1

CHAPTER 1

INTRODUCTION

1.1 PASSIVE ENERGY DISSIPATION SYSTEM

Passive energy dissipation systems encompass a range of materials and devices for

enhancing damping, stiffness and strength, and can be used both for seismic hazard

mitigation and for rehabilitation of aging or deficient structures. In general, such systems are

characterized by their capability to enhance energy dissipation in the structural systems in

which they are installed.

1.1.1 Principles of Operation

These devices generally operate on principles such as frictional sliding, yielding of

metals, phase transformation in metals, deformation of viscoelastic (VE) solids or fluids,

fluid orificing and sloshing.

1.1.2 Basic Function

The basic function of passive energy dissipation devices when incorporated into the

superstructure of a building is to absorb or consume a portion of the input energy, thereby

reducing energy dissipation demand on primary structural members and minimizing possible

structural damage.

Figure 1.1 Conventional Structure

Figure 1.2 Structure with Passive Energy Dissipation (PED)

Excitation Structure Response

Excitation Structure Response

PED

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1.2 CLASSIFICATION OF PASSIVE ENERGY DISSIPATION SYSTEMS

A large number of passive control systems or PED devices have been developed and

installed in structures for performance enhancement under earthquake loads.

A variety of passive energy dissipation devices are available and have been

implemented worldwide for seismic protection of structures. Passive energy dissipation

systems are classified herein in three categories as follows.

1. Rate-dependent system

2. Rate-independent system

3. Others

1.2.1 Rate-Dependent System

Rate-dependent system consists of dampers whose force output is dependent on the

rate of change of displacement across the damper. The behaviour of such dampers is

commonly described using various models of linear viscoelasticity.

This system is also called as velocity-dependent or viscoelastic system. It may or may

not impart additional stiffness to the structure. This system works on the principle of fluid

orificing or deformation of viscoelastic solids.

Examples: Viscoelastic Fluid dampers and Viscoelastic Solid dampers.

1.2.2 Rate-Independent System

Rate-independent systems consist of dampers whose force output is not dependent on

the rate of change of displacement across the damper but rather upon the magnitude of the

displacement and possibly the sign of the velocity i.e., the direction of motion.

The behaviour of such dampers is commonly described using various nonlinear

hysteretic models. This system is also called as displacement-dependent or hysteretic system.

It always adds stiffness to the structure. This system works on the principle of yielding of

metals or sliding friction.

Examples: Metallic dampers and Friction dampers.

3

Energy dissipation systems which cannot be classified by one of the above basic

systems depicted are classified as other systems. These systems work on the various principle

of operation and can be further classified as follows.

1. Re-centering System

2. Dynamic Vibration Absorbers

1.2.3 Re-centering System

This system utilizes either a preload generated by fluid pressurization or internal

springs, or a phase transformation to produce a modified force-displacement response that

includes a natural re-centering component.

Examples: Pressurized fluid dampers, Preloaded spring-friction dampers, and Phase

transformation dampers.

1.2.4 Dynamic Vibration Absorbers

In these systems, supplemental oscillators involving mass, stiffness and damping are

introduced in order to significantly enhance performance, the dynamic characteristics of the

supplemental oscillators must be tuned to those of the primary structure. The objective of

incorporating a dynamic vibration absorber into a structure is basically to reduce energy

dissipation demand on the primary structural members under the action of external forces.

The reduction, in this case, is accomplished by transferring some of the structural\vibrational

energy to the absorber

Examples: Tuned mass dampers and Tuned liquid dampers

Explanations on these various dampers are given in the following chapters.

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CHAPTER 2

METALLIC DAMPERS AND FRICTION DAMPERS

2.1 METALLIC DAMPERS

Metallic dampers are hysteretic systems that dissipate energy with no significant rate

dependence and utilize the yielding of metals as the dissipative mechanism. The mechanism

involved in energy dissipation in metallic dampers can be categorized as one form of internal

friction. One of the effective mechanisms available for the dissipation of energy input to a

structure from an earthquake is through inelastic deformation of metals.

