Stone Masonry English

7/30/2019 Stone Masonry English

1/92

First Edition, July 2011

A UORIAL:Improving the Seismic Perormance

o Stone Masonry Buildings

Jitendra Bothara Svetlana Brzev


2/92


3/92

A UORIAL:Improving the Seismic Perormance

o Stone Masonry Buildings

Jitendra BotharaSvetlana Brzev

First Edition, July 2011

Publication Number WHE-2011-01


4/92

2011 Earthquake Engineering Research Institute, Oakland, Caliornia 94612-1934.All rights reserved. No part o this book may be reproduced in any orm or by any means without the prior written permissiono the publisher, Earthquake Engineering Research Institute, 499 14th St., Suite 320, Oakland, CA 94612-1934.

Tis tutorial is published by the Earthquake Engineering Research Institute, a nonprot corporation. Te objective othe Earthquake Engineering Research Institute is to reduce earthquake risk by advancing the science and practice o

earthquake engineering by improving understanding o the impact o earthquakes on the physical, social, economic,political, and cultural environment, and by advocating comprehensive and realistic measures or reducing the harmuleects o earthquakes.

Production o this tutorial has been supported in part by generous contributions rom the New Zealand Society orEarthquake Engineering and the Earthquake Engineering Center o the University o Engineering and echnology,Peshawar, Pakistan.

Tis tutorial was written and reviewed by volunteers, all o whom participate in EERI and IAEEs World HousingEncyclopedia project. Any opinions, ndings, conclusions, or recommendations expressed herein are the authors and donot necessarily reect the views o their organizations.

Copies o this publication may be ordered rom:

Earthquake Engineering Research Institute499 14th Street, Suite 320Oakland, CA 94612-1934 USAelephone: 510/451-0905Fax: 510/451-5411E-mail: [email protected] site: www.eeri.org

ISBN: 978-1-932884-48-7EERI Publication Number WHE-2011-01

echnical Editor:Andrew Charleson

Production coordinators: Svetlana Brzev, Marjorie Greene, Ruben Negrete, Emmett SeymourLayout & Design: Rachel BeebeIllustrators: Ruslan Idrisov, Simon John HarrisonCover Photo: Te construction o the Kuleshwor Primary School in the Tumki village, Kaski District, Nepal. Tebuilding was built by the Smart Shelter Foundation and uses stone, since it is a locally available material. Te building islocated at 1100 m elevation in a hilly area close to the mountains (photo: Smart Shelter Foundation)


5/92

Acknowledgments

Tis tutorial was developed and reviewed by an international team o experts, who volunteered their time and knowledgeto develop this document over the last three years. Te primary authors are Jitendra Bothara (New Zealand) and SvetlanaBrzev (Canada). Te authors are particularly grateul to those who provided many useul suggestions as reviewers. Teauthors are especially grateul to Qaisar Ali (Pakistan) and om Schacher (Switzerland) or perorming a thorough reviewo the manuscript and contributing photographs. Te authors would like to acknowledge the individuals and organiza-tions who provided useul review comments and contributed photographs and illustrations, including Marjana Lutmanand Miha omazevic (Slovenia), Martijn Schildkamp (Smart Shelter Foundation), Randolph Langenbach (U.S.A.), Mo-hammed Farsi (Algeria), Stavroula Pantazopoulou (Greece), Krishna Vasta (India), and Robert Culbert, Builders WithoutBorders (Canada). Te authors appreciate valuable eedback provided by Mel Green (U.S.A.). Te authors o all the vari-ous WHE housing reports cited in this tutorial provided much useul inormation in their reports, or which the authorsare very grateul.

Te authors are grateul to C.V.R. Murty (India), ormer WHE Editor-in-Chie, who supported the idea o developingthis tutorial and contributed in the early stages o its development. Special thanks are due to Andrew Charleson (NewZealand), current WHE Editor-in-Chie who served as the echnical Editor o this publication and has reviewed its manydrats. Tis publication would not have been possible without Marjorie Greene (EERI) and Heidi Faison (U.S.A), WHE

Associate Editor, who played a critical role in developing the nal drat o the publication. Te authors are grateul toDr Richard Sharpe (New Zealand) or reviewing the nal drat o the tutorial on behal o the New Zealand Society orEarthquake Engineering. Te quality o the publication would not be the same without superb illustrations developedby Ruslan Idrisov and Simon John Harrison (New Zealand), and editorial eort by Rachel Beebe (U.S.A.). Te authorsappreciate contributions by Ruben Negrete and Emmett Seymour, EERI Interns, in the editing stage o this document.

Production o this tutorial has been supported in part by generous contributions rom the New Zealand Society orEarthquake Engineering and the Earthquake Engineering Center o the University o Engineering and echnology,Peshawar, Pakistan. Te nancial support was used to enable the development o graphics and production o thispublication.


6/92

Qaisar Ali

NWFP Uv Eg. & ThgPk

Takim AndrionoP Ch UvId

Marcial BlondetCh Uv PuPu

Jitendra BotharaBNw Zd

Svetlana BrzevBh Cub Iu ThgCd

Craig ComartnCD C I.U.S.A.

Junwu DaiIu Egg MhCh

Dina DAyalaUv BhUd Kgd

Jorge GuterrezUv C R, Dp. Cv EggC R

Andreas KapposUv ThkG

WORLD HOUSING

ENCYCLOPEDIA

EDITORIAL BOARD

Editor-in-Chief

Andrew CharlesonV Uv WgNw Zd

Associate EditorHeidi FaisonP Ehquk Egg Rh CU.S.A

Managing Editor

Marjorie Greene

Ehquk Egg Rh Iu

U.S.A.

Associate EditorDominik Lang

NORSAR FudNw

Chitr Lilavivat

Cug EgThd

Marjana LutmanSv N Bdg.& Cv Eg. IuSv

Leo MassoneUv ChCh

C.V.R. MurtyId Iu Thg MdId

Farzad Naeim

Jh A. M & AU.S.A.

Tatsuo NarafuJp I Cp AgJp

Sahar SafaieTh Wd BkU.S.A.

Baitao SunIu Egg MhCh

Sugeng WijantoTk Uv

Id


7/92

WORLD HOUSING ENCYCLOPEDIA

CONTRIBUTORS

Abdbv, M

Agw, AbhhkAh, Mud Nu

A-Mz, Y

Aj, Azdh

A Dbbk, J N.

A, Sg

A, Fz

Ad, Vj

A, Q

Ad, Azhg

A-Jwh, Abd Hk W.

A, F Lpz

A-Sdq, Hz

Ab, Vj R.

Ab-Shz, MA, Mhd

Ad, Ch

Az L., E

Ahh, Mk

Ahbv, M U.

Ah, Mh Gh

Az, Mx

Awd, Ad

Azbkh, Az

Bh, Hug

Bhud, Bhh

B, Hwj

Bzzu, P

Bgv, Uugbk T.

Bh, T

Bvdz, Gd

B, Ad

B, R

Bh, Mhh

B Ad, Az

Bd, M

Bgdv, J

B, Ju

Bu D, M

Bh, Jd Ku

Bzv, Sv

Cd, R

C G., Ag

C, Ch

Chdk, Rjj

Ch, Adw

Chv, Nk Bvh

Ch, Shd

Chudh, Mdhuud

C, A

C, Cg

DA, D

DE, F

Dv, I

Db, Sj K.

D, RjdDIz, Mu

Djv, Rdv

Dwg, D

Ebg, Jb

E, Rhd

Eu, Fdk

Ewd, Kh

F, Hd

F, Mhd

F, Au

Fhg, Mj

Fh, Mhw A.

Gz, C

Gdv, YuG, Ag

G, Ak

G, Mj

Guv-Pz, T

Gk, P

Gup, Bjbhuh J.

Guz, Jg A.

Hh, Mhud M.

Hh, Bhkh H

Igu, Ah

Ikv, Ig Evh

J, Sudh K.

Jw, Kh S.

Jqu, F GK, P

Kpp, Ad

Kv, P

Khkv, Sh

Kh, Akh N

Kh, A A

Khz, Mhd H. K.

Khk, Mk

Kv, Fd

Kuu, V

Kgd, Fd

Ku, A

Lv, Gupp

Lg, K

Lzz, Fh

Lgg, Muz

Lvhh, Vvd

Lvv, Ch

Lu, W Gug

Lz F., C

Lp, M

Lpz, W

Lpz M, Mu A.

Lu, Pu B.

Lu, Mj

Mk, NMv, D

Mukvk, V.

Md, T

Mgu, K

Mh, Mhdd

Mj, Lu Gz

M, Rb P.

M, Khd

M, Fbz

M, O

Mhkh, Ig

Mu, M

Muhd, Tj

Muvjv, NkMu, C. V. R.

N, Fzd

N, C J.

Ng, Ig

Nhu, Sjd

Nbk, Sudh

Nudg, Ig

Nuv, Bkh

Op Ng, D U.

Odz, Ju

Oz R, Ju C

O G., Lu Ib

Ozz, G

P, Sh KuP, J

P, Jh

Pp, S

Pju, Yghw Kh

Pdh, Phd M

Pud, Jw

Quu, D

R, Dugh

Rb, Sg

Rdguz, Vg I

Rdguz, M

S, Lu

S, R. Bjh

S, I

Sdu, I

Sqb, Kh

Su, Mu

Shwzu, Ew

Shbb, Muz

Shp, Rhd

Shh, Ap

Shu, M.S.

Sgh, Ndp

Sgh, Bhupd

Sh, Rv

Sk, KS, Dvd

Sphu, A

Shz, D S

Sp, Rb

Spz, E

Su, B

Skz, K

Tgh Bk, N

T, Ib

Tk, Sh

T, T. P.

Tzv, Mh

Tu Chk, Tu

NhTug, Su Ch

Updh, Bj Ku

Uv, Sv

Vuzz, M R

Vu, C E.

Vu, Rd

V, Eug

Wj, Sugg

Xu, Zhg G

Y, M I

Yku, Ah

Y, Gg C.

