Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering [611308]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

1
Chapter One
Introduction and Literature Review

1.1 Introduction
Geographical regions where the earthquakes were common and suspected the design of
general construction should take the seismic action in consideration to resist seismic action and
avoid collapse. The design of seismic action was depend on basis of return period of time and
events of maximum intensity occur at the place. [1]
Historically earthquakes were the greatest hazard to human, structures and property, also
earthquakes give very good chance for engineers to improve the criteria of structural design an d
provide effective solutions for the seismic design problems. Last decades, application of base
isolation technology considered as most important approach to protect structures from damage.
[2] Many comparative studies have shown that the isolated structu res are significantly less
affected than the fixed base structure. [3, 4, 5, 6, 7 ]

1.2 Description of the Study
This dissertation is structured on six chapters; Chapter 1, Introduction – represents the brief
presentation of the base isolation of bridges and the materials from which the bridges are made,
Chapter 2, Seismic Action and basic principles of the seismic action . Chapter 3, Basic
knowledge about the bridge . In Chapter 4, Seismic Isolation Systems, and Chapter 5 represents
the case study calculat ion and results . The paper ends with chapter 6, the conclusion of the study .

1.3 Aims of Study
Based on the forthcoming presentation, the present study was planned to study the
seismic isolation system in bridges on a model designed mathematically, analyzed on the
seismic analysis principles and apply the Romanian and European cods to assess the model with
comparison between the result before and after use base isolation system in application.

1.4 Literature Review
1.4.1 Base Isolation Systems
1.4.1.1 Development of Seismic Base Isolation Systems

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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1.4.1.2 Historical Background
Surprisingly, J.A. Calanterients, in 1909, who is a medical doctor proposed the first
seismic base isolation design; He claimed that if a structure is built on a fine material such as
sand, mica, or talc, this fine soil would permit the structure to slide and resist an earthquake. The
primitive isolation system that Mr. Calanterients proposed was earthquake resistant design; the
basic idea is same with the seismic base isolation today. [8]
John Milne was the early base isolation designer in University of Tokyo, composed of
sliding basement, balls, sliding rollers etc.; he performed his first seismic base isolation trials on
sliding balls and rollers to improve the wind resistance of seismic isolation system. [9]

1.4.2 Basic principle of Seismic Base Isolation System in bridges
1.4.2.1 Base Isolation System (Overview)
The basic concept of isolation systems is fairly simple. They reduce the stiffness of the
structure, therefore its period increases and accelerations are reduced, while also providing more
flexibility to the structure to decrease or eliminate inelastic de formations.
Energy dissipation devices increase damping of the structure to lessen the seismic energy
input. [10]
Bridges are highly important structures in a modern transportation system. There were
570,000 bridges in the United States by 1994, and 60% of them were constructed prior to 1970.
[11] Any collapsed or heavily damaged bridges will possibly delay transportation of emergency
services after or during a seismic event. In this manner, ductile design took the place of
conventional design for brid ges.
Several research projects have been conducted on the seismic isolation of structures.
Significant amount of those researches conducted during investigation of seismic isolation were
mainly focused on material science. Material properties were investig ated and different types of
isolation devices were invented.
One type of isolator device, which has been used on several projects, is lead -rubber
bearings. It was first proposed by W. H. Robinson in 1975. [12] A study done by Robinson
(1982) [13] showed th e advantages and disadvantages of the use of lead -rubber bearings in the
seismic isolation of structures.
As awareness of seismic isolation has increased, questions and research have also
increased. Simo and Kelly (1984, 170) [14] studied stability of mul tilayer elastomeric bearings,
which act as bridge bearings and as seating pads. It was found that the horizontal stiffness of the
bearings decreases due to roll -off at the end plates with increased load and displacement. A finite
element formulation was pr esented for elastic stability problems to be used for adequate end
plate design for multilayer elastomeric bearings.
Since seismic isolation has been a growing earthquake -resistant design technique, isolation
design methods as well as isolation devices are being developed. Kikuchi and Aiken (1997, 230)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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[15] proposed an analytical lagged effect model for elastomeric bearings in order to suspect the
seismic response of base -isolated structures. Accuracy of the proposed analytical model was
confirmed by compar ing earthquake simulation tests of two isolated structures with dynamic
analysis, using a total of four different types of elastomeric bearings. The advantage of this
proposed model is its strong dependence on shear strains, being applicable for high shear strains.
It was concluded that the analytical behavior well captured the experimental response.
Du, Han, and Zhan (2008) [10] studied nonlinear seismic response of continuous girder
bridges isolated with lead -rubber bearings. Purpose of their study was pr oposing a solution
method to account for changing bilinear force -deformation behavior of lead -rubber bearings due
to bidirectional interaction of restoring forces under bidirectional horizontal seismic excitations.
A two -span bridge model with a dimensiona l scale factor of 0.1 was used in shake table tests to
validate the accuracy of the proposed method. It concluded that the differences in peak bearing
force between experimental and analytical results are within 10 percent. This study should be
considered for design of isolated bridges under bidirectional excitations regardless of selected
isolation method, either partial or full isolation.
Typically, seismic isolation is applied to the whole bridge structure. However, there are
some examples of partial iso lation of bridges. Tsai (2008) [16] studied transverse earthquake
response of commonly used bridge types in Taiwan, which are partially restrained in the
transverse direction with abutment restrainers. From the analytical experiment, it was noted that
the composite damping ratio of the transverse behavior may be decreased due to partial restrains.
It is concluded that partial isolation is effective for the purpose of reducing shear forces
developed at bridge piers, but increased seismic demands of the abutm ents in the transverse
direction may result.
Another well examined seismic behavior of partial isolation was studied by Hu and Ryan
(2011). [17] Typical highway Bridge structures used in the state of Utah, which consists of two
spans, was examined and comp ared with conventional and fully isolated design options. A static
design procedure was developed with a parametric study. Partial isolation in this study considers
decoupling of the columns from the superstructure while the bridge is fixed at its abutment s. Hu
and Ryan (2011) [17] achieved reduced displacement demand and inertial force of bridge
columns with nonlinear type isolators, which have elastic perfectly plastic force -displacement
hysteresis. Increased force demands of the columns and abutments occ ur with linear type
isolators, even though the displacement demand of the columns is reduced.

1.4.2.2 Types of Base Isolation System in Bridges
Until the ends of 70’s, development of laminated elastomer isolators was the practical
method of earthquake res istant design in Japan. [8] Firstly, rubber was used under building
basements to isolate the structures; then steel plates were vulcanized with rubber to increase the
vertical stiffness of the isolators (Figure 1 -1).

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Figure 1 -1: The steel reinforced elastomer isolator, SREI

Lead -plug rubber bearings are steel reinforced elastomeric isolators with one or more
circular holes as shown in Figure 1 -2. [8] The lead -plug is introduced in these holes to increase
the damping of the isolator. The adding of damping may increase the contribution of secondary
modes on the response of structure; this may lead to decreasing of efficiency of the isolation
system.

Figure 1 -2: The lead -plug rubber bearing

Because of steel plates inside the SREI samples used under buildings, it is very heavy; that
makes the production and construction of elastomeric isolators’ difficult task, and causes
significant increase in the co st of the isolation system, to solve this problem, Kelly et al. use
lightweight fiber reinforcement inside the elastomeric isolators. [18]
Fiber -reinforced elastomeric isolators are a newly introduced technique in the field of
seismic base isolation. [19] The elasticity of the fiber material is an important factor affecting the

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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compression modulus of fiber reinforced elastomeric isolators. Later on Tsai, Kelly and Takhirov
were conducted an experimental and analytical studies on compression behavior of fibe r
reinforced elastomeric isolators. [19, 20, 21, 22, 23 ]
Early sliding -based seismic isolation methods were deficient to re -center the building to its
original location. Then Zayas et al. studied the friction pendulum system to handle re -centering
deficien cy of sliding rollers. [24] The system is formed of two concave Teflon spherical surfaces
with an articulated slider in between these concave surfaces. The Friction Pendulum System is
capable of re -centering the structure to its original position by the ef fect of horizontal component
of the resting structure weight on the isolation system. The energy dissipation is ensured through
the friction between the surface of the concave plates and the articulated slider that are presented
in Figure 1 -3.

Figure 1 -3: The Friction Pendulum System, FP
The equation below indicated the period of the structure resting on friction pendulum
system depends on the radius of the concave surface of friction pendulum system (FP), but did
not indicate the mass of the structure. This characteristic of friction pendulum system (FP) also
enabled seismic base isolation of lightweight structures.

The TASS system, the Resilient -Friction Base Isolator System, Sliding Disc Bearing and
Helical Spring system are common other restoring sy stems considered to isolate the structures.
[25, 26 ]
In TASS system, parallel rubber blocks were used to produce the re -centering capability,
Figure 1 -4.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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The Resilient -Friction Base Isolator system was consisting of Teflon -coated steel plates
with a rubber core to produce the re -centering of the isolation system.

