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Vibration Control of Structure Using Passive Damper

1. Breif Idea of Earthquake and its Protection Using Dampers:
As early as in the sixteenth century, Galileo Galilee began to study the vibratory Phenomena. Since then, the vibration theory has been expanding from discrete systems to continuous systems, from harmonic vibration analysis to random vibration problems, from linear vibration theory to nonlinear vibration analysis, and from vibration analysis to vibration control systems design. From theoretic research to engineering applications, scientists and engineers have taken advantages of the expanded knowledge to benefit the world. An earthquake is the most extreme condition that any building may be required to survive during its lifetime. To survive the natures might safely and surely also poses the greatest challenge to the architects and structural engineers. However the modern day computational power and the technological advances in the earthquake protection industry have made the solution once considered un-surmountable a reality. There are numerous companies specializing only in Earthquake Protection. Today most medium and high-rise buildings are following Life-Safety Design, more popularly referred as Earthquake Resistant Design for protection against earthquakes. However the awareness amongst people living in the seismic regions is increasing and they are now aware that for a small additional cost they can get a much higher Earthquake Protection for their buildings than what is mandatory as per the seismic codes. As the seismic codes are based on the Life-Safety / Earthquake Resistant design so they are aiming to prevent a total building collapse in case of a major earthquake, thereby saving lives. For the user/owner of the property this implies that even an Earthquake Resistant building does not provide any guarantee that it would be habitable for living / doing business after a major earthquake. The earthquake will structurally damage the building and incase the damage is above a threshold level there would be no option but to demolish and re-construct. When a building is subjected to a major quake, energy is absorbed by cracking of concrete and elongation of steel beyond the elastic limits. This damage to the structural members if beyond a threshold level can be dangerous. There does exists another way of absorbing earthquake energy i.e. Dampers. The most efficient and cost effective way to achieve energy dissipation in buildings is by using Earthquake Dampers. Dampers are mechanical devices that look somewhat like huge shock absorbers. Dampers function is to absorb and dissipate the energy supplied by the
-1Dept of Civil Engg BVBCET Hubli

Vibration Control of Structure Using Passive Damper

ground movement during an earthquake so that the building remains unharmed, their functioning is also akin to shock absorbers. Whenever the building is in motion during a earthquake tremor they help in restricting the building from swaying excessively and thereby preventing structural damage. The earthquake energy absorbed by these dampers gets converted into heat which is then dissipated into the atmosphere. Dampers thus work to absorb earthquake shocks ensuring that the structural members i.e. beam and columns remain unharmed. There are four types of dampers i.e. Viscoelastic, Friction, Metallic Yield and Fluid Viscous. India's success story of economic growth and the projections for the immediate future, coupled with the heightened seismic activity in the region over the past few years, has led many to look at India as a attractive market destination. For low-rise buildings base isolation technique is also extremely popular. In BaseIsolation the structure above ground is separated from the foundation by inserting rollers/pads between the foundation and the building. These isolators allow the structure to move independently of the shifting ground below, thereby effectively isolating it from the ground motion. Base Isolation is however not appropriate for all buildings and is suitable for only low rise buildings up to 2-3 storey‟s that have a much larger spread than its height. Dampers on the other hand are most suitable for high-rise buildings and are in extensive use the world over. High rises also happen to be the most susceptible to earthquakes. Over the years Fluid Viscous Dampers have come out as clear leaders in seismic applications. The cost effect for Fluid Viscous Dampers is in the range of Rs. 150 to 200 per square foot. Dampers stay hidden in partition walls and inconspicuous locations and, therefore, are not visible to occupants. Some of the other high-profile buildings incorporating dampers are Sky-bridge of Petronas tower Malaysia, JR Tokai Shin Yokohama station in Japan, Jan-Ron Ritz building in Taiwan, 67 storey Park Hyatt hotel in Chicago, Yerba Buena tower in San Francisco, 55 storey Torre Mayor in Mexico, which also happened to win the award for the best seismically engineered structure in 2005 after the structural engineers monitored the building performance during and post an real life earthquake of magnitude 7.6 on the Richter scale which hit just off the coast of Colima, Mexico (January 21, 2003).

