Earthquake Resilience of Pol houses In Ahmedabad

Faculty of Architecture M. Arch in Conservation and Regeneration

Earthquake Resilience of Pol houses In Ahmedabad

Student Name : Saatvika Pancholi Student Code : PG190814 2020

Ahmedabad, India This work was undertaken by Saatvika Pancholi, Masters of Conservation and Regeneration, Faculty of Architecture, CEPT University with guidance and support from Dr. Arun Menon, IIT Madras, Chennai. Further, this work was undertaken within the Conservation Frameworks Studio at CEPT University.

Abstract The research is focused on the identification of earthquake-resilient features of pol houses that were responsible for their survival in the devasting Bhuj earthquake of 2001, which is centered around the broad question that ‘will the heritage city of Ahmedabad survive another earthquake?’ the question of survival depends on the critical understanding of the structure and its conservation, hence the study adopts both qualitative and quantitative methodologies for the analysis.

The thesis adopts the method of rapid visual survey through GNDT (Gruppo Nazionale per la Difesa dai Terremoti) methodology for mean damage assessment of three typologies of pol houses. This led to the formulation of vulnerability graphs and the identification of critical parameters. The vulnerability graphs for good and poor conditions diverged in all the cases. Hence the conservation state is one of the most critical parameters that would determine the damage grade. A comparative analysis of pol house structure with pombalino structures of Portugal helped to draw parallels between the typologies and seismic strengthening measures. The study also connects with on-ground issues, earthquake memory, and conservation approaches by conducting resident surveys and studying previous restoration projects in Ahmedabad.

The thesis concludes with the identification of critical parameters that cannot be compromised during the conservation to preserve the structural integrity and hence the authenticity of the pol houses. The study paves the way forward for the analysis of the structures at the settlement level, disaster risk reduction, and a detailed resident survey for developing the policies.

i

Foreword Indian society is deeply hierarchical in its thinking. In a historical travesty of sorts, we tend to ascribe moralistic intellectual superiority to some groups or professions.

Thus, engineers/IITians reign untrammeled in the middle-class psyche as the practitioners of some voodoo mathematical jugglery and the custodians of esoteric equations, incomprehensible to the 'artist type' architects like me.

As a counter maneuver, architects tend to gravitate towards the other extreme. They anoint themselves as the 'knights Templar' of the realm of 'beauty & aesthetics', protecting heritage from the marauding scalpels of cultural insensitivities and ruthless pragmatism of the crude engineers.

Unfortunately, the Indian education system, fails to nurture an endearing universal ethic in both of the camps.

An ethic which doesn't antagonize, art with science, culture with technology, history with engineering; but understands them as useful classifications to celebrate the continuum of ever-expanding human thought.

Thankfully, through this project, Earthquake resilience of pol houses in Ahmedabad, I was able to bring a bit of mathematical rigor to my traditional architectural tool kit. I can now empathize deeply with the beauty and relevance of structural engineering. I wish engineers would evolve the same empathy towards architecture.

This was possible only due to 'structurally robust' and 'aesthetically pleasing' mentorship of Dr. Arun Menon. He is the perfect embodiment of the ethic I mentioned above. A thorough professional and academic, he brings an unique chisel to shape the minds of his learners, with just enough 'scaffolding' to ensure that the learner carries the 'load' on her own and navigates her own unique path.

I hope this small project inspires other architects to explore the heritage structures of Ahmedabad in greater detail. ii

Table of Contents Undertaking

i

Certificate

iii

Acknowledgments

v

Abstract

vii

Foreword

ix

Table of contents

xi

List of figures

xiv

List of tables

xviii

List of Abbreviations

xix

Chapter 1: Introduction – ........................................................................................ 1 1.1 Premise of the study ..................................................................... 1 1.2 Rational for research ..................................................................... 2 1.3 Aim, Objectives, and Research questions ..................................... 4 1.4 Flow of study ................................................................................ 6 1.5 Scope and limitations .................................................................... 8

Chapter 2: Earthquakes and Ahmedabad – ........................................................ 9 2.1 Earthquake effects on buildings ..................................................... 9 2.1.1. Introduction ....................................................................... 9 2.1.2. Ground Shaking Effect on buildings ................................. 10 2.1.3. Failure Mechanisms Of earthquakes ............................... 11 2.1.4. Basic principles of seismic design ................................... 12 2.2 Ahmedabad as a world heritage city ............................................. 13 2.3 Historical earthquakes in Gujarat ................................................. 16 2.3.1. Long Interval severe intensity .......................................... 16 2.4 Bhuj earthquake of 2001 .......................................................... 19 2.4.1. Deadliest earthquake ....................................................... 19 2.4.2. Earthquake effects on Ahmedabad old city ...................... 20

Chapter 3: Methodology – .................................................................................... 22 3.1 Framework of Analysis ................................................................. 22 iii

3.2 Literature review ........................................................................... 25 3.2.1. Fundamental study .......................................................... 26 3.2.2. Traditional seismic resistant building practices ............... 27 3.2.3. Background study .......................................................... 29 3.2.4. Current scenario ............................................................. 30 3.2.5. Approaches for structural conservation ........................... 33 3.2.6. Urban seismic risk evaluation ......................................... 35 3.3 Surveys and interviews ............................................................... 36 3.3.1. Pol house residents ........................................................ 36 3.3.2. Expert interviews ............................................................ 37 3.4 Analysis method ........................................................................... 39 3.4.1. R.V.S. based on GNDT method ...................................... 39 3.4.2. Parameters for Analysis .................................................. 41

Chapter 4: Case studies – .................................................................................... 49 4.1 Identification and selection of case studies ..................................... 49 4.2 Case study 1 - Documented pol house typologies

......................... 50

4.2.1. Shared wall typology ...................................................... 50 4.2.2. Corner house typology ................................................... 53 4.2.3. Haveli typology .............................................................. 56 4.3 Case study 2 – Interventions to improve the seismic performance of historic structures .................................................................. 58 4.3.1. Earthquake resistant structures of Portuguese pombalino buildings ................................................................................... 58 4.4 Case study 3 - Conservation of pol house typology ......................... 68 4.4.1. Tankshal ni haveli ............................................................ 68 4.4.2. Deewanji ni Haveli ........................................................... 70 4.5 Case study 4 - Disaster risk preparedness ....................................... 73 4.5.1. Study by NIDM for disaster risk preparedness – case of shanti nath ni pol ..................................................................... 73

Chapter 5: Critical Analysis – .............................................................................. 76 5.1 Analysis of cases for vulnerability index (GNDT) ............................... 76 5.1.1. Case 1 - Shared wall typology 5.1.2. Case 2 - Corner house typology

..................................... 77 ................................... 87 iv

5.1.3. Case 3 - Haveli typology

.............................................. 96

5.2 Conclusions on vulnerability analysis ............................................. 101 5.2.1. Case 1 - Shared wall typology 5.2.2. Case 2 - Corner house typology 5.2.3. Case 3 - Haveli typology

..................................... 96 ................................... 96

.............................................. 96

5.3 Comparative Analysis of pol houses and pombalino houses .......... 107 5.4 Analysis of restoration projects ..................................................... 110 5.5 Survey Analysis of pol house residents .......................................... 112

Chapter 6: Conclusions – ................................................................................... 116 6.1 Critical structural health parameters .............................................. 116 6.2 Authenticity and strengthening

..................................................... 120

6.3 Vulnerability assessment at settlement level

................................ 122

6.4 Overall conclusion and way forward ............................................. 123

References – ......................................................................................................... 124 Appendix 1 – ......................................................................................................... 131 Appendix 2 – ......................................................................................................... 134

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List of figures Figure 1: Concrete house adjacent to old house in Zaweriwad, Ahmedabad, January 2020 (source - author) ...................................................................................... 1 Figure 2: Pol houses in Zaweriwad, Ahmedabad, January 2020 (source - author) ......... 1 Figure 3: Recurrence of Earthquakes and Local Seismic Culture Level. Credits: (Ferrigni, 2015). ............................................................................................................... 3 Figure 4: Flow of Study, Source – Author ............................................................... 6 Figure 5 Tectonic Plates division, Source - https://www.usgs.gov/.................................. 9 Figure 6 Understanding of earthquake forces on a basic masonry structure, Source – Author ..............................................................................................................12 Figure 7 Evolution of Historic city of Ahmedabad, Source - (UNESCO, 2016) ...............14 Figure 8 Pol houses in Ahmedabad, source - varied......................................................15 Figure 9 Seismic Zones of India, Source - (India, 2019) ................................................16 Figure 10 Seismic zones of Gujarat, Source- (India, 2019) ............................................17 Figure 11 Damage report of old city by A.M.C. Source- (Shah, Modan, & Chayya, 2006) ........................................................................................................................20 Figure 12 Pol house post earthquake, Source - (Langenbach R. , conservationtech.com, 2001) ...............................................................................................................21 Figure 13 Partial collapse of a Pol house - 2001, Source - (Langenbach R. , conservationtech.com, 2001) ...........................................................................21 Figure 14 Framework for analysis, Source – Author .....................................................24 Figure 15 Vernacular Urban Reinforcing measures, Source - (Correia, Carlos, & Rocha, Vernacular architecture?, 2015) .......................................................................28 Figure 16 Newspaper reports, Source – Times of India .................................................31 Figure 17 2018 times of india report that mentions about the workshop regarding the disaster management in pol, Source - Times of india .......................................32 Figure 18 Approach towards risk reduction for historic structures, Source- Author ........34 Figure 19 Map of Barcelona old city with vulnerability index, Source - (Lantada, Pujades, & Barbat, 2009)................................................................................................35 Figure 21 Determining Ax and Ay where Ax = (1+2+3+4+5) c/c x tx , Ay = (a+b+c+d+e) c/c x ty ......................................................................................................................44 Figure 20 Determining the average height H=(a+b+c)/3 ................................................44 Figure 22 Defining the length a and b in the building plan .............................................45 Figure 23 to determine the supported roof length, l= a+b+a1+a3+b1+b3.......................47 Figure 24 Location of shared wall house, Source - (Modan, 2006) ................................50 Figure 25 Typical ground floor plan at 700mm level, spaces, columns marked on the original source. Original Source - (Modan, 2006) .............................................51 Figure 26 Section A-A', Marked on original source, Original Source - (Modan, 2006) ....52 Figure 27 Part G.F.Plan at 1000m level showing the timber ties, Source - (Modan, 2006) ........................................................................................................................52 Figure 28 Reduction in masonry mass as the floor increase, Source - (Modan, 2006)...52 Figure 29 Location of corner house typology, Source- (Modan, 2006) ...........................53 vi

Figure 30 Ground floor plan at 700mm level, Source - (Modan, 2006) ...........................54 Figure 31 Section B-B', Source - (Modan, 2006)............................................................54 Figure 32 Decrease in masonry mass as the floor increase, Ground to second floor from top, Source - (Modan, 2006) ............................................................................55 Figure 33 Ground floor plan at 2400 mm level (top), Ground floor plan at 1000 mm level, Source- (Modan, 2006) ....................................................................................55 Figure 34 Location of haveli with in the settlement, Source - (Modan, 2006) .................56 Figure 35 Ground floor plan of Haveli, Source - (Modan, 2006) .....................................57 Figure 36 Section A-A’, Source- (Modan, 2006) ............................................................57 Figure 37 - 1755 Lisbon earthquake seismic waves analysis, Source - (Public seismic network, 2010) .................................................................................................58 Figure 38 Pombalino structural system,Source – Author ...............................................59 Figure 39 “gaiola” frame, Source - (Cardoso, Lopes , & Bento , 2004)...........................60 Figure 40 Plan of typical floor of the analysed building, Source - (Cardoso, Lopes , & Bento , 2004) ...................................................................................................61 Figure 41 Graphs shows the out of plane displacements of the front façade, Source (Cardoso, Lopes , & Bento , 2004) ...................................................................61 Figure 42 Collpase of the external walls without the collapse of entire structure, Source (Cardoso, Lopes , & Bento , 2004) ...................................................................62 Figure 43 Sketch of Pombalino houses facades, Source – Author.................................63 Figure 44 Pombalino structures, Source - (Cardoso, Lopes , & Bento , 2004) ...............64 Figure 45 (1 and 2)Damaging of timber section for installing pipes, (3) demolished wall replaced with metallic element,Source - (Cardoso, Lopes , & Bento , 2004) ....64 Figure 46 Roof hammering during seismic event - connection between roof and masonry walls ................................................................................................................65 Figure 47 Out of plane failure of the front facade ...........................................................65 Figure 48 Connection of the roof to the walls .................................................................65 Figure 49 Preservation of the original timber members,Source - (Paula & Cóias, 2015) 65 Figure 50 Connection of orthogonal walls through ductile steel anchorage ....................65 Figure 51 Masonry wall to wall connections, Source - (Paula & Cóias, 2015) ................65 Figure 52 Deformation and failure of two leaf wall, Source - Author...............................66 Figure 53 Rendering of masonry wall(left) and tying of masonry leaves with steel ties(right), Source - Author ...............................................................................66 Figure 54 Masonry walls in forced with UHPR, Source - (Paula & Cóias, 2015) ............66 Figure 55 Timber joints, Source - Author .......................................................................66 Figure 56 Strengthening of timber members, base drawing source - (Paula & Cóias, 2015) ...............................................................................................................66 Figure 57 (1) Reconstruction of timber framed walls (2) Repair of decayed ends, Source - (Paula & Cóias, 2015)....................................................................................66 Figure 58 Typical detail for double leaf masonry and timber ties, Base drawing source (Polimi, 2010) ..................................................................................................67 Figure 59 Failure of masonry wall due to deterioration of Timber ties, Base drawing source - (Polimi, 2010) .....................................................................................67

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Figure 60 Wall to floor connecting devices, Base drawing source - (Paula & Cóias, 2015) ........................................................................................................................67 Figure 61 (1) Wall to wall connection devices (2) Wall to floor connection device, Source - (Paula & Cóias, 2015)....................................................................................67 Figure 62 Front facade photograph(right),Source - (Pandya, 2020), Location of Tankshal ni haveli (left),Source - (Joshi, 2005)................................................................68 Figure 63 Condition before restoration (left), During restoration (middle and right), Source - (Joshi, 2005)......................................................................................68 Figure 64 Elevation (left), Plan (right), Section (bottom right), Source - (Joshi, 2005) ....69 Figure 65 Deewanji ni haveli – Ground floor plan(top), Section A-A’ (Below), Source (Shah S. , 2013)...............................................................................................70 Figure 66 Before and after restoration images, Source - (CHC , 2017) ..........................71 Figure 67 Addition of new column, Source - (Shah S. , 2013)........................................71 Figure 68 Damaged floor (left) floor during restoration (right), Source – (Shah S. , 2013) ........................................................................................................................72 Figure 69 Original flooring detail(left), Restored flooring detail(right), base drawing source - (Shah S. , 2013) .................................................................................72 Figure 70 Restoration of roof, Source - (Shah S. , 2013) ...............................................72 Figure 71 Vulnerability analysis survey by NIDM, Base map Source - (Bhandopadhyay, 2020) ...............................................................................................................75 Figure 72Timber lacing, masonry and door opening, Source - Author ...........................77 Figure 73 Timber beams and masonry cross walls connecting the orthogonal walls.

Timber frame structure of courtyard. Base drawing source - (Modan, 2006) ....78 Figure 74 The orthogonal wall with flat brick masonry and rubble core, Source – Author ........................................................................................................................79 Figure 75 Ground floor plan - wall area in X and Y directions, Base drawing source (Modan, 2006) .................................................................................................79 Figure 76 Floor wise area and specific weight per floor(t/m2),Base drawing source (Modan, 2006) .................................................................................................80 Figure 77 Calculation of specific weight of floor, Source – Author..................................80 Figure 78 Floor joist connection with the masonry wall, Source - Author .......................82 Figure 79 Composite floor connections, Source - Author ...............................................82 Figure 80 center to center I and a length in ground floor plan ........................................82 Figure 81 Front elevation sketch showing no projections, Source – Author ...................83 Figure 82 Wall maximum inter axis, length l between the major masonry cross walls and t is the thickness of the main orthogonal wall ...................................................83 Figure 83 Roof structure, Source – Author ....................................................................84 Figure 84 Part section representing absence of major over hangs, Source – Author, reference - (Modan, 2006) ...............................................................................84 Figure 85 Effective tying of masonry by timber lacing/bands, Source – Author ..............87 Figure 86 Timber beams and masonry cross walls connecting the orthogonal walls.

Timber frame structure of courtyard. Base drawing source - (Modan, 2006) ....88 Figure 87 Orthogonal wall section, Source – Author ......................................................89

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Figure 88 Ground floor plan - wall area in X and Y directions, Base drawing source (Modan, 2006) .................................................................................................90 Figure 89 Floor wise area and specific weight per floor(t/m2), Base drawing - (Modan, 2006) ...............................................................................................................90 Figure 90 Floor connection with masonry cross wall, Source – Author ..........................91 Figure 91 Wall maximum inter axis, length l between the major masonry cross walls and t is the thickness of the main orthogonal wall, Base drawing source - (Modan, 2006) ...............................................................................................................92 Figure 92 Roof connection front façade, Roof structure, Source – Author ....................93 Figure 93 Part front section showing projections, Source – Author, Reference - (Modan, 2006) ...............................................................................................................93 Figure 94 Timber beams and masonry cross walls connecting the orthogonal walls.