Figure 1 -4: The TASS System

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Chapter Two
Seismic Action

2.1 Seismic Action
2.1.1 Introduction
Earthquake was take place duo to seismic waves which arise from sudden movements in
the rupture zone ( active fault ) of the earth crust. These waves of different types and velocities
were traveled in different directions before reaching the building locations and causing various
motions to the ground. The ground subjected to moves rapidly backward and forward and in al l
directions, mainly in horizontal plan, but also may be in vertical direction. [27]
The effects of each earthquake on buildings are determined by the time histories of the
three directions of ground motion parameters; ground acceleration (a g), velocity (v g), and
displacement (d g), with their own specific frequency contents for each parameters. The study of
an example of the linear horizontal ground motion chart shown that the dominant frequencies of
acceleration (a g) are substantially higher than the veloc ity (v g) and much higher than the
displacement (d g). [27]
The ground motion parameters (a g), (v g) and (d g); as well as, the other characteristic values
at a location caused by an earthquake of a certain magnitude may vary strongly. The ground
motion parame ters depend on numerous factors, for example the distance, direction, depth and
the mechanism of the fault zone in the earth crust (epicenter), in addition to, other factors
particularly the local soil criteria such as layer thickness and shear wave veloci ty. In comparison
with rock the softer soils are more subjected to significant local increase of the seismic waves.
Regarding the response of structures to the ground motion, it depends mostly on the structure
criteria like Eigen frequency, type of structu re and ductility. [27]

2.1.2 Basic representation of the seismic action
2.1.2.1 General spectrum for the representation of Seismic Action
The earthquake motion in certain location of the surface of a structure was usually
represented by the so -called “elastic response spectrum”. Such a structure is considered to be
subject to a uniform displacement applied to the base support. It is thus imp licitly assumed that
all support points are subject to the same uniform excitation. If this assumption cannot be made
realistically, a so -called spatial model of the seismic action should be used. [28]
The horizontal seismic action is described by two orth ogonal components considered as
independent and represented by the same elastic response spectrum. The vertical component of
the seismic action should be represented by the response spectrum as defined for the horizontal
seismic action. [28]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Application of the above described elastic response spectrum assumes a linear elastic
behavior of structures were subjected to the seismic action. However most structures will rather
show a non -linear behavior in such circumstances, as a considerable amount of energy wi ll be
dissipated due to the ductile behavior of the structural elements and connections. [28]
For the representation of the seismic action the seismic movement in certain location of the
surface should generally be represented by the elastic response spect rum representing the
acceleration of the ground. [29]

2.1.2.1.1 Ground condition
The seismic action is defined as being a geotechnical action, it is an action transmitted to
the structure by the ground or the water of the land. As the seismic action consi sts of a
movement of the ground under the structure, the characteristics of these grounds will be of great
importance for its definition. [29]

2.1.2.1.1.1 Identification of ground types
Studies of characterization will have to be done in order to classify the geotechnical
conditions in accordance with the types of ground, defined in table 3.1 of § 3.1.2 of the EN 1998 –
1, decreasing in terms of rigidity and resistance of the ground from A to S2. Each country will be
able to define in its national annex the parameters S (Amplitude, translated by the peak ground
acceleration) and TC (Content of frequency), which translate the influence in the seismic action
of the local geotechnical conditions. [29]
Ground types A, B, C, and D described by the stratigraphic pr ofiles and parameters given
in Table 2 -1 (4) may be used to account for the effect of local ground conditions on the seismic
action. Also description may be done by taking in consideration the effect of deep geology on the
Seismic action. [30]
Compared to the RSA, that only categorizes the ground in 3 types, EC8 enters into greater
detail regarding this aspect, where 7 types of ground are defined. This greater detail not only
allows the consideration of a larger number of types of ground foundation, but als o defines in a
more precise way the parameters of each type of ground that will influence the definition of the
seismic action. [29]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Table 2 -1: Ground types [29]

2.1.2.1.2 Seismic zones
In accordance with the EC8, [31] the seismic zoning will have to be made by the national
authorities of each country, dividing the domestic territory in zones with constant seismic hazard.
The seismic hazard of each zone will have to be described by an only parameter, which
corresponds to the reference value of the peak of the acceleration in a rock type ground, a gR,
whose value will have to be determined by each national authority. This parameter is defined as
being the maximum absolute acceleration obtained for the component of the seism ic movement
in one determined direction, being obtained, on the basis of attenuation relations, for a period of
return of 475 years (or a probability of exceedance of 10% in 50 years). For Portugal the
following seismic zoning is proposed for a near seism and of small magnitude (Type II seism in

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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EN 1998 -1) and for a distant seism and of moderate or raised magnitude (Type I seism in EN
1998 -1), for a seismic hazard associated to a period of return of 475 years: [31]

Figure 2-1, Figure 2 -2 and Figure 2-3: Proposal to the Portuguese seismic zoning for
the two types of seism prescribed in EC8 (indicating the accelerations of project in rock,
agR, for an importance factor of 1,0) and seismic zoning in RSA, proposed by the Task
Group GT -8 of the Portuguese Nat ional Annex of the EN 1998 -1.

Comparatively to the RSA, it is observed the continuation of the existence of two types of
seism’s (distant and near) being that in the EC8 the zoning is different consonant the type of
seism, situation that did not occur in the RSA, where the zoning was only one for the two types
of seism. [29]
It is noticed that this fact represents a clear evolution facing the previous regulation,
because it did not make sense to establish the same seismic zoning for two different seismic
design situations. [29]
Another fact that is suggested by the analysis of the above displayed figures is the
reduction of the area of the zone corresponding to the biggest hazard (red -color) from the RSA to
the EC8. [29]
Relatively to the values of the refe rence acceleration, a gR, it is verified a great disparity of
values, being that, e.g., for a distant seism, it is observed an increase from 107 to 250 cm/s2
(RSA value to the EC8 value), in the zone of bigger hazard. For a near seism, the comparison of
the values of RSA/EC8 presents sufficient similarities, being that for the zone of bigger hazard, it
is prescribed the value of 177 cm/s2 in the RSA and the value of 150 cm/s2 in the EC8. It is
noticed however that this consideration between ground accelerati ons should not be overrated,
because there are some supplemental factors that have to be taken in account:
1. Effect of the consideration of the design envelope of two scenarios;
2. Different partial security factor of the seismic action in the EC8 (1,0) facin g to the
RSA (1,5);

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3. Different configuration of the response spectrum in the two regulations (e.g, the
different value of the behavior factor in the two norms and the new soil
parameters).

2.1.2.1.3 DESIGN CONCEPTS
To assure that a structure remains elas tic during the design seismic action, typically
associated to a probability of exceedance of 10% in 50 years, it is necessary that the same is
designed for lateral forces in the order of magnitude of 50% or more than its weight. Despite it
being technicall y possible to design a structure to answer in elastic regimen to the seismic action,
it is unnecessary to do it so, because being a seism a dynamic action, it represents for the
structure a certain total of energy input and a requirement of tolerance to a certain level of
displacements and deformations, but not a requirement of resistance to specific forces. Besides,
an elastic design to the seismic action would result in prohibitive economic costs and numerous
practical difficulties. In this way, it is gen erally accepted by the various seismic norms to take
advantage of the non linear behavior of the structure for the seismic action, provided that the
magnitude of the inelastic deformations does not place in danger the integrity of the diverse
structural el ements and of the structure as a whole. Traditionally, to take in consideration the
non-linear behavior of the structure in the analysis, a linear elastic analysis is executed, that
provides the design forces in each element through the action of a specifi ed set of lateral forces
in the structure. These design forces are obtained from a design response spectrum of
accelerations, which generally is obtained through the division of the elastic response spectrum
with a behavior factor, q. In this way, each str uctural element may designed to resist to the forces
obtained from analysis, having equally to be detailed (especially in the “critical regions”) to be
capable to develop the inelastic deformations associated to the respective value of the behavior
factor. Thus, the value of the behavior factor to be adopted will depend on the type of structure,
of the permissible degree of ductility of the same and, finally, of the nature of the materials that
constitute it. The global behavior of a reinforced concrete ele ment, subject to repeated and
alternated loads, will be a function of the behavior of the materials that constitute it, reflecting
the available ductility one of the basic aspects for the description of the global seismic behavior
of the structure. [29]

2.1.2.1.4 Capacity design
A good performance of a structure during an intense seism consists in the development of a
mechanism that dissipates efficiently, in a hysteretic way, the absorbed energy. The zones of the
structure where this energy dissipation will be given (critical zon es), that is, the zones where the
inelastic deformations will be situated, will have therefore, at the conception level, to be detailed
to be able to accommodate the ductility adopted in the design processes and models of analysis.
Currently, the normativ e philosophy consists in the adoption of rules that look to define
conception norms and designs that guarantee an appropriate behavior of the structures during a
seism, taking advantage of the effective resistant capacity of each structural element. This
purpose is considered an explicit way in diverse regulations, because in these there are adopted
rules of design that are based on the attribution of a relative resistance for evaluation of the

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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effective resistant capacity of the various elements, for each type of effort, or either to adopt a
capacity design, as alternative to a direct design, which considers only one distribution of the
elastic efforts for the structure, diminished by the behavior factor. The capacity design allows the
designer to define th e form of how the structure will behave during an intense seism,
independently of the characteristics of this one. With this procedure, the designer imposes the
zones where the plastic hinges will form, as well as their respective order of formation. So, t he
designer imposes the values of resistance and ductility on the diverse structural elements through
different disposals consonants of zone to consider, guaranteeing, on one hand, the existence of an
excess of resistance in the zones where he does not int end that plastic hinges form, and, on the
other hand, that in the zones where he intends that these occur, that the calculated effort reaches
the value of the resistant effort. It should be noticed that in this way the plastic hinges will have
to be charac terized by an adequate ductility and capacity of energy dissipation, preventing fragile
rupture or loses of resistance during the formation of these plastic hinges, resulting of the
deformations in these zones imposed by the seismic action . [29]