Many of these devices use mild steel plates with triangular or X shapes so that

yielding is spread almost uniformly throughout the material. Single round hole metallic

damper and double X shaped metallic damper are commonly used.

Figure 2.1 X-shaped Plate Damper Figure 2.2 Triangular Plate Damper

The idea of utilizing supplemental metallic hysteretic dampers within the

superstructure is to absorb a large portion of the seismic energy during earthquakes. The

performance objectives of using metallic dampers within the superstructure are energy

dissipation and strength enhancement.

Other configurations of steel yielding devices include bending type of honeycomb and

slit dampers and shear panel type. Two major types of metallic dampers are

Buckling-Restrained Brace (BRB) dampers

Added Damping and Stiffness (ADAS) dampers.

5

2.1.1 Buckling-Restrained Brace 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 behaviour is essentially identical to its

behaviour in tension. Since buckling is prevented, significant energy dissipation can occur

over a cycle of motion. In many cases, BRB dampers are installed within a chevron bracing

arrangement

Figure 2.3 Typical Arrangement of BRB Damper

Figure 2.4 Sectional View of BRB Damper

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2.1.2 Added Damping and Stiffness Dampers

An ADAS damper consists of a series of steel plates wherein the bottom of the plates

are attached to the top of a chevron bracing arrangement and the top of the plates are attached

to the floor level above the bracing.

As the floor level above deforms laterally with respect to the chevron bracing, the

steel plates are subjected to a shear force. The shear forces induce bending moments over the

height of the plates, with bending occurring about the weak axis of the plate cross section.

The geometrical configuration of the plates is such that the bending moments produce

a uniform flexural stress distribution over the height of the plates. Thus, inelastic action

occurs uniformly over the full height of the plates. For example, in the case where the plates

are fixed-pinned, the geometry is triangular. In the case where the plates are fixed-fixed, the

geometry is an hourglass shape.

To ensure that the relative deformation of the ADAS device is approximately equal to

that of the story in which it is installed, the chevron bracing must be very stiff. ADAS damper

will be damaged after an earthquake and may need to be replaced.

Figure 2.5 Typical Arrangement of X-plate Metallic Damper (ADAS)

The advantages and disadvantages of friction dampers are as follows.

Advantages

Stable hysteretic behaviour

Long-term reliability

7

Insensitivity to environment factors like temperature, humidity etc.

Materials and behaviour familiar to practicing engineers

Inexpensive

Disadvantages

Devices damaged after earthquake; may require replacement

Nonlinear behaviour; may require nonlinear analysis

2.2 FRICTION DAMPERS

Friction dampers are hysteretic systems that dissipate energy with no significant rate

dependence and utilize the mechanism of solid friction that develops between two solid

bodies sliding relative to one another to provide the desired energy dissipation.

Several types of friction dampers have been developed for the purpose of improving

seismic response of structures. Damping using frictional dampers is considered to be the most

effective and economic solution for seismic upgrade.

In late seventies, frictional dampers were developed inspired with the principle of

friction brakes in automobiles. They usually consist of series of steel plates specially treated

to develop most reliable friction. The plates are clamped together with high strength steel

bolts.

During severe seismic excitations, friction dampers slip at a predetermined optimum

load before yielding occurs in other structural members and dissipate a major portion of the

seismic energy.

This allows the building to remain elastic or at least yielding is delayed to be available

during maximum credible earthquakes.

Another feature of friction damped buildings is that their natural period varies with

the amplitude of vibration. Hence the phenomenon of resonance is avoided. The performance

objectives are energy dissipation and strength enhancement.

Nowadays, several frictional dampers are being used. They are available for tension

cross bracing, single diagonal bracing and for chevron bracing. A short description on various

types of friction dampers as follows.

