energy dissipation devices by ali murtaza rasool

SEISMIC PERFORMANCE OF BUILDINGS WITH PASSIVE

ENERGY DISSIPATION DEVICES

Year: 2009

Year 2012

ENGR. ALI MURTAZA RASOOL 2008-MS-STRU-17

DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY

LAHORE, PAKISTAN

i

SEISMIC PERFORMANCE OF BUILDINGS WITH

PASSIVE ENERGY DISSIPATION DEVICES

Year: 2012

ENGR. ALI MURTAZA RASOOL 2008-MS-STRU-17

INTERNAL EXAMINER EXTERNAL EXAMINER Dr. Asif Hameed Dr. Munir Ahmed CHAIRMAN DEAN Civil Engineering Department Faculty of Civil Engineering This thesis is submitted in partial fulfillment of the requirements for the Degree of Master

of Science in Structural Engineering

DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF ENGINEERING AND TECHNOLOGY

LAHORE, PAKISTAN

ii

In The Name of Allah, the Most Beneficent, the Most Merciful

iii

DEDICATED TO

To my Beloved Parents, Wife, Brothers, Sisters and

their children

iv

ACKNOWLEDGEMENTS

All praises and gratitude to The Almighty Allah; the most gracious, most merciful and

most beneficent; who bestowed upon me the enlightenment and courage to complete this

thesis successfully.

I am very thankful to my worthy thesis supervisor Dr. Asif Hameed and would like to

express sincere thanks for his supervision, valuable suggestions and keen supervision all

the way through this project.

I am thankful to Engr. Shaukat Qadeer, General Manager, National Engineering Services

Pakistan (Pvt.) Ltd., Lahore and would like to extend my heartiest gratitude for his kind

guidance and enthusiastic encouragement during my research project.

I am also very gratified to my parents, brothers, sisters and their children for their prayers,

encouragement and support throughout my career.

In the end, I would like to articulate special thanks to Idress Raza, Khalil Ahmad, Bilal

Zulkarnain, and Farhan Tahir for support and co-operation before and during thesis.

Author

2012

v

ABSTRACT

Earthquake mitigation strategies, of which in-structure damping is one attempt to reduce

the demand on a structure rather than the more usual approach of adding capacity. The

three general classifications of seismic mitigation hardware are Seismic Isolation, Passive

Energy Dissipation and Active Control. This research is restricted to the range of devices

within the Passive Energy Dissipation classification. Most of the effectiveness of isolation

is the period shift effect, lengthening the period of response, with a lesser effect from

damping. In-structure damping has a minor effect on period and in fact often shortens the

period if anything. Response reductions rely entirely on energy dissipation. Almost by

definition, buildings not suitable for base isolation are the best candidates for in-structure

damping. It is most effective on flexible buildings with slender lateral load systems and is

also suitable for soft soil sites. The suitability of flexible buildings arises from the fact

that in-structure damping is activated by inter-story movement, either velocity or

displacement. The greater the movement the greater the damping which gives rise to a

paradox in that the aim of the damping is to reduce the movements which give rise to the

damping. The purpose of this research is to study the performance of building by using

passive energy dissipation devices, different type of devices used are Hysteretic dampers,

Friction dampers Viscous and Visco-elastic dampers. The finite element modeling

technique ETABS version 9.7.2, which is a product of Computer & Structure Inc., is used

in this research to observe the behavior of structure by using different types of dampers.

Three prototype concrete buildings (3, 5 and 10 Story) with same configuration are

analyzed by using different types of damper and using time history analysis. In general,

this research indicates first the response of structure building in terms of storey drifts,

base shear and displacement without using dampers and just by increasing damping ratio

from 0 to 40%, then buildings are analyzed by using different types of dampers and by

using different variation and response of buildings is observed in terms of, displacements,

base shear and floor accelerations. Viscous and Visco-elastic dampers are more effect for

3 & 5 storey buildings while Friction and Hysteresis dampers are effective for 10 storeys.