-2Dept of Civil Engg BVBCET Hubli

Vibration Control of Structure Using Passive Damper

2. Introduction:
Passive energy dissipation systems for seismic applications have been under development for a number of years with a rapid increase in implementations starting in the mid-1990s. The principal function of a passive energy dissipation system is to reduce the inelastic energy dissipation demand on the framing system of a structure (Constantinou and Symans 1993). The result is reduced damage to the framing system. A number of passive energy dissipation devices are either commercially available or under development. Device that have most commonly been used for seismic protection of structures include viscous fluid dampers, viscoelastic solid dampers, friction dampers, and metallic dampers. Other devices that could be classified as passive energy dissipation devices or, more generally, passive control devices include tuned mass and tuned liquid dampers, both of which are primarily applicable to wind vibration control, recentering dampers, and phase transformation dampers. In addition, there is a class of dampers, known as semiactive dampers, which may be regarded as controllable passive devices in the sense that they passively resist the relative motion between their ends but have controllable mechanical properties. Examples of such dampers include variable-orifice dampers, magnetor heological dampers, and electroheological dampers. Semi active dampers have been used for seismic response control in other countries, notably Japan, but not within the United States (Soong and Spencer 2002). The growth in application and development of passive energy dissipation devices has led to a number of publications that present detailed discussions on the principles of operation and mathematical modeling of such devices, analysis of structures incorporating such devices, and applications of the devices to various structural systems. In addition, a state-of-the-art and state of- the-practice paper was recently published on the general topic of supplemental energy dissipation wherein both passive and active structural control systems were considered (Soong and Spencer 2002). In contrast, this paper focuses exclusively on passive energy dissipation systems and their application to building structures for seismic response control, providing a concise summary of the current state of practice and recent developments in the field.

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Vibration Control of Structure Using Passive Damper

3. Literature review:
The TMD concept was first applied by Frahm in 1909 to reduce the rolling motion of ships as well as ship hull vibrations. A theory for the TMD was presented later in the paper by Ormondroyd and Den Hartog(1928),followed by a detailed discussion of optimal tuning and damping parameters in Den Hartog„s book on mechanical vibrations. Hartog„s book on mechanical vibrations (1940). The initial theory was applicable foran undamped SDOF system subjected to a sinusoidal force excitation. Extension of the theory to damped SDOF systems has been investigated by numerous researchers. Passive And Active Fluid Dampers In Structural Applications by M. Shinozuka et al (Oct1992) it gives the difference between active passive, & they conclude that passive dampers can achieve reduction in response of structural system which are equivalent to those achieved by active control, moreover, fluid dampers are substantially more reliable, have demonstrated longevity, demand no power and no cost significantly less than active system. Development of passive viscoelastic damper to attenuate excessive floor vibrations I. Saidi et al (May2011), Paper proposes a new innovative passive viscoelastic damper to reduce floor vibrations. This damper can be easily tuned to the fundamental frequency of the floor and can be designed to achieve various damping values. The paper discusses the analytical development of the damper with experimental results presented on a prototype to demonstrate its effectiveness and with that they conclude developed viscoelastic damper can be easily tuned to given properties and optimised to fit in available spaces. The testing and analyses conducted demonstrate clear advantages of such a viscoelastic damper over conventional viscous dampers for floor vibration applications where displacements are small. By using several dampers in one location or in a distributed system a large frequency range of effectiveness can be addressed. Seismic design of viscoelastic dampers for structural applications Soong et al (1992).The seismic behavior of structure with added viscoelastic damper is studied experimentally. Experiment is conducted using a model structure simulating firstly a single degree of freedom structure and degree of freedom structure. The degree of reduction in relative displacement and absolute accerlation is used as a measure of effectiveness of added dampers. Temperature dependency is carefully examined
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Vibration Control of Structure Using Passive Damper