Zhu, Fu L


8/92


9/92

v

Durable and locally available, stone has been used as a construction material since ancient times. Stone houses, palaces,

temples, and important community and cultural buildings can be ound all over the world. With the advent o newconstruction materials and techniques, the use o stone has substantially decreased in the last ew decades. However, it isstill used or housing construction in parts o the world where stone is locally available and aordable material.

raditional stone masonry dwellings have proven to be extremely vulnerable to earthquake shaking, thus leading tounacceptably high human and economic losses, even in moderate earthquakes. Te seismic vulnerability o these buildingsis due to their heavy weight and, in most cases, the manner in which the walls have been built. Human and economiclosses due to earthquakes are unacceptably high in areas where stone masonry has been used or house construction. Bothold and new buildings o this construction type are at risk in earthquake-prone areas o the world.

Tis document explains the underlying causes or the poor seismic perormance o stone masonry buildings and oerstechniques or improving it or both new and existing buildings. Te proposed techniques have been proven in eldapplications, are relatively simple, and can be applied in areas with limited artisan skills and tools. Te scope o this

tutorial has been limited to discussing stone masonry techniques used primarily in the earthquake-prone countries o Asia,mostly South Asia. Nevertheless, an eort has also been made to include some stone masonry construction techniquesused in other parts o the world, such as Europe. For more details on global stone masonry housing practices, readers arereerred to reports published in the World Housing Encyclopedia (www.world-housing.net).

Te authors o this document believe that by implementing the recommendations suggested here, the risk to the occupantso non-engineered stone masonry buildings and their property can be signicantly reduced in uture earthquakes. Tisdocument will be useul to building proessionals who want to learn more about this construction practice, either or thepurpose o seismic mitigation or or post-earthquake reconstruction.

About the Tutorial


10/92


11/92

v

Contents

1. INTRODUCTION 1

S M Cu Aud h Wd 1

K Budg Cp 3

W Cu P 8

2. SEISMIC DEFICIENCIES AND DAMAGE PATTERNS 15

Lk Suu Ig 16

D W Wh 22

Ou--P W Cp 24

I-P Sh Ckg 27

P Qu Cu 28

Fud Pb 29

3. STONE MASONRY CONSTRUCTION WITH IMPROVED

EARTHQUAKE PERFORMANCE 31

Budg S 31Budg Cgu 32Suu Ig (Bx A) 33

S Bd (Rg B) 34

S M W 39F d R Cu 44

Fud 46

Cu M 47

4. RETROFITTING A STONE MASONRY BUILDING 53

S Rg: K Sg d Chg 53Ehg Budg Ig 54

Ehg h L Ld R S M W 63Sghg Fud 69

5. CONCLUSIONS 71

6. REFERENCES 73

7. GLOSSARY 77


12/92


13/92

1

Stone masonry is a traditional orm o constructionthat has been practiced or centuries in regionswhere stone is locally available. Stone masonry hasbeen used or the construction o some o the mostimportant monuments and structures around theworld. Buildings o this type range rom culturaland historical landmarks, oten built by highlyskilled stonemasons, to simple dwellings builtby their owners in developing countries wherestone is an aordable and cost-eective buildingmaterial or housing construction. Stone masonry

1. Idu

buildings can be ound in many earthquake-proneregions and countries including MediterraneanEurope, North Arica, the Middle East, andSoutheast Asia. Te World Housing Encyclopediacurrently contains 15 reports describing stonemasonry housing construction practices inAlgeria, Greece, India, Iran, Italy, Nepal, Pakistan,Palestinian erritories, Slovenia, and Switzerland(see Reerences section). Examples o stonemasonry around the world are shown in Figures1.1 to 1.6.

Figure 1.1 S budg G: ) d u Nh G, d b) u (ph: S. Pzpuu)

Figure 1.2 S I: ) w S Gu d Pug, h vg d b h 2002 M hquk, d b)

d wh hu S, vg bw R d Np (ph: R. Lgbh)

S M Budg Aud h Wd

a) b)

b)


14/92

2

Stone Masonry Tutorial

Figures 1.3 Tp hu Tuk (ph: M. Ebk)

Houses o this construction type are ound in urbanand rural areas around the world. Tere are broadvariations in construction materials and technology,shape, and the number o stories. Houses in ruralareas are generally smaller in size and have smaller-sized openings since they are typically used by a sin-gle amily. Multi-amily residential buildings in ur-ban areas are oten o mixed use - with a commercialground oor and a residential area above. Houses inrural areas and suburbs o urban centers are built asdetached structures, whilehousing units in urban cen-ters oten share a commonwall.

In hilly Mediterranean areasthe number o stories variesrom two (in rural areas) tove (in urban centers). Tesebuildings have oten expe-rienced several interior andexterior repairs and renova-tions over the course o theiruseul lives.

ypically, stone masonryhouses are built by buildingowners themselves or by lo-cal builders without any or-mal training. Te quality oconstruction in urban areasis generally superior to thatound in rural areas.

Figure 1.4 Sx- budg Ag, Ag (ph: S . Bzv)

ypically, stone masonryhouses are built by theowners themselves or bylocal builders withoutany ormal training.


15/92

3

Chapter 1: Introducon

K Budg Cp

Te key components o a typical stone masonrybuilding include oor/roo systems, walls, andoundations. Te walls are vertical elements whichsupport the oors and/or roo, and enclose thebuilding interior. In some cases, a dual gravityload-bearing system is used (Figure 1.7). Tis sys-

Figure 1.7 Du gv d-

bg : ) p

budg wh x

w d -

b Mhh-

, Id (u: GOM 1998),

d b) budg

wh du ud u-

Pk (u: Bh

d Hz 2008)

Figure 1.5 Tp u hug Mhh, Id (ph: S. Bzv) Figure 1.6 Tp u hug Np (ph: M. Shdkp)

tem consists o a timber roo structure supportedby timber columns and beams, and stone masonrywalls at the exterior. In this case, the walls may notprovide support to the oor/roo structure. Tistype o construction can be ound in Maharash-tra, India and in Pakistan. It perormed poorly inpast earthquakes due to the absence o wall-to-rooconnections and walls collapsing outward (e.g., the1993 Maharashtra earthquake, India).

Timber postStone column pedestal

Intermediate piece

Mud overlay

Uncoursed random rubble

stone masonry wall

Timber planks along

the wall between

successive beams

a)

b)

Timber planks

Transverse mber

beam

Longitudinal mber

beam


16/92

4


Figure 1.8 Bk vu: ) jk h , d b) bk -

vu uppd b w (u: M. Lu)

Figure 1.9 Vu budg I: ) d b)

vu LAqu (ph: T. Shh) d ) xp

bk vu Pv (ph: S. Bzv)

F d R Suu

Floor and roo structures in stone masonry build-ings utilize a variety o construction materials and

systems. Te choice is oten governed by the regionalavailability and cost o materials, and local artisanskills and experience. Floor and roo systems includemasonry vaults, timber joists or trusses, and rein-orced concrete slabs.

Vud F/R

Brick or stone masonry vaults are typical oor/roosystems ound in Mediterranean Europe and theMiddle East. Figure 1.8a shows a typical early 20thcentury oor structure in Slovenia, in which ironbeams support shallow brick masonry arches (thisis known as a jack arch system), while Figure 1.8bshows a typical 19th century brick masonry vault inSlovenia. In multi-story buildings, jack arches are o-ten ound at the ground oor level, and timber joistoors at upper levels. Figure 1.9 shows examples ovaulted oor and roo structures rom Italy.

a)

b)

a)

b)

c)


17/92

5


Tb J Tu

imber oor construction maybe in the orm o wooden beams

covered with wooden planks,ballast ll, and tile ooring, asshown in Figure 1.10. A timberoor structure overlaid by planksand bamboo strips is also com-mon (Figure 1.11). In hot cli-mate regions, a thick mud over-lay is provided on top o the rooor thermal comort, as shown inFigure 1.12. imber truss roosare common in the area aectedby the 2005 Kashmir earthquakein Pakistan, as shown in Figure1.13. In most cases, timber joists are placed on top owalls without any positive connection; this has a nega-tive eect on seismic perormance.

Figure 1.10 Tp u I wh wd b

d pk, b , d g (u: M . 2006)

Figure 1.13 Tb u uu h d b h

2005 Kh hquk Pk (u: M. Tzv 1999)

Figure 1.11 A b uu Np (u: WHE Rp 74)

Figure 1.12 A b uu wh ud v Mhh-

, Id (ph: S. Bzv)

Ballast ll

Wooden planks

Tile ooring

Wooden beams


18/92

6


Rd C F/R

It is a common structural/seismic rehabilitation prac-tice to replace the original oor structures in historicbuildings with either a precast concrete joist systemor solid reinorced concrete (RC) slabs; examples othis practice were reported in Italy (WHE Report28) and Slovenia (WHE Report 58). Te use o RCslabs is increasingly popular because cement-basedconstruction materials and technology are becoming

widely accessible. An example o a stone masonrybuilding with an RC roo in Pakistan is shown inFigure 1.14. RC slabs are aordable because they re-quire low maintenance and use space efciently.

S M W

Stone masonry walls are constructedrom stone boulders bonded to-gether with mortar; alternatively,dry stone masonry is used whenthe stones are at in shape and nomortar is used. Figure 1.15 shows anexample o dry stone masonry romDuao, Chile, a small town aectedby the February 27, 2010 earth-quake (M 8.8) and the subsequenttsunami. Tis building was locatedon a beach (the Pacic Ocean can beseen in the background).

In some cases, walls are built usingconcrete with smaller stone boul-ders or rubble; this type o com-posite construction is called stone-

crete in India. Concrete construction which usessmall stone pieces is known as plum concrete(Figure 1.16).

Stone masonry construction practices, includingtypes o stone and wall congurations, are otenregion-specic. Dierences in stone masonry wallconstruction also depend on economic actors, theavailability o good quality construction materials,

and artisan skills and experience.

