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An Introduction to Earthquake and Earthquake

Resistant Building Construction

07/05/2013

Mr. S.C.SharmaO.S.D BOT/PPPPublic Works Department, Rajasthan



2

Why earthquake …

• Seismological & geographicalchanges in composition of earth

• Local convective currents in themantle

• Movement in plate tectonics

• Earth mass consisting sevenmajor tectonic plates

– North American plate

– African plate

– South American plate

– Antarctic plate

– Pacific plate

– Eurasian plate

– Indo-Australian plateContd…

Crust T 5 to 40 km

Basalt granite

Mantle T-2900 Km

Outer core T-2200km

Liquid t-2500C

Inner core T-1290 km

Nickel, iron

Inside the Earth

Local conviction current in

the mantle



3

Contd …

• Release of elastic strain energy stored in interface of rocks

• Seismic waves – Resulting due to faulting and volcanic action

– P-waves longitudinal waves, V 5 to 13 km/sec

– S-waves transverse shear, V 3 to 8 km/sec

– R (Rayleigh) and Q are surface waves propagate on earth surface.

Stage A

Stage B

Stage C

Slip

Elastic strain built-up and brittle rupture



4

Strong motion earthquake records

• Messina (Sicily) – Dec 28, 1908 – 160,000 people killed, 98% building completely destroyed

• Kansu and Shansi Provinces (China) – Dec 16, 1920

– 100,000 people died, 90% building collapsed

• Konto (Japan) – Sept 1, 1923

– Tkyo and Yokohama cities destroyed, 100,000 people died, 43,000 remained

missing, over 300,000 houses were damaged, 59,000 houses burned, 45 %

brick building collapsed and 10% reinforced concrete building

• Fuchu (Japan) – June 28, 1948

– 5,268 people were killed and 35,437 structures were destroyed



How the ground shakes

Rock

Hypocenter or focus

Soil

Rock

Epicenter distance

Epicenter

Focus depth



Earthquake magnitude and intensity

• Magnitude of an earthquake is a measure of its size in terms of energyreleased and radiated in the form of seismic waves.

• Magnitude of earthquake is standardized as “Logarithm (is the base 10) of the

maximum amplitude of the ground motion as recorded in millimeters at adistance of 100 km from the epicenter on a seismograph with a period of 0.8seconds and magnification of 2,800.”

• Relationship between strain energy „E‟ and magnitude „M‟ by Richter is: Log10 E=11.4+1.5M

M=Log A-Log Ao

A – Trace amplitude at any station

Log Ao – Distance correction

• Intensity when used to describe earthquakes is generally intended to denotethe potential destructiveness os an earthquake at a particular location .Commonly used intensity scale is the modified Mercalli (mm)

I = 3 Log a + 1.5 ; a – ground acceleration

mm – Ranges from 2 to 12 to corresponding approximate ground acceleration from 2cm/sec to 6000

cm/sec



7

Relationship between M, MM Intensity & FELT area

EQ-M ExpectedAnnualNumber

MaximumExpected

Intensity MSK

Radius of FeltArea Km

Felt Area Km2

4.6-4.9 6,200 IV-V 50 7,700

5.0-5.9 800 VI-VII 110 38,000

6.0-6.9 120 VII-VIII 200 125,000

7.0-7.9 18 IX-X 400 500,000

8.0-8.9 1 XI-XII 800 2,000,000



8

Where are the seismic zones in India?

Narmada

Plain

Mahanadi

PlainGodavari

Plain

Indo - Gangetic

Plain

Geographic layout and tectonic

plate boundaries at India

Some past earthquakes



9

India seismic map

1970 2002



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Earthquake hazard in Rajasthan

• Moderate 3.4% area close to zone IV & V is Barmer, Jalore, Bharatpur,Alwar are more sensitive to MSK VIII. Equally Jaipur, Dausa are alsosensitive due to fault zone.

