Proceedings of the 16th International Conference on Nuclear Engineering
ICONE16
May 11-15, 2008, Orlando, Florida, USA
ICONE16 - 48554
SERB DEVICES FOR THE ISOLATION OF BUILDINGS AND EQUIPMENT AGAINST
SHOCKS, VIBRATIONS AND SEISMIC MOVEMENTS
Viorel Serban
Adrian Panait
Subsidiary of Technology and Engineering for Nuclear
Projects,
Bucharest-Magurele, Romania
Subsidiary of Technology and Engineering for Nuclear
Projects,
Bucharest-Magurele, Romania
Phone:40-1-4574431,
Fax:40-1-4574431
serbanv@router.citon.ro
Phone:40-1-4574431,
Fax:40-1-4574431
panaita@router.citon.ro
Marian Androne
George Alexandru Ciocan
Subsidiary of Technology and Engineering for Nuclear
Projects,
Bucharest-Magurele, Romania
Subsidiary of Technology and Engineering for Nuclear
Projects,
Bucharest-Magurele, Romania
Phone:40-1-4574431,
Fax:40-1-4574431
andronem@router.citon.ro
Phone:40-1-4574431,
Fax:40-1-4574431
ciocang@router.citon.ro
ABSTRACT
The paper presents the advantage of non-oscillating systems
– SERB type – for the seismic isolation of buildings compared
with other solutions for seismic protection of the buildings
which are now employed worldwide.
The non-oscillating isolation devices – SERB type – have a
capsulated structure and are capable to overtake large
compression and tension loads on vertical direction with very
small deflection and cut off the seismic action in horizontal
direction.
The stiffness of the devices is zero for the translations on
any direction in horizontal plane upto a pre-set displacement
which usually, is between 0.6 - 0.8 of the maximum seismic
soil displacement. After having reached that value, a non-linear
increase of the device stiffness is occurring on the horizontal
direction in order to provide a non-shock limitation of some
random seismic displacements higher than the maximum
displacement accommodated by the device. The motion inside
the device is restricted all time by the dinamic friction.
On vertical direction, the stiffness of the devices is big in
order to avoid the additional stresses on the structural elements
of the isolated suprastructure, due to the differential settlement
of the devices on the suprastructure permanent loads that could
appear. The system provides very small deflection of the device
on vertical direction with high damping. On request, SERB
isolators can be so fabricated to have the desired stiffness on
vertical direction.
Standard devices (960x960x230) are capable to overtake a
permanent compression load of 3000KN and tensile load of
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Copyright © 2008 by ASME
1500KN, respectively, over which dynamic loads of similar
values may overlap.
The maximum seismic acceleration transferred to the
isolated structure on horizontal direction is ranging between
0.03g and 0.05g depending on the friction coefficient. The
maximum relative displacement between the isolated
suprastructure and the infrastructure embedded into the ground,
is about 3 times smaller than the maximum seismic
displacement showed by the oscillating systems employed
today and smaller then the maximum seismic soil displacement.
In series SERB device (960x960x230) allows for a
maximum seismic displacement of 230mm.
An application of the new seismic isolation system as the
solution to seismically isolate the heavy water detritiation
system building at Cernavoda NPP, is presented.
1.
GENERAL PRESENTATION
The construction of buildings capable to withstand seismic
actions can involve various techniques. Such techniques depend
both on the type of the building and the characteristics of the
seismic movement. Considering the fact that the seismic action
on the building is dependent on : the type of the earthquake
focus, the distance between the building site and the earthquake
focus, the local geological conditions, it results that the design
solutions for buildings to withstand future earthquakes need to
consider the above mentioned parameters. The current trend to
apply the same design considerations to all the types of seismic
actions for all the types of buildings irrespective of the kinetic
characteristics of the ground seismic movement, of the local
geological conditions and of the type of the building [1, 2] is an
error which will lead to great material and human losses with
the future earthquakes.
In order to get a quantitative understanding of the
differences among various building seismic design solutions,
herein below there is a brief presentation of the various
alternatives. The great difference in the building behavior
during an earthquake results from the fact that a building (along
with its foundation ground) make-up an oscillating system
which represents a BUILT-UP of kinetic and potential energy of
repeated seismic movement oscillations.
The oscillating system may OVERTAKE and BUILT-UP or
NOT the seismic energy from each soil oscillation, function of
the location of the important eagen vibration periods of the
building within the spectral component of the seismic action.