Figure 1.14 A budg wh RC b Pk (ph: J. Bh)

Figure 1.15 A hu bu ug Du, Ch (ph: S. Bzv)


19/92

7


Figure 1.16 C w u ug ubb: ) R w, d

b) -u u wh ubb Pk (ph: T. Shh)

Fud

Foundations support the wall weight and provide aninterace between the underlying soil and the build-ing structure. In most cases, stone masonry walls aresupported by continuous stone masonry strip oot-ings (Figure 1.17). In some cases, ootings do notexist at all (Figure 1.18).

Figure 1.18 A w whu ud h

d b h 1993 Mhh, Id, hquk

(ph: S. Bzv)Figure 1.17 Tp ud Np (u: WHE Rp 74)

a)

b)

Mud plaster

Stone wall

Mud plaster

Mud oorStone

ooring

Compacted earth

In most cases, stone masonrywalls are supported by con-tinuous stone masonry strip

ootings.

Stone masonry

in mud mortar


20/92

8


W Cu P

Tp S d M

Stone boulders rom various sources, including riverstones, eld stones, and quarried stones, are used orstone masonry construction. River stones or eldstones are oten used in their natural round or ir-regular orms (Figure 1.19); this is especially the casewhen the materials, expertise, or labor required toshape these stones are either not available or not a-ordable. An artisan stone-cutter (see Figure 1.20)can shape stones to produce semi-dressed stones,which have at least one exterior at surace (wedgedstone), as shown in Figure 1.21. In some cases, stones

can be ully dressed into regular shapes to better suitconstruction.

Stone masonry walls are constructed using a varietyo mortars, such as mud, lime, or cement/sand mor-tar. Mud and lime mortars are considered to havelow strength. When cement mortar is used, the ce-ment-to-sand ratio is 1:6 or leaner. In some areas, ce-ment mortar has replaced other types because o itsincreased aordability and availability. Te use o ce-ment mortar does not necessarily imply an increasein wall strength, and it oten creates a alse sense o

Figure 1.19 Rud bud ud d

u Pdg, Id (ph: J. Bh)

security in terms o expected superior building per-ormance. As a result, there has been a signicantincrease in story height and the number and size o

openings in stone masonry buildings

where cement mortar has been used.

Stone masonry walls can be classiedinto three types: uncoursed randomrubble stone, uncoursed semi-dressedstone, and dressed stone. Tis clas-sication is made based on the typeo stone, extent o shaping, and thelayout. In all these wall constructiontypes, common deciencies include:lean cement mortar, the use o soil orvery ne sand mixed with sea sand, andthe absence o curing.

Figure 1.20 A -u wk Mhh,

Id (ph: S. Bzv)


21/92

9


Figure 1.21 S-dd d w u: ) wdgd Mhh, Id (ph: S. Bzv), d b) hpd

Pk (ph: T. Shh)

Uud Rd Rubb SM

Stone used or this type o construction is o ir-regular shape, including small or medium-size riverstones, smooth stone boulders with rounded edg-es, or stones rom a quarry (Figures 1.22 to 1.25).Sometimes, these round stones are partially dressedto achieve a relatively regular shape (Figure 1.25).

Tese stones are usually laid in a low-strength mor-tar such as mud or lime mortar. Te walls consisto two wythes and the space between the wythes islled with mud, small stones and pieces o rubble.Trough-stones (long stones that extend through allwythes), which are essential or bonding the wythesand ensuring wall integrity, are usually absent. Tewall thickness is usually on the order o 600 mm,but it can be excessively largeup to 2 m. In manyinstances, the exterior walls in the building are con-structed rst and the interior walls are constructedlater without any connection. Rooms in these build-ings are generally small and there are ew small wallopenings (i any).

Figure 1.22 Tp

uud d

ubb w: ) uud d ubb

w Mhh,

Id, hwg x

wh d ubb

ud bw

(ph: S. Bzv) d b)

p vw w

ud u

Np ( ubb

bw h w wh) (ph: S Sh Fud)

Rooms in buildings with un-coursed stone masonry wallsare generally small and thereare ew wall openings.

a)

b)

b)a)


22/92

10


Figure 1.24 Cu uud d ubb w

Pk h 2005 Kh hquk (ph: M. Tzv)

Figure 1.23 Cu uud d ubb w

Mhh, Id (ph: S. Bzv)

Figure 1.25 A budg wh uud

w LAqu,

I ( ud bud) (ph: T.

Shh)

Uud S-DdS M

Tis construction type is similarto random rubble stone masonryin that there are two external wallwythes and an interior wythelled with rubble or dirt. How-ever, in the case o semi-dressedstone masonry, the exterior wy-thes are dressed. As a result, theconstruction has a better appear-ance, although its seismic peror-

mance may not be signicantlyimproved. Examples o uncoursedsemi-dressed stone masonry romSwitzerland and Pakistan are


23/92

11


Figure 1.28 S w Mhh, Id: ) uud d ubb w (u: CBRI 1994); b) -

dd w wh x wh bu ug wdg-hpd dd (Su: CBRI, 1994), d ) xp -dd

w (ph: S. Bzv)

shown in Figures 1.26 and 1.27. Figure 1.28 shows a comparisonbetween uncoursed random rubble stone masonry and semi-dressedstone masonry. In many parts o the world, including South Asia, itis common to build the exterior wythe o the wall using dressed orsemi-dressed stone (Figure 1.28b and 1.28c) and the interior one withrandom rubble masonry (Figure 1.28a).

900 mm thick and abovea) b)

Figure 1.26 Uud -dd w Suh- Swzd (ph: T. Shh)

Figure 1.27 S w bu ug ud v budwh hpd x u Bk, Pk (ph: T. Shh)

900 mm thick and above

c)


24/92

12


In some regions o the world, timber or brick bandsare used to enhance the wall stability in both un-coursed random rubble and semi-dressed masonry.Tis is a traditional practice in some parts o Ne-pal, India, Pakistan, urkey, and Greece. Examples

rom Italy and Pakistan are shown in Figures 1.29and 1.30. Use o timber bands (hatils) in urkishstone masonry construction has been discussed byErdik (1990). Figure 1.30 shows a stone masonrybuilding in Italy with brick bands, which are ex-pected to have an eect similar to timber bands.

Figure 1.30 A w wh bk bd LAqu, I

(ph: T. Shh)

Figure 1.29 S -

u wh b bd

Pk (ph: T. Shh)

In some regions o the world,timber or brick bands areused to enhance the wall sta-bility in both uncoursed ran-dom rubble and semi-dressedstone masonry.


25/92

13


Figure 1.31 Dd : ) vw p w, d b) x w Ub, I (u: M . 2006)

Figure 1.32 Dd u Suh Swzd: ) p budg G, d b) d h x

(ph: T. Shh)

a)b)

a)

Dd S M (Ah M)

Dressed stone masonry is constructed using stoneso regular shape that look like solid blocks, as shownin Figure 1.31. A stone with a rectangular or squareace is also called ashlar, hence the name ashlar ma-sonry (Shadmon 1996). Dressed stone masonry canbe ound in Europe. A ew examples rom Italy andSwitzerland are shown in Figures 1.31 and 1.32. Itshould be noted that some types o stone are easier toshape than the others. For example, the widespread

use o dressed stone masonry in Italy is due to theavailability o calcareous stones and tus (rocksormed rom volcanic ash), which are relatively easyto shape. Mortar in dressed stone masonry walls isusually o poor quality, however the seismic resis-tance is superior compared to other types o stonemasonry due to rictional orces between adjacentstones. Te thickness o dressed stone masonry wallsis in the range o 300 to 600 mm.

b)


26/92


27/92


28/92

16


In the 2005 Kashmirearthquake 74,000

people died, most bur-ied under the rubbleo traditional stonemasonry dwellings.

Te key deciencies o stone masonry buildings are:

Lack of structural integrity

Roof collapse

Delamination of wall wythes

Out-of-plane wall collapse

In-plane shear cracking

Poor quality of construction

Foundation problems

Figure 2.4 Cpd budg, 2009 Bhu hquk (ph-

: K. V)

Lk Suu Ig

Te seismic perormance o an unreinorcedmasonry building depends on how well thewalls are tied together and anchored to theoor and the roo (omazevic 1999). Con-sider a simple building as shown in Figure2.5. When the walls are not connected atthe intersections, each wall is expected tovibrate on its own when subjected to earth-quake ground shaking (see Figure 2.5a). Inthis situation, the walls perpendicular to

the direction o the shaking (trans-verse walls) are going to experienceout-o-plane vibrations and are

prone to instability, and possiblycollapse when anchorage to the rooand transverse walls is not adequate.

Walls parallel to the direction o theshaking (shear walls) are also sus-

ceptible to damage. When the walls are well con-nected, there is a rigid roo, and a horizontal ringbeam (band) at the lintel level acts like a belt, thebuilding vibrates as a monolithic box; that is a sat-isactory seismic perormance (see Figure 2.5b).It should be noted that a stone masonry buildingwith a exible roo may show good seismic peror-

mance provided that the walls are well connectedand the roo maintains its integrity.

Figure 2.3 Cp budg, 2009 Bhu hquk (ph: K. V)


29/92

17

Chapter 2: Seismic Deciencies and Damage Paerns

Figure 2.5 M budg dug hquk hkg: ) d w whu b h v, d b) budg wh w-

d w d b (u: Tzv 1999)

A lack o integrity is characterized by the ollowingdamage patterns:

Damage and/or separation of walls at intersections

Floor and/or roof collapse from inadequate wall-to-

oor (or wall-to-roo) anchorage

Dg d/ Sp W I

Wall intersections are particularly vulnerable to earth-quake eects due to signicant tensile and shear stressesdeveloped when seismic orces are transerred rom

walls B (transverse walls) to walls A (shear walls), asillustrated in Figure 2.6. When wall connections areinadequate or absent, vertical cracks may develop or

separation may take place at wall intersec-tions. Tese damage patterns have beenobserved in past earthquakes, as shown inFigures 2.7 to 2.9. In some cases, intersect-ing walls are built using dierent materials(a combination o brick or block and stonemasonry), and are more susceptible todamage compared to other walls, as shownin Figure 2.38.