Timber frame structure of courtyard. Base drawing source - (Modan, 2006) ....96 Figure 95 Wall area is x and y directions, Base drawing source - (Modan, 2006) ..........97 Figure 96 Floor wise area and specific weight per floor(t/m2), Base drawing source (Modan, 2006) .................................................................................................98 Figure 97 a/l length ratio in ground floor plan, Base drawing source - (Modan, 2006) ....99 Figure 98 Wall maximum inter axis distance, Base drawing source - (Modan, 2006) ...100 Figure 99 Roof connections, Base drawing source - (Modan, 2006) ............................100 Figure 100 Part front section showing projections, Source – Author, Reference - (Modan, 2006) .............................................................................................................101 Figure 101 Mean damage grade and intensity relation - vulnerability curve graph, Source -Author ...........................................................................................................104 Figure 102 Mean damage grade and intensity – vulnerability graph for case 2, Source Author ............................................................................................................105 Figure 103 Mean damage grade v/s Intensity - Vulnerability graph for case 3, Source Author ............................................................................................................106 Figure 104 Timber frame, Source - (Cardoso, Lopes , & Bento , 2004) .......................108 Figure 105 Timber lacing, Source - (Modan, 2006) ......................................................108 Figure 106 Pombalino structure, Source - Author ........................................................109 Figure 107 Pol house structure, Source - Author .........................................................109 Figure 108 Pombalino flooring detail, Source - Author .................................................109 Figure 109 Pol house flooring detail, Source -Author ...................................................109 Figure 110 Pombalino building state, Source - (Carlos, et al., Lisbon: Downtown’s reconstruction after the 1755 earthquake, 2015) ............................................110 Figure 111 Pol house conservation state, Source - Sarjan Dalal 2020 ........................110 Figure 112 "peeled" walls in Italy due to change of floors to R.C. Source - (Ferrigni, Vernacular architecture: A paradigm of the local seismic culture, 2015) ........111 Figure 113 Disaster management cycle. Source -. Arun Menon .................................112 Figure 114 Representation of survey observations, Source – Author ..........................115 Figure 115 Identification of critical parameters and possible strengthening measures, Source - Author..............................................................................................118 Figure 116 Damages at settlement level, Base source - (Polimi, 2010) .......................119

ix

Figure 117 Functions of authenticity and strength and durability, Reference source (Attar, 1991) ................................................................................................121 Figure 118 Stability v/s Authenticity graph, Source - (Attar, 1991) ...............................121 Figure 119 Vulnerability assessment at settlement level (conceptual), Source – Author ....................................................................................................................122 Figure 120: Impact assessment table, Source - (Attar, 1991) ......... Error! Bookmark not defined.

List of Tables Table 1 Parameters for the identification of vulnerability of masonry buildings and related scores and weights, Source - (le, 2005 ) .....................................................40 Table 2 Definition of the vulnerability classes for parameter P1, Source - (le, 2005 ) .....42 Table 3 Definition of the vulnerability classes for parameter P2, Source - (le, 2005 ) .....42 Table 4 Definition of the vulnerability classes for parameter P3, Source - (Shakya, 2014) ....................................................................................................................44 Table 5 Definition of the vulnerability classes for parameter P4, Source - (Shakya, 2014) ....................................................................................................................45 Table 6 Definition of the vulnerability classes for parameter P5, Source - (Shakya, 2014) ....................................................................................................................45 Table 7 Definition of the vulnerability classes for parameter P6, Source - (le, 2005 ) .....46 Table 8 Definition of the vulnerability classes for parameter P7, retrieved from the manual. Original text Source - (le, 2005 ) ....................................................46 Table 9 Definition of the vulnerability classes for parameter P8, Source - (le, 2005) ......47 Table 10 Definition of the vulnerability classes for parameter P9, Source - (Shakya, 2014) ...........................................................................................................47 Table 11Definition of the vulnerability classes for parameter P10, retrieved from the manual. Original text Source - (le, 2005) .....................................................47 Table 12 Definition of the vulnerability classes for parameter P11, Source - (Shakya, 2014) ...........................................................................................................48 Table 13 Case study identification table ........................................................................49

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List of Abbreviations •

AMC – Ahmedabad Municipal Corporation

•

GNDT - Gruppo Nazionale per la Difesa dai Terremoti (National Group for Protection against Earthquakes)

•

NIDM – National Institute of Disaster Management

•

MSK - Medvedev–Sponheuer–Karnik scale

•

IIT – Indian Institute of Technology

•

ICOMOS – International Council on Monuments and Sites

•

ISCARSAH – International Scientific committee on the Analysis and restoration of Structures of Architectural heritage

•

RC – Reinforced Concrete

•

RVS – Rapid Visual Survey

•

UNESCO – United Nations Educational, Scientific, and Cultural Organization

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Earthquake resilience of Pol houses in Ahmedabad

1. Introduction 1.1 Premise of the study ‘Pol’ houses are the traditional urban residential settlements within the walled city of Ahmedabad, Gujarat. They are known for their intrinsic wooden carvings, climateresponsive characteristics, and their construction techniques, which were passed down the generations. For ages, Ahmedabad has been the center and home for merchants and businessmen. Interestingly enough, one finds different pol house clusters, categorized on the basis of occupation and religion.

Pol houses have been extensively studied for their spatial qualities, wooden carvings, climate responsiveness, its significance with religious beliefs, etc. But the devastating earthquake of Bhuj in 2001, opened a new chapter of study, which was ‘earthquake resistant nature of pol houses’, because the damage and casualty within the old city were considerably less than the new city (Langenbach, 2002). The structural typology and construction technique of the pol houses have been a subject of research interest since then.

Figure 2: Pol houses in Zaweriwad, Ahmedabad, January 2020 (source author)

Figure 1: Concrete house adjacent to old house in Zaweriwad, Ahmedabad, January 2020 (source - author)

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Earthquake resilience of Pol houses in Ahmedabad

1.2 Rationale for the research Disasters occurrence of disasters such as earthquake cannot be predicted certainly, which can cause major damage to the built environment. Though earthquakes with high magnitude do not occur frequently, once it does, it potentially takes the life of any city back by at least 5 years (Sengupta, 2019). Sometimes, damages can be so severe that they are beyond repair. At times, the earthquake disaster is followed by other disasters such as fires and floods, resulting in further loss and damage. Therefore, it is important that the effect of these natural disasters on existing infrastructure and their disaster-preparedness and vulnerabilities are investigated towards efforts to make infrastructure and populations disaster-resilient, in line with UNDP’s Sustainable Development Goals (SDG 2030).

Architectural Conservation as an interdisciplinary field of science, restores, repairs and focuses on the maintenance of heritage structures. One of the greatest threats to these traditional structures comes from natural disasters. Developmental pressures, and lack of widespread awareness on heritage conservation in our country, already pose challenges to conserve heritage structures. In the aftermath of an earthquake, this challenge is almost doubled, as in many cases, the easiest option then becomes to knock down such heritage structures, despite the values associated with it, citing reasons of structural safety of the historic construction, or due to the nature of damages sustained. Unscientific structural interventions, carried out due to a lack of appreciation for the traditional construction materials and techniques, also can result in undesirable behavior during future events.

In addition, focused research on vernacular architecture contributes to preserving the traditional knowledge system, intrinsic to a region.

A phenomenon of “experience gap”, which is explained further has an important role in defining the Local Seismic Construction techniques. (Ferrigni, Vernacular architecture: A paradigm of the local seismic culture, 2015).

As shown in Figure 3 (a-low occurrence) the regions of infrequent large earthquakes (e.g.

Gujarat: 1819 AD, 2001 AD – big earthquakes occur ~180 years apart, and very rarely do moderate earthquakes occur), the earthquake effects are not experienced by every generation, which affects the local seismic culture, drastically. Whereas (Figure 3) in the regions affected by frequent moderate or even large earthquakes (e.g. Italy, Japan, NZ, California, Greece, Turkey, etc.), the memory of the effects of the disaster is transferred 2

Earthquake resilience of Pol houses in Ahmedabad

to the next generation and translates to necessary action to mitigate the effects, which can be seen in the local construction techniques.

Figure 3: Recurrence of Earthquakes and Local Seismic Culture Level. Credits: (Ferrigni, 2015).

India is characterized by “low frequency of moderate earthquakes and a rather high frequency of large earthquakes”. But it is the former that is responsible for large casualties in Indian earthquakes (e.g. Bhuj, Latur, and several Himalayan quakes). (Jain, 2005 ) This aspect has far-reaching ramifications on adopting earthquake mitigation efforts in India, including vulnerability assessment and retrofit strategies. In a region such as Bhuj, we see an abundance of arched, vaulted, and domed constructions. These are structural typologies notorious for their poor performance under earthquake shaking. But we see the entire territory of Kutch spotted with these constructions since the 1800s (e.g. Rao Lakha Chattri, Bhuj), which have completely collapsed in subsequent earthquakes. (Jain, 2005 ). Hence, there is a tendency of losing the memory of the event resulting in the loss of knowledge (Ferrigni, 2015).

A similar situation can be seen in the case of pol houses. Many studies were conducted right after the earthquake in 2001, but with time the research reduced considerably, and a certain complacency sets in, which can have implications on disaster-preparedness and mitigation.

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Earthquake resilience of Pol houses in Ahmedabad

1.3 Aim, Objectives, and Research questions Aim – The current research aims to focus on ‘The preparedness of Ahmedabad pol houses for the incidence of earthquakes’. The research would require an understanding of critical aspects of earthquake-resilient structures and examining the vulnerability to the earthquake hazard, to get a holistic perspective on necessary interventions for conservation. It also aims to develop conservation methodologies which would include techniques of repair and reconstruction for pol houses, including the case studies of local seismic construction from other parts of the world.

Another purpose of this thesis is to contribute to the vast pool of knowledge of studies on pol house construction. The research aims to be useful for conservation works to be carried out in the future for the pol house. The study shall focus on the current scenario of pol houses, which in turn will lead to the development of measures that can be taken to conserve these built heritage structures and settlements for disaster preparedness.

Objectives and Expected Outcomes I.

To study the construction and structural system of pol houses from the previous studies, secondary data, and personal experience with the site. This study will help in identifying the structural configuration, components, and joinery details, which are important and significant for earthquake resistance. Such identification and appreciation are important for identifying the critical features that must be conserved and/or enhanced in any rehabilitation or renovation exercise.

II.

To enquire and study the post-earthquake measures that were taken after 2001, to conserve the pol houses. This study shall help in identifying the changes that have taken place since then, and to understand if these changes pose any danger in case of a future earthquake.

III.

To study the damage pattern in pol houses and formulate conservation measures for the same. Developing recommendations that are aimed at the improvement of seismic performance, and those aimed at the general functional health of the building. This is where vulnerabilities to other hazards (e.g. fire,

4

Earthquake resilience of Pol houses in Ahmedabad

floods, etc.) can be handled within necessary functional changes (e.g. adaptive reuse).

IV.

A comparative study on case studies of LSC - Local seismic construction around the world in order to understand the concept and practice of seismic retrofitting.

V.

The introduction of GNDT methodology for assessing the vulnerability of pol houses and identification of critical parameters. The implementation of a new methodology will give a different perspective for future research.

Research Questions Various studies all over the world conclude that the traditional, vernacular constructions, which were known to have good earthquake performance can only be conserved if regular maintenance and structural interventions are carried out to keep the basic structural system that provides the earthquake resilience in good health, which requires a good understanding of the traditional construction.

Otherwise, with subsequent ad hoc changes and interventions on these structures (or no maintenance at all), they may become vulnerable to earthquakes. And then, as seen in Nepal, these structures will be classified for their poor earthquake performance, and simply replaced with modern constructions, which if not designed, detailed, and constructed properly, would only lead to an increase in earthquake risk of the region.

(Menon, Pauperio, & Ramao, 2015) These observations from the above study have been identified as the primary basis for formulating the below-mentioned research questions“To what degree is Ahmedabad, a world heritage city, prepared for earthquakes in the future?”

“Will the pol houses survive another 2001-like earthquake or will the heritage city suffer a major loss in terms of historic vernacular structures?”

“How can a conservation thesis contribute towards analyzing the current ground reality after 20 years of the disaster and formulate significant measures for maintenance, repair, and reconstruction to keep the city’s rich heritage safe?”

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Earthquake resilience of Pol houses in Ahmedabad

1.4 Flow of study

Primary study Secondary study

Figure 4: Flow

of

Study, Source – Author

6

Earthquake resilience of Pol houses in Ahmedabad

Topic selection The topic holds importance as it is one of the crucial aspects of structural conservation.

The topic has been chosen primarily as the site is well known and explored. Also, the background research will lead to the identification of gaps in previous research done on the topic, which shall be addressed in the current research.

Approach of the study Due to the current pandemic situation of COVID-19, the research is primarily based on the available secondary data. The research involves critically analyzing the previous studies and observations. Online communication with the experts is thought of for collating the information. The study shall also involve analysis and interpretation of case studies from around the world with earthquake-resilient vernacular structures.

Literature review The literature review has been spread out throughout the research document for correlating the concepts and the previous research on similar topics. The summarized literature review has been divided into background study, fundamental study, conservation approaches, etc., which has been elaborated in chapter 3, section 3.2.

Case studies The case studies were identified as per the approach of analysis, identification of gaps in previous works, comparative analysis, and previous survey conducted. The study has four detailed case studies which have been elaborated in chapter 4.

Critical analysis The analysis is based on four case studies. The analysis includes the vulnerability assessment through rapid visual survey using GNDT methodology, comparative analysis of pol houses with the earthquake resistant structures of Portugal, approach analysis for the conservation projects of pol houses in Ahmedabad, and survey analysis. All the four individual cases and analysis are interrelated and justified in the overall conclusion and scope.

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Earthquake resilience of Pol houses in Ahmedabad

1.5 Scope and limitations The scope of the research applies to the field of conservation of heritage structures. This shall involve the formulation of techniques for the repair and reconstruction of the vernacular houses. The research would also serve as initial work towards developing possible guidelines for assessment and retrofitting pol houses. The study would introduce a new method for analysis of pol houses for an earthquake disaster as a pilot project that can be implemented at the settlement level in the future by government bodies like A.M.C. for effective conservation strategies.

The pandemic situation of COVID -19, affirms the need for the ‘risk preparedness’ topic to be researched upon. Given the situation, one of the major limitations of the current research is on-site research and collecting primary data and observations. The study shall be based mostly on the available secondary data. A limited study on the identification of pol house typologies can be conducted from the past thesis reports from CEPT university.

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Earthquake resilience of Pol houses in Ahmedabad

2. Earthquakes and Ahmedabad 2.1 Earthquake effects on buildings (Non engineered structures) 2.1.1 Introduction The Earth’s crust is divided into “plates”1 that are always slowly moving. An earthquake occurs when the two blocks of the Earth suddenly slip past or thrust into one another. In a normal scenario, the energy is used to move these plates continuously but when an unlikely striking between the blocks happens the energy is released in the form of seismic waves2 through the faults3 in all directions. These waves shake the earth as it moves through it and on reaching the earth’s surface the ground is shaken which is termed as an “earthquake disaster”. This shaking leads to the collapse and damage of structures.

Earthquakes are concentrated along these plate boundaries. (U.S. Geological Survey, 1879 )

Figure 5 Tectonic Plates division, Source - https://www.usgs.gov/

1

Plates – Technically known as tectonic plates - Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth's mantle.

2 Waves - disturbance that travels through a medium from one location to another location.

3

Faults - The surface where the earth blocks slip is called the fault or fault plane.

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Earthquake resilience of Pol houses in Ahmedabad

2.1.2 Ground shaking effect on buildings • • •

Resultant earthquake force Seismic waves Inertia force direction Building mass

Figure 6 Inertia force action during earthquake, Source – Author

How much will be the damage in the structure? Will there be loss of lives due to the collapse? Will the building completely collapse? Or there will be partial damages that can be repaired later? The answer to all these questions lies in the structure of the building and how that structure will perform during the earthquake. Though the damages majorly depend on the intensity4, duration, and frequency5 content of the ground motion, type of soil, and other geologic conditions, the building design and quality of construction play a major role in the degree of damages and loss of lives.

During an event of an earthquake when the earth vibrates, all the buildings on the ground surface will respond differently. (IAEE, 2004) The seismic loads are difficult to determine due to the random nature of earthquake motions, however by understanding the structural behavior, the building designs can be formulated and studied to reduce the damages.

Following are the ground shaking effects on buildings (IAEE, 2004):

i.

Inertia Force – Every built structure on the ground has its mass, when the ground shakes and the base of the building moves towards the right there is a tendency of the building to move towards left, this resistance is termed as inertia force.

During an earthquake, the ground shakes in all directions and the inertia force acts in all the directions.

4

Intensity - The intensity is a number (written as a Roman numeral) describing the severity of an earthquake in terms of its effects on the earth's surface and on humans and their structures. Several scales exist, but the ones most commonly used is the Modified Mercalli scale. (U.S. Geological Survey, 1879 ) 5 Frequency content – The physical signal (earthquake) which is decomposed into a number of discrete frequencies, or a spectrum of frequencies over a continuous range. The frequency content of ground motions seems to be the most important parameter to explain the structural damage experienced during strong earthquakes. The frequency content of ground motions can be characterized using various stochastic and/or deterministic indicators. (Pavel, 2012)

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Earthquake resilience of Pol houses in Ahmedabad

ii.

Seismic Load – Though the earthquake force acts in all the directions, for engineering calculations and seismic design it is considered as a resultant lateral force acting on the built structure and termed as a seismic load. The factors6 which affect the seismic load are – Earthquake zone factor, soil foundation factor, hazard factor, stiffness, and dampening of structure and weight of the superstructure.

2.1.3 Failure Mechanisms of Earthquakes To study the seismic resistance of traditional structures it is important to understand the basic failure7 mechanisms of earthquakes.

Figure 7 represents a basic masonry structure with openings and a flat roof on top. Wall A represents the longer wall whereas wall B represents the shorter wall connecting the two parallel long walls. When the resultant direction of force is along the x-axis, Fx, the longer wall acts as a shear8 wall, when the resultant is Fy, the shorter wall acts as a shear wall. During the former case, the shorter wall would develop cracks at the junction. In the latter condition the longer wall which has more mass will try to resist due to the inertia force. When the resultant force is Fx, the wall B will tend for out of plane failure, but the connections with wall A and the roof together prevents the complete failure, thereby acting as a box.

Now, the roof plays an important role in the overall behavior of the structure. If the roof is rigid and connected well to the walls, it acts as a horizontal diaphragm9, its inertia will be distributed equally on the walls A and B. If the roof is flexible its inertia will go on the support wall.

