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

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.

2.Literature review2.1 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 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%

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.

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.

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, uSingle 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

Fig. 5: Distribution of power spectral density of earthquakes according to their site conditions

uD = u cos θ

The force in the damper is given as:

FD = C.uD = 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

\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:

5.Effect of sesmic demand on Rock site,Medium soil site ,soft soil analysis in Stadd pro as per IS 1893-2002/2005City:Aurangabad, Damping ratio- 1

Dimention Node no

Plan view

In Hard rock displacement detail of node in X,Y,Z direction

Mediam soil displacement detail of node in X,Y,Z direction

Soft soil displacement detail of node in X,Y,Z direction

6.Case studyCrystal 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

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

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

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.

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-

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

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

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’