This document discusses seismic behavior of short period structures with diagonal dampers. It examines the relationship between force modification factor and global ductility demand for short period structures with dampers. Dampers with high damping ratios can keep structural response in the elastic range even for high force reductions. The document reviews several studies on the effect of dampers on seismic demand of short period structures founded on different soil types, including rock, soft soil, and deep cohesionless soil. The studies found that dampers can reduce ductility demand and bring short period structural behavior closer to that of long period structures. Seismic codes should account for differences between short and long period structures.

1. 1.Introduction
Seismic behavior of a single bay frame with diagonal damper that represents
short period structures is evaluated in response to the excitation of a set of earthquake
records. The frame system is modeled as a Single Degree of Freedom SDOF system, and is
earthquake records representative of the range of dominant site conditions. The relationship
between the force modification factor and the global ductility demand for short period
structures, in the presence of dampers, tends to approach those of long period ones. Dampers
with high damping ratios tend to keep the structural response in the elastic range even for
high values of force reductions. Seismic code provisions should be revised to account for
short period effect under seismic excitation.
Earthquake-resistant structures are generally designed with strength much less
than their elastic strength demand due to earthquake excitation According to modern seismic
codes, typically well-detailed structures may be designed with strength capacity as low as
12% of their elastic strength demand. This reduction in strength demand is possible due to
many factors such as ductility, energy dissipation and frequency shift. In general, such
strength reduction imposes special demand on structures in terms of detailing to achieve
specified levels of ductility and energy dissipation which are function of the specified levels
of strength reduction.
Seismic codes, in general, utilize parameters such as force modification
factor, R, and global ductility demand, μd, to implicitly account for strength reductions. Force
modification factor is defined as the ratio of elastic strength demand to actual yield force of
the structure, whereas, global ductility demand is defined as the maximum inelastic
displacement under seismic excitation to the actual yield displacement of the structure.
However, the codes do not explicitly address the damping of structures which is an indication
of the energy dissipation capacity of the structure. Furthermore, codes do not distinguish
between short period and long period structures in their treatment of strength and ductility
requirements for the design of earthquake-resistant structures. Many research results on
seismic demand indicate that even though ductility demand is feasible for long period
structures (tall buildings), they impose high levels of ductility for short period structures
which may not be achievable (Nassar and Krawinkler, 1991). Furthermore, research results
also indicate that ductility demand is very sensitive to strength reduction for short period
structures. Consequently, short period structures should rely on factors other than ductility to
achieve strength reduction such as energy dissipation. Therefore, this study focuses on

2. examining the effect of explicit damping on ductility demand on one hand, and on the
feasibility of dampers as an alternative to ductility requirements for short period structures on
the other.Thus evaluation of influence of structural parameters, characteristics of earthquake
records and soil conditions on input energy are important.

3. 2.Literature review
2.1 Nazzal S. Armouti [2011]
Effect of Dampers on Seismic Demand of Short Period Structures in Rock Sites In view of
the extreme randomness of earthquake characteristics and the reflection of this randomness
on the response of structures, and since both short period structures and earthquakes in rock
sites vibrate in the high frequency range, this study focuses on the response of structures
founded on rock sites. The obtained results in this paper indicate, in statistical sense, that the
response of short period structures founded on rock to earthquakes after yielding is in fact
less sensitive and less demanding than the case of response to earthquakes under general site
conditions. In addition, they indicate that the dampers with damping ratios up to 20% of
critical damping tend to reduce the ductility demand consistently with the period values.
However, dampers with higher critical damping (more than 20%) seem to bring the behavior
of short period structures to levels of the behavior of long period ones. Even more, they show
that higher damping improves the behavior of short period structures to levels that are
feasibly achievable in practice. It has also been found that the higher the damping presence in
the structure, the higher will be the presence of elastic behavior of the structure at even higher
values of force reduction. It can be concluded that, even though, response of short period
structures founded on rock sites is less demanding than that of short period structures founded
in general site conditions. Structures with short periods should still be carefully designed
taking into consideration additional measures other than ductility to include some acceptable
levels of safety. Furthermore, as this issue is overlooked in seismic codes, the codes thought
to revisit the concept of force reduction and distinguish between long period structures and
short period structures. Short period structures may need additional provisions to provide
them with enough safety measures.
2.2Nazzal S. Armouti [2013]
Effect of Dampers on Seismic Demand of Short Period Structures in soft Site In view of the
extreme randomness of earthquake characteristics and the reflection of this randomness on
the response of structures, and since short period structures and earthquakes in soft sites
vibrate on the opposite sides of the frequency range; this study focuses on the response of
structures founded on soft sites. The obtained results in this paper indicate, in statistical
sense, that the response of short period structures founded on soft soil to earthquakes after
yielding is in fact more sensitive and more demanding than the case of response to