6

The equation used for determining the seismic load is – F=S.Fs.I.C.W, where F is the seismic force, S is the earthquake zone factor, I is the hazard factor depending on the usage, C is the factor depending on stiffness and dampening and w is the total weight of the super structure.

7 Failure - when the material in a structure is stressed to its strength limit, thus causing fracture or excessive deformations.

8 Shear - When a structural member experiences failure by shear, two parts of it are pushed in different directions.

9 Diaphragm - diaphragm is a structural element that transmits lateral loads to the vertical resisting elements of a structure (such as shear walls or frames).

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Earthquake resilience of Pol houses in Ahmedabad

Legend: •

•

Deformations when the resultant force is Fy Deformations when the resultant force is Fx Cracks

•

Vertical load direction

•

Figure 6 Understanding of earthquake forces on a basic masonry structure, Source – Author

2.1.4 Basic Principles for seismic resistant design From the above failure mechanics, there are some basic principles for seismic resistant design, which are as follows (IAEE, 2004):

1. The structure should not collapse immediately, hence the materials used should not be brittle. Brittle materials can be made ductile by adding ductile materials for example adding wood members in an adobe structure. The structure must have the ability to deform to a certain extent.

2. Walls, roofs, and other elements should be effectively tied together so that during the event of an earthquake, the whole structure acts together and prevents separation.

3. The built structure should be well connected to a good foundation and the earth, making it act together during an earthquake.

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Earthquake resilience of Pol houses in Ahmedabad

4. Symmetrical structures (in both the directions) perform better during an earthquake, as an asymmetric structure would experience torsion10 5. Simple rectangular shapes in plan behave better than the one with many projections.

6. The building should be constructed using good quality of materials.

7. When the built structures are adjacent to each other there should be a gap between the two blocks like an expansion11 joint to avoid the hammering12 action. If the gap is not there, there can be a filling of weak material.

8. An earthquake responsive structure should be simple in terms of least compromise on structural integrity. The decoration should not hinder the main crucial joinery responsible for earthquake resistance.

9. Horizontal reinforcement is required in the walls to transfer the out of plane forces to the shear walls, else the walls can suffer from collapse.

10. Extra support must be provided to the main beams or columns, which will be responsible for the complete collapse in case of an earthquake.

2.2 Ahmedabad as a world heritage city Ahmedabad – “Ahmed” – “Aabad”, a bustling busy city today was founded by the Sultanate ruler Ahmed Shah, in the year 1411. The city is located on the banks of river Sabarmati.

Ahmedabad's old city is a walled city with its unique urban settlement and architectural styles. The city got its title of UNESCO World Heritage City in the year 2017. It is the first world heritage city in India. The settlement and self-sufficient house form were one of the most important criteria for the world heritage city nomination. The following is the criteria (v) description from the outstanding universal value document of UNESCO – “Criterion (v): Ahmadabad city’s settlement planning in a hierarchy of living environment, with streets as also community spaces, is representative of the local wisdom and sense of strong community bondage. The house is a self-sufficient unit with its own provisions for water, sanitation, and climatic control (the courtyard as the focus). Its image and its conception with religious symbolism expressed through wood

10

Torsion – Twisting due to applied forces Expansion joint – or movement joint that allows the contraction and expansion of the building materials, also allows the structure to move.

12 Hammering action – due to non-availability of adequate space between the buildings, they tend to collide with each other during an earthquake, that action is termed as hammering action (or pounding).

11

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Earthquake resilience of Pol houses in Ahmedabad

carving and canonical bearings is an ingenious example of habitat. This, when adopted by the community as an acceptable agreeable form, generated an entire settlement pattern with community needs expressed in its public spaces at the settlement level and composed the self-sufficient gated street “pol”. Thus, Ahmadabad’s settlement patterns of neighboring close-packed pol provide an outstanding example of human habitation.”

These pol houses with their unique timber and masonry construction typology were sufficient to put a historic city on the world map as a world heritage city.

Figure 7 Evolution of Historic city of Ahmedabad, Source - (UNESCO, 2016)

The nomination dossier highlights the evolution of the Ahmedabad city from 1411 AD, Figure 8 suggests the settlement chronology within the walled city. The narrow lanes and settlement clusters, pols, which are formed through linear arrangement of houses, commonly termed as pol houses. The evolution study suggests that these pol houses are an integral part of the world heritage city.

The unique typology and the settlement pattern are the identifying feature for the old city of Ahmedabad, hence the research’s rationale for addressing the seismic resilience of pol houses is crucial for the world heritage city status.

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Earthquake resilience of Pol houses in Ahmedabad

With in the pol settlement, pol houses constructed during different times and styles. (2020)

Old vacant pol house with traditional todla door and timber lacing. (Author 2020)

Entrance to chaumukhji (Author 2020)

ni

pol.

Exquisite wooden carving on front façade, second floor constructed in R.C. (Author 2020)

Entrance of Shantinath ni pol with the chabutra – the bird feeder, (NIDM, 2011)

Pol lane – (2002)

Elaborate carved brackets are a unique feature for Ahmedabad pol houses.

(Author 2020)

Pol house in Doshivada ni pol (Anushka Mital,2020)

Figure 8 Pol houses in Ahmedabad, source - varied

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Earthquake resilience of Pol houses in Ahmedabad

2.3 Historical earthquakes in Gujarat 2.3.1 Long interval, severe intensity The city of Ahmedabad lies in the zone-III (concerning seismic zones in India), which has a moderate risk for the occurrence of an earthquake (www.gsdma.org, 2002)

Figure 9 Seismic Zones of India, Source - (India, 2019)

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Earthquake resilience of Pol houses in Ahmedabad

The Vulnerability Atlas of India has classified the state of Gujarat into four classes based on the 10.3 million buildings as per the census of 1991 and the BIS standard. (www.gsdma.org, 2002) The four classes based on the MSK scale are as follows •

Very High Risk: >MSK IX (19 percent)

•

High: MSK VIII (13 percent)

•

Moderate: MSK VII (66 percent)

•

Low Damage: <= MSK VI (1 percent)

Figure 10 Seismic zones of Gujarat, Source- (India, 2019)

The state has been classified into 4 zones based on the return period and intensity of the earthquake. (www.gsdma.org, 2002)These four categories are as follows – •

25-year return period – few pockets of Kutch district with low to moderate intensity possibility of an earthquake.

•

50-year return period – high-intensity pockets have been identified in the Kutch region, as well as in Rajkot and Jamnagar districts.

17

Earthquake resilience of Pol houses in Ahmedabad

•

100-year return period – a complete region of Kutch falls under the very severe intensity zone, and major cities like Ahmedabad, Baruch, Rajkot, and Bhavnagar fall into the severe zones.

•

200-year return period – North, central and south saurashtra region falls into severe intensity zones.

The above classification makes it clear that the occurrence of an earthquake in Ahmedabad would be 100 to 200 years, but the intensity of the earthquake will be high.

This demands for the seismic-resistant designs and technical retrofit in the historic city structures.

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Earthquake resilience of Pol houses in Ahmedabad

2.4 Bhuj Earthquake of 2001 2.4.1 Deadliest earthquake Gujarat experienced one of the deadliest earthquakes in January 2001, in which more than 18,600 human lives were lost, over 167000 injured and 1,205,198 houses were fully or partially damaged in 16 districts (EERI, 2001) The epicenter of the earthquake was in the Kutch region of Gujarat.

Randolph Langenbach in his article “A rich heritage lost, The Bhuj India earthquake” describes the situation of Bhuj city (epicenter13), which was also a walled city in historic times as – “The first view of the inner precincts of the walled city of Bhuj was shocking. In the area immediately inside the city gate, the buildings had almost totally disappeared into rubble piles that lay along either side of the road like great waves. Riding on these “waves” were the still whole pieces of the upper floors of broken newer concrete buildings” The expression demonstrates the scene right after the collapse and suggests the modern intervention of concrete structures on the rubble masonry. Some of the traditional houses in Kutch with timber balcony protruding were not completely collapsed, which has suggested that the possible use of timber and effective tying of ground floor structure due to the balcony saved the houses from complete collapse. (Lagenbach, A Rich heritage lost, The Bhuj, India, Earthquake, 2001)

Figure 12 Rubble ruins in a part of Walled city of Bhuj, Source - (Lagenbach, A Rich heritage lost, The Bhuj, India, Earthquake, 2001)

13

Epicenter – The point on the earth surface which is directly above the origin of earthquake.

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Earthquake resilience of Pol houses in Ahmedabad

2.4.2 Earthquake effects on Ahmedabad old city The walled city of Ahmedabad is situated on the banks of river Sabarmati. The landform of the old city is almost uniformly flat, unlike the newer city which has small hillocks, known as tekaras in Gujarati.

It was observed that the walled city showed extremely low damage and no complete collapse when compared to the newer R.C. structures. According to the survey conducted by the Ahmedabad Municipal Corporation in 2001 roughly, only 10% of the structures in the old city showed major cracks and signs of damage post-earthquake. (Modan, 2006) .Randolph Langenbach also mentions in his report that only one traditional structure was completely collapsed in the old city. The analysis was also pointed out that as the city is located 400kms away from the epicenter the seismic waves were longer, hence the possibility of complete collapse of taller structures was larger. Still, comparatively the old city with traditional houses suffered little damage and no casualties were reported due to falling of structures. It was also observed that one of the traditional pol houses which suffered the collapse due to the falling of the newer R.C. structure adjacent to it. (Shah K. , 2020)

Figure 11 Damage report of old city by A.M.C. Source- (Shah, Modan, & Chayya, 2006)

A contrast in the usage of materials is observed in Bhuj's old city, which was ruled by Hindu rulers and Ahmedabad's old city, which predominantly had Sultanate and Mughal

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Earthquake resilience of Pol houses in Ahmedabad

rulers, the latter has traditional pol houses with timber lacing and masonry construction, while in Bhuj stone was majorly used. A hypothesis can be developed here that the technique of pol house construction is similar to the houses in Turkey and other regions with Ottoman empire rule which is discussed in the coming chapter of the literature review.

Figure 13 Partial collapse of a Pol house 2001, Source - (Langenbach R. , conservationtech.com, 2001)

Figure 12 Pol house post earthquake, Source (Langenbach R. , conservationtech.com, 2001)

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Earthquake resilience of Pol houses in Ahmedabad

3. Methodology 3.1 Framework of Analysis The research topic for earthquake resilience of pol houses was fragmented into three major topics viz. earthquakes, Ahmedabad, and pol settlements. The related studies and establishment of research questions was an iterative process. The literature study has been also classified in relation to the topic fragmentation which has been detailed out in the next section.

The major secondary base source for the research were the previous studies done on similar lines. Research thesis was identified and thoroughly studied to identify the gaps, its need, and its relevance. Various news reports and workshop proceedings were noted to understand the scenario of pol houses and steps taken in terms of disaster risk management. To establish link between previous studies it was important to know the current scenario which is being formulated by conducting telephonic survey and expert interviews.

The Figure 16 – Framework of analysis, summarizes the research methodology, flow of work and positioning of research in the field of conservation. For the analysis to progress the identification of case studies and its rationale was an important step, based on the literature review and previous thesis four domains of case studies have been identified.

The first case study that is based on the previous research focuses on the construct of pol houses, which has been detailed further in the coming sections. Interpretations established before were studied and then the framework for current analysis was established with understanding of the gaps identified in previous work.

The analysis being done is qualitative as well as quantitative. The method of Rapid Visual Survey has been chosen due to the limited data available. The GNDT methodology has been identified to calculate the vulnerability index for pol house which would be used to calculate the possible damage in a pol house. The GNDT methodology is based on 11 parameters which has been explained and detailed out in this chapter later. Here the qualitative and quantitative observations and understandings are quantified and helps to estimate the possible damage. The research here aims to give a new direction to understand these traditional structures. If taken further the process can be used on a larger scale by Government bodies and for conservation of pol houses.

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Earthquake resilience of Pol houses in Ahmedabad

The second case study is ‘Interventions to improve the seismic performance of historic structures – earthquake resistant structures of Portuguese Pombalino buildings’, which is then structurally compared with the pol houses.

The third case study is the conservation of pol house typology in Ahmedabad which focuses on the approach and on ground issues, which gives the site level idea.

The three case studies are followed by the NIDM report and conducted survey analysis to understand the resident’s perspective, earthquake memory and on ground issues.

These case studies are chosen to establish a holistic view and a broader picture in terms of earthquake resilience of pol houses. It has been thought that the analysis of the data from the current survey and the workshops would help to formulate the policy level interventions and will give a picture of other hazards like fire and floods which are faced by the pol houses.

This framework of analysis links the research to its first research question of to “what degree the old city of Ahmedabad is prepared for a future earthquake?”

23

Primary study Secondary study

Figure 14 Framework for analysis, Source – Author

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Earthquake resilience of Pol houses in Ahmedabad

3.2 Literature Review Earthquakes are natural disasters that have been researched for many years now.

Humans have been able to identify the phenomena of tectonic plates, epicenters, and the causes of their movement. But, till today we cannot accurately predict the occurrence of earthquakes. The disaster is sudden and unexpected. Saving human lives is the priority after a disaster and most of the deaths occur due to poor performance of the built structures.

The Kyoto Declaration 2005 states that “cultural heritage is a priceless and non-renewable asset, and it is our duty to raise awareness and undertake all necessary measures for protection of cultural heritage from disasters.”

The literature review focuses on the understanding of the disaster, local seismic cultures around the world, previous research on pol houses, and conservation strategies with the lens of seismic resilience.

The research domain was divided into three keywords which formulated the area of study •

EARTHQUAKES

•

AHMEDABAD

•

POL HOUSES

A lot has been researched and studied on the above three topics individually, hence it was important to fragment the study and then combine and relate with each other. The aim of the study was articulated as “critically understanding the pol houses which are situated in Ahmedabad with the lens of earthquake resilience, that would contribute to the field of conservation.”

Hence, the literature study was divided into 6 major aspects – 1. Establishing the rationale (Fundamental study) 2. Traditional seismic resistant building practices 3. Seismic resilience in Indian context and Bhuj earthquake (Background study) 4. Current scenario 5. Approaches for structural conservation 6. Urban seismic risk evaluation

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Earthquake resilience of Pol houses in Ahmedabad

3.2.1 Fundamental study – Various research papers focusing on different earthquake-prone zones, for example, Nepal, Kashmir, Turkey, Italy, Egypt, Greece, were studied. The studies were based on traditional vernacular architecture and its performance during the earthquake.

Fundamental study is the initial study for the research that forms the research rationale.

The observations post the Earthquake of Nepal, suggested that the concrete structures performed better than the traditional constructions which have survived previous earthquakes. The research paper ‘Traditional construction in high seismic zones: A losing battle? The case of the 2015 Nepal earthquake’ by Ramao et al, 2015 concluded that Nepal suffered an immense loss of vernacular heritage due to improper restoration and lack of maintenance of structures. The study has been supported by the example of Cyasilin Mandap14 in Bhaktapur15 durbar square. The mandap was reconstructed in 1969, after the 1934 earthquake. The construction focused on the seismic strengthening of the structure using traditional materials. The good performance of the Mandap in 2015, concluded that proper repair and strengthening must be seriously considered in the reconstruction of collapsed or partially collapsed structures. Incorporation of new details that improve the vernacular designs, where warranted is important for earthquake survival and conservation. The need of critical review of why certain structural typologies survive earthquakes and some others do not emerged as a important aspect which needs to fed into conservation proposals in disaster prone areas.

The concept of local seismic culture was studied through various research papers. F. Ferrigni in his study of ‘vernacular architecture – A paradigm of the local seismic culture’ explains the importance of recognizing LSC features in vernacular architecture. It mentions that a sudden knowledge and expansion for local seismic construction is seen right after the earthquake and there is a tendency of repressing the memory of the event resulting in the loss of knowledge. After the analysis of case studies by EUCCH ( European University Of Cultural Heritage) field research, it was found that the places where the memory of earthquakes remains alive have ‘prevention LSC’ and places which have less frequent earthquakes have ‘retrofitting LSC’, i.e. adding new structures or mending the existing ones. Compatible retrofitting is important to negate the damages.

14

Mandap – a covered platform with an open pillared hall served to provide lodging and meeting place for people Bhaktapur - known as the city of the temples, is a city in the east corner of the Kathmandu Valley in Nepal about 8 miles from the capital city, Kathmandu.

15

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Earthquake resilience of Pol houses in Ahmedabad

3.2.1 Traditional seismic resistant building practices – The study on ‘Seismic-resistant building practices resulting from Local Seismic Culture’ by J. Ortega & G. Vasconcelos M.R. Correia, formulates the characteristics of vernacular seismic-resistant constructions as: •

The building should be symmetrical in both plan and elevation - reduces torsion.

•

Height to base ratio should be low - to minimize overturn.

•

Materials like timber which are ductile to resist tensile forces are preferred.

•

Stress concentrations are avoided

•

Failure of certain members is tolerated - e.g. masonry is collapsed but the frame is intact.

•

Good state of conservation, proper maintenance, post-earthquake repairs, and strengthening works.

The study also mentions the characteristic observations from the LSC in European Mediterranean16 countries as: •

Elevation configuration - low centre of gravity

•

Use of timber elements

•

Structural timber frames

•

The connection between structural elements

•

Ties

•

Traditional joining system

•

Stabilization of floors and roofs - improving the diaphragmatic behaviour by reducing their excessive deformability.

16

•

Reinforcement of the openings

•

Elements neutralizing the horizontal forces

•

Urban reinforcing measures

•

Position within the urban fabric

Mediterranean countries – countries which surround Mediterranean Sea.

27

Earthquake resilience of Pol houses in Ahmedabad

(left) Historical solution to out-of-plane mechanisms at an urban level (Borri et al., 2001); (right) Reinforcement arches in Dolce-Aqua, Italy (credits: Ferrigni et al.,1995).