2.1.2.1.5 Ductility
The concept of ductility can be defined as the possibility of a structure to dissipate, by an
hysteretic process, the energy that the dynamic action transmits to it, imposing this same capacity
of waste that the constituent elements of the struc ture have the possibility to deform themselves
beyond its elastic limits, accommodating, without great reductions of resistance and rigidity,
successive cycles of alternated loads of great amplitude. Therefore, the global behavior of the
structure, are inf luenced by the available ductility . [29]
For this effect, the EN 1998 -1 defines a zone for each primary seismic element called
"critical region" in which the biggest efforts proceeding from the most unfavorable combination
will occur and where probably the plastic hinges will be formed. It is expected that it is in these
so called "critical regions" where the biggest energy dissipation will occur (zones where the
inelastic deformations will be situated), having therefore, at the conception level, these to b e
detailed to be able to accommodate the ductility adopted in the design processes and models of
analysis. Out off the critical regions, the design and detailing will have to observe the disposals
related in the EN 1992 -1-1. However, the Eurocode 8 gives t he freedom to the designer for,
having in mind the concepts of ductility above described, to design the reinforced concrete
building with a bigger resistance and minor ductility, or vice versa, defining for this effect the
following classes of ductility, w hich will influence the rules of design and the value of the
behavior factor to adopt: [29]
1) DCL (Ductility Class Low) – It corresponds to the philosophy of design for resistance
instead of ductility (without practically any requirements being added to t hose of the EN 1992 -1-
1). Thus, practically all the structure will reply elastically, being that the resistance to the
horizontal forces of a seism will have to be assured by the proper resistance of the structural
elements and not for its ductility. A beh avior factor, q, could be admitted, with the maximum
value of 1, 5 (with this value, in a common design practice it is assured an over -resistance).
2) DCM (Ductility Class Medium) – This Class corresponds to the design strategy for
energy dissipation and ductility. This class will give origin to structures designed according to

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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the principles of seismic resistance of the EC8, that is, with good ductility and the capacity to
suffer hysteretic cycles, without the occurrence of a fragile rupture.
3) DCH (Duc tility Class High) – Corresponding equally to the philosophy of design for
energy dissipation and ductility, this class is characterized by high requirements of ductility and
of high plasticity levels, leading therefore that the design requirements and det ailing to be more
complex and expensive that those of DCM. These reasons will cause that, in the current design
practice, this class of ductility will not be used frequently.

2.1.2.2 Seismic design spectrum for linear analysis
2.1.2.2.1 Use of the design spectrum
The philosophy for developing design specifications of bridges depends on various criteria
defining their performance based on their importance category in case of seismic events. Force
based design and displacement based design are determined in a way that the required
performance of the bridge is met. In recent years, it has become more crucial to understand the
behavior of the structures under flexible performance criteria. These criteria were established to
consideration for the design and ret rofit of bridges. Under this philosophy, capacity design is
used for the seismic design of capacity protected members assuming unity for the importance
factor and modification factor. [32]

2.1.2.2.2 Design and analysis requirements in codes
Several codes have addressed the issue of structural base isolation. Parameters of analytical
design of such elements and the structure itself have been mostly discussed in codes like:
 American Association of State Highway and Transportation Officials -AASHTO LRFD
Bridge Design Specifications (AASHTO, 2007 and 2012). [33]
 AASHTO guide specifications for seismic isolation design (2010). [34]
 National Building Code of Canada (NBCC, 2015). [35]
 Canadian Highway Bridge Design, CSA S6 (2006, 2014). [36]
 Eurocode 8 – Design of Structures for Earthquake Resistance. [31]
 Bridges (BSI, 2005). [37]

2.1.2.2.3 Seismic parameters
The key parameter in the seismic design is the elastic seismic response coefficient, which
describe the seismic hazard at a site. Code s have proposed similar equations to calculate this
coefficient. The ductility however is considered differently in various codes. In the following, the
provisions for the calculation of seismic response coefficient for isolated and non -isolated
bridges ar e discussed briefly for different codes. [32]

2.1.2.2.3.1 Eurocode 8

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Shape of elastic response spectrum in Eurocode 8 (2005) is taken as being the same for the
two levels of no -collapse requirement (ultimate limit state design) and for the damage limitati on
requirement. The Importance factor in this code is used to reflect the impact of a bridge failure
on the society. This factor modifies the design hazard level (Fardis et al., 2005). [38]
For non -isolated structures, the elastic response spectrum Se (T) was defined by four
expressions at four ranges of period of a linear single degree of freedom system. The soil factor
in design ground acceleration (a g) on rock or other rock -like ground types was determined at a
probability of exceedance of 10% in 50 year s and the damping correction factor are three
parameters that define the coefficient.
The first descending branch of the elastic response spectrum was inversely proportionate to
the period (1/T), and the second branch up to T=4s is inversely proportional to the second order
of the period (1/T2). [39]
Deep geology features describe the geological settings criteria of the site by the scale of
kilometers. [39] For shallow or local soil conditions with site geotechnical description by the
scale of ten meters [40] (Bulajić et al., 2013) with the purpose of probabilistic hazard assessment,
the earthquakes that contribute most to the seismic hazard go with a different type of spectrum.

2.1.2.2.3.2 Canadian Highway Bridge Design, CSA S6 (2006) and AASHTO
(2007 and earlier)
According to the “Recommended Provisions for the Development of Seismic Regulations
for Buildings” prepared by the National Earthquake Hazards Reduction Program (NEHRP,
1998), the design spectra are defined by the Peak Ground Acceleration (PGA ) and the Peak
Ground Velocity (PGV). Later, AASHTO brought a modification to the spectra by taking the
PGA only and similarly the CSA S6 (2006) adopted the same approach (CSA S6 commentary,
2006). The zonal acceleration ratio in CSA S6 (2006) is based on the PHA from NBCC (1995)
representing a seismic event with a 10% probability of exceedance in 50 years.

2.1.2.2.3.3 Canadian Highway Bridge Design, CSA S6 (2014)
It is the basis to find out the seismic hazard in 2006 edition of CSA S6 and its previous
editions was the 10% in 50 -year probability of exceedance, (return period of 475 years).
Seismic hazard levels in the 2014 version of CSA S6 are at 2%, 5% and 10% probability of
exceedance in 50 years for the performance assessment of bridges. For all thre e return periods,
the spectral response accelerations are presented with 5% damping up to 10s.
The horizontal spectral response acceleration values in the National Building Code of
Canada (2015) are given on the website of the Geological Survey of Canada
(www.earthquakescanada.ca). The uniform hazard spectral acceleration values at periods 0.2s,
0.5s, 1.0s, 2.0s, 5.0s and 10s are given for each seismic hazard level which is modifiable for each
site. The values between the designated periods can be obtained by interpolation that may cause
some conservatism, especially in longer periods.

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2.1.2.2.3.4 French standard PS92 [41]
In the French standard PS92, the design ground acceleration is referred to as the nominal
acceleration aN. Values for aN are specified not only as a function of the seismic zone (0, Ia, Ib,
II & III), but also as a function of the so called hazard class:
 Class A: for the buildings of minor importance for public safety, e.g. Agricultural buildings.
 Class B: for the “ordinary ” buildings, of which, collapse during earthquakes establishes a normal
risks for the inhabitants
 Class C: for the buildings required a seismic resistance as an importance in view of the civil and
economic sequel associated with damage, e.g. public buildin gs.
 Class D: for the buildings with integrity during earthquakes was of vital importance for civil
survival and protection, e.g. hospitals, fire stations, power plants.

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Master of Structural Engineering

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Chapter Three
Basic Knowledge about Bridges

3.1 Structural Types of Bridges
3.1.1 Bridges Types
Bridges can be categorized in several different ways. The following characteristics are
used in bridge type identification: [42]
I. Function :
a) Transportation of vehicles
b) Railroad transportation
c) Use of pedes trians
d) For the material handling
II. Span length:
a) Short: less than 100 -200 feet.
b) Intermediate: from 100 -600 feet.
c) Long: greater than 400 -600 feet.
III. Span type:
a) Simple span (beam, girder or truss)

Figure 3 -1: Simple span (beam, girder or truss)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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b) Rigid frame

Figure 3 -2: Rigid frame

c) Cantilever (beam, girder or truss)

Figure 2 -3: Cantilever (beam, girder or truss)

d) Continuous (beam, girder or truss)

Figure 3 -4: Continuous (beam, girder or truss)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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e) Arch (girder or truss)

Figure 3 -5: Arch (girder or truss)

f) Suspension

Figure 3 -6: Suspension bridge

g) Cable stayed

Figure 3 -7: Cable stayed bridge

h) Movable

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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1. Swing: (girder or truss)

Figure 3 -8: Movable Swing: (girder or truss)
2. Lift: (girder or truss)

Figure 3 -9: Movable Lift: (girder or truss)
3. Bascule: (girder or truss)

Figure 3 -10: Movable Bascule: (girder or truss)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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20
i) Floating
j) Non-bridges:
1. Culverts
2. Tunnels
IV. Structure materials
a) Timber
b) Steel
c) Concrete:
1. Reinforced
2. Pre-stressd
3. Post-tesioned
d) Composite: (decks and girders)
e) Others: less frequently used in modern construction.
1. Masonry