4. earthquakes under general site conditions. In addition, they indicate that the dampers with
damping ratios up to 20% of critical damping tend to be more critical than the case of general
site conditions with dampers. Except of period of 0.1, dampers with higher critical damping
than 20% seem to bring the behavior of short period structures to levels of the behavior of
long period ones. Even more, they show that the higher damping improves the behavior of
short period structures to levels that are feasibly achievable in practice. It has also been found
that the higher the damping presence in the structure, the higher will be the presence of
elastic behavior of the structure at even higher values of force reduction.
The study also indicates that dampers have little effect on the behavior of
structures with period of 0.1 sec, therefore, structures of period of 0.1 sec needs measures to
elongate the period rather than increase damping, for example, seismic isolation systems. It
can be concluded that response o short period structures founded on soft sites is more
demanding than the response of short period structures founded on general site conditions,
which emphasizes that structures with short periods founded on soft soil need even more
attention to be carefully designed taking into consideration additional measures other than
ductility to include some acceptable levels of safety. Furthermore, as this issue is overlooked
in seismic codes, the codes ought to revisit the concept of force reduction and distinguish
between long period structures and short period structures. Short period structures may need
additional provisions to provide them with enough safety measures.
2.3Nazzal S. Armouti [2011]
Effect of Dampers on Seismic Demand of Short Period Structures in deep cohesion less Sites
In view of the extreme randomness of earthquake characteristics and the reflection of this
randomness on the response of structures, and in order to explore the deviation of the
behavior of
short period structures founded on specific site conditions from those founded on the general
site
conditions, this study focuses on the response of structures founded on deep cohesion less
sites. The obtained results in this study indicate, in statistical sense, that the response of short
period
structures founded on deep cohesion less soil to earthquakes after yielding is in fact close but
less
sensitive and less demanding than the case of response to earthquakes under general site
conditions. Except of periods of 0.1 second, dampers with higher critical damping than 20%

5. seem to bring the behavior of short period structures to levels of the behavior of long period
ones. Even more, they show that higher damping improves the behavior of short period
structures to levels that are feasibly achievable in practice. It has also been found that the
higher the damping presence in the structure, the higher will be the presence of elastic
behavior of the structure at even higher values of force reduction. This study also indicates
that dampers have little effect on the behavior of structures with period of 0.1 second,
therefore, structures of period of 0.1 second need measures to elongate the period rather than
increasing damping, for example, seismic isolation systems. It can be concluded that response
of short period structures founded on deep cohesionless sites is close, but less demanding
than the response of short period structures founded on general site conditions, which
emphasizes that structures with short periods founded on deep cohesion less soil still need
attention to be carefully designed taking into consideration additional measures other than
ductility to include some acceptable levels of safety.

6. 3.Soil Structure Interaction
As waves from an earthquake reach a structure, they produce motions in the
structure itself. These motions depend on the structure’s vibration characteristics and the
building or structural layout. For the structure to react to the motion, it needs to overcome its
own inertia, which results in an interaction between the structure and the soil. The extent to
which the structural response may alter the characteristics of earthquake motions observed at
the foundation level depends on the relative mass and stiffness properties of the soil and the
structure. Thus the physical property of the foundation medium is an important factor in the
earthquake response of structures supported on it. There are two aspects of building
foundation interaction during earthquakes, which are of primary importance to earthquake
engineering. First, the response to earthquake motion of a structure founded on a deformable
soil can be significantly different from that would occur if the structure is supported on a
rigid foundation. Second, the motion recorded at the base of a structure or in the immediate
vicinity can be different from that which would have been recorded had there been no
building. Observations of the response of the buildings during earthquakes have shown that
the response of typical structures can be markedly influenced by the soil properties if the soils
are sufficiently soft. Furthermore, for relatively rigid structures such as nuclear reactor
containment structures, interaction effects can be important even for relatively firm soils
because the important parameter apparently is not the stiffness of the soil, but the relative
stiffness of the building and its foundation. In terms of the dynamic properties of building
120 N. Anand, C. Mightraj and G. Prince Arulraj foundation system, past studies have shown
that the interaction will, in general, reduce the fundamental frequency of the system from that
of the structure on a rigid base, dissipate part of vibrational energy of the building by wave
radiation into the foundation medium and modify the base motion of the structure in
comparison to the freefield motion. Although all these effects may be present in some degree
for every structure, the important point is to establish under what conditions the effects are of
practical significance.