8

2.2.1 Slotted-Bolted Friction Damper

The slotted-bolted damper consists of steel plates that are bolted together with a

specified clamping force. The clamping force is such that slip can occur at a pre-specified

friction force. At the sliding interface between the steel plates, special materials are utilized to

promote stable coefficients of friction.

Figure 2.6 Slotted-Bolted Friction Damper Assembly

2.2.2 Pall Cross-Bracing Friction Damper

The Pall cross-bracing friction damper consists of cross-bracing that connects in the

centre to a rectangular damper. The damper is bolted to the cross-bracing. 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.

Figure 2.7 Pall Cross-Bracing Friction Damper

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2.2.3 Sumitomo Friction Damper

Sumitomo friction damper is a cylindrical friction damper that dissipates energy via

sliding friction between copper friction pads and steel. The copper pads are impregnated with

graphite to lubricate the sliding surface and ensure a stable coefficient of friction.

Figure 2.8 Sumitomo Friction Damper

2.2.4 Energy Dissipation Restraint

The design is similar to the Sumitomo concept, since this device also includes an

internal spring and wedges encased in a steel cylinder. However, there are several novel

aspects of the Energy Dissipation Restraint (EDR) that combine to produce very different

response characteristics.

Figure 2.9 Energy Dissipation Restraint

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The EDR utilizes steel compression wedges and bronze friction wedges to transform the axial

spring force into normal pressure acting outward on the cylinder wall. Thus, the frictional

surface is formed by the interface between the bronze wedges and the steel cylinder. Internal

stops are provided within the cylinder in order to create the tension and compression gaps.

Consequently, unlike the Sumitomo device, the length of the internal spring can be

altered during operation, providing a variable frictional slip force.

The advantages and disadvantages of friction dampers are as follows.

Advantages

Simple and foolproof in construction

Insensitivity to environment factors like temperature, humidity etc.,

Large energy dissipation per cycle

Compact in design and can be easily hidden within drywall partitions

Do not need regular inspection, maintenance, repair or replacement before and

after the earthquake

Disadvantages

Sliding interface conditions may change with time (reliability concern)

Strong nonlinear behaviour, may excite higher modes and require nonlinear

analysis

Permanent displacements if no restoring force mechanism provided

Adds Large Initial Stiffness to System

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CHAPTER 3

VISCOELATIC FLUID DAMPERS VICOELASTIC SOLID DAMPERS

3.1 VISCOELASTIC FLUID DAMPERS

Viscoelastic Fluid dampers are viscoelastic systems that dissipate energy with

significant rate dependence and utilize the fluid orificing and deformation of viscoelastic

fluids as the dissipative mechanism.

A Viscoelastic Fluid damper generally consists of a piston within a damper housing

filled with a compound of silicone or similar type of oil, and the piston may contain a number

of small orifices through which the fluid may pass from one side of the piston to the other.

Thus, it dissipates energy through the movement of a piston in a highly viscoelastic fluid

based on the concept of fluid orificing. Viscoelastic fluid dampers are commonly installed

either within chevron bracing or diagonal bracing.

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.

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.

3.1.1 Orifice Fluid Damper

It contains compressible silicone oil which is forced to flow via the action of a

stainless steel piston rod with a bronze head. The head includes a fluidic control orifice

design. In addition, an accumulator is provided to compensate for the change in volume due

to rod positioning. Alternatively, the device may be designed with a run-through piston rod

to prevent volume changes. High strength seals are required to maintain closure over the

design life of the damper. These uniaxial devices, which were originally developed for

military and harsh industrial environments, have recently found application in seismic base

isolation systems as well as for supplemental damping during seismic and wind-induced

vibration.

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Figure 3.1 Orifice Fluid Damper

3.1.2 Viscous Damping Wall

In this design, the piston is simply a steel plate constrained to move in its plane within

a narrow rectangular steel container filled with a viscous fluid. For typical installation in a

frame bay, the piston is attached to the upper floor, while the container is fixed to the lower

floor. Relative inter-story motion shears the fluid and thus provides energy dissipation.