Related to the ground response seismic spectrum, the
important eagen vibration periods of the building may fall-in
the left part, in the transfer range of the seismic action (transfer
without energy built-up), on the right , in the isolation range of
the seismic action ( non-transfer and non-build-up range of
energy) or in the resonance range of the seismic action
(maximum transfer and maximum built-up range of energy).
Among these ranges, there are transition ranges in which the
seismic energy transfer and built-up phenomena evidence
different weights.
In order to specify such dynamic behavior regimes of the
buildings, the seismic action defined by the seismic ground
response spectrum is divided into 5 areas which may be defined
as follows for a seismic action with only one dominant
harmonic component of T period:
𝑇
Area a) resonance area ranging between
and √2 ∙ 𝑇;
√2
Area b) isolation area ranging between 3𝑇 and ;
𝑇
Area c) transfer area ranging between 0 and ;
3
Area d) transfer area 1, transfer - resonance, ranging between
𝑇
𝑇
and
;
3
√2
Area e) transfer area 2, resonance - isolation, ranging between
√2 ∙ 𝑇 and 3𝑇.
Buildings, which in point of the dynamic behavior fall-in
areas ‘a’, ’d’ and ‘e’, are building-up seismic energy during an
earthquake which leads to the amplification of the building
seismic response. The buildings falling-in areas ‘b’ and ‘c’ do
not build-up seismic energy and additionally, in area ‘b’ the
energy transfer from the ground to the building is not totally
accomplished.
For real seismic actions, which are different due to their
design ground response spectrum, the 5 areas may be defined as
follows:
area a) resonance area encompassed between 𝑇𝐵 and 𝑇𝐶 ;
area b) isolation area encompassed between 3𝑇𝐶 and ∞;
𝑇
area c) transfer area encompassed between 0 and 𝐵 ;
3
area d) transfer –resonance area encompassed between
𝑇𝐵
√2
𝑇𝐵
3
and
;
area e) transfer-resonance area encompassed between √2 𝑇𝐶
and 3𝑇𝐶 .
TB and TC may be defined by the possible dominant
periods of the seismic action on that site, namely, 𝑇𝑚𝑖𝑛 and
𝑇𝑚𝑎𝑥 .
Considering the large variety of the kinetic characteristics
of the seismic actions, a proposal of classification in function of
their spectral component, is presented below:
a) “fast”earthquakes are the earthquakes having the dominant
repetition periods of ground movement below 0.5 seconds.
These earthquakes are generated by surface foci (shallow
earthquakes) on hard and average soils;
b) “slow”earthquakes are the earthquakes having the dominant
repetition periods of the ground movement higher than 1
second. These earthquakes are generated by intermediate
and deep foci on soft and average soils;
c) “moderate” earthquakes are the earthquakes having the
dominant repetition periods of the ground movement
ranging between 0.5 seconds and 1 second. This is also the
class of the earthquakes generated by surface and
intermediate foci in function of the site soil characteristics.
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Copyright © 2008 by ASME
The main problem that needs to be solved by the seismic
design of buildings consists in the TRANSFER OF A
MINIMUM QUANTITY OF SEISMIC ENERGY FROM THE
GROUND TO THE BUILDING and in so that the transferred
energy should not build-up in the building-ground oscillating
system.
Herein below all the measures which make-up and
demonstrate the increase of a building capacity to withstand a
seismic action is called: ”seismic qualification”.
2.
POSSIBLE SOLUTIONS TO
QUALIFY THE BUILDINGS
SEISMICALLY
Alternative 1 – Elastic behavior of the building (classic
solution)
In this case, dynamically, the building is usually located in
the transfer area of the response spectrum or in the transfer and
resonance areas, function of the spectral range in which the
dominant vibration period of the building-foundation ground
assembly is situated. The seismic energy transferred to the
building in repeated cycles, may be built-up in the buildingground oscillating system when its eagen vibration period is in
the transfer or resonance range with the seismic movement. A
small part of the seismic energy built-up by the building is
consumed due to the low damping capacity of the system,
leading to the limitation of the seismic response amplitude of
the building at large values.
With Alternative 1, the amplifications of the seismic
acceleration in a building are 4-6 times higher than the
maximum ground acceleration, function of the damping
capacity, specially of the non-structural elements of the
building.
If the building is located in the transfer area, though the
building accepts seismic energy with each seismic action
repetition cycle, the oscillating system is not building it up. The
relative movement of the building is in-phase with the seismic
action and the seismic energy per one cycle is equal with the
kinetic energy of the building (the system potential energy is
actually zero). In case that the building is in the resonance
range with the seismic movement, there occurs a de-phase of
the building seismic response with the seismic action of about
90 degrees and the system is building –up kinetic and potential
energy. The maximum value of the built-up energy depends on
the system damping capacity.
