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MATERIALS FORUM VOLUME 33 - 2009

Edited by Dr Steve Galea, Associate Professor Wingkong and Professor Akira MitaInstitute of Materials Engineering Australasia Ltd

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SEISMIC MONITORING OF STRUCTURAL AND GEOTECHNICAL

INTEGRATED SYSTEMS

G. Fabbrocino, C. Laorenza, C. Rainieri, F. Santucci de Magistris

Structural and Geotechnical Dynamic Laboratory StreGa, University of Molise, Termoli (Cb), Italy

ABSTRACT

Several applications of Structural Health Monitoring and several techniques exists in order to assess the health state of acivil engineering construction. Bridges and buildings are the structural typologies usually monitored: therefore,

currently the dynamic behaviour of a number of superstructures is extensively studied. Geotechnical aspects, instead,are less investigated: in particular, the dynamic behaviour of a flexible retaining wall under seismic load conditions iscurrently not fully understood. The Structural Health Monitoring system of Casa dello Studente at University ofMolise has been designed and is currently under construction in order to obtain a deeper knowledge of the dynamicbehaviour also of geotechnical structures. The above mentioned SHM system is an example of cooperation of severaldifferent skills: geotechnical and structural engineers have worked together during all phases of design and installation

of the system and a large effort for a full integration of geotechnical and structural models is currently underdevelopment. As regards geotechnical aspects, data coming from the SHM system, together with centrifuge tests andnumerical models, will be used to increase the knowledge about the dynamic behaviour of the soil-retaining wall systemin case of earthquake. On the other hand, data coming from the building of Casa dello Studente can be used forclassical SHM applications. Anyway, the most important aspect is related to the possibility of combining structural andgeotechnical knowledge and models and apply them in different fields.In the present paper, the main aspects of an integrated SHM system at University of Molise will be described, pointing

out the targets which oriented its design and implementation. A specific sensor module, developed by PCB PiezotronicsInc. under the supervision of the workgroup of University of Molise, will be described together with the phases ofinstallation within the instrumented piles.

1 INTRODUCTION

Structural Health Monitoring for civil structures isbecoming increasingly popular in Europe andworldwide also because of the opportunities that itoffers in the fields of construction management and

maintenance. Main advantages related to theimplementation of such techniques are: reduction ofinspection costs; research resulting in the possibility ofbetter understand behavior of structures under dynamicloads; seismic protection; real or near real-timeobservation of the structural response and of evolutionof damage; possibility to develop post-earthquake

scenarios and support rescue operations.

Structural Health Monitoring (SHM) is defined as theuse of in-situ, non-destructive sensing and analysis ofstructural characteristics in order to identify if a damagehas occurred, define its location and estimate itsseverity, evaluate its consequences on the residual life of

the structure [1]. Even if SHM is a relatively newparadigm in civil engineering, the assessment of thehealth state of a structure by tests and measurements is acommon practice, so that evaluation and inspectionguidelines are available since a long time [2]. SHMobjectives are consistent with this practice but it takes

advantage of the new technologies in sensing,instrumentation, communication and modeling in order

to integrate them into an intelligent system. Thus,Structural Health Monitoring is a very multidisciplinaryfield, where a number of different skills (seismology,electronic and civil engineering, computer science) and

institutions can work together in order to increaseperformance and reliability of such systems, whose

promising perspectives seem to be almost clearly stated.Informations obtained from such systems could beuseful for maintenance or structural safety evaluation ofexisting structures, rapid evaluation of conditions ofdamaged structures after an earthquake, estimation ofresidual life of structures, repair and retrofitting of

structures, maintenance, management or rehabilitationof historical structures. As reported in [3, 4], reductionof down time and improvement in reliability enhancethe productivity of the structure and the results ofmonitoring can be used to have a deeper insight in thestructural behavior which is useful for design

improvement of future structures. In order to get all

these objectives, an effective Structural HealthMonitoring system should be based on integration ofseveral types of sensors in a modular architecture.Moreover, the advances in the field of InformationTechnology and communications assure data

transmission also in critical conditions.In the present paper, the main aspects of an integratedSHM system under development at University of Molise(Italy) will be described, pointing out the targets whichoriented its design and implementation. In fact, it is aninteresting result from cooperation of different skills

(structural, geotechnical, seismological). Data comingfrom the system will be useful for damage assessment of

monitored structures, but also to study effects ofearthquakes. In particular, specific studies about soil-structure interaction will be carried out starting from


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experimental results. Finally, closeness to a fault allowsimplementation and testing of site specific early warningstrategies [5], so that integration between structural

health monitoring and seismic early warning systems asa tool for seismic protection of strategic structures andinfrastructures will be experienced.

2 CURRENT TRENDS IN SHM

A monitoring system consists of a variety of sensors to

monitor the environment and the structural response toloads. A typical architecture of the monitoring systems

is based on remote sensors wired directly to acentralized data acquisition system. However, theexpensive nature of this architecture, due to highinstallation and maintenance costs associated with

system wires [6], is causing replacement of wire-basedsystems with new low-cost wireless sensing units by

spreading knowledge over the entire monitoringnetwork. As a consequence, a larger effort is currentlyrequired in order to build effective data processingalgorithms, in particular taking into account such a new

architecture. Another relevant task is related to thestrategies to be implemented to manage data and

combine informations coming from a variety of sensorsand, therefore, related to different physical variables.In the field of damage detection, a lot of algorithms hasbeen proposed on the base of several different

mechanical and physical principles. However, they canbe classified into two main classes: a first group of

techniques, the so-called modal-based algorithms,aims at tracking changes in structural response directlyor indirectly related to the mechanical characteristics(such as natural frequencies, etc.) of the structure beforeand after damage. Conversely, the second approach isbased on the post-processing of measurement data to

detect anomalies from measurements (ARMAVmodelling, wavelet decomposition, etc.). In both cases,the trend is in using methods able to automate the

detection process by taking advantage of the recentadvances in information technologies [7]. In thisframework, identification of the modal parameters of the

structures under operational conditions plays a primaryrole. Recently, some strategies have been set up in orderto automate identification and tracking of modalparameters [8, 9, 10, 11, 12, 13] and allowing a fullintegration of modal identification within SHM systems.Reliable procedures are necessary also towards data

reduction and transmission, in particular after anearthquake, when a limited communication bandwidth isavailable: wavelet-based approaches seems to beparticularly promising in this field [14, 15]. However,real-time interpretation of data can fail due their poorquality and, in particular, in case of sensors failure:

therefore, in case of automated applications, thisverification must be conducted by the data processing

system itself. Recently, some interesting approacheshave been proposed in this field [16].The most recent and innovative applications concern of

possible interaction among earthquake early warning,structural health monitoring and structural control.However, unlike traditional seismic monitoring, an

event driven monitoring system is not useful:continuous condition assessment and performance-basedmaintenance of civil infrastructures are necessary inorder to assess the short-term impact due to earthquakes

and the long-term deterioration process due to physicalaging and routine operation. In this framework, a

monitoring system can be used for disaster andemergency management, traffic control, damageevaluation, post-earthquake scenarios definition. Theuse of monitoring systems on underground pipeline

systems may be considered as an example of post-earthquake emergency management: damaged gas

utilities, in fact, can cause secondary disasters and, as aconsequence, serious losses. In this case, informationsabout abnormal pressure changes in gas pipelines canlead to an emergency shut-off. Similar controls canaffect traffic, if informations about structural integrity of

Table 1. Relevant worldwide SHM systems

Country Structure Year N of

sensors

Seismic

zone

Sensors type Main features

Canada Pipelines 2004 N.A. No FOS N.A.