• 19% area under intensity VII (M 5.5 to 7.1)

• Remaining area of state is also under earthquake zone II

Contd …



11

Name of district

Houses indistrict

MSK VIII or more % area

MSK VII% area

Building typeA-cat (clay) A-cat (stone) B-cat (Brick)

Alwar 540870 59.3 38.9 25.07 64.09 9.19

Barmer 301115 15.4 63.5 64.1 19.68 2.9

Bharatpur 372175 18.2 25.4 32.1 29.37 36.62

Jalore 259110 11.5 67.4 67.63 8.57 20.33

Source – census of housing GOI 1991

Structure ‘A’ –

Building in field stone, rural structures, unburnt brick houses, clay houses

Structure ‘B’ – Ordinary brick buildings, large block pre-fabricated type, half timbered

structure.

Contd …



12

List of earthquakes in Rajasthan



13

List of earthquakes in Alwar, Rajasthan



14

Seismic zones

Zone Covers area liable toseismic intensity

Degree of damage

V MM, IX Most severe, very high damage

IV MM, VIII High damage risk

III MM, VII High damage risk, moderatedamage risk

II MM, VI, V Low damage risk to very lowdamage risk



15

Relevant IS codes applicable for earthquake resitantbuilding design and construction practice

• IS: 1893-1966 – Practice for design of structural timber in building• IS: 4326-1993 – Earthquake resistant design and construction of

buildings

• IS: 1893 (part1) – 2002 – Criteria for earthquake resistant design of structures

• IS: 13827-1993 – Improving of earthquake resistance of earthernbuilding – guidelines

• IS: 13828-1993 – Improving earthquake resistance of low strengthmasonary buildings – guidelines

• IS: 13920-1993 – Ductile detailing of reinforced concrete structuressubjected to seismic forces

• IS: 13935-1993 – Repair and seismic strengthening of building -guidelines



16

Categories of seismic damage

• O – No damage

• G1 – Slight non structural damage

• G2 – Slight structural damage

• G3 – Moderate structural damage

• G4 – Severe structural damage (Bhv)

• G5 – Collapse (RC)



17

Building design for earthquake resistance

• Design of structure as per seismic coefficient as per IS 1893

• Design of base shear in buildings

• Distribution of earthquake along building height

• Load combimation and increase in permissible stresses

• Design horizontal earthquake load

• Design vertical earthquake load

• Design for two or three component motion.



18

Building configuration …

L<3b

b

L<3b, L<45 m

a (a<0.15L)

b

c (c< 0.15b)

L<45m

b<45mAh

Ah<0.5 Ag Ag = bXL

• Lateral support to long wall

– Shear walls

– Moment resistant frames

– Braced frames

– Separation of wingsUse of separation section : T - Plan



19

Typical damage and failure of masonry buildings

• Non structural damages – Parapet, balconies, plaster,

partition wall, cladding ceiling,glass panes, loosely placeobjects, overturning of cupboards etc.

• Structural damages – Failure of bearing walls,

foundation, roof and floors,displacement in masonry.



20

General construction aspects of masonry buildings

• Mortar

• Wall thickness t<190 mm, wall height < 20 t, L < 40 t

• Openings in walls < 0.5 l (1st), < 0.42 l (2nd), < 0.33 l (3rd)

• Masonry bond

• Horizontal reinforcement in walls

• Horizontal bonds or ring beams, plinth bend, lintel bend, roof bend, gablebend

• Dowels at corners and junctions

• Vertical reinforcement in walls



21

Typical damage and failure of stone buildings

• Separation of walls at corners and junctions

• Wall delaminated with buckled wythes

• General construction aspects

• Providing through „stones‟ or „bond‟ elements

t < 450

1200> 1200

> 1200

Wall Plan Wall Section

600

1600



22

Reinforced building details

• Need for ductility in structure

• Critical zones in reinforced frames

• Ends of beams up to length of 2d of beam area of large negative moments andshear develop

• Ends of columns where maximum moments develop due to lateral force

• Joint regions between beams and columns

• Concrete and steel grades

• Detailing of foundation, plinth beam, column joint.



