recent developments in design and construction techniques of brick masonry buildings

8/2/2019 Recent Developments in Design and Construction Techniques of Brick Masonry Buildings

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Recent Developments in Design and Construction

Techniques of Brick Masonry Buildings

3-4 March, 2012

Department of Civil Engineering

Institute of TechnologyBanaras Hindu University

Varanasi-221005, India

Proceedings of the

Workshop

Editors

P. K. Singh P. R. Maiti


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Recent Developments in Design and Construction

Techniques of Brick Masonry Buildings

3-4 March, 2012

Proceedings of the

Workshop

Organized by


Institute of Technology

Banaras Hindu University

Varanasi-221005, India

Sponsored by

University Grants Commission

New Delhi

(Under SAP Scheme)

Editors

P. K. Singh P. R. Maiti


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Department ofCivil Engineering, IT- BHU

March-2012

ISBN: 978-81-921121-1-4

Published by


Institute of Technology

Banaras Hindu University

Varanasi, India

DISCLAIMER: Neither the editors nor Department of

Civil Engineering, IT-BHU is responsible for statementsand opinions printed in this publication. Editors andpublishers bear no responsibility with regard toaccuracy or authenticity of the information containedin this proceedings and do not accept liability of anykind for any error or omissions towards thispublication.


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Proceedings of the Workshop on Recent Developments in Design and Construction Techniques ofBrick Masonry Buildings, 3-4 March 2012

ii

In Commemoration of 150th Birth Anniversary

Mahamana Pandit Madan Mohan Malaviya ji

(25.12.186112.11.1946)

Founder of Banaras Hindu University, Varanasi, India


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iii

Preface

Masonry buildings are widely constructed for housing inrural and urban areas. This type of buildings basically consists of

un-reinforced masonry wall panels with or without confining

element. Earthquake resistant buildings are required to withstand

the largest earthquake of a certain probability that is likely to occurat their location, and loss of life should be minimized by preventing

their possible damage or collapse.

In the recent earthquakes of Bhuj 2001, Kashmir 2005 and

Sikkim 2011, several masonry houses collapsed, causing loss of life

and properties which occurred due to non-engineered buildings.

These earthquakes have exposed the seismic vulnerability of

construction practices being followed in the country. For centuries,

masonry construction has been used for buildings in the areas

where good quality bricks are economically produced. Confined

brick masonry, i.e. masonry with vertical tie columns andhorizontal bands, represents one of the most widely used

construction systems in India and other parts of the world.

Confinement of brick masonry prevents its brittle failure and

improves the ductility of the masonry when subjected to severe

seismic loading.

Numerical modeling of the seismic behavior of masonry

structures presents a complex problem due to the constitutive

characteristics of the structural materials. In India the seismic

design of the buildings is based on IS 1893-2002, IS 4326-1993

and National Building Code of India-2005. But these codes do not

fully cover this type of construction. However, Euro code covers

confined brick masonry construction in detail. The main objective of

this workshop is to disseminate design and construction practices

of earthquake resistant brick masonry buildings.

P. K. Singh & P. R. Maiti


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iv

Acknowledgement

To give shape to the proceedings and the workshop in general a

large number of individuals and groups have contributed in many

ways and it is our pleasure to acknowledge their efforts. We are

extremely thankful to the speaker for their contribution. The

contributory authors deserve praise for their contribution and co-

operation, which is resulted in the timely publication of the

proceedings.

We are especially grateful to our colleagues namely Prof. V. Kumar,

Dr. S. Mandal and Dr. Rajesh Kumar of the Civil Engineering

Department for their support at different stages of the workshop.

We are thankful to University Grants Commission, New Delhi for

providing necessary funds for the workshop.

We wish to acknowledge the help we received from various

individuals and institutions in the preparation of the proceedings.

P. K. Singh & P. R. Maiti


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v

Contents

Mahamana Pandit Madan Mohan Malaviya ji ii

Preface iii

Acknowledgement iv

Contents v-vi

Masonry Structures: Prospects, Problems and Tasks

K. S. Jagadish

1-14

Failure and Behavior of Masonry Structures in RecentSikkim Earthquake 2011

D. Bandyopadhyay and J. S. Ali

15-28

A Systematic Design Approach of Coupled Shear WallBuildings during Earthquake

Dipendu Bhunia

29-58

Effect of Constituent-Characteristics on Durability ofMasonry and Concrete Structure

V. Kumar

59-66

Provisions of Different Codes in Brick MasonryBuildings: A Critical Review

Rajesh Kumar

67-100


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vi

Earthquake Resistant Confined Brick Masonry Buildings

P. K. Singh

101-124

Analysis of Confined Brick Masonry Buildings

P. R. Maiti

125-152

A Study on Indian Codes and Performance Based Design

Dipendu Bhunia

153-170

Earthquake Scenario of India and Its Relation to Various

Rock Types

Medha Jha

171-184

The Effect of Dynamic Loading on Structural Integrity

Assessment

Debasish Khan

185-198


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1

Masonry Structures: Prospects, Problems and Tasks

K. S. Jagadish

Formerly Professor, Department of Civil Engineering, Indian

Institute of Science, Bangalore, India

Currently Professor of PG Studies Department of Civil Engineering,R V College of Engineering

1. INTRODUCTIONMasonry structures have fallen into disrepute in recent years in

India. The reinforced concrete framed structure is considered to be

superior even for two storeyed buildings. Part of the problem is the

dependence on the burnt brick, its energy intensity and the

resource depletion due to loss of top soil. It is however, necessary to

note that there has been a revival of masonry even for moderate

high rise structures in the West. Switzerland and Denmark, whodid not have a steel industry of their own, preferred to built 15 to

16 storey buildings out of high strength bricks which were locally

available. England and U.S also had high rise masonry going up to

17 storeys Figs (1, 2, 3and 4). In the US, the masonry is built out of

hollow concrete blocks which can accommodate vertical

reinforcement for earthquake resistance.


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2


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3

2. Why Masonry?

It is now pertinent to ask why one can think of masonry in the

Indian context. Table-1 presents the energy content and carbon

emission of building blocks, cement and steel. It is seen that the

burnt brick, cement and steel require higher amount of energy thanthe other. Their carbon emission is also high. The stabilized mud

block is made using 7% cement addition to sandy soil.


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4

Figure 5: SMB being made in soil block press.


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5

Fig 6 and 7 shows hollow concrete and hollow clay blocks.

TABLE-1: ENERGY AND EMISSION OF BUILDING MATERIALS

SL.NO

MATERIAL UNITENERGY/UNIT MJ

CO2 /UNIT Kg

1 CEMENT Kg 3.60 0.80

2 STEEL Kg 28.10 2.2 - 2.8

3 BRICK ONE BRICK 3.75 - 4.5 0.33

4STABILISED MUDBLOCK

BRICKEQUIVALENT

0.90 0.19

5

HOLLOW

CONCRETE BLOCK --DO-- 0.9 - 1.18

0.14 -

0.18

6HOLLOW CLAYBLOCK

--DO-- 1.80 0.18

7SANDSTONEBLOCK (BHUJ)

--DO-- 0.88 0.09

8GRANITE(BANGALORE)

--DO-- 0.00 0.00

9GEOPOLYMER +SOIL

--DO-- NA 0.06


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6

From the table it is clear that use of cement, steel and burnt brick

are not desirable if energy consumption and CO2 emission are to be

reduced. Since buildings in India take up about 30% of the carbon

emission in the country, there is a great need to reduce their

emission. Table-2 describes the energy and emission due to

different building technologies.