Figure 3.2 Viscous Damping Wall

3.1.3 Types of Arrangements

The Viscoelastic fluid dampers can be installed by any of the following arrangements

3.1.3.1 Chevron Bracing Arrangement

The chevron bracing arrangement is attractive since the full capacity of the damper is

utilized to resist lateral motion. However, the bracing is subjected primarily to axial forces

and thus, to be effective, the bracing must have high axial stiffness.

Excessive flexibility in the brace reduces the effectiveness of the damper. Note that,

in many installations, the chevron bracing arrangement is inverted such that damper is located

near the floor rather than near the ceiling. This facilitates installation and future inspection of

the dampers.

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Figure 3.3 Chevron Bracing Arrangement

3.1.3.2 Diagonal Bracing Arrangement

The diagonal bracing arrangement may be less effective since only a component of

the damper force (the damper axial force multiplied by the square of the cosine of the angle

of inclination) resists lateral motion. However, the bracing is subjected only to axial forces

and thus is inherently stiff. As an example, for a damper inclined at 45 degrees, the damper

effectiveness is reduced by 50% due to the inclination.

For convenient access, the damper is commonly installed near the bottom corner of

the structural framing and is pin-connected to the framing.

Figure 3.4 Diagonal Bracing Arrangement

3.1.3.3 Toggle Bracing Arrangement

For stiff structures, the motion of the damper can be amplified via a mechanical

linkage known as a toggle brace system.

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Figure 3.5 Toggle Bracing Arrangement

Viscoelastic fluid dampers generally exhibit minimal stiffness over a range of

frequencies that often includes the fundamental natural frequency of building or bridge

structures. Thus, such dampers generally have minimal influence on the fundamental natural

frequency of the structure.

The advantages and disadvantages of viscoelastic fluid dampers are as follows

Advantages

High force and displacement capacity

No added stiffness at lower frequencies

Moderate frequency and temperature dependency

May be able to use linear analysis

Disadvantages

Possible fluid seal leakage (reliability concern)

3.2 VISCOELASTIC SOLID DAMPERS

Viscoelastic solid dampers are viscoelastic systems that dissipate energy with

significant rate dependence and utilize the shear deformation of viscoelastic solids as the

dissipative mechanism.

Viscoelastic solid dampers used in civil engineering structural applications are

usually copolymers or glassy substances that dissipate energy when subjected to shear

deformation. These dampers consist of viscoelastic layers bonded with steel plates or solid

15

thermoplastic rubber sheets sandwiched between steel plates. 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. The shearing action results 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.

3.2.1 General Characteristics

Some characteristics of viscoelastic solid dampers are:

They have no threshold or activation force level, thus they dissipate energy for

all levels of earthquake excitation and wind even while the structure remains

elastic or at the early stages of cracking

They can be manufactured to add significant damping to building frames for

improved structural response. The hysteretic characteristics of dampers are

functions of shear strain level, excitation frequency, damping material type,

thickness and temperature.

They make a substantial contribution to the initial stiffness of the structure.

While the stiffening effect may lead to better control of lateral deformations,

the same stiffening may lead to larger seismically induced forces from the input

ground motions.

When mounted in a structure, shear deformation and hence energy dissipation takes

place when the structural vibration induces relative motion between the outer steel flanges

and the centre plate.

Figure 3.6 Cross-section of Viscoelastic Solid damper

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Figure 3.7 Longitudinal-section of VE Solid damper configuration

If the viscoelastic damper material properties are not strongly frequency or

temperature-dependent over the expected range of frequencies of motion, linear analysis may

be used if the structure remains elastic.

Nonlinear analysis is generally applicable for seismic analysis of structures with

viscoelastic solid dampers since, under strong earthquakes, it may be difficult to completely

eliminate inelastic response.