together with problem of damper placement. Experiment shows that significant improvement of structural performance under seismic condition can be realize with addition of viscoelastic damper. Optimum design for passive tuned mass dampers using viscoelastic materials. A D Mohammed et al (2007). This paper forms part of a research project which aims to develop an innovative cost effective Tune Mass Damper (TMD) using viscoelastic materials. Generally, a TMD consists of a mass, spring, and dashpot which is attached to a floor to form a two-degree of freedom system. TMDs are typically effective over a narrow frequency band and must be tuned to a particular natural frequency. The paper provides a detailed methodology for estimating the required parameters for an optimum TMD for a given floor system. The paper also describes the process for estimating the equivalent viscous damping of a damper made of viscoelastic material. Finally, a new innovative prototype viscoelastic damper is presented along with associated preliminary results.

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Vibration Control of Structure Using Passive Damper

4. Types of Structural Control:
4.1. Passive Control Systems 4.2. Active Control Systems 4.3. Semi Active Control Systems

4.1. Passive Control Systems: A passive control system may be defined as a system which does not require an external power source for operation and utilizes the motion of the structure to develop the control forces. Control forces are developed as a function of the response of the structure at the location of the passive control system. A passive control system may be used to increase the energy dissipation capacity of a structure through localized, discrete energy dissipation devices located either within a seismic isolation system or over the height of the structure. Such systems may be referred to as supplemental energy dissipation systems. The objective of these systems is to absorb a significant amount of the seismic input energy, thus reducing the demand on the structural system. Seismic isolation systems represent another form of passive control systems. In these systems, a flexible isolation system is introduced between the foundation and superstructure so as to increase the natural period of the system. The increase in flexibility typically results in the deflection of a major portion of the earthquake energy; reducing accelerations in the superstructure while increasing the displacement across the isolation level.

Fig. 1 Block diagram of Passive Control System (Fujino et al 1996)

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Vibration Control of Structure Using Passive Damper

4.2. Active Control System: An active control system may be defined as a system which typically requires a large power source for operation of electro hydraulic or electromechanical actuators which supply control forces to the structure. Control forces are developed based on feedback from sensors that measure the excitation and/or the response of the structure. The feedback from the structural response may be measured at locations remote from the location of the active control system. The control forces within an active control system are typically generated by electrohydraulic or electromechanical actuators based on feedback information from the measured response of the structure and/or feed forward information from the external excitation. The recorded measurements from the response and/or excitation are monitored by a controller (a computer) which, based on a pre-determined control algorithm, determines the appropriate control signal for operation of the actuators. The generation of control forces by electrohydraulic actuators requires large power sources, which are on the order of tens of kilowatts for small structures and may reach several megawatts for large structure.

Fig. 2 Shows the Active Control Structural system (Fujino et al 1996)

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Vibration Control of Structure Using Passive Damper

4.3. Semi-active control systems: A semi-active control system may be defined as a system which typically requires a small external power source for operation (e.g. a battery) and utilizes the motion of the structure to develop the control forces, the magnitude of which can be adjusted by the external power source. Control forces are developed based on feedback from sensors that measure the excitation and/or the response of the structure. The feedback from the structural response may be measured at locations remote from the location of the semi active control system. Semi-active control systems have only very recently been considered for structural control applications. A semi-active control system generally originates from a passive control system which has been subsequently modified to allow for the adjustment of mechanical properties. The mechanical properties of these systems may be adjusted based on feedback from the excitation and/or from the measured response. The control forces in many semi-active control systems primarily act to oppose the motion of the structural system and therefore promote the global stability of the structure. Semiactive control systems generally require a small amount of external power for operation (on the order of tens of watts).

Fig. 3 Semi Active Control System (Fujino et al 1996)

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Vibration Control of Structure Using Passive Damper

5. Passive Energy Dissipation Devices: Mechanical Behavior and Mathematical Models:
A variety of passive energy dissipation devices are available and have been implemented worldwide for seismic protection of structures. To limit the scope of this paper, emphasis is given to passive energy dissipation devices that are commonly used worldwide. In this section, the mechanical behavior and mathematical models of such devices are presented. Passive energy dissipation devices are classified here in three categories: 1) Rate-dependent devices; 2) Rate-independent devices; 3) Others. Rate-dependent devices consist of dampers whose force output is dependent on the rate of change of displacement across the damper. The behavior of such dampers is commonly described using various models of linear viscoelasticity. Examples of such dampers include viscoelastic fluid dampers and viscoelastic solid dampers.

