Basic concepts of Earthquake- Resistant Design and ...solutions.ait.ac.th/wp-content/uploads/2016/08/... · Basic of Seismic Design on the application of construction techniques,

Seminar on

Earthquake Resilient Construction for School Buildings

Naveed Anwar, PhD

Post-earthquake School Reconstruction Project

Basic concepts of Earthquake-Resistant Design and Construction

Day-1Session 1

2

•Earthquakes cause disasters!• Why do they cause disasters?

• Understanding the Risk

•Can such disasters be minimized?• How can we reduce the consequences of such disasters

• Understanding the Response and Performance

• How structures, specially schools can be made safer

Why do Earthquake Cause Disasters?

4

What is a disaster

6

Climate Change

Environmental Sustainability

Population Growth

Urbanization and Un-planned

development

Low Quality of Built Environment

Lack of Resources for Communities

Lack of post-event management and recovery, and re-bound capacity

Natural Phenomena

Disaster Hazard Exposure Vulnerability

Increased Consequences

7

Seismic Risk

Seismic Risk = Seismic Hazard x Seismic Vulnerability

What is Seismic Hazard

9Source: Murty (2004)

For Hazard

Earthquake

10

Arrival of Seismic Waves at a Site

Source: Murty (2004)

11

Reducing illumination with distancefrom an electric bulb

Effected by “Medium in between”

Clear, FogReflection, Abortion

Source: Murty (2004)

12

Seismic hazard Maps

Seismic hazard map of Asia, from the Global Seismic Hazard Assessment Program (GSHAP)http://www.seismo.ethz.ch/static/gshap/

What is exposure

14

Exposure to Seismic Hazard

• The people, property, assets, infrastructure that could be effected by the damage caused by earthquake

• No exposure > No disaster• Earthquake in a desert causes no disaster• Same earthquake in a crowded city is disastrous• Unoccupied building has no exposure to life, but exposure to assets still

present

• Nepal Earthquake of 2015 less disastorus due to reduced exposure• Schools closed• Day time, on a holiday

What is vulnerability and its causes

16

Seismic Vulnerability

• The weaknesses in the location and structure that will be exploited by the earthquakes

• Site Vulnerability• Soil type and profile that may amplify the hazard

• Structural Vulnerability• The factors that will increase the seismic demands and or reduce capacity

17

Causes of Vulnerability

Innovate l Integrate l Collaborate

• Lack of awareness

• Inappropriate site location

• Poor soil condition

• Poor design and construction practice

• Inappropriate use of building materials

18

Causes of Vulnerability


• Type of building construction (Brick/stone masonry, mud mortar, RCC

frame, timber frame etc.)

• Non-engineered construction

• Low quality of construction & building materials

• Negligence of existing building design codes

• Untrained masons

The Special Case of Nepal

20

Nepal lies in an active seismic belt

.

21

The Historical Formation of the Earth

22

Location of Nepal

• Nepal sits astride the boundary

between the Indian and the

Tibetan plates along which a

relative shear strain of about 2

cm per year has been

estimated.

23

Location of Nepal


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Himalayan Range

• Existence of the Himalayan Range

with the world’s highest peaks is

evidence of the continued

tectonic activities beneath the

country. As a result, Nepal is very

active seismically.

25

Continuous Movement

Indian subcontinent pushes against Eurasian, pressure is released in the form of earthquakes.

The constant crashing of the two plates forms the Himalayan mountain range.

26

History of Earthquakes

• Nepal has a long history of

destructive earthquakes.

• The earliest recorded

earthquake event 1255.

• Significant earthquakes in 1833,

1934, 1960,1988 and 2015.