Alternative 2 – Plastic hinges in the building (classic
solution).
In this case, dynamically, the building may be located in
the transfer or resonance area in its non-damaged condition but,
due to damaging, it may pass to the isolation or resonance area,
function of the type of the seismic action (i.e. fast or slow or
moderate) and the building characteristics.
It is aimed that the reduction of the building seismic
response be accomplished by the occurrence of some structural
local damages (i.e. in the location of beam joints, columns and
foundation-column joints) during a big earthquake, generically
called:” plastic hinges”. The damage is modifying the dynamic
behavior of the building in two directions:
Direction 1 – Due to the friction developed in the plastic
hinges, a further dissipation of the seismic energy built-up in
the building is generated , leading to the reduction of seismic
energy built-up in the building-foundation oscillating system
and implicitly to a reduction of the seismic response which
may get decreased by 20% -30% as to the non-damaged
condition. From that viewpoint, Direction 1 is equivalent to
inserting some hydraulic dampers into the building (Alternative
3).
Direction 2 – Due to the damage of the links between the
beams-columns and columns-foundation, there occurs an
important reduction of the building stiffness which make the
damaged building eagen vibration periods get higher. In this
case the dynamic behavior of the building in the condition of a
forced excitation of the seismic movement, is substantially
modified. The seismic energy transferred to the building per
one oscillation cycle may be smaller or bigger than with the
case of the non-damaged building and the maximum energy
which is built-up by the building- ground oscillating system
may be smaller or bigger.
Dynamically, the seismic response of the structure may
fall-in the two cases:
Case 2a – the building enters the isolation area due to
damaging. By the increase of the damaged building eagen
vibration period, the building passes from the transfer or
resonance area to the isolation area. Due to that phenomenon, a
reduction of the building seismic response by 2-4- times as to
the situation in which, dynamically, the building remains in
resonance with the seismic action, is occurring. The reduction
depends on the distance from the resonance area due to the
increase of the vibration period. In this case, Direction 2 is
equivalent to the building seismic isolation (alternative 5). In
fact, the damage is leading to a self - isolation of the building
against the seismic movement. This method was developed in
Japan and U.S.A. where most of the recorded earthquakes have
the dominant repetition period of the ground movement below
0.5 seconds. Alternative 2 of seismic qualification with platic
hinges may be successfully applied to “fast” and “moderate”
earthquakes, which is the case of the most earthquakes in the
world.
Case 2b – the building enters or stays in the resonance range
due to damaging. By the increase of the building eagen
vibration period due to damaging, the building passes to the
resonance range and it cannot shift out because the relative
level displacements are increasing so much that the building is
destroyed before entering the isolation area. This case may be
frequently met with “slow” earthquakes whose dominant
repetition period of the ground movement is greater than 1
second or even with moderate earthquakes, function of the type
of the building. The relative level displacement of the building
that needs to increase very much so to reach the condition in
which the damaged building eagen vibration period may be
greater than the dominant period of the seismic movement,
cannot be obtained. If the damaged building cannot reach an
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Copyright © 2008 by ASME
oscillation period greater than the repetition period of the
seismic movement, the phenomenon to reduce the seismic
response cannot occur and thus, the seismic energy built-up in
the half-damaged building is occurring with the amplification
of the seismic response rather than the reduction of the seismic
response , because the energy dissipation due to the increase of
damping, cannot compensate the energy built-up in the
oscillating system which is not shifted out of the resonance
range of the seismic movement.
By the reduction of the building assembly stiffness and the
increase of the eagen vibration period, case 2 b is similar with
alternative 5 only if the damaged building eagen vibration
period exceeds (preferably 3 times so that the effect be
significant) the dominant repetition period of the seismic
movement (period may be considered Tc of the ground
response spectrum if other information is not available). For
“fast” earthquakes this phenomenon is usually occurring
without reaching an advanced damaged condition of the
building, condition which might jeopardize the building safety.
With “slow” earthquakes at which TC > 1 second the increase of
the damaged building eagen vibration period so that
dynamically the building may reach the isolation area, T>3T C ≥
3 seconds, is practically impossible because the relative level
distortions should
increase 10 times as to the values
corresponding to the elastic behavior
of the building,
distortions which usually cannot be achieved in case of slow
earthquakes and also maintaining the building stability.
Alternative 3 - the control, limitation and damping of
relative level displacements by hydraulic dampers or
mechanical devices with damage (modern solution).