Building complexes in: (left) Anavatos village in Chios Island, Greece (Efesiou, 2001); (right) Mandraki, in Nysiros Island, Greece (credits: Ferrigni et al., 1995).

Figure 15 Vernacular Urban Reinforcing measures, Source - (Correia, Carlos, & Rocha, Vernacular architecture?, 2015)

The central and eastern Asian regions is highly earthquake prone. Three approaches for LSC been discussed here (Ferrigni, The central and eastern Asian local seismic culture: Three approaches, 2015) : 1. Deformability approach 2. Rigidity approach 3. Passive approach Buildings built on rocks are the safest structures in terms of seismic resistance. Rock minimizes the side effects.

Deformability approach (resistance by friction) – The use of timber helps to deform the structure in shearing. In this approach the building height is not more than 3 floors and

28

Earthquake resilience of Pol houses in Ahmedabad

center of gravity is lowered down. The lower portion of the building which has more mass absorbs the energy while the upper lighter portion dissipates the energy.

Rigidity approach (resistance by redundancy) - heavy stone and masonry structures come under this approach. There is an increase in structural plan density by availability of shear resistance through wall cross section.

Passive approach – the structures are made light with timber and plant-based paper. The construction is such that the structure is made to collapse during an earthquake. It can be rebuilt quickly without causing any casualties.

3.2.2 Background study – The background study mainly focused on the performance of specific structures during earthquakes, examples from the Indian context, reports from the Bhuj earthquake, and understanding of seismic forces. In the Indian context, Randolph Langenbach has extensively researched the seismic-resistant vernacular structures of the Himalayan belt.

The studies mention the most destructive earthquake of 2005, in Kashmir valley, in which the traditional structures survived better than the R.C. buildings. The author mentions three typologies which are found in the Himalayan region •

Taq(bhatar) Construction - where horizontal timber members are embedded in the masonry. It does not have vertical reinforcement hence the masonry walls take the load and are in compression. The timber floor penetrating the walls helps the masonry not to spread out.

•

Cator and cribbage – A 1000-year-old technique with intensive timber usage compared to the timber laced masonry structure. It is a robust typology in an earthquake prone region.

•

Dhajji dewari - evolved because of economic and efficient use of materials, as a response to soft soils, complete timber frame integrated with masonry, it is a membrane structure, walls with many smaller panels have performed well during an earthquake, ground floor - taq system, upper floor dhajji dewari system.

Due to their performance in Kashmir earthquake, reconstruction work was executed using the Dhajji Dewari system. A similar case is also found in Portugal, after the Lisbon earthquake of 1755, the Gaiola technology was rediscovered. “Their resilience was proven by their survival, and so they inspired the design and mandatory use of the Gaiola -

technology that

became such a compelling part

of

Lisbon’s subsequent

rebirth.” (Langenbach R. , conservationtech.com, 2001) 29

Earthquake resilience of Pol houses in Ahmedabad

Jain (2005), IIT Gandhinagar, in his article ‘the Indian earthquake problem’ mentions the scenario post- earthquake in India. After the earthquake strikes people feel assured that now the construction will be seismic responsive, and efforts will be taken in this direction.

The houses are seismic resistive when people are not killed while living inside. He states that during Bhuj earthquake “Multi-storey buildings fall like a pack of cards and realized that these housing types are similar to the ones in which they are living or have plans to retire into.” “Structural Engineers Forum of India (www.sefindia.org) clearly show that a huge number of unsafe buildings continue to be built every day”. Hence, he emphasises that it is more important to construct building robust rather than finding solutions for public awareness, because if the buildings survive and less casualties occur, it will become an example way forward. Retrofitting for old vernacular structures is a promising solution in terms of seismic resistance, “to develop systems, policies and methodologies for seismic retrofitting of existing structures to prepare for sensible retrofitting programmes.”

3.2.3 Current scenario The current scenario study focuses on the existing condition of pol houses which were studied through recent works. Residents were approached telephonically to gather the information related to 2001 earthquake scenario and current damages and issues which they are facing. Municipal corporation was approached to understand the policies and role of A.M.C. for disaster management and conservation of residences.

With the development of heritage cell at the municipality level and the city receiving its title of world heritage city, the awareness within the community towards the heritage structures has increased. (Nayak).The newspaper reports related to the conservation within the historic city were referred. From the workshop proceedings of “disaster risk reduction of historic cities – a framework of building resilience”, organized by NIDM (national institute of disaster management) and A.M.C. in 2018 it is evident that the concern for earthquake resilience has been identified. The report mentions a lack of policy level conservation strategies and guidelines.

30

Earthquake resilience of Pol houses in Ahmedabad

Figure 16 Newspaper reports, Source – Times of India

31

Earthquake resilience of Pol houses in Ahmedabad

Figure 17 2018 times of india report that mentions about the workshop regarding the disaster management in pol, Source - Times of india

The disaster risk reduction of historic cities workshop was a research conducted by identifying the issues related to disaster risk by survey of Shantinath ni pol as a pilot project. The residences were studied, and their conditions were marked by interviewing the residents. It was observed that out of 50 properties, 22 traditional houses were completely altered or rebuilt with T girders and concrete and 12 houses were the only surviving cluster with traditional materials but in a bad state. (Bhandopadhyay, 2020)

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Earthquake resilience of Pol houses in Ahmedabad

3.2.4 Approaches for structural conservation – The approaches for structural conservation study focus on the rationale and purpose of the research. It establishes the bridge between the field of earthquake engineering and conservation, where this thesis is placed.

Understanding the concepts – Conservation and restoration The technical definition of conservation based on the Nara charter (ICOMOS, Nara Charter , 1994 ), can be “All actions or processes that are aimed at safeguarding the characterdefining elements of a cultural resource, so as to retain its heritage value and to extend its physical life.”

The concept of restoration can be understood as an action or process of accurately revealing, recovering, or representing the state of a cultural resource, or of an individual component, as it appeared at a particular period in its history, while protecting its heritage value. (Lourenço, Varum, Vasconcelos, & Rodrig, 2015) whereas Rehabilitation is the action or process of making possible a continuing or compatible use of a resource through repair, alterations, additions while protecting its heritage value.

Stabilisation, Repair and strengthening – Stabilization - Action to stop the process of deterioration which involves structural damage or material decay.

Repair - an action to recover the initial mechanical or strength properties of material, structural component, or structural system.

Strengthening - action providing additional strength to the structure.

Approach towards risk reduction – The research on structural conservation and vernacular construction (Lourenço, Varum, Vasconcelos, & Rodrig, 2015) identifies the approach as shown in figure 20-

33

Earthquake resilience of Pol houses in Ahmedabad

Higher risk Buildings Characterise the built heritage

Analysis of it

What interventions are required?

Lower risk Buildings

Implementation Figure 18 Approach towards risk reduction for historic structures, Source- Author

ISCARSAH Guidelines The very first lines of the ISCARSAH17 guidelines issued by ICOMOS18, mentions that – “A combination of both scientific and cultural knowledge and experience is indispensable for the study of all architectural heritage.” “Conserving architectural heritage usually requires a multidisciplinary approach involving a variety of professionals and organizations.”

Also, the guidelines clearly mention the importance of both qualitative and quantitative analysis which is required for structural conservation. The main purpose for the approach is to conserve the historical and cultural values associated with the structures. It is important to study the structural behaviour of the building parallel to the historical construction methods and archival research for conservation. The guidelines also mention that to understand the structural behaviour the study of shape and connections, construction materials and forces, and deformations are the main factors to be studied.

Low intrusive approach Modern conservation respects authenticity of the ancient materials and structure. Which implies that the interventions should be based on the structural integrity and core causes

17

ISARSAH - The International Scientific Committee on the Analysis and Restoration of Structures of Architectural Heritage (ISCARSAH) was founded by ICOMOS in 1996 as a forum and network for engineers involved in the restoration and care of building heritage.

18 ICOMOS - The International Council on Monuments and Sites (ICOMOS; French: Conseil international des monuments et des sites) is a professional association that works for the conservation and protection of cultural heritage places around the world.

34

Earthquake resilience of Pol houses in Ahmedabad

of damage or alterations. ( Ortega, Vasconcelos, & Correia, 2015 ) The approach for structural conservation should be a low intrusive approach, which includes (ICOMOS, 2003 ) –

•

The interventions for historic structures should be minimum work to ensure safety and durability, also it should not compromise on the heritage values. The materials should be compatible with the features of historic buildings.

•

Conservation of the original construction concept and of resistant components.

•

Strengthening should be achieved through low invasive methods

•

New products and techniques can be used for rehabilitation of constructions.

3.2.5 Urban seismic risk evaluation It is important to estimate the risk associated with the structures at the urban level. To evaluate the risk for the masonry structures, GNDT (refer section 3.4) is one of the methodologies used as a vulnerability index method.

The research studied here is of the city of Barcelona. It is the political and economic capital of Catalonia and second city of Spain. The city falls under low to moderate hazard zone, as per the Geological institute of Catalonia. The city was divided into 4 major soil zones based on the soil survey and the data from the previous earthquake of 1448. (Lantada, Pujades, & Barbat, 2009). The existing survey maps were used for determining the vulnerability index of the settlement.

Figure 19 Map of Barcelona old city with vulnerability index, Source - (Lantada, Pujades, & Barbat, 2009)

35

Earthquake resilience of Pol houses in Ahmedabad

3.3 Survey and interviews 3.3.1 Pol house residents The residents are divided into two categories, the first category is of old and middle-aged men and women, who have a fair understanding and memory of the 2001 earthquake.

The second category includes adults who are the current residents of the pols.

Category 1 – Old and middle-aged people Aim: To get the idea regarding the scenario during and post-earthquake of 2001, from a resident’s perspective, also to understand the immediate damages and repair techniques adopted by them (if any).

Rationale: the survey and professional reports have a limited eye to investigate small issues at the level of individual houses. It has already been 19 years since the earthquake, the knowledge will be further lost in time within a few years.

Methodology: Due to the pandemic situation only telephonic/online interviews are possible, hence from the previous contacts in the old city.

Category 2 – Current residents of pol Aim: To get the current idea of the situation of repairs and awareness regarding earthquake retrofitting as well as seismic resistance of pol houses.

Rationale: Pol houses being a living heritage, residents become the most important and significant point of concern. It is the community’s awareness that could bring changes in the conservation scenario.

Methodology: Due to the pandemic situation only telephonic/online interviews are possible, hence from the previous contacts in the old city.

3.3.2 Expert Interviews Expert interviews included the architects, professionals who have worked in old city as conservation architects (Khushi Shah, Debashish Nayak). Secondly, conservation architect working at Ahmedabad municipal corporation to understand the role of A.M.C. and what are the current amendments in policies if any (Shivani). To know the workshop proceedings and methodology of the disaster risk workshop organized by NIDM (National institute of disaster management) Chandrani Bandyopadhyay, the moderator of the workshop was approached.

36

Earthquake resilience of Pol houses in Ahmedabad

Questionnaire for Pol residentsBASIC INFORMATION 1)

Name -

2)

Age group - <20

21-30

70-80

>80

3)

Sex – female

4)

Name of the pol -

5)

Size of the house – 1 story stories

male

30 – 40

40 – 50

50 – 60

60- 70

other RESIDENTIAL INFORMATION

2 stories

3 stories

4 stories

>4

Floor area (if known) 6)

Owner

Tenant

7)

Duration of stay – 0-10years

10-15 years

15-20 years

>30years

2001 EARTHQUAKE RELATED INFORMATION 8)

9)

Were you present inside the building during the earthquake on 26th January 2001(8:45am)?

– Yes No If ‘Yes’ for (8), what was your experience during that time? (explain briefly)

10)

If ‘No’ for (8), if you were present outside your house within your pol during earthquake, what was your experience?

11)

Was there any visible damage in the building?

Yes

No

If yes, please describe -

12)

Any repairs done recently or before? what were they?

Yes

No

If yes, please describe -

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Earthquake resilience of Pol houses in Ahmedabad

OTHER RELATED ISSUES 13)

Is there a termite problem in house?

14)

Yes No Have you ever experienced fire related hazards in pols?

Yes

No

If yes, please describe -

15)

What are problems faced during heavy rains? Example – leaking, flooding

16)

Has there been an expansion of house done? Example – increasing number of floors Yes

No

If yes, when was it executed and what was the material used?

17)

What are the problems faced due to drainage, water supply and plumbing lines? (if any please describe)

18)

Have you/or is there/ installed Air conditioner in your house?

Yes

No

Were there any issues related to it?

19)

Have you changed the interiors of your house? (modernisation/for looks/need?)

Yes

No

If yes, please describe it and mention the reason -

20)

How do you find your stay in pols? *optional THANK YOU

38

Earthquake resilience of Pol houses in Ahmedabad

3.4 Analysis method 3.4.1 RVS based on GNDT Method For the analysis of pol houses, Rapid visual Screening (survey) has been adopted, using the GNDT method for determining the vulnerability and possible damage. Broadly total risk can be defined as the product of vulnerability, hazard, and exposure. Where vulnerability is the measure of a building’s strength and weakness. The hazard here is the earthquake. And exposure is the measure of how long and how many buildings have experienced loss.

Total risk19 = vulnerability20 X hazard21 X exposure Rapid visual screening – RVS is a preliminary method to estimate the seismic vulnerability of structures quickly when less precise data is available. The method is based on correlations between the buildings; predicted seismic performance, structural typology, nature of materials, designing, and detailing of joinery. The estimation is based on expert opinions and past performance of the structures. This method is extremely useful as a quantitative tool for government authorities to decide if and how much remedial work is required in a particular region.

GNDT II (Gruppo Nazionale per la Difesa dai Terremoti) method – GNDT II level approach was developed in Italy and is being time tested from the past 25 years. This approach is based on the experimentation and observation from previous earthquakes. The vulnerability index (V) is calculated to estimate the amount of structural damage that will be caused in a structure for a particular intensity of the earthquake.

The methodology can be termed as both qualitative and quantitative in terms of analysis.

The GNDT vulnerability assessment form for masonry buildings is composed of 11 parameters. Each parameter is differentiated into 4 classes (A, B, C, and D), having a score Cvi varying between 0 and 45. A weight (importance) pi is assigned to each parameter ranging from 0.5 to 1.5. Table 1 shows the 11 parameters used in the assessment and their corresponding scores (Cvi) and weight (pi). The vulnerability index 19

Risk - the probable loss, combining the hazards of location and the vulnerability of buildings and their contents. Risk can be removed transferred, shared, accepted, or accommodated (Fieldon, 1987) 20 Vulnerability - the degree of loss that will be sustained by an element from an earthquake of given intensity 21 Hazard - the probability that a disastrous event of given intensity will occur in a particular place (Fieldon, 1987)

39

Earthquake resilience of Pol houses in Ahmedabad

is calculated by summing the different scores and the relative weights attributed to these parameters, according to the following equation: 𝑽 = ∑𝒊 𝑪𝒗𝒊 𝒑𝒊

(𝒊)

The normalized vulnerability index, 𝑉̅, is given by:

𝑉̅ =

𝑽 𝟑𝟖𝟐. 𝟓

× 𝟏𝟎𝟎

(𝒊𝒊)

Table 1 Parameters for the identification of vulnerability of masonry buildings and related scores and weights, Source - (le, 2005 )

PARAMETER 1 2 3 4 5 6 7 8 9 10 11

A 0

Type and organization of resisting system Quality of the resisting system Conventional resistance Position of the building and foundations Floors Configuration in plan Configuration in elevation Walls maximum inter axis Roof Non-structural elements Current conditions

CLASS Cvi B C 5 20

D 45

WEIGHT pi 1.00

0 0 0

5 5 5

25 25 15

45 45 45

0.25 1.50 0.75

0 0 0 0 0 0 0

5 5 5 5 15 0 5

25 25 25 25 25 25 25

45 45 45 45 45 45 45

0.75 0.50 1.75 0.25 0.5 0.25 1.00

The vulnerability index calculated from the GNDT method can be related to the vulnerability index, 𝑉 used in the Macro seismic Method using the equation (iii). An analytical expression, proposed by Bernardini et al. (2007), correlates hazard with the mean damage grade (0 ≤ 𝜇𝐷 ≤ 5; corresponding to damage grades Dk; k = 0, 1, 2, 3, 4, 5) of the damage distribution in terms of the vulnerability value, as shown in the following equations: ̅ 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒𝑽 𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝑰 + 𝟔. 𝟐𝟓𝑽 − 𝟏𝟐. 𝟕 ) × 𝒇(𝑽, 𝑰) 𝑸

(𝒊𝒊𝒊) (𝒊𝒗)

𝑽

( )(𝑰−𝟕)

𝒇(𝑽, 𝑰) = 𝒆 𝟐 for 𝑰 ≤ 𝟕 𝒇(𝑽, 𝑰) = 𝟏 for 𝑰 > 𝟕

(𝒗)

Where 40

Earthquake resilience of Pol houses in Ahmedabad

•

I is the macro seismic intensity (considered equivalent to the MSK Intensity scale adopted by IS:1893)

•

V refers to the vulnerability index estimated in Eq (iii)

•

Q is the ductility factor

•

𝝁𝑫 is the mean damage calculated.

The classes (A, B, C, D) of the 11 parameters are defined by qualitative as well as quantitative methods. For example, the position of the building and foundation is a qualitative aspect for the specifications for individual classes that are studied from the Eurocode – guidelines of soil type concerning earthquake phenomenon.

While the parameter of conventional resistance is calculated by formulating shear strength and specific weight of the masonry. The 11 parameters are explained in the next section.