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History of Earthquake in Nepal

2,2

00

100

100

2,5

00

6,0

00

4,5

00

4,0

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6,5

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750

3,5

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8,5

19

80 200

1,0

91

111

8,9

22

213

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

7 J

un

e 1

255

1260

1344

Au

gu

st 1

408

6 J

un

e 1

50

5

Jan

ua

ry 1

68

1

July

176

7

26

Au

gu

st 1

833

7 J

uly

18

69

28

-Au

g-1

6

15

-Ja

n-3

4

27

-Ju

n-6

6

29

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l-8

0

20

-Au

g-8

8

18

-Se

p-1

1

25

-Ap

r-1

5

12

-Ma

y-1

5

Fatalities

7.8

7.1

7.9 8

.2

8.8

8 7.9 8

6.5

7.7

8.4

6.3 6.5 6.6 6

.9

7.8

7.3

0

1

2

3

4

5

6

7

8

9

10

7 J

un

e 1

25

5

1260

1344

Au

gu

st 1

408

6 J

un

e 1

505

Jan

ua

ry 1

681

July

1767

26

Au

gu

st 1

833

7 J

uly

18

69

28

-Au

g-1

6

15

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n-3

4

27

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0

20

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g-8

8

18

-Se

p-1

1

25

-Ap

r-1

5

12

-Ma

y-1

5

Magnitude

28



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Nepal: 2015 Earthquakes


• On April 25, 2015 at 11.56 NST

• 7.8 on Richter Scale

• Shallow: only 11 km below the ground

• >40 sec trembling

• Moved Kathmandu about 1.5m

• At least 240 aftershocks

• May 12, 2015: 7.3 on Richter Scale

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Nepal: 2015 Earthquakes

AFTERMATH

31

Impacts of Nepal Earthquake

Kathmandu Durbar Square

Patan Durbar Square

32


Dharahara

Bhaktapur Durbar Square

Swoyambhu Boudha

33


Barpak Village Bhaktapur Kathmandu

Gorkha Sindhupalchowk Dhading

34


Nuwakot Kavrepalanchowk Rasuwa

Dolkha Makwanpur Sindhuli

35

Nepal is exposed to High Seismic risk

Risk = Vulnerability X Hazard

Consequences - Disaster

(Death-Dollars-Downtime)

High Vulnerability High HazardHigh Risk

How to Reduce Damage due to EarthquakesAnd save human lives and property

37

What needs to be Done

Minimize Disaster Consequences

Reduce Risk to Disaster(and manage consequences due to disaster)

Reduce Vulnerability to match Acceptable Risk

Define Acceptable Risk

Determine the Hazard

(R = V x H)

Difficult to reduce Hazard

Difficult to reduce Exposure

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Hazard-Vulnerability-Risk-Consequences

Structural Displacement

Load

ing

Seve

rity

Resta

urant

Resta

urant

Resta

urant

Haz

ard

Vulnerability

Consequences

School

39

Restaurant Restaurant

Resta

uran

t

Operational (O) Immediate Occupancy (IO) Life Safety (LS) Collapse Prevention (CP)

0 % Damage or Loss 99 %

Ref: FEMA 451 B

CasualtiesLowest Highest

Rehab Cost to Restore after eventLowest Highest

Downtime for RehabLowest Highest

School School

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Basic Concepts of Earthquake-Resistant Construction


Basic of Seismic Design on the application of construction techniques, methods and criteria

used for the design and construction of building structures exposed to earthquakes.

A. Proper Site Selection

B. Appropriate Planning

C. Good foundation resting on a Firm Base

D. Building has to act as a single unit for a good earthquake resistance

E. Better bonding within masonry

F. Controlled size and location of openings

G. Light construction

41

Considerations for Site Selection

Proper Site Selection: Very important for stable & disaster safe construction

i. Steep & Unstable Slopes

ii. Areas susceptible to landslides & rock fall

iii. Filled area

iv. River banks

v. Water logged area

vi. Geological fault & Ruptured areas

vii. Trees

42

Earthquake effects are Different

• Earthquake is different from all other loads• It is not an applied external force

• Earthquake effects are generated by the structure itself in response to ground shaking• Basically depends on stiffness and mass distribution

• Can be controlled by damping, ductility and energy dissipation mechanisms

43

43

Concept of 100% g (1g)

Most loads

Earthquake

FFKuuCuM NL

44

Earthquake Inertial Forces

Source: Murty, (2004)

Effect of Inertia in a building when

shaken at its base

Flow of seismic inertia forces

through all structural

components

Inertia force and

relative motion within a

building

45

Building Behavior during Earthquakes

46

Appropriate Planning

• Shape, size and proportion of the building

• Sudden deviation in load transfer path along the height lead to poor performance of buildings.

(a) Setbacks

(b) Weak or Flexible Story

(c) Sloppy Ground (d) Hanging or Floating Columns

(e) Discontinuing Structural Members

47


Regular Configuration: Seismically ideal.