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Vibration Control of Structure Using Passive Damper

Viscous Fluid Damper Basic Construction

Viscoelastic Damper

Metallic Damper

Friction Damper

Idealized Hysteretic Behavior

Idealized Physical Model

Idealized Model Not available

Advantages

Disadvantage

1.Activated at low displacements 2. Minimal restoring Force 3.For linear damper modeling of damper is simplified 4.Military application 1)Possible Fluid seal leakage

1. Activated at low displacement 2.provides restoring forces 3. Linear behavior therefore simplified modeling of damper

1. Stable hysteretic behavior 2.Long term reliability 3.Insensitivity to ambient temperature 4. Material and behavior familiar to practicing engineers

1.Large energy dissipation per cycle 2.Insenstivity to ambient temperature

1.Limited deformation Properties are frequency and temperature dependent 2.Possible debonding and tearing of VE material

1.Device damaged after earthquake may require replacement 2.Non linear behavior may require non linear analysis

1. Sliding interface may change with time 2. Strongly non linear behavior may excite higher modes and require non linear analysis 3. Permanent displacement if no restoring force mechanism provide d

Table 1 Shows Summary of construction, hysteretic behavior, physical models, advantages, and disadvantages of passive energy dissipation devices for Seismic protection applications (M.D Symans et al 2001)

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Vibration Control of Structure Using Passive Damper

6. Types of Passive Structural Control System:
6.1 Viscoelastic Solid Damper 6.2 Metallic Damper 6.3 Friction Damper 6.4 Viscous Fluid Damper

6.1. Viscoelastic Solid Dampers: Viscoelastic solid dampers generally consist of solid elastomeric pads (viscoelastic material) bonded to steel plates (see Table 1). The steel plates are attached to the structure within chevron or diagonal bracing. As one end of the damper displaces with respect to the other, the viscoelastic material is sheared resulting in the development of heat which is dissipated to the environment. By their very nature, viscoelastic solids exhibit both elasticity and viscosity (i.e., they are displacement and velocity dependent , Experimental testing (Bergman and Hanson 1993, Lobo1993); and Chang et al. 1995) has shown that, under certain conditions, the behavior of viscoelastic dampers can be modeled using the Kelvin model of viscoelasticity P (t) = Ku (t) +C ̇ (t)……………………………………(1) where K=storage stiffness of the damper; and C=damping coefficient which is equal to the ratio of the loss stiffness to the frequency of motion. The physical model corresponding to Eq. 1 is a linear spring in parallel with a linear viscous dashpot (see Table 1) wherein a component of the damper force the restoring force (is proportional to the displacement and the other component the damping force is proportional to the velocity. Thus, the damper has the ability to store energy in addition to dissipating energy. For viscoelastic materials, the mechanical behavior is typically presented in terms of shear stresses and strains rather than forces and displacements. The mechanical properties then become the storage and loss moduli that define the properties of the viscoelastic material rather than properties of the damper. In general, the storage and loss moduli are dependent on frequency of motion, strain amplitude, and temperature. At a given frequency and shear strain amplitude, the storage and loss moduli have similar values that increase with an increase in the frequency of motion. Thus, at low frequencies, viscoelastic dampers exhibit low stiffness and energy dissipation capacity. Conversely, at high frequencies, stiffness
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Vibration Control of Structure Using Passive Damper

and energy dissipation capacity are increased. Note that increases in temperature, due to cycling of the damper, can significantly reduce the storage and loss moduli, resulting in reduced stiffness and energy dissipation capacity. Thus, temperature dependencies must be considered in the design of such dampers. One approach to considering temperature dependencies, as well as- shear strain and frequency ependencies, is to employ a mathematical model that is based on nonlinear regression analysis of experimental cyclic response data. Alternatively, a simplified bounding analysis can be employed where in lower and upper bound temperatures are used to predict maximum forces and displacements, respectively.