Figure 3 -11: Masonry Bridge
2. Iron
3. Aluminum
V. Cross section
a) Deck

Figure 3 -12: Cross section Deck

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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b) Half through

Figure 3 -13: Cross section (Half through)
c) Through

Figure 3 -14: Cross section (Through)
I. Degree of redundancy
a) Determinate
b) Indeterminate
II. Floor system
a) Conventional deck
b) Orthotropic deck

Figure 3 -15: Floor system (Conventional and Orthotropic deck)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3.1.2 Bridges Component

Figure 3 -16: Bridges Component
3.1.2.1 Superstructure
The superstructure is defined as, the entire part of the bridge structure which primarily
receives and supports the load and, in turn, transfers the resulting reactions to the bridge
substructure. The superstructure consists of beam, girder, and truss or c able construction. The
superstructure components include: [42]

Figure 3 -17: Superstructure of bridge

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

23
a) The floor beams
b) The girders
c) The stringers
d) The diaphragms:
1. Intermediate
2. End
3. Continuity
e) The deck
1. The roadway
2. The sidewalk / overhang
f) The parapet and railings
g) The expansion dam
h) The truss members
1. The chords (top and bottom)
2. The vertical and web members
3. The lateral bracing
4. The portal
5. The end post
i) The struts and wind bracing
j) The cable system
k) The hangers: fixed and expansion type

3.1.2.2 Substructure
The substructure is the foundation portion of the bridge that supports the superstructure
and transfers the load to th e earth. The substructure includes: [42]
a) Abutments
1. The breast wall
2. The wing walls
3. The bridge seat
4. The back wall
5. The footing or pile cap

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Figure 3 -18: The footing or pile cap

b) The piers
1. The stem wall
2. The column or pier shaft
3. The web wall

Figure 3 -19: The column or pier shaft
4. The pier cap
5. The footing or pile cap

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

25

Figure 3 -20: solid and open Pier
c) The pile bent
1. The piles (steel, concrete, or timber)
2. The bent cap

Figure 3 -21: The Pile Bent and Steel Bent
d) The caisson
e) The piling
f) The dolphins and fenders: pier protection

3.1.2.3 Bearings
Bearing transmit and distribute the superstructure load to the substructure and permit the
superstructure to u ndergo necessary movements without development harmful overstress. The
two general types of bearings are fixed and expansion. The principle difference is that fixed
bearing allow rotation but no translation; while the expansion bearing permit both rotation and
translation. Without the ability of bearing to rotate, otherwise determinate structures would
become statically indeterminate; bending moment would be induced in piers and footings.
Expansion bearings are designed primarily to allow longitudinal move ment (translation)
resulting from thermal growth and contraction. Inhibiting this movement can result in buildup of
stresses reaching enormous values. [42]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3.2 Basic Behavior of Bridges
3.2.1 Introduction
The long span suspension bridges design of, particularly the suspended bridges; the primary
concern was the wind action. The realization of the potential aeroelastic nature of the wind
phenomena, which causing the failure of the Tacoma Narrows suspension b ridge in 1940 in
Washington, was established whole over the world.
The aerodynamic effects of wind on bridges were primarily vortex shedding, galloping,
torsional -divergence, flutter and buffeting. [43]

3.2.2 Criteria for the bridge design
The criteria for the long spanned suspension bridges design were concentrated on the
static and dynamic responses of a bridge exposed to wind load.
The design of long span suspension bridges was mainly controlled by the aeroelastic
instability. The aerody namic design concerned with calculation of critical velocity for the onset
of flutter. It is essentially important issue to be considered that the wind velocity does not exceed
the suspected critical velocity to avoid failure due to flutter.
Arrol and Chat terjee (1981) [44] reported that frequencies other than the basic ones
should be considered in the bridge design. They declare that the bridge designers should keep in
mind that the position of maximum stress should not be always at mid -span, or a support,
moreover the stress value will depend on the mode shape of bridge. In a simply supported span,
the second mode of maximum stress is at the quarter points and will have a value four times than
that of the fundamental mode maximum stress, which occur at the mid span.
There are static and dynamic concerns, which should be considered for a safer designing
of bridges; as discussed by Simiu and Scanlan (1986) [45] and Larsen (1992) . [46] Which are
described below in Figure 3.22.

Figure 3.22 : Relative bending moment diagrams due to 1st and 2nd modes of vibration.
(Picture from Arrol and Chatterjee, 1981)

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3.2.2.1 Static behavior
The considerations in static behavior are the reverse, excessive lateral deflection,
divergence, and lateral buckling (Selvam et. al., 1998) . [46] The static phenomena, in general,
are not critical issue for the design of bridges design. The issues that correlated to static behavior
could be checked by the aerodynamic force components like the drag force, lift force and the
pitching moment. The static issues are concerned with the plot of the coefficients of drag force,
lift force and pitching moment against the angle of incidence of wind.

3.2.2.2 Dynamic behavior
According to the Newton’s second law, the movement of mass is described by the
differential equation

Where:
F(t) is the time dependent load which act on the mass, k is the stiffness coefficient and
c is the coefficient of damping. This equation can be rewritten in the form

Where .

Here ω is the natural circular frequency and 2mω is the critical damping coefficient.
Three cases arise based on ζ being less than, equal to, or greater than unity resulting in under –
damped, critically damped and over -damped response respectively.
Selvam found in 1998 t hat the dynamic behavior includes the responses obtained due to
vortex shedding excitation, self -excited oscillations and the buffeting by the wind turbulence.
[46] Also Sachs in 1978 states that suspension bridges could oscillate in two natural modes,
vertical and torsional modes. [48] In the vertical mode, all the joints shift the same distance in
vertical direction, while in the torsional mode every cross -section was twisted about a
longitudinal axis parallel to the horizontal direction.
The importance of dynamic behavior was unlike the static behavior because it was
critical and considered in the bridge design.

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3.2.3 Aerodynamic Instability
Aeroelasticity is the subject which deals with the study of interaction between
aerodynamic fo rces and structural motions. When a structure is exposed to wind flow, it will
either vibrate or suddenly deflected in the airflow. The motion of the structure leads to change in
the pattern of air flow around the structure. When pattern of wind around the structure was
modified by aerodynamic forces that will escalate rather than reducing the vibration, thus the
giving rise to subsequent deflections of oscillatory and/or divergent character aeroelastic
instability will occur (Simiu and Scanlan, 1986). [45] The aeroelastic processes that are dealt
with in wind engineering are vortex shedding, torsional divergence, galloping, flutter and
buffeting.
3.2.4 Vortex Shedding
Simiu and Scanlan (1986) [45] found that when a structure was subjected to wind flow,
the separation of air flow will occur around the structure. Separation of air flow will produce
forces on the structure, which are the pressure force on the facing side and the suction force on
the o pposite side. The pressure and suction forces result in the formation of tornadoes in the
wake region leading to deflections on the structure. The shedding of vortex balances the change
in momentum of fluid along the structure sur face (Larsen and Walther, 1997). [49]The frequency
of the vortices shedding dictates the response of the structure. When the vortex was induced and
the natural frequencies overlap; that lead to what is called lock -in. During the lock -in state, the
structural member will oscillates with increasing amplitude but seldom exceeding half of the
across wind dimension of the structure (Simiu and Scanlan, 1986 ). [44] The lock -in condition is
explained in Figure 3.23.

Figure 3.23: Qualitative trend of vortex shedding frequency with wind velocity during lock –
in (Simiu and Scanlan, 1986).

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3.2.5 Galloping
Simiu and Scanlan (1986) [44] proved that galloping is an instability state which is
typical of slender structures. This is a relatively low -frequency oscillatory process of elongated,
direct structures operated upon by a wind stream. The frequency at which the object reacts is
much lower than the frequency of vortex shedding. There are two types of galloping: Wake and
Across -wind galloping.

3.2.5.1 Wake galloping
It was produced when two c ylinders one facing the wind, and the another one opposite
the air flow direction, within that wake separated by distance away from each other. In wake
galloping the downstream cylinder is subjected to galloping oscillations induced by the turbulent
wake o f the upstream cylinder; so that the upstream cylinder tends to rotate clockwise and the
downstream cylinder rotate in anti -clockwise direction that will lead to torsional oscillations.
Figure 3 -24 explain the process.

Figure 3 -24: Wake galloping Picture from Simiu and Scanlan (1986)

3.2.5.2 Across wind galloping
The across -wind galloping is an instability state of bridge that is initiated by a turbulent
wind blowing in transfer direction across the deck. It causes a crosswise vibration in the bridge
deck (Liu, 1991). [49]As the cross section vibrates crosswise in a stable wind velocity U, so it
changing the angle of attack (α). Because of the change in α, an enhancement or reduction on the
lift force of the cylinder will occur. In case of increase of α a n increase in the lift force in the
opposite direction of motion; that is mean the situation is stable, but on the vice versa, when an

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

30
increase of α causes a decrease in lift force, subsequently the situation is unstable and galloping
occurs. Figure 3 -25 explain the process.
A classical example of this phenomenon is observed in ice covered power transmission
lines. Galloping is reduced in these lines by decreasing the distance between spacing of the
supports and increasing the tension of the lines.

Figure 3 -25: Across wind galloping: Wind and motion components, with resultant lift and
drag, on a bluff cross section. (Picture from Simiu and Scanlan, 1986)
Where: U= wind velocity, Ur= relative wind velocity with respect to moving body, ẏ= velocity
across-wind, B= dimension of the section, L= lift force, D= drag force.