vi

TABLE OF CONTENTS

DEDICATIONS iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF FIGURES ix

LIST OF TABLES xii

1. Introduction 1 1.1 General 1

1.2 Objectives 3

1.3 Scope of Research 3

1.4 Limitations 3

1.5 Thesis Overview 3

1.6 Utilization of Research 4

2. Literature Review 5 2.1 General 5

2.2 Earthquake Characteristics 5

2.3 Causes of Earthquake 6

2.3.1 Plate tectonic Theory 6

2.3.2 Faulting 7

2.3.3 Seismic Waves 7

2.4 Response of Building Structures 7

2.4.1 Behavior of Structure during Ground Motion 7

2.4.2 Structural Response Characteristics 7

2.5 Types of Energy Dissipation Devices 8

2.6 Seismic Performance of Passive Energy Devices 9

2.7 Types of Passive Energy Dissipation Devices 12

2.7.1 Hysteretic Metal Yielding Damper 13

2.7.1.1 Damper Description 13

2.7.1.2 Properties of Damper 14

vii

2.7.1.3 Generic Hysteretic Properties 16

2.7.1.4 Advantages of Hysteretic Damper 16

2.7.1.5 Disadvantages of Hysteretic Damper 16

2.7.2 Friction Damper 17

2.7.2.1 Damper Description 17

2.7.2.2 Damper Characteristics 18

2.7.2.3 Advantages of Friction Damper 18

2.7.2.4 Disadvantages of Friction Damper 19

2.7.3 Viscous Damper 19


2.7.3.2 Advantages of Viscous Damper 24

2.7.3.3 Disadvantages of Viscous Damper 24

2.7.4 Visco-elastic Damper 24


2.7.4.2 Advantages of Visco-elastic Damper 27

2.7.4.3 Disadvantages of Visco-elastic Damper 27

3. Methodology 28 3.1 General 28

3.2 Building Description 28

3.2.1 Building-1 28

3.2.2 Building-2 29

3.2.3 Building-3 30

3.3 Material Properties 31

3.4 Loading 32

3.4.1 Dynamic Loading 22

3.5 Dampers Application 32

3.5.1 Dampers Characteristics 34

3.5.2 Dampers Variations 35

3.5.3 Dampers Locations 37

3.5.4 Total Analysis Performed 38

3.6 Computer Analysis Performed 38

3.6.1 Defining Grid System 39

viii

3.6.2 Defining Frame Sections 40

3.6.3 Defining Hysteretic Damper 40

3.6.4 Defining Friction Damper 42

3.6.5 Defining Viscous Damper 42

3.6.6 Defining Visco-elastic Damper 43

3.6.7 Defining Time History Data 44

4. Results & Discussions 46 4.1 General 46

4.2 Response of Buildings without Dampers 46

4.2.1 Effects of Damping on Drift & Base Shear 47

4.2.2 Effects of Damping on Displacements 48

4.3 Response of Buildings with Dampers 50

4.3.1 Effect of Damping Parameter on Displacement 50

4.3.1.1 Hysteretic Damper 50

4.3.1.2 Friction Damper 52

4.3.1.3 Viscous Damper 54

4.3.1.4 Visco-elastic Damper 56

4.3.2 Effect of Damping Parameter on Base Shear 58





4.3.3 Effect of Damping Parameter on Floor Accelerations 66





5. Conclusions and Future Recommendations 75 5.1 Conclusions 75

5.2 Future Recommendations 76

References 77

ix

List of Figures

Serial Description Page

Fig.- 1.1 Collapse of Office Building During Kobe Earthquake, Japan 2

Fig.- 2.1 Worldwide tectonic plates distribution 6

Fig.- 2.2 Different Dampers Configurations 9

Fig.- 2.3 Story Displacement Comparisons 11

Fig.- 2.4 Hysteretic Metal Yielding Damper Bracing System 13

Fig.- 2.5 ADAS Elements and Installation 14

Fig.- 2.6 Yielding Hysteresis Damper 15

Fig.- 2.7 Pall Friction Damper 17

Fig.- 2.8 Hysteresis Loop for Friction Damper 18

Fig.- 2.9 Fluid Viscous Damper 20

Fig.- 2.10 Damper Coefficient 22

Fig.- 2.11 Damper Exponent, , For Constant, C 22

Fig.- 2.12 Damper Exponent, , For Constant Damper Force 22

Fig.- 2.13 Velocity Cut-off on Viscous Damper 23

Fig.- 2.14 Loading Frequency 23

Fig.- 2.15 Displacement Amplitude 23

Fig.- 2.16 Visco-elastic Damper and Installation 25

Fig.- 2.17 Force displacement Relationship for Visco-elastic Damper 26

Fig.- 3.1 Frame Elevation of Building -1 29



Fig.- 3.4 E-W Direction Time Acceleration Graph of El-Centro

Earthquake 32

Fig.- 3.5 El-Centro Spectral Acceleration 33

Fig.- 3.6 El-Centro Spectral Velocity 33

Fig.- 3.7 El-Centro Spectral Displacement 33

Fig.- 3.8 Damper Variation 35

Fig.- 3.9 Damper Distribution with Height 36

x

Fig.- 3.10 3-Storey Building 37



Fig.- 3.13 Defining Grid System 39

Fig.- 3.14 Defining Frame Section 40

Fig.- 3.15 Defining Hysteretic Damper 41

Fig.- 3.16 Defining Friction Damper 42

Fig.- 3.17 Defining Viscous Damper 43

Fig.- 3.18 Defining Visco-elastic Damper 44

Fig.- 3.19 El-Centro Time History function 45

Fig.- 4.1 Graph b/w Drift & Increasing Damping Ratio 47

Fig.- 4.2 Graph b/w Base Shear & Increasing Damping Ratio 47

Fig.- 4.3 Graph b/w Time & Displacement (3-Storey Building) 48



Fig.- 4.6 Graph b/w Displacement & Damping Parameter (3-Storey

Building) - Hysteretic Damper

50



51



51


Building) - Friction Damper

52



53



53


Building) - Viscous Damper

54



55

Fig.- 4.14 Graph b/w Displacement & Damping Parameter (10-Storey 55

xi




56


Building) - Visco-elastic Damper

57



57

Fig.- 4.18 Graph b/w Base Shear & Damping Parameter (3-Storey


58



59



59



60



61



61



62



63



63

Fig. 4.27 Graph b/w Base Shear & Damping Parameter (3-Storey


64



65



65

Fig.- 4.30 Graph b/w Acceleration & Damping Parameter (3-Storey 67

xii


Fig.- 4.31 Graph b/w Acceleration & Damping Parameter (5-Storey


67



68



69



69



70



71



71



72



73



73



74

List of Tables Table- 3.1 Material Properties 31

Table- 3.2 Damper Properties 34

Table- 3.3 Damper Variation 36

1

Chapter 1

INTRODUCTION 1.1 General

Earthquake has always adverse effects on mankind. Building structures are susceptible to

severe damage and/or collapse during moderate to strong ground motion. This has been

illustrated after study of recent and past earthquake damages. Residential buildings,

bridges, industrial and port facilities could get adversely damage with and an earthquake

magnitude of six or more, with such magnitude structures could get adversely damaged.

Therefore result in great financial and economic loss. Several destructive earthquakes

have hit Pakistan over the times (October 08, 2005 earthquake being the one in renown

recently). Major area of Pakistan has always under the danger of this natural hazard

(earthquake). Engineers are now well equipped with knowledge to cope up with this

natural hazard but even now very less attention and research has been carried out on one

of the major effects of earthquake i.e. use of Control devices. In seismic design of

structure, the design forces are generally calculated using an elastic response spectrum.

To account for energy dissipation through inelastic action a response modification factor

Rw (Uniform Building Code, 1994) is used to reduce the calculated elastic forces. The

philosophy in permitting inelastic action is that during severe earthquakes, the structure

can sustain damage without collapse due to the ductility of members and redundant load

paths. Structural members are significantly damaged by inelastic action contributed to

substantial energy dissipation. In addition, the hysteretic behavior of members degrades

with repeated inelastic cycles. Non-structural elements such as in-fill walls, partitions,

doorways, windows, and ceilings are also affected by large inter-storey drifts which

usually result in considerable damage to these elements because of inelastic action.

Major portion of earthquake-induced energy can be absorbed by energy dissipation

members such as beams, columns, or walls. Inter-storey drifts can be considerably

2

reduced by these devices and consequently nonstructural damage. In addition, lower

accelerations and smaller shear forces lead to lower ductility demands in structural

components.

Passive energy dissipation systems have been developed to achieve the above objectives.

Passive energy systems include a wide range of devices for enhancing damping, stiffness,

and strength and passive materials. In general, they are characterized by their capability to

dissipate energy either by transfer of energy among different modes of vibration or by

translation of kinetic energy to heat. The former category, referred to as passive dampers,

includes supplemental devices which function on principles such as frictional sliding

surfaces (friction dampers), yielding of metals (hysteretic and metallic dampers), phase

transformation in metals (shape memory alloys), deformation of Visco-elastic solids

(Visco-elastic dampers), and fluid orificing (fluid dampers). Figure 1.1 showing the effect

of earthquake on building in which no energy dissipation devices was installed.

Fig.- 1.1 Collapse of Office Building During Kobe Earthquake, Japan

3

1.2 Objectives

The basic objective of this research is to study seismic behavior of buildings by using

Passive Energy Dissipation Devices. Energy dissipation systems of different types will be

used for study, as well as their behavior will also be observed in this research. These will

be Viscous dampers, Metallic dampers, and Friction dampers. The particular

characteristics of passive energy systems will be briefly described in research. The further

sub-objectives of research will be:

i. Varying Damper properties in Uniform, Triangular and Reverse-triangular

variation.

ii. Analyzing effect of Passive Energy Dampers on different configuration of

buildings.

1.3 Scope of Research

Scope of this research includes following main activities:

To analyze building behavior by using Hysteretic, Friction, Viscous and Visco-elastic

damper.

Analyze dampers behavior on three, five and ten storey building frames.

Varying dampers properties in uniform, triangular and reverse triangular mode.

Finally comparison will be made between different types of Passive Energy

Dampers.

1.4 Limitation

The scope of this research is limited to medium to low rise buildings in low to moderated

seismic zone that remain in elastic range, i.e. no plastic hing mechanism should develop.

1.5 Thesis Overview

The research thesis consists of five chapters, overview of these chapters is explained

below.

Stage 1: Introduction

This chapter includes the introduction of the research, research methodology, objectives,

scope, input and output.

4

Stage 2: Literature Review

This chapter includes detailed literature on all the relevant topics related to passive energy

dissipation devices. It includes different types of passive energy dissipation devices e.g.

Friction damper, Viscous damper and Metallic or Yielding damper, their uses, advantages

and disadvantages, their behavior in different types of buildings etc. It also includes how

different types of passive energy devices can be used in buildings with different bracing

strategies. This literature is collected from various books, research papers and through

web browsing.

Stage 3: Methodology

It completely explains the computer modeling, model details and includes the analysis

results of model, computation and comparison of various parameters such as

displacement, base shear and floor accelerations etc for different types of dampers.

Stage 4: Results & Discussions

This chapter contains detailed analysis of buildings with each type of damper along with

the discussion on the analysis and results.

Stage 5: Conclusion and Recommendations

In last chapter conclusions and recommendations for future research on similar topic is

discussed in this chapter.

1.6 Utilization of Research

Normally in Pakistan, due to lack of modern research conventional types of retrofitting

techniques are used comprising of providing shear wall and column jacketing. The

proposed study is based on latest development and outcome of this will be helpful for the

structural engineers to observe phenomenon of passive energy dampers and incorporate it

in their designs. This research will also be helpful in the following respect.

Use of different passive energy dampers that not only provide adequate energy

dissipation under earthquake excitation, but also are easy to install and inspect.

Use of different bracing strategies with Passive Energy Dampers.

Use of different passive energy dampers to reduce the damages of structures and

hence preventing loss of lives.