Fig. Shows the Viscoelastic Damper (Y.M Parulekar & G.R Reddy 2007)

Fig. 5 Installation of Viscoelastic Damper (F. Sadek et al 1996)

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Vibration Control of Structure Using Passive Damper

6.2. Metallic Dampers: Two major types of metallic dampers are buckling-restrained brace BRB dampers and added damping and stiffness ADAS dampers. A BRB damper consists of a steel brace usually having low-yield strength with a cruciform cross section that is surrounded by a stiff steel tube. The region between the tube and brace is filled with a concrete-like material and a special coating is applied to the brace to prevent it from bonding to the concrete. Thus, the brace can slide with respect to the concrete-filled tube. The confinement provided by the concrete-filled tube allows the brace to be subjected to compressive loads without buckling (i.e., the damper can yield in tension or compression with the tensile and compressive loads being carried entirely by the steel brace). Under compressive loads, the damper behavior is essentially identical to its behavior in tension. Since buckling is prevented, significant energy dissipation can occur over a cycle of motion. Additional details on the behavior of BRB dampers are provided by Black et al. (2004.) During the initial elastic response of the BRB damper, the device provides stiffness only. As the BRB damper yields, the stiffness reduces and energy dissipation occurs due to inelastic hysteretic response. The hysteretic behavior of a BRB damper can be represented by various mathematical models that describe yielding behavior of metals. One example is the Bouc–Wen model which is described by Black et al. (2004) and compared with experimental test data therein. The model is defined by P(t)=Ku(t)+(1-)KuyZ(t).................................................(2) where =ratio of pos- to preyielding stiffness; K=preyielding stiffness; uy=yield displacement; and Z(t)=evolutionary variable that is defined by Uy ̇ +[ ̇ (t)|Z(t)|-1+ ̇ (t)|Z(t)|- ̇ (t)=0…………………………(3) Where  , and  =dimensionless parameters that define the shape of the hysteresis loop.

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Vibration Control of Structure Using Passive Damper

Fig. 6 X-shaped ADAS device (F. Sadek et al 1996)

6.3. Friction Dampers: Friction dampers dissipate energy via sliding friction across the interface between two solid bodies. Examples of such dampers include slotted-bolted dampers (Grigorian et al. 1993) wherein a series of steel plates are bolted together with a specified clamping force (Table 1). The clamping force is such that slip occurs at a prespecified friction force. At the sliding interface between the steel plates, special materials may be utilized to promote stable coefficients of friction. An alternate configuration, known as the Pall cross-bracing friction damper, consists of crossbracing that connects in the center to a rectangular damper (Pall and Marsh 1982; Soong and Dargush 1997). The damper is bolted to the cross-bracing and, under lateral load, the structural frame distorts such that two of the braces are subject to tension and the other two to compression. This force system causes the rectangular damper to deform into a parallelogram, dissipating energy at the bolted joints through sliding friction. Other conFig.urations include a cylindrical friction damper in which the damper dissipates energy via sliding friction between copper friction pads and a steel cylinder. The copper pads are impregnated with graphite to lubricate the sliding surface and ensure a stable coefficient of friction. Experimental testing has shown that a reasonable model for defining the behavior of friction dampers is given by the idealized Coulomb model of friction …………………………………….. (4) Where =coefficient of dynamic friction, and N=normal force at the sliding interface. The idealized hysteretic response of a friction damper for cyclic loading reveals that
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Vibration Control of Structure Using Passive Damper

the force output is bounded and has the same value for each direction of sliding (Table 1). The hysteresis loops are rectangular, indicating that significant energy can be dissipated per cycle of motion. However, the rectangular shape of the hysteresis loops indicates that the cyclic behavior of friction dampers is strongly nonlinear. The deformations of the structural framing are largely restricted until the friction force is overcome thus, the dampers add initial stiffness to the structural system.