7. 4.STRUCTURAL MODEL
The structural model is selected as a frame having four nodes 1 through 4 as
shown in Fig. 1. The frame consists of one bay frame fixed at both supports which is
considered typical of low rise steel buildings, hangars, and storage facilities. The frame is
provided with explicit diagonal viscous damper with coefficient of damping, C, between
nodes 2 and 4. The frame may be modeled as a Generalized
Fig. 1: Frame layout Fig. 2: Lumped mass as GSDOF
Fig. 3: Generalized damping due to velocity, u
Single Degree of Freedom, GSDOF, system by assuming the total mass to be lumped at one
node, node2, as shown in Fig. 2. The generalized degree of freedom in this case is the mass
displacement in the direction of, u, at node 2. The generalized resistance of the frame without
the damper is obtained due to an induced displacement of the mass in direction, u, as a
generalized spring force, FS *, whereas the component of the reactive force of the damper in
the direction of displacement, u, is obtained due to induced velocity in the direction of, u, as
the generalized damping force,FD.
In case of elastic analysis, the generalized stiffness,k*, is simply evaluated by
subjecting the frame to a unit displacement in direction of u, which can be easily obtained by
any structural analysis software. The generalized coefficient of damping C*, can be obtained
as function of the damper coefficient of damping C,with reference to Fig. 3 as follows: Since
damper velocity is
Fig. 4: Generalized SDOF

8. Fig. 5: Distribution of power spectral density of earthquakes according to their site
conditions
uD = u cos θ
The force in the damper is given as:
FD = C.uD = C.cos θu
The generalized force of the damper in the direction of,
u, becomes:
FD = FD cos θ = C.cos2 θu = C* u
Therefore, the generalized damping becomes:
C*= C.cos2 θ
The frame system, therefore, can be represented by a system with a generalized single
dynamic degree of freedom consists of a lumped mass subjected to a generalized forces and
displacements as shown in Fig. 4. The equation of motion in this case takes the form:
FI*+ FD*+ FS* = -m*ug
In case of elastic analysis:
m* u’’+ C* u’ + k* u = -m*ug
u’+ 2 ζ ωu’ + ω2 u = - ug
where,
u = Generalized displacement
u’ = Generalized velocity
u’’ = Generalized acceleration
u’’g = Ground acceleration (earthquake)
m* = Generalized mass
FI* = Generalized inertial force
C* = Generalized coefficient of damping
FD* = Generalized damping force
k* = Generalized stiffness
FS* = Generalized spring force

9. ω = Frequency of the generalized system
ζ = Damping of the generalized system
Since the parametric study uses predefined values of period and damping ratios, the exact
values of these parameters, in this study, become immaterial. Therefore, the values of the
mass, stiffness, damping, and level of ground motion are adjusted to produce the intended
parameter values of the study. Consequently, the force reduction factor R, is defined as the
ratio of the elastic strength demand of the structure Fe, to the actual yield strength Fy,
whereas global ductility demand μd, is defined as the ratio of the maximum displacement that
is reached during the excitation history umax, to the actual yield displacement of the structure
uy. These ratios are given in mathematical form as follows:

10. 5.Effect of sesmic demand on Rock site,Medium soil site ,soft soil analysis in Stadd pro
as per IS 1893-2002/2005
City:Aurangabad, Damping ratio- 1
Dimention Node no
Plan view
• In Hard rock displacement detail of node in X,Y,Z direction

11. • Mediam soil displacement detail of node in X,Y,Z direction
• Soft soil displacement detail of node in X,Y,Z direction