Seismic Retrofit Techniques for MasonryBuildings: an Overview



24

24

TOPICS:

Seismic performance of masonrybuildings

Masonry walls: behaviour and failure

modes

Seismic retrofit methods



Before…

Vancouver, Canada



26

After… ?

Seattle, USA



27

Source: Seattle PI , March 3, 2001; p. B32001 Nisqually (Washington), USA

Source: S. Chang (VSEG 2001)



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Due to the presence of many structural walls,masonry buildings tend to be rather stiff (with

fundamental periods of 0.3 sec or less for low

to medium-rise buildings). As a result, even

moderate earthquakes can subject masonry

buildings to rather large lateral base shear

forces.

A l ti t



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Acceleration response spectra



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Typical earthquake damage patterns

Cracks between the walls and the floors;

Cracks at the wall corners and intersections;

Out-of-plane collapse of exterior walls;

Cracks in spandrel beams and/or parapets;

Diagonal cracks in structural walls;

Partial disintegration or collapse of structural walls;

Partial or complete collapse of the building.



31

Source: Tomazevic (1999)



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Typical URM Damage:

Shear walls in one direction only

Layout prob lem



33

Buildings with structural walls in one (usually

transverse) direction only collapsed catastrophically

in earthquakes with predominant ground motion in

the weak direction of the building

(e.g. Skopje, Yugoslavia, 1963, Neftegorsk, Russia,1995);

Regular layout - extremely important !



34

+

=



35

1995 Neftegorsk, Russia:

Source: M. Tomazevic (1999)

In- Plane Masonry Walls: Behaviour and Failure



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Modes



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Mode of failure – depends on the combination of appliedloads, wall geometry, properties of the materials, details of

reinforcement



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Behaviour Mode Type of Action

Diagonal tension cracking throughunits

Force- controlled

Crushing at the compression toe Force- controlled

Shear sliding along bed joints Deformation- controlled

Rocking about the compressiontoe

Deformation- controlled



39

• Deformation-controlled: ductile actions that

are limited by extents of lateral deflection.

• Force-controlled : limited by a stress (brittle)



40

Sliding (shear slip) failure

•

Occurs on a stair-stepped crack along bed joints and head joints or along a horizontal bed joint (wall-foundationinterface)

• Low axial loads+ high shear forces;

• Results from the lateral shear force exceeding the

adhesion and shear-friction resistance between the mortar and the units OR the mortar and the floor

Bed joint sliding resistance



41

Bed-joint sliding resistance

Eq. 7-3 (FEMA 356)

n me b js Av V

V b js



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Pier Rocking Failure

• Flexural mode of failure

• Relatively slender walls with small amount of vertical compressivestress

• Bed-joint cracks develop and propagate across the pier length

• Shear forces transferred as a result of the friction at the wall toe.

Pier Rocking Resistance



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Pier Rocking Resistance

P CE

L

h

V r

h

LP 9 .0 V CE r

Eq. 7-4FEMA 356




44


Research labReal life…

Di l i f il



45

Diagonal tension failure

• Due to high shear + high axial load

• Shear strength associated with diagonal tension cracking; depends onthe tensile strength of the units and the mortar bond strength.