In this case, dynamically the building may be within the
ground response spectra range. The effect is maximum for the
resonance range and the transfer ranges near-by the resonance
range. In the isolation range, the increase of damping leads to
the increase of the building response in accelerations if the
building is situated in the resonance and transfer range. In the
transfer range, the damping has no effect on the building
seismic response.
With this alternative (compared with alternative 1) there is
a reduction of the seismic response of the building structure due
to the controlled dissipation of a large quantity of seismic
energy built-up in the building-ground oscillating system by the
hydraulic dampers or the mechanical devices with damage.
The building structure need to stay in the elastic behavior
range for an efficient control of its behavior. If the building
shifts to the plastic stress range, the hydraulic dampers or the
mechanical devices with damage, might have a negative effect
on the building safety because the forces developed in the
devices oppose the revert of the building to the un-distorted
position. In this case, the cooperation between the dampers
with the building is altered.
Specially after the earthquake in Kobe in 1995 when
many buildings which were designed according to alternative 2
with plastic hinges, were destroyed, in Japan, a change in the
seismic design happened, in the sense that the occurrence of
plastic hinges is no longer acceptable and an increase of the
building damping capacity is obtained by the insertion of
specialized mechanical devices in braces (alternative 3).
Alternative 4 – the control, limitation and damping of
relative level displacements by telescopic devices with
non-linear strengthening and large damping (modern
solution).
In this case, dynamically, the building may situate in all
the areas of the ground response spectrum. Additionally,
compared to alternative 3 , for buildings one may allow a slight
exceeding in the non-linear range of behavior.
This alternative is different from alternative 3 because the
place of the hydraulic dampers or mechanical devices with
damage in braces, telescopic devices with high strengthening
and damping are installed. As per this alternative 4 one may
control the relative level displacements of the building and limit
these displacements to pre-set values because of the elastic nonlinear forces developed in the telescopic strengthening devices.
The telescopic devices provide a great dissipation of the
seismic energy including the case of very small relative level
displacements. The telescopic devices have a force-distortion
characteristic – hysteresis type - with strengthening in order to
limit the relative level displacements to pre-set values. The
devices are capsulated and pre-tightened in their boxes in order
to provide a satisfactory operation with the building structure
on any load level without introducing additional forces in the
building due to prestressing, also eliminating the effects of
shocks.
As per this alternative 4 the seismic behavior of the
building is controlled by elastic forces and by the damping
developed in the telescopic devices providing thus both the
reduction of the seismic response and the reduction of the
building relative level displacements to pre-set values. The
exceeding of the elastic limit of the building structural material
may be allowed because the elastic forced developed in the
mechanical devices are capable to make the building revert to
its undistorted position. The amplification of the seismic
accelerations, according to this alternative 4, is smaller than
with alternative 3 reducing thus the maximum seismic
accelerations in the building by about 2-3 times than with
alternative 1.
Alternative 5 - seismic isolation of the building by
oscillating devices (novative solution).
In this case, dynamically the building may situated only in
the isolation range of the ground response spectrum.
The seismic qualification of the building is so done that
the seismic action given by the ground movement is partially
transferred to the building and the building-isolator oscillating
system is building-up a small quantity of seismic energy. With
this alternative the building structure is divided in 2 parts: the
infrastructure which is embedded in the ground, on which the
oscillating devices are installed; and the supra-structure
installed on the oscillating isolation devices. The seismic
energy associated to the ground oscillating cycles is transferred
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Copyright © 2008 by ASME
in a small percentage to the isolated supra-structure and the
oscillating system made-up of the supra-structure and the
isolation devices build-up a small quantity of seismic energy
from the infra-structure seismic movement, function of the
magnitude of the ratio between the building eagen vibration
period and the dominant from the seismic movement and
function of the isolation system dissipation capacity.
For the system to satisfy the safety requirements for
buildings and of isolation for the seismic action transferred to
the building, the system has to be stiff on vertical and flexible
on any horizontal direction. The separation surface between the
infra-structure and the supra-structure has to remain plane and
untilted (horizontal) on permanent loads imposed by the suprastructure and the random loads, including the loads due to
seismic events. In case that an isolation device gets distorted
more (or even yield), a large concentration of stress may occur
in the supra-structure and lead to local damage or loss of its
stability.