Table 2: Energy and Emission due to building technologies

BUILDINGTYPE

EMBODIEDENERGYGJ/M2

CARBONEMISSION

T/M2

OPERATIONALENERGY, 25

YEARS GJ/M2

CO2, 25YEARST/M2

8 STOREYRC FRAME

+ BRICK IN-FILL

4.2 0.41 9.3 0.91

4 STOREYRC FRAME+ BRICK IN-

FILL

2.7 0.25 9.3 0.91

4 STOREYSMB

MASONRYWITH RCFLOORS

1.33 0.13 9.3 0.91

2 STOREY

SMBMASONRYWITH SMB

FLOOR

0.62 0.06 9.3 0.91

It is clear that the RC frame construction with brick in-fill is the

worst for energy and emission. Masonry using stabilized mud block

(or Hollow Concrete block) leads to 50% less energy and carbon


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7

emission. It is hence important to utilize masonry for as great

height as is feasible. With the example of hollow concrete block

(reinforced for earthquake resistance), one can easily think of

masonry buildings for 10 storeys. With stabilized mud blocks one

can construct upto 5 storeys. A large majority of the high rise

buildings in India range from 4 to 10 storeys and it is essential to

explore this option. Already, there are more than 300 buildings

using hollow concrete blocks for high rise housing. There is a hotel

in Nashik going upto 9 storeys built by Mr. Ganesh Kamat of

Ganaka Engineers.


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8

Figure 8 & 9: 6 storeyed building, Mumbai and 9 storeyed building in

Nashik.

Figure 10: An SMB wall.


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9

3. Barriers to Use of Masonry

It is now necessary to understand why India has missed this

opportunity of using low energy building technique.

a. Firstly, brick production is a time, energy and labour

consuming industry and grinds to a halt in the rainy season. It

also requires significant area of land for making and drying

bricks. Its cost is hence rising rapidly.

b. Engineers of today do not learn masonry design. Two storeyed

buildings are built on thumb rule by using brick of 3.5MPa

strength. For higher storeys, the requirements of brick/ block

strength, type of mortar to be used is not known.

c. There is hardly any research in our universities on masonry so

that recent innovations of hollow concrete blocks, reinforced

masonry and stabilized mud blocks are unknown. Only 4 or 5

reports/ papers have been published in India, between 1947 to

1990.

d.The quality of most of the concrete blocks is very poor andthey cannot be used for more than two storeys. There is a need

to set up quality hollow concrete block manufacturing units

like Besser Co.

The knowledge that load bearing masonry using hollow concrete

blocks/ stabilized blocks/ hollow burnt clay blocks is cost effective

and energy efficient is not known to the user public or the

professionals.


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10

4. Recent Positive Developments

As a corrective to the above lacunae, the Dept of Civil Engineering,

Indian Institute of Science launched a detailed R & D programme

from 1990 onwards. About 6 Ph.D.s and 3 M.Sc.s have been

produced under the guidance of the author between 1990 and

2004. Currently, 5 more Ph.D. programmes and several M.Tech

dissertations are underway at the Visvesvaraya Technological

University. Electives on Masonry have been introduced in

Undergraduate and Post-graduate courses. The author is also

working on a Text book on Structural Masonry which is likely to bepublished before the end of the year.

Two companies in Bangalore are manufacturing high quality hollow

concrete blocks with strength of 6.0 to 7.0 MPa. They can be

comfortably used upto 5 or 6 storeys. Machines to make stabilized

mud blocks are available in Bangalore, Auroville and New Delhi.

5. Tasks to be undertakenCourses on structural masonry must be started in all leading

Engineering colleges. Short term courses are to be organised for

training teachers and practicing engineers in masonry. Periodic

conferences and workshops to be organized for wider dissemination

of ideas.


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11

6. Outline of masonry research

Structural masonry has been extensively researched in the west.

One can refer to the books by HENDRY (1), SAHLIN (2), DRYSDALE

& HAMID (3), and NARENDRA TALY (4) to obtain comprehensive

information on western literature. This is however inadequate in the

Indian context since our bricks have low strength and lower elastic

modulus. The research thesis by MATTHANA (5), SARANGAPANI

(6), RAGHUNATH (7) AND GUMASTE (8) give comprehensive

information on brick masonry in India. The paper by GUMASTE et

al [9] is also useful.

Research in masonry is based on the strength of masonry unit

(brick or block), strength of mortar and strength of masonry

element like prisms and wallettes. In general the strength of

masonry element is less than the strength of masonry unit and the

ratio may be referred as masonry efficiency. Fig 11 shows the

sketch of typical masonry prisms, Fig 12 shows prisms after test.


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12

The strength of masonry wall depends further on the slenderness

ratio and eccentricity of loading. There is hence a need to test storey

height walls. Fig 13 shows a storey height wall under test.


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13

Such tests need a very tall loading frame which may not be

available in all colleges. Such frames have been set up at Indian

Institute of Science, B.M.S. College of Engineering and R.V. College

of Engineering.

More detailed research on the strength of walls using hollow

concrete blocks and hollow clay blocks is necessary if high masonry

has to become a reality in India.


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14

REFRENCES

[1] A.W.HENDRY, STRUCTURAL MASONRY MACMILLAN PRESS,

LONDON,1998.

[2] S.SAHLIN,STRUCTURALMASONRYPRENTICEHALL,N.J.,1971.

[3] R.G. DRYSDALE AND A.A.HAMID, MASONRY STRUCTURES

BEHAVIOUR AND DESIGN,THE MASONRY SOCIETY, BOULDER,COLORADO,2008.

[4] NARENDRA TALY, DESIGN OF REINFORCED MASONRY

STRUCTURESMCGRAWHILL,2001.

[5] M.H. MATTHANA, STRENGTH OF BRICK MASONRY AND

MASONRYWALLSWITHOPENINGS,PH.D.THESIS,DEPTOFCIVIL

ENGINEERING, INDIAN INSTITUTE OF SCIENCE, BANGALORE,

DEC1996.

[6] G.SARANGAPANI, STUDIES ON THE STRENGTH OF BRICK

MASONRY

[7] PH.D.THESIS, DEPT OF CIVIL ENGINEERING, INDIAN INSTITUTE

OFSCIENCE,BANGALORE,MAY1998.

[8] S. RAGHUNATH, STATIC & DYNAMIC BEHAVIOUR OF BRICK

MASONRY, PH.D.THESIS, DEPT OF CIVIL ENGINEERING, INDIAN

INSTITUTEOFSCIENCE,BANGALORE,JAN2003.

[9] K.S. GUMASTE, STUDIESONTHE STRENGTH & ELASTICITY OF

BRICK MASONRY WALLS, PH.D. THESIS, DEPT OF CIVIL

ENGINEERING, INDIAN INSTITUTE OF SCIENCE, BANGALORE,

JAN2004.

[10] GUMASTE.K.S, K.S.NANJUNDA RAO, B.V.V.REDDY AND

K.S.JAGADISH, STRENGTH & ELASTICITY OF BRICK MASONRY

PRISMS AND WALLETTES UNDER COMPRESSION, MATERIALSAND STRUCTURES,40,241-253,2007.


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Proceedings of the Workshop on Recent Developments in Design andConstruction Techniques of Brick Masonry Buildings, 3-4 March 2012

15

Failure and Behavior of Masonry Structures inRecent Sikkim Earthquake 2011

D. Bandyopadhyay1 and J. S. Ali2

1Associate Professor, Department of Construction Engineering,Jadavpur University, Kolkata & NPEEE Fellow2Assistant Professor, Department of Civil Engineering, Alliah

University, Kolkata

1. INTRODUCTIONMost of the structures in structures in Indian subcontinent are

built as unreinforced masonry structures built with bricks or

stones bonded with cement or lime-mud or simply mud mortar.