Figure 3.8 Viscoelastic Solid Damper of a Bracing Member

Advantages

Economically feasible

Activated at low displacements

Provides restoring force

Simple modelling

Disadvantages

Lower Force and Displacement Capacity

Moderate frequency and temperature dependency

17

Possible debonding and tearing of VE material (reliability concern)

Necessity for nonlinear analysis in most

practical cases (as it has been shown that it is generally not possible to add

enough damping to eliminate all inelastic response)

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CHAPTER 4

TUNED MASS DAMPERS

4.1 GENERAL

Tuned mass dampers are dynamic vibration absorbers which consist of an auxiliary

mass-spring-dashpot system anchored or attached to the main structure. The mass moves

relative to the structure and is attached to it by spring and viscous damper in parallel.

The objective of incorporating a tuned mass damper into a structure is basically the

same as that with other energy dissipation devices discussed above, to reduce the energy

dissipation demand on the primary structural members under the action of external forces.

This reduction is a accomplished by transferring some of the structural vibration

energy to the tuned mass damper (TMD) which, in its simplest form, consists of an auxiliary

mass-spring dashpot system anchored or attached to the main structure.

When the structure vibrates, it excites the TMD and the kinetic energy is transferred

from the structure to the structure to the TMD and is absorbed by the damping component of

the device.

A number of practical considerations must be observed in the engineering design of a

TMD system. First and foremost is the amount of added mass that can be practically placed

in the building. The TMD travel relative to the building is an important design parameter. A

large movement often needs to be accommodated for a reasonable reduction of response of

the building.

Another major technique associated with a sliding mass arrangement is to provide a

low-friction bearing surface so that the mass can respond to the building movement at low

levels of excitation.

This becomes more critical when TMD functions are used as an additional damper to

improve occupant comfort. Finally, cost is an issue which must be addressed in the evaluation

of a TMD for a specified application

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Figure 4.1 A Building with Tuned Mass Damper

The principle of a tuned mass damper is based on the fact that by setting its natural

frequency equal to one of the natural frequencies of the structure, its mass always opposes the

motion of the structure and hence suppresses or reduce the structures vibratory motion.

During an earthquake, TMD will move against the direction of main structural

vibration and an inertia force will be acted on the structure to reduce the response of the

structure.

One TMD can attenuate only the first mode response of a structure with its frequency

tuned to the fundamental frequency of the structure. First several modes of a high rise

structure are primary and the anticipated response reduction cannot be achieved if only the

first mode is controlled.

Figure 4.2 Modes of the Structure

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A short description of the various types of tuned mass dampers follows.

4.1.1 Translational Tuned Mass Damper

The Configuration of a unidirectional translational tuned mass damper has mass

which rests on bearings that function as rollers and allow the mass to translate laterally

relative to the floor.

Springs and dampers are inserted between the mass and the adjacent vertical support

members, which transmit the lateral force to the floor level and then into the structural frame.

Bidirectional translational dampers are configured with springs/dampers in two orthogonal

directions and provide the capability for controlling structural motion in two orthogonal

planes.

Figure 4.3 Translational Tuned Mass Damper

4.1.2 Pendulum Tuned Mass Damper

PTMDs replace the translational spring and damper system with a pendulum, which

consists of a mass supported by a cable which pivots about a point.They are commonly

modelled as a simple pendulum.

Figure 4.4 Pendulum Tuned Mass Dampers

21

For small angular oscillations they will behave similarly to a translational TMD and can be

modelled identically with an equivalent stiffness and equivalent damping ratio. Pendulum

tuned mass damper can significantly reduce the excessive floor vibrations during

earthquakes.