12. 6.Case study
Crystal Tower (Nagase and Hisatoku, 1990) The tower, located in Osaka,
Japan, is 157 m high and 28 m by 67 m in plan, weighs 44000 metric tons, and has a
fundamental period of approximately 4 s in the north south direction and 3 s in the east-west
direction. A tuned pendulum mass damper was included in the early phase of the design to
decrease the wind-induced motion of the building by about 50%. Six of the nine air cooling
and heating ice thermal storage tanks (each weighing 90 tons) are hung from the top roof
girders and used as a pendulum mass. Four tanks have a pendulum length of 4 m and slide in
the north-south direction; the other two tanks have a pendulum length of about 3 m and slide
in the east-west direction. Oil dampers connected to the pendulums dissipate the pendulum
energy. Figure 4.10 shows the layout of the ice storage tanks that were used as damper
masses. Views of the actual building and one of the tanks are presented The cost of this tuned
mass damper system was around $350,000, less than 0.2% of the construction cost. Tuned
Mass Damper

13. 7.Type Of Damper
Dampers are classified based on their performance of friction, metal (flowing),
viscous, viscoelastic; shape memory alloys (SMA) and mass dampers. Among the advantages
of using dampers we can infer to high energy absorbance, easy to install and replace them as
well as coordination to other structure members.
7.1 Friction Dampers- In this type of damper, seismic energy is spent in overcoming friction
in the contact surfaces. Among other features of these dampers can be classified as avoiding
fatigue in served loads and their performance independent to loading velocity and ambient
temperature. These dampers are installed in parallel to bracing

14. 7.2 Penguin Vibration Damper - It is another type of friction damper and due to ease to
installation, is one of the most widely used damper in structures ( Warn,2004). PVD damper
can be used to create necessary damping for flexible structures, such as bending steel frame
or to provide effective damping to relative stiffness of structures (Naeim,1995). PVD damper
is designed to installation where displacement can generate necessary damping such as
installation of metal skeleton brace or concrete moment frame.
1. PVD damper acts effectively on low displacements. For example, one 1MN PVD
damper can acts effectively for 0.5 mm to 5 mm displacement.
2. PVD damper requires no maintenance and does not have any lubrication or winder
components.
3. PVD damper behavior is like the behavior of a metal damper
7.3 Pall Friction Damper- This damper includes a bracing and some steel plate with
friction screws. And they should be installed in the middle of bracing. Steel sheets are
connected to each other by high strength bolts and they have a slip by a certain force, to
each other

15. 7.4 Metallic Dampers In this damper, transferred energy to the structure is spent to
submission and non-linear behavior in used element in damper. In these dampers, metal
inelastic deformation is used such as for formability metals such as steel and lead for energy
dissipation. In all conventional structures, energy dissipation is based on deformation of steel
members after the submission
In braces, using submission metallic dampers is more common. These dampers are often
created by some parallel steel plates. And in combination with a bracing system, they
undertake the role of absorption and energy dissipation. This part of bracing can acts as a fuse
in structure. And by focusing on nonlinear behavior prevent non-linear behavior and damage
in other major and minor structure parts. X-shaped metal dampers have a significant
performance. Massive submission on steel volume, providing Hysteretic damping and
extraordinary energy dissipation are unique features of this type of damper. These dampers
have a high lateral stiffness, in addition to providing damping. So, they were entitled as
Added Damping And Stiffness (ADAS).
7.5 Lead Injection Damper (LED) This damper is made of a two-chamber cylinder, piston
and lead inside piston. And by piston moving during earthquake, lead moves from larger
chamber to smaller chamber. And with plastic deformation, the kinetic energy is wasted as
heat.
7.6 Shape Memory Alloy (SMA)
Shape Memory alloy (SMA) are created from metals which have the following properties:
1. their flexibility is very similar to the flexibility of the rubber piece.
2. after applying many deformation, they can back to their original state, by heating.
The alloy of nickel and titanium has good resistance to corrosion, in addition to have these
properties
7.7 Viscous Dampers
 In this damper, by using viscous fluid inside a cylinder, energy is dissipated. Due to
ease of installation, adaptability and coordination with other members also diversity in
their sizes, viscous dampers have many applications in designing and retrofitting.
damper installation in the floor or foundation ( in the method of seismic isolation)
 connecting dampers in stern pericardial braces
 damper installation in diagonal braces.