3.2.6 Torsional divergence
The torsional divergence is an example of a static response of structures. Torsional
divergence was at first related to aircraft wings because of their suscept ibility to twisting off at
excessive speeds of air flow (Simiu and Scanlan, 1986). [44] Liu, 1991, [49] found that when the
wind flow occurred a drag, lift, and moment are created on the structure. The created moment
cause a twist on the structure, and that lead to increase of the angle of incidence α. Later on, the
increase in α will resulted in higher tor sional moment with the increase of the wind velocity. If
the structure hasn’t sufficient torsional stiffness in order to stand against this increasing moment,
the structure will becomes unstable and will be twisted till f ailure. Simiu and Scanlan, 1986,
[49]found that the torsional divergence depends on the structural flexibility and the manner in
which the aerodynamic moments develop with twist; and didn’t depend on the ultimate strength
of structure. Figure 3 -26 explain the process.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Figure 3.26 a. Tors ional divergence of an airfoil, b. Torsional divergence of Bridge deck
(Picture from Liu, 1991)

3.2.7 Flutter
The flutter is a very serious issue in the bridges design. Now, it is well realized that
failure of the Tacoma’s narrows bridge was due to the fl utter. The term flutter has been used
widely to describe different types of wind induced behaviors of bridges. The flutter was defined
as a state of negative aerodynamic damping in which the deflection of the structure grows to high
levels till failure was started. It is also known as classical flutter. [44]

3.2.8 Critical wind speeds for Flutter
When the critical wind speed expected to cause flutter is exceeded, the structure will
become unstable and developed excessive deflections. Thus it is an important factor to be
measured in the design of bridges. [43]

3.2.9 Buffeting
Buffeting is defined as the unsteady loading of a structure by velocity fluctuations in the
incoming flow and not self -induced (Simiu and Scanlan, 1986). [44] The buffeting vibration was
produced by the turbulence of air flow. There are two types of buffeting. The first is gen erated
by turbulence in the airflow, and the second type is caused by disturbances generated by an
upwind beside structure or obstacle. The first type of buffeting caused a noticed vertical and
torsional motions of the bridge even at low speeds. The motion produced by buffeting causing a
gradual transition to large amplitude torsional oscillations, which may lead to the failure of the
bridge.

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3.3 Seismic Damages of Bridges
Study effects of seismic damages on bridges to provide a strategy for undertaking bridge
inspections following a significant earthquake and to give guidance on where to look for, and
how to evaluate damage to atypical highway bridges.
Emergency works to open the bridges, or to clear roads or waterways below may
sometimes commence very s hortly after the earthquake. Even if total demolition is going to be
the final fate of the bridge it is desirable to investigate, record and photograph the damage before
the evidence is a destroyed. It is preferable that this work be done by an experienced bridge
designer, who has experience in forensic investigation of seismic damage and who is not
involved in the emergency work. [50]

3.3.1 Objectives of Seismic Damage Assessment of Bridges [51]
Tire overall objectives of seismic damage assessment are to
 Minimise loss of life;
 Minimise the economic loss to the region.
For the reading networks, the hierarchy of objectives will be to ensure the safety of:
 Bridges known to be vulnerable, with potential for loss of life
 Primary routes for the passage of emerge ncy vehicles concerned with the saving
of life and property
 Primary routes for the passage of vehicles concerned with the distribution of
essential supplies and restoration of essential services
 Secondary route for the passage of emergency vehicles
 All routes for general use.

3.3.2 STRATEGY AND INSPECTION LEVELS
To ensure that a route or network is safe for the public, bridges should be inspected
following an earthquake of sufficient intensity to cause concern about the possibility of damage.
All bridge s within an area subjected to MM VIII intensity shaking or greater should be inspected.
Two levels of inspection are appropriate:
 A Preliminary Safely Check, conducted immediately following the earthquake to
check for safely for immediate use and for obvio us damage.
 A Detailed Structural Check, which may or may not be required, and which would
be conducted at some later time.

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In most areas of the country, seismic screening of the State Highway bridges will have
already identified those bridges likely to be most vulnerable to damage with potential to cause
loss of life.

3.3.3 PRELIMINARY SAFETY CHECK
The fallowing order of priority should be considered for the Preliminary Safely Check of
the bridges:
 Inspect first those brides known to be most vulnerable wit h potential for loss of
life (e.g. as identified by the seismic screenings), giving priority to those carrying
the highest traffic volumes
 Inspect all other bridges along the primary routes required for the passage of
emergency vehicles concerned with the saving of life and property
 Inspect all other bridges all other primary routes required for the distribution of
essential supplies and restoration of essential cervices
 Inspect all remaining bridges.

Each bridge should be examined quickly but with suffici ent care to identify problems that
could lead to collapse and compromise public safety.
Fortunately serious damage can often be detected at read level. Nevertheless the
underside of the deck and the substructure should also be briefly examined.
At the brid ge, the lines of the handrails, kerbs and centreline markings should be checked
for horizontal and vertical discontinuities as these will be quick indicators of problems below.
Differential settlement between piers and abutments, of any one support relativ e to the others,
may indicate serious damage to substructure members. Also, it will alter the stress distribution in
continuous superstructures which could lead to overstressing and damage at some sections.
Other indicators of problems that can be seen a t deck level are:
 Evidence of excessive movement of expansion joints during the earthquake;
 Expansion joints closed up;
 Knock -off devices at abutment backwalls displaced backwards and / or upwards
by impact;
 Spalling of kerbs and decks either side of expansion joints;
 Buckling of handrails or traffic barriers.

If damage is found, several courses of action can be taken. The bridge may be:
 Left open to the public unrestricted, but noted for a Detailed Structural Check at a
later date;

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

34
 Left open to the public but with restricted speeds and/or axle loads;
 Left open only for emergency vehicles;
 Closed until temporary repairs are completed or until shoring has been installed;
 Closed indefinitely.

In deciding on what course of actio n to take, the engineer should take account of the risk
of the bridge collapsing against the consequences of placing restrictions on it. That in turn will
depend on the importance of the route and the alternatives available. The likely effect of
aftershock s should also be considered.
It should be remembered that a bridge can sustain a great deal of superficial damage
including loss of cover concrete without the vertical load -carrying capacity being affected too
greatly.
Lastly, any damage discovered should recorded, photographed, and confirmed as recent
and likely to have been caused by the earthquake.

3.3.4 DETAILED STRUCTURAL CHECK
3.3.4.1 Approach Embankments
High approach embankments on soft ground are notorious for settling or slumping in
earthquakes. If settlement is associated with failure of underlying soils, especially liquefaction,
then soil flow through the abutment is likely to have occurred.
If lateral displacement has occurred it can be detected by such evidence as:
 Heave at the toe of the embankment;
 Longitudinal cracking of the approach road surface;
 Movement of the abutment;
 Sand volcanoes and / or ground cracking on the flat ground.
Soil flow through the abutments will increase the lateral load on piles and it may have
caused damage to t hem that can only be seen by excavation. If the rotational and lateral
movements of the abutment can be quantified it may be possible to carry out a back analysis
which gives an indication of the risk of pile damage. Abutments on raked pile groups cannot
sustain much movement without damage.
Flow through the abutments can occur even where there are no approach embankments
but where the natural ground is weak. There are many recorded cases of river banks moving
closer together in earthquakes (usually but not necessarily associated with liquefaction).

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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3.3.4.2 Abutments
Apart from the problems with moving ground discussed above, abutments are vulnerable
in other ways. Particularly with more recently designed bridges, the superstructures are often
designed to act independently of abutments in an earthquake and large relative movements
between the abutment and the superstructure can take place. If the intensity was sufficient to
cause yielding in the substructure this relative movement could be greater than that provided for
normal service. In such cases damage is likely to include:
 Hammering and concrete spalling;
 Failure of expansion joints or at least of their seals;
 Knock -off devices displaced backward and/or upwards;
 Linkage hardware distressed;
 Shear keys d amaged.
Such damage is considered to be acceptable, repairable and not necessarily cause for
closing the bridge completely.
In the ideal situation, bearings should still cope with post -elastic movements but they
should be checked carefully for damage.
Wher e the abutment is independent of longitudinal superstructure movements but
provides lateral restraint, the mechanism for providing that restraint should be checked, i.e.
check for damage to shear keys, linkage devices, mechanical dampers, etc.