Fig. 7 Pall Friction Damper (F. Sadek et al 1996)

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Vibration Control of Structure Using Passive Damper

6.4. Viscous Fluid Dampers Viscoelastic fluid dampers generally exhibit minimal stiffness over a range of requencies that often includes the fundamental natural frequency of building or bridge structures. Thus, such dampers generally have minimal influence on the fundamental natural frequency and are therefore often regarded simply as viscous fluid dampers. Viscoelastic solid dampers, on the other hand, exhibit stiffness to the extent that the dampers will influence the natural frequencies of the structure. Rateindependent systems consist of dampers whose force out. Viscous fluid dampers are commonly used as passive energy dissipation devices for seismic protection of structures. Such dampers consist of a hollow cylinder filled with fluid see Table 1, the fluid typically being silicone based. As the damper piston rod and piston head are stroked, fluid is forced to flow through orifices either around or through the piston head. The resulting differential in pressure across the piston head very high pressure on the upstream side and very low pressure on the downstream side can produce very large forces that resist the relative motion of the damper (Lee and Taylor 2001). The fluid flows at high velocities, resulting in the development of friction between fluid particles and the piston head. The friction forces give rise to energy dissipation in the form of heat. The associated temperature increase can be significant, particularly when the damper is subjected to long-duration or large-amplitude motions. In this case, the temperature rise can be reduced by reducing the pressure differential across the piston head (e.g. by employing a damper with a larger piston head. Interestingly, although the damper is called a viscous fluid damper, the fluid typically has a relatively low viscosity (e.g. silicone oil) with a kinematic viscosity on the order of 0.001 m2/s at 20°C). The term viscous fluid damper is associated with the macroscopic behavior of the damper which is essentially the same as that of an ideal linear or nonlinear viscous dashpot (i.e., the resisting force is directly related to the velocity. As an alternative to viscous fluid dampers, viscoelastic fluid dampers, which are intentionally designed to provide stiffness in addition to damping, have recently become available for structural applications (Miyamoto et al. 2003). These dampers provide damping forces via fluid orificing and restoring forces via compression of an elastomer. Thus, more accurately, the dampers may be referred to as viscoelastic fluid/solid dampers.
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Vibration Control of Structure Using Passive Damper

Fig. 8 Taylor device fluid Damper (F. Sadek et al 1996)

Fig. 9 (Structural control guidelines by Felix Weber et al 2006)

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Vibration Control of Structure Using Passive Damper

7. Design Philosophy
The basic approach followed in developing the chapter on structures with damping systems in the 2003 NEHRP Recommended Provisions (BSSC 2004) and the 2005 ASCE/SEI-7-05 Standard (ASCE 2005) is based on the following concepts: 1. The methodology is applicable to all types of damping systems, including displacement-dependent damping devices (hysteretic or friction systems) and velocity-dependent damping devices (viscous or viscoelastic systems) 2. The methodology provides minimum design criteria with performance objectives comparable to those for a structure with a conventional seismic-force-resisting system (but also permits design criteria that will achieve higher performance levels) 3. The methodology requires structures with a damping system to have a seismicforce-resisting system that provides a complete load path thus, the detailing requirements that are in place for structures without damping systems may not be relaxed for structures which include damping systems. 4. The methodology requires design of damping devices and prototype testing of damper units for displacements, velocities, and forces corresponding to those of the maximum considered earthquake, and 5. The methodology provides linear static and response spectrum analysis methods for design of most structures that meet certain configuration and other limiting criteria (for example, at least two damping devices at each story con figured to resist torsion). In addition, nonlinear response history analysis is required to confirm peak response for structures not meeting the criteria for linear analysis (and for structures close to major faults).