Adequate connections between inter-secting walls are critical or ensuringthe satisactory seismic perormanceo a building as a whole. However, evi-dence rom past earthquakes has shownthat the presence o ring beams/bands(or alternative provisions such as ties orbandages) is very eective in enhancingstructural integrity (reer to Chapters

Figure 2.6 W h bx-k budg: W A

(dd h g d) upp W B (dd hwk d) (u:Mu 2005)

Inera force

Direcon of

earthquake

Toothed joints

in masonry

courses or L-

shaped dowel

bars

a) b)


30/92

18


Figure 2.7 V k w

du h 1993 Mhh, Id, hquk

(ph: S. Bzv)

Figure 2.8 Dg

w G (u:

WHE Rp 16)

Figure 2.9 Dg w g- -

budg h 2009 Pdg, Id, hquk ( b-

bd d v) (u: Bh . 2010)

Te evidence rompast earthquakes has

shown that the pres-ence o ring beams/bands, or alternative

provisions such as tiesor bandages, is veryeective in enhancingstructural integrity.

3 and 4 or more details on bands and bandages).An example o a stone building with an RC rooband that remained undamaged in the 2005 Kash-mir earthquake in Pakistan is shown in Figure 2.10.Figure 2.11 shows a building with an RC lintelband that showed good perormance in the sameearthquake.

Ater the 2005 Kashmir earthquake, a signicantresearch program related to evaluating and improv-ing the seismic resistance o stone masonry buildings

was undertaken at the NWFP University o Engi-neering and echnology, Peshawar, Pakistan (Ali etal. 2010). Tree one-third scale models o a single-story stone masonry house were tested on a shake-table. One o the models had semi-dressed stonemasonry walls built in cement mortar and an RCroo slab (SM1). Te other model, named SM2, haduncoursed rubble stone masonry walls in mud mor-tar and a timber roo with a mud overlay. VerticalRC members were also provided at the wall intersec-tions. Te third model (SM3) was similar to SM2,but additional horizontal bands were provided at sill,lintel, and roo levels. Te models were subjected tothe same earthquake record, but they showed sub-stantially dierent responses. Model SM1 collapsedat a signicantly lower shaking intensity, and lostintegrity once the separation o the roo slabs andthe walls took place at a peak ground acceleration(PGA) o 0.22 g. Te walls demonstrated a brittleresponse and ultimately ailed. Te presence o verti-cal RC members at the wall intersections in modelSM2 caused a slight increase in strength as well as

Figure 2:10 A budg Muzzbd w ud-

gd h 2005 Kh, Pk, hquk; h w bud

h p RC bd h v v (ph: J. Bh)


31/92

19


Figure 2.12 Dgd d h d h : ) u d SM1, d b) d SM3 h d h xp (u: A . 2010)

F d/ R Cp Id-qu W--F d W--RAhg

Reports rom many past earthquakes have con-rmed that wall-to-oor and wall-to-roo anchor-ages are critical or ensuring the integrity o abuilding and preventing oor and roo collapse.When an anchorage is not adequate, the wallsperpendicular to the direction o the earthquakeshaking move away rom the oors and roo, andmight topple; this is known as out-o-plane col-lapse (illustrated in Figure 2.13).

Figure 2.11 A budg wh RC bd h uvvd h 2005 Kh hquk Pk: ) h budg ud

d dg h p p, d b) p h w k p p h bd ( dqu hg

h bd ) (ph: Bud Whu Bd)

displacement capacity. However, they did not im-prove the overall capacity o the structure, as themodel aced moderate damages at a PGA o 0.16 gand major damages at a PGA o 0.26 g. Model SM3showed an excellent response, and maintained its in-tegrity until the base acceleration (PGA) o 0.27 gwas reached. Model SM1, with semi-dressed stonewalls in cement mortar, showed worse perormancethan model SM2, which had uncoursed rubble wallsin mud mortar. It was concluded that bands pro-vided at several levels are eective in maintaining theintegrity o a building because these elements dividethe walls into smaller portions. Figure 2.12 showsmodels SM1 and SM3 at the end o the test.

a) b)

a) b)


32/92

20


In the Anjar area o Gujarat, India, whichwas aected by the 2001 Bhuj earthquake,

buildings are characterized by thick stonemasonry walls (thickness around 750 mm)built in sandstone and lime mortar (Jainet al. 2002). In this area, the traditionalbuildings have timber roos with ratersspanning two walls in a room, instead ospanning the ull length o the building. Asa result, the oor in each room acted as anindependent system, and had a tendencyto pull apart rom the other oors duringthe strong ground shaking. Tis caused apartial or total collapse o many stone ma-sonry buildings in the area (Figure 2.14).

Evidence rom past earthquakes has shownthat buildings with good oor-wall androo-wall anchorages are able to resist earth-quake eects and maintain integrity with-out collapse (Figures 2.15 and 2.16).

Hipped roos made o timber or lightmetal are common in areas aected by

Direcon of

inera forces

No shear transfer connecon

Shear failure of

masonry wall

Direcon of

ground moon

Figure 2.14 R d

h d b h 2001

Bhuj, Id, hquk: ) d-

uu v

w, d b) dqu w-

- ud h

v budg dg (ph-

: C.V.R. Mu)

Figure 2.13 Idqu w-- hg

a)

b)


33/92

21


Figure 2.15 A budg

wh hz w

h h v

uvvd h 2009 LAqu,

I, hquk (ph:

T. Shh)

Figure 2.16 A budg wh --w h uvvd h 2009

LAqu, I, hquk (ph: T. Shh)

Figure 2.17 Cp budg wh hppd h 2005 Kh, Pk, hquk (u: Bh d

Hz 2008)

the 2005 Kashmir, Pakistan, earthquake. Tesebuildings have a ew important seismic deciencies,such as an absence o eective ties or ring beams(bands) at the eaves level (beneath the roo), inad-equate wall-to-roo anchorage, and an absence othrough-stones in the walls. Buildings o this type

showed poor perormance in the earthquake due

to the collapse o stone masonry walls, as shownin Figure 2.17. It should be noted that the seismicperormance o hipped roos in the earthquake wasexcellent in terms o maintaining their integrityand shape. Ater the earthquake, people were ableto lit the roo o their collapsed house and rebuild

the walls (Bothara and Hiylmaz 2008).


34/92

22


D W Wh

Stone masonry walls constructed o two exteriorwythes are prone to delamination. As discussed inChapter 1, the space between the wythes is usu-ally lled with small stones and pieces o rubblebonded together with mud mortar. Tese wythesare usually constructed using large stone boulders

(either round stones or partially dressed stones).Te large wall thickness is required to ensure thethermal comort and/or personal security o theinhabitants.

R Cp

Roo collapse is one o the major causes o atalitiesin masonry buildings during earthquakes, and it can

take place when either the walls lose the ability to re-sist gravity loads and collapse, or when the roo struc-ture collapses (e.g. timber post-and-beam construc-tion) (Coburn 1987). Roo collapse is oten caused byinadequate wall-to-roo anchorage. Te roo structurecan simply walk away rom the walls and cave intothe building. Roo collapse can also be caused by thecollapse o supporting walls, as shown in Figure 2.18.

Some stone masonry buildings have heavy roos thatcontribute to their seismic vulnerability. Heavy RCroo slabs contributed to the collapse o buildings inthe 2005 Kashmir earthquake (Figure 2.18a). radi-tional buildings in the Marathwada area o Maharash-tra, India, aected by the 1993 earthquake, were char-acterized by a timber plank-and-joist roo supporting

a)

Figure 2.18 Cp uu du h gv d-bg p w h 2005 Kh, Pk, hquk:

) d , d b) b d (ph: M. Tzv)

b)

Figure 2.19 W p h 1993 Mhh, Id, hquk: budg wh b d hv ud v

(ph: S. Bzv)

a 500 to 800 mm thick mud overlay (GOM 1998).Te roos were supported by interior timber rames(called khands) which were not connected to the walls,as shown in Figure 2.19. In the earthquake, heavy roo

mass caused lateral swaying o the rames, which pushedthe stone walls outward and caused their collapse.


35/92

23


Delamination takes place when vertical wall layers(wythes) bulge and collapse outward due to earth-quake ground shaking, as shown in Figure 2.20.One o the causes o delamination is the absence othrough-stones (long stones which tie the wythestogether). Other actors inuencing delaminationinclude intensity o ground shaking, shape o stone

(round, irregular, or regular), and the magnitude othe gravity load.

A detailed experimental and analytical researchstudy on the delamination o stone masonry wallswas perormed by Meyer et al. (2007). Accordingto the study, delamination is triggered by high-re-quency vibrations that cause inter-stone vibrations.Tis results in a reduction o rictional orces thathold the stones together, particularly when wedge-

Figure 2.20 D w: ) d pg (u: Mu 2005),

d b) d w wh du h 1993 Mhh, Id, hquk (ph: S. Bzv)

Figure 2.21 D w: ) w-wh w wh ubb ;

b) dpd du vb; ) pu du ubb ,

d d) h w p (u: M . 2007)

Figure 2.22 D w h 2000 B-

Ou, Ag, hquk (ph: M. F)

Half-dressed

oblong stones

Mud mortar

Outward bulging

of vercal wall

layer

Vercally split

layer of wallVercal gap

a)

a) b) c) d)

shaped stones are used. Anotherpossible cause o delaminationis an increase in internal lateralpressure rom the soil or rubble

core o the wall, which pushesthe wall wythes outward. Tedelamination process observedduring the testing is illustratedin Figure 2.21.

Delamination o the wythes instone masonry walls has beenobserved in several earthquakesaround the world, as shown inFigures 2.22 and 2.23. Delami-nation is usually initiated in theupper portion o the wall, and

the appearance o the damagedwall is as i the exterior wythe hasbeen peeled o. It was reportedater the 2002 Molise earthquakein Italy that spreading (delami-nation) damage in stone mason-ry walls begins at the top o thebuilding, where the lack o over-burden weight allows the mason-ry to vibrate apart. Te stabilityo the wall can be most at riskwhen the masonry units vary insize and are laid with a minimumo horizontal bedding (Deca-nini et al. 2004).

b)


36/92

24


Te chances o delamination can be considerablyreduced i wall wythes are stitched by means othrough-stones (also known as bond stones or head-ers). An experimental study by Meyer et al. (2007)

demonstrated the eectiveness o through-stones in en-hancing the out-o-plane seismic perormance o stonewalls. Te results showed that a regular untied wallspecimen collapsed at an acceleration o 0.19 g, whilea similar specimen with two through-stones or a givenwall surace area ailed at an acceleration o 0.32 g, andthe specimen with our through-stones ailed at an ac-celeration o 0.45 g. Te installation o through-stonesin new and existing stone masonry walls is discussed inChapters 3 and 4, respectively.