These structures are normally designed for vertical loads and they

do behave well under that considering the fact that bricks and

stones have a decent compressive strength. As soon as they are

subjected to lateral forces, typical in case of earthquakes, high

shear and flexural forces arise leading to the failures of these

structures. The strength of masonry under these conditions often

depends on the bond between brick and mortar (or stone andmortar), which is quite poor. This bond is also often very poor when

lime mortars or mud mortars are used. This is quite evident in the

recent Sikkim earthquake 2011, in which large parts of India

including Sikkim, northern parts of West Bengal etc. were affected.

A masonry wall can also undergo in-plane shear stresses if the

inertial forces are in the plane of the wall. Shear failure in the form


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of diagonal cracks is observed due to this. However, catastrophic

collapses take place when the wall experiences out-of-plane flexure.

This can bring down a roof and cause more damage. Masonry

buildings with light roofs such as tiled roofs are more vulnerable to

out-of-plane vibrations since the top edge can undergo large

deformations. The behaviour of masonry buildings after an

earthquake is significantly important and useful to identify any

inadequacies in earthquake resistant design. Studying types of

masonry construction, their performance and failure patterns helps

in improving the design and detailing aspects. After the Sikkim

earthquake on the 18th September 2011, causing severe damage in

masonry structures in the region of Sikkim and North Bengal the

authors have visited the affected areas thrice to study the damages

to buildings.

2. The Sikkim Earthquake 2011The earthquake of magnitude M6.9 struck at 18:10:48 IST on

September 18, 2011 with its epicentre located near India-Nepal

border region, about 68 km NW of Gangtok, Sikkim as shown in

Fig. 1. It was a shallow focus event, which was felt in India, Nepal,

Bhutan, Bangladesh and China. The tremors lasted for about 30-40

seconds and felt in several Indian states such as Assam, parts of

West Bengal, Bihar, Uttar Pradesh, and Delhi. Three aftershocks

were also felt in Sikkim within 30 minutes of the initial earthquake.

About 100 deaths are reported in India including at least 60 in

Sikkim state though the affected area has low population density of

an average of 88 persons/sq. km. The state capital Gangtok is the

biggest city in the area and Chungthang, Lachung and Mangon in

North Sikkim are major towns which have suffered considerable

damage to structures. Kalimpong and Darjeeling towns in north

side of West Bengal have also suffered significant damages

particularly in masonry structures. The affected region lies in the

high risk seismic zones of IV of Indian seismic code IS: 1893, 2002


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with the expected intensity VIII. This region has experienced

relatively moderate seismicity, with several earthquakes in the last

few decades prior to the recent event on the September 18, 2011.

The earthquake followed by heavy seasonal rains triggered more

than 300 landslides, rock/mudslide causing much devastation.

Landslides cut off the severely affected areas from the rest and

hampered the rescue and relief work in this difficult terrain.

General damage to buildings and other structures agreed well with

the intensity of ground shaking observed at various places.

Other major towns

Aftershock reported by IMD

Main Boundary Thrust

(MDT)

Field Trip on Road

Major towns damaged

Aftershock reported by USGS

Main Central Thrust (MCT)

River / Stream


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However, unexpected severe damage in Gangtok and Kalimpong

were also observed.

3. General ObservationsExtensive damage to masonry structures like school, Church and

hospital buildings was reported in the worst affected regions of

Sikkim and North Bengal. Many unique and inherently poor

architectural and construction features such as unsymmetrical,

weak partition walls in brick/block masonry or in lightly

reinforced/plain concrete, extended floor plans in upper stories

supported on cantilevered beams and slabs, construction on sloped

ground, unstable slopes, weak retaining walls, poor construction

material etc., significantly added to the seismic vulnerability of

structures. It was common practice in Sikkim to construct

residential buildings using bamboo/wood, prior to early nineties.

These traditional constructions (Shee-khim & Ikra) have better

earthquake resistance as observed in the present and past

earthquakes. Major RC-frame structures both governmental and

private buildings have seriously lacked earthquake-resistantfeatures compatible to the design level shaking. Most of the RC

buildings in Gangtok suffered varying degree of damage, from

moderate to collapse during this earthquake. The area has a

number of highway and pedestrian bridges on rivers, rivulets, and

gorges. Only minor damage to a few highway bridges was noticed..

The concrete gravity dams of National Hydroelectric Power

Corporation (NHPC) over Teesta River near Dikchu and Rangit River

near Rangit Nagar have not suffered significant damage due to

earthquake shaking or landslide. The poor earthquake performance

of cultural heritage such as monasteries, churches and old school

buildings is a source of concern as almost all historic structures

suffered varying degree of damages in this earthquake. The exterior

walls of these historical structures are constructed of stone

masonry mostly random rubble with low strength mortar. Heavy

damages have been observed to exterior walls at those historical old


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structures. In Kalimpong, in West Bengal, front masonry elevation

of the historic Church has severly cracked and posed alarming

threat to its safety.

4. Case Studies & DiscussionStudies have been made to two numbers five storied residential

building at Gangtak, one at Temi and two at Mangan. Much of the

construction in Gangtak is of empirically constructed reinforced

concrete (RC) buildings of four to nine stories adjoining each other

on adjacent small plots, with buildings extending to the property A

majority of these buildings exhibited extensive damage to

unreinforced masonry (URM) infill panel walls due to weak masonry

and large unsupported length or heightto-thickness ratio. Most

buildings had a symmetric and uniform grid of beams and columns.

Some buildings that had open stories had severely damaged.

Likewise, buildings with asymmetry in placement of URM infill

walls, causing torsion, also were severely punished. Traditional

Ekra housing made of bamboo or wood framing with lightweight

infill panels of straw and plaster behaved exceptionally well like

past earthquakes. The inadequate stirrups in columns of a building

at Gangtak constructed with bad materials and poorly maintainedhave suffered severe damage. The 250 mm square column size for

four story building at Mangan, North Sikkim with bad material have

cracked and damaged to an extent. Landslides have resulted in

differential settlement of column foundations and suffered damage

as observed in Temi, East Sikkim.


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Figure 2: Severely Damaged Building under Demolition, Gangtak, Sikkim

Figure 3: Collapse ofObservatory Shed, Mangan

Figure 4: Wall crack

continued to Water Basin,

Man an


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A Stone Masonry Historical School Building constructed about 100

years ago at Darjeeling, North Bengal is surveyed in detail. The

building is a three storied combined type of structure, part of which

is constructed as simply unreinforced stone masonry and another

part is retrofitted with reinforced concrete structure with in-filled

stone masonry after severely damaged by the 1934 Bihar-Nepal

earthquake. The masonry portions are built using stones bonded

with cement-lime mortar. The structure is full of Gothic

architectural features which have been largely affected in the recent

earthquake. The C type of unsymmetrical plan of the building

suffered significant damages during the earthquake. The legs of C

are unequal which has further aggravated the plan asymmetry

contrary to the earthquake resistance features. Asymmetric parts

have invited torsion in the structure resulting in out-of-plane

flexural failure. In addition, there was a large number. of non-

structural temporary sheds and other structures like masonry

chimneys and rooms made of wooden roof system used as

dormitory for students, above the second floor of the building.


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These structures have undergone large deformations during the

earthquake and being made of brittle masonry materials, have even

collapsed. A bizarre structural arrangement was observed in the

second floor of the structure with floating columns. This floor was

probably constructed later and uniform structural arrangement was

not followed which resulted in vertical asymmetry. Evidently there

was no clear load path in this floor and this floor was worst affected

by the earthquake. Arrangement of staircase plays a very important

role in determining seismic performance of a structure. Since at the

location of staircase there occurs a discontinuity in the floor

diaphragm action and also the stiffness of the staircase region is

inconsistent with other portions of the structure, it is always much

vulnerable to seismic activity. Same has been observed in case of

this structure where vertical cracks along with settlement have

been observed in the region of staircase due to flexural failure.