5

Chapter 2

LITERATURE REVIEW 2.1 General

Ductility and inelastic deformations are important part of seismic design. The

performance of a reinforced concrete framed buildings subjected to a high magnitude

earthquake in regions of inelastic deformation depends on fine seismic detailing of its

components. Sufficient ductility may not be incorporated in many structures constructed

before the development of severe seismic design. Studied performed by different

researchers have shown that during severe earthquakes non-ductile concrete farmed

buildings are generally damaged or also collapse. Modern technical developments in

field of earthquake engineering have led to an increase in the significances of the repair

and strengthening of existing buildings.

A detailed evaluation of the type and extent of damage should be required for repairing a

fully or partially damaged concrete structure. The repairing techniques should be selected

in accordance with the position of the damage and its influence on the overall response of

structure. Improving seismic performance of a structure usually engages an increase in

the strength and stiffness of the strengthened members.

2.2 Earthquake Characteristics

Earthquakes do not directly produce building collapse. Ground motions are the real cause

of seismic damage. The dynamic response of buildings to ground shaking motions is real

cause of seismic damage. The dynamic response of structures to ground motions is most

important cause of earthquake-induced damage in buildings. Therefore, it is very

important to understand in which way sudden movements of the source are transformed

in ground motions at building site.

Observations of the damage after the earthquake have shown that the earthquake

characteristic, very different from one site to another, can have a strong influence on the

6

structure performance. The characteristic reflect not only the source properties, but also

local effects and site earths configuration. In order to be considered in seismic design of

structure, it is very important to underline the main characteristic of these ground motion

types, taking into account the source typologies. The target can be obtained by processing

the recorded earthquakes, or, as a new challenge in Earthquake Engineering, by studying

the rupture processes and propagation of seismic waves by numerical modeling.

2.3 Causes of Earthquake

2.3.1 Plate Tectonic theory

Today it is accepted that the earth is covered by some rigid tectonic plates which slides

across the surface of earth, over and on a partially molten interior layers. According to

geological terms, the lithosphere forms from the earths solid rock plates. The rigid

lithosphere can be considered to float on the ductile asthenosphere, which flows. So the

lithosphere (surface of earth) is broken up into what are called tectonic plates; Plate

tectonics (from the Greek tecton, meaning one who construct and destroys) being the

theory of geology developed to explain the phenomena of continental drift. This theory

thus defines the tectonic plate and their boundaries. Figure 2.1 shows the worldwide

distribution of tectonic plates.

Fig.2.1 Worldwide tectonic plates distribution

7

2.3.2 Faulting

Elastic strain energy due to tectonic processes will be stored and then released through the

boundary zone, when two ground-masses slide with respect to each other. Earthquake will

be produced when the distorted blocks shatter back towards equilibrium.

2.3.3 Seismic Waves

Up-to 10% of the total earths plate tectonic energy in the form of seismic waves will be

dissipated due of fault fractures of the earths crust. Two types of seismic waves, body

and surface waves are generally responsible for earthquake shaking.

2.4 Response of Building Structures

2.4.1 Behavior of Structure during Ground Motion

The main effect of ground motions on a structure is the dynamic nature of the earthquake

loading. As a consequence of time variability, the ground motions are characterized by

the time history of the three ground motion parameters at the level of foundation,

acceleration, velocity and displacement. For the structure subjected to such ground

motions, these actions will propagate through the structure as waves, causing large

oscillations. Therefore, the structural response also varies with time, involving dynamical

movements. The structure performs a series of forced oscillations during the earthquake,

having a much complex chaotical movement, characterized by peaks of displacement

velocity and, acceleration, produced by different times. After finishing seismic action, the

structure continues to move under form of free oscillations, which depend on its level of

damping. For strong damping, the movements stop quickly, while for weak damping

structure continues to move a long time after the end of the seismic action. Generally, the

maximum values of movements occur during the forced oscillations, but for short seismic

actions (such as pulse loading), the maximum values can be reached during free

oscillations.

2.4.2 Structural Response Characteristic

The structure movements are characterized by vibration modes, being a superposing of

these modes in function of participation factor. The vibration modes are horizontal,

vertical and torsional. For horizontal modes, generally the most important for seismic

8

design, the number of vibration modes depends on the number of masses. But, in the

majority of cases, the first three modes are the most important for the structural analysis.

Which mode is determinant for the structural response depends on the ground motion and

the structure characteristic. Looking to ground motions and structural response, one can

see that the later is much larger than the input movements. The reason of this

amplification is due to the phenomena of resonance, which is maximum when one of the

natural frequencies of the structure is equal to the one of frequencies of the ground

motion oscillation. In this situation, there be a very important amplification of structural

response, as a function of damping effects.

2.5 Types of Energy Dissipation Devices

Since the early 1970s for earthquake engineering applications, many kinds of dissipation

devices have been tested and used. These devices can be classified into three categories:

1) Seismic isolation system:

Seismic elastomeric bearings

Lead rubber bearings

Sliding and Combined elastomeric bearings

Friction sliding pendulum system

Sliding bearing with restoring force

2) Supplemental energy dissipation devices:

i. Passive energy dissipation ii. Active and Semi-active systems

Metallic dampers Active bracing systems (ABS)

Friction dampers Active mass dampers

VE solid dampers Variable damping & stiffness system.

Viscous fluid/VE dampers Smart materials

Tuned mass dampers (TMD)

Tuned liquid dampers (TLD)

9

2.6 Seismic Performance of Passive Energy Devices

Fixed base system involves the dissipation of seismic energy during ground motion

through various dissipation devices, widely favored for enhancing the seismic

performance through a current strategy. The demand on primary structural members are

thereby reduced by adding passive energy devices to conventional structures, the passive

energy thereby absorb seismic energy. Therefore, significant reduction of structural and

non-structural damage could be achieved through a good design which reduces the

inelastic demand on primary structural members. Generally, these devices are introduced

in the form of bracing. While the conventional bracing members dissipate the input

energy by means of axial plastic deformations, this energy can be dissipated by shear or

flexural yielding of these devices according to some arrangement.

De Matteis et al., 2006, many of passive energy devices have been recently proposed and

tested. Some of them are presented in following figure 2.2 shows a device placed on a

rectangular frame which is inserted at the intersection of the two braces in an X-braced

system. This frame is made of thick steel plate shaped in order to have a uniform flexural

resistance. The inverted Y-braced frames, having a vertical link, behave as a passive

control system, where the link allows a large amount of input energy to dissipate, without

and damage to external framed structure. The improving of the dissipation capacity can

be obtained by adding some special devices, known as ADAS (Added Damping and

Stiffness Elements) systems: honeycomb shaped, X shaped, inclined shaped, U shaped,

omega shaped, E shaped, etc.

Fig.2.2 Different Dampers Configurations

10

Constantinou et al., 1998, Conventional design procedure is not appropriate in situation

when a structure have to remain functional after earthquake. Under such cases, the

structure must be designed with sufficient strength which is enough to minimize the

inelastic deformations, however, this approach is very expensive. Furthermore, in such

type of structures, special safety measures need to be taken in safeguard against damage

of important secondary system, which are needed for continuing serviceability. Over

couple of past decades the outstanding developments have been made in alternate design

strategies, which incorporate earthquake protective systems in the structure. By allowing

structural members to dissipate and absorb the transmitted seismic energy, inelastic

deformations seek to prevent occurrence of conventional design approach, therefore

inelastic cyclic deformations produced in specially created regions. As a result the

structure may not remain longer repairable due to this strategy that implies the structural

damage.

Carlos Y.L. et al., 2003, In this research rehabilitation of a 3-storey steel structure with

one basement level is carried out. The precast concrete panels and buildings steel-framed

system did not satisfy current building code seismic requirements. The panels, framing

and their connections would most likely suffer severe damage in a major seismic event.