With oscillating type isolation systems the isolation
device need to have a very small stiffness on horizontal so that
the first eagen vibration period of the supra-structure supported
on the isolation devices may be much greater (preferably over
3 times) than the dominant repetition period of the seismic
movement (period Tc of the ground response spectrum if no
information is available) and than the first eagen vibration
period of the supra-structure considered to be embedded at the
level of the isolation surface. It is only this situation when the
seismic energy build-up in the oscillating system made-up of
the supra-structure and the isolation system is small and a small
amplification of the seismic acceleration and of the relative
displacements between the infrastructure and the suprastructure is resulting.
Since with the oscillating isolation systems the suprastructure relative movement is anti-phase as to the ground
seismic movement (the infrastructure translation movement),
than in order to limit the relative displacements between the
infrastructure and the supra-structure (relative displacement
governing the isolation system safety) within the oscillating
isolation system, an additional damping (usually by means of
hydraulic devices installed horizontally between the
infrastructure and the supra-structure) is installed.
The increase of the oscillating isolation system damping
capacity will also lead to the increase of the seismic
accelerations transferred to the supra-structure and to the
increase of the seismic loads. For that reason a damping of
maximum 30% (of the critical fraction at the first two vibration
modes of the supra-structure) is recommended [1, 3].
Moreover, for the seismic isolation devices be also applied
to tall buildings where during an earthquake or wind loads a
turn-up moment greater than the stability moment (given by the
building self-weight) may occur, at the surface of separation
between the infrastructure and the supra-structure the isolation
devices should also overtake the tensile forces in order to
provide the isolated supra-structure stability against turning-up.
The existing oscillating isolation systems do not provide the
overtaking of some tensile forces in order to assure the building
stability.
Alternative 6 – building seismic isolation by nonoscillating devices (novative solution).
In this case, dynamically, the building is situated on the
right of the isolation area (the eagen vibration period is infinite
because the building supra-structure is not oscillating and it is
semi-borne by the infrastructure).
Alternative 6 is different from alternative 5 due to the fact
that the isolation devices do not develop elastic forces on
horizontal and do not built-up a potential energy for a relative
displacement pre-set around the position of balance (relative
displacement which depends on the kinetic characteristics of
the seismic movement, i.e. the maximum ground seismic
movement). In order to limit the maximum horizontal
displacements (accidental) of the supra-structure versus the
infrastructure and the elimination of some possible shock
effects, the non-oscillating isolation system has to develop a
non-elastic force after having consumed the relative
displacement pre-set around the position of balance.
The non-oscillating isolation devices can achieve a gliding
movement with small friction around the position of balance in
the pre-set range of values. Within that interval the isolated
supra-structure is no longer developing an oscillation
movement during an earthquake because there is not the
possibility of a potential energy built-up in the system. The
supra-structure shall be “semi-borne” around the position of
balance, by the infra-structure which is embedded in the
ground, with displacements smaller than the ground seismic
displacements. By gliding the isolation system is actually
totally “cutting-off” the transfer of the seismic action from the
infra-structure borne by the ground, to the building suprastructure. The supra-structure with the isolation system is no
longer making-up an oscillating system which is building-up
the kinetic and potential energy which generate an
amplification of the seismic movement in accelerations and
displacements (like the case of alternative 1-5).
The relative seismic displacement between the suprastructure isolated with the non-oscillating systems (alternative
6) and the infra-structure embedded in the ground is much
smaller than in the case of employing the oscillating isolation
systems (alternative 5) and also smaller than the maximum
ground seismic displacement.
The seismic acceleration
transferred to the isolated supra-structure in fractions of
gravitational acceleration,”g”, is equal to the friction-gliding
rate,”μ”, of the non-oscillating isolation devices. For that
reason it is desirable to have a relative small friction rate which
could assure the required stability of the supra-structure and
also allow a slight displacement between the infra-structure and
the supra-structure, with very small accelerations.
The
minimum rates for gliding that can be reached today without
“rolling” or with active friction control systems, are
encompassed between 0.03 – 0.05, which lead to a maximum
supra-structure acceleration of 0.05 g. In case of using some
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Copyright © 2008 by ASME
ball gliding systems (rolling), the friction ratie is reduced to
values below 0.01, which is not sufficient to provide a stability
of the isolated supra-structure.
In order to provide the stability of the supra-structure, the
isolation systems have to achieve a shock-free limitation of the
accidental displacements between the supra-structure and the
infra-structure. For that reason the ideal solution is that after a
pre-set relative displacement, in which non-oscillating seismic
movements are developing and in which the force-distortion
characteristic is horizontal (no increase of the force with the
increase of displacement occurs), the isolation system may
achieve a non-linear increase of the force with the displacement
in order to shock-free limit the possible accidental
displacements.