3.3.4.3 Pie rs
Cracking of piers to a greater or lesser extent should be noted, and considered on a case –
by-case basis for sealing, repair, encasing or replacing.
The piers are the visible part of the substructure and ideally are the locations chosen by
designers for the development of plastic hinges in the design intensity earthquakes.
For modern bridges at least, spalling of cover concrete at the top or bottom of piers may
indicate that the bridge has been subject to a design intensity earthquake and has yielded
according to prediction.
If the reinforcing cage is largely intact and the core concrete properly confined, the
vertical load capacity is likely to be adequate. Repairs will be required but it may be possible to
carry them out with the bridge in service.
Piers should be checked for verticality. If they have moved out of plumb significantly
during the earthquake the reason should be determined. If it is caused by yielding of the pier and
displacement of superstructure then it may be straighten them before repair to yield zones are
attempted. However, if piers are out of plumb and the superstructure is not displaced, there is a
strong inference of foundation displacement.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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3.3.4.4 Foundations
The foundations are the hidden part of the substructure and ideally, i n modern (post –
1972) bridges, have been designed with sufficient overstrength to ensure they remain elastic up
to and after the bridge structure has started to form a collapse mechanism.
However, that design approach will not have been applied in older bri dges, and even in
modern bridges that ideal is not always achieved and piles can yield.
Tell tale signs are:
 Large relative movements between piles and the soils;
 Relative displacement between pile caps;
 Piers out of plumb.
From each of these signs a defle ction of the top of the pile can be measured and a back
analysis using a range of soil parameters can be used to indicate the likelihood of pile yielding.
The final check is to dig them out and examine them but usually that is not easy to do.
Vertical disp lacement of piles does not always mean that pile yielding has taken place,
particularly if there are no raked piles in the group. Furthermore, temporary loss of bearing
capacity (e.g. from liquefaction) does not necessarily mean that capacity is lost perma nently.
Vertical displacement can have serious consequences for the
superstructure andparticularly so for indeterminate (continuous) spans. The effect should be
assessed.
For simply supported spans, the rotational capacity of bearings may have been exceede d
because of the settlement.
For short deep continuous spans, distress could have been caused by small settlements
that are only detected by taking levels. This should be considered as part of a thorough
investigation.

3.3.4.5 Linkage Devices and Shear Ke ys
Linkage devices and shear keys are installed in bridges to limit relative movements
between adjacent spans, and between spans and theirsupports. If they have been worked very
hard by the earthquake they may have been damaged and require replacement.
To check the linkages properly it may be necessary to remove some for close inspection.

3.3.4.6 Expansion Joints
Expansion joints that have operated beyond their design range may be damaged and
require repair or replacement. Many joints have very little capa city for lateral displacement and
damage can be caused by very small movement.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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3.3.4.7 Holding Down Bolts
Holding down bolts that have been subject to large transverse shears are likely to have
yielded. That does not necessarily mean that replacement is required. Recent design practice is to
provide no holding down bolts at all in most cases. Each case should be assessed on its merit.

3.3.4.8 Bearings
Bearings are vulnerable in earthquakes, particularly if they are also required to carry
transverse shear.
(a) Elastomeric Bearings:
Bearings that have been deflected beyond their design shear may be ruptured internally,
but usually damage manifests itself at the surface and can be seen.
Deep lead -rubber bearings are used for base isolation and can be s ubject to large lateral
deflections. They should be carefully checked after an earthquake. If there is any suspicion of
damage it may be necessary to remove one and check its capacity for continued performance.
Bearings not positively restrained in positio n may "walk". There is a recorded case of a
lead-rubber bearing escaping from its keeper ring during an earthquake.
(b) Sliding Bearings:
If the design capacity for sliding has been exceeded, damage is likely.
(c) Pot Stay Bearings:
If pot stay bearing has failed in shear it will be obvious.

3.3.5 INVESTIGATION REPORT
The results of the investigation should be recorded in a report that includes:
 An assessment of the ground acceleration at the site.
 An assessment of how the loads were transmitted to and from the ground and their
magnitude (i.e. trace the load paths).
 A record, including photographs, of damage and permanent deformations.
One of the potential difficulties of investigating earthquake damage is confirming that all
the damage observed occurred during the earthquake. If investigation is sufficiently soon after
the event it is easier to differentiate between new and old damage.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Chapter Four
Seismic Isolation System

4.1 Basic Principles of Seismic Isolation for Bridges
Two important concepts have been considered in earthquake resistance design of the
structures.
 The first concept is to increase the capability of the structures to resist the
earthquake load effects (which are mainly horizontal forces) or to boost the
dynamic stiffness such as like the seismic energy dissipation capacity by adding
damping systems (both devices and/or structural fuses). [52]
 The second concept considered the seismic isolation systems to decrease the input
load effects on the structures. App arently, both concepts can be integrated to get an
optimal design for the seismic flexible structures. [52]
From the structural response point of view of the community control, the seismic protective
systems are usually classified as passive, active and se mi-active systems. The passive control
system formed of many different categories like energy dissipation systems, toned mass systems
and the vibration isolation systems. [53]
The seismic isolation and energy dissipation systems offered effective technique s to
improve the resist seismic forces of the structures. These techniques decrease the seismic forces
by altering the stiffness and/or damping of the structures, while the conventional seismic design
is required to provide additional strength and ductilit y to resist seismic forces. [54]

4.1.1 CLASIFICATION OF SEISMIC ISOLATION SYSTEMS
The seismic isolation systems of structures were usually used as method to separate the
foundation of the structure from its superstructure. Two types of classification of the devices can
be considered according to their location in the building and its op eration principles.
According to the classification of the seismic isolation systems by their location in the
building, isolators can be considered as external and internal types.
 The external types are located outside the building and they are often fixe d to the
foundations.
 The internal types are depending on the energy dissipation mechanisms.
Also the response control systems are classified according to their principles of action as active
control systems, passive control systems and hybrid systems. [54, 55]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

39
4.1.1.1 Active Control Systems
The mechanism of action of the active control systems was depending on providing of
continuous energy from outside. The system will manage the acceleration, displacement or
velocity of the structure. The active co ntrol systems were usually consisting of electronic
components like computers, actuators and starters. The system changes its stiffness or the
amount of action according to the severity of the ground motion. There are three major
application forms for the active control systems:
 Active Mass Damper: controlled by computer systems which affected by lateral
forces affected by the actuator control force, the acceleration, displacement and
velocity of the structure.
 Active Variable Stiffness: In this system, the re is no need for forming of actuator
control force; it’s developed for utilization in case of strong ground motion.
 Active Passive Composite Tuned Mass Dumper: it considered as hybrid
structural control systems, which were developed recently, it depend on
employment of both active and passive systems. [54, 55]

4.1.1.2 Passive Control Systems
The action of passive control systems did not use any external energy source. These
systems could be able to control displacement for a certain limit. Passive control systems are
consisted of dampers and isolators. Passive control systems have many types. [54, 55]
 Irreversible displacement systems consist of balls or rolls (Figure 4 -1).

Figure 4 -1: Irreversible displacement system
 Sliding systems: They consist of plenty of rolls placed vertical to each other or
steel balls between the steel plates.
 Plastic systems: depend on the plasticity of lead which facilitates energy absorption
for seismic isolation (Figure 4 -2).

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

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Figure 4 -2: Plastic system
 Elastic systems : Rubber or neoprene dampers were usually used as examples for
these systems. The isolati on was achieved by insertion of dampers between the
foundation and the columns.
 Viscous systems: These systems consist of polymer or viscous liquid which fitted
between two cross sections.
 Kinematical systems: These systems consist of balls, rolls, ellipt ic balls and small
columns with elliptic ends. The geometric shapes of these devices permit its return
its original positions. Figure 4 -3.

Figure 4 -3: Kinematic -Elastic systems
 Friction sliding systems: The principle of action depends on dissipating
energy by the friction forces. These systems are used both as base isolation systems
between the foundation and the columns, and as energy dissipating mechanisms in
the superstructure. Figure 4 -4(a).

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

41

Figure 4 -4: New Zealand bearing system (a) Sectional det ails (b) Schematic diagram (c)
Force deformation behavior
 Another type of kinematical -elastic systems is the Hercules Systems (Figure 4 –
4(b). Hercules system was suitable isolator for the isolations of small and medium
scale foundation of structures.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
Master of Structural Engineering

42
4.2 Types of Seismic Isolators
The strength of the structure in usual seismic design is measured to stand against
earthquake forces. The base isolation technology act to separate the structure from the seismic
ground motions, by separation of the structure from its foundation. The base isolation systems
have the criteria of flexibility and energy absorbing capacity.
Currently the base isolation techniques are principally classified into three types:
 Passive base isolation devices.
 Compound base isolation with semi -active devices.
 Compound base isolation with passive energy devices.

4.2.1 Types of Passive base Isolation Devices
1- Mud layer below the structure [56, 57]
2- Flexible first storey [57]
3- Roller bearings in foundations
4- Rubber layer as foundation support [57]
5- Laminated rubber bearing system [57]
6- New Zealand bearing system [58]
7- Resilient – friction base isolation system
8- Electric de -France system
9- Sliding resilient – friction system
10- High damping rubber bearing
11- Pure friction system . [59]
12- Friction pendulum system
13- Spring type systems [59]
14- Sleeved pile isolation system [59]
15- Rocking systems [59]
16- Base isolation using Geo – Synthetic materials [60]
17- BS cushion [61]

4.2.2 COMPOUND ISOLATION SYSTEM WITH SEMI -ACTI VE DEVICES
[62]
Compound isolation system adopted the passive isolation systems with the semi -active or
active controlling systems. The analyses showed that considerable diminution of the structure
accelerations (up to 50%) can be achieved with the compound system. [62]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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4.2.3 COMPOUND BASE ISOLATION WITH PASSIVE ENERGY
DEVICES
These types of devices developed whole over the world; it can be fitted at the foundation of
the structure or in superstructure at suitable places. They can be mixed with passive base
isolation devi ces.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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44
4.3 Advantages/Disadvantages of Seismic Isolation
The base isolation structures, besides being more efficient, safe, functional and
economical, it may achieve new design prospects in seismic regions. [63]
4.3.1 Benefits and savings of seismic isolation system [64]
1. Base isolation reduces number of component of the structure with less ductile details.
2. Crawl spaces or basements which created can be of multiple benefits such as
generating additional income fro m a car park and flexibility for the future planning
and development.
3. Protection of the contents found inside the building from damage.
4. Protection of the integrity of the internal structures of the structures.
5. Building being safer for habitants.
6. Life activ ities could be Continue after seismic events.