The building is being retrofitted to diminish structural deficiencies and meet life safety

performance levels by using friction damper devices. Seismic dampers provide the

benefits of reducing seismic forces and movement in the structure by absorbing part of

the seismic forces generated in the ground. In this scheme, twenty four (24) 250kip

friction dampers are placed at the ground level and twenty four (24) 200kip friction

dampers are placed at the 2nd floor. The analysis follows the guideline of FEMA 356.

The analysis results illustrate that the retrofitted structural framing is able to dissipate the

seismic energy in a controllable manner because of the friction dampers capability to

absorb a constant force with varying storey displacement. Figure 2.3 shows that, the

displacement of stories has been reduced about 50% because of using friction damper.

11

Fig.2.3 Story Displacement Comparisons (Carlos Y.L. et al., 2003)

The research undertaken by Madsen et al., (2001) was concentrated on using dampers

within tall buildings that contain shear walls to enhance their seismic response. This new

method of retrofitting buildings involves the implementation of Visco-elastic dampers

placed within the shear wall of the building structure. According to results of this project,

it was shown that it is more effective to place VE dampers in the lowest storeys. The

hypothesis behind this being the highly damped and rigid lower part of a multi storey

building modulates the seismic dynamic excitation resulting more effectively from strong

ground shakings. This result in increasing the natural time period hence reducing the

amount of seismic energy that is attracted to it, and decreasing the stiffness at the base of

the structure. Therefore, the lower storeys of buildings are most effective position for

installing the dampers.

A 12-storey concrete building was considered for retrofit by a number of engineers. Shao

and Miyamoto (Shao et al., 1999), who were also involved in the study, suggested that

passive dampers could be the most cost-effective solution. During preliminary study

several damping systems were selected and studied for seismic retrofit. Linear and non-

linear time history analyses were performed. Performance comparisons of earthquake

response parameters were analyzed. The results of this study revealed that the best

performance was achieved by the combination of nonlinear viscous dampers with

supplemental friction devices. These systems met the performance target with great

Stor

ey D

ispla

cem

ent (

in)

Level

Storey Displacement Comparison E/W Direction

Scheme A Braces on all Levels

Scheme B Braces with Dampers below

Scheme C Existing Moment Frames

12

saving over the previously proposed retrofit schemes. Friction damping system had

significant saving over the viscous damping system due to the damper unit price

difference. In contrast, viscous dampers with supplemental friction dampers would have

25% lower floor acceleration responses over friction damping system. These higher floor

acceleration responses could increase the cost of the tile wall strengthening. Based on

these results the authors suggested that combination of a nonlinear viscous damper system

with friction damper revealed great potential for the further seismic retrofit.

2.7 Types of Passive Energy Dissipation Devices

Damping of the structures could significantly decrease the displacement and acceleration

responses, and decrease the shear forces, along the height of building. The use of passive

dampers in buildings is desirable for the following reasons.

1. Dampers can provide the building with additional stiffness and damping to reduce

the response.

2. Energy dissipation in building can be confined mainly to passive dampers.

3. Damage to the building can be limited to passive dampers which are easier to

replace than structural components and do not affect the gravity load-resisting

system.

Passive energy dissipation devices are used extensively in other areas of vibration control

such as shock absorber for vehicles, vibration isolators for equipment, pipe restraints, and

shock isolation devices for mitigation of blast effects. In the last two decades, much effort

has been directed towards applying passive energy dissipation techniques to seismic

applications. Many of the devices that have emerged for passive control were first

developed as damping devices for seismic base isolation system. Several passive damping

devices have been suggested and used for wind and earthquake loads. The devices are

categorized according to how they operate. Following is a brief discussion of the

application of each device:

13

2.7.1 Hysteretic Metal Yielding

2.7.1.1 Damper Description

The mild steel yielding properties have been recognized and used to enhance the seismic

performance of the structures. Energy dissipation can be concentrated primarily at shear

links, by using the eccentrically braced frame that represents a widely accepted concept.

Such types of shear links correspond to part of the structural system which is probable to

undergo damage in severe earthquakes conditions. The ability of braced frames to

dissipate energy over extended periods is questionable because the repeated buckling and

yielding of the braces may cause degradation of their stiffness and strength.

Several devices which function as an integral part of seismic isolation system have been

researched and developed in New-Zealand (Tyler, 1978; Skinner et al., 1981). Tyler

(1984) introduced an energy dissipater fabricated from round steel bars for cross-braced

structures. Figure 2.4 shows the rectangular steel frame has disconnected the compression

brace to prevent pinched hysteretic and behavior buckling. Energy is dissipated during

earthquake excitation by inelastic deformation of the diagonal direction of the tension

brace in the rectangular steel frame. This concept has been used in building and several

warehouses. Variations of the steel cross-bracing dissipaters have been developed in Italy.

A 29-storey suspended steel building with floors hung from the central core with tapered

steel devices acting as energy dissipaters between the core and the suspended floors was

constructed in Naples, Italy.

Fig.2.4 Hysteretic Metal Yielding Damper Bracing System

(Tyler, 1978; Skinner et al., 1981)

14

Fig.2.5 ADAS Elements and Installation (Bachtel Power Corporation)

Another device, referred to as added damping and stiffness (ADAS) consisting of

multiple X-shaped steel plates, Figure 2.5 was introduced by Bachtel Power Corporation.

By using rigid boundary members, the plates deform in double curvature, and yielding

takes place over entire plate surface. The device can sustain repeated inelastic

deformation by avoiding concentrations of yielding and premature failure. Extensive

experimental research has been carried out to observe the performance of ADAS elements

in energy dissipation system. The test showed stable hysteretic behavior without any sign

of pinching or stiffness degradation for the displacement up to 13.6 times the yield

displacement of device. It should be noted that the ADAS elements and their braces on

which it is supported primarily resist shear forces. The ADAS elements are designed in

such a way that it yield in a predetermined manner and ease the main frame from

excessive ductility demand.

2.7.1.2 Properties of Dampers

Hysteretic yield damper is defined by an elastic stiffness, KD, and a yield force, FY, as

shown in Figure 2.6. Elastic stiffness of the structure, KE, and function of these damper

properties is used to describe the performance of damper.

15

Fig.2.6 Yielding Hysteresis Damper

Following shows the properties of damper in terms of structure properties,

=

, is the ratio of total structure stiffness over damper stiffness 2-1

=

, is the ratio of total structure force over damper yield force 2-2

The equivalent viscous damping can be calculate by using above definitions as described

below,

=

2-3

WD is defined as hysteretic energy dissipation which is equal to area under the hysteresis

loop, at which displacement is calculated as:

= 4( ) 2-4 Where, Y is defined as yield deformation of hysteretic damper which is equal to FY/KD

WS, is the strain energy which is calculated as

= ( + ) 2-5 From equation 2-4 & 2-5, the damping is defined as

= ()() 2-6

Now substituting value of FY = KD Y and KD = fKE, equation 2-6 will become

Displacement

Structure

Damper

Forc

e FE KE

Fy

16

= () () 2-7

Cancelling out the value of KE gives an equation for damping as a function of the damper

properties and displacement, relative to the structure:

= ()() 2-8

2.7.1.3 Generic Hysteretic Properties

, is defined as the ultimate displacement which can be expressed in terms of elastic

properties of structure as:

=

2-9

Y, is defined as the yield displacement of brace which can also be expressed in terms of

the elastic properties of structure as:

= = 2-10 Substituting values of equation 2-9 & 2-10 in equation 2-8, we will get:

= ()() 2-11

Equation for damping is obtained by cancelling out values of displacements. , which is a

function exclusively of the ratio of damper yielding force to elastic force, g, and equation

2-12 shows the ratio of elastic stiffness of damper to the elastic stiffness of structure, f,

= ()() 2-12

2.7.1.4 Advantages of Hysteretic damper

Force-Limited

Relatively Inexpensive

Adds both Damping and Stiffness

2.7.1.5 Disadvantages of Hysteretic damper

Hysteretic damper need to be replaced after major Earthquake

Behavior of hysteretic damper is highly nonlinear

Hysteretic damper also adds stiffness to system

17

2.7.2 Friction Damper

2.7.2.1 Damper Description

A wide range of friction devices has been proposed and developed for energy dissipation

in structure. Most of these devices generate rectangular hysteresis loop, which shows that

the performance and behavior of friction damper is comparable to Coulombs friction.