Fig ure7: View of C shaped School Stone MasonryBuilding, Darjeeling

Fi ure 8: Crack above Arch Ground Floor


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23

Failures of several Stone Masonry Historical cottage buildings and

church constructed more than 100 years ago at Kalimpong, North

Bengal is also studied in detail. There are a common features of

vertical cracks initiated from centre of the arches over the ground

floor window continued to the corner of the window seal at the first

floor (Fig.13). In many occasions the key stones are separated and

dislodged. Out of plane failure of random rubble stone masonry

walls is another common failure symptom in these cottages. These

Masonry buildings with light slope roofs appears to be more

vulnerable and responsible for the out-of-plane vibrations since the

top edge can undergo large deformations. The weak bonds between

random sized stones with lime-mud mortar have contributed for the

failures. Uses of random stones in withes without through-stones

have further aggravated the problem.Separations of wall have been

observed at the corners of the outer walls. The long unsupported

length of the front wall of a historical church have separated from

the cross walls and severely cracked.

Figure 9: Out of Plane Failure of Walls aboveLintel


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Figure 10:Cracked Stone Masonry Wall Figure 11: View of theChurch, Kalimpong

Figure 12: Cracked Arch Crown

and Masonry

Figure 13: Cracks fromArch Crown to Window


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5. Concluding RemarksThe damage to built environment, economic loss and human

casualties caused by the Himalayan earthquakes are increasing

rather proportionally with the growth of population and subsequent

settlements in its upper reaches. The general pattern of damage to

structures, particularly of masonry buildings, landslides, etc. is

consistent with the recent M6.9 Sikkim 2011 earthquake, except a

few building collapses due to faulty design and or constructionpractices. Monasteries being old and weak were deficient in

strength and needs to be retrofitted against future tremors. It is

unfortunate that society is not adequately prepared and therefore

the seismic risk in the region has risen to unacceptable levels which

may lead to a large-scale disaster. Based on the observations of the

damages caused to a variety of masonry structures during the

Sikkim earthquake 2011, the following conclusions could be drawn.


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Majority of the multi-storied buildings exhibited extensive

damage to unreinforced masonry (URM) infill panel walls due

to weak masonry and large unsupported length or height to

thickness ratio.

Major RC frame structures both governmental and private

buildings have seriously lacked earthquake resistant features

compatible to the design level shaking. The earthquake

followed by heavy seasonal rains triggered many landslides,

rock/mudslide causing much devastation.

Unsymmetrical plan, uses of floating columns and aseismic

construction of chimney etc have suffered severe damage in a

three storied stone masonry school building about 100 years

old historical structure.

Masonry buildings in mud mortar or lime mortar are prone

to severe damage due to lack of bond strength.

Uses of random stones in withes without through-stones

have further aggravated the problem. The failures of such

structures are essentially due to out-of-plane flexure.

Masonry with cement mortar (which has higher bond

strength) has generally behaved better, but only good

masonry bonding is not sufficient for earthquake resistance.

Traditional constructions (Shee-khim & Ikra) have better

earthquake resistance as observed in the present and past

earthquakes.

Use of lintel band, as suggested by the Bureau of Indian

Standards (IS 13828:1993), with additional horizontal bands,

possibly at the seal level and at plinth level seems to be

required for better performance. The horizontal

reinforcement in the lintel band alone does not seem to

improve the ductility to the desired level for stone masonry

structure.

The provision of corner reinforcement in corners and

junctions, again as suggested by BIS, has to be properly

bonded with the surrounding masonry possibly with dowels

or keys to prevent separation.


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27

Masonry buildings with light slope roofs appear to be more

vulnerable and responsible for the out-of-plane vibrations

since the top edge can undergo large deformations.

References

[1]Report on Evaluation of Sikkim 2011 Earthquake damagedStructures, Jadavpur University, Kolkata.

[2] National Information Centre of Earthquake Engineering, IIT

Kanpur

[3] EERI News Paper, November, 2011

[4] Behaviour of Masonry Structure during Bhuj Earthquake,

2001, IISc, Bangalore.


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29

A Systematic Design Approach of Coupled Shear Wall

Buildings during Earthquake

Dipendu Bhunia

Assistant Professor, Department of Civil Engineering, Birla Instituteof Technology & Science, Pilani, Rajasthan, India

1. INTRODUCTIONThe growth of population density and shortage of land in urban

areas are two major problems for all developing countries including

India. In order to mitigate these two problems the designers resort

to high-rise buildings, which are rapidly increasing in number, with

various architectural configurations and ingenious use of structural

materials. However, earthquakes are the most critical loading

condition for all land based structures located in the seismically

active regions. The Indian subcontinent is divided into different

seismic zones as indicated by IS 1893 (Part 1) (2002), facilitating

the designer to provide adequate protection against earthquake. A

recent earthquake in India on 26th January, 2001 caused

considerable damage to a large number of RCC high-rise buildings

(number of storey varies from 4 to 15) and tremendous loss of life.

The reasons were: (a) most of the buildings had soft and weakground storey that provided open space for parking; (b) poor quality

of concrete in columns and (c) poor detailing of the structural

design (http://www.nicee.org/eqe-iitk/uploads/EQR_Bhuj.pdf).

Therefore, this particular incident has shown that designers and

structural engineers should ensure to offer adequate earthquake

resistant provisions with regard to planning, design and detailing in

high-rise buildings to withstand the effect of an earthquake to

minimize disaster.


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As an earthquake resistant system, the use of coupled shear walls

is one of the potential options in comparison with moment resistant

frame (MRF) and shear wall frame combination systems in RCC

high-rise buildings. MRF system and shear wall frame combination

system are controlled by both shear behavior and flexural behavior;

whereas, the behavior of coupled shear walls system is governed by

flexural behavior. However, the behavior of the conventional beam

both in MRF and shear wall frame combination systems is governed

by flexural capacity and the behavior of the coupling beam in

coupled shear walls is governed by shear capacity. During

earthquake, infilled brick masonry cracks in a brittle manner

although earthquake energy dissipates through both inelastic

yielding in beams and columns for MRF and shear wall frame

combination systems; whereas, in coupled shear walls earthquake

energy dissipates through inelastic yielding in the coupling beams

and at the base of the shear walls. Hence, amount of dissipation of

earthquake energy and ductility obtained from both MRF and shear

wall frame combination systems are less than coupled shear walls

system in the high-rise buildings [Jain (1999), Englekirk (2003),

Park and Paulay (1975), Penelis and Kappos (1997), Smith and

Coull (1991), Naeim (2001) & Paulay and Priestley (1992)]. However,

the Indian codes of practice governing the earthquake resistant

design, such as IS 1893 (Part 1) (2002) and IS 4326 (1993) do not

provide specific guidelines with regard to earthquake resistant

design of coupled shear walls. On the other hand, IS 13920 (1993)

gives credence to the coupled shear walls as an earthquake

resistant option but it has incorporated very limited design

guidelines of coupling beams that are inadequate for practical

applications. It requires further investigations and elaborationsbefore practical use.

Further, it is reasonably well established that it is uneconomical to

design a structure considering its linear behavior during

earthquake as is recognized by the Bureau of Indian Standards [IS

4326 (1993), IS 13920 (1993) and IS 1893 (Part 1) (2002)] currently

in use. Hence an alternative design philosophy needs to be evolved

in the Indian context to consider the post-yield behavior wherein

the damage state is evaluated through deformation considerations.


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31

In the present context therefore, performance-based seismic design

(PBSD) can be considered to offer significantly improved solutions

as compared to the conventional design based on linear response

spectrum analysis.