Figure 2.23 D w dg p bvd h 1993 Mhh, Id, hquk (ph: S. Bzv)

Ou--P W Cp

Out-o-plane wall collapse is one o the major causeso destruction in stone masonry buildings, particu-

larly in buildings with exible oors and roos. Asdiscussed earlier in this chapter, overall buildingintegrity is critical or the satisactory seismic per-ormance o stone masonry buildings. Te connec-tions between structural components are importantor maintaining building integrity, as discussed inChapter 3. Integrity is absent or inadequate whenthe walls are not connected at their intersections andthere are no ties or ring beams at the oor and roolevels. As a result, each wall vibrates on its own whensubjected to earthquake ground shaking and is there-ore likely to collapse. In multi-story buildings, thistype o collapse usually takes place at the top oorlevel due to the signicant earthquake accelerationsthere (Figures 2.24 and 2.25).

Figure 2.24 Ou--p vb w

pud h p v (u: Tzv 1999)

Figure 2.25 Ou--p p h p

budg h 2003 Bud hquk Ag (ph: M. F)

More pronounced

response at higher levels


37/92

25


Depending on the intensity o earthquake ground shaking, this

ailure mechanism is characterized either by vertical cracks de-veloped at the wall intersections, or by tilting and collapse o anentire wall. Tis collapse mechanism was observed ater the 2002Molise, Italy, earthquake (Maei et al. 2006) (Figure 2.26).

When cross walls parallel to the direction o earthquake shak-ing are ar apart, the central areas o long walls are subjectedto signicant out-o-plane vibrations and may collapse (Figure2.27). Te inadequacy o connections between the cross wallsand long walls is one o the key actors inuencing out-o-planewall collapse. When connections are inadequate, long walls aremore susceptible to the eects o out-o-plane vibrations andthe chances o collapse are higher (Figure 2.28).

Out-o-plane wall collapses were reportedin the area aected by the 2009 Padangearthquake in Indonesia. Te two-storybuildings shown in Figure 2.29 had lightmetal roong supported by timber truss-es. Te oors were inadequately connect-ed to the walls. Stone masonry walls were250 mm thick and relatively slender. Tewalls were constructed using 100 to 120mm diameter round or angular stonesin lime/sand mortar. Te walls collapsed

due to the absence o oor and roo an-chorages and bands (reer to Chapter 3).

Out-o-plane wall collapse is common inbuildings with exible roos and oors,and where wall-to-roo connections areinadequate, as shown in Figure 2.30.

Figure 2.26 Rdd g budg dgd h 2002 M (I) hquk: ) h u dgd h

ug gv upp; b) d w h d dphg (u: M . 2006)

Figure 2.27 Ou--p p g w h 1988

E Np hquk (ph: TAEC Cu, Np)

Figure 2.28 Ou--p p w p

w, NWFP Pk (ph: SDC)


38/92

26


Figure 2.29 (le and above) Ou--p p w h

2009 Pdg, Id, hquk (u: Bh . 2010)

Figure 2.30 Ou--p p w bud-

g wh xb d dqu w-- :

) h 2005 Kh, Pk, hquk (ph: M. Tzv);

b) h 2003 Bud, Ag, hquk (ph: M. F)

Adequate connec-tions between cross

walls and longwalls are critical orpreventing out-o-plane wall collapse.

a)

b)


39/92

27


Buildings with pitched roos have gable walls. Teseare taller than other walls and tend to vibrate as ree-standing cantilevers during earthquakes, unless theyare tied to the roo structure. Tese walls are oten in-adequately connected to the roo, as shown in Figure2.31. Out-o-plane collapse o gable walls is oten re-ported ater earthquakes. Several stone masonry gablewalls collapsed in the 2010 and 2011 New Zealandearthquakes, as shown in Figure 2.32.

Figure 2.32 Cp gb w Nw Zd hquk: ) p p h 2010 Dd hquk, d b)

p h budg h 2011 Chhuh hquk (ph: J. Bh)

I-P Sh Ckg

Damage to stone masonry walls due to in-plane

seismic eects (in the direction o the wall length)is less common than damage due to out-o-planeseismic eects. Vulnerability is mainly caused bythe manner in which the walls are constructed, o-ten using irregular stones and weak mortar.

A typical masonry wall consists o piers betweenopenings, plus a portion below openings (sill ma-sonry) and above openings (spandrel masonry), asshown in Figure 2.33a. When subjected to in-planeearthquake shaking, masonry walls demonstrateeither rocking or diagonal cracking. Rocking is il-lustrated in Figure 2.33b, and is characterized by

the rotation o an entire pier, which results in thecrushing o pier end zones. Alternatively, masonrypiers subjected to shear orces can experience di-agonal shear cracking (also known as X-cracking),as shown in Figure 2.33c. Diagonal cracks developwhen tensile stresses in the pier exceed the masonrytensile strength, which is inherently very low. Tistype o damage is typically observed in the bottomstory o a building.

Several actors inuence the in-plane ailuremechanism o stone masonry buildings, includingpier dimensions, wall thickness, building height,

and masonry shear strength. Rocking behavior ismore desirable than diagonal shear cracking. In-plane wall damage patterns observed in past earth-quakes are illustrated in Figure 2.34.

a) b)

Figure 2.31 A gb w Np h k du h b

w-- (ph: S Sh Fud)


40/92

28


Figure 2.34 Sh u w: ) h k

d h pg h 2005 Kh, Pk-

, hquk (Ph: Bh d Hz, 2008), d b)

h kg p dgd b h

hquk (ph: Bud Whu Bd)Figure 2.33 I-p dg w: ) p w wh

pg; b) kg u, d ) dg h kg (dpd :

Mu 2005)

P Qu Cu

Reports rom past earthquakes conrm that the use o lowquality building materials and poor construction practicesoten result in signicant earthquake damage or destruction.For example, evidence rom the 2001 Bhuj earthquake inIndia indicates that semi-dressed/dressed stone masonry incement mortar generally suered less damage than random

rubble stone masonry in mud mortar (Jain et al. 2002).During earthquake shaking, irregularly placed stones tend tomove out (displace) rom the wall and cause localized dam-age or even collapse in extreme cases, as shown in Figure 2.35.When the stone surace is not clean, or smooth river bouldersare used, the bond between stones and mortar can be weak.Poor bond strength is generally a problem under earthquakeconditions. During lateral movement in the structure themortar crumbles as the stones move and the walls lose in-tegrity and may suer damage or collapse (see Figure 2.36).

Figure 2.35 Lzd w u ud b gu

(u: WHE Rp 74)

a)

b)

c)

a)

b)


41/92

29


Figure 2.36 D w u ud b gu (u: Bh d Hz

2008)

When the mortar used or construction is made o mud insteado cement and/or lime, the mortar becomes the weak link andprevents a proper bond between the mortar and the stones. Insome cases, mud mortar is excessively thick (Figure 2.37). Even

when cement mortar is used, minimum quality standards (as dis-cussed in Chapter 3) are oten not met during construction.

Another problematic construction practice is the use o more thanone type o masonry unit or wall construction, or example, stoneand brick. Because o the dierences in size and shape o units, thebond between orthogonal walls is inadequate. Figure 2.38 shows abuilding in which one wall is constructed o brick masonry and theother o stone masonry. Te use o mixed structural units and sys-tems results in variable wall strength and stiness in dierent partso a building. Tis can cause torsional eects once damage beginsto accrue in the building. It is acceptable to mix materials providedthat only one material is used or each story. Te stronger materials

should be used or the ground oor wall construction.

Figure 2.37 A w wh

hk ud (hk h d

80 ) h d b h 2001

Bhuj, Id, hquk (ph: J. Ak)

Figure 2.38 V kg w

h 2005 Kh, Pk, hquk du

b bw h g

w, d bk- w

(u: Bh d Hz 2008)

Fud Pb

Foundations are not considered to be critical or the seismicperormance o stone masonry buildings. However, it was re-ported ater the 2005 Kashmir, Pakistan, earthquake that build-ings on oundations o adequate size suered less damage thanthose supported by shallow oundations. Foundation soils maybe prone to instability, in the orm o soil spreading or land-slides (Figure 2.39). Buildings in hilly areas were most aectedby the 2005 Kashmir earthquake due to soil movement.

raditional oundations in non-engineered buildings are oten veryshallow and inadequate or sot soil conditions. For example, in thearea aected by the 1993 Maharashtra earthquake in India, ounda-tion depth was on the order o 600 mm, which is signicantly lessthan required or buildings located in the region where expansiveblack cotton soil is common. As a result, cracking in the walls dueto oundation movement was common even beore the earthquake.

Figure 2.39 S pdg h 2005 Kh,

Pk, hquk - wd k h

w (u: Bh d Hz 2008)

F

F

F


42/92


43/92

31

Chapter 3: Stone Masonry Construcon with Improved Earthquake Performance

3. S M Cu wh Ipvd

Ehquk P

Damage is expected during major ground shakingeven in buildings designed and constructed accord-ing to the latest building codes. However, even insevere earthquake shaking, buildings should not col-lapse, threatening the lie saety o the occupants.It is usually not economically viable to construct astone masonry building to resist a strong earthquakewithout signicant damage. However, the provisiono seismic measures during construction is criticalor limiting the extent o damage and preventingcollapse. Tis chapter provides important consider-

ations to be taken into account beore and duringthe construction o a new stone masonry house toensure its enhanced seismic perormance.