16. 7.8 Hybrid and Semi-Active System
The term of hybrid control systems is used for a hybrid using of active and passive control
systems. Semi-active systems are extracted from active control systems. In this cases, the
required output energy is lower than active control system. And it is only the producer of
electric pulse to provide control system. Semi active control components dose not add
mechanical additional energy to structure system ( which includes structural and stimulus
control), so the stability of input and output connections are guaranteed. Semi-active control
components often can be seen as passive control components. Particularly, more resistant or
depreciate forces are produced by internal mechanism based on feedback output sensor. So
the combination ability of the best active and passive systems or against less reduction of
desired components and due to low power, have high control ability. Semi-active systems are
an attractive alternative for active and hybrid systems.
7.9 Active Seismic Control Systems (Active)-Compared with passive control system, active
control system structural response is controlled, effectively by 2 factors,
1. By a special amount of output power or required energy.
2. The process of decision-making based on measured real-time and involved data.
In this respect, active control includes a widespread technology. In terms of engineering
control, active control system is composed of 4 connected components, these includes:
Structure, sensor, computer control and controller and actuators, each of them works as
lateral system. And they are integrated that an output of a systems is an input of another
system is a feedback control system. So, priority of an active systems is in widespread use
due forces controlling and they are created by real stimulating and structural behavior. In
active system, when the output excitation is considered as an output. And it is called open-
loop system. When the structure response is used as an input, the system us called closed-

17. loop. When both excitation and response are used, system is called open-close control
system (Hwang et al,2007).
7.10 Passive Seismic Controlling System-People when are in moving train or they are stand
in a bus, try to maintain their balance by their foot and by relying on spine and abdominal
muscles. In the same way or by providing same features for structure, structure can damped
vibrations at the time of earthquake. This system includes movable mass which is set to the
spring and it is added to damping components. And by creating frequency dependent to
hysteresis, it increases damping in first structure. And by connecting a TMD to structure,
structure seismic energy is transferred to TMD and its energy depreciates in TMD
damper(Jangid,2004). As a result, it is used to reduce the structure dynamic response.
Passive control system does not need t0 a power supply to provide external power. And
reaction of passive control components in response is dependent to structure movement
during earthquake. In structure passive controlled system, energy which includes passive
components can not increase its stability by passive control components(Saiidi,1999). Passive
components methods are strongly dependent to exact setting and must be specifically design
for each structure, because they are not able to adapt structural changes and usable
parameters changes. And for all conditions, required loads are not optimized. As a result,
passive systems can be effective only for violation cases that are designed or adapted,
accurately(Jangid,2004)
Conclusion
1.the response of short period structures founded on rock to earthquakes after yielding is in
fact less sensitive and less demanding than the case of response to earthquakes under general
site conditions

18. 2.the response of short period structures founded on soft soil to earthquakes after yielding is
in fact more sensitive and more demanding than the case of response to earthquakes under
general site conditions
3.the response of short period structures founded on deep cohesion less soil to earthquakes
after yielding is in fact close but less sensitive and less demanding than the case of response
to earthquakes under general site
4.The percentage of decrease in base shear for all the building frames varies from 0 to 26.5%
when the type of soil changes for medium to hard 2.0 to 18.5% when the type of soil changes
for soft to medium. The lateral displacement value increases when the type of soil changes
from hard to medium and medium to soft for all the building frames
5.The percentage of decrease in lateral displacement for all the building frames varies from 0
to 26.5% when the type of soil changes for medium to hard and 0 to 18.7% when the type of
soil changes for soft to medium. The Axial force and Moment in the column increases when
the type of soil changes from hard to medium and medium to soft. Since the base shear, axial
force, column moment and lateral displacements increase as the soil type changes, soil
structure interaction must be suitably considered while designing frames for seismic forces.
References
1. Nazzal S.Armouti ‘Effect of Dampers on Seismic Demand of Short Period Structures’
2010
2. Nazzal S.Armouti ‘Effect of Dampers on Seismic Demand of Short Period Structures in
Rock Sites’ 2011

19. 3. Nazzal S.Armouti ‘Effect of Dampers on Seismic Demand of Short Period Structures in
Soft Sites’ 2013
4. Nazzal S.Armouti ‘Effect of dampers on seismic demand of short Period structures in deep
cohesion less sites’ 2011
5. G.Ghodrati Amiri1, G. Abdollahzadeh Darzi2 and M. Khanzadi3 ‘Earthquake Duration
and Damping Effects on Input Energy’ 2007
6. Alireza Heysami ‘Types of Dampers and their Seismic Performance During an
Earthquake’ 2015
7. Ketan Bajaj*,JiteshT Chavda,Bhavik M Vyas ‘Seismic Behavior Of Buildings On
Different Types Of Soil’ 2013
8. Anand N. Mightraj C. Prince Arulraj G.‘Seismic Behaviour of RCC Shear Wall Under
Different Soil Conditions’