• Low heights to base ratio

• Symmetrical plane

• Uniform section & elevation

• Balanced resistance

These configurations would have maximum torsional resistance due to

location of shear walls and bracings. Uniform floor heights, short spans and

direct load path play a significant role in seismic resistance of the building.

48


Irregular Configuration:

Buildings with irregular configuration

Buildings with abrupt changes

in lateral stiffness

Buildings with abrupt changes

in lateral resistance

49


Fig. Buildings with one of their overall dimensions

much larger or much smaller than the other two, do

not perform well during earthquake.

Fig. Simple plan shape buildings do well during earthquake

50


Adjacency of building:

• 2 buildings too close to each other, may

pound on each other during strong

shaking.

• With increase in building height, this

collision can be a greater problem.

• When the two building heights do not

match, the roof of the shorter building may

pound at the mid-height of the column of

the taller one. This is very dangerous.

Fig. Pounding can occur between adjoining

buildings due to horizontal vibrations of the

two buildings.

51


• Architectural features that are detrimental to earthquake response of

buildings should be avoided or minimized.

• When irregular building features are included, a considerably higher

level of engineering effort is required in the structural design. Even after

doing so the building may not be as good as one with simple

architectural features.

• Decisions made at the planning stage on building configuration are

more important.

52

Earthquake-Resistant Construction

The building has to act as a single unit for a good earthquake resistance:

Can be achieved by incorporating;

• Vertical Reinforcement

• Horizontal bands well connected to the vertical reinforcements and

embedded in masonry

• Diagonal bracing (horizontal and vertical)

• Lateral restraints

53

Proper Load Path

Fig. Load path from structure slab to the ground

The structural frame must

have enough strength to

securely bear the gravity

loads throughout the entire

life span of the building..

54


An adequate load bearing system is based on a continuous load path

throughout the structure:

• Slabs carry the floor loads of each story.

• Beams carry the loads transferred to them by the slabs as well as the

weight of the walls seated on them.

• Columns carry the beam loads and they transmit them to the foundation.

• Footings (foundation) carry the column loads and transfer them to the

ground.

55


Structural frame must be

able to withstand not

only the gravity loads but

also the loads imposed in

a few but vital cases

during its life span such as

during an earthquake.

Fig. Frame deformation due to seismic action

56


• A seismic band is the most critical earthquake-resistant provision usually in a masonry building.

• Usually provided at lintel, floor, and/or roof level in a building, the band acts like a ring or belt.

• Seismic bands hold the walls together and ensure integral

box action of an entire building.

A seismic band acts like a belt (adapted from: GOM 1994)

Pulling and bending of a lintel band in a stone

masonry building (adapted from: Murty 2005)

57


• Seismic bands are constructed using

either reinforced concrete (RC) or

timber.

• Proper placement and continuity of

bands and proper use of materials and

workmanship are essential for their

effectiveness.

Locations of seismic bands in a stone masonry building

(roof omitted for clarity) (adapted from: UNCRD 2003)

58


Seismic bands should always be continuous; an offset in elevation is not acceptable (adapted from: GOM 1998)

RC seismic bands should always remain level without any

dips or changes in height (adapted from: GOM 1998)

Merging RC floor and lintel bands

Combining floor/roof and lintel band:

a) timber band, and b) RC band

Importance of Foundations

60

Good foundation resting on a Firm Base foundation

:

Quality of foundation and the base

on which the foundation rests

Fig. Structural Foundation

61

Good foundation


Fig. Strip Footing on Brick and Stone Masonry

Vertical

Reinforcement

Tie Beam

Horizontal

ReinforcementShear

Reinforcement

PCC

Brick

Soling

Stone Masonry

Reinforcement

62

Good foundation resting on a Firm Base


: Quality of foundation and the base on which the foundation rests

Fig. Foundation consisting of flexible & rigid spread footings

63

Good foundation

Fig. Foundation consisting of flexible spread footings and connecting beams

64

Good foundation

Innovate l Integrate l CollaborateFig. Strip Foundation with connecting beams

65

Good foundation

Innovate l Integrate l CollaborateFig. Foundation consisting of spread footings eccentrically constructed