Denmark Wind turbine 2002 N.A. No FOS, MEMSaccelerometers

N.A.

USAPrestressed

concrete pile2008

8(4 + 4)

NoAccelerometers,

Strain gaugesEmbedded

wireless sensors

USAGolden Gate

Bridge2000-

0664

nodesYes

Wirelessaccelerometers

The largestwireless sensor

network for SHM

ChinaDonghaiBridge

2006 8 Yes GPS AntennasGPS-based SHM

system

SwedenGrndalBridge

2004 30 No FOS, LVDTsComparison FOS-

LVDT

PortugalHistoricalstructures

2005 10 Yes AccelerometersSHM of historical

structures

ItalySchool of

EngineeringTower

2006 30 Yes Accelerometers Automated OMA


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infrastructures are available. Knowledge of still operablebridges can help decision makers to arrange a route tothe disaster area for rescue personnel and goods.

3 SHM SYSTEMS: A SHORT REVIEW

SHM systems have been applied to a variety of

structures, such as building, bridges, pipelines [17],wind turbine blades [18]. A synthesis is reported inTable 1.SHM of bridges can provide a reduction in maintenancecosts and confidence in the performance of the structure.Several applications of health monitoring to bridges arereported in the literature [19, 20, 21, 22]. The Donghai

Bridge SHM system in China [21] is an interestingexample of application of GPS antennas in structuralmonitoring: however, low sampling rates (10 Hzmaximum) are currently available and, therefore, GPS isnot yet suitable for a wide range of applications. In [23]a performance comparison of the Fiber Optic Sensors

(FOS) and LVDTs for SHM applications pointed outthe effectiveness of FOS but also the high cost of theFOS-based monitoring system, which resulted moresuitable for periodic than for continuous monitoring.Geotechnical applications of FOS are reported in [24],where such sensors have been used extensively in

Geosynthetics and above all in micro piles for corrosionand damage detection purposes. However, a fewapplications of embedded sensors in piles are reported inthe literature. Song and Zhou [25] have monitored steelreinforcement and soil stresses for static purposes.Szyniszewski et al. [26], instead, installed wireless

sensors during casting of prestressed concrete piles in

order to monitor stresses and accelerations duringdriving: however, their interest was focused only onpreventing microcracking of piles during driving, thusextending life of such elements in a marineenvironment.

Monitoring of buildings is desirable particularly in areasprone to earthquakes and strong winds, or for historical

or heritage structures [27, 28, 29, 30]. In [31] anautomatic data management system based on MatlabWeb Server, with several buildings monitored at thesame time, is described.

The School of Engineering Tower SHM system inNaples is an example of Italian application in this field.

It is an example of integration between structuralmonitoring and seismic early warning [32, 33].

4 INTEGRATED STRUCTURAL AND

GEOTECHNICAL SHM SYSTEM:

MOTIVATIONS AND APPROACH

Flexible retaining walls are a widespread geotechnical

structure. Even if a number of design methods arealready available, they have to be validated andimproved.

Real scale experimental data concerning soil-structureinteraction, in particular in case of seismic events,cannot be easily found in technical literature. Thus, an

integrated structural and geotechnical monitoring system

has been designed and it is currently underimplementation at StreGaLaboratory at the Universityof Molise. It takes advantage of different skills and it is

a good chance to mix knowledge and models comingfrom different scientific areas but characterized byseveral common aspects.Data coming from the system under operationalconditions will be processed and used to enhancenumerical models and improve the current knowledge

about flexible retaining walls.On the other hand, data recorded during seismic eventsare also crucial to have a deeper insight in the dynamicbehaviour of such structures and in the soil-structureinteraction during string motion events: in fact, thesedata will be useful to improve seismic design procedures

for this kind of constructions.Linear and non-linear models and data processing

techniques will be used to correctly interpretate thedynamic behaviour of the structure and its interactionwith soil. Geotechnical and structural skills will act

together to this aim.Currently, two piles belonging to the flexible retainingwall have been instrumented with embedded

piezoelectric accelerometers. System design, sensorcharacteristics and installation phases will be describedin detail in the following sections. Monitored piles havebeen chosen in order to avoid as much as possible

boundary effects (Figure 1).The structural health monitoring system will be

completed by installing a number of sensors on thebuilding which will be constructed on the excavated sideof the wall (Figure 1). Closeness between the twostructures (Figure 2) suggests that a kinds of interaction:

can exist. Thus, knowledge about structural behaviourcan help in understanding measurement results obtained

from the geotechnical sensors.In the following sections, after a review of typologies ofretaining structures, some aspects related to structuraland seismic design of flexible retaining walls will bediscussed. They will be useful to better understand theidea at the base of design of the monitoring system and

some structural changes necessary to assure thatinstrumented piles have the same strength and stiffnesslike the other close piles.

5 RETAINING WALLS: AN

OVERVIEW

A retaining wall is any wall that retains material tomaintain a change in elevationA large variety of type of soil-supporting structures areemployed in civil engineering works. A short review ofthe main wall typologies is done here. Readers mightrefer for instance to [34, 35, 36] for details on thissubject.

The most common types of retaining walls are gravityconcrete, cantilever T-type reinforced concrete, andcantilever and anchored sheet pile walls. Alternate types

of retaining walls, including mechanically stabilizedbackfill and precast modular gravity walls, might also beemployed. Counterfort and buttressed reinforced

concrete walls are less commonly used.


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A gravity wall consists of mass concrete, generallywithout reinforcement. It is proportioned so that theresultant of the forces acting on any internal plane

through the wall falls within, or close to, the kern of thesection. A small tensile stress capacity is permissible forlocalized stresses due to extreme and temporary loadingconditions. Gravity walls rely on their significant massand geometrical dimensions for stability against slidingor overturning. Small or no contribution at all to

stability is assumed to be provided by passive resistanceof any soil acting on the face of the wall.A cantilever T-type reinforced concrete wall consists ofa concrete stem and base slab which form an inverted T.The structural members are fully reinforced to resistapplied moments and shears. The base is made as

narrow as practicable, but must be wide enough toensure that the wall does not slide, overturn, settle

excessively, or exceed the bearing capacity of thefoundation. The bottom of the base should be below thezone subject to freezing and thawing or other seasonal

volume changes. The T-type wall is usually the mosteconomical type of conventional wall and is widelyused.