4.3.2 Maintenance of seismic isolation system [64]
1. Unlike the belief, seismic isolation devices need no maintenance, during the life of the
structure.
2. After any seismic event isolation systems should be inspected to ensure that its
components are still working effectively.
3. There is no need to replace the isolation devices after an earthquake unless it was
damaged; some devices recommend for removal for testing purposes.
4. Repairing costs after seismic even ts will be lower, because the structure is protected
from major damage.
5. The effectiveness of seismic isolation in the protection of structures is not only of the
external structure but also the contents and in maximizing the potential for immediate
busine ss continuation.
4.3.3 Historic and heritage structures [64]
1. Traditional earthquake strengthening methods can detract from the aesthetics of
historic and heritage buildings
2. Many heritage buildings are appropriate for base isolation
3. Base isolation can be retrofitted to achieve earthquake protection without
compromising the aesthetic integrity of the building

4.3.4 Economic and social benefits [64]

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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45
If functions and offered services of the buildings and places of work were continued a nd
secure the employee; then they will be able to survived and share later on in the reconstruction
and recovery of their community after the earthquake.
4.3.5 Advantages of Base isolation systems [65, 66]
1. Reduced the seismic protection requirements of st ructure, so that reducing the cost of
building.
2. Reduce the displacements of constructions during an earthquake.
3. Improves safety measures of buildings.
4. Reduced the damages occurred due to an earthquake. That will facilitate the
performance of structure afte r seismic event; and maintains functions after an
earthquake or speed up the recovery of function.
5. Improve the functions of structure under seismic effect.
6. Protection of property.
7. Prevent furniture and fixtures from overturning and falling
8. Ensure an escape route
9. Ease anxiety of habitants.

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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Chapter Five
Calculation
5.1 Structure Analyzed
A 4-aperture concrete bridge was analyzed. The bridge consists of two collections, 3
lamellar piles, prestressed concrete beams and reinforced concrete slab. The geometric
characteristics of the bridge are shown in Figure 5 -1 and Figure 5 -2
Figure 5 -1: Longitudinal section
Figure 5 -2: Cross section

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5.2 Purpose of the Study Implemented
In this paper, the behavior of a structure subjected to seismic action, using accelerograms,
was studied in two situations:
 The first situation in which classical neoprene support appliances were used.
 The second situation where neoprene isolators were use d.

5.3 Analytical Structure
To obtain the seismic response of the structure, a 3D model with finite elements was made
according to the figure 5 -3 below.

Figure 5 -3: Structured discretization
5.3.1 Loads we take into account.
Load patterns are defined in "Load Patterns". After charging is defined, they are hooked up
in Load Cases load cases to run specific analyzes. Load cases can be multiplied by different load
factors and can form a Load Combinations load combination.
Only permanent loads and seismic lo ading were taken into account.

5.3.2 Results
Formulas for Calculation:

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1. Determine the mass of the deck

Where:
M(deck)=mass of the deck
g = ground Acceleration

2. Assume the period of the isolation system.
Tisolation = 2.5 (S)
Where:
Tisolation= period of isolation system

3. The angular frequency
𝜔=2π
𝑇𝑖𝑧 [1
𝑠]

4. Determine Stiffness of the isolation
Kisolation =M(deck )∙𝜔2 [Kn
𝑚]
Where:
Kisolation = Stiffness of the isolation
5. Take into account the Damping coefficient
ζ= 10%
Where:
ζ= Damping coefficient
6. The rigidity of the compression of isolation
𝐶isolation =2∙M(deck )∙𝜔 ∙ ζ [Kn∙s
𝑚]
Where:
𝐶isolation =the rigidity of the compression of isolation

The supports used are: 12 cm on the Abutment and 14 cm Pier classical. M(deck )=𝐹(𝐾𝑛)
𝑔 [ton]

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Table 5 -1: Period of Isolation

For the load case (time history) we used in sap2000 the Acceleration as shown in the
figures below.

Figure 5 -4: Acceleration INCERC -VRANCEA1977

-2.04 m/s21.87 m/s2
-2.5-1.5-0.50.51.52.5
0 10 20 30 40 50 60 70Acceleration[m/s2]
Time [s]INCERC -Vrancea 1977
Tiz (S)ωiz(1/s)Kiz(KN/m) ζ Ciz(KN.s/m)
2 3.141593 409.4125 10% 26.06401
2 3.141593 393.6171 10% 25.05844
2 3.141593 956.3154 10% 60.88093
2 3.141593 936.6164 10% 59.62685
2 3.141593 1135.276 10% 72.27392
2 3.141593 1085.646 10% 69.1144
2 3.141593 1234.787 10% 78.60899
2 3.141593 1184.493 10% 75.40719
2 3.141593 352.0159 10% 22.41003
2 3.141593 336.7235 10% 21.43649349.89 35666.66667
334.69 34117.22732Element
950.54
930.96
1128.42Abutment 1
Pier 2
Pier 3
Pier 4
Abutment 2 Period of isolation T iz = 2 s and ζ=10%
1177.34 120014.2712Mass=F/g (Kg)
41482.16106
39881.75331
96895.0051
94899.08257
115027.5229
109998.9806
125110.09171079.09
1227.33Axial force(F)kn
406.94
391.24

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Figure 5 -5: Acceleration INCERC -VRANCEA1990

Figure 5 -6: Acceleration Drumul Sarii -VRANCEA1990

By using SeismoSignal software we get the Amplitude of power spectrum for each
Acceleration as shown in the figures below.
-0.74 m/s20.98 m/s2
-1.2-0.8-0.400.40.81.2
0 10 20 30 40 50 60 70Acceleration[m/s2]
Time [s]INCERC -Vrancea 1990
1.018 m/s2
-0.88 m/s2
-1.3-0.8-0.30.20.71.2
0 10 20 30 40 50 60Acceleration[m/s2]
Time [s]Drumul Sarii -Vrancea 1990

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Figure 5 -7: Acceleration power spectrum INCERC – Vrancea 1977

Figure 5 -8: Acceleration power spectrum INCERC – Vrancea 1990
00.10.20.30.40.50.60.7
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Amplitude of power spectrum
Period, T [s]INCERC – Vrancea – 1977
1.221.63
1.7
2.4
2.6
00.050.10.150.20.250.3
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Amplitude of power spectrum
Period, T [s]INCERC – Vrancea 1990
0.540.630.98
1.32
1.992.15
2.4

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Figure 5 -9: Acceleration power spectrum Drumul Sării – Vrancea 1990
By using sap2000 software we get the time period for Structure with classic supports
(without Isolation)
Table 5 -2: Mode of time period

Figure 5 -10: Structure with classic supports Modal 1 T1=0.72
00.020.040.060.080.10.120.140.160.18
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Amplitude of power spectrum
Period, T [s]Drumul Sarii – Vrancea 1990
0.33
0.49
0.7
1.9
2.56
Mode
mode1
mode2
mode3
mode4
mode5time period (s)
0.72
0.72
0.56
0.36
0.3

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Figure 5 -11: Structure with classic supports Modal 2 T1=0.72

Figure 5 -12: Structure with classic supports Modal 3 T1=0.56

Figure 5 -13: Structure with classic supports Modal 4 T1=0.36

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Figure 5 -14: Structure with classic supports Modal 5 T1=0.3
The time period for Structure with base Isolation supports (with Isolation 3 second)

Figure 5 -15: Structure supports with Isolation 3 second Modal 1 T1=2.87

Figure 5 -16: Structure supports with Isolation 3 second Modal 2 T1=2.83

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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Figure 5 -17: Structure supports with Isolation 3 second Modal 3 T1=2.76

Figure 5 -18: Structure supports with Isolation 3 second Modal 4 T1=0.35

Figure 5 -19: Structure supports with Isolation 3 second Modal 5 T1=0.31

Eng. Ameer Tawfeeq Fakhir AL-AQBI Base Isolation in Bridges Engineering
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Table 5 -3: Structure with and without Isolation system

After modify the modal in sap2000 and put the Isolation system with
(2,2.5and,3second)We can see the difference in bending moment and displacement as shown in
the figures below

Figure 5 -20: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier1 (Drumul Sarii)

-0.0025-0.002-0.0015-0.001-0.000500.00050.0010.0015
0 10 20 30 40 50 60Bending moment [kNm]
Time [s]Bending moment in pier 1 [kNm] (X-Direction)
without Isolation
with Isolation 2 sec
mode1 0.72
mode2 0.72
mode3 0.56
mode4 0.36
mode5 0.3Modetime period (s) with
Isolation 2(s)time period (s) with
Isolation 2.5(s)time period (s)with
Isolation 3(s)time period (s)
without Isolation
2.87
2.83
2.76
0.35
0.312.4
2.36
0.43
0.35
0.311.92
1.89
1.84
0.35
0.31

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Figure 5 -21: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier3 (Drumu l Sarii)

Figure 5 -22: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (Y -Direction) pier1 (Drumul Sarii)

-0.004-0.003-0.002-0.00100.0010.0020.003
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 3 [kNm] (X-Direction )
without Isolation
with Isolation 2 sec
-1500-1000-500050010001500
0 10 20 30 40 50 60 70Bending moment [kNm]
Time [s]Bending moment in pier 1 [kNm] (Y-
Direction)
without Isolation
with Isolation 2 sec