Generally, these devices have good performance characteristics, and their behavior is

relatively less affected by load frequency, number of load cycles, or variations in

temperature. Furthermore, these devices have high resistance to fatigue. The friction

devices differ in the material used for the sliding surface and in their mechanical

complexity. An example of friction dampers proposed by (Pall and Marsh, 1982) and

(Pall et al., 1987) is a device that can be placed at the junction of intersecting (cross)

bracing in frames as shown in Figure 2.7.

Fig.2.7 Pall Friction Damper (Pall et al., 1987)

The tension, when loaded, induces slippage at the friction joint. Consequently, the

compression brace slip because of these four link force. Even though the braces are

designed in such a way that these are effective in tension only but still in this way, in both

braces, energy is dissipated. The device is designed to prevent slippage under normal

service loads. Results have shown that effectiveness of these devices in reducing inter-

storey displacements in comparison to moment resisting frames and providing a

significant increase in energy dissipation capacity without such devices.

18

A stable rectangular hysteresis is generated by the majority of friction devices even

though some devices, with slip load proportional to displacement, provide non-

rectangular hysteresis shapes, such devices also configured such as they produce a self-

centering force. Rectangular hysteresis which is common in most common of types is

shown in Figure 2.8.

Fig.2.8 Hysteresis Loop for Friction Damper

2.7.2.2 Damper Characteristic

By setting the ratio of damper stiffness to structure stiffness, f, to , and by considering

the damper alone, the equivalent viscous damping can be calculated by modifying the

equation 2-12, providing the formula:

= () 2-13

2.7.2.3 Advantages of Friction Dampers

Friction dampers are normally force dependent.

Their main advantage is that they are easy to fabricate and construct.

Friction dampers are comparatively cheaper.

Damper

Displacement

Forc

e

19

2.7.2.4 Disadvantages of Friction Dampers

Friction damper are difficult to maintain over period of time.

Behavior of friction damper is highly nonlinear.

Friction dampers adds initial stiffness to the system.

In friction dampers undesirable residual deformations are possible.

2.7.3 Viscous Dampers

Dampers which utilize the viscous properties of fluids have been developed and used in

structural applications. A viscous-damping (VD) wall system was developed by

Sumitomo Construction Company, Japan. The device consists of an outer steel casing

attached to the lower floor and filled with a highly viscous fluid. An inner moving steel

plate hanging from the upper floor is contained within the steel casing. The viscous

damping force is induced by relative velocity between the two floors. The principle of

fluid viscous dampers on which they operate is of fluid flow through orifices, which have

been used since many years in automotive, aerospace, and defense industries. They are

beginning to emerge in structural applications. These dampers possess linear viscous

behavior and are relatively insensitive to temperature changes. Experimental and

analytical studies of building and bridges with fluid viscous dampers manufactured by the

Taylor Devices, have been carried out by (Constatinou and Symans, 1992) and

(Constatinou et al., 1993).

Figure 2.9 shows the Taylor device which consists of an accumulator and a bronze orifice

head with a stainless steel piston and which is filled with silicon lubricate. The flow

through orifice allows the device to process over a temperature range of -40O C to 70O C,

a passive bi-metallic thermostat compensates it. The volume of fluid is condensed by the

product piston rod area and travel distance, and the force in the damper is generated

across the piston head by a pressure differential. Due to incompressibility of fluid, the

reduction in volume causes the restoring force which is prevented by the accumulator.

20

Fig.2.9 Fluid Viscous Damper (Taylor device Inc.)

2.7.3.1 Damper Properties

The viscous damper is generally described by the formula

= ||() 2-14 Figures 2-1 to 2-6, illustrates the impact of C, parameters, and the effect of the

characteristics of the loading system, each generated for the sinusoidal displacement

trace. The damper functions defined in the above equations of viscous damper ate the

exponent , damping force coefficient C, and a limit of velocity, if there is any. The

formula for the velocity, , and displacement, , are expressed as:

= 2-15 =

= 2-16

The legend identified the values of the parameters; C represents damping coefficient, T

represents time period of applied sine wave, a is the damping exponent, which will be

used for the figures shown below.

The graph in Figure 2.10 shows the effect of varying, C. The damping force is

linear with C, equation (2-14) shows damping constant C. The value of damping

force is doubled when for the same velocity value of C is doubled. The shape of

the velocity trace is followed by the shape of the displacement versus damping

curve which is elliptical.

ACCUMULATOR HOUSING

HIGH STRENGTH ACETAL RESIN SEAL

CYLINDER

COMPRESSIBLE SILICON FLUID

PISTON ROD

SEAL RETAINER

CHAMBER 1 CHAMBER 2

PISTON HEAD WITH ORIFACES

CONTROL VALVE

ROD MAKE-UP ACCUMULATOR

21

Figure 2.11 remain the coefficient C, constant and varies value of the exponent

from 0.3 to 1.0, which happens in typical range of the practical dampers. The

damping force decreases the damping force function tends from an elliptical shape

to a more rectangular form as value of decreased from 1.0 to 0.3.

also varies Figure 2.12, but the value of coefficient C is adjusted in such a

way that total damping force does not change. When is reduced to 0.3 the

value of damping coefficient must increase from 5.5 to 20 in order to sustain the

damping force provided by = 1.0. The changing of the shape from ellipse to a

rectangle as the exponent is decreased is clearly shown in this plot.

The effect of a velocity limit is shown in Figure 2.13 which confines damper

force, as the value of C increases from 5 to 20, to 50 units. The limit truncates

the ellipse, as the value of C increases. This decrease has a same effect to reduce

exponent in such a way that the elliptical shape become more rectangular.

The graph in Figure 2.14 illustrate the effect on damping force of varying time

period of sine curve displacement by keeping same amplitude. For same

displacement greater damping force is provided by a shorter period. The velocity

is inversely proportional to T, which is a period of response, from equation

(3-16).

The damping force for varying displacements is plotted in Figure 2.15. The

displacement is directly proportional to velocity for a constant period. The damper

force is proportional to power of the exponent of displacement. Value of the

exponent is 0.5, in this case, therefore value of damping force will increase by a

factor of 4 = 2, if displacement is increased by a factor of 4.

The value of coefficient C could be selected in such a way that it could be assorted by

simply installing more or less dampers in the structure, this could be represented in terms

of available damper properties. The variation limit of exponent is from 0.3 and 1.0.

Generally, the higher value of exponent gives a direct relationship between velocity and

damping force which will presents best results, hence exponent value of 1.0 is most

commonly used. Even though velocity limit might be helpful in limiting forces and these

forces are out of phase with displacements, this feature will take out part of the desirable

properties of viscous dampers.

22

Fig.2.10 Damper Coefficient

Fig.2.11 Damper Exponent, , For Constant, C

Fig.2.12 Damper Exponent, , For Constant Damper Force

(Holmes Guidelines Passive Energy Devices)

Displacement

Dam

ping

For

ce

Displacement

Dam

ping

For

ce

Displacement

Dam

ping

For

ce

23

Fig.2.13 Velocity Cut-off on Viscous Damper

Fig.2.14 Loading Frequency

Fig.2.15 Displacement Amplitude

(Holmes Guidelines Passive Energy Devices)

Displacement

Dam

ping

For

ce

Displacement

Dam

ping

For

ce

Displacement

Dam

ping

For

ce

24

2.7.3.2 Advantages of Viscous Dampers

Viscous dampers are highly reliable.

Displacement capacity and forces are high.

Viscous dampers are force limited when the velocity exponent is less than 1.0.

Viscous dampers are available through many manufacturers worldwide.

There is no added stiffness in viscous dampers at lower frequencies

In viscous dampers damping forces are possibly out of phase with the structure

elastic forces.

Temperature dependency of viscous dampers is moderate.