Retaining walls using mechanically stabilized backfill

and precast modular gravity walls can be substantiallymore economical to construct than conventional walls[37]. However, a short life, serious consequences of

failure, or high repair or replacement costs could offset alower first cost. In addition, the design engineer mustassure the overall adequacy of the design since themanufacturer of the wall may provide only that part ofthe design above the foundation.Embedded walls are constructed from contiguous or

interlocking individual piles or diaphragm wall-panelsto form a continuous structure. Embedded walls may becantilever, anchored or propped.Cantilever walls derive their equilibrium from the lowerembedded depth of the wall. They rely on the passiveresistance of the soil in front of the lower part of the

wall to provide stability. Anchored or propped wallsderive their equilibrium partly from the embedded

portion of the wall and partly from an anchorage or propsystem which support the upper part of the wall.Braced sheet pile, consists of a row of vertical

prestressed concrete sheet piles, backed by batter pilesconnected to the sheet piles by a cast-in-place horizontalconcrete beam with shear connectors as required to

resist the vertical component of load in the batter pile.

Figure 1. Schematic view of flexible retaining wall and of the monitored pile location


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This type of wall has been used for coastal flood walls.It is ideal for wet areas because no excavation ordewatering is required to construct the wall. The

disadvantage is that it is more indeterminate than otherwall types.Steel sheet pile walls are constructed by driving steelsheets into a slope or excavation. Their most commonuse is within temporary deep excavations. They areconsidered to be most economical where retention of

higher earth pressures of soft soils is required. Theyhave an important advantage in that they can be drivento depths below the excavation bottom and so provide acontrol to heaving in soft clays or piping in saturatedsands. This is not possible with the soldier pile which isalso a more permeable structure. However sheet piles

are more costly and less adaptable to hard drivingconditions particularly where boulders or irregular rock

surfaces occur.Easy driving conditions are experienced in clays, sands,and clay-sand mixture due to the comparatively small

displacement of soil. However they may permit largemovements in weak soils and also effective de-wateringis often required since they do not provide a watertight

boundary. Seepage commonly occurs through theinterlocks and this can be sufficient enough to causeconsolidation of organic soils and soft silty clays,(compressible materials). For sandy soils ravelling will

not occur if the interlocks are tight, but driving sheetpiles into loose sand can cause subsidence.

Cantilever sheet pile walls are mainly used fortemporary excavations of moderate depth. Because ofthe large earth pressures and deflections that maydevelop they are rarely used to retain excavations

greater than a depth of 5 m. However even this may beexcessive where soft or loose soils occur in front of the

wall. Stiffer cantilever walls, of concrete or steelincluding diaphragm walls and heavy composite walls,may be satisfactory to heights of 12 m providing theground is string enough. The required penetration depthis high because the support is totally derived from thepassive pressure exerted on the embedded portion of the

pile. The deflections at the head of the wall might behigh. Well constructed anchor walls undergo less lateraldeflection than braced walls and so provide a better

control of backslope subsidence. Anchor installationonly requires a small excavation to allow equipmentaccess. However for braced wall installation there isoften a requirement to excavate below the level ofsupport.Anchored walls are always pre-stressed which

essentially removes the slack from the system. Theanchors will maintain their load throughout theexcavation sequence unless creep occurs. The anchorsalso place the entire soil mass between the anchors andthe wall in compression, thus creating a very largegravity wall.

Propped walls may have one of more levels of prop inthe upper part of the wall. They can be designed to have

fixed or free earth support at the bottom and derive theirstability from the props. They are common incofferdams.

For propped walls in the free earth condition thepenetration of the piles should be such that the passivepressure in front of the piles will resist forward

movement of the toes of the piles but will not preventrotation. The piles are supported by ties at the top of thewall and the soil at the base of the wall. In fixed earthconditions further penetration of the pile is required to

ensure that not only the passive pressures in front of thewall resist forward movement but also that the rotation

of the toe is restrained by the passive pressures locatednear the toe at the rear of the wall. The above conditionsalso apply to anchored sheet pile walls.Soldier piles, also known as Berlin Walls, are

constructed of wide flange steel H sections spaced about2 - 3 m apart, driven prior to excavation. As the

excavation proceeds, horizontal timber sheeting(lagging) is inserted behind the H pile flanges. Thehorizontal earth pressures are concentrated on thesoldier piles because of their relative rigidity comparedto the lagging. Soil movement and subsidence isminimised by maintaining the lagging in firm contact

Figure 2. Scheme of the flexible retaining wall and of Casa dello Studente building foundations


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with the soil.Bored piles are used when a soil replacement rather thana soil displacement method of piling is required and also

when there is a need to minimise vibration. They areunsuitable where the ground water level on the retainedside is high. The best application is for cohesive soils.The advantage of the bored pile is that only one pileneed be bored at a time. Therefore when working closeto a foundation only a short length of the foundation

need be exposed to any risk at a given time. It is alsoeasier to overcome ground obstructions than with sheetpiling or diaphragm walls. Also bored piles are able topenetrate moderately hard bedrock materials more easilythan other methodsClose bored or contiguous piles are constructed in a line

with a clear spacing between the piles of 75 to 100 mm.Therefore they cannot be used as water retaining

structures.Their main use is in clay soils where water inflows arenot a problem. However they have also been used to

retain dry granular materials or fills. Where water is nota problem the spacing of the piles can be adjusted solong as the gap between piles is such as to prevent soil

collapse between them. In water bearing granular soilsloses are likely to occur in the gaps between the piles.This can be prevented by providing a seal betweenadjacent piles.

Secant piles are constructed so that there is anintersection of one pile with another. The usual practice

is to construct alternative piles along the line of the wallleaving a clear space of a little under the diameter of therequired intermediate piles. The exact spacing isdetermined by the construction tolerances which can be

achieved. These initially placed piles do not have to beconstructed to the same depth as the intermediate piles

which follow, depending on the way in which the wallhas been designed and reinforced. Although the pilescan be use to form a continuous watertight wall, it isdependant upon the control of tolerance for planposition and boring direction. A lack of intersectionquickly makes the wall non-water tight.

Finally, diaphragm walls provide a water tight barrierand are constructed with a minimum backslopesubsidence. They formed from reinforced concrete andare constructed as normal cast-in-place walls withsupport which become part of the main structure. The

slurry trench method is commonly used which involvesthe excavation of alternating panels along the proposedwall using bentonite slurry to prevent the sides of theexcavation collapsing. Diaphragm walls can beconsidered to be impervious and therefore the de-watering of granular soils is often neglected. However

care must be taken to ensure that there are no openingsor joints since they may result in sudden loss of soil.