46

1979 Montenegro, Yugoslavia

Source: M. Fischinger (EASY)

Sh F il i f d ll



47

Shear Failure – reinforced masonry walls

Source: M. Fischinger (EASY)

Diagonal Tension Resistance



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Diagonal Tension Resistance

00 .1 h L0.67 for

d t

a n d t d t

' f f 1

h LA' f V

Eq. 7-5

FEMA 356

V dt P = f a A

Toe Crushing Failure



49

Toe Crushing Failure

• Flexural mode of failure

• Occurs when, as a result of the overturning moment, verticalcompressive stress exceeds the compressive strength of masonry

• Combined effect of axial load and bending moment

• Localized failure

Toe Crushing Resistance



50

Toe Crushing Resistance

m

a

CLt c ' f 7 .0

f

1 h

L

P V Eq. 7-6FEMA 356

V tc P CL

Seismic Retrofit Techniques



Seismic Retrofit Techniques

Long Beach,California, 1933



52

Seismic Retrofit for Masonry Buildings

Objectives

• Improve wall-to-diaphragm anchorage;

• Improve structural integrity;

• Enhance in-plane wall performance;• Increase out-of-plane wall capacity.

Wall to Diaphragm Anchorage



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Wall-to-Diaphragm Anchorage

Problem

• Most important, and in many cases the most vulnerable, feature related to

seismic performance.

Solution Wall Anchors



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SolutionWall Anchors

Relatively expensive and disruptive to the occupants

More hazard reduction value per $$ than any other URM retrofittechnique

Inadequate Wall Anchors Before Eq. No Privacy After Eq



55

No Privacy After Eq.

Types of Wall Anchors



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Types of Wall Anchors

Tension Anchors Resist the out-of-plane forces induced by the diaphragm

motion.Design based on the out-of-plane wall demand

Shear Anchors Resist the in-plane slippage of roof and floor systems along theface of the masonry walls.

Shear anchor capacity need to be equal to diaphragmcapacity

Lack of shear anchors perpendicular walls punched out



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perpendicular walls punched out

Lack of tension anchors wall separation



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Lack of tension anchors wall separation

2001 Nisqually (Washington), USA

Source: G. Trahern (VSEG 2001)

Wall Anchors



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Wall Anchors

Source: TMS (1994)

Wall Anchors



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Wall Anchors

Source: NRC (1995)

Wall Anchors: Stone Masonry Buildings



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Wall Anchors: Stone Masonry Buildings

Source: M. Lutman, Slovenia (WHE)

Anchor Performance in the 1994 Northridge Eq.



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g q

Some anchors fai led! Causes:

• anchors pulling through the wall due to poor quality masonry.

• anchor pulling through the wall due to lack of overburden or edgedistance.

• flexibility of ties – anchors pulling away from the diaphragm, insome cases causing a loss of vertical support.



63

Source: TMS (1994)



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Source: TMS (1994)

How to Enhance the Performance ?



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• Avoid placement of anchors near the tops of the walls or near openings;

• Limit allowable anchor capacities to 33% of the full value;

• Employ oversized or continuous wall washers;

How to Enhance the Performance ?



66

• Install a concrete bond beam, doweled to vertically confine themasonry.

• Strength and deformation of ties to be considered at actual expected

earthquake demand (to account for flexibility of ties).



Wall Anchors: Applications



68

Long Beach, California




69





70

Vancouver

Photo: Bill McEwen




71



73




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Example: a Historic Stone Masonry Building



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Wall Enhancement Methods



76

• Grout and epoxy injections

• Surface coatings

• Adhered fabrics

• Shotcrete overlays

• Reinforced cores



77

• Majority of the wall enhancement methods – aimed at increasing the

lateral in-plane strength of a component.

Note:If the lateral capacity of an existing wall or pier component is governed by a deformation-controlled action, a rehabilitation scheme will

be most effective if it preserves or enhancesthat type of action.



Grout and Epoxy Injection



79

• By injecting grout into CMU cells, a cavity between wythes, or into large voids in acollar joint can improve the wall shear strength as a result of the increased shear area.

• Wall slenderness ratio can be reduced.