Performance-based seismic design (PBSD) implies design,

evaluation, and construction of engineered facilities whose

performance under common and extreme loads responds to the

diverse needs and objectives of owners, tenants and societies at

large. The objective of PBSD is to produce structures with

predictable seismic performance. In PBSD multiple levels of

earthquake and corresponding expected performance criteria are

specified [ATC 40 (1996)]. This aspect emphasizes nonlinear

analyses for seismic design verification of any structure. This

procedure gives some guidelines for estimating the possible local

and global damages of structures. A retrofitted structure can be

evaluated with the help of PBSD. Similarly, economics in the form

of life-cycle cost along with construction cost of the structure is

inherently included in PBSD [Prakash (2004)].

On the basis of the aforesaid discussion, an effort has been made in

this paper to develop a comprehensive procedure for the design of

coupled shear walls.

2. INVESTIGATION OF COUPLING BEAMCoupled shear walls consist of two shear walls connected

intermittently by beams along the height. The behavior of coupled

shear walls is mainly governed by the coupling beams.


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The coupling beams are designed for ductile inelastic behavior in

order to dissipate energy. The base of the shear walls may be

designed for elastic or ductile inelastic behavior.

The amount of energy dissipation depends on the yield moment

capacity and plastic rotation capacity of the coupling beams. If the

yield moment capacity is too high, then the coupling beams will

undergo only limited rotations and dissipate little energy. On the

other hand, if the yield moment capacity is too low, then the

coupling beams may undergo rotations much larger than their

plastic rotation capacities. Therefore, the coupling beams should be

provided with an optimum level of yield moment capacities. These

moment capacities depend on the plastic rotation capacity available

in beams. An analytical model of coupling beam has been developed

to calculate the rotations of coupling beam with diagonal

reinforcement and truss reinforcement.

2.1 Results & Discussion

The literatures [Paulay 2002; Hindi and Sexsmith 2001; FEMA356

2000; Xuan et al. 2008; ATC 40 1996; FEMA 273 1997; FEMA 356

2000; Munshi & Ghosh 2000; Galano & Vignoli 2000 and Englekirk

2003] and the results obtained from the ATENA2D (2006) software

package show the inconsistent modeling parameters and

inconsistent evaluative parameters. Therefore, a new model has

been created with some assumptions in the following manner to

carry out further study.


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33

Assumptions:

The effect of gravity loads on the coupling beams has been

neglected.

Deflection of the coupling beam occurs due to lateral loading.

Contra flexure occurs at the mid-span of the coupling beam.

The confined concrete, due to the confining action is

provided by closely spaced transverse reinforcement in

concrete, is assumed to govern the strength.

Total elongation in the horizontal direction (Figure 1) due to lateral

loading can be written as:

bbb dL = (1)

and strain in the concrete,b

bc L

L= (2)

Lb

db

bbd

2

bbd

2

Figure 1: Schematic diagram of coupling beam


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Hence, considering Equations (1) and (2) the following equation can

be written as:

coupling beam rotation, bbc

b d

L

=

(3)

The results, considering Equation (3) with maximum strain in

confined concrete ( cu ) of 0.02 [Confining action is provided by

closely spaced transverse reinforcement in concrete as per ATC 40

(1996)], have been tabulated in Table 1.

Table 1: Maximum rotations in radians

Type of

Reinforce

ment b

b

d

L

Value as

per

Equation

(3)

Galano

and

Vignoli

(2000)

Englek

irk

(2003)

ATC40 (1996),FEMA273

(1997) and

FEMA356

(2000)

Diagonal 0.3g to four storey houses.

However confined brick masonry wall buildings which conform with

the specifications for structural configuration and quality of

materials, the dimensions of the building are not limited by the


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87

code. In this case the dimensions of the house are determined by

design calculations based on the load bearing capacity of the

masonry. The building should be verified according to ultimate limit

states. On the other hand based on the experience from past

earthquake as well as the existing technologies for masonry

housing construction it is recommended that the height and

number of storeys.

6. Distance between masonry bearing walls and wall openings

In EC 8 there is no requirement for maximum distance between

walls. However based on experience for different type of masonry

houses it is recommended that the distance between walls conform

to Table 5.

Table 5-Recommended maximum distance between structural walls

Another essential factor is the structural wall continuity. This

means that the size and configuration of openings in walls should

be carefully planned. The following recommendations regarding the

configuration and size of openings should be observed:

Openings should be vertically aligned from storey to strorey

The top ends of openings in the storey should be horizontally

aligned

Openings should not stop continuous RC bond beams (at

lintel and/or roof level)

Openings should be located symmetrically in the plan of the

building so that not to get in the way of the uniform

Design ground

acceleration ag

< 0.2

[g]

0.2 - 0.3

[g]>= 0.3 [g]

Unreinforced masonry [m] 10 8 6

Confined Masonry [m] 15 12 8

Reinforced masonry [m] 15 12 8


93/195

distribution of strength and stiffness in two orthogonal

directions.

7. Simple houses

According to EC 8 certain class of masonry housing can be exempt

from seismic resistance verification provided that the quality of

materials and construction rules specified in the code are met.

Such houses are named "simple buildings". According to EC 8

simple buildings are regular buildings with an approximately

rectangular plan. The ratio between the long to shorter side of the

house is no more to four and the projections or recesses from the

rectangular shape are not greater than 15% of the length of the side

parallel to the direction of projection. Such houses have thefollowing limitations regarding number of storeys above ground

(Table 6)

Table 6: Number of storeys above ground, allowed for simple buildings

For masonry house to comply with a simple building a number of

specifications are given for the masonry walls. The structural walls

should be symetrically located in plan in two orthogonal directions.

A minimum of two structural walls per orthogonal direction. The

length of each wall should be greater than 30% of the length of the

building in the wall plane and the distance between these walls

should be maximum 75% of the size of the building in the other

direction. The minimum cross sectional area of the structural walls

is also specified in EC 8. At every floor, the area of the structural

walls in two orthogonal directions is provided as a percentage of the

total floor area above the level considered. Table 7 below gives the

minimum horizontal structural wall cross-section.

Table 7: Minimum horizontal structural wall cross-section, given as 96 of

the total floor area above the level considered (6)

Design ground

acceleration ag< 0.2 [g] 0.2 - 0.3 [g] >= 0.3 [g]

Unreinforced masonry 3 2 1

Confined Masonry 4 3 2

Reinforced masonry 5 4 3

Design ground < 0.2 [g] 0.2 - 0.3 [g] >= 0.3 [g]


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89

To enforce reguliarity, the difference in structural walls cross-

sectional area in two orthogonal directions from storey to storey

should be maximum 20%. The difference in the mass of structural

walls in two orthogonal directions from storey to storey should be

as well maximum 20%. For such buildings it is also required that

75% of the vertical load is carried from the structural walls.

8. Details for seismic resistance

8.1 Concept

The performance of building subject to an earthquake motions is

governed by the inter-connectivity of structural components as well

as the individual component's strength, stiffness and ductility.

Thus the details to provide seismic resistance can be classified in

two categories:

Details for complete load path

Provide wall-to-wall connection ie. tying of walls

Provide means for walls to foundations connection

Provide connection of bond beams to roof

Provide connection of walls to bond beams

Provide stiff in their plane floors/roofs

Details to improve structural components strength and ductility

Improve the compressive strength of structural components

acceleration ag

Unreinforced masonry 3 5 6

Confined Masonry 2 4 5

Reinforced masonry 2 4 5


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Improve the bending strength of structural components

Improve the shear strength of structural components

Improve the ductility, m of the structural components

9. Bond beams

In the case of confined masonry construction bond beams are

constructed as part of the vertical and horizontal masonry confining

elements. Bond-beams should be constructed in-situ from

reinforced concrete and cast simultaneously with the floor slab.

Bond-beams should be cast on top of all structural walls at every

floor level. The minimum bond beam's cross section is

recommended to be 150x250. The bigger dimension being the

thickness of the wall. Typical examples of monolithic cast in-situRC bond beams with RC slabs are shown below on Fig. 11.