66

Good foundation

Innovate l Integrate l CollaborateFig. Raft Foundation consisting connecting beams Fig. Two level foundation

67

Proper Foundation

Different foundation depths are required for building

sites with variable soil properties (source: GOM 1998)

Special Considerations for Massonry

69

Better bonding within masonry

Better bonding within masonry: Type & quality of bond within the walling units

Based on the type of individual units used for masonry walls and their

functions, types of masonry walls:

• Load Bearing Masonry Walls

• Reinforced Masonry Walls

• Hollow Masonry Walls

• Composite Masonry Walls

• Post-tensioned Masonry Walls

70


Fig. Load Bearing Masonry Walls Fig. Reinforced Masonry Wall

71


Fig. Hollow Masonry Wall

Fig. Composite Masonry Wall

72


Fig. Post-tensioned Masonry Wall

73


Fig. Good bonding with stone masonry

74


Proper placement of through-stones in stone

masonry walls (adapted from: GSDMA 2001)

75


Through-stones in stone masonry walls: a) through stones act like interlaced fingers; b) a wall with through-stones, and c) a wall without through-stones (source: GOM 1998)

Wooden battens can be alternatively used instead

of long stones at wall (adapted from: Bothara et al. 2002)

76


Other Alternative Ways instead

of long stones.(adapted from: Bothara et al. 2002)

Wall stitches made from reinforced concrete with steel reinforcement

Construction of stitches made from wire mesh

embedded in mortar at the wall intersection Stitches made from wood dowels at wall corners and intersections

77



Fig. Good bonding with brick masonry

Vertical

Reinforcement

Horizontal

Reinforcement

U-Hook

Vertical

Reinforcement

U-HookHor.

Reinforcement

78

Masonry failure mechanisms

Fig. (a) Joist Displacement; (b) Joint Slipping; (c) Unit direct tensile cracking; (d) Masonry crushing; (e) Unit diagonal tensile cracking.

79

Masonry failure mechanisms

Fig. Masonry building during earthquake shaking: (a) loosely connected walls without

slab at the roof level; (b) a building with well-connected walls and a roof slab

80

Controlled size and location of openings

• Location and size of openings in walls has significance in deciding the

performance of masonry buildings in earthquakes

Recommendations regarding the length

and story height of stone masonry walls

81


• Large un-stiffened openings

create soft story effect

leading to a deformation of

building during an

earthquake.

• To prevent such effects the

opening size and location

has to be controlled.

Recommended location and size of openings for stone masonry walls (source: IAEE 2004)

82


Figure: Regions of force transfer

from weak walls to strong walls in

a masonry building.

Wall B1 pulls walls A1 & A2, while

wall B2 pushes walls A1 & A2.

83

Shera Board

GFRG PanelCGI Sheet

Plywood/OSBGypsum Board

Fiber Cement Board

Light construction

Lighter structures absorbs less seismic force, hence less effect.

Different types of light weight materials available in Nepal

84

Features for Rural Masonry Houses


• Horizontal Bands in different levels

• Corner strengthening with stitches

• Vertical Reinforcement

• Tying floor/roof rigidly with lateral load resisting elements

(walls/columns)

• Diagonal Bracing

85

Conclusion

• Building has to act as a single unit for a good earthquake resistance.

• Should be designed with the application of proper seimic design and construction principles

• Proper Site Selection

• Appropriate Planning

• Good foundation resting on a firm Base

• Better bonding within masonry

• Controlled size and location of openings


86

Even if the buildings are designed properly using the best practices…

They can not perform well in earthquakes if the construction is not done properly!

87

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Reference

• Amod M. Dixit, 2004, 13th World Conference on Earthquake Engineering, Vancouver, B.C.,

Canada, Promoting Safer Building Construction in Nepal

• Ministry of Physical Planning and Works, Earthquake Risk Reduction and Recovery

Preparedness Programme for Nepal

• gharpedia.com. How Configuration of the Building Affect During Earthquakes?

• Building How: Earthquake Resistant Buildings

• Satish Kambaliya, Earthquake and Earthquake Resistant Design


Documents

Basic concepts of Earthquake- Resistant Design and ...solutions.ait.ac.th/wp-content/uploads/2016/08/... · Basic of Seismic Design on the application of construction techniques,