Cement grouting of historic stone masonrywalls



80

Source: M. Tomazevic (1999)M. Lutman (2001)

InIn--situ Tests after the 1998 Earthquakesitu Tests after the 1998 Earthquake

the Influence of Cementthe Influence of Cement--groutinggrouting

0

50

100

150

200

0 5 10 15 20 25 30 35

H (kN)

d (mm)

original

grouted



Surface Coatings



83

• Provide steel tie-down bolts (min. ¼” dia) spaced sufficiently close

so that the coating will not delaminate from the wall surface• Minimum horizontal/vertical bolt spacing 16” o/c



84

Source: NIST (1997)

Surface Coating : Brick masonry applications



85


Surface Coating : Stone masonry applications



86

Source: M.

Tomazevic (1999)



Surface Coating : Research results



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Adhered Fabrics (FRC overlays)



89

• Use of overlapping strips of high-strength fabric made out of Fibre

Reinforced Composites (FRCs) epoxied to the surface of an URM wall.

• Different types of fibres: glass, carbon, etc.



Construction Procedure:



91

• Fabric can be applied to one or both sides of a masonrywall.

• Fabric strips should be aligned with their principal strengthparallel to the shorter of the horizontal or vertical wallspan.

• For vertical strips: the bottom edge of a fabric should beanchored into the existing footing or floor slab with steelanchors.

• Horizontal strips: the side edges should be anchored tothe wall edges with steel anchors.



92Source: NIST (1997)



94

Test results: response of walls with and without TYFO strips

Source: Paquette, Bruneau, and Brzev (2004)



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TYFO strips at the base of the wall

Source: Paquette, Bruneau, and Brzev (2004)



96

TYFO strips failed in shear at the top of the pier

Shotcrete/Reinforced Concrete Overlays



97

• Shotcrete is sprayed onto the surface of an URM wall over a layer of reinforcement.

• Reinforcement typically consists of conventional reinforcing bars placed inthe horizontal and vertical directions.

Shotcrete/Reinforced Concrete Overlays



98

• Similar to cast-in-situ RC shear walls.• Overlay often designed to resist the entire lateral load.



Construction procedure:

• Dowels drilled into a wall to provide improved composite action and to



100

Dowels drilled into a wall to provide improved composite action and to

anchor the masonry to the shotcrete for out-of-plane loadings.

• Spacing approx. 3’ c/c

• Thickness not less than 6”.



101Source: NIST (1997)



104

Source: M. Klyachko, Russia (WHE)

Reinforced Cores

• Used when the preservation of exterior or interior wall finishes precludes



105

the use of surface applied rehab techniques.

• A conventional reinforcing bar bonded with grout within a vertical and/or

horizontal core that is drilled into an URM wall.



Centre Core Technique – U.S. Practice



107

Source: Kehoe (1996)

Centre Core Technique: Applications



108




Centre Core Technique: Applications



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Vancouver Project: Bogdonov PaoPhoto: Bill McEwen

Construction Procedure:

• The diameter of drilled cores should not be less than 4 times thediameter of the embedded reinforcing bar; bar size usually 20M (#6)



111

diameter of the embedded reinforcing bar; bar size usually 20M (#6)

to 25M (#9). • Often, cores provided at each end of pier and at 6” c/c elsewhere.

• Grouts: cement grout, sand/epoxy grout, sand/polyester grout; groutpumped from the top of the wall to the bottom.



113

Proprietary product:

CINTEC

Seistec System

Cintec Application: Seismic Rehab of a Mosque inCairo, Egypt



114

Out-of-Plane Wall Resistance



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Out-of-Plane Seismic Response of Masonry Walls

• Lateral seismic inertia forces cause out-of-plane wall vibrations that result inbending and shear stresses.



116

bending and shear stresses.

• Out-of-plane bending results into cracking at the most stressed zones of the wallsand, ultimately, out-of-plane collapse of the walls perpendicular to the direction of seismic motion.



Wall Out-of-Plane Bracing Alternatives

Strongbacks



121

Knee-bracing

Almost all wall enhancement methods (as mentioned previously)

Strongbacks



122

Need to be stiff enoughto ensure that wall

deflections are within

the limits



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