Figure 11: Details of cast in-situ RC slabs with bond beams

Maximum vertical distance between bond-beams is 4 m. Bond-

beams are constructed because:


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91

Forms confined masonry shear walls in combination with tie-

columns

Improves the in-plane stiffness of floors to provide diaphragm

action

Transfers the horizontal load from the diaphragm to the

structural walls

Connects the structural walls together and provides out-of-plane support

Connects the RC tie-columns

EC8 specifies the following minimum requirements:

Concrete of class 15 should be used

Cross section size should be not less than 150x150 mm

Four mild steel rebars with total area 240 mm2

To ensure integrity of the bond beam the longitudinal rebars

at corners and wall intersections should be spliced a lengthof 60f

Transverse reinforcement-stirrups rebars f6 @ 200 mm

intervals (Fig. 12)


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Figure 12- Detail of RC bond showing splicing of rebars at wall corners

According to EC 8 the resistance of the RC bond-beam should not

be taken into consideration in the design calculations.

Consequently there is no mandatory design through calculation for

the bond-beams. As was discussed in the confined masonry section

the design parameters are determined on empirical basis. In Table 7

the members reinforcement can be determined based on the

seismicity of the location the number of stories and position.

Table 8:Recommended reinforcement of horizontal

RC bond-beams

Number

of

storeys

Position

(storey)

Low:

< 0.2 [g]

Moderate:

0.2 - 0.3 [g]

High:

>= 0.3 [g]

2 1-24 bars,

8 mm

4 bars, 10

mm

4 bars, 12

mm


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93

10. Tie-columns

Although the tie-columns and bond beams do not provide framesystem adequate splicing and anchoring of rebars is required at all

joints. Sixty rebar diameters splices are required according to EC8.

The cross-sectional area of rebars for tie-columns can be selected in

dependence of seismicity of the location and number of storeys in

the house. On Fig. 13 below is illustrated the splicing of rebars

between bond beam and tie-column.

4 1-24 bars,

10 mm

4 bars, 12

mm

4 bars, 14

mm

4 2-44 bars,

8 mm

4 bars, 10

mm

4 bars, 12

mm

6 1-2 4 bars,12 mm

4 bars, 14mm

4 bars, 16mm

6 3-44 bars,

10 mm

4 bars, 12

mm

4 bars, 14

mm

6 5-64 bars,

8 mm

4 bars, 10

mm

4 bars, 12

mm


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Figure 13: Construction of tie-column for confinedbrick masonry house

11. Floors and roofs

In EC 8 it is specified that the floor and roof structure can be

constructed in timber or reinforced concrete, provided a diaphragm

action can be achieved. When building confined masonry houses,

RC floor slabs cast in-situ are preferred.

Apart from developing diaphragm action and transfer of the seismic

forces onto the walls the floors and roof should support the walls

out of their plane, ie. all structural walls should be restrained at

floor/roof level. In the case of RC slab the connection is provided

naturally by constructing RC bond beam onto the structural walls.

12. Lintels and cantilever elements


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95

Lintels are load-bearing elements which support the weight of the

wall and floor above opening. Lintels can be made from in-situ

reinforced concrete, timber and reinforced masonry. In seismic

zones cast in-situ RC lintels are recommended. If the distance

between the top of the opening to the top of the floor above is less

than 600 mm the lintel can be cast simultaneously with the bond

beam and floor slab as shown on Fig. 14. In cases where the

distance is bigger the lintels can be cast separately (Fig. 14) and

care should be taken to bond the RC lintels to the masonry of the

adjoining wall through horizontal rebars.


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Figure 14: Requirement for lintels in seismic zones

13. CONCLUSIONS

Confined brick masonry is also quite ductile, and it can absorb

significantly high energy and undergo large deformation during

earthquake. The confined brick masonry technology also ties up the

entire building together for better seismic performance. Confined

brick masonry construction makes a building very safe against

differential settlement and wind load. Also, the confined brickmasonry construction results in better aesthetics and is convenient

to construct using economically available local material and labour.

In the IS 4326-1993 there exists provision for tying up the building

members together, but the concept of confined brick masonry is not

utilized except in clause 8.5. However, there is clear provision for

confined brick masonry in the Euro Code 8, 1998. The

recommended technology is fully supportedbyEuro Code 8 and IS:

4326-1993 (Clause 8.5), and therefore, there should be no

hesitation in application of the technology in the Gangetic plain, as

detailed in the report.

REFERENCES

[1]Brzev, S. Sinha, R.., Unreinforced brick masonry building

with RC roof slab, World Housing Encyclopedia,

Report/India, EERI and IAEE.

[2] IS: 1905-1980, Indian Standard Code of Practice for

Structural Safety of Buildings-Masonry Walls, Second

Revision-1981, Bureau of Indian Standards, New Delhi.


Earthquake Resistant Design and Construction of Buildings,

Bureau of Indian Standards, New Delhi.


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97


Improving Earthquake Resistance of Low Strength Masonry

Buildings, Bureau of Indian Standards, New Delhi.


Ductile Detailing of Reinforced Concrete Structures

Subjected to Seismic Forces, Bureau of Indian Standards,

New Delhi.


Repairs and Seismic Strengthening of Buildings-Guidelines,

Bureau of Indian Standards, New Delhi.

[7]National Building Code of India 2005, Bureau of Indian

Standards, New Delhi.

[8]Eurocode 8: Design provisions for earthquake resistance of

structures. Part 1-2: General rules- General rules for

buildings. ENV 1998-1-2: 1995 (CEN, Brussels, 1995).[9] Eurocode 8: Design provisions for earthquake resistance of

structures. Part 1-3: General rules- Specific rules for various

materials and elements. ENV 1998-1-3: 1995 (CEN, Brussels,

1995).

[10] Eurocode 6: Design of masonry structures. Part 1-1:

General rules for buildings. Rules for reinforced and un-

reinforced masonry. ENV 1996-1-1: 1995 (CEN, Brussels,

1995).

[11] Singh, k. Pramod, (2006), A Report on CompositeConfined Brick Masonry Construction for Four Storey

Apartment Buildings in The Gangetic Plain,

Report/Department of Civil Engineering, IT, BHU, Varanasi.


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101

Earthquake Resistant Confined Brick Masonry

Buildings

P. K. Singh

Professor & Head, Department of Civil Engineering, Institute ofTechnology, Banaras Hindu University, Varanasi, India

1. INTRODUCTIONAs per Euro Code 81, a construction system where plain masonry

walls are confined on all four sides by reinforced concrete members

or reinforced masonry is called confined brick masonry (CBM). In

case of CBM buildings the design philosophy adopted is that

neither the brick masonry nor reinforced concrete gets damaged

during earthquake condition.

Euro Code 8 limits the construction of CBM houses located in

seismic zones having design ground acceleration (ag) greater than

or equal to 0.3g to four storeys (Table 1).

Table 1: Recommended maximum height of building (H) and number of

storeys (n).

Design ground

acceleration ag

< 0.2

[g]

0.2 - 0.3

[g]

0.3

[g]

Unreinforcedmasonry

H [m] 12 9 6n 4 3 2

Confined

Masonry

H [m] 18 15 12

n 6 5 4

Reinforced

masonry

H [m] 24 21 18

n 8 7 6


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1.1Significance of Brick Masonry Buildings in India

As being followed in China and Chile brick masonry apartment

buildings can be the future of the apartment buildings in India also.

Since 1990, base isolated brick masonry buildings with reinforced

concrete floors/roof have been used more widely in China.

Figure 1: Brick Masonry buildings in China

Figure 2: Brick Masonry buildings in Chile

Buildings of confined brick masonry type (Fig 2) are found in all

regions of Chile.