Compared with the oscillating isolation system, with the
non-oscillating isolation system with friction-gliding there is no
danger if the insulator yielding because the components are
subjected to very low shear forces(loads) and the yielding of
the contact parts due to compression cannot occur because of
the specific geometry of the isolators.
By now, 3 types of non-oscillating systems have been
developed in this domain.
Type 1 - The isolation system developed in Japan consists
of a PTF end anchored in a steel and rubber structure is gliding
on a horizontal stainless steel plate. The system cannot limit
the relative displacement between the supra-structure and the
infra-structure to pre-set values and neither is it capable to
overtake tensile forces. For that reason the isolation system can
be used only by installing (in parallel) some elastic devices and
of damping devices installed between the infra-structure and
the supra-structure, and which are arranged in the horizontal
separation plane. In the literature, the system is referred to as
“Flat surface slider with dampers”. The system was applied in
Japan and Italy, e.g. NATO HEADQUARTERS in Napoli in
2007 -2008.
Type 2 - The isolation system developed by THK
company in Japan starting with 1996, is a system according to
which the movement in horizontal plane is produced by the
combination of two perpendicular movements produced on
profiled bars and balls. The system, called “Linear Motion
guide with Caged Ball”, has a <0.01 friction rate which may
provide a seismic acceleration transferred to the suprastructure, smaller than 0.01g. Since the system does not
provide stability upon small horizontal actions and a minimum
force for reverting to the initial position, it can be used only by
the in-parallel installation of some oscillating isolators in the
ratio of (2/3 THK) / (1“Elastomeric isolators”). By this
combination, THK non-oscillating isolation system is
practically transformed into an oscillating isolation system with
large vibration period. In point of safety, the system may yield
at great accidental loads due to the fact that the displacement in
two perpendicular directions generate the occurrence of some
great moments in the guiding-sliding system and the oscillating
isolators may yield.
Type 3 - SERB type non-oscillating isolation system
developed in Romania starting with the year 2000, is a
capsulated system with non-linear limitation of the relative
displacements in the isolation surface , to a pre-set value, after
performing a pre-set relative displacement. For this type of
isolation system it is no longer mandatory to install horizontal
mechanical devices to control. Limit and damp the relative
displacements between the infra-structure and the suprastructure because the limitation is achieved inside the isolation
device as per a pre-set law. With SERB devices the relative
movement in horizontal plane is produced by gliding with small
friction between several surfaces which operate in parallel and
are located in two stiff semi-bodies, with the possibility of a
controlled relative displacement among them. On horizontal
direction the devices have hysteresis characteristic parallel with
the displacement axes upto a pre-set value and next a non-linear
elastic increase of the force is occurring in order to avoid
shocks at large accidental displacements. With these SERB
devices there is not the possibility to lose the isolation capacity,
or to yield or get destroyed. On vertical direction, SERB
device has a stiff behavior, small distortions (1-2 mm) also
having a hysteresis loop. SERB isolation devices can also
overtake tensile loads upto 60% of the maximum compression
load.
The maximum acceleration of a building supra-structure
isolated by non-oscillating isolation devices, SERB type, is
maximum 0.05g and the maximum relative seismic
displacement between the infra-structure and the suprastructure is smaller than the maximum seismic displacement of
the ground and of about 3 times smaller than the relative
displacement of the oscillating isolation systems (alternative 5).
SERB devices are the only devices existing today, which
can provide the desired correlation between the maximum
acceleration transferred to the structure and the maximum
relative displacement between the infra-structure and the suprastructure so that an advanced isolation of the supra-structure is
assured without overloading the technological connections
between the infra-structure and the supra-structure.
By now this alternative was applied in Romania. Starting
with 2003, semi-oscillating and non-oscillating isolation
systems which were applied to some heavy equipment have
been developed [7, 9, 10]. Case studies including nuclear
objectives have also been developed [8]. There were also
achievements in the production of 1:1 scale building isolation
devices and they were experimentally tested with the most
developed installations in Romania. The experimental results
are the closest to the ideal isolation solution in the sense that
the hysteresis diagrams show a constant force transferred to the
isolated supra-structure equivalent to a 0.03g seismic
acceleration for a pre-set displacement range, followed by a
non-linear increase with a big hysteresis loop.
3.
ANALYSIS ON THE ENERGY TRANSFER FROM
THE SEISMIC MOVEMENT TO THE BUILDING
AND ITS BUILDING-UP IN THE BUILDING
In order to substantiate the seismic qualification
alternatives, function of the dynamic characteristics of the
buildings and of the seismic action kinetics (expressed by the
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Copyright © 2008 by ASME
Variation of Kinetic and Potential energy am plitude versus period ratio.