3.4.2 Parameters for analysis As mentioned in GNDT method for calculating the vulnerability index 11 parameters are used. These 11 parameters are broadly grouped in 4 parameter groups, each parameter is defined from the existing literature, expert opinions, and parametric analysis. The classes A, B, C, and D, are formulated from the qualitative observations as well as modeling (Shakya, 2014) (modeling is not in the scope of this research). These four groups are as follows: •

Structural system

•

Irregularities and interaction

•

Horizontal structure and roofing

•

Conservation status and other elements

Parameter 1 - Type and organization of resisting system – Parameter 1 focuses on the quality of distribution of structure, the efficiency of connections, connections between the horizontal diaphragm, and orthogonal walls. This parameter does not consider the constituents of masonry. For this parameter, the corner connections are given importance. The significant element is the presence and

41

Earthquake resilience of Pol houses in Ahmedabad

effectiveness of the connections between the orthogonal22 walls, such as to ensure the efficiency of the box like behavior23 of the structure.

Table 2 explains the criteria for the classification of the classes – Table 2 Definition of the vulnerability classes for parameter P1, Source - (le, 2005 )

Class A

B

C D

Description Structures built according to earthquake-resistant construction codes.

Strengthening or consolidation of the building masonry complying to rules earthquake resistance codes, thus ensuring the connection requirements and efficient connection between orthogonal walls.

The structure has good links and bonding between orthogonal walls. Existence of ring beams and/or steel ties well distributed in sufficient number with good anchorage, thus ensuring the conditions for binding and effective connection between the vertical elements.

The structure does not have the effective connections defined in class B, however it presents good connection quality between orthogonal walls, guaranteed by the appropriate bonding or interlocking units in all the walls.

The structure does not present effective connection of loadbearing walls. Total absence of steel tie rods and/or ring beams.

Parameter 2 - Quality of the resisting system – Assessment of quality of masonry work is based on three dimensions, (a) homogeneity of the material, shape, size, and nature of the units, (b) unit laying configuration and arrangement of units, (c) type of cross-linking elements.

Table 3 explains the criteria for the classification of the classes – Table 3 Definition of the vulnerability classes for parameter P2, Source - (le, 2005 )

Class A

B C D

Description Brick masonry of good quality. Well-cut stone masonry units (squared) with homogeneous and uniform in size throughout the length of the walls. Irregular stone masonry well mortared and locked/arranged, existence of cross–connection between the two sides of the wall.

Brick masonry of average quality and carved stone masonry units with homogeneity over the whole extension of the walls. Stone masonry with irregular crosslink elements between the two sides of the wall.

Brick masonry of low quality with irregularities in laying and bonding. Masonry stone units, not squared and heterogeneous dimensions. Irregular stone masonry without cross linking elements, and average mortar quality.

Brick masonry of poor quality with inlay of stone fragments. Stone masonry with very irregular units, nesting irregularly and without locking care (creating gaps). Irregular stone masonry without cross–connection and poor mortar quality.

22

Orthogonal – walls which are perpendicular to each other.

Box like behavior – when the building acts as a jointly assemblage of walls and roofs, with mainly in-plane response of the walls.

23

42

Earthquake resilience of Pol houses in Ahmedabad

Parameter 3 - Conventional resistance – Conventional resistance is the quantitative estimate of the shear strength available for a masonry structure, involving the quality of material, geometry of the structure and gravity loads borne by the masonry in the building.

For determining the conventional resistance of the masonry building (how much resistance does this building has?) the hypothesis of a box like behavior is made for the structure.

The value of conventional resistance is calculated by the following steps and values: N – Number of floors present in the structure At – Average total area covered (m2) Ax – Area of walls excluding the openings in x direction (m2) Ay – Area of walls excluding the openings in y direction (m2) 𝜏 - Shear resistance of the masonry (kN/m2) H – Average inter-story height (m) Pm – Average specific weight of the masonry (kN/m3) Ps - Average weight per unit area for each floor (kN/m3) A – Minimum value between Ax and Ay B – Maximum value between Ax and Ay a0 - A/At (minimum structural plan density) 𝛾 – B/A (measure of the uniformity of the structural walls) The value of resistance 𝛼 is determined by the following equations – 𝑞 = (𝐴 + 𝐵) × 𝐻𝑃𝑚⁄𝐴𝑡 + 𝑃𝑠

𝐶=

𝑎0 𝜏𝑘 𝑞𝑁 √1 + 𝑞𝑁 1.5𝑎0 𝜏𝑘 (1 + 𝛾) α = C/0.4

43

Earthquake resilience of Pol houses in Ahmedabad

Table 4 Definition of the vulnerability classes for parameter P3, Source - (Shakya, 2014)

Class A Class B Class C Class D

Buildings with 𝛼 ≤ 1 Buildings with 0.6 ≤ 𝛼 < 1 Buildings with 0.4 ≤ 𝛼 < 0.6 Buildings with 𝛼 < 0.4

Figure 21 Determining Ax and Ay where Ax = (1+2+3+4+5) c/c x tx , Ay = (a+b+c+d+e) c/c x ty

Figure 20 Determining the average height H=(a+b+c)/3

Parameter 4 - Position of the building and foundations – This parameter assesses the importance of factors such as the topography, type, and consistency of the ground foundation and evaluates the risk of landslide or slipping of foundation soils when subjected to seismic action. The following factors are assessed here which are based on the Eurocode24 8 – •

% Slope of the land

•

Presence of rock foundation

•

Presence of loose soil – thrusting or non-thrusting

•

Foundation height difference

24

Eurocode 8 – Eurocode 8: Design of structures for earthquake resistance (abbreviated EN 1998 or, informally, EC 8) describes how to design structures in seismic zone, using the limit state design philosophy, which is approved by the European Committee for Standardization.

44

Earthquake resilience of Pol houses in Ahmedabad

Table 5 Definition of the vulnerability classes for parameter P4, Source - (Shakya, 2014)

Foundation soil

Foundation land ‘𝒑’(%) Soil type A with or without the foundation or soil 𝑝 ≤ 10 type B and C with the foundation 10 < 𝑝 ≤ 30 30 < 𝑝 ≤ 50 𝑝 > 50 Soil type B and C without the foundation 𝑝 ≤ 10 10 < 𝑝 ≤ 20 20 < 𝑝 ≤ 50 𝑝 > 50 Soil type D and E with the foundation 𝑝 ≤ 50 𝑝 > 50 Soil type D and E without the foundation 𝑝 ≤ 30 𝑝 > 30

slope Class A B C D A B C D C D C D

Parameter 5 - Floors – The quality and type of structural system of the floors have a major influence on the overall structural behaviour. It is proposed in this parameter the definition of the classes according to the connection of floors to the main walls. The floors must be well connected to the walls, so that, they transmit vertical and horizontal loads. The aspects of staggered floors, rigid floors, and deformable floors are used to determine the class for parameter 5.

The manual of GNDT also considers the status of conservation for the floors and mentions to downgrade the class by one if the state is not good.

Table 6 Definition of the vulnerability classes for parameter P5, Source - (Shakya, 2014)

Class A B C D

Structural type and connection condition of flooring Rigid or semi–rigid and well connected Deformable and well connected Rigid or semi–rigid and improperly connected Deformable and poorly connected

Parameter 6 – Configuration in plan – The seismic behaviour of a building also depends, on the plan form of the building. In the case of rectangular buildings, the ratio of a/l is taken which is between the size of the smaller side (a) and the larger side (l). In the Figure 22 Defining the length a and b in the building plan

45

Earthquake resilience of Pol houses in Ahmedabad

case of plans that deviate from the rectangular shape, in addition to the elongated shape of the main body (b) the extent of this variance is considered. 𝑎 𝛽1 = 𝑙 𝛽2 =

𝑏 𝑙

The classes are determined as follows Table 7 Definition of the vulnerability classes for parameter P6, Source - (le, 2005 )

Class Class A Class B Class C Class D

Ratio between the dimensions β1 ≥ 80, β2 ≤ 10 60 ≤ β1 < 80 ,10 < β2 ≤ 20 40 ≤ β1 < 60, 20 < β2 ≤ 30 β1 < 40, β2 > 30

Parameter 7 – Configuration in elevation – This parameter evaluates the elevational aspect in terms of presence of towers or porticos, and % increase and decrease of mass. The ratio between the projecting part (T) and building height (H) is used to determine the class. The classes are determined as follows – Table 8 Definition of the vulnerability classes for parameter P7, retrieved from the manual. Original text Source - (le, 2005 )

Class Class A Class B Class C Class D

Configuration ratio in elevation Buildings with uniform mass and elements/ decreasing continuously and uniformly. 𝑇/𝐻 < 10 Buildings with small portico or staggered elevation. 10 ≤ 𝑇/𝐻 < 20 Buildings with towers and elevations that affect the floor area. 𝑇/𝐻 ≤ 20 Buildings with major/drastic change in elevation. 20 ≤ 𝑇/𝐻 < 40

Parameter 8 – Walls maximum inter axis – This parameter accesses the slenderness ratio of the wall by taking the ratio of the maximum spacing between two parallel walls with the thickness of the main wall on which the parallel walls meet. It evaluates the presence of long wall which is unsupported by cross walls. If the cross-wall support is not present the long wall is susceptible to out of plane failure.

46

Earthquake resilience of Pol houses in Ahmedabad

Table 9 Definition of the vulnerability classes for parameter P8, Source - (le, 2005)

Class Class A Class B Class C Class D

Inter axis/thickness ratio Buildings with an inter axis/thickness ratio of not more than 15 Buildings with an inter axis/thickness ratio greater than 15 and not greater than 18 Buildings with an inter axis/thickness ratio greater than 18 and not greater than 25 Buildings with an inters axis/thickness ratio greater than 25.

Parameter 9 – Roof – The roofs are classified primarily as thrusting, slightly thrusting and non-thrusting roofs based on presence of tie members in the structural system. The joinery details connecting the walls with the roof are analysed for determining the class. The support length of the roof is determined by calculating the total perimeter minus the length of the openings.

Figure 23 to determine the supported roof length, l= a+b+a1+a3+b1+b3 Table 10 Definition of the vulnerability classes for parameter P9, Source - (Shakya, 2014)

Class A B C D

Structural type and connection condition of roofing Rigid or semi–rigid and well connected Deformable and well connected Rigid or semi–rigid and improperly connected Deformable and poorly connected

Parameter 10 – Nonstructural elements – Non-structural elements include the presence of balconies or chimneys. Table 11 describes the classes – Table 11Definition of the vulnerability classes for parameter P10, retrieved from the manual. Original text Source - (le, 2005)

Class A B C D

Description No presence of non-structural elements Presence of non-structural elements/projections but they are well connected to the walls There are projections and non-structural elements but not well connected Badly connected non-structural elements

47

Earthquake resilience of Pol houses in Ahmedabad

Parameter 11 – Current Conditions – This parameter considers the conservation status of the building. Table 12 describes the classes for current conditions – Table 12 Definition of the vulnerability classes for parameter P11, Source - (Shakya, 2014)

Class A B C D

Description Masonry walls in good condition with no visible damage.

Walls with small cracks (less than 0.5mm), was not widespread. Signs of moisture problems which deteriorates the characteristics of the masonry and lead to degradation or decay of wood.

Walls crack opening of about 2 to 3mm. Structures with a state of poor conservation of masonry walls. Serious problems of deformability in the structural members Walls with deterioration and even if not widespread severe cracking. Walls with physical features and materials that show extremely poor or severe decrease of resistance. Cracking in locations, such, as near the corners (signs of disconnection between orthogonal walls). Damage introduced by thrusts transmitted by the roof, bulging of load–bearing walls, cracking due to settlement of foundations. Slip wooden framework with respect to the walls of the framework. Decomposition and degradation of wood along the walls. Signs of rotation and walls out of plumb

These 11 parameters determine the seismic vulnerability for the building based on the structural configuration and dimensions. Parameters 1 to 10 take into account the quality of construction and structural aspects, importantly parameter 11 describes about the damages and conservation status, there by implying that to what extent the conservation status makes the building vulnerable in case of a seismic event.

48

Earthquake resilience of Pol houses in Ahmedabad

4. Case Studies 4.1 Identification and selection of case studies The case studies have been identified with the rationale established after referring to the available secondary sources, the flow of the study, and parameters that are required for developing strategies. The case studies were finalized periodically as the research progressed. An identification table was prepared to sort the possible case studies based on rationale, typology, and resources. (Table 13)

1

2

3

4

Reason for the Case

Typology of the Case study

Options

Finalized Case study

The rationale for the Case chosen

Establish the understanding of the overall structural system, that would help to relate with the earthquake forces acting as well as to understand the pattern of damage and defects.

To understand post-earthquake repairs, which would include modern strengthening techniques in a structural typology that is similar to the pol houses.

Understand the restoration that has happened in pol houses that can be an example of adaptive reuse and would give an understanding of site-specific restoration To take a case study that involves the community’s perception and highlights the onground issues and condition within the pols

An example of either existing or nonexisting pol house which has almost all the ‘features’ that contribute towards an ‘ideal’ pol house

Previous studies/resear ch

Research thesis 2005 cases (Modan, 2006)

The work is based on similar lens of earthquake resilience.

The case will be a base for the quantitative analysis and hence will take forward the work done previously in 2005.

Timber laced structures in Mediterranean region, (structures with timber and brick masonry)

Published research papers on the typology

Case of pombalino structures, seismic strengtheni ng of traditional timber structures

A designed seismic resistant urban settlement in 18th century, which poses similar issue as pol houses in Ahmedabad.

An ongoing project or a completed project of a pol house in Ahmedabad

Architects who have done restoration of pol houses, AMC, (City heritage center in Ahmedabad)

Tankshal ni haveli and Deewanji ni haveli

Restoration project within the old city of Ahmedabad. The architects involved could be interviewed for understanding the approach of the project.

Previous studies and surveys

Previous thesis, NIDM workshop report

NIDM and AMC disaster risk preparedn ess report of 2011

The work is based on similar issues of earthquake and other disasters. Involves a pilot project study of shantinath pol

Table 13 Case study identification table

49

Earthquake resilience of Pol houses in Ahmedabad

4.2 Case Study 1 – Documented Pol house typologies The cases are studied to understand the basic typology of a ‘typical’ pol house situated in a cluster within a pol settlement. The case study is based on the previous research done in 2005 at CEPT University, under the title ‘study of systems of construction in the traditional Ahmedabad houses – query in seismic resistance’. The analysis in the coming chapters is based on these existing case studies and documentation.

4.2.1 Shared wall house typology – Kameshwar ni pol

Figure 24 Location of shared wall house, Source - (Modan, 2006)

The ‘shared wall house’ typology is the characteristic feature of pol settlement. Here the house shares longer parallel masonry walls with the adjacent houses. The structural aspect and behavior thus depend hugely on the connections with the parallel walls.

50

Earthquake resilience of Pol houses in Ahmedabad

Figure 25 Typical ground floor plan at 700mm level, spaces, columns marked on the original source. Original Source - (Modan, 2006)

Plan - The house is a composite structure with brick masonry and timber structural members. Pol house is rectangular with the length being almost 2.5 times the width. The chowk which is open to the sky courtyard is usually (and in this case) located on one side of the structure, dividing the building into two halves. When the above floor plans are compared with the ground floor plan certain observations are evident; the mass of the structure reduces as the floor increases, the main columns are aligned with each other which ensures effective load transfer till the foundation. The main structural columns and thick masonry wall act together and hence the structure can be termed as composite. The main beams are unidirectional and are parallel to the cross walls.

The linear typology of the house is functionally divided into semiprivate and private spaces.

Section – The number of wooden members increases as the floor increases, and hence the mass reduces. As seen in Figure 28 the rear part of the house is larger in mass than the front portion. The roof is made up of wooden members connecting the two parallel walls, with clay tiles as a roofing material. The horizontal tie members in-ground floor elevation acts like reinforcement to the brick masonry.

The timber framing can be termed as full framing as all the timber members are interconnected with each other forming a skeleton. The ground floor has the masonry

51

Earthquake resilience of Pol houses in Ahmedabad

cross walls connecting the two parallel walls, which is not seen on the floors above. On the first and second floors, the walls become timber partition walls. The upper floors project outwards which is supported by the wooden circular columns located in the otla.

Materials – Traditionally the main materials used in construction are- flat bricks with mud and lime mortar for masonry walls, timber for beams, columns and frames, stone for the column base and flooring, and tiles as the roof covering.

Figure 26 Section A-A', Marked on original source, Original Source - (Modan, 2006) The anchored connection using wooden peg between the masonry wall and timber column

Figure 28 Reduction in masonry mass as the floor increase, Source - (Modan, 2006)

Figure 27 Part G.F.Plan at 1000m level showing the timber ties, Source - (Modan, 2006)

52

Earthquake resilience of Pol houses in Ahmedabad

4.2.2 Corner house typology – Kameshwar ni pol

Figure 29 Location of corner house typology, Source- (Modan, 2006)

The ‘corner house’ is the house which is located towards the end of the linear pol. Usually the size of the corner house is larger than the adjacent shared wall house typology. Here one of the parallel walls is not shared.

Plan - The house is a composite structure with brick masonry and timber structural members. Pol house is rectangular in plan with the length being almost 2 times the width.

The chowk here is not connected to the main masonry walls, but off centered in plan, dividing the building into two halves.

When the above floor plans are compared with the ground floor plan certain observations are evident; the mass of the structure reduces as the floor increases, the main columns are aligned with each other which ensures effective load transfer till the foundation, but unlike the shared walled typology wooden columns are not much present in the edge wall.

Here the unsupported wall is thicker than the parallel masonry wall. The main structural

53

Earthquake resilience of Pol houses in Ahmedabad

columns and thick masonry wall act together and hence the structure can be termed as composite.

Here also the main beams are unidirectional and parallel to the cross walls. In this case the crossed walls are laced with timber bands running parallel to the wall length that might act as horizontal reinforcements. The smaller wooden members then are perpendicular to the main members providing further reinforcement to the thickness of the masonry. Such timber bands are found at three levels that roughly divides the masonry wall into 4 parts.

Figure 30 Ground floor plan at 700mm level, Source - (Modan, 2006)

Figure 31 Section B-B', Source - (Modan, 2006)

54

Earthquake resilience of Pol houses in Ahmedabad

Section – In this case also the number of wooden members increases as the floor increases, and hence the mass reduces. As seen in Figure 33, the rear part of the house in larger in mass than the front portion. The roof is made up of wooden members connecting the two parallel walls, with clay tiles as a roofing material. Here the tie wooden member is present connecting the roof ends unlike the first case.