Viscous dampers can be analyzed by linear analysis.

2.7.3.3 Disadvantages of Viscous Dampers

Viscous damper are somewhat higher in cost than other dampers.

Viscous dampers particularly are not force-limited when exponent is equal to 1.0.

It has been experienced that it is generally not possible to add enough damping to

eliminate all inelastic response therefore nonlinear analysis in most practical cases for

viscous dampers.

2.7.4 Visco-elastic Dampers

Visco-elastic (VE) damper is one of important kind of passive energy devices these have

been used as energy dissipation devices in many structures where the damper undergoes

shear deformations. Visco-elastic materials exhibit combined features of viscous liquid

and elastic solid when deformed, as their name implies, in other words they dissipate a

certain amount of energy as heat and return to their original shape after every cycle of

deformation. The characteristic of constrained double layer Visco-elastic shear damper is

described by (Mahmoodi, 1969) and he also mentioned that it can be efficient in

decreasing the dynamic response of buildings. Visco-elastic dampers made of bonded

acrylic polymers (Visco-elastic) layers, 3M Company have developed this material and

dampers and they used to control vibrations induced due to wind in buildings, the 3M

dampers are known to have a stable behavior with good aging properties and resistance to

environmental pollutants. The extension of VE shear damper to seismic applications is

more recent. For seismic applications, more effective use of VE materials is required

25

since large damping ratios than those for wind are usually required. Figure 2-16 shows a

typical diagonal visco-elastic shear damper consists of visco elastic layers bonded to steel

plate. When these dampers are mounted to a building structure shear deformations occur,

as a result energy dissipation take place when relative motions occur between the out steel

flanges and centre plate.

Fig.2.16 Visco-elastic Damper and Installation (Mahmoodi, 1969)

2.7.4.1 Damper Properties

The force in Visco-elastic damper may be expressed by equation:

FD = keff + Cu 2-17

Where the effective stiffness of damper is keff, C is the damping coefficient, the

displacement is , and the velocity is u. Unlike viscous dampers, for all visco-elastic

devices, the velocity dependent damping is a linear function of velocity, that is, the

26

exponent =1.0. The above equation presents a force displacement function of the form as

shown in Figure 2.17.

Fig.2.17 Force displacement Relationship for Visco-elastic Damper

The terminologies which are used to describe visco-elastic dampers are different from

that used for such kind of other devices. The shear stiffness is defined in terms of G,

which is generally used to define the shear storage modulus, therefore the effective

stiffness is defined from this as below:

= 2-18 In the above equation, t is the total thickness (sum of all layers) of visco-elastic material

in the device, and Ab is the bonded area of the device.

The damping coefficient, C, can be defined in terms of the shear loss modulus, G, as

below:

=

3-19

Where, in above equation, represents the frequency. The loss modulus is usually

normalized by the frequency, as G/ so that it can be factored directly by damper

dimensions Ab/t, as for the storage modulus.

Displacement Fo

rce

27

2.7.4.2 Advantages of Visco-elastic Dampers

Visco-elastic dampers are highly reliable.

Viscous dampers can also be analyzed by using linear analysis.

Viscous dampers are somewhat lower in cost than other dampers.

2.7.4.3 Disadvantages of Visco-elastic Dampers

Viscous dampers are strongly temperature dependent.

Viscous dampers have low force and displacement capacity.

Viscous dampers are not force limited.

It is generally not possible to add enough damping to eliminate all inelastic response

therefore, nonlinear analysis in most practical case for viscous dampers.

28

Chapter 3

METHODOLOGY 3.1 General

The theoretical equation for the dampers provides a way of calculating properties of

damper devices and calculating the damping provided by these devices as described in the

previous chapter. Because of difficulties in defining strain energy of the real structures,

damping is at best a very approximate estimate calculated in this way. The damping

provided by overlapping analytically a physical method of measuring damping by a

variety of devices is evaluated in this chapter. The ultimate method of determining

whether this has been achieved is to calculate the behavior of a structure with passive

energy dampers installed in building. Three different prototype buildings have been used

in this research, the buildings are of concrete frame with varying heights of 3, 5 & 10

storeys respectively. These buildings are designed for moderate seismic zone and the

performance of these buildings are evaluated for seismic records corresponding to a high

seismic zone with different passive energy devices.

3.2 Buildings Description

In order to observe the behavior of buildings under seismic excitations and to observe the

performance of passive dissipation energy devices, plane frames from these three

prototype concrete buildings are selected and used for evaluation. The further information

about the building is described below,

3.2.1 Building -1

Building-1 is a three storey frame and following are the parameters of the concrete frame:

No. of bays in X-direction = 3

No. of bays in Y-direction = 1

Width of bay in X-direction = 7.5 m

29

No. of stories = 3

Height of first storey = 4.570 m

Height of other storey = 3.650 m

Column size = 500x500 mm

Beam size = 400x600 mm

Time Period in fundamental mode = 0.468 sec

Elevation of the building frame is shown in Figure 3.1.

Fig.3.1 Frame Elevation of Building -1

3.2.2 Building -2

Building-2 is a five storey frame and following are the parameters of the concrete frame:




No. of stories = 5







3 bays @ 7.5m each

30

Fig.3.2 Frame Elevation of Building -2 3.2.3 Building -3

Building-3 is a ten storey frame and following are the parameters of the concrete frame:




No. of stories = 10







3 bays @ 7.5m each

31

Fig.3.3 Frame Elevation of Building -3 3.3 Material Properties

Following table describes the material properties which are used in analysis of above

described building frames.

Table 3.1 Material Properties

Properties Units (metric)

fc 21 MPa

Ec 21538 MPa

Fy 420 MPa

fy (For Structural Steel) 250 MPa

3 bays @ 7.5m each

32

3.4 Loading

The building frames are subjected to gravity and dynamic loadings. Gravity loading

includes dead and live load on building, while dynamic loading consists of time history

loading. Details of dynamic loads considered in this study are given below;

3.4.1 Dynamic Loading

The objective of this research is to observe the behavior of building with passive energy

dissipation devices in high seismic zone so E-W component of EL-Centro earthquake

1940 time history data is applied in X- direction of all the buildings. Following is time

acceleration graph.

Fig.3.4 E-W Direction Time Acceleration Graph of El-Centro Earthquake

The peak ground acceleration value is 0.318 g in above graph. El-Centro response

spectrum for acceleration, velocity and displacement is shown in figures 3.5, 3.6 & 3.7.

3.5 Dampers Application

In order to observe the performance of buildings under earthquake loading four different

types of damper variations are used in this part of research. Hysteretic, Friction, Viscous

and Visco-elastic damper are used to observe the performance of buildings. These

dampers are installed in the middle bay of frame as shown in Figures 3.10, 3.11 & 3.12,

the dampers characteristics, properties and variations are described below.

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 5 10 15 20 25 30

Time (sec)

Acc

eler

atio

n (g

)

33

Period (sec)

Fig.3.5 El-Centro Spectral Acceleration

Period (sec)

Fig.3.6 El-Centro Spectral Velocity

Period (sec)

Fig.3.7 El-Centro Spectral Displacement

43.532.521.510.50

0.8

0.6

0.4

0.2

0

43.532.521.510.50

80

70

60

50

40

30

20

10

0

43.532.521.510.50

80

70

60

50

40

30

20

10

0

Acc

eler

atio

n V

eloc

ity

Dis

plac

emen

t

34

3.5.1 Dampers Characteristic

Dampers types and properties are defined in following Table 3.2.

1. H is Hysteretic steel damper, modeled as Plastic-Wen element. The values listed

in Table 3.2 are the yield force, Py, applied in kN. Maximum force is 1000 kN.

2. F is a Friction damper, which is also modeled as Plastic-Wen element. The

values enlisted is the friction force, Fy in kN same as the H type damper. The

stiffness, by a factor of 10 is increased for the friction damper as compared to

Hysteretic damper.