Critical dam ping ratio = 20%
ratio between the building dominant vibration period and the
dominant period in the seismic movement T/Ts), Figs 3.1 - 3.4
illustrate the variations of the amplitude and power transferred
from the excitation to the oscillating system Pe and of the
power dissipated by the oscillating system Pa, as well as the
variation of the kinetic energy amplitude Ekin and potential
energy Wpot built-up in the oscillating system versus the
amplitude of the power and excitation energy for a mass unit of
the oscillating system, for a 5% and 20% damping of the
Variation of Damping and Seismic ground power amplitude.
oscillating system
[…].
versus period ratio. Critical damping ratio = 5%
Pd
Ekin
Wpot
Kinetic / potential energy
1000
100
ratio  1.56
10
1
0.1
0.01
ratio  0.65
0.001
0.1
ratio  2
1
10
ratio = T/Ts
Pe
Damping and Seismic ground power
100
Fig. 3.4. amplitude of power transferred from the excitation, to the
oscillating system and the power dissipated in the system versus the
10
1
excitation amplitude function of
T Ts ,   20%
0.1
0.01
0.001
0.01
0.1
1
10
100
ratio = T/Ts
Fig. 3.1. Amplitude of power transferred from the excitation, to the
oscillating system and the power dissipated in the system versus the
excitation power function of
T Ts ,   5 %
Variation of Kinetic and Potential energy amplitude versus period ratio.
Critical damping ratio = 5%
Ekin
Wpot
Analyzing the diagrams, it results that the most efficient
solution for the building protection against seismic events is the
building isolation by non-oscillating systems (infinite vibration
period). In this case, the acceleration of the isolated suprastructure is limited to the value of the isolation device friction
rate and the relative displacement between the isolated suprastructure and the infra-structure embedded in the ground, is
smaller than the maximum ground displacement.
Kinetic and Potential energy
1000
4.
100
Ratio = 0.61
10
1
Ratio = 0.63
0.1
Ratio = √2
0.01
0.001
0.1
1
10
ratio = T/Ts
Fig. 3.2. Amplitude of power transferred from the excitation, to the
oscillating system and the power dissipated in the system versus the
excitation amplitude function of
T TS ,   5%
Variation of Damping and Seismic ground power amplitude versus period
ratio. Critical damping ratio = 20%
Pd
Pe
Damping and Seismic ground power
100
10
1
0.1
0.01
0.001
0.01
SEISMIC ISOLATION OF THE DETRITIATION
BUILDING ON CERNAVODA N.P.P. SITE
0.1
1
10
100
ratio = T/Ts
Fig. 3.3. amplitude of power transferred from the excitation, to
the oscillating system and the power dissipated in the system
versus the excitation power function of T Ts ,   20%
CTRF Building on Carnavoda N.P.P. site is situated within
Unit 1 enclosure, in the vicinity of HPECC Building and D 2O
Tower Building. The building infra-structure is sectioned at 5
cm above the arranged ground at El. + 15.80 dnMB. That is the
elevation where the gliding plane between the ground
embedded infra-structure and the supra-structure isolated by 28
non-oscillating SERB 960x960x220 devices ( see Fig 4.1.) are
located and can overtake a compression load of 3000 KN and
tensile load of 1800 KN.
The sealing between the ground embedded infra-structure
and the isolated supra-structure is made by an elastic-gliding
system – SERB 300x15xX type – which provides the
satisfaction of sealing requirements in any condition.
The maximum seismic acceleration transferred to the
isolated supra-structure on horizontal is 0.05g and equal at all
the building elevations because the supra-structure installed on
SERB isolation devices are behaving like a stiff body. The
maximum seismic displacement between the ground embedded
infra-structure and the isolated supra-structure is estimated at
about 60 mm, as per the preliminary analyses. This result shall
be verified by experimental testing conducted with a 1:1 scale
isolation device in installation conditions identical with the
conditions on site.
The isolation devices can overtake 3000 KN compression
loads and 1500 KN tensile loads.
Figs. 4.2. – 4.4. illustrate the experimental determinations
and the obtained results with a SERB prototype loaded on a
7
Copyright © 2008 by ASME
minim 15m inaltime
JIKA rig and for which the maximum possible displacement on
horizontal is 160 mm.
Analyzing the hysteresis diagrams it results that on
horizontal direction, SERB devices do not build-up potential
energy for a pre-set relative displacement because they have a
constant hysteresis followed by a non-linear increase with the
displacement and a large energy dissipation on the hysteresis
loop.