The bearing support structure used in the translational TMD assembly is expensive

and susceptible to wear over the lifespan of the system. As a result PTMD designs can be less

expensive to manufacture and last longer

The advantages and disadvantages of viscoelastic fluid dampers are as follows

Advantages

Easy to design and construct

No external power required for their operation

Respond to small level of excitation

Properties can be adjusted in the field

Can be considered in new design as well as in upgrading work

A single unit can be effective in reducing vibrations induced by small

earthquakes, wind and traffic.

Economically cost effective

Require low maintenance

Disadvantages

Large mass and space are needed for their effectiveness and installation

respectively

Effectiveness largely depend on the accuracy of their tuning

Only effective to control the response of a structure in one of its modes.

Several dampers are needed, thus, when the response of the structure is

important in more than one mode.

Friction limits its effectiveness to react to low level excitations

Special features are needed if a damper is to control low level excitations

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CHAPTER 5

TUNED LIQUID DAMPERS

5.1 GENERAL

Tuned Liquid dampers are dynamic vibration absorbers which involves the dissipation

of energy either through the sloshing of liquids in a container or via the passage of liquids

through orifices.

The basic principles involved in applying a tuned liquid damper (TLD) to reduce the

dynamic response of structures is quite similar to that of tuned mass damper. In particular, a

secondary mass of liquid (usually water) is introduced into the structural system and tuned to

act as a dynamic vibration absorber.

In the case of TLDs, the damper response is highly nonlinear due either to liquid

sloshing or the presence of orifices. Tuned liquid damper absorbs structural energy by means

of viscous actions of the fluid and wave breaking.

Different shapes of container, such as rectangular or circular can be used as TLD

implementations. TLD is more effective when it is placed at the top storey of the structure.

To increase the energy dissipation of the sloshing liquid, the flow-damping devices such as

screens or posts in the container are required.

5.1.1 Tuned Sloshing Damper

Tuned Sloshing Dampers are generally rectangular type or circular type and are

installed at the highest floor according to building type. The structure of a TLD is quite

simple; it is a liquid tank partially filled with liquid (or water) A TSD can be classified as

shallow water type or deep water type depending on height of water in the tank.

If the height of water h against the length of the water tank in the direction of

excitation L (or diameter D in case of circular tank) is less than 0.15 it can be classified as

shallow water type else as deep water type if is more than 0.15.

The depth of the liquid in a container could be deep or shallow, depending on the

natural frequencies of the structure under control. Shallow water type has a large damping

effect for a small scale of externally excited vibration, but it is very difficult to analyse the

23

system for a large scale of externally excited vibration as sloshing of water in a tank exhibits

nonlinear behaviour.

Figure 5.1 Tuned Sloshing Damper dimensions

In case of deep water type, the sloshing exhibits linear behaviour for a large scale of

externally excited force. Tuned sloshing damper dissipates energy through the liquid

boundary layer friction, the free surface contamination, and wave breaking.

Generally tuning the fundamental sloshing frequency of the tuned sloshing damper to

the structures natural frequency causes a large amount of sloshing & wave breaking at the

resonant frequencies of the combined TSD-Structure system, this dissipate a significant

amount of energy.

5.1.2 Tuned Liquid Column Dampers

The structure of a TLCD is also quite simple, it is a long U-shape vessel partially

filled with fluid (or water). The U-shape vessel is a long circular or rectangular tube. The

length of the tube should be at least ten times greater than the diameter or the in-plane

dimension of the cross section.

The cross section of a TLCD can either uniform or non-uniform, but it is usually

symmetrical about the vertical centre line of a TLCD. The ends of the vertical columns of a

TLCD are usually open.

Figure 5.2 Tuned Liquid Column Damper dimensions

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Tuned Liquid Column Dampers (TLCDs) dissipates structural vibration by combined action

involving the motion of the liquid mass in the tube, where the restoring force is due to the

gravity acting upon the liquid and the damping effect as a result of loss of hydraulic pressure

due to the orifices installed inside the container.

In simple, the fluid flow and oscillation inside the U-shape vessel due to resonance

can provide a force opposite to the direction of the vibration and can reduce the vibration of

the structure effectively

The damping capacity of TLCD can be controlled through controlling orifice opening.