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Vibration Control of Structure Using Passive Damper

8. Improvement of Irregularity Conditions:
Mostly in retrofit situations, passive damping systems have been added to improve the response of irregular buildings (e.g., buildings having a soft story or a geometrical configuration in which excessive deformations are concentrated in local areas). By arranging damper locations and selecting damping values so that the resulting damper forces are in proportion to structure displacements, displacements in these areas can be reduced and overall response improved. However, if the dampers were located only in that story, the Provisions require that nonlinear analysis be performed. Linear static and response spectrum analysis can only be performed if the damping system is distributed over the full height of the structure with at least two dampers per story. The performance of structures with plan irregularities that induce torsion can also be improved via strategic placement of dampers.

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Vibration Control of Structure Using Passive Damper

9. Damper Placement and Damper Installation Configuration:
In general, the effectiveness of each damper in a structure is proportional to its maximum displacement and/or velocity and the damper design parameters. For a single mode of vibration, the effectiveness of the dampers can be maximized by positioning devices in accordance with the largest inter story displacements of the corresponding mode shape (or, conversely, the effectiveness of dampers for any single mode of vibration will be reduced if the dampers are located in stories having little interstory displacement for that mode). As an example, locating devices at each story within the core of a building may be effective for regular, symmetric structures, but might be ineffective for torsionally irregular structures since, although the fundamental translational vibration modes may be effectively damped, the torsional modes might have little added damping , Of course, the above approach to damper placement is based on the assumption that the mode shapes remain constant which is only valid if the structure remains elastic and the damping is distributed in a proportional manner. Other approaches to damper placement, including formal optimization of damper placement, have been developed Dampers are attached to the main structural framing system via a bracing system. The bracing system may be diagonal bracing, chevron bracing, or cross-bracing. If the main structural framing is relatively stiff (e.g. reinforced concrete structures), the damper effectiveness is limited due to low displacements and velocities across the damper. This is particularly problematic when the damping system is also used to resist wind loading since wind-induced inter story drifts are usually much smaller than seismically induced drifts. To improve the effectiveness of dampers under such conditions, alternative damper bracing systems have been developed to amplify the motion of the damper.

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Vibration Control of Structure Using Passive Damper

10. Recent Applications of Passive Energy Dissipation Systems:
Some of the earliest applications of damping systems were used to reduce deflections in very tall buildings. In such buildings, large amplitudes of sway oscillations, from either wind forces or seismic effects, can be very discomforting to the occupants. Damping systems were found to be highly effective in reducing the amplitudes of vibration. More recently over the past decade or so, damping systems have been specified for application to buildings with a wide variety of structural configurations. The growth in application of damping systems in buildings has been steady to the extent that there are now numerous applications Soong and Spencer 2002. Given that, examples are provided below for only a few relatively recent applications to building for seismic protection.

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Vibration Control of Structure Using Passive Damper

Fig. 10 Shows the Photos of (a) renovated Hotel Stockton

(b) View of installed fluid viscoelastic damper (M. D. Symans et al 2008)

Fig. 11 Shows the Photo (a) Torre Mayor Tower under construction showing partial view of megabraces

(b)View of installed fluid dampers (M. D. Symans et al 2008)
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Vibration Control of Structure Using Passive Damper

Fig. 12 Photos of (a) Wallace F. Bennett Federal Building

(b) View of building without cladding showing installed buckling-restrained braces (M. D. Symans et al 2008)

Fig. 13 shows the Photos of: (a) Santa Clara Medical Center Hospital under construction

(b) Close up view of installed buckling-restrained braces (M. D. Symans et al 2008)

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Vibration Control of Structure Using Passive Damper

Fig. 14 Photos of (a) Monterey County Government Center showing precast concrete panel cladding;

(b) Close up view of installed friction damper

Fig. 15 Photos of (a) patient tower

(b)View of installed cross-brace friction dampers (M. D. Symans et al 2008)
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Vibration Control of Structure Using Passive Damper