On vertical, SERB devices are practically stiff but with
damping capacity
+28,0
Detail
B
-0,01
SERB
isollation
devices
1100
459
25
10
55
-0,596
Incinta pentru ventilatoare si putul de
montaj al tubulaturii de legatura
1000
596
541
500
325
200
+24,50
400
-0,956
+20,0
300
4500
700
700
700
300
300
3500
400
200
350
Et 4
+15,50
700
Et 3
Detail
A
SERB
sealing
devices
700
300
350
300
200
+12,0
4000
200
-0,01
400
Et 2
500
200
+8,00
300
400
4000
-0,956
Et 1
300
4000
200
+4,00
Parter
325
325
400
-0,956
440
400
20
=
=
400
20
B
700
400
Ø37
65
225
3500
800
220
4500
A
225
400
300
700
440
541
-0,596
10
459
596
200
-0,01
-0,596
-0,956
=
-4,550
65
=
220
225
65
500
800
4700
4700
4900
A
225
B
C
4700
D
Detail - fixing column
4900
E
F
Fig. 4.1. Cross –section view of the Detritiation Installation Building
Fig. 4.2. Non-oscillating capsulated SERB isolation device 960 x 960
x 230 prototype
Fig. 4.3. Non-oscillating capsulated SERB isolation device 960 x 960
x 230 prototype. The experimental hysteresis horizontal load diagram
for +/- 150 mm. Preload 1200KN and 1800KN
REFERENCES
[1] Rapoarte de calificare seismica AECL, pentru Cladirea
reactorului, Cladirea serviciilor si cladirile auxiliare
nucleare;
[2] Cod de proiectare seismica – Partea I – Prevederi de
proiectare pentru cladiri, indicativ P100/2006;
[3] Japanese retrofitting technologies for buildings – Base
isolation and/or Damping devices – Application example
of Un-Bond Brace – Prof. Akira Wada – Tokyo Institute of
Technology; Dr.Hideaki Kitajima – Japon Structural
Consultants Association; Mr. Takashi Kaminosono – JICA
Expert; Dr.Izuru Okawa – Building Research Institute,
Tsukuba – Technical University of Civel Engineering of
Bucharest - February 2005;
[4] Changes of Seismic Design
in Japon after Kobe
Earthquake - Prof. Akira Wada – Tokyo Institute of
Technology - Report;
[5] “Consolidare, extindere si reamenajare corp B din
complexul administrativ NAVROM in solutia SERBSITON de control, limitare si amortizare a miscarilor
seismice” premiul AGIR 2007 – Lucrare SITON – Iunie
2007;
[6] Rubber bearing – Catalog FIP INDUSTRIAL UK LTD PO
BOX 504 Cambridge CB1 OAP – UK;
[7] An efficient shock isolation system for forging
hammer, Second International Conference of Romanian
Society of Acoustics on Sound and Vibration, 14 – 17
October 2004 – Bucuresti Romania;
[8] Solutia SERB-SITON de izolare seismica a unei centrale
nuclearo-electrice de tip CANDU PHWR 700 si ACR
1000” Forumul regional al energiei – FOREN 2008,
Neptun, Romania, 15-19 iunie 2008.
[9] SERB devices for the mitigation of seismic action –
V.Serban, M.Androne, G.A.Ciocan, Technical Scientific
International Symposium on “Modern System for
mitigation of seismic action” - Friday, 2008 – October, 31AGIR – Bucuresti – Romania;
[10] Mechanical devices to control, limit and attenuate shocks,
vibrations and seismic movements in buildings, equipment
and piping networks” “SUSI – 2008 - Tenth International
Conference on Structures Under Shock and Impact”
ALGARVE – PORTUGALIA, 13 – 17.05. 2008;
[11] Design Guidelines – Base Isolation of Structures – Trevor
E. Kelly, S.E. Holmes Consulting Group Ltd;
[12] European Standard. Anti-seismic devices. CEN/TC 340
Date 2008-05 prEN 1529:2008;
[13] Eurocode 8: Design of structures for earthquake resistance.
Part 1: General rules, seismic actions and rules for
buildings. Doc CEN/TC250/SC8/N335 – January 2003;
[14] THK Base Isolation Catalog – Technical Book – Catalog
No.A-02-E.
Fig.4.4. Non-oscillating capsulated SERB isolation device 960 x 960 x
230 prototype. The experimental hysteresis vertical load diagram.
Preload 600KN
8
Copyright © 2008 by ASME