The timber members are evident as columns, beams and timber lacing which is present in masonry walls. The ground floor has masonry cross walls connecting the two parallel walls, which is not seen on the second floor. On the third floor, the walls become timber partition walls. The upper floors project outwards which is supported by the wooden circular columns located in the otla. The second-floor projection is supported by the wooden bracket detail connecting the column on the first floor.

Figure 32 Decrease in masonry mass as the floor increase, Ground to second floor from top, Source (Modan, 2006)

Figure 33 Ground floor plan at 2400 mm level (top), Ground floor plan at 1000 mm level, Source- (Modan, 2006)

55

Earthquake resilience of Pol houses in Ahmedabad

4.2.3 Haveli typology – Dwarkadheesh Mandir

Figure 34 Location of haveli with in the settlement, Source - (Modan, 2006)

The Dwarkadheesh mandir also known as haveli mandir are larger in plan than typical pol houses, but the typology of construction is same. The case is a masonry and timber composite structure located within the settlement.

Plan – The haveli can be termed here as a larger version of pol houses. As seen in the plan the courtyard is centrally located that divides the structure into parts, similar to the first two cases the rear portion of the structure is higher than the front portion. The main orthogonal masonry walls are supported by cross masonry walls, which are load bearing walls constructed from flat bricks and mud-lime mortar. The structure is not a perfect rectangule in plan, the front is slanted responding to the site conditions, the presence of room in west also breaks the rectangular nature of plan.

Section – The first floor of the structure protrudes outwards and is supported by the front wooden columns on ground floor and brackets. The rear portion is much higher than the front section, when compared to the first two cases. Timber reinforcement members (timber lacing) has been used in masonry walls. The masonry wall thickness is constant in all the floors, but the number of openings increase as the floor increases there by some

56

Earthquake resilience of Pol houses in Ahmedabad

mass reduction is seen in upper floors. As seen in the section, the roof is supported by the three masonry walls and knee braced trusses.

Figure 35 Ground floor plan of Haveli, Source - (Modan, 2006)

Figure 36 Section A-A’, Source- (Modan, 2006)

57

Earthquake resilience of Pol houses in Ahmedabad

4.3 Case Study 2 – Interventions in Heritage Buildings for Seismic Performance Improvement The case study aims to understand the seismic retrofitting techniques in a masonry timber laced vernacular construction derived from the local seismic culture in European Mediterranean region.

The European Mediterranean region is located at the junction of Eurasian and African plate. It is the region with prominent local seismic culture due to the occurrence of frequent earthquakes. The traditional systems of construction have inherent earthquake resilient features which have evolved with time and experience (refer 3.2.4). Major reasons identified for the vulnerability of these structures are – •

Substantial modifications in structures like adding of floors, changing the original structural concept specially on ground floor, major increase in the opening sizes and addition of reinforced concrete. (Paula & Cóias, 2015)

•

Aging and deterioration of materials.

•

Low quality of reconstruction

For seismic retrofitting low intrusive approach (refer 3.2.4) is adapted in the following case of Pombalino, which protects the authenticity of the historic structure.

The comparative analysis relating the Pombalino buildings (tentative world heritage list) and the case of pol houses has been done in the Chapter 5, section 5.2.

4.3.1 Earthquake resistant structures of Portuguese Pombalino buildings –

Lisbon, Portugal

Figure 37 - 1755 Lisbon earthquake seismic waves analysis, Source - (Public seismic network, 2010)

58

Earthquake resilience of Pol houses in Ahmedabad

After the devastating Lisbon earthquake of 1755, a seismic resilient style of architecture emerged in Portugal, which was known as Pombaline Portuguese style. The houses were designed with the concept of timber frames and masonry structure, which included the anti-seismic provisions though there is no major written evidence of the same. The major feature was the three-dimensional timber frame structure known as “gaiola”, resisting the horizontal shear force (refer 2.1.3) during an event of earthquake. The earthquake was followed by a major fire, hence the buildings also include anti – fire provisions, like presence of thick masonry walls between two adjacent structures. No major record of the construction system is available for the structures, but later scientific analysis has identified the seismic resilient features of this typology.

Structural system –

Wooden roof structure with clay tiles as roof cover

Adjacent house wall

Timber floor – deformable

Wooden staircase

Masonry wall (front side)

Gaiola timber frame

Vaults of block ceramic and stone

Wooden piles – foundation

Figure 38 Pombalino structural system,Source – Author

59

Earthquake resilience of Pol houses in Ahmedabad

•

Foundation – the foundations include wooden piles connected with a timber grid system.

•

Masonry exterior walls - the masonry exterior walls are constructed using bricks/stones with lime mortar.

•

Floors – the floor diaphragm is constructed using timber joists with timber floor slabs. The timber floors make the floors deformable.

•

Timber frame – the “gaiola” structure is on the first and second floor, which has timber frames and masonry in fill. It is this timber frame that provides ductility to the structure. The non-load bearing partition walls divide the upper floor spaces functionally.

•

Openings – the openings (windows) are aligned with each other on respective floors.

•

Roof – Roof is constructed using timber trusses and ceramic tiles.

Structure of the “gaiola” system – Pombalino structures are classified under masonry structure. The presence of timber framing system prevents the out of plane failure during an event of earthquake. The system resembles a bird cage with horizontal and vertical members braced with diagonalmembers known as St. Andrews crosses. The members are either notched or nailed with each other. (refer figure 41)

Andrews crosses

Brick and lime masonry

Horizontal timber lacing

Figure 39 “gaiola” frame, Source - (Cardoso, Lopes , & Bento , 2004)

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Earthquake resilience of Pol houses in Ahmedabad

Comparative analysis of dynamic behavior –

Masonry wall Gaiola timber frame wall

Figure 40 Plan of typical floor of the analysed building, Source - (Cardoso, Lopes , & Bento , 2004)

The study conducted at Instituto Superior Técnico, Portugal, justified the design of gaiola system using the structural modeling of the Pombalino settlement with and without the presence of gaiola system. The study concluded that the presence of timber system increases the global stiffness25 of the structure, as the major observations were – •

The presence of ‘gaiola’ prevented local vibration modes of the masonry walls as the out-of-plane displacements of each masonry wall (facades and masonry walls between adjoining buildings) no longer occurred independently from the rest of the structure.

•

The out-of-plane displacements are equal for parallel masonry walls connected by the same ‘gaiola’ wall.

Figure 41 Graphs shows the out of plane displacements of the front façade, Source - (Cardoso, Lopes , & Bento , 2004)

25

Global stiffness – behaviour of the complete structural system during a seismic action

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Earthquake resilience of Pol houses in Ahmedabad

The Figure 43 represents the out of plane displacement of front facade during a seismic activity of a Pombalino building (Portuguese code of actions) with and without gaiola. The presence of gaiola reduces the out of plane displacement by 70%.

Expected collapse mechanism – The major reasons identified for the collapse of the masonry buildings in Europe are (Croci, 1988) •

Out of plane bending of facades (refer 2.1.3)

•

Shear at the plane of the walls of ground floor (refer 2.1.3)

In the pombalino structures the timber framing is only present on the first and second floors. The transition of the structural system from a complete masonry structure on ground floor to timber frame is also a contributing factor in the collapse as the stiffness 26 of the structure changes on the upper floors. Another weakness of the structure is the presence of bad quality of masonry walls, due to the different times of construction.

The collapse mechanism analysis results correlated with the damages that occurred in the pombalino structure during the 1998 Aezorus earthquake. It has been analyzed that the pombalino structural system can have out plane failure for the facade but would prevent the complete collapse of the building (refer figure 44).

Collapsed masonry walls postearthquake

Figure 42 Collpase of the external walls without the collapse of entire structure, Source - (Cardoso, Lopes , & Bento , 2004)

26

Stiffness - extent to which an object resists deformation in response to an applied force

62

Earthquake resilience of Pol houses in Ahmedabad

Constant height

Figure 43 Sketch of Pombalino houses facades, Source – Author

Conservation state – The major structural changes observed in the pombalino structures are •

Most of the pombalino houses are completely converted into banks or commercial usage in the 20th century, as the city of Lisbon is the major economic center in Portugal. The structures are not maintained, and damages such as broken roof causes water infiltration leading to masonry and timber degradation.

•

The ground water level change is another major reason observed for the cracks developed on the ground floor near openings, as the city has presence of soft soil.

•

Major changes on the ground floor without following the structural continuity is one of the major risk factors, as it increases the possibility of shear base collapse.

•

Another important structural change is the non-thoughtful demolition of the existing floors for new facilities like elevators. The demolition of timber partition walls also breaks the structural integrity of the structure making it more vulnerable.

•

Increasing the number of floors for functional demand is also critical, as it increases the mass above, hence the risk of out of plane failure also increases. (figure 46)

•

The bracing capacity is reduced when the pipelines are fixed by removing the timber members from the gaiola system. (figure 47)

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Earthquake resilience of Pol houses in Ahmedabad

Increased number of floors for due to change in requirement and usage

Major structural changes on ground Interrupted continuity of masonry structure due to the floor changes on ground floor.

Figure 44 Pombalino structures, Source - (Cardoso, Lopes , & Bento , 2004)

Figure 45 (1 and 2)Damaging of timber section for installing pipes, (3) demolished wall replaced with metallic element,Source - (Cardoso, Lopes , & Bento , 2004)

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Earthquake resilience of Pol houses in Ahmedabad

Conservation and Structural strengthening – The following table represents the conservation and structural strengthening of a Pomablino building. The strategy for intervention was based on the preservation and rehabilitation of all the existing structural elements to preserve its authenticity and structural integrity, along with structural reinforcement. (Paula & Cóias, 2015) Table 14 Conservation and structural restoration measures in Pombalino structures, Source - Author

Critical connection/ parameter

Structural deficiency

Connection between roof and Low resistance to out-ofmasonry walls plane seismic effects (overturning of facades) and fall of the roof

Strengthening provision

Conservation measures

Introduction of a concrete, timber or steel beam at the top of the building, Substitution or repair of broken tiles and measures to waterproofing the connecting roof to walls and confining masonry. The beam is executed roof. along the whole perimeter of the building. Beams are executed at skirting board level of all floors above ground floor.

Damaged timber elements are removed and substituted by new timber elements of the same geometry.

Roof covering New timber joists Concrete beam

Timber truss

Old timber joists

Steel connectors

Masonry wall Figure 46 Roof hammering during seismic event - connection between roof and masonry walls

Figure 47 Out of plane failure of the front facade

Figure 48 Connection of the roof to the walls Figure 49 Preservation of the original timber members,Source - (Paula & Cóias, 2015)

Connections between facades Low resistance due to bad Introduction of steel elements or ties (pre-stressed or not), cables or Devices fixed to the wall throughout injected rods that were put inside the and perpendicular masonry quality of masonry at anchors connecting parallel masonry walls. thickness of the masonry wall, thus not being noticed in the other face of walls connections, and lack of the wall. In the exterior, ductile anchors were used These anchors are less interlocking by regular rigid that the traditional ones. courses in the masonry between intersecting walls.

Steel Anchorage

Exterior

Figure 50 Connection of orthogonal walls through ductile steel anchorage

Structural reinforcement with steel ties anchored in the masonry walls.

Figure 51 Masonry wall to wall connections, Source - (Paula & Cóias, 2015)

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Earthquake resilience of Pol houses in Ahmedabad

Critical connection/ parameter Reinforcement of masonry walls

Structural deficiency

Masonry low shear strength may be critical to shear failure of the building due to the formation of a global shear collapse mechanism.

Strengthening provision

Conservation measures

Introduction of a steel mesh confining masonry structural elements of UHPR –Ultra-High-Performance Render, carbon fibre mesh, embedded in facades. The injection of masonry walls, under controlled pressure and an inorganic matrix, that is compatible with the old masonry substrate. using a grout that contains an inorganic binder, improves its strength properties, because of its increased cohesion and density.

Masonry wall

Grout

Steel ties Steel mesh Compatible

Figure 52 Deformation and failure of two leaf wall, Source - Author

Foundation

Timber members with in gaiola frame

Figure 53 Rendering of masonry wall(left) and tying of masonry leaves with steel ties(right), Source - Author

Figure 54 Masonry walls in forced with UHPR, Source - (Paula & Cóias, 2015)

Settlements due to foundation Micro piles failure. (not observed much – settlement problem) Low strength connection Use of FRP in the Strengthening of Timber Reinforced Masonry Load- Prefabricated timber elements, usually to replace a damaged portion or between timber elements. bearing Walls. the whole member to provide ‘hidden’ strengthening solutions, steel Single or multiple configurations of bars or plates, as overall bars or FRP composites can be embedded in existing strengthening components, or shear connectors. wooden beams and joints.

Gaiola timber members L connections connecting perpendicular wall Steel plate for low strength connections

Steel connectors for masonry walls Figure 55 Timber joints, Source Author

Figure 56 Strengthening of timber members, base drawing source - (Paula & Cóias, 2015)

Steel plate

Repair of decayed ends

Figure 57 (1) Reconstruction of timber framed walls (2) Repair of decayed ends, Source (Paula & Cóias, 2015)

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Earthquake resilience of Pol houses in Ahmedabad

Critical connection/ parameter

Structural deficiency

Connection between masonry wall and timber floor, connection between walls

Low strength connection between timber elements and masonry walls-

Strengthening provision

Conservation measures

Introduction of steel elements, like ties, that connect timber elements to Installation of a set of reversible connectors masonry

Masonry wall Roof structure Timber lintel L connections connecting wall and timber floor

Floor structure Timber lacing Masonry wall inner core

Wooden floorboards Timber joists Figure 58 Typical detail for double leaf masonry and timber ties, Base drawing source - (Polimi, 2010)

Figure 59 Failure of masonry wall due to deterioration of Timber ties, Base drawing source - (Polimi, 2010)

Wall to wall connection Figure 60 Wall to floor connecting devices, Base drawing source - (Paula & Cóias, 2015)

Wall to floor connection

Figure 61 (1) Wall to wall connection devices (2) Wall to floor connection device, Source (Paula & Cóias, 2015)

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Earthquake resilience of Pol houses in Ahmedabad

4.4 Case Study 3 – Conservation of Pol house typology 4.4.1 Tankshal Ni Haveli Tankshal ni haveli was restored in the year 2005 by Ahmedabad heritage cell, A.M.C. funded by the Embassy of France in India.

25m long façade

Restored haveli

Figure 62 Front facade photograph(right),Source - (Pandya, 2020), Location of Tankshal ni haveli (left),Source (Joshi, 2005)

Haveli is located in Haja patel ni pol and used to possess the longest wooden intricately carved façade (25m). The haveli has been under Ahmedabad Municipal Corporation since 1925. It was used as a girl’s school previously and then was abandoned for more than 25 years, before restoration. The entire rear portion of the haveli was dilapidated.

Figure 63 Condition before restoration (left), During restoration (middle and right), Source - (Joshi, 2005)

68

Earthquake resilience of Pol houses in Ahmedabad

Front elevation

Model for front room and façade

The front room – khadki was retained as original structure.

The roof was completely re constructed using timber, but with a greater number of supports than before.

The timber joists were replaced and repaired by local crafts men.

The rear portion and the connecting bridge are a completely new structure made in R.C., steel members and cables.

Figure 64 Elevation (left), Plan (right), Section (bottom right), Source - (Joshi, 2005)

As mentioned by Ar. Shirish Joshi (the then architect for the project) in his website the restoration work had been scheduled in four parts 1) stabilization of the structure through comprehensive reinforcement. 2) Reconstruction of the dilapidated rear part in brick and R.C. 3) Introducing a new steel gallery bridging the old wooden structure and the new structure 4) Internal refurbishment including finishing and furniture.

69

Earthquake resilience of Pol houses in Ahmedabad

4.4.2 Deewanji Ni Haveli –

Ground floor plan

Section A-A’

Figure 65 Deewanji ni haveli – Ground floor plan(top), Section A-A’ (Below), Source - (Shah S. , 2013)

Deewaji ni haveli is located in Sankdi Sheri, Khadia, Ahmedabad. The haveli has been restored in the year 2016, by the city heritage center which is sited in the haveli. The haveli which was a private residence is now reused as a bread and breakfast place, along with the office and conference room.

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Earthquake resilience of Pol houses in Ahmedabad

Figure 66 Before and after restoration images, Source - (CHC , 2017)

The structure is four storied with a basement what opens in the north façade i.e. the main street. There are two water tanks known as tankas, the smaller one being located at southern part while the larger one located below the central courtyard. The room adjacent to the courtyard is used for accessing the tank and drawing water.

The restoration involved addition of wooden columns as beam sagging was observed.

One of the leaning walls was strengthened through post tensioning using wire rope and turn buckle mechanism. (Shah S. , 2013)

Figure 67 Addition of new column, Source - (Shah S. , 2013)

71

Earthquake resilience of Pol houses in Ahmedabad

Figure 68 Damaged floor (left) floor during restoration (right), Source – (Shah S. , 2013)

The floors had typical detail of the wooden joists with brick bat coba. (figure 71) During the restoration process the floors of the structure have been reconstructed using the concrete foam boards. (figure 71) ½” mud and cow dung plaster 10” brick bat coba 1” tar layer Wooden planks Wooden rafters

Concrete poured between the blocks and 2” above Prefabricated concrete foam blocks Bison panel boards 18mm thick Wooden joists Wooden rafters

Wooden joists

Figure 69 Original flooring detail(left), Restored flooring detail(right), base drawing source - (Shah S. , 2013)

The roof truss was repaired using cast iron plates and bolts, the roof covering of country tiles was removed and replaced using G.I. (Galvanized Iron) sheets.