3. V is Viscous damper, which link the adjacent floors and slope in diagonal. The

values of damping coefficient ate listed in Table 3.2. The units of damping

coefficient, C, are kN-sec/m. and the value of exponent, a, is assumed to be 1.0

for all types of analysis.

4. Visco-elastic or VE damper, which also link the adjoining floors and therefore

oriented in diagonal. The values of damping coefficient are listed in Table 3.2.

The units of damping coefficient, C, are of kN-sec/m, which are the same as for

viscous dampers. KEFF, is the corresponding effective stiffness of Visco-elastic

dampers, in units of kN/m, with a value numerically equal to 2 times of damping

coefficient, C. Effective stiffness is the reasonable ratio of modulus loss to the

storage modulus for smaller frequency responses.

Table 3.2 Damper Properties

Analysis No. Types

H and F Types

H and F Types

H and F Types

V and VE 10 Story 5 Story 3 Story ALL

Yield Strength (kN) Damping (kN-sec/m) 1 0 0 0 0 2 100 50 30 1000 3 200 100 60 2000 4 300 150 90 3000 5 400 200 120 4000 6 500 250 150 5000 7 600 300 180 6000 8 700 350 210 7000 9 800 400 240 8000 10 900 450 270 9000 11 1000 500 300 10000

35

3.5.2 Dampers Variation

The property variation of ach damper type is modeled with three different types of

distributions as show in the Figure 3.8, these distributions are described below.

1. U represents Uniform Distribution. The properties of dampers for uniform

distribution are listed in Table 3.3, which are used for analyzing dampers at each

storey level.

2. T represents Triangular Distribution. The properties of dampers for triangular

distribution are listed in Table 3.3, which are used to define the dampers at

uppermost floor. The damper at bottom floor is defined by using a value of of

the value which is used at the top floor. For damper values at intermediate storeys,

linear interpolation method is used.

3. R represents Reverse triangular distribution. The properties of dampers are listed

in Table 3.3, which are used to define the dampers at bottom floors. The damper at

top floor is defined by using a value of of the value used at the bottom floor.

For damper values at intermediate storeys, linear interpolation method is used.

Fig.3.8 Damper Variation

Uniform U

Triangular T

Reverse Triangular

R

1.0 1.0 0.25

1.0 0.25 1.0

36

Table 3.3 Damper Variation

No.

of S

tore

ys

Without Dampers With Dampers

Ana

lysis

Dri

ft,

Disp

lace

men

t &

Bas

e Sh

ear Hysteretic

Damper Friction Damper

Viscous Damper

Visco-Elastic Damper

U T R U T R U T R U T R

3 1 5 10 10 10 10 10 10 10 10 10 10 10 10

5 1 5 10 10 10 10 10 10 10 10 10 10 10 10

10 1 5 10 10 10 10 10 10 10 10 10 10 10 10

TOTAL NUMBER OF ANALYSIS PERFORMED = 378

Fig.3.9 Damper Distribution with Height

37

3.5.3 Dampers Locations

Dampers are installed in central bay as shown in Figures 3.10, 3.11 & 3.12.

Fig.3.10 3-Story Building


Damper location

Damper location

38


3.5.4 Total Analysis Performed By using damper properties described in Table 3.2, and using damper variation described

in Table 3.3 and shown in Figures 3.9, 3.10, 3.11 & 3.12, total number of 379 analysis

have been performed for observing behavior of Hysteretic, Friction, Viscous and Visco-

elastic dampers.

3.6 Computer Program Used

ETABS 9.7.2 is used for analysis purpose, which is a product of Computer & Structures

Inc. Buildings are modeled by using graphical user interface (GUI). Modeling involves

defining grid system, beam, column, Hysteretic, Friction, Viscous and Visco-elastic

damper and time history data. Following is the step-by-step procedure explaining the

modeling, analysis and design process.

Damper location

39

3.6.1 Defining Grid System

After opening new file, grid system is defined by giving x, y and z coordinates. To define

grid system, select new model command from the file menu and choose an option to

initialize the model to access the building plan grid system and storey data definition.

Then choose the custom grid spacing option in the grid dimensions and enter the spacing

of your system. Different types of structural objects like, steel deck, staggered truss, flat

slab, flat slab with perimeter beams, waffle slab, two way or ribbed slab and grid only can

be selected. But for our case we will select grid only option. Similarly units can be

selected according to choice, as SI system has been used in this research, there for units

are kN-m. The building in analyzed in 2-D bay, the number of bays in x-direction are

three, while the number of bay in Y-direction is one, height of building is varied to 3, ,5

& 10 storeys respectively.

Fig.3.13. Defining Grid System

Option for grid system

40

3.6.2 Defining Frame Sections

To define the frame sections, select the option of frame sections from the define menu.

Go to add property drop down list select the type of your section e.g. (circle,

rectangular, tube etc.) and give the dimensions and material type and at the end specify

the frame section type whether it is column or beam.

Fig.3.14 Defining Frame Section

3.6.3 Defining Hysteretic Damper

The building frames have been analyzed in Latest Engineering software, ETABS Non-

linear version 9.7.2. Link support properties of the model are defined, the link support

property used to define Hysteretic damper is PLASTIC1. The Hysteretic dampers are

modeled in ETABS by assigning a panel zone with a non-linear link element property

diagonally to the column base at each floor. The link element uses the property of uni-

axial spring i.e. PLASTIC1 and therefore this provide beam-brace connectivity with

nonlinear shear behavior in the 1-2 plane, in U1 direction. The link elements undergo

shear deformation, under this arrangement and the displacements are transferred between

the frames. A single rigid diaphragm is allocated to each floor level, which connects the

objects at each floor. No axial force will occur in the beam members because of this rigid

diaphragm. Therefore a rigid zone factor of 1 is assigned to all members. Figure 3.15

shows that the value of post yield stiffness ratio is taken as 0.99% in both the models. For

hysteretic damper only yield force value will be taken.

41

Fig.3.15 Force-Displacement Relationship & Defining Hysteretic Damper

3.6.4 Defining Friction Damper


linear version 9.7.2. Link support properties of the model are defined, the link support

property used to define Friction damper is PLASTIC. The Friction dampers are modeled

in ETABS by assigning a panel zone with a non-linear link element property diagonally

to the column base at each floor. The link element uses the property of uni-axial spring

i.e. PLASTIC1 and therefore this provide beam-brace connectivity with nonlinear

behavior shear in the 1-2 plane, in U1 direction. The link elements undergo shear

deformation, under this arrangement and the displacements are transferred between the

frames. A single rigid diaphragm is allocated to each floor level, which connects the



shows the value of post yield stiffness ratio is taken as 0.99% in both the models. For

Friction damper stiffness as well as yield force value will be taken.

42

Fig.3.16 Force-Displacement Relationship & Defining Friction Damper 3.6.5 Defining Viscous Damper


linear version 9.7.2. Link support properties of the model are defined and the link support

property used to define viscous damper is DAMPER. The Viscous dampers are modeled

in ETABS by assigning a panel zone with a non-linear link element property diagonally

to the column base at each floor. The link element uses the property of uni-axial spring

i.e. DAMPER and therefore this provide beam-brace connectivity with nonlinear behavior

shear in the 1-2 plane, in U1 direction. The link elements undergo shear deformation,

under this arrangement and the displacements are transferred between the frames. A

single rigid diaphragm is allocated to each floor level, which connects the objects at each

floor. No axial force will occur in the beam members because of this rigid diaphragm.

Therefore a rigid zone factor of 1 is assigned to all members. Figure 3.17 shows the value

of post yield stiffness ratio is taken as 0.99% in both the models. For viscous damper only

damping constant will be given.

43

Damper Displacement, u

Fig.3.17 Force-Displacement Relationship & Defining Viscous Damper

3.6.6 Defining Visco-elastic Damper


linear version 9.7.2. Link support properties of the model are defined and the link support

property used to define Visco-elastic damper is DAMPER. The Visco-elastic dampers are

modeled in ETABS by assigning a panel zone with a non-linear link element property

diagonally to the column base at each floor. The link element uses the property of uni-

axial spring i.e. DAMPER and therefore this provide beam-brace connectivity with

nonlinear behavior shear in the 1-2 plane, in U1 direction. The link elements undergo

shear deformation, under this arrangement and the displacements are transferred between

the frames. A single rigid diaphragm is allocated to each floor level, which connects the



shows the value of post yield stiffness ratio is taken as 0.99% in both the models. For

Visco-elastic damper stiffness along with damping constant will be given.