Figure 3.1 A pd budg p p h 2005 Kh hquk, Pk-

(u: Bh d Hz 2008)

Budg S

Te rst step in constructing a new buildingshould involve careul selection and review o pos-sible building sites. Te site should provide a stableand rm base or the building. It is best to buildin areas that have rm soil or rock underneath thetopsoil. Sot soils can ampliy building movementdue to earthquakes, cause excessivesettlement, and require more elabo-rate oundations. Te selected build-ing site should have a consistent soiltype across the entire building area.Variations in base soil types can causeunequal settlement problems and un-even support conditions that couldjeopardize integrity o the building.Te key considerations related to theselection o a suitable building siteare discussed below.

Buildings should not be constructednear or on steep slopes due to thehigh risk o damage (Figure 3.1).Flat sites are preerable; they reducethe need or excessive earthworksprior to construction and help en-sure a simple building design andconstruction process. Special pre-cautions should be taken to avoid

soil instability, and consequent destruction o thebuilding i it is constructed on sloping ground; thiscan be achieved by ollowing the procedure illus-trated in Figure 3.2.

Under normal conditions, the slopes may be stable,but an earthquake could trigger landslides or rock-alls, which can cause a partial or complete buildingcollapse (see Figure 3.3). Retaining walls, rock barriersand green barriers can provide protection. A simpleindication o slope instability is the presence o in-

clined standing trees.

Te site should be located away rom riverbanks andlarge trees. Also, construction o buildings at sites withpredominantly loose sand, uncompacted soil, or sotclay should be avoided. However, when that is notpossible, sufcient drainage should be provided andthe ground level o the building should be raised bycompacted earth orming a plinth. When a buildinghas to be constructed on ll, the oundations shouldbe deep enough to rest on the rm ground suracebelow the ll. Pile oundations are required in somecases.


44/92

32


Budg CguBudg P

Building plans should be regular, simple, and sym-metrical. Buildings with square, rectangular, or cir-cular plans have shown better seismic perormancein past earthquakes than buildings with irregularplans.

Buildings with -, L-, or C-shaped plans are prone totwisting, localized damage or even collapse and dis-integration at wall intersections. When the proposedplan o a building is irregular, it should be dividedinto smaller blocks o regular plans (see Figure 3.4).

Long and narrow buildings appear to suer moreextensive damage during earthquakes. Without thesupport o cross walls, long walls are very exible andmay collapse during ground shaking. When a build-ing is longer than three times its width, it should bedivided into smaller blocks with sufcient gaps be- Figure 3.3 A budg dgd b dd h 2005 Kh,

Pk, hquk (u: Bh d Hz 2008)

Figure 3.2 Sp pv budg u p p (u: Shh 2009)

Start the retaining wall 3 ft below1.

vegetable soil and prepare a

base half as wide as the nished

wall height.

Maximum heigth of a retaining2.

wall should not exceed 8 ft. The

lower the wall, the stronger it will

be.

Incline the front of the wall in a3.

ratio 1:5. That is, for every 5 ft of

height, go 1 ft back.

Incline the stones at a right angle4.

to the front.

Place as many through-stones5.

as possible, but at least every

2 ft along the height and length

of the wall.

If mortar is used, leave 4x46.

drainage holes in the lower part

of the wall, every 2 ft.

Instead of making one high wall,7.

subdivide it into several lower

walls, stepping back each time

the same distance as the heigth

of the lower wall.

Keep the building away from the8.

retaining walls.

On the lower side at least the

same distance as the heigth of

the wall.

On the upper side at least 3 ft

from the retaining wall.

Curved retaining walls are9.

stronger.

3 ft

H

max 8 ft

2 ft

H

1

Vegetable ear th

24

Stones at

right angle

9

1/5 H

H

1 ft

5 ft

3

Slope of front 1/5

Example

5 6

Through-stones Drainage holes

2ft

2 ft

2ft

8H

min Hmin 3 ft

(better h)

7

h h

tween them; these blocks could be built on the sameoundation (see Figure 3.4). Another approach is toconstruct buttresses or interior cross walls (these willbe discussed in Chapter 4).


45/92

33


Figure 3.4 Budg gu: DO d DON'T (dpd : IAEE 2004)

Budg Ev

A stone masonry building should beas regular as possible up its height

(see Figure 3.5). Setbacks are notrecommended. However, i theycannot be avoided, a load-bearingwall should be provided beneatheach wall in the upper story.

Budg Hgh

Non-engineered stone masonrybuildings with walls built using ce-ment mortar should be limited totwo stories in high seismic zones,and three stories in moderate tolow seismic zones. However, whenmud mortar is used or wall con-struction, building height shouldbe limited to one story in highseismic zones, and two stories inmoderate and low seismic zones.Te denition o seismic zones iscountry-specic and is usually pre-scribed by national building codes.

Suu Ig (BxA)

Past earthquakes have shown thatdamage to unreinorced masonrybuildings is signicantly reducedwhen building components are wellconnected and the building vibrateslike a monolithic box, as discussedin Chapter 2. In many cases, unrein-orced masonry buildings have exi-ble oors (in-plane), so there is a needto provide additional elements to tiethe walls together and ensure accept-able seismic perormance. Structural

integrity o a building can be achievedby developing a box action by ensur-ing good connections between allbuilding componentsoundations,walls, oors, and roo. Key require-ments or the structural integrity ina masonry building are illustrated inFigure 3.6. A ring beam (band) at lin-tel level is one o the critical provisionsor ensuring structural integrity.

Figure 3.6 K qu ug bx budg (dpd

: Mu 2005)

Lintel band

Good connecon be-

tween roof and walls

Roof that stays together as

a single integral unit during

earthquakes

Walls

with smallopenings

Good connecon

between walls

and foundaon

Good connecons

at wall corners

S foundaon

Figure 3.5 Budg gu v d: gu budg dd,

d budg wh bk vhg .


46/92

34


S Bd (Rg B)

Bkgud

A seismic band is the most critical earthquake-re-sistant provision in a stone masonry building. Usu-ally provided at lintel, oor, and/or roo level in abuilding, the band acts like a ring or belt, as shownin Figure 3.7. Seismic bands are constructed usingeither reinorced concrete (RC) or timber. Properplacement and continuity o bands and properuse o materials and workmanship are essential ortheir eectiveness.

Seismic bands hold the walls together and ensure in-tegral box action o an entire building. Also, a lintelband reduces the eective wall height. As a result,

Figure 3.7 A bd k b (dpd : GOM 1994)

bending stresses in the walls due to out-o-planeearthquake eects are reduced and the chances owall delamination are reduced.

During earthquake shaking, a band undergoes bend-ing and pulling actions, as shown in Figure 3.8. Aportion o the band perpendicular to the directiono earthquake shaking is subjected to bending, while

the remaining portion is in tension.

Seismic bands can be provided at plinth, lintel,oor, and roo levels (see Figure 3.9). In somecases, a lintel band is combined with a oor orroo band. An RC plinth band should be providedatop the oundation when strip ootings are madeo unreinorced masonry and the soil is either sotor uneven in its properties (as discussed later inthis chapter).

Figure 3.9 L bd budg

( d ) (dpd : UNCRD 2003)

Pulling of lintel bandBending of lintel band

Lintel band

Ground movement

Roof band

Floor Band

Figure 3.8 Pug d bdg bd

budg (dpd : Mu 2005)


47/92

35


A oor/roo band is not re-quired in buildings with RCoor/roo structures. In suchcases, the slab itsel ties thewalls together.

A seismic band must becontinuous (like a loop or abelt), otherwise they are in-efcient. Some examples oundesirable discontinuitiesin lintel band constructionare illustrated in Figures3.10 and 3.11.

Lintel beams (commonly known as lintels) are re-quired atop all the openings in a wall. However, ia band is provided at the lintel level, a lintel beam

can be cast as an integral part o the lintel band tominimize construction costs, as illustrated in Figure3.12. Details or combining a lintel and oor/rooband are shown in Figure 3.13. Te band must becontinuously reinorced at the wall intersections, asshown in Figure 3.14.

Figure 3.10 S bd hud w b uu; v -

pb (dpd : GOM 1998)

Figure 3.11 RC bd hud w v whu dp hg hgh

(dpd : GOM 1998)

Figure 3.13 Cbg / d bd: ) b bd,

d b) RC bd

Do This Avoid This

Do This Avoid This

Plinth band

Lintel band

CGI sheet

Lintel comb

with RC ban

Roof band

Lintel band

RC slab or

oor band

combined

with lintel

Figure 3.12 Mgg RC d bd

A lintel-level band is required in most cases. Seismicbands at both the oor and the roo level are requiredunder the ollowing conditions:

Te oor structures are exible (e.g., timber oors),

Te vertical distance between lintel and oor levelexceeds 400 mm, or

The total story height exceeds 2.5 m.

A seismic bandmust be contin-

uous, like a loopor a belt.

a) b)

Timber lintel

Timber band


48/92

36


Figure 3.14 Rdd dg b d RC bd (dpd : T. Shh

d C.V.R. Mu)

Rd bd

RC bands are generally a better choice than timberbands due to their low maintenance, long service lie,and improved integrity with the stone (provided the

concrete is properly mixed, placed, and compacted).Stone masonry buildings with RC bands perormedwell in past earthquakes, such as the 2005 Kashmir,Pakistan, earthquake, as discussed in Chapter 2, andwere used in post-earthquake rebuilding eorts inIndia, as shown in Figure 3.15.

Te required number and size o reinorcing barsin RC bands depends on the room span (distance

between adjacent cross walls), the

importance o the building in thecommunity, the expected inten-sity o earthquake shaking (seismiczone), and the number o stories.Usually, two or our longitudinalbars o 10 to 16 mm diameter su-ce. Tese bars must be tied with

links or ties at a maximum spacing o 150 mm, asshown in Figure 3.16. Te bars must be bent at wallintersections with 400 mm hooks. Te requiredband depth depends on the number o bars: a 75mm depth is sufcient when two bars are used,while a depth o 150 mm is needed when our bars

are used, as shown in Figure 3.17. Te band widthshould match the wall thickness.