1.2 Socio-Economic Impact


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103

Figure 3: Seismic zones II, III & IV of the Gangetic plain having more than75m soil cover

Seismic zones II, III & IV of the Gangetic plain are shown in Fig 3,

where alluvial soil deposit is having a depth of more than 75m and

goes up to few kilometers in some areas. Total population residing

in the area is approximately 32.91 crores. Therefore, earthquake

resistant confined brick masonry building for the area will have

very high socio-economic impact.

1.3 Technical Details

According to Euro Code 8 the cross-sectional area of rebars for tie-

columns can be selected in dependence of seismicity of the location

and number of storeys in the house. In composite confined brick

masonry buildings the column shall be of 230 mm x 230 mm

having 4 bars of 12 mm diameter as longitudinal reinforcement and

6 mm diameter stirrups at the spacing of 150 mm centre to centre.

The details of column are shown in the Fig. 4.


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230 mm

4x12 dia

bars

M2 0

Concrete

230mm

6 dia sti rrups @ 150 c/c

6 dia sti rrups @

85 c/c

150mm

230 mm

4x12 dia bars

a) Column de tailsb) Band de tails

Figure 4: Details of composite column and Lintel level band

The foundation details corresponding to allowable bearing capacity

of 100 kN/m2 is given in Fig.5. The width of strip footing for brickmasonry shall be 1200 mm and the dimensions for column footing

shall be 1200mm x 1200 mm. The column footing shall be

reinforced with 6 bars of 10 mm diameter in both the directions.

4x12 dia

bars

230 mm

250mm

Lean Concrete

6 dia stirrups @

150 c/c

M20

Concrete

0

6x10 dia barseither way

1200 mm

100mm

Figure5: Details of foundation for a four storey CBM building

1.4 Site Effect

Seismic effect of local soil conditions on peak ground acceleration

are shown in figure 6.


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105

Figure 6: Effect of local soil conditions on peak ground acceleration.

From the figure, it is seen that maximum seismic acceleration is

considerably lower in the alluvium deposit in comparison to the

rock mass.

Fig.7 gives a relationship between the natural period of soil and

alluvium depth.


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Figure 7: Relationship between the natural period of soil and

alluvium depth

As the depth of soil deposit increases, fundamental period of the

deposit also increases. Due to plastic deformation and cracking of

the soil, high frequency content of the earthquake waves can not be

supported by the soil, and it quickly dies out in the soil. Therefore,

in deep alluvial soil deposit area only low frequency and high

amplitude earthquake waves are experienced at the ground level.

Fig. 8 shows relationship between damage and the fundamental

period of the soil in the 1967 Caracus earthquake.


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107

Figure 8: Damage and the natural period of the soil in the 1967 Caracus

earthquake

As reported for the 1967 Caracus earthquake , buildings up to 3 to

5 storeys constructed at places having soil cover more than75

meters suffered minimal damage, and suffered considerable damage

at places having soil depth less than 75 meters. Similarly, buildings

up to 10 to 14 storeys suffered considerable damage at places

where soil cover was more than 75 meters and suffered minimal

damage at places where soil cover was less than 75 meters.

1.5 Structural Action of CBM

Some structural actions of CBM are presented here for its clear

structural understanding.

1.5.1 Load Sharing

In the CBM building, flexible nature of the slab and the lintel level

band, helps the brick masonry wall and the reinforced concrete

column to act together to support all the vertical loads in direct


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compression. Load redistribution between reinforced concrete

column and brick masonry wall mainly at the offsets, ensures equal

strain in the reinforced concrete and the brick masonry at their

interface (Fig. 9).

Brick Masonry

RC Column

a) From column to wall b) From wall to column

Approximately 1 mm

Figure 9: Load redistribution between reinforced column and brick

masonry wall

1.5.2 CBM Action under In-Plane Static Loading

Singh et al.2 conducted experiment on three models, namely; (i)

Reinforced concrete frame without infill (ii) Brick masonry infilled

reinforced concrete frame having no shear connection, and (iii)

Brick masonry infilled reinforced concrete frame with shear

connection. The Load Deflection Curves for the tested models are

given in Figure 10.


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109

Load(kN

)

0

0

2

50

100

150

200

250

300

10

Deflection (mm)

4 6 8 12 13

Infilled frame withoutshear connection

Infilled frame withshear connection

Frame without infill

Figure 10: Load deflection curves for static loading

According to them, in-plane strength of CBM wall may go up

approximately 10 times in comparison to unconfined brick

masonry.

1.5.3 Continuous Lintel Band Action

Effect of continuous lintel band on out of plain vibration of the wall,

and in plane strength of the wall are discussed below.

a) Out of plane effect

In case of CBM building continuous lintel band is provided all

around the building. This lintel band breaks the wall height and

thereby increases stiffness of the wall and results in its reduced

deflection to about one fifth (Fig. 11).


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ww

wslab

slab

slab

slab

lintel band

Figure 11: Deflection of BM wall with and without lintel band

Deflections of the wall for the two cases are compared below.

Deflection without lintel band action, = EIwh

384

4

Deflection with lintel band action = EIwh

384

44

3

2

=

38481

16 4 wh

/5

Thus, out of plane deflection of the wall reduces to about 1/5th due

to the continuous lintel band where the wall is assumed to be

supported.

b) In-plane effect

Singh, P.K. et al.3 have reported experimental results of in-plane

effect of continuous lintel band. They have tested models of infilled

frame without opening, infilled frame with opening having

continuous lintel band, and infilled frame with opening having

isolated lintel band.

The ultimate load carrying capacity of infilled frame with openinghaving continuous lintel band was reported to be 1.7 times that of

the infilled frame with opening having isolated lintel.

1.5.4 Separation of Orthogonal Walls at the Corner

In the CBM buildings, the corner column, which is tied at the lintel

and floor level, provides flexural support to the two orthogonal walls


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111

at the corner. This action prevents wall separation at the corner

during earthquake.

2. MODEL TESTS

2.1 Scale effect

The models have been prepared and tested on 1/5th scale. In the

direct model studyresponse of the prototype is directly determined

from measurement of response of the model(5).

2.2 UBM Building model Test

An UBM 2-storey model was prepared on geometrically reduced

scale of 1/5th which is seen as mounted on the shake table in Fig.

13.

Materials used for the brick masonry and RC works in the

experiment are; (i) Portland pozzolana cement, (ii) 1st class country

bricks of size 462314mm, having average water absorption of

10.7% and compressive strength of 35MPa, (iii) Coarse sand of size

4.0mm downgraded to 1mm having FM of 6.29 used as coarse

aggregate, and (iv) washed locally available Ganga river sand used

as fine aggregate having FM of 2.81.

Concrete mix of 1:1.5:3 by weight with water cement ratio of 0.5

was adopted for all RC works, and cement mortar of ratio 1:3 byweight was used for the brick masonry.


114/195

Figure 13: UBM model Mounted on shake table

2.3 Test Results

The building model after failure is seen in Fig. 14.

2.3.1 Amplitude Measurement

Detailed measurements are taken using Laser sensors and

CATMAN Easy software. The amplitude at the roof slab level was

also measured by using a scale mounted on the stand and a pointer

fixed to the model, with the help of video recording.


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113

Fig. 14 Test results viewed from East Face

2.3.2 Frequency and amplitude

Amplitude of the shake table was fixed at 10mm. In this model

rate of change of frequency was 0.033Hz /s. Total number of cycles

subjected to the model was 122 cycles in 87sec. The time intervalwas kept as 3sec for each frequency step.

The plots between time and amplitude at top of the model are

shown in figures 15 and 16, which represent plot for the first 27sec,

and last 54 to 84sec, respectively. From figure 16, it is clear that

model vibrated with maximum amplitude of 12.5mm at the top,

with a storey drift of 2.5mm.