Diaphragm walls of shallow depths are often leftunsupported since they are classed as semi rigidstructures. However for deeper excavations support isrequired to restrict lateral deflections. Diaphragm walls

are ideal for soft clays and loose sands below the water

table where there is a need to control lateral movements.However they are relatively costly. They are alsounsuited to strong soils conditions where penetration isslow and difficult due to the use of the slurry trench

method.The retaining wall considered in this research is anembedded wall, cantilever sheet pile type made of two

set of contiguous piles disposed along two lines (Figure1). A top beam connects all the piles.

5.1 Design of retaining walls for earthquake loadings

Earthquakes might cause permanent deformations ofretaining structures and even failures. In some cases,these deformations originated significant damages withdisastrous physical and economic consequences. Forgravity walls, the dynamic earth pressures acting on the

wall can be evaluated by using the Mononobe-Okabemethod, while Newmark rigid sliding block scheme issuitable to predict the displacements after the shaking,as demonstrated by several experimental tests. Instead,this simplified approach is not very useful for embeddedretaining walls for various reasons and then, there is

room for innovative approaches in design of such

structures. Here, for sake of simplicity, reference ismade only to flexible walls. Readers might refer forinstance to [38] for a large overview of design methodof retaining walls under static and seismic actions.

5.1.1 Design of embedded retaining walls with limit

equilibrium methods

In this procedure, the wall is assumed rigid, the soil hasa rigid-perfectly plastic behaviour and the pressuresderiving form the interaction depend on the expectedmovements of the wall. The kinematical mechanism isaffected from the constraints applied on the wall.

Generally, the free embedded cantilever walls aredistinguished from the anchored or multi-anchoredwalls. Here, only the former are considered. First, a

short recall of the static methods is reported and then theseismic actions are included.

5.1.2 Static design of free embedded walls

As specified before, the stability of a cantilever wall isguaranteed from the passive resistance of the soil inwhich the wall is embedded. In the limit equilibrium

methods the wall movement that conducts to limitconditions is constituted by a rigid rotation around a

point O placed near to the bottom of the wall. Thetheoretical earth pressures distributions on the wall areplotted in Figure 3.To eliminate stresses discontinuities in correspondence

of the rotation point and to obtain a simplified shape ofthe pressures distributions, different simplifications and

assumptions were proposed in literature. (Figure 4 andFigure 5).In a first case, the net pressure distribution is simplifiedby a rectilinear shape. It is assumed that the passiveresistance below the dredge level is fully mobilized. The

rotation point coincides with the zero net pressure point.At the bottom of the wall the soil strengths, active andpassive, are mobilized and the net pressure assumes thevalues reported in Figure 4.A second method assumes that the net pressure


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distribution below the point of rotation can substitutedwith the net force R applied at a distance z = 0.2d fromthe bottom of the wall.

h

d

H

AK

PK

PKAK

AK d K (h+d)P

d'

z'

O

Figure 3. Earth pressures distributions assumed in limit equilibrium

method

AK

P(K - K ) A

[K (h+d) - K d] P A

h

dd'

z'

Figure 4. Simplified earth pressures distributions: Full Method

h

d

AK

PK

d'

R

0.2

d'

Figure 5. Simplified earth pressures distributions: Blum Method

The main problem for the design of embedded walls isthen the right choice of the earth pressure coefficientsKA and KP when the soil-wall friction would beconsidered. It is well-recognized that the Coulombtheory provides unrealistic values of the passive earthpressure coefficient when > '/2.

Different suggestions can be found in the literature [39,40, 41]. Since knowledge on this field is limited, in thecurrent practice is commonly adopted A = 2/3 ' forthe active case and P= 0, for the passive case. In this

manner, passive resistance of soil on the dredge side ofreinforced concrete walls, realized with piles or

diaphragm, is largely underestimated.

Padfield and Mair [39] assert that reasonable values ofthe soil-wall friction for the calculation of the earthpressure coefficients are A= 2/3 ' and P= 1/2 '.

5.1.3 Seismic design of free embedded walls

In the EuroCode 8 Part 5 [42] is described a simplified

pseudostatic approach to analyze the safety conditionsof retaining walls. The seismic increments of earthpressures may be computed with the Mononobe-OkabeM-O method. Its application for rigid structures is moreprompt than for embedded walls for which the stabilityis mainly due to the passive resistance of the soil in the

embedded portion.As for the Coulomb theory in static conditions, the M-Otheory gives very high values for passive earth pressurecoefficient when the soil-wall friction is considered. Forthis reason, the evaluation of passive pressure should beconducted assuming zero soil-wall friction.

In the pseudostatic analyses, the seismic actions can be

represented by a set of horizontal and vertical staticforces equal to the product of the gravity forces and aseismic coefficient. For non-gravity walls, the effects ofvertical acceleration can be neglected. In the absence ofspecific studies, the horizontal seismic coefficient khcan

be taken as:

g

a

r

Sk

gh = (1)

where S is the soil factor that depends to the seismic

zone and considering the local amplification due to the

stratified subsoil and to the topographic effects, agis thereference peak ground acceleration on type A ground, gis the gravity acceleration and the factor r is a functionof the displacement that the wall can accept. For nongravity walls, the prescribed value is r = 1 [42].Furthermore, for walls not higher than 10m, the seismic

coefficient can be assumed constant along the height.The point of application of the force due to the dynamicearth pressures should be taken at mid-height of thewall, in the absence of a more detailed study taking intoaccount of the relative stiffness, the type of movementsand the relative mass of the retaining structure.

Assuming that the position of the point of rotation O

near to the bottom of the wall is the same of the staticcondition, the application of the Blum method to searchthe seismic limit equilibrium of a free embedded wallcan be conducted adopting the loading systemrepresented in Figure 6. The earth pressure thrusts have

the following expressions:

( )

( ) ( )2AAEAE

2

AA

'dhKK2

1S

'dhK2

1S

+=

+=

(2)


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( ) 2PPEPE

2PP

'dKK2

1S

'dK2

1S

=

=

(3)

in which the earth pressure coefficients with thesubscript E are referred to the seismic conditions while

those without the subscript E are the static coefficients.

h

d PSd

'

R

0.2

d'

AS

AES

PES

Figure 6. Earth pressures on a free embedded wall subjected to seismic

loadings according to EC8-5 pseudostatic analysis

The moment equilibrium of the forces around the pointO provides a simple relationship for the limit depth ofembedment:

13

3

2.1

3

=

AAE

PPE

KK

KK

hd (4)

If the seismic horizontal coefficient kh = 0 (staticconditions), the seismic earth pressure coefficients areequal to the corresponding static values.The EC8-5 indications on the soil-wall friction conduct

to a very conservative design of the depth ofembedment, underestimating the soil passive resistance.

The use of the Blum method with the seismic passiveearth pressure coefficient given by the lower-boundlimit method proposed by Lancellotta [43] allowsestablishing more reasonable depths of embedment for

cantilever walls.

