, 12, pp. 91 – 120 (Kluwer
Academic Publishers).
Baessler, R., Mietz, J., Raupach, M. and Klinghoffer, O., Corrosion
monitoring sensors for durability assessment of concrete structures. In
Proceedings of SPIE, edited by S.C. Liu, 3988, pp. 32 – 39, 2000 Smart
Structures and Materials 2000, Smart Systems for Bridges, Structures,
and Highways (SPIE Press: Bellingham, WA).
Bentley, J.P., An Introduction to Reliability and Quality Engineering, 1993
(Longman: Essex).
Blanchard, B.S., System Engineering Management, 1997 (Wiley-
Interscience: New York).
Catallo, L., Progettazione prestazionale nei sistemi strutturali complessi:
fidatezza strutturale. PhD Thesis (in Italian), Department of Structural
and Geotechnical Engineering, School of Engineering, University of
Rome ‘La Sapienza’, 2005.
Catallo, L., Sgambi, L. and Silvestri, M., General aspects of the structural
behaviour in the Messina Strait Bridge design. In Proceedings of the
Second International Conference on Structural and Construction En-
gineering, edited by F. Bontempi, pp. 2487 – 2494, 2003 (A.A. Balkema:
The Netherlands).
Eren, H., Acceleration, Vibration and Shock: the Measurements, Instru-
mentation and Sensors Handbook, edited by J.G. Webster, 17, pp. 1 – 32,
1999 (CRC Press: New York).
Farrar, C.R., Doebling, S.W. and Nix, D.A., Vibration-based structural
damage identification. Phil. Trans. R. Soc.: Math., Phys. Eng. Sci., 2001,
359(1778), 131 – 149.
Farrar C.R. and Sohn, H., Pattern recognition for structural health
monitoring, in Workshop on Mitigation of Earthquake Disaster by
Advanced Technologies, Las Vegas, NV, USA, 2000.
Frangopol, D.M., Kong, J.S. and Gharaibeh, E.S., Reliability-based life-
cycle management of highway bridges. J. Comput. Civ. Eng., 2001, 15(1),
27 – 34.
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

Gkoumas, K., Metodologie per il monitoraggio di sistemi strutturali
complessi con particolare riferimento al caso dei ponti. Graduate thesis
(in Italian), Department of Structural and Geotechnical Engineering,
School of Engineering, University of Rome ‘La Sapienza’, 2004.
Haimes, Y.Y., Risk Modelling Assessment and Management, 1998 (Wiley:
New York).
Lauwagie, T., Sol, H. and Dascotte, E., Damage identification in beams
using inverse methods. In Proceedings of the International Conference on
Noise and Vibration Engineering, edited by P. Sas and B. van Hal, 2002
(on CD-ROM).
Lynch, P.J., Partridge, A., Law, H.K., Kenny, W.T., Kiremidjian, S.A. and
Karryer, E., Design of piezoresistive MEMS-based accelerometer for
integration with wireless sensing unit for structural monitoring. J. Aero.
Eng., 2003, 16(3), 108 – 114.
National Aeronautics and Space Administration (NASA), Systems
Engineering Handbook, 1995. Available online at: www.nasa.gov
(accessed 15 May 2006).
Papadimitriou, C., Beck, J.L. and Katafygiotis, L.S., Updating robust
reliability using structural test data. Prob. Eng. Mech., 2001, 16, 103 –
113.
Partridge, A., Reynolds, J.K., Chui, B.W., Chow, E., Fitzgerald, A.M.,
Zhang, L., Maluf, N.I. and Kenny, T.W., A high-performance planar
piezoresistive accelerometer. IEEE J. Microelectro. Mech. Syst., 2000,
9(1), 58 – 65.
Rizos, C., Precise GPS positioning: prospects and challenges, in Proceed-
ings of 5th International Symposium on Satellite Navigation Technology &
Applications, 2001, paper 37 (on CD-ROM).
Roberts, G.W., Dodson, A.H., Brown, C.J., Karuna, R. and Evans, E.,
Monitoring the height deflections of the Humber Bridge by GPS,
GLONASS and finite element modelling. In Proceedings of IAG
Symposia 2000, edited by Schwarz, 121, pp. 355 – 360, 2000 (Springer-
Verlag: Berlin).
Rytter, A., Vibration based inspection of civil engineering structures. PhD
thesis, Department of Building Technology and Structural Engineering,
University of Aalborg, Denmark, 1993.
Schultz L.W., Udd E., Seim M.J. and McGill E.G., Advanced fiber grating
strain sensor systems for bridges, structures and highways, in Proceed-
ings of SPIE, 3325, pp. 212 – 221, 1998, Smart Structures and Materials
1998: Smart Systems for Bridges, Structures, and Highways.
Senaud, G., Strategie per la qualificazione prestazionale ed il monitoraggio
strutturale. Graduate thesis (in Italian), Department of Structural and
Geotechnical Engineering, School of Engineering, University of Rome
‘La Sapienza’, Italy, 2004.
Schodek, D.L., Structures, third edition, 1998 (Prentice Hall: Columbus,
Ohio).
Sgambi, L., I metodi dell’intelligenza artificiale nell’analisi e nella
progettazione dei ponti sospesi. PhD thesis (in Italian), Department of
Structural and Geotechnical Engineering, School of Engineering,
University of Rome ‘La Sapienza’, 2005.
Silvestri, M., Gli aspetti concettuali del performance-based design e la loro
applicazione nel progetto dei ponti sospesi. Graduate thesis (in Italian),
Department of Structural and Geotechnical Engineering, School of
Engineering, University of Rome ‘La Sapienza’, 2002.
Skelton, R.E., Structural system: a marriage of structural engineering and
system science. J. Struct. Control, 2002, 9, 113 – 133.
Smith, I., Increasing knowledge of structural performance. Struct. Eng.
Int., 2001, 12(3), 191 – 195.
Sørensen, R.E., Buhr, B. and Frølund, T., Sensoring corrosion – the
Danish way. In Proceedings of the 2nd International Conference of the
International Association for Bridge Maintenance and Safety (IAB-
MAS’04), edited by E. Watanabe, D.M. Frangopol and T. Utsunomiya,
2004.
Stewart, M.G. and Melchers, R.E., Probabilistic Risk Assessment of
Engineering systems, 1997 (Chapman and Hall: London).
Sydenham, P.H., Systems Approach to Engineering Design, 2004 (Artech
house: Boston).
Wong, K., Man, K. and Chan, W., Real-time kinematic spans the gap.
GPS World, 1 July 2001. Available online at: www.gpsworld.com
(accessed 15 May 2006).
Downloaded
by
[Universita
Studi
la
Sapienza]
at
04:08
05
October
2011

Systemic approach for the maintenance of complex structural systems

Recommended

Recommended

More Related Content

Similar to Systemic approach for the maintenance of complex structural systems

Similar to Systemic approach for the maintenance of complex structural systems (20)

More from Franco Bontempi Org Didattica

More from Franco Bontempi Org Didattica (20)

Recently uploaded

Recently uploaded (20)

Systemic approach for the maintenance of complex structural systems