Links and ties are used to tie longitudinal bars, thatis, hold them in place and prevent them rom bendingoutward (buckling) in an earthquake. Proper bendingo ties and links is critical or the eectiveness o RCbands in earthquakes. ies are used in bands with ourbars, and they must be bent in the orm o a closed

Stone masonry build-ings with RC bands

perormed well inpast earthquakes.

Figure 3.15 S hu wh RC

bd bu h 1993 Mhh-

, Id, hquk (u: GOM 1998)


49/92

37


Figure 3.18 Idqu bdg RC bd: )

k, d b) (ph: S Sh Fud)

loop. Te ends o the bars must be bent into 135hooks, as shown in Figure 3.17a. Figure 3.18b showsan example o poor construction practice, when tiesare not bent in the orm o a closed loop; this should

be avoided. Links are used or bands with two bars.In order or links to be eective, their ends must bebent into 180 hooks, as shown in Figure 3.17b. Inad-equately bent links are shown in Figure 3.18a.It is very important to provide sufcient cover to thereinorcement in RC bands. Inadequate cover resultsin corrosion o the reinorcement accompanied bycracking o the concrete. An example o exposedand corroded reinorcing bar in an RC lintel band isshown in Figure 3.19a.

A proper concrete cover can be achieved by castingconcrete spacers, as shown in Figure 3.19b. Te spac-

ers can be made by cutting PVC pipes into 25 mmthick rings. Tese rings are lled with concrete (madeusing a small-sized aggregate). A steel wire is embed-ded in the center (wire is used to tie the spacers to thereinorcing bars). Tese spacers were successully usedby Smart Shelter Foundation in their school projectsin Nepal. An example o an RC band under construc-tion using spacers is shown in Figure 3.19c.

When reinorcing bars remain exposed ater the re-moval o ormwork, a 15 to 20 mm thick mortaroverlay (1:3 cement:sand mix) should be provided atthese locations.

a)

b)

Figures 3.16 R u RC bd (dpd : GOM

1998)

min 400 mm

Links at 150 mm spacing c/c

Figure 3.17 RC bd -: ) bd wh u b d ,

d b) bd wh w b d k

a)

b)link

180 hook

wall thickness

wall thickness

150mm

75mm

min 10 mm

min 30 mm cover

6 mm @ 150 mm c/c

6 mm @ 150 mm c/c

e

135 hook


50/92

38


Once the concrete is mixed and placed into orm-work, it is essential to ensure proper compact-ing using steel rods. I compacting is not doneproperly, segregation (honeycombing) o con-crete may take place, as shown in Figure 3.20.Tis will result in concrete with poor compres-sive strength and corroded reinorcement. Notethe excessively large aggregate size used or theconcrete construction shown in Figure 3.20.

Tb bd

In many countries, such as urkey, Nepal, Pakistan,and India, timber bands have been used in stone ma-sonry construction or centuries. At the present time,however, a scarcity o timber leads to unacceptably highcosts and makes the use o timber in new constructionimpractical. imber bands are made using a pair o par-allel planks or runners nailed together with small crossmembers. Te corners o the timber band should bestrengthened by diagonal knee-braces that match the

size o the cross members (see Figure 3.21). Te crossmembers should be placed either perpendicular to thelong runners (like rungs on a ladder), as shown in Fig-ure 3.21, or diagonally at approximately 45 degrees, to

Figure 3.19 C v RC bd: ) xpd b du -

dqu v, b) p d PVC pp, d ) RC

bd ud u hwg u p (ph:

S Sh Fud)

Figure 3.20 P u qu RC bd

(ph: S Sh Fud)

In many countries, such asurkey, Nepal, Pakistan, and

India, timber bands have beenused or centuries.

a)

b)

c)


51/92

39


orm a horizontal truss (see Figure 3.22). Te long tim-bers o the eaves-level timber band should be attachedto the stone wall at regular intervals (this is required totie the top band to the roo).

Te detailing o a timber band is o critical importance.

Wood spacers (the short timber pieces) should be prop-erly nailed and the long runners should be properlyspliced to achieve continuity (see Figure 3.23).

Te required size and number o timber elements de-pends on the distance between cross walls, the type otimber, the importance o the building, the seismiczone, and the building height. Usually, long paralleltimber runners with dimensions o 50 mm by 100mm and cross members with dimensions o 50 mmby 50 mm, placed at spacing o hal a meter along therunners should sufce or a span up to 5 m.

Figure 3.23 Dg b bd - j d p

S M W

Proper wall construction is o critical importance orseismic saety. Important considerations that need tobe ollowed are summarized below.

W hghTe story height in stone masonry buildings should belimited to 3.5 m when cement mortar is used or wallconstruction, and 2.7 m when mud mortar is used.

W gh

Recommendations regarding the wall length are il-lustrated in Figure 3.24. Te maximum distance be-tween adjacent cross walls in a building should be lessthan 5 m when mud mortar is used, and 7 m when

cement mortar is used. When

longer walls are required, itis possible to introduce but-tresses at 5 m spacing; howev-er, this requires more detailedplanning and a higher qualityo construction. For more de-tails about buttresses in ma-sonry construction reer toIAEE (2004). Recommenda-

Figure 3.21 Tb bd wh k-b h

Figure 3.22 Tb bd hz u wh b

pd 45 g u hg

Raers

Wired overwall

to mber blockspassing through

wall

pg


52/92

40


tions regarding the maximum length and height o

stone masonry walls are summarized in Figure 3.25.

When possible, construction o stone masonry gablewalls should be avoided (see Figure 2.31). Te use olight-weight materials such as galvanized iron sheetsor wood panels is recommended instead.

Sz d pg

Special consideration must be made regarding thesize and locations o doors and windows within awall, to ensure satisactory building perormance inan earthquake. Recommendations related to open-

Figure 3.24 Rd d h w gh (u: Bh . 2002)

Long walls are NOTrecommended.

Well-distributed crosswalls are a must.

Use buresses tostabilize long walls.

Stone masonry walls Length (L) Story Height (H)In mud mortar 5 m 2.7 mIn cement mortar 7 m 3.5 m

Figure 3.25 Rd gdg h gh d hgh w

L

H

ing size and locations are summarized in Figure

3.26.

Te ollowing guidelines can be ollowed when plan-ning the openings in a stone masonry building:

Te number and size o openings should be mini-mized since excessive openings weaken the walls.

Ideally, openings in opposite walls should be osimilar size.

Openings should be located away rom the wallintersections, and placed as ar apart as possible.


53/92

41


1 S: b1+ b

2+ b

3< 0.5L

1

b6

+ b7 0.5L

2

2 S: b1+ b

2+ b

3< 0.42L

1

b6

+ b7 0.42L

2

b4

0.5h2

d b4

600

b5

0.25h1

d b5

600

b1

+ b2

0.33L

b4

0.5h2

d b4

600

b5

0.25 h1d

b

5 600

Figure 3.26 Rdd d z pg w (u: IAEE 2004)

W u

Stone masonry walls are traditionally constructed us-ing mud mortar. However, the use o cement or ce-ment/lime mortar is becoming more common in

modern construction. A detailed discussion on mortarproperties is included later in this chapter.

W hk

Te maximum thickness o a stone masonry wallshould be limited to 450 mm. Seismic orces areproportional to building mass (i.e., a wall o a largerthickness attracts higher seismic loads). Construc-tion o thicker walls is uneconomical and also un-

sae. However, excessively thin walls can be unstable,and these are difcult, i not impossible, to constructadequately. Te recommended minimum wall thick-ness is 380 mm. Examples o good stone masonryconstruction practice are shown in Figure 3.27.

Bdg w wh wh hugh-

Trough-stones (also known as bond stones) are longstones placed through the wall to tie wall wythes to-gether and prevent delamination, which is one o themain causes o the collapse o stone masonry wallsin earthquakes (see Chapter 2 or more details). Tepresence o through-stones in stone masonry walls

L

b1 b4

b5

b2

b4

h2

h1

L1

L2

h2

b4

b7

b4

b6

h1

b5

b1

b4

b2

b4

b3

Walls in Mud Mortar

Walls in Cement Mortar


54/92

42


Figure 3.27 Exp wh w hk d 450

( hugh-) (ph: S. Bzv)

is one o the most important earthquake-resistantprovisions. Trough-stones make the wall wythesperorm like hands with interlaced ngers, as shownin Figure 3.28a. A wall with through-stones is shownin Figure 3.28b and one with two external wythesand an interior rubble core is shown in Figure 3.28c.Te dierence can be seen only when a vertical orhorizontal wall section is exposed (the presence othrough-stones in the wall cannot be easily con-rmed by visual inspection).

Figure 3.28 Thugh- w: ) hugh-

k d g; b) w wh hugh-, d

) w whu hugh- (u: GOM 1998)

Trough-stones extending over the ull wall thicknessmust be used every 600 mm in height and at a 1.2m maximum spacing along the length (Figure 3.29).Constructing walls in lits not exceeding 600 mm canacilitate the installation o through-stones.

When long stones are not available, a pair o over-lapping stones can be used, each extending at leastthree-quarters o the wall thickness.

Contrary to the name, through-stones can also bemade o concrete, wood, or steel bars with hookedends embedded in concrete. Even though theseelements are not made rom stone, they serve thesame purpose as through-stones, that is, they act ascontinuous members that tie wall wythes together.Provided that good quality concrete and steel rein-orcement are used, cast-in-situ RC through-stones

(bonding elements) are an appropriate solution sincethey provide bond between adjacent stones. It is im-portant to provide reinorcement in RC bonding el-ements: or example, one 8 mm diameter steel bar isrequired or a bonding element.

Cu d w

It is important to detail and construct wall in-tersections careully. All intersections should be

b) c)

a)


55/92

43


Figure 3.29 Pp p hugh- w (dpd : GSDMA 2001)

strengthened with stitches toensure the integral, box actiono the building during earth-quake shaking. Tese stitchescould be constructed usinglong stones, RC bonding ele-ments, steel mesh, or timber,depending on the availabilityo building materials and con-struction costs, as shown inFigures 3.30 to 3.33. When-ever possible, these stitchesshould be placed no urtherapart than 600 mm up thewall height.