This allows us to actively control the damping in TLCD system, and frequency of a TLCD

can be tuned by adjusting the liquid column in the tube.

Figure 5.3 A Tall Structure with TLCD

5.1.2.1 Types of Tuned Liquid Column Dampers

Liquid Column Vibration Absorber (LCVA)

Double Tuned Liquid Column Damper (DTLCD)

Hybrid Tuned Liquid Column Damper (HTLCD)

Pressurized Tuned Liquid Column Damper (PTLCD)

5.1.2.1.1 Liquid Column Vibration Absorber

The major difference between a Tuned Liquid Column damper and a Liquid Column

Vibration Absorber is that, the cross section of the LCVA is not uniform. Since it has

different dimensions for vertical and horizontal portions of container, it has benefits of easy

25

tuning and wide range of natural frequency, as the natural frequency of the LCVA is

determined not only by the length of the liquid column but also the geometric configuration.

5.1.2.1.2 Double Tuned Liquid Column Damper

One of the major disadvantages of TLCD and LCVA system is their unidirectional

nature of action, and hence they can be applied effectively to the structure, which oscillates in

only one predominant plane, but not to the structure that oscillates in bidirectional plane. To

overcome this difficulty, a system has been proposed, named Double Tuned Liquid Column

Damper (DTLCD), which consists of two TLCD in orthogonal directions.

Figure 5.4 Double Tuned Liquid Column Damper

5.1.2.1.3 Hybrid Tuned Liquid Column Damper

A Hybrid fluid dynamic system, named Hybrid Tuned Liquid Column Damper

(HTLCD), has also been provided to overcome the above difficulty. This system consists of a

unidirectional TLCD fixed on the surface of a rotatable circular platform whose motion is

controlled by an electrical-mechanical system.

Figure 5.5 Hybrid Tuned Liquid Column Damper

26

This hybrid system is passive in generation of control force to attenuate the displacement

amplitudes, whereas active in searching the right direction.

5.1.2.1.4 Pressurized tuned liquid Column Damper

By implementing a static pressure inside two sealed air chambers at two ends of a

TLCD, a new kind of TLCD is formed, whose frequency can be adjusted by both the length

of its liquid column and the pressure inside its two air chambers. This is called Pressurized

tuned liquid Column Damper

Figure 5.6 Pressurized tuned liquid Column Damper

The advantages and disadvantages of Tuned liquid dampers are as follows

Advantages

Low initial cost and virtually free of maintenance

Ease of frequency tuning

Containers can be utilized for building water supply

The water in the tank can be used for fire fighting

Ease to apply as a retrofitting tools to existing structures

Disadvantages

All the water mass does not participate in counteracting the structural motion

The phenomenon of beating where a fraction of the energy absorbed by TLD

returns back to the structure after the excitation stops

The mechanism to achieve the optimal damping ratio of a TLD is complicated

Highly non-linear behaviour of the sloshing motion, especially under large

excitation amplitudes

Due to the low density of water, a relatively large space is required in order to

achieve the desired mass for the secondary system.

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CONCLUSION

The objective of this report is to present a brief overview of different passive energy

dissipation systems which have been proposed and used for structural applications. The main

points of the report are summarized below.

1. Significant reductions in response can be achieved using supplemental

damping devices.

2. Passive energy dissipation devices enhance energy dissipation in structures

and reduce the energy dissipation demand on structural components. This

category of dampers include: metallic, friction, viscoelastic fluid and solid

dampers. Most of these devices show stable behaviour and are effective in

reducing the seismic response.

3. The performance of tuned systems in reducing the seismic response are also

effective

4. The acceptance of innovative systems in structural engineering is based on a

combination of performance enhancement versus construction costs and long-

term effects. Continuing efforts are needed in order to facilitate wider and

speedier implementation.