5.1.4 The New Italian Building Code

The new Italian Building Code [44] introduced someinnovations on the seismic design of embedded walls toeliminate some discrepancies existing on the applicationof the pseudostatic analyses for embedded walls (see forinstance [45]).The pseudostatic analysis of an embedded retaining wallshould be carried out assuming that the soil interacting

with the wall is subjected to a value of the horizontalacceleration which is:

constant in space and time (this is implicit in apseudostatic analysis);

equal to the peak acceleration expected at thesoil surface.

Deformability of the soil can produce amplification of

acceleration, that is incorporated into the soil factor S,but that can be better evaluated through a site responseanalysis.

For many structures, including embedded retainingwalls, there may be reasons to question the assumptionthat the structure should be designed assuming aconstant peak acceleration. The validity of the twoassumptions (spatial and temporal invariance) will beexamined separately for clarity.

Figure 7 shows a M-O active wedge which interactswith a vertically propagating harmonic shear wave offrequency f and velocity VS, characterized by awavelength = VS/f larger than the height of the wedgeH. In this case, the variation of the acceleration alongthe height of the wedge is small, inertial forces (per unit

mass) are about constant and the motion of eachhorizontal element is approximately in phase.

SH

a(z,t)

Figure 7.Mononobe-Okabe wedge interacting with harmonic wave

characterized by large wavelength

SH

a(z,t)

Figure 8. Mononobe-Okabe wedge interacting with harmonic wave

characterized by small wavelength

In Figure 8 a case is depicted in which, either becauseVSis smaller (the soil is more deformable) or f is larger,

is small if compared to H. In this case, at a given timet, different horizontal wedge elements are subjected to

different inertial forces, and their motion is out of phase.Therefore, at each t the assumption of spatial invarianceof the acceleration is no longer valid, and, at each t, theresultant inertial force on the wedge must lead to a

smaller resultant force SAE than that predicted with theM-O analysis.

Steedman and Zeng [46] have proposed a method for

evaluating the effect of spatial variability of the inertialforces on the values of SAE, maintaining the hypothesisthat the wedge is subjected to a harmonic wave.


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It should be clear that coefficient r in equation (1)depends on the displacements that the structure canaccept with no loss of strength. That is, it may be

acceptable that over a small temporal period during anearthquake the acceleration could be higher than acritical value producing limit conditions, provided thatthis will lead to acceptable displacements and that thesedisplacements do not produce any strength degradation.This is equivalent to state that the behaviour of the

structure should be ductile, i.e. that strength should notdrop as the displacements increase.

0.2

0.4

0.6

1.2

1.0

0.8

5

H (m)

10 15 20 25 30 35 40 45 50

D

C

B

Ground type A

Figure 9. Diagram for evaluation of deformability factor (NTC,

2008)

To account these aspects, in the latest Italian BuildingCode NTC two coefficients were introduced. In theabsence of specific studies, the seismic horizontalcoefficient khcan be estimated with the relationship:

g

Sak

gh = (5)

where 1 and 1 are factors for the deformabilityof the soil that interacts with the wall and for the

capability of the structure to accept displacementswithout losses of strength, respectively. Their values arereported in Figure 9 and Figure 10.

The points of application of the forces due to thedynamic earth pressures can be assumed to be the sameof the static earth thrusts, if the wall can acceptdisplacements.

0.2

0.4

0.6

1.0

0.8

us(m)

0.1 0.2 0.3

Figure 10. Diagram for evaluation of displacement factor (NTC,

2008)

Instead they should be taken at mid-height of the wall,in the absence of more detailed studies, accounting for

Figure 11. Scheme of developed sensor module (courtesy of PCB Piezotronics Inc.)


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the relative stiffness, the type of movements and therelative mass of the retaining structure. From the shortnote reported above it might then concluded that even

though retaining walls are well widespread, designmethods need to be validated and improved, especiallywhen dealing with flexible retaining structures.

6 THE EMBEDDED SENSORS

Taking into account the previously mentioned

uncertainties in flexible retaining wall design, twocontiguous piles, one for each line constituting the

flexible retaining wall, have been instrumented withsome embedded accelerometers.The singularity of application and a number of issuesdirectly related to sensor embedment required design of

a specific enclosure for the manufacturer. As a result, anew sensor module for embedded applications has born

from cooperation among technicians and scientists ofUniversity of Molise and engineers of the factory.Each sensor module consists of two seismic, highsensitivity (10 V/g) ceramic shear ICP accelerometers

model 393B12 by PCB Piezotronics Inc., placed in twoorthogonal directions and encapsulated in a stainless

steel enclosure which assures impermeability andprotection against concrete pressure. Sensor bandwidthgoes from 0.15 Hz to 1 kHz, with a broadbandresolution of 8g rms. Measurement range is 0.5g pk.

For its features, this sensor is suitable for applicationboth in operational conditions and under extreme events

such as earthquakes. Moreover, they have an overloadlimit (shock) of 5000 g: therefore, even if specificprocedures for concrete casting have been adopted,through a pipe progressively raised in order to avoiddirect impact of concrete against sensor enclosure, thehigh shock limit has been fundamental in order to assure

effectiveness of sensors, which are buried in concreteand, therefore, not repairable, in operational conditions.

Figure 12. Prototype of embedded sensor module

Sensors in each enclosure have been encapsulatedthrough a hard non-conductive epoxy resin in order to

assure rigidity to the walls of the enclosure, which hasnot to suffer any damage during casting operation or for

concrete pressure. It assure also waterproofing of the

inside of the enclosure. Design drawings of sensormodule are shown in Figure 11. A picture of theprototype of the sensor module is, instead, shown in

Figure12. A 1-1/2 NPT conduit hub, which has a gasketthat seals against the outside of the enclosure, and a 1-1/2 NPT x 4 straight nipple have been used to connectpipes, for cable routing, to the enclosure (Figure 13).Each enclosure has been equipped with a pipe for cablerouting during installation.

(a)

(b)

Figure 13. Conduit hub (a) and straight nipple (b) for pipe connection

to module

7 DESIGN OF INSTRUMENTED PILES

Instrumented piles had to show similar characteristicswith respect to the adjacent ones, in order to assure

significance to the present study and avoid singularity inthe overall behaviour of the structure. For this reason,due to the not negligible dimensions of sensor modules

which caused some changes in pile geometry, specificcomputations and additional reinforcement have beenprovided in order to assure that the instrumented pileshad similar strength and stiffness with respect to thenominal characteristics of the adjacent piles.Three sensor modules have been placed in each pile:positions have been chosen in order to be as far as

possible from the computed locations of the center ofrotation in both the building and operational phases.Additional two sensors have been placed on top of eachpile, into a box over the top beams which connects allpiles. A schematic view of instrumented piles is shownin Figure 14. Dimensions of sensor modules have

required design of an additional reinforcement to beplaced around them: in fact, where a module is located,due to its dimensions, pile section can be considered nomore circular but it becomes an hollow section whose


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exterior diameter is 800 mm and whose interiordiameter is 300 mm, that is the size of instrumentation.The additional reinforcement has been computed so that

the resulting section has similar strength and stiffness tothose ones in the rest of the retaining wall.