Removal of original country clay tiles

Fixing of G.I. sheet on existing wooden joists and rafters

Repaired roof truss

Figure 70 Restoration of roof, Source - (Shah S. , 2013)

72

Earthquake resilience of Pol houses in Ahmedabad

4.5 Case Study 4 – Disaster risk preparedness The case study is based on the study conducted by National Institute of Disaster Management (NIDM) in the year 2011 and 2017. The case here aims to understand the on-ground scenario with respect to the conservation status of the pol houses at individual as well as settlement level. The case study is analyzed correlating with the telephonic survey conducted by the author in the Chapter 5, section 5.4.

4.5.1 Study by NIDM for Disaster risk preparedness of Historic cities – Case of Shantinath ni Pol The survey conducted through the study identified the following physical vulnerability factors for the pol house settlement within the old city of Ahmedabad – •

Demolition, poor quality construction and alteration work

•

Subdivision and grouping of plots

•

Diverse ownership

•

Vacant houses

•

Insensitive commercialization – conversion of residences into storage go downs.

•

Traffic and congestion

•

Dampness and termite attack

•

Incompatible changes

The study of Shantinath ni pol settlement – Shantinath ni pol is a predominantly Jain pol that has around 60 houses with ground plus two or three floors. The houses are arranged on both the sides of the main street in a row house pattern. The houses found here mostly dates back to second half of the 19th century. (bmtpc.org, 1990) The survey was conducted for the analysis of vulnerability to earthquake, fire, and floods.

All the households filled the questionnaire and vulnerability was assessed based on observation of the structure by experts.

The survey noted the following aspects – •

Building details – number of floors and building height

•

Architectural significance and components – elements, associated history

•

Ownership – privately owned, multiple ownership, tenants

•

Capacity – the load transfer pattern

•

Vulnerability – based on existing conditions, alterations, vacancy etc.

73

Earthquake resilience of Pol houses in Ahmedabad

•

Photographic documentation

The map (figure 73) summaries some of the critical observations from Shanti nath ni pol survey.

74

Earthquake resilience of Pol houses in Ahmedabad

Figure 71 Vulnerability analysis survey by NIDM, Base map Source - (Bhandopadhyay, 2020)

75

Earthquake resilience of Pol houses in Ahmedabad

5. Critical Analysis 5.1 Analysis of the cases for vulnerability index The three case studies from the previous thesis were identified (refer chapter 4) for the analysis of vulnerability index and damage assessment. Rapid visual screening based on GNDT method has been used here for analysis, which has been explained in the previous chapters. In the following chapter the method has been applied both qualitatively by analyzing the drawings and construction details of the cases, as well as quantitatively by calculations. The current research is the first attempt for analyzing the pol houses through GNDT methodology, which when applied on larger scale could determine the possible damage at the settlement level. The analysis is an attempt to give a new direction within the research domain of pol house construction.

The parameters for each case are individually analyzed and then finally the cumulative GNDT table is formulated, which is followed by the estimation of vulnerability index and damage assessment.

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Earthquake resilience of Pol houses in Ahmedabad

5.1.1 Case 1 - Shared wall house typology – Kameshwar ni pol Parameter 1 – Type and Organization of resisting system – Class B •

The house has presence of timber beams connecting the orthogonal walls.

•

The box behavior is maintained at the ground floor but at the upper floor the building is separated in to two boxes due to the presence of courtyard. However, the presence of timber beams throughout the periphery of courtyard ensures the effective connection between the walls.

•

Timber beams are present at the lintel level also.

The timber beams ensure the cross connection between the walls, that eventually builds up a better resisting system, hence it is classified under Class B.

Figure 72Timber lacing, masonry and door opening, Source - Author

77

Earthquake resilience of Pol houses in Ahmedabad

Wall prone to failure – but will be supported by the connections of the adjacent house.

No presence of timber beam connecting the courtyard structure.

Figure 73 Timber beams and masonry cross walls connecting the orthogonal walls. Timber frame structure of courtyard. Base drawing source - (Modan, 2006)

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Earthquake resilience of Pol houses in Ahmedabad

Parameter 2 – Quality of resisting system – Class C •

Narrow flat brick with mud and lime is used traditionally for the construction of masonry work in pol houses.

•

The main orthogonal wall is double leaf masonry wall filled with rubble, mud, and lime. The internal cross walls are single leaf brick masonry walls with mud and lime mortar.

•

Though there is presence of timber ties connecting the orthogonal walls, there is no effective connection between the two masonry leaves of the main orthogonal wall.

The absence of cross connection between the two leaves of masonry walls classifies the case into Class C. Brick masonry

Flat and broad bricks

Rubble core

Figure 74 The orthogonal wall with flat brick masonry and rubble core, Source – Author

Parameter 3 – Conventional resistance – Class C For determining the conventional resistance parameter, the masonry wall areas are determined as explained in figure 77.

Figure 75 Ground floor plan - wall area in X and Y directions, Base drawing source - (Modan, 2006)

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Earthquake resilience of Pol houses in Ahmedabad

Ax = (15.6+15.6) x 0.6 = 18.72 m2 Ay = {(3.3+1.4) x 0.45} + {(2.5 + 0.8) x 0.4} + {(0.5+0.9+0.4+0.4+0.5) x 0.4} + {(0.4+1.7+0.6+0.6) x 0.4} + (5.8x.6) = 9.3 m 2

Figure 76 Floor wise area and specific weight per floor(t/m2),Base drawing source - (Modan, 2006)

Figure 77 Calculation of specific weight of floor, Source – Author

A = 9.3 m2 B = 18.72 m2 At = 82.6 + 82.6 +20 + 80 / 4 = 66.3 m2 a0 = A/At = 9.3/66.3 = 0.14 𝛾 = B/A = 2.01 H = 2.6m Ps = 0.85 x 82.6 + 0.85 x 82.6 + 0.8 x 20 + 0.17 x 80 / 265.2 = 2.56 t/m2 Pm = 1.8 t/m2 q = (18.72 + 9.3)2.6 x 1.8 / 66.3 + 2.56 = 1.96 t/m2 80

Earthquake resilience of Pol houses in Ahmedabad

For 𝜏 (𝑚𝑖𝑛) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

𝑞𝑁

√1 + 1.5𝑎

0 𝜏𝑘 (1+𝛾)

𝐶=

. 14 ∗ 6.1 1.96 ∗ 4 √1 + 1.96 ∗ 4 1.5 ∗ .14 ∗ 6.1(1 + 2.01)

C = 0.18 α = C/0.4 = 0.4

For 𝜏 (𝑚𝑎𝑥) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

𝑞𝑁

√1 + 1.5𝑎

0 𝜏𝑘 (1+𝛾)

𝐶=

. 14 ∗ 9.4 1.96 ∗ 4 √1 + 1.96 ∗ 4 1.5 ∗ .14 ∗ 9.4(1 + 2.01)

C = 0.2 α = C/0.4

= 0.5 The conventional resistance calculated is in the range of 0.4 ≤ 𝛼 < 0.6, hence Class C. Parameter 4 – Position of building and foundation – Class B Ahmedabad old city has an alluvial sandy loam soil formed due to the river deposits. The old city of Ahmedabad is located on the flat land with no significant level differences; the gradient of the ground is typically zero, hence the foundations of the structure are the same level, which is a positive point for seismic resistance. But the soil quality of Ahmedabad is loose which amplifies the seismic waves unlike hard and rocky soils. From the criteria with respect to soil the classification is Class B. Parameter 5 – Floors – Class B The floors are composite structures with timber joists and brick bat coba. The floors are well connected to the orthogonal walls. the joists are nailed to the wall plate making it a fixed joint. The joists are tied together with wooden wedges using tongue and groove joints. The floorboards are nailed to the joist but joint together with tongue and grove joinery.

The floor structure is not completely deformable due to the presence of nails; however, the deformable nature of timber members and presence of groove joints allows deformability, hence can be classified under Class B.

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Earthquake resilience of Pol houses in Ahmedabad

Masonry wall Timber floor joist nailed to wall plate Wall plate

Figure 78 Floor joist connection with the masonry wall, Source - Author

Flooring tile Brick bat coba Floorboards nailed and grooved with the rafters Timber joists

Figure 79 Composite floor connections, Source - Author

Parameter 6 – Configuration in plan – Class C The breadth and length ratio for the house is 𝑎 𝛽1 = 𝑙 5.8 𝛽1 = 15.6

𝛽1 = 0.37 From the criteria the class for parameter 6 is

Figure 80 center to center I and a length in ground floor plan

Class C.

82

Earthquake resilience of Pol houses in Ahmedabad

Parameter 7 – Configuration in elevation – Class A The T/H ratio is zero in case of the house, as there is no typical vertical projection. The elevation has a uniform height throughout, hence the class for parameter 7, is Class A.

Figure 81 Front elevation sketch showing no projections, Source – Author

Parameter 8 – Wall maximum inter axis – Class A Maximum ratio l/s = 8.6/.6 = 14.3, where l is the distance between wall 1 and wall 2 and s is the thickness of the main wall.

The

wall

maximum

inter

axis

determines the slenderness27 ratio for the building along the length. As the ratio is less than 15, the class for parameter 8 will be Class A.

Figure 82 Wall maximum inter axis, length l between the major masonry cross walls and t is the thickness of the main orthogonal wall

Parameter 9 – Roof– Class D The roof is constructed from timber logs and rafters. There is no presence of effective connections with the orthogonal walls. For the deformable and not well-connected roof the class for this parameter is taken as Class D.

27

Slenderness - quotient between the height and the width of a building, here the similar concept is used for the length of the building.

83

Earthquake resilience of Pol houses in Ahmedabad

Wooden logs inserted in the parallel masonry walls

Timber rafters of roof

Masonry wall supporting the roof

Masonry wall (back side) Vertical timber post Timber joist supporting the vertical posts

Figure 83 Roof structure, Source – Author

Parameter 10 – Nonstructural elements – Class A There are no hanging elements like balconies, found in this case, hence the class for the non-structural elements is taken as Class A.

Timber Roof structure Only roof overhang and railings Second floor Timber beam connecting the orthogonal walls Window

First floor

The façade is straight and uniform following the floor wise column

Load bearing masonry wall with timber lacing

Ground floor

Figure 84 Part section representing absence of major over hangs, Source – Author, reference - (Modan, 2006)

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Earthquake resilience of Pol houses in Ahmedabad

Parameter 11 – Current Conditions – Parametric Analysis As the information on the conditions is not available for the case, parametric analysis will be conducted in the final derivative of the vulnerability index, maximum and minimum values, indicating the change in vulnerability index if the condition is good and worst with respect to conservation.

Determination of Vulnerability index When the parameter for current conditions - class A – the structure is in good condition with no defects.

Table 15 Parameters table for case1, Source- Author

PARAMETER 1 2 3 4 5 6 7 8 9 10 11

A

Type and organization of resisting system Quality of the resisting system Conventional resistance Position of the building and foundations Floors Configuration in plan Configuration in elevation Walls maximum inter axis Roof Non-structural elements Current conditions

CLASS Cvi B C 5

D

25 25

WEIGHT pi 1.00 0.25 1.50 0.75

5 5 25 0 0 45 0 0

0.75 0.50 1.75 0.25 0.5 0.25 1.00

𝑽 = ∑ 𝒄𝒗𝒊 𝒑𝒊 𝒊

V = (5x1) +(25 x .25) +(25x1.5) +(5x0.75)+(5x0.75)+(25x0.5)+0+0+(45x0.5)+0+0 = 5+6.25+37.5+3.75+3.75+12.5+22.5 = 91.25 𝑽 𝑉̅ = × 𝟏𝟎𝟎 𝟑𝟖𝟐. 𝟓

𝑉̅ =

𝟗𝟏. 𝟐𝟓

× 𝟏𝟎𝟎 = 𝟐𝟑. 𝟖 𝟑𝟖𝟐. 𝟓 When the parameter for current conditions - class D – the structure is in a bad condition with several defects like major structural cracks due to previous earthquakes.

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Earthquake resilience of Pol houses in Ahmedabad

𝑽 = ∑ 𝒄𝒗𝒊 𝒑𝒊 𝒊

V = (5x1) +(25 x .25) +(25x1.5) +(5x0.75) + (5x0.75) +(25x0.5) +0+0+(45x0.5) +0+0 = 5+6.25+37.5+3.75+3.75+12.5+22.5+45 = 136.25

𝑉̅ =

𝟏𝟑𝟔. 𝟐𝟓 𝟑𝟖𝟐. 𝟓

× 𝟏𝟎𝟎 = 𝟑𝟓. 𝟔

Determination of Damage Assessment For intensity 6, the damage assessment when the current conditions are assumed good will be ̅ 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒𝑽 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟐𝟑. 𝟖 = 𝟎. 𝟕𝟏𝟐 𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝝁𝑫 = [𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝑰 + 𝟔. 𝟐𝟓𝑽 − 𝟏𝟐. 𝟕 ) × 𝒇(𝑽, 𝑰) 𝑸

.𝟕𝟏𝟐 𝟔 + 𝟔. 𝟐𝟓𝟎 ∗. 𝟕𝟏𝟐 − 𝟏𝟐. 𝟕 ( )(𝟔−𝟕) )] × 𝒆 𝟐 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟏𝟕 For intensity 6, the damage assessment when the current conditions are assumed worst will be 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟑𝟓. 𝟔 = 𝟎. 𝟕𝟖𝟕 𝝁𝑫 = [𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

.𝟕𝟖𝟕 𝟔 + 𝟔. 𝟐𝟓𝟎 ∗. 𝟕𝟖𝟕 − 𝟏𝟐. 𝟕 ( )(𝟔−𝟕) )] × 𝒆 𝟐 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟑𝟖

86

Earthquake resilience of Pol houses in Ahmedabad

5.1.2 Case 2 - Corner house typology – Kameshwar ni pol Parameter 1 – Type and Organization of resisting system – Class B •

The house has timber beams connecting the orthogonal walls.

•

The box behavior is maintained at the ground floor but at the upper floor the building is separated in to two boxes due to the presence of courtyard. However, the presence of timber beams throughout the periphery of courtyard ensures the effective connection between the walls. Here the courtyard has individual wooden framing forming the box.

•

The masonry for case 2, is timber laced at three levels, with two beams parallel to each other along with wooden wedges connecting them.

•

All the four masonry walls are connected with timber beams horizontally.

Timber beam connecting orthogonal walls

Wooden wedges connecting the parallel members as per the masonry wall thickness

Wooden lintel

Masonry wall

Wooden lintel

Horizontal timber lacing throughout the length of the wall

Figure 85 Effective tying of masonry by timber lacing/bands, Source – Author

87

Earthquake resilience of Pol houses in Ahmedabad

Wooden beam parallel to the masonry wall

Courtyard structure independent of masonry walls

Load bearing masonry walls with timber lacing

Figure 86 Timber beams and masonry cross walls connecting the orthogonal walls. Timber frame structure of courtyard. Base drawing source - (Modan, 2006)

88

Earthquake resilience of Pol houses in Ahmedabad

Parameter 2 – Quality of resisting system – Class B •

The main orthogonal wall is double leaf masonry wall filled with rubble, mud, and lime. The internal cross walls are single leaf brick masonry walls with mud and lime mortar.

•

The connection of wooden members between the two leaves of masonry walls is an important joinery detail for the resisting system, which is effectively present in the case of corner house.

The effective linkage between the masonry wall classifies the parameter into Class B.

Window

Brick masonry inner leaf

Flooring – tile

Brick bat coba Timber joists with rafters and floorboards Timber beams Horizontal timber connection between the masonry leaves Timber lacing

External masonry leaf

Figure 87 Orthogonal wall section, Source – Author

89

Earthquake resilience of Pol houses in Ahmedabad

Parameter 3 – Conventional resistance – CLASS B

Figure 88 Ground floor plan - wall area in X and Y directions, Base drawing source - (Modan, 2006)

Roof area

0.17 t/m2

Second floor area

0.85 t/m

2

First floor area 0.85 t/m

2

Specific weight

Floor area

Figure 89 Floor wise area and specific weight per floor(t/m2), Base drawing - (Modan, 2006)

Ax = (15.1) x 0.5 + 15.1 x 0.8 + 4.1 x 0.45 = 21.43 m2 Ay = 8.6 x 0.5+ (2.1+3+1.2) x 0.4 + (1.5 + 1.5 +0.68+0.43) x 0.6 + (0.63+2+1.4) x 0.4 + 2.7 x 0.5= 12.25 m2 A = 21.43 m2 B = 12.25 m2 At = 119.3 + 126.1 + 126.1 / 3 = 123.83 m2 a0 = A/At = 21.43/123.83 = 0.17 𝛾 = B/A = 0.57 H = 2.5m 90

Earthquake resilience of Pol houses in Ahmedabad

Ps = (0.85 x 119.3) + (0.85 x 126.1) + (0.17 x 126.1)/ 123.83 = 1.85 t/m2 q= 𝑞 = (𝐴 + 𝐵) × 𝐻𝑃𝑚⁄𝐴𝑡 + 𝑃𝑠 = (21.43 + 12.25) x 2.5 x 1.8 / 123.83 + 1.85 = 3.07 t/m2 For 𝜏 (𝑚𝑖𝑛) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

𝑞𝑁

√1 + 1.5𝑎

0 𝜏𝑘 (1+𝛾)

0.17 ∗ 6.1 3.07 ∗ 3 √1 + 3.07 ∗ 3 1.5 ∗ .17 ∗ 6.1(1 + 0.57)

𝐶=

C = 0.24 α = C/0.4 = 0.6

For 𝜏 (𝑚𝑎𝑥) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

√1 + 1.5𝑎

𝑞𝑁

0 𝜏𝑘 (1+𝛾)

𝐶=

0.17 ∗ 9.4 3.07 ∗ 3 √1 + 3.07 ∗ 3 1.5 ∗ .17 ∗ 9.4(1 + 0.57)

C = 0.32 α = C/0.4

= 0.8 The conventional resistance calculated is in the range of 0.6 ≤ 𝛼 < 1, hence Class B.