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Figure 5 -23: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (Y -Direction) pier3 (Drumul Sarii)

Figure 5 -24: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier1 (INCERC – Vrancea 1977)

-1500-1000-5000500100015002000
0 10 20 30 40 50 60 70Bending moment [kNm ]
Time [s]Bending moment in pier 3 [kNm] (Y-Direction )
without Isolation
with Isolation 2 sec

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Figure 5 -25: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier3 (INCERC – Vrancea 1977)

Figure 5 -26: The difference between Classic supports and supports with Isolation system
(2second) in bendin g moment (Y -Direction) pier1 (INCERC – Vrancea 1977)

-0.006-0.004-0.00200.0020.0040.006
0 10 20 30 40 50 60Bending moment [kNm]
Time [s]Bending moment in pier 3 [kNm] (X-Direction )
without Isolation
with Isolation 2 sec
-10000-8000-6000-4000-20000200040006000800010000
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 1 [ kNm] (Y-Direction )
without Isolation
with Isolation 2 sec

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Figure 5 -27: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (Y -Direction) pier3 (INCERC – Vrancea 1977)

Figure 5 -28: The difference bet ween Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier1 (INCERC – Vrancea 1990)

-10000-8000-6000-4000-20000200040006000800010000
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 3 [kNm] (Y-Direction )
without
Isolation
-0.0015-0.001-0.000500.00050.0010.00150.002
0 10 20 30 40 50 60Bending moment [kNm]
Time [s]Bending moment in pier 1 [kNm] (X-Direction )
without Isolation
with Isolation 2 sec

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Figure 5 -29: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (X -Direction) pier3 (INCERC – Vrancea 1990)

Figure 5 -30: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (Y -Direction) pier1 (INCERC – Vrancea 1990)

-0.0025-0.002-0.0015-0.001-0.000500.00050.0010.00150.0020.00250.003
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 3 [kNm] (X-Direction)
without Isolation
with Isolation 2 sec
-6000-4000-20000200040006000
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 1 [kNm] (Y-Direction)
without
Isolation

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Figure 5 -31: The difference between Classic supports and supports with Isolation system
(2second) in bending moment (Y -Direction) pier3 (INCERC – Vrancea 1990)

Figure 5 -32: T he difference between Classic supports and supports with Isolation system
(2second) in Displacement (X -Direction) pier1 (Drumul Sarii)

-6000-4000-20000200040006000
0 10 20 30 40 50 60Bending moment [kNm ]
Time [s]Bending moment in pier 3 [kNm] (Y-Direction )
without
Isolation

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Figure 5 -33: The difference between Classic supports and supports with Isolation system
(2second) in Displacement (X-Direction) pier3 (Drumul Sarii)

Figure 5 -34: The difference between Classic supports and supports with Isolation system
(2second) in Displacement (X -Direction) pier1 (INCERC – Vrancea 1977)

-0.0005-0.0004-0.0003-0.0002-0.000100.00010.00020.00030.0004
0 10 20 30 40 50 60Displacement [m]
Time [s]Displacement in pier 3 [m](X-Direction)
without Isolation
with Isolation 2 sec
-0.008-0.006-0.004-0.00200.0020.0040.006
0 20 40 60Displacement [m]
Time [s]Displacement in pier 1 [m](X-Direction)
without Isolation
with Isolation 2 sec

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Figure 5 -35: The difference between Classic supports and supports with Isolation system
(2second) in Displacement (X -Direction) pier3 (INCERC – Vrancea 1977)

Figure 5 -36: The difference between Classic supports and supports with Isolation system
(2second) in Displacement (X -Direction) pier1 (INCERC – Vrancea 1990)

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Figure 5 -37: The difference between Classic supports and supports with Isolation system
(2second) in Displacement (X -Direction) pier3 (INCERC – Vrancea 1990)

Comparison between Classic supports and supports with Isolation (2, 2.5 and 3 sec ond) in
bending moment (X and Y Direction) and in displacement (X Direction) in pier (1) and pier (3)

Table 5 -4: Bending moment (Y -Direction) in pier (1) and pier (3)
(Drumul Sarii -Vrancea -1990)

pier1 pier3
1352.42 1380.88
424.1459 456.20858
69% 67%
435.66841 456.02623
68% 67%
400.90866 438.94376
70% 68%Bending moment (Y-Direction) Drumul Sarii-Vrancea-1990
Classic supportsElement
Isolation 2 sec
Reduction coefficient
Isolation 2.5 sec
Reduction coefficient
Isolation 3 sec
Reduction coefficient

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Table 5 -5: Bending moment (Y -Direction) in pier (1) and pier (3)
(INCERC -Vrancea -1990)

Table 5 -6: Bending moment (X -Direction) in pier (1) and pier (3)
(Drumul Sarii -Vrancea -1990)

Table 5 -7: Bending moment (X -Direction) in pier (1) and pier (3)
(INCERC -Vrancea -1977)

pier1 pier3
8683.274 8922.252
6333.307 6536.05
27% 27%
6648.186 6858.409
23% 23%
4493.789 4634.083
48% 48%Reduction coefficient
Isolation 3 sec
Reduction coefficientElement
Classic supports
Isolation 2 sec
Reduction coefficient
Isolation 2.5 secBending moment (Y-Direction) INCERC-Vrancea-1977
pier1 pier3
0.00185 0.00288
0.0004129 0.00117
78% 59%
0.0004064 0.00113
78% 61%
0.0004036 0.00108
78% 63% Reduction coefficientIsolation 2 sec
Reduction coefficient
Isolation 2.5 sec
Reduction coefficient
Isolation 3 secBending moment (X-Direction) Drumul Sarii-Vrancea-1990
Element
Classic supports
pier1 pier3
0.00296 0.00501
0.0007779 0.00227
74% 55%
0.000753 0.00219
75% 56%
0.0003369 0.0009449
89% 81%Reduction coefficient
Isolation 2.5 sec
Reduction coefficient
Isolation 3 sec
Reduction coefficientBending moment (X-Direction) INCERC-Vrancea-1977
Element
Classic supports
Isolation 2 sec

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Table 5 -8: Bending moment (X-Direction) in pier (1) and pier (3)
(INCERC -Vrancea -1990)

Table 5 -9: Displacement (X -Direction) in pier (1) and pier (3)
(Drumul Sarii -Vrancea -1990)

Table 5 -10: Displacement (X -Direction) in pier (1) and pier (3)
(INCERC -Vrancea -1977)

pier1 pier3
0.00152 0.00241
0.000345 0.00103
77% 57%
0.0003365 0.0009904
78% 59%
0.0007395 0.0021
51% 13%Isolation 2.5 sec
Reduction coefficient
Isolation 3 sec
Reduction coefficientBending moment (X-Direction) INCERC-Vrancea-1990
Element
Classic supports
Isolation 2 sec
Reduction coefficient
pier1 pier3
0.0008863 0.000967
0.0002741 0.0003141
69% 68%
0.0002851 0.0003188
68% 67%
0.0002587 0.0003018
69% 71%Reduction coefficient
Isolation 3 sec
Reduction coefficientElement
Classic supports
Isolation 2 sec
Reduction coefficient
Isolation 2.5 secDisplacement (X-Direction) Drumul Sarii-Vrancea-1990
pier1 pier3
0.00568 0.00624
0.00415 0.00457
27% 27%
0.00436 0.0048
30% 23%
0.00295 0.00325
48% 48%Isolation 3 sec
Reduction coefficientClassic supports
Isolation 2 sec
Reduction coefficient
Isolation 2.5 sec
Reduction coefficientDisplacement (X-Direction) INCERC-Vrancea-1977
Element

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Table 5-11: Displacement (X -Direction) in pier (1) and pier (3)
(INCERC -Vrancea -1)

pier1 pier3
0.00321 0.0035
0.0006676 0.0007349
79% 79%
0.0007702 0.0008595
76% 75%
0.0006001 0.0006672
81% 81% Reduction coefficientIsolation 2 sec
Reduction coefficient
Isolation 2.5 sec
Reduction coefficient
Isolation 3 secDisplacement (X-Direction) INCERC-Vrancea-1990
Element
Classic supports

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Chapter Six
Conclusion
1. Comparing the structure before and after using the seismic isolation technique with 2, 2.5
and 3 seconds; the obtained reduction coefficient ranged 23% – 81%, this difference in
reduction coefficient was due to strength of seism ic action, vibration period content of the
accelerograms and the vibration period of the isolation system .

2. When we shift the vibration period from 0.7 close to 2, 2.5 and 3 seconds in the case of
the accelerogram from Drumul S arii (Vrancea source, 1990 ) the reduction coefficient is
around 70%, because the structure is far from the pick point on the seismic action as
shown in Figure 5 -9 and Figure 5 -8; also for the accelerogram recorded at INCERC
(Vrancea source, 1990 ).

3. In the case of the accelerogram recorded at INCERC (Vrancea source, 1977 ) we get
reduction coefficient about 23% because the seismic action is more powerful due to the
far distance of structure from the pick point on seismic action as shown in Figure 5 -7.

4. Generally the seismic isolatio n achieve the purpose for it s use and instillation; and could
save the structure and preserve people safety which is an important target for the structure
designing engineers.

5. We can implement the seismic isolation technique to ensure the construction of the
earthquake resistant structures ; moreover, we can recommend confidently the use of
seismic isolation system in seismic area.

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Master of Structural Engineering

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