Figure 3.30 P g w (dpd : Bh . 2002)

Alternaves to Through-Stones

Wood plank

Hooked steel e

S-shaped steel e

Wall Secon

>600mm

< 450 mm

600mm

Wall Plan

< 1200 mm < 1200 mm

< 450

600mm

600mm


56/92

44


Figure 3.32 Sh d wd dw w d (dpd : Bh . 2002)

Figure 3.33 W h d d wh (dpd : Bh . 2002)

F d R Cu

b b

bb

b b

600 mm

600mm

60 x 38 mm Cross-Secon

of Timber

50 x 30 mm

Cross-Secon of

Timber Baens

600 mm 600 mm

600mm

50 x 30 mm

60 x 38 mm

b = W Thk

600mm

600 mm 600 mm

b

b 600 mm

600mm

4.75 mm Steel Cross Link

8 mm Steel Bar

b

b

Roo structures should be as light as possible. Also, theintegrity o oor and roo structures and their connec-tions to the supporting walls are o critical importancebecause these structures act as a lid on top o a box.

An example o a light roo is a timber or steel roostructure with metal roong. Adequate connectionsbetween the roo raters, oor joists, and the lintel orroo-level seismic band are critical or seismic saety,as shown in Figures 3.34 and 3.35.

Compared to masonry walls, timber and steel oorsand roos are exible in their own planes, so they

should be braced. Examples o diagonal bracingschemes are shown in Figure 3.36.

RC oor or roo slabs are heavy compared to timberand metal roos, and that may be a disadvantage. How-ever, these slabs are sti in their own planes, which is apositive eature. In most cases, wall-to-slab connectionsare adequate, but the top wall surace should remainrough to ensure a satisactory bond between the wallsand the RC slab built on top o the walls.


57/92

45


Figure 3.35 Tg h v v

It is important to ensure anadequate connection between theroo and the wall.

Figure 3.36 D d bg Floor Structure

Roof Bracing

Detail A

Raer

Collar e

Roof band

Cross-bracing inplane of roof

Use double 3 mm wire to anchor the

joist and make a notch to prevent

movement in the beam.

Figure 3.34 Tg j h w

Roof band and raf-

ters ed together

with wire


58/92

46


Fud

Recommendations related to oundation construc-tion are outlined below.

Fud dph

A 600 mm minimum depth is recommended or aoundation on hard sti soil, and 1.8 m or a ounda-tion built in a sot or clay soil area. As recommendedearlier in this chapter, the building site should have a

consistent soil type across the entire building area. Ithis is not possible, a oundation o variable width ordepth may be required, as illustrated in Figure 3.37.

It is desirable to avoid the use o mud mortar inthe construction o stone masonry oundations. I

mud mortar is used, it is advisable to provide an RCplinth band to avoid uneven building settlement andto tie building elements together at the plinth level.I a timber plinth band is used, it should be installed300 mm above ground (see Figure 3.38). Figure3.39 shows an RC plinth band under construction.

Fud wdh

A 750 mm wide continuous strip ooting is recom-mended or 450 mm thick stone masonry walls con-

structed on hard soil. When the wall thickness is lessthan 450 mm, the ooting width may be reduced,but should not be less than 600 mm. Note that a750 mm oundation width may not be sufcient insot soil areas. Local practices should be ollowed indeciding the type and width o the oundation.

Figure 3.38 S

ud wh ph

bd: ) RC bd, d b)

b bd

100mm

300mm

a) b)

Soil A: So Soil

Soil B: Hard Soil

Figure 3.37 D ud dph qud budg wh vb pp (u: GOM 1998)


59/92

47


Figure 3.39 Cu RC ph bd ug g ubb ( kw "-

") (ph: S. Bzv)

Cu M

Stone masonry must be con-structed using good qualitymaterials and ollowing soundconstruction practices. Gen-eral recommendations are out-lined below.

S

Good building stone should behard, tough, compact grained,uniorm in texture and color,and crack-ree. A simple test toprove that stone is hard is to

try to scratch it with a kniehard stone cannot be scratchedeasily.

Round-shaped stone boulders commonly oundin river valleys should not be used without urthershaping (dressing). Figure 3.40 illustrates the collec-tion o stones in a hilly area o Nepal.

Figure 3.40 S u h Np: )

, d b) dv h budg (ph: S Sh

Fud)

Sd

Sand used or mortar mix should be clean and ree oorganic matter. It should not contain more than 10%clay or silt (note that excess clay or silt can be removedrom the sand by washing). Te suitability o sand canbe tested, as shown in Figure 3.41.

Good building stone shouldbe hard, tough, compact

grained, uniorm in textureand color, and crack-ree.


60/92

48


The sand test is performed as follows:

Take a bole and ll it with the sand unl it is half full. Pour in clean water unl the bole

is three-quarters full. Shake it violently for about half a minute and leave to sele for about

one hour. Clean sand will sele immediately, while silt and clay will sele slowly on top ofthe sand. The thickness of the clay and silt layer should not exceed one-tenth of the sand

layer below.

Water

10% clay/silt

90% sand

Figure 3.41 Tg d

Dierent types o sand and their uses are illustrat-ed in Figure 3.42. I the sand is too coarse, smallpebbles must be sieved out. Tese pebbles could beadded to aggregate or concrete construction. Sandrom the sea or ocean should not be used due to the

presence o salt (chlorides), which causes corrosiono steel reinorcement.

C

Cement is a key ingredient o both concrete andmortar. It must be o good quality and resh. Ithe cement has large lumps, it indicates that it is staleand should not be used (see Figure 3.43).

M

Mud mortar has been used in stone masonry con-

struction or centuries in spite o its low strengthand poor durability. Te properties o mud mortar,including its strength, can be improved by stabi-lizing it with cement, lime, etc. Te use o cementor cement/lime mortar has been recommended byvarious codes and guidelines. A recent research studyby Ali et al. (2010) has shown that use o cementmortar does not necessarily lead to improved seismicresistance o stone masonry buildings unless earth-quake-resistant provisions are also incorporated.

Figure 3.42 Sd d u: ) d p u-

; b) d d u, d ) x-

v d (ph: S Sh Fud)

Te authors o this document recommend the use ostabilized mud mortar at the minimum. Te use ocement mortar or cement/lime mortar is also recom-mended, as its strength and durability are superiorcompared to mud mortar. Te use o mud mortaris also acceptable provided that stones are shaped(dressed), the wall thickness is not excessively large,and through-stones are provided as per the recom-mendations presented earlier in this chapter.

a) b)

c)


61/92

49


Properties o dierent types o mortar are briey dis-cussed below.

C

Cement mortar mix used or wall constructionshould preerably be 1:6 cement:sand or 1:2:9cement:lime:sand. Te use o leaner (lower strength)cement-based mortars should be avoided.

Mud

Mud mortar must be o good quality and ree o or-ganic matter, pebbles, and other large particles whichaect the mortar thickness. Te sand content o themud should be less than 30% in order to achievesufcient cohesiveness. Soil should be thoroughly

kneaded with water to achieve a dense mortar paste.Te addition o lime helps increase the strength omud mortar.

Sbzd ud

Te strength o mud mortar can be increased bymodiying (stabilizing) its soil properties. Dier-ent additives such as ash, lime, cement, bers, orcow dung can be used or this purpose. o achievegood results, it is important that the additives aremixed well with the soil.

Figure 3.43 C wh g up hud b ud u (ph: S

Sh Fud)

Ash, produced by burning coal, coke, or rice husks,can be used to stabilize mud mortar (usually 5 to10% by volume). Ash can be somewhat pozzola-nic and additional improvements are possible when

combined with lime.

Lime can also be added or stabilization, usually 3to 10% by volume (the higher, the better). In orderto make the soil easier to work and compact, limeshould be added at least 2 hours (preerably 8 to 16hours) beore short-term stabilization. It is appropri-ate to mix lime with soils characterized by a relativelyhigh proportion o clay.

Mud can also be stabilized by adding cement, whichimproves both the dry and wet compressive strength.Some soils require only a 3% cement by volume, but

usually 5 to 8% is recommended. A variety o -brous additives including straw, cha or husks, hay,hemp, millet, sisal, or elephant grass can be used.Alternatively, cow, horse, or camel dung can also beused or stabilization.

L

Lime mortar is a mix o lime putty and an aggregate(usually sand). Lime mortar has a lower compressivestrength than cement mortar, but its strength is usu-ally adequate or stone masonry construction. Limemortar is more workable than cement mortar, and

it is also less brittle. When lime mor-tar is subjected to tension, numerousmicrocracks develop and subsequentlyrecrystallize when exposed to air. Limemortar thus has an ability to sel-heal,which is not true o other mortar types.

A typical lime mortar mix ratio is1:3 lime putty:sand. Te sand mustbe washed, well graded, and sharp.Other materials could be used insteado sand, such as pozzolan, powdered

brick, heat-treated clay, silica ume,y ash, or volcanic materials.

Care should be taken to avoid shrink-age and cracking in lime mortar. Tiscan happen due to the use o poor-quality lime putty and sand, exces-sively ne sand, high water contentin the mortar mix, or excessive mor-tar thickness.


62/92


63/92

51


D d D

Tis section provides a list o dos and donts that must be ollowed when selecting and using constructionmaterials.

Mortar Dos:

Use clean sand or mortar and concrete con-struction.

Use resh and lump-ree cement or mortarand concrete.

Mix the dry ingredients (sand and cement) to-gether beore adding water.

Protect the mortar or concrete-mixing arearom wind, rain, and sunshine.

Mortar Donts

Dont use excessively thick mortar joints.

Dont use or re-use mortar that has alreadyhardened. As cement mortar sets relativelyquickly (in approximately 30 minutes), itshould never be mixed in huge quantities.

Dont use sea sand or sand containing a largeamount o silt or clay.

Dont use cement that has already set.

Masonry Dos

Use shaped/dressed stones.

Use through-stones to stitch wall wythes to-gether.

Masonry Donts

Documents

Stone Masonry English