11. Conclusion:
This paper has provided a discussion on the key features of the most commonly utilized passive energy dissipation devices and an explanation of the current code-based approach to analysis and design of structures incorporating such devices. 1. In this paper Damping systems were used to reduce deflections in very tall buildings. In such buildings, large amplitudes of sway oscillations, from either wind forces or seismic effects, can be very discomforting to the occupants. Damping systems were found to be highly effective in reducing the amplitudes of vibration. 2. Passive fluid dampers can achieve reduction in response of structural systems which are equivalent to those achieved by active control. Moreover, fluid dampers are substantially more reliable, demand no power and cost significantly less than active system. 3. Wide acceptance of passive energy dissipation devices in building and other structure will depend on the availability of information on their performance criteria as well as standards for evaluation and testing. More research is required d to provide standardized performance evaluation. 4. The comparison of the results indicates that the use of passive dampers for the purpose of the seismic rehabilitation of the existing structures is quite valuable. With the application of the passive energy absorbers in the structures, the earthquake energy is dissipated via these devices while the other structural elements can remain undamaged. On the other hand the comparison of the base shears induced in the structure, demonstrates that the use of the passive dampers in the structures can substantially reduce the base shear and base moment and usually eliminates the expensive works on foundation strengthening or local retrofitting. 5. The use of the viscous dampers is particularly useful for the structures that contain weak columns. Because this type of damper exerts its maximum forces in out of phase with displacement, most of the columns remain elastic.

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Vibration Control of Structure Using Passive Damper

12. References:
[1] Constantinou, M. C., and Symans, M. D. “Experimental study of seismic response of buildings with supplemental fluid dampers.” Structural Design & Tall Buildings. (1993) 2: 93–132. [2] Constantinou, M.C and Symans, M.D. “Experimental study of seismic response of buildings with supplemental fluid dampers.” Structural Design of Tall Buildings. (1993) 2:93 132. [3] Abe M Fujino. Y et al “Dynamic characterization of Multiple tuned mass damper “Earthquake Engg & Structural Dynamics (1994) 23:813-835. [4] Black C. J. Makris, N., and Aiken, I. “Component testing, seismic evaluation and characterization of buckling-restrained braces.” Journal of Structural Engg. (2004) 6: 880–894. [5] Constantinou, M. C., and Symans, M. D. “Seismic response of structures with supplemental damping.” Structural Design & Tall Build., (1993 b) 2: 77–92. [6] Fahim Sadek, Bejan Mohraj, Andrew Taylor & C.M Riley “Passive energy dissipation devices for seismic application” National Institute of standards & technology (1996). [7] Goel, R. K “Seismic behavior of asymmetric buildings with supplemental damping.” Earthquake Engg & Structural Dynamics,(2001) 29: 461–480. [8] I.Saidi a, E.F. Gada,b, J.L. Wilson a, N. Haritos b “Development of passive viscoelastic damper to attenuate excessive floor vibrations” Engineering Structures (2011) 33: 3317–3328 [9] M. D. Symans, M. C. Constantinou, M. W. Johnson ” Energy Dissipation Systems for Seismic Applications: Current Practice and Recent Developments Journal Of Structural Engineering ASCE (2008) 154:112-139. [10] Swaroop K. Yalla , Ahsan Kareem Jeffrey C. Kantor Semi-active tuned liquid column dampers for vibration control of structures, Engineering Structures (2001) 23: 1469–1479 [11] Symans, M.D Constantinou, M.C., Taylor, D.P and Garnjost, K.D “Semiactive fluid iscous dampers for seismic response control.” Proc. 1st World Conf. on Structural Control (1995), 4:3–12. [12] Soong, T.T., and Spencer, B.F “Supplemental energy dissipation: state of- theart and state-of-the-practice.” Engineering Structures (2001) 56: 132-146.
- 26 Dept of Civil Engg BVBCET Hubli

Vibration Control of Structure Using Passive Damper

[13]

Taylor, D.P.and Constantinou, M.P “Fluid dampers for applications of seismic energy dissipation and seismic isolation.” Proc. 11th World Conf. on Earthquake Engg. (1994) Acapulco, Mexico. Y.M Parulekar & G.R Reddy “Passive response control systems for seismic response reduction: A art of the review” International Journal of Structural Stability & Dynamics (2009) 9:151-177

[14]

- 27 Dept of Civil Engg BVBCET Hubli

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