(a)

(b)

(c)

(d)

Figure 14. Scheme of monitored piles (a); details of head of piles and sensor housing (b), (c); layout of intermediate enclosures (d)


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The additional reinforcement consists of a longitudinalreinforcement made by 8 14 bars and stirrups made by10 bars placed at a distance of 200 mm each other. As

said before, the additional reinforcement has beenplaced just around sensor modules and extended at bothsides for the anchorage of longitudinal bars.The additional reinforcement has been connected to thetypical one by mean of four lattices of the standard typeBaustrada, 8/10/6, h = 125 mm (Figure 14a-d).

However, they cause a negligible variation in strengthand stiffness as proved by computations. In Figure 15,in fact, the strength domains of the typical pile sectionwithout additional reinforcement, of the pile sectionwhen lattices are present, and of the hollow section arereported: the maximum strength variation has been

estimated in +5% for the hollow section with respect tothe typical section and in +3% for the section plus the

four lattices with respect to the typical section. Suchvalues can be assumed in the limit of dispersion ofstrength.

A similar computation has been carried out consideringthe shear stress: also in this case the increase in strengthfor the hollow section is lower than 5% with respect to

the typical section of the piles.Shear strength for the circular and the hollow sectionshave been computed according to [47, 48].As regards the effects of the embedded sensors on the

stiffness of piles, moments of inertia for the circular andthe hollow section have been computed and compared.The effects of the four lattices and of the additional

longitudinal reinforcement have been taken into account(Table 2): an increment of 0.9% of the moment ofinertia has been obtained for the circular section withlattices with respect to the typical circular section; anincrement of 0.6% has been, instead, obtained for themoment of inertia of the hollow section with respect to

that one of the typical section.

Table 2. Changes in moment of inertia of instrumented piles.

Section Moment of

inertia [cm4]

Scatter with respect

to circular section

[%]

Circular(typical)

2.945.584 /

Circular +4 lattices

2.971.369 + 0.9%

Hollow 2.962.194 + 0.6%

It is clear, therefore, that negligible variations in termsof strength and stiffness have been produced by theinstallation of sensors within the pile.

The additional reinforcement, the presence of thesensors and of pipes for cable routing, and, finally,

Black: CircularMagenta: Circular + lattices

Green: Hollow section

Figure 15. Comparison of flexural strength of the modified sections of the pile (1 t 10 kN).


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installation of three inclinometers (Figure 14) madeconcrete casting more difficult. A pipe with a diameterof 120 mm has been used for casting: it has been raised

during casting operations but being careful that its endwas always under the surface of concrete.The large amount of reinforcement near sensorspositions and the use of a pipe for concrete castingcharacterized by a reduced diameter required adequatestudies about concrete properties. Concrete workability

and fluidity were crucial for this application: thus, aSelf-Compacting Concrete (SCC) and has been designedin order to obtain Rck = 30 MPa, which was the designvalue of concrete strength of the adjacent piles.Adoption of a self-compacting concrete made castingpossible even in these particular conditions, without

segregation phenomena.

8 SENSOR INSTALLATION

Sensor enclosure has been connected to the additionalreinforcement by mean of a steel plate welded to thelongitudinal bars. Four bolts have been used to fix the

enclosure over the plate.The main issue in the mounting phase was related to

sensor alignment. In order to assure it with very lowtolerances, connection between sensor module and platehas been obtained by mean of four slot on the enclosureand by using three stud nut and a bolt in order to fix the

enclosure at each point (Figure 16).The slots allowed rotations in the measurement plane of

sensor module while the bolts allowed rotation along thepile axis, translations in the measurement plane androtation with respect to the plane orthogonal to the latterand to the pile axis. By using three straight lines asreferences (Figure 17a) and checking parallelism of thewalls of the enclosures, a precise alignment of sensors

has been obtained.Proper orientation of sensors in the hole has beenobtained by tracking some reference straight lines on thetop of the adjacent piles and by checking parallelismbetween them and measurement directions, reproducedon the top of the instrumented pile reinforcement.

Figure 18. Embedded sensor record

Some slope measurements have been carried out in

order to verify verticality of pile reinforcement and oflattices after their introduction in the hole and beforeconcrete casting. This assured a proper installation of

sensors, with pile axis and normal to the retaining wallsurface as measurement directions. In fact, computationof deflection of the system made by the four lattices andthe additional reinforcement near the enclosures duringthe installation phase has shown that deformations arewithin the elastic limit of steel and, therefore, no

permanent strain was expected after raised the system.Slope measurements will be periodically carried outthroughout the life of the structure for static monitoringpurposes. Moreover, displacements of the head of thepiles will be monitored during excavation process usingtopographic methods. A sample record from an

embedded sensor after concrete casting is shown inFigure 18.

9 CURRENT ANALYSIS CAPABILITY

AND FUTURE RESEARCH

DIRECTIONS

At completion, the SHM system will combine differentskills and models (mainly structural and geotechnical)and data coming from the flexible retaining wall, andfrom the structure and foundations of Casa dello

Studente building will be processed and used to createa database of measurements and processed data able to

deeply enhance knowledge about the dynamic behaviourof structural and geotechnical systems (namely, flexibleretaining walls and foundations) and about soil-structureinteraction.

Operability of the SHM system also in the case ofextreme events such as earthquakes will be assured by

adopting particular hardware solutions and redundanttransmission systems.Measurements will be stored locally on a MySQLdatabase and continuously processed in order to achievea substantial data reduction. Processing results will bepermanently stored on the database, and a remote access

to such data will be assured for remote assessment of thehealth state of the monitored systems. Rawmeasurements, instead, will be periodically deleted if nomeaningful events (earthquakes) occur.Currently, a number of data processing procedure are

already available and extensively applied [8, 49, 50, 51],but they are mainly referred to structural dynamics.They allow a continuous automated identification ofmodal parameters, whose variations could be in someway related to presence of damage. However, a numberof models and data processing procedures is under

development and test within the research group of theStructural and Geotechnical Dynamic Lab StreGa at

University of Molise. Numerical simulations of thesystem are under both in the static and dynamic field.When experimental data are considered, new dataprocessing procedures can be easily implemented and

integrated into the structural health monitoring system

thanks to the capabilities and versatility of LabViewenvironment [52]. Home-made software allows easy andfast integration of new data processing algorithms, orthe updating of the existing ones. Moreover, the


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monitoring system can be easily expanded thanks to thepresence of the remote database which works asinformation collector.