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Figure 15: Time Vs amplitude plot of UBM model (0-27sec)

Figure 16: Time Vs amplitude plot of UBM model (54-84sec)

g- level at failure of the UBM model

If the displacement / amplitude is given by;

y = a sin t

Then, = a cos t

= - a 2

sin tAnd, max = - a 2

Maximum acceleration at the base level= -a 2

= 0.010 * 17.582

= 3.09 m/ sec2

= 0.32g

Maximum acceleration at the top slab level= -a 2

= 0.0125 * 17.582

= 3.86 m/ sec2

= 0.39g

-15-13-11

-9-7-5-3-1135

79

111315

0123456789101112131415161718192021222324252627282930

amplitudeinmm

Time in sec

Series1

-15

-10

-5

0

5

10

15

5455565758596061626364656667686970717273747576777879808182838485

amplitudeinmm

Time in sec

Series1


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115

The main conclusion drawn from the above experimentation is that

the UBM building model failed at 0.32g level in bending. Therefore,

reinforcement at the corners was found to be necessary to enhance

the g-level of the building before failure.

3. Building Model as per IS 4326-1993.

A building model geometrically similar to UBM model was prepared

as per IS 4326-19934 provisions, except confinement of openings (

Fig. 17 and Fig. 18).

Fig.17 shows the model where masonry up to window sill level with

corner reinforcement welded to the base plate is completed.

Figure17: Masonry up to window sill level with corner reinforcement

The complete building model mounted on the shake table is seen in

Fig.18.


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Figure18: Building model as per IS4326 with Laser sensors

3.1 Test Results

The building model after failure is seen in Fig. 19. The failure took

place at 0.65g level at base level and 1.04g at top. The mode of

failure was failure of the corner steel in tension.

Figure 19: Test results viewed after failure


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117

3.3 Frequency and amplitude

Amplitude of the shake table was fixed at 5mm. In this model rate

of change of frequency was 0.037Hz /s. The amplitude with respect

to time at roof slab level, middle floor slab level and base level are

measured with laser sensors.

The plots between time and amplitude at top, middle and bottom of

the model are shown in figures 20, 21 and 22, which represent plot

for 14.9-16.08sec, 75.82-76.8sec and 98.8 to 100.0sec,

respectively. Observed maximum amplitude at the top is 8.0mm.

Figure 20: Time Vs amplitude plot of UBM model (14.9-16.08sec)


-10

-5

0

5

10

14.5 15 15.5 16 16.5

Series1

Series2

Series3Amplitud

einmm

-10

-5

0

5

10

75.5 76 76.5 77

At Top

At Middle

At Bottom


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The main conclusion drawn from the above experimentation is that

the building model failed at 5.7Hz frequency i.e. at 0.65g level by

the way of rupture of vertical reinforcement at base level. No other

failure mode was noticed.

4. CBM Building Model

A building model on 1/5th scale and geometrically similar to UBM

model was prepared (Fig.23). Reinforcement details adopted in the

CBM model (at 1/5th scale) are given in the table 6.

Table 6: Reinforcement details of the model

Sl.

No

Particulars Dia of rebars

As per Euro

code 8

Nos./spacin

g

Dia of

wire

used in

the

model

1. Column

reinforcement

12 mm 4 2.4 mm

2. Slab reinforcement 8 mm 22mm c/c 1.6 mm

3. Beam

reinforcement

12mm 2.4 mm

4. Stirrups 6mm 2- legged @

17 mm c/c

1.2 mm

5. Lateral ties 6mm 2- legged @

30 mm c/c

1.2mm

6. Binding wire 22 gauge 26

gauge

-10

-5

0

5

10

98.5 99 99.5 100 100.5

Top

Middle

BottomTime in sec


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119

Figure 23: Complete CBM model after mounting on shake table

The model after test is shown in figure 24. As seen from here, there

is no damage to the model at all after the test. The test had to be

stopped due to limitation of the shake table which became unstable

at 7.2Hz frequency.

Figure 24: CBM model after test


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4.1 Frequency and amplitude

Amplitude of the shake table was fixed at 5mm. Time vs.

amplitude plot for the CBM model are shown in figures 25 and 26.

The CBM model was subjected to amplitude at the top level of

model of 9mm and base amplitude of 5mm.

Figure25: Time vs amplitude plot for CBM model ( 0-27sec)

Figure26: Time vs amplitude plot for CBM model (111- 120sec)

The CBM model did not fail even at 7.2 Hz frequency. The

maximum g-level of CBM at the base level was 1.04g and at the top

slab level it was 1.88g.

-6-5-4-3-2-1

0123456

0 1 2 3 4 5 6 7 8 91011121314151617181920212223242526272829

amplitudein

mm

Time in sec

-10-9-8-7-6-5-4-3-2-1

0123456789

10

111 112 113 114 115 116 117 118 119 120 121

amplitudeinmm

Time in sec


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121

5. CONCLUSIONS

On the basis of experimental study, the following salient

conclusions are drawn.

1. In the UBM model initial cracks due to flexure appeared at

0.32g 0.39g at the base in the horizontal direction at afrequency of 2.82Hz, which lead to final failure. Therefore, there

is need for sufficient vertical reinforcement at the corners to

prevent this type of failure.

2. Building model as per IS4326-1993 failed at the maximum

shake table frequency of 5.7Hz. Fixed amplitude at the base

level was +5mm, and the observed maximum amplitude at the

roof slab level was +8.0mm. The corresponding g-level at the

base was 0.65g and at the roof slab level was 1.04g. Model failed

by the way of corner reinforcement rupture at the base level.

Hence, it is concluded that single bar as the vertical corner

reinforcement is insufficient.

3.The CBM model was subjected to maximum practically possible

frequency of the shake table of 7.2Hz ( 5mm base amplitude)

in 486 cycles. No damage to the model was observed, and the

model remained intact after the test.

4. In case of CBM, the shake table amplitude was fixed at 5mm,

and maximum roof slab amplitude of the model was observed to

be 9mm. The corresponding g-level at maximum possible

frequency and amplitude was 1.04g at the base, and it was

1.88g at the roof slab level.

5. In the CBM model no separation of the brick masonry and RC at

the interface was observed even at 1.88g level. Therefore, it is


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concluded that for the CBM buildings, there is no necessity to

provide offsets, as given in Euro code 8.

6. In the CBM Building model there is no failure or crack observed

at openings and at junction of concrete and masonry even at

1.88 g-level. Hence, it is concluded that there is no need to

confine the openings as given in the IS 4326-1993.

7.The CBM building model, tested without bond beams, exhibited

no deficiency during the test even at 1.88g level. Therefore, it is

concluded that in CBM buildings provision of bond beam below

the slab level, as given in Euro code 8, is not necessary.

ACKNOWLEDGEMENT

The research work was carried out under Special Assistance

Program of the University Grants Commission, New Delhi in the

Department of Civil Engineering, Institute of Technology, Banaras

Hindu University.

REFERENCES

[1] Euro Code 8: Design provisions for earthquake resistance of

structures. Part 1-2: General rules for buildings. ENV 1998-1-

2:1995 (CEN, Brussels, 1995).

[2] Singh, P.K. Saxena S. and Roy. B N (2001) 'Behavior Of Brick

Masonry Infilled Reinforced Concrete Frames Subjected to Static

Loading Journal of the Institutions of Engineers (India), vol 82,

no 01, pp 23-29.

[3] Singh, P.K., Singh ,V. and Yadav, S. (2006) Effect of Opening on

Behavior of the Infilled Frame with and without Continuous

Lintel Band Journal of the Institutions of Engineers (India), vol

87, pp 33-37.


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[4] IS 4326-1993, Earthquake resistant design and construction of

buildings Code of Practice, Bureau of Indian Standards, New

Delhi.

[5] Ganeshan, T.P. Model Analysis of Structures , University Press

(India) Limited.

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