webinar on disaster resistant construction technology · 2020. 10. 5. · philosophy of earthquake...

Webinar on

Disaster Resistant Construction

Technology(25th September 2020)

Organized by

GIDM, Gandhinagar

Recent Developments in

Construction Technology &

Materials(25th September 2020)

by

Major Dr C S Sanghvi

Professor & Head

Applied Mechanics Department

L D College of Engineering

Ahmedabad

Philosophy of earthquake resistant structure

Damage is allowed but no collapse

• Fact: Buildings are still collapsing duringearthquake

1994 Northridge Earthquake 1995 Kobe Earthquake

1999 Kocaeli Turkey Earthquake 2001 Bhuj, India Earthquake

Structural failures during recent strong motion earthquakes.

• Earthquakes are uncontrollable & IncreasedSeismicity

• CAPACITY > DEMAND

• Earthquake induces inertia forces F = ma

• For increased value of F, increase thestrength of building, the capacity must beincreased to avoid damage.

CAPACITY > DEMAND

Qi- Design Lateral Force at floor

Q4

Q3

Q2

Q1

EQ

Wihi2

Qi = VB

n

Σ Wihi2

j=1

2005 NPEEE Earthquake Design Concept : Lecture 9: Overview of EQ resistant Structural Systems

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INTRODUCTION

• Earthquake are natural Threats

• Today’s technological advances allow us to control the consequences

• such advances rarely utilize in earthquake resistant design, in common building

• Recent Trend In Construction – Increase In Number Of Multistory Buildings

INTRODUCTION• Basic Eq. for Free Damped vibration

Mü+ Cù+ Kx=0

• To reduce excessive vibration, stiffnessshould increase but it will also increase themass .

• It is not feasible for the tall building.

• So to reduce the excessive vibration wemay switch over to the term C

Although the energy will dissipate by thejoint, provided in structural element

But it is not sufficient for the tallbuilding where larger amount of energy isrequired to dissipate.

So dissipate the larger amount of energysome extra arrangement should be therewhich is called “structural controlsystem”

• Incorporating external elements tothe structure to control its dynamicresponses called “Structural controlsystem”

• Protective structural systemsstudied by the structural control areclassified:

Definition

Structural Control

Passive ControlActive and Semi

Active Control

Hybrid Control

(active+passive)

Seismic isolation

Energy Dissipation

Devices

Mass Dampers

Figure for STRUCTURAL CONTROL SYSTEM

• This approach consists ofincorporating ‘Passive’ (i.e. neitherpowered nor ‘smart’) devices to thestructure

• Whose motion is to be controlled bydynamic parameters ( i.e. damping &stiffness)

Passive Control System

Passive Control

• Requires noexternal energy

• Requires deviceswith favorableenergy dissipation

Friction

device

• Isolation means the state of beingseparated.

• The structure is separated from itsfoundation.

• Concept in base isolation is to reduce thefundamental frequency of structuralvibration to a value lower than thepredominant frequencies of earthquakeground motions

• Provide a means of energy dissipation withwhich to reduce the transmittedacceleration to the superstructure

Base Isolation

• Hospital, school building, Fire station,Institutional buildings are called life linestructure and these structure we need in workingcondition even after major event took place.

BASE ISOLATION

….CONTD

• Reduction in Seismic force

– It is stated that base isolation mayreduce seismic force significantly incomparison with conventional structures.

Objectives

To Protect the structures from severdamages during strong shaking

CONCEPT

• To reduce effective motion

• To dissipate energy at isolation level

Frequency

Seis

mic

resp

on

se

No Control

With Control

PRINCIPLE OF BASE ISOLATION

• It consist a setting device which isflexible in horizontal direction andvery stiff in vertical direction

• This system is located betweenfoundations and main structures

• Isolator will produce new mode ofvibration

• New mode will increase thefundamental period.

• Not add inter story drift

Period Shift Effect

• Elastomeric-based systems

High Damping rubber bearings (HDRB)

Lead rubber bearings (LRB)

• Isolation System Based on Sliding

• Spring-Type Systems

• Sleeved-Pile Isolation System

• Rocking Systems

ISOLATION SYSTEM COMPONENTS

CONT…

ELASTOMERIC (RUBBER) BEARINGS

Most Popular

Consist of thin rubber & steel plates

Steel Plates – Stiffness, carry vertical load, prevent

bulging of rubber, laterally constrain the rubber

sheet.

Rubber – Horizontal flexibility

Elastomeric-based systems

CONT…

LEAD RUBBER BEARING

Consist of thin natural rubber &

steel plate and a lead cylindrical

plug.

Lead is provided to give initial

rigidity to structure.

SEISMIC ISOLATION DEVICES

TYPE OF SEISMIC ISOLATION SYSTEM

SLIDINING ISOLATION SYSTEM

A layer with a define coefficient

of friction

Coefficient of friction will limit

acceleration & forces

No restoring force

Restoring force is given by

combining the elastomeric

bearing & also provided by

FPS system.

ISOLATION IN REAL BUILDING

ISOLATED BUILDING IN INDIA

Base isolation have been used in numerous building in

countries like Italy, USA, Japan, New Zealand etc

Today around 1000 building in the world have been isolated

In India first demonstrate in killari (Maharastra) in 1993.

After 2001 earthquake, the four-storey Bhuj hospital was built

with base isolation technique.

Bhuj Hospital

• It consist mass elements connectedelastically to the main structure

• Such connection allow the relativemotion between the mass damper &the structures

• Natural period of the added massmust be close to the fundamentalperiod of the structure known asTuned Mass Damper (TMD)

TUNED MASS DAMPERS

Application :

To reduce the horizontal vibrationsof tall and/or slender constructions(skyscrapers, TV towers, Chimney,etc)

COMPONENTS OF TMD

• Spring

• Oscillating Mass

• Viscous damper

WORKING

• TMD is a system of spring and mass.

• TMD is tuned exactly to the structure anda certain natural frequency of it.

• Due to the physical properties of thesystem, the damper moves out of phasewith the building

• If the building moves east, the dampermoves west.

A 3-D view of a pendulum type tuned mass damper

Fig. Amplitude - Frequency response of a low damped system with (Yellow) and

without (Blue) tuned mass damper

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A tuned mass damper designed for the PetronasTowers in Malaysia

TAIPEI 101

• Energy dissipation by inelasticdeformation of metals

• First implemented in New Zealand &Japan, then Mexico & USA

(Soong and Spencer Jr. 2002.)

• Unbounded braces –Yielding of braces

Metallic Yield Dampers

Metallic Yield Dampers

• very similar to a shock absorber

Viscous fluid dampers

• Uses the friction between steel platessliding over each other to dissipateseismic energy.

• Casino of Montreal - the rehabilitation ofeight-story steel building (Pasquin et al.1994.)

Friction damper

Friction damper

Various way to installations

Friction damper

• From bellow table it is seen that theEnergy Dissipaters will be moreadvisable.

Comparison between passive control system

Active control• On line

measurement of forces

• Application of counteracting forces

• Requires more energy

• Stable feedback system

sensoractive devices

computer

• Use advance techniques with soundfundamental knowledge

• understand impact/behavior of eachtechnique

• Every technique has its own advantages aswell as disadvantages One has to be verycareful in selecting particular technique forspecific purpose

• One has to think financial aspects alongwith fundamental behavior aspects.

Conclusion

Thank you

webinar on disaster resistant construction technology · 2020. 10. 5. · philosophy of earthquake...

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