CONCLUSION

Several worldwide applications of Structural HealthMonitoring in civil engineering are reported in theliterature and several techniques exists in order to assessthe health state of a structure. Bridges and buildings arethe structural typologies usually monitored: therefore,currently the dynamic behaviour of superstructures is

extensively studied. Geotechnical aspects, instead, areless investigated: in particular, the dynamic behaviour ofa flexible retaining wall under seismic load conditions iscurrently not fully understood.

The Structural Health Monitoring system of Casa delloStudente at University of Molise has been designed and

is currently under construction in order to obtain adeeper knowledge of the dynamic behaviour also ofgeotechnical structures. It is an example of cooperationof several different skills: geotechnical and structural

engineers have worked together during all phases ofdesign and installation of the system and a large effort

for a full integration of geotechnical and structuralmodels is currently under development.As regards geotechnical aspects, data coming from theSHM system, together with centrifuge tests and

numerical models, will be used to increase theknowledge about the dynamic behaviour of the soil-

retaining wall system in case of earthquake. On theother hand, data coming from the building of Casadello Studente will be used for classical SHMapplications and for studies in the field of soil-structureinteraction. Anyway, the most important aspect isrelated to the possibility of mixing structural and

geotechnical skills and models and apply them indifferent fields.In this paper, the main aspects of design andimplementation of the integrated SHM systemdeveloped at University of Molise have been illustrated.A specific sensor module, developed by PCB

Piezotronics Inc. under the supervision of theworkgroup of University of Molise, has been described.Since it is embedded into the piles, a specific design of

the instrumented piles has been necessary: the mainideas underlying structural design of instrumented piles,and the procedure and phases for installation of sensors

within the instrumented piles have been extensivelyreviewed.

Acknowledgments

The research described in the present paper has beenpromoted by University of Molise, whose primaryfinancial support is acknowledged. Contribution ofINTERREG CARDS-PHARE MEETING project has tobe recognized.

Many people and friends gave their contribution.Authors would like to tank Dr. Carmine Salzano fromPCB Piezotronics for his support and competence, Mr.

Ciro Visone who has in charge the dynamic numericalsimulations of the system. Mr. Marco Santone for hiswork on the field together with people from StreGa Lab.

A final acknowledgement to Caparelli Impianti s.r.l. thatplays the difficult role of the contractor involved in aseismic monitoring research project.

References

1. C. Silkorsky, Development of a HealthMonitoring System for Civil Structures using aLevel IV Non-Destructive Damage EvaluationMethod, Proceedings of the 2nd InternationalWorkshop on Structural Health Monitoring,

Stanford, CA, USA, 1999.

2. A. Mufti, Guidelines for Structural HealthMonitoring, University of Manitoba, ISIS,

Canada, 2001, pp. 1-127, ISBN 0-9689006-0-7.

3. A. E. Aktan, C. J. Tsikos, F. N. Catbas, K.

Grimmelsman and R. Barrish, Challenges andOpportunities in Bridge Health Monitoring,Proceedings of the 2

ndInternational Workshop

on Structural Health Monitoring, Stanford,CA, USA, 1999.

4. F. K. Chang, Structural Health Monitoring,Proceedings of the 2

ndInternational Workshop

on Structural Health Monitoring, Stanford,CA, USA, 1999.

5. M. Wieland, M. Griesser and C. Kuendig,Seismic Early Warning System for a NuclearPower Plant, Proceedings of the 12th WorldConference on Earthquake Engineering,

Auckland, New Zealand, 2000.

6. J. P. Lynch, Decentralization of wirelessmonitoring and control technologies for smart

civil structures, Blume Earthquake EngineeringCenter, Technical Report #140, Stanford

University, Stanford, CA, USA, 2002.

7. A. E. Aktan, S. K. Ciloglu, K. A.Grimmelsman, Q. Pan and F. N. Catbas,

Opportunities and challenges in healthmonitoring of constructed systems by modalanalysis, in Proceedings of the InternationalConference on Experimental Vibration

Analysis for Civil Engineering Structures,Bordeaux, France, 2005.

8. C. Rainieri, G. Fabbrocino and E. Cosenza,Key Engineering Materials, 2007, Vol. 347, pp.479-484.

9. R. Brincker, P. Andersen and N. J. Jacobsen,Automated Frequency Domain Decompositionfor Operational Modal Analysis, in

Proceedings of the 25th SEM International

Modal Analysis Conference, Orlando, FL,

USA, 2007.10. P. Verboven, E. Parloo, P. Guillaume and M.

Van Overmeire, Journal of Sound andVibration, 2003, 265(2003):647-661.


15/16

418

11. P. Verboven, E. Parloo, P. Guillaume and M.Van Overmeire, Mechanical Systems andSignal Processing, 2002, 16(4):637-657.

12. A. Deraemaeker, E. Reynders, G. De Roeckand J. Kullaa, Mechanical Systems and SignalProcessing, 2008, 22:34-56.

13. H. Guan, V. M. Karbhari and C. S. Sikorski,Time-domain output only modal parameterextraction and its application, inProceedings of

the 1st

International Operational ModalAnalysis Conference, Copenhagen, Denmark,2005, pp. 577-584.

14. J. Li, Y. Zhang and S. Zhu, Smart Materialsand Structures, 2007, 17(2008) 015020 (11

pp.).

15. Y. Mizuno and Y. Fujino, Waveletdecomposition approach for archiving and

querying large volume of Structural Health

Monitoring data, in Proceedings of the 3

rd

International Conference on Structural HealthMonitoring of Intelligent Infrastructure,

Vancouver, Canada, 2007.

16. P. Kraemer and C. P. Fritzen, Key EngineeringMaterials, 2007, Vol. 347, pp. 387-392.

17. http://www.ishmii.org/News/2004_07_15_FOSpipeline.html

18. B. F. Srensen, L. Lading, P. Sendrup, M.McGugan, C. P. Debel, O. J. D. Kristensen, G.C. Larsen, A. M. Hansen, J. Rheinlnder, J.Rusborg and J. D. Vestergaard, Fundamentalsfor remote structural health monitoring of windturbine blades - a preproject,Ris-R-1336(EN),

Ris National Laboratory, Ris, Denmark,2002.

19. C. Seim and M. G. Giacomini, Instrumentingthe Golden Gate Bridge to Record SeismicBehaviour and to Deploy Rapid InspectionResponse, in Proceedings of the 12

th WCEE,

Auckland, New Zealand, 2000.

20. P. Omenzetter, J. M. W. Brownjohn and P.Moyo, Mechanical Systems and SignalProcessing, 2004, Vol. 18, pp. 409-430.

21. C. Liu, X. Meng and L. Yao, A Real-TimeKinematic GPS Positioning Based StructuralHealth Monitoring System for the 32 kmDonghai Bridge in China, inProceedings of the6th International Workshop on Structural

Health Monitoring, Stanford, CA, USA, 2007.