44

Fig.3.18 Force-Displacement Relationship & Defining Visco-elastic Damper

3.6.7 Defining time history data

For defining the time history, go to time history function from the define menu and from

drop down list select the option function from file. Give the path of input file and mention

the ground excitation time interval. Figure 3.19 shows the El-Centro time history function

at the time interval of .02 sec. It is noticeable that, free vibration analysis is carried out to

obtain natural frequencies while time history and response spectrum analysis that will

appear shortly, are carried out to obtain response of structure.

45

Fig.3.19 El-Centro Time History function

After modeling and defining the load cases the building is subjected to Time Histories.

The natural time period, displacements, frequency, acceleration, velocity, effective

stiffness and initial stiffness of buildings is determined. Variation in these factors

corresponding to changes in stiffness of building (Stiffness Ratio) will help to comment

on the vibration and damage in the building.

46

Chapter 4

RESULTS & DISCUSSIONS 4.1 General

In the previous chapters theoretical background and methodology of analyzing dampers

was discussed. Also the theoretical equations for the dampers discussed in the previous

sections had provided a way of calculations the properties of damper devices and

estimating the damping these devices will provide. However, due to difficulties in

defining the strain energy of the most of actual structures, the damping for the devices

calculated in such way is at best a very approximate. In this chapter three prototype

buildings with heights of 3, 5 and 10 storeys respectively, each of concrete fame, were

used for the study. The prototypes buildings taken in this research were designed for low

seismic zone and the performance of these buildings were evaluated with different

damper devices for earthquake corresponding to a high seismic zone. The main objective

of this research was to determine which types of dampers and their configuration could

improve the performance of buildings or structures so as to be satisfactory for the higher

seismic zones.

4.2 Response of Buildings without Dampers

The purpose of all passive energy dissipation devices is generally same, they convert the

kinetic energy from external sources or loads into heat energy. It is necessary to be

mentioned that, the prototype buildings is modeled with and without different types of

dampers, and then, the response of structure is compared within the different models. The

seismic behavior of the building, free vibration and time history analyses have been

considered to be performed. In order to determine the behavior of buildings, response of

as-designed buildings was analyzed for increasing level of viscous damping from 0% to

40% and effect of increasing damping value is studied on drift, displacement and base

shear.

47

4.2.1 Effect of Damping on Drift & Base Shear

Fig.4.1Graph b/w Drift & Increasing Damping Ratio

Fig.4.2 Graph b/w Base Shear & Increasing Damping Ratio

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0% 5% 10% 15% 20% 25% 30% 35% 40%

3 Storey-Drift 5 Storey-Drift

10 Storey-Drift

Damping (% of Critical)

Dri

ft (m

/m)

0

500

1000

1500

2000

2500

3000

0% 5% 10% 15% 20% 25% 30% 35% 40%

3 Storey-Baseshear

5 Storey-Baseshear

10 Storey-Baseshear

Damping (% of Critical)

Bas

e Sh

ear

(kN

)

48

Maximum drift in all three prototype buildings as viscous damping is increased from 0%

to 40% is shown in Figure 4.1. The figure shows the drift behavior tends to decrease with

the increasing damping value. For El-Centro 1940 earthquake record maximum effect for

the 10 storey building but also increased damping reduce drifts for all types of buildings.

Under this level of earthquake loading, the variation in the effect of the viscous damping

is a feature of non-linearity of these structures. The effect of viscous damping on the base

shear is shown in Figure 4.2. For base shear in structures there is much less variation than

the case of drifts. It is because of the fact that beam hinging mechanism is formed in each

building and the base shear is limited by the strength of this mechanism. The beam

reaches to yield moment under the initial loading phase and deforms to plastic rotation of

0.008 radians. The beam moment decreases when the load is released but it does not

reach its negative moment capacity. Consequently, the hysteretic loop does not close and

the free vibration causes the beam to vibrate along its elastic stiffness curve.

4.2.2 Effect of Damping on Displacement

Fig.4.3 Graph b/w Time & Displacement (3-Storey Building)

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0 5 10 15 20 25 30 35

3 Storey 5% Damping

3 Storey 25% Damping

49



-200

-150

-100

-50

0

50

100

150

0 5 10 15 20 25 30 35

5 Storey 5% Damping


-800

-600

-400

-200

0

200

400

600

800

0 5 10 15 20 25 30 35



50

Figure 4.3, 4.4 & 4.5 shows the effect of roof displacements is studied by increasing the

damping, from 5 to 25% for the El Centro record, on roof displacements, which shows

throughout the record, the roof displacement more significantly reduces the permanent set

occurring in 3 and 10 storey buildings,.

4.3 Response of Buildings with Dampers

The purpose of installing passive energy devices into a building is normally to decrease

building displacements under moderate or high seismic loads, as building deformations

are very important to observe during earthquake, and so efficiency of these dampers is

mainly calculated by the degree to which these deformations are reduced. Other important

issues that might be included are floor accelerations and base shear.

4.3.1 Effects of Damping Parameter on Displacement

The main objective of installing passive energy devices into buildings is normally to

reduce building deformations under seismic loads, therefore the significance of these

dampers is mainly measured by degree to which these deformations are reduced.

4.3.1.1 Hysteretic Damper

Fig.4.6 Graph b/w Displacement & Damping Parameter (3-Storey Building)

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350

H U-3 Storey Displacement

H T-3 Storey Displacement

H R-3 Storey Displacement

Damping Parameter

Disp

lace

men

t (m

m)

51



100

105

110

115

120

125

130

135

140

145

150

0 100 200 300 400 500 600




Damping Parameter

Disp

lace

men

t (m

m)

300

350

400

450

500

550

600

650

0 200 400 600 800 1000 1200




Damping Parameter

Disp

lace

men

t (m

m)

52

The hysteretic damper reduces displacement for all types of building and all types of

displacements as shown in Figures 4.6, 4.7 & 4.8. Some hysteretic dampers are

indistinguishable from a structural member, such as the yielding brace, they act as a

structural member. The purpose of installing hysteretic dampers in buildings is to

dissipate energy more dominantly than the strength and/or added stiffness. Hysteretic

dampers are usually designed in such a way that they yield before the existing structure.

For 3-storey building displacement reduces 15.9% for uniform distribution, 6.94% for

triangular distribution and 12.61% for reverse triangular distribution. Similarly for 5-

storey building displacement reduces 17.73% for uniform distribution, 8.68% for

triangular distribution and 14.29% for reverse triangular distribution. Hysteretic dampers

are most effective for 10-storey building which reduces displacement 38.36% for uniform

distribution, 22.95% for triangular distribution and 32.20% for reverse triangular

distribution. For all types of buildings triangular distribution is more effective than

uniform and reverse-triangular distributions.

4.3.1.2 Friction Damper


30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350

F U-3 Storey Displacement

F T-3 Storey Displacement

F R-3 Storey Displacement

Damping Parameter

Disp

lace

men

t (m

m)

53



80

90

100

110

120

130

140

0 50 100 150 200 250 300 350




Damping Parameter

Disp

lace

men

t (m

m)

400

450

500

550

600

650

0 50 100 150 200 250 300 350




Damping Parameter

Disp

lace

men

t (m

m)

54

Figure 4.9, 4.10 & 4.11 shows that the friction damper reduces displacement for all types

of building and all types of displacements. Friction dampers are also most likely to be

placed in diagonal braces of building. Some friction devices are configures such that they

generate stable rectangular h

energy dissipation devices by ali murtaza rasool

Documents

structure damping

seismic isolation

period of response

period shift effect

technology lahore

research project

asif hameed

base isolation