22. M. Enckell, Structural Health Monitoring ofbridges in Sweden, in Proceedings of the 3rd

International Conference on Structural HealthMonitoring of Intelligent Infrastructure,


23. B. Tljsten, A. Hejll and G. James, ASCEJournal of Composites for Construction, 2007,

Vol. 11, pp. 227-235.

24. W. R. Habel, M. Schallert, K. Krebber, D.Hofmann, N. Dantan and N. Nther, Fibreoptic sensors for long-term SHM in civil

engineering applications, inProceedings of the3

rd International Conference on Structural

Health Monitoring of Intelligent Infrastructure,Vancouver, Canada, 2007.

25. J. Song and T. Zhou, Working state monitoringof a pile-supported 18-storey frame-shearwallstructure, in Proceedings of the 3rdInternational Conference on Structural HealthMonitoring of Intelligent Infrastructure,


26. S. Szyniszewski, H. R. Hamilton III and Y.Chih-Tsai, Wireless Sensors in Prestressed

Concrete Piles Combining Driving Controlwith Long Term Monitoring, inProceedings of

IABSE Conference on Information andCommunication Technology (ICT) for Bridges,

Buildings and Construction Practice, Helsinki,Finland, 2008.

27. L. Ramos, L. Marques, P. Lourenco, G. DeRoeck, A. Campos-Costa and J. Roque,Monitoring historical masonry structures with

operational modal analysis: two case studies, inProceedings of the 2nd International

Operational Modal Analysis Conference,Copenhagen, Denmark, 2007.

28. B. Glisic, D. Posenato, N. Casanova, D. Inaudiand A. Figini, Monitoring of heritage structuresand historical monuments using long-gage fiber

optic interferometric sensors an overview, inProceedings of the 3rd InternationalConference on Structural Health Monitoring ofIntelligent Infrastructure, Vancouver, Canada,

2007.

29. M. Turek and C. E. Ventura, A method forimplementation of damage detection

algorithms for civil SHM systems, inProceedings of the 2

nd International

Operational Modal Analysis Conference,Copenhagen, Denmark, 2007.

30. K. Thibert, C. E. Ventura, M. Turek and S.

Guerriero, Dynamic soil-structure interactionstudy of a reinforced concrete high-risebuilding, in Proceedings of the 2ndInternational Operational Modal Analysis

Conference, Copenhagen, Denmark, 2007.

31. A. Mita, T. Inamura and S. Yoshikawa,Structural Health Monitoring system for

buildings with automatic data managementsystem, in Proceedings of the 4

thInternational

Conference on Earthquake Engineering,Taipei, Taiwan, 2006.

32. C. Rainieri, G. Fabbrocino, G. Manfredi and E.

Cosenza, Integrated technologies for seismicprotection: an Italian experience, inProceedings of Cansmart 2006 InternationalWorkshop, Toronto, Canada, 2006.


16/16

419

33. C. Rainieri, G. Fabbrocino, E. Cosenza and G.Manfredi, Structural Monitoring andearthquake protection of the School of

Engineering at Federico II University inNaples, in Proceeding of ISEC-04, Melbourne,Australia, 2007.

34. I. G. N. Smith, A. Oliver and J. Oliphant,

WallAid: A Knowledge-based System for theSelection of Earth Retaining Walls, inProceedings of the 11th InternationalConference on Industrial and EngineeringApplications of Artificial Intelligence and

Expert Systems, Castellon, Spain, 1998.

35. C. R. I. Clayton, J. Milititski and R. I. Woods,Earth pressure and earth-retaining structures,

Second Edition, SPON PRESS, Taylor &Francis Group, London, 1993, pp. 1- 414.

36. USACE, U.S. Army Corps of Engineers,Retaining and flood walls, Department of the

Army, Engineering Manual, EM 1110-2-2502,1989.

37. R. M. Leary and G. L. Klinedinst, RetainingWall Alternates, in Proceedings of the 34th

Annual Highway Geology Symposium, Atlanta,USA, 1984.

38. C. Visone and F. Santucci de Magistris, Areview of design methods for retainingstructures under seismic loading, in Strategiesfor reduction of the seismic risk, ISBN 978-88-88102-15-3, 2008, pp. 51-64.

39. C. J. Padfield, and R. J. Mair, Design ofretaining walls embedded in stiff clays, ReportNo. 104, London: Construction IndustryResearch and Information Association,England, 1984.

40. K. Terzaghi, Transactions, American Society ofCivil Engineers, 1954, N. 119, pp. 1243-1280.

41. W. C. Teng,Foundation Design, Prentice Hall,Englewood Cliffs, NJ, 1962.

42. CEN European Committee for Standardization,EN 1998-5, Eurocode 8: Design of structuresfor earthquake resistance Part 5: Foundations,retaining structures and geotechnical aspects,Bruxelles, Belgium, 2003.

43. R. Lancellotta, Geotechnique, 2007, Vol. 57,

No. 3, pp. 319-321.

44. Consiglio Superiore dei Lavori Pubblici,NuoveNorme Tecniche per le Costruzioni, D.M.Infrastrutture 14/01/2008, published on S.O. n.30 at the G.U. 04/02/2008 n. 29 (in Italian).

45. L. Callisto, Pseudo-static seismic design of

embedded retaining structures, in Proceedingsof the Workshop of ETC12 EvaluationCommittee for the Application of EC8, Athens,

2006.

46. R. S. Steedman and X. Zeng, The seismicresponse of waterfront retaining walls, in

Proceedings of ASCE Specialty Conference onDesign and Performance of Earth Retaining

Structures, Special Technical Publication 25,Cornell University, Ithaca, New York, USA,1990, pp.872-886.

47. D.C. Rai, Review of Code Design Forces for

Shaft Supports of Elevated Water Tanks,Proceedings of 12thSymposium on Earthquake

Engineering, IIT Roorkee, Dec. 16-18, 2002.

48. M. P. Collins, E.C. Bentz, Y.J. Kim, ShearStrength of Circular Reinforced ConcreteColumns. ACI Special Publication 197-3 S.M.

Uzumeri Symposium - Behavior and Design ofConcrete Structures for Seismic Performance,

pp. 45-85, 2002.

49. C. Rainieri, G. Fabbrocino, E. Cosenza and G.Manfredi, Implementation of OMA Procedures

Using LABVIEW: Theory and Application, in

Proceedings of the 2nd

InternationalOperational Modal Analysis Conference,Copenhagen, Denmark, 2007, pp. 1-12.

50. C. Rainieri, G. Fabbrocino and E. Cosenza, Anapproach to automated modal parameteridentification for structural health monitoringapplications, in Proceedings of The NinthInternational Conference on Computational

Structures Technology, Athens, Greece, 2008.

51. C. Rainieri, G. Fabbrocino and E. Cosenza,structural health monitoring systems as a tool

for seismic protection, in Proceedings of the

XIV World Conference on EarthquakeEngineering, Beijing, China, 2008.

52.National Instruments, LabView Fundamentals,LabView manual, 2005, pp. 1-165.

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