Masonry cross wall

Composite Floor Timber beam

Timber lacing

Figure 90 Floor connection with masonry cross wall, Source – Author

91

Earthquake resilience of Pol houses in Ahmedabad

Parameter 4 – Position of building and foundation – Class B (same as case 1) Parameter 5 – Floors – Class B (same as case 1) Parameter 6 – Configuration in plan – Class C The breadth and length ratio for the house is 𝑎 𝑙 8.6 𝛽1 = 15.1 𝛽1 =

𝛽1 = 0.56

From the criteria the class for parameter 6

Figure 91 center to center I and a length in ground floor plan, Source- (Modan, 2006)

is Class C. Parameter 7 – Configuration in elevation – Class A The T/H ratio is zero in case of the house, as there is no typical vertical projection. The elevation has a uniform height throughout, hence the class for parameter 7, is Class A. Parameter 8 – Wall maximum inter axis – Class A Maximum ratio l/s = 7.1/.6 = 11.8, where l is the distance between wall 1 and wall 2 and s is the thickness of the main wall.

The wall maximum inter axis determines the slenderness ratio for the building along the length. As the ratio is less than 15, the class for parameter 8 will be Class A. Figure 91 Wall maximum inter axis, length l between the major masonry cross walls and t is the thickness of the main orthogonal wall, Base drawing source (Modan, 2006)

92

Earthquake resilience of Pol houses in Ahmedabad

Parameter 9 – Roof– Class B The roof is constructed from timber logs and rafters. There is no presence of effective connections with the orthogonal walls, but the connection of tie member provides the roof structure support and can be classified as deformable and well connected, as class B Timber rafters

Masonry parapet supporting the roof Timber rafters

Horizontal wooden members between orthogonal walls

Eaves board

Timber post as vertical supports

Partial truss

Figure 92 Roof connection front façade, Roof structure, Source – Author

Parameter 10 – Nonstructural elements – Class B The case 2, has the projecting second floor which is well connected to the first-floor timber columns. Also, the projecting roof is supported by the bracket. Hence it can be classified under Class B. Masonry parapet Projecting second floor Continuous floor rafter connecting floor with the structural system

Second floor

Wooden bracket support

First floor

Timber lacing on orthogonal and cross walls

Ground

Figure 93 Part front section showing projections, Source – Author, Reference - (Modan, 2006)

93

Earthquake resilience of Pol houses in Ahmedabad

Parameter 11 – Current Conditions – Parametric Analysis As the information on the conditions is not available for the case, parametric analysis will be conducted in the final derivative of the vulnerability index, maximum and minimum values, indicating the change in vulnerability index if the condition is good and worst with respect to conservation.

Determination of Vulnerability index When the parameter for current conditions - class A – the structure is in good condition with no defects.

Table 16 Parameters table for case 2, Source - Author

PARAMETER 1 2 3 4 5 6 7 8 9 10 11

A

Type and organization of resisting system Quality of the resisting system Conventional resistance Position of the building and foundations Floors Configuration in plan Configuration in elevation Walls maximum inter axis Roof Non-structural elements Current conditions

CLASS Cvi B C 5

D

WEIGHT pi 1.00

5 5 5

0.25 1.50 0.75

5

0.75 0.50 1.75 0.25 0.5 0.25 1.00

25 0 0 5 5 0 𝑽 = ∑ 𝒄𝒗𝒊 𝒑𝒊 𝒊

V = 5 x 1 + 5 x 0.25 + 5 x 1.5 + 5 x 0.75 + 5 x 0.75 + 25 x 0.5 + 0 + 0 + 5 x 0.5 + 5 x 0.25 + 0 = 37.5

𝑉̅ = 𝑉̅ =

𝑽 𝟑𝟖𝟐. 𝟓

× 𝟏𝟎𝟎

𝟑𝟕. 𝟓

× 𝟏𝟎𝟎 = 𝟗. 𝟖 𝟑𝟖𝟐. 𝟓 When the parameter for current conditions - class D – the structure is in a bad condition with several defects like major structural cracks due to previous earthquakes.

94

Earthquake resilience of Pol houses in Ahmedabad

V = 5 x 1 + 5 x 0.25 + 5 x 1.5 + 5 x 0.75 + 5 x 0.75 + 25 x 0.5 + 0 + 0 + 5 x 0.5 + 5 x 0.25 + 45 = 82.5

𝑉̅ =

𝟖𝟐. 𝟓 𝟑𝟖𝟐. 𝟓

× 𝟏𝟎𝟎 = 𝟐𝟏. 𝟓𝟔

Determination of Damage Assessment ̅ 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒𝑽 For intensity 6, the damage assessment when the current conditions are assumed good will be 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟗. 𝟖 = 𝟎. 𝟔𝟐

𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝑰 + 𝟔. 𝟐𝟓𝑽 − 𝟏𝟐. 𝟕 ) × 𝒇(𝑽, 𝑰) 𝑸

𝟎.𝟔𝟐 𝟔 + 𝟔. 𝟐𝟓(𝟎. 𝟔𝟐) − 𝟏𝟐. 𝟕 ( )(𝟔−𝟕) )× 𝒆 𝟐 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟔𝟒 For intensity 6, the damage assessment when the current conditions are assumed worst will be 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟐𝟏. 𝟓𝟔 = 𝟎. 𝟔𝟗 𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝟎.𝟔𝟗 𝟔 + 𝟔. 𝟐𝟓(𝟎. 𝟔𝟗) − 𝟏𝟐. 𝟕 ) × 𝒆( 𝟐 )(𝟔−𝟕) 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟖𝟒

95

Earthquake resilience of Pol houses in Ahmedabad

5.1.3 Case 3 – Haveli typology – Parameter 1 – Type and Organization of resisting system – Class B

Timber lacing on orthogonal and cross walls

Masonry orthogonal wall without timber lacing

Timber courtyard frame on ground floor

Figure 94 Timber beams and masonry cross walls connecting the orthogonal walls. Timber frame structure of courtyard. Base drawing source - (Modan, 2006)

96

Earthquake resilience of Pol houses in Ahmedabad

•

The structure has effective connections between the orthogonal walls due to the presence of masonry walls at all the levels that acts like cross walls between the two parallel walls.

•

The cross-masonry walls would also act as shear walls in case of an earthquake providing stability due to inertia.

•

For the courtyard, the box behavior is completed by the timber beams connecting the orthogonal walls.

•

Presence of timber connections at the lintel level, also resists the horizontal forces.

The masonry walls ensure the cross connection between the orthogonal walls, that eventually builds up a better resisting system, hence it is classified under Class B. Parameter 2 – Quality of resisting system – Class C

No details from the documented drawings assure an effective connection between the two leaves of the masonry wall.

Parameter 3 – Conventional resistance – Class C

Figure 95 Wall area is x and y directions, Base drawing source - (Modan, 2006)

Ax = (2 + 0.3 + 1.2 + 11.4 + 2.3) x 0.7 + (3 + 1.3 + 0.6 + 0.6 + 0.6 + 0.7 + 0.6 + 5.6) x 0.26 + 6.7 x 0.3 + (0.7 + 1.3 + 0.8 + 14.6) x 0.5 + (0.8 + 7.3) x 0.4 = 12.04 + 3.4 + 2 + 8.7 + 3.24 = 29.4 m2

97

Earthquake resilience of Pol houses in Ahmedabad

Ay = (10.1 x 0.53) + (3.1 + 2.6 + 1.4) x 0.3 + (2.1 + 0.4 + 2 + 0.64) x 0.3 + (1.2 + 2.5 + 2.4 + 3.1)x0.3 + (3.2 + 3.1 + 2 + 1.8) x 0.5 = 16.74 m2

Roof area

Second floor 0.17 t/m2

First floor

0.85 t/m 0.85 t/m

Per floor area

2

2

Specific weight

Figure 96 Floor wise area and specific weight per floor(t/m2), Base drawing source - (Modan, 2006)

A = 29.4 m2 B = 16.74 m2 At = 264.3 + 244.4 + 244.4 / 3 = 251.03m2 a0 = A/At = 0.11 𝛾 = B/A = 0.56 H = 2.5 m Ps = (0.85 x 264.3) + (0.85 x 244.4) + (0.17 x 244.4)/ 251.03 = 1.88 t/m2 q= 𝑞 = (𝐴 + 𝐵) × 𝐻𝑃𝑚⁄𝐴𝑡 + 𝑃𝑠 𝑞 = (29.4 + 16.74) × 2.5 ∗ 1.8⁄251.03 + 1.88 𝑞 = 2.7 For 𝜏 (𝑚𝑖𝑛) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

√1 + 1.5𝑎

𝑞𝑁

0 𝜏𝑘 (1+𝛾)

𝜏 (𝑚𝑖𝑛) 𝐶 =

0.11 ∗ 6.1 2.7 ∗ 3 √1 + 2.7 ∗ 3 1.5 ∗ 0.11 ∗ 6.1(1 + 0.56)

C = 0.203 α = C/0.4 = 0.5

98

Earthquake resilience of Pol houses in Ahmedabad

For 𝜏 (𝑚𝑎𝑥) 𝐶 =

𝑎0 𝜏𝑘 𝑞𝑁

√1 + 1.5𝑎

𝑞𝑁

0 𝜏𝑘 (1+𝛾)

𝜏 (𝑚𝑖𝑛) 𝐶 =

0.11 ∗ 9.4 2.7 ∗ 3 √1 + 2.7 ∗ 3 1.5 ∗ 0.11 ∗ 9.4(1 + 0.56)

C = 0.266 α = C/0.4

= 0.6 The conventional resistance calculated is in the range of 0.4 ≤ 𝛼 < 0.6, hence Class C. Here the case of minimum 𝜏 value is chosen for classifying as per conservative28 analysis.

Parameter 4 – Position of building and foundation – Class B (same as case 1, section 5.1.1) Parameter 5 – Floors – Class B (same as case 1, section 5.1.1) Parameter 6 – Configuration in plan – Class B The breadth and length ratio for the house is 𝑎 𝛽1 = 𝑙 𝛽1 =

10.15 = 0.47 21.15 𝛽2 =

𝛽2 =

𝑏 𝑙

3.2 = 0.15 21.15

Figure 97 a/l length ratio in ground floor plan, Base drawing source - (Modan, 2006)

From the criteria the values of 𝛽1 and 𝛽2 (60 ≤ β1 < 80 ,10 < β2 ≤ 20) is in the CLASS B.

28

Conservative analysis – Analysis when the values are assumed low to be on the safer side.

99

Earthquake resilience of Pol houses in Ahmedabad

Parameter 7 – Configuration in elevation – Class A (same as case 1, section 5.1.1) Parameter 8 – Wall maximum inter axis – Class A Maximum ratio l/s = 9.4/.7 = 13.42, where l is the distance between wall 1 and wall 2 and s is the thickness of the main wall. The wall maximum inter axis determines the slenderness ratio for the building along the length. As the ratio is less than 15, the class for parameter 8 will be Class A.

Figure 98 Wall maximum inter axis distance, Base drawing source - (Modan, 2006)

Parameter 9 – Roof– Class B The roof is well supported by the masonry load bearing wall. There is no presence of effective connections with the orthogonal walls, but the connection of tie member provides the roof structure support and can be classified as well connected deformable as Class B. Masonry wall

Roof Timber logs

Masonry wall supporting the roof

Figure 99 Roof connections, Base drawing source - (Modan, 2006)

100

Earthquake resilience of Pol houses in Ahmedabad

Parameter 10 – Nonstructural elements – Class C There are non-structural elements like roof overhang and railings present. The nonstructural elements are well connected and supported with wooden brackets, but the presence of projections at first and second floor classifies it into Class C.

Masonry wall supporting the roof

Second floor

Projecting first and Second floor

Wooden railing – nonstructural element

First floor

Timer lacing

Wooden bracket support

Ground floor

Figure 100 Part front section showing projections, Source – Author, Reference - (Modan, 2006)

Parameter 11 – Current Conditions – Parametric Analysis As the information on the conditions is not available for the case, parametric analysis will be conducted in the final derivative of the vulnerability index, maximum and minimum values, indicating the change in vulnerability index if the condition is good and worst with respect to conservation.

101

Earthquake resilience of Pol houses in Ahmedabad

Determination of Vulnerability index When the parameter for current conditions - class A – the structure is in good condition with no defects.

PARAMETER 1 2 3 4 5 6 7 8 9 10 11

A

Type and organization of resisting system Quality of the resisting system Conventional resistance Position of the building and foundations Floors Configuration in plan Configuration in elevation Walls maximum inter axis Roof Non-structural elements Current conditions

CLASS Cvi B C 5

D

25 25 5 5 5 0 0 5 25 0

WEIGHT pi 1.00 0.25 1.50 0.75 0.75 0.50 1.75 0.25 0.5 0.25 1.00

𝑽 = ∑ 𝒄𝒗𝒊 𝒑𝒊 𝒊

V = 5x1 + 25x.25 + 25x1.5 + 5x0.75 + 5x0.75 + 5x0.5 + 0 + 0 + 5x.5 +25x.25 + 0 = 61.25

𝑉̅ =

𝑽

× 𝟏𝟎𝟎 𝟑𝟖𝟐. 𝟓 𝟔𝟏. 𝟐𝟓 𝑉̅ = × 𝟏𝟎𝟎 = 𝟏𝟔. 𝟎𝟏 𝟑𝟖𝟐. 𝟓 When the parameter for current conditions - class D – the structure is in a bad condition with several defects like major structural cracks due to previous earthquakes.

V = 5x1 + 25x.25 + 25x1.5 + 5x0.75 + 5x0.75 + 5x0.5 + 0 + 0 + 5x.5 +25x.25 + = 106.25

𝑉̅ =

𝟏𝟎𝟔. 𝟐𝟓 𝟑𝟖𝟐. 𝟓

× 𝟏𝟎𝟎 = 𝟐𝟕. 𝟕

Determination of Damage Assessment ̅ 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒𝑽

102

Earthquake resilience of Pol houses in Ahmedabad

For intensity 6, the damage assessment when the current conditions are assumed good will be 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟏𝟔. 𝟎𝟏 = 𝟎. 𝟔𝟔 𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝑰 + 𝟔. 𝟐𝟓𝑽 − 𝟏𝟐. 𝟕 ) × 𝒇(𝑽, 𝑰) 𝑸

𝟎.𝟔𝟔 𝟔 + 𝟔. 𝟐𝟓 ∗ 𝟎. 𝟔𝟔 − 𝟏𝟐. 𝟕 ( )(𝟔−𝟕) )× 𝒆 𝟐 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟎𝟓 For intensity 6, the damage assessment when the current conditions are assumed worst will be 𝑽 = 𝟎. 𝟓𝟔 + 𝟎. 𝟎𝟎𝟔𝟒 ∗ 𝟐𝟕. 𝟕 = 𝟎. 𝟕𝟑 𝝁𝑫 = 𝟐. 𝟓 + 𝟑𝒕𝒂𝒏𝒉 (

𝟎.𝟕𝟑 𝟔 + 𝟔. 𝟐𝟓 ∗ 𝟎. 𝟕𝟑 − 𝟏𝟐. 𝟕 ( )(𝟔−𝟕) )× 𝒆 𝟐 𝟐. 𝟑

𝝁𝑫 = 𝟎. 𝟐

103

Earthquake resilience of Pol houses in Ahmedabad

5.2 Conclusions for Vulnerability Analysis From the above vulnerability index and damage analysis, the correlation between the intensity and mean damage was established for each case, based on the EMS -9829 scale of vulnerability .This correlation is formulated by calculating the mean damage values for intensity of earthquake ranging from III to IX on MSI scale. The red vulnerability curve denotes the situation when the condition of the building is poor while blue denotes good condition.

5.2.1 Case 1 – Shared wall house typology The Graph (figure 103) represents the damage grade of the pol house for a given intensity of earthquake. It is evident from the graph that the poor condition of the structure significantly increases the damage. For the case 1, (house with shared wall typology), for the earthquake with intensity VII, the damage expected is in the range of slight to moderate. For the higher intensity earthquake some substantial damage is expected. The parameters 1,3,7, and 11 have significant role in ensuring the low vulnerability, thus the presence of effective connections (1), adequate shear resisting wall area and quality of material (3), regularity along the height (7), and current conditions are the critical parameters. The case is analyzed individually, however the building will behave

Mean damage grade

collectively with other pol houses that are connected with the orthogonal masonry walls.

5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00

Good Poor

3

4

5

6 Intensity

7

8

0

No Damage

1

Slight

2

Moderate

3

Substantial to Heavy

4

Very Heavy

5

Destruction

9

Figure 101 Mean damage grade and intensity relation - vulnerability curve graph, Source -Author

29

EMS – 98 Vulnerability scale- Macro seismic scale referring to the vulnerability classes which is a method to group together the buildings of same seismic behaviour in classes A to F.

104

Earthquake resilience of Pol houses in Ahmedabad

5.2.2 Case 2 – Corner house typology The mean damage values here are lower than the above case. From the graph (figure 104) it is observed that even at the VII-intensity earthquake the damage is slight. However, the poor conditions significantly increase the damage grade, making the structure more vulnerable. The critical parameters of effective connections, adequate shear resisting wall area and quality of material, regularity in height and current conditions determines the vulnerability index of the case. As the house is situated in corner with no support on one side, it was possible to conclude it more vulnerable, but from the analysis it is clear that the geometry and the shear wall area of the masonry makes it less vulnerable.

While some confinement will be available at settlement level, earthquake effects can be transferred from neighboring building too. A last/corner building will be most vulnerable as

Mean damage grade

there is no confinement on one side.

5.00 4.50 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 3

0

No Damage

Good

1

Slight

Poor

2

Moderate

3

Substantial to Heavy

4

Very Heavy

5

Destruction

4

5

6 Intensity

7

8

9

Figure 102 Mean damage grade and intensity – vulnerability graph for case 2, Source Author

5.2.3 Case 3 – Haveli typology The haveli typology is the largest typology in terms of area, when compared to the cases 1 and 2. The structure here has inherent earthquake resistant features which is explained in the graph (figure 105), as during an earthquake of intensity VII the structure would suffer slight damages but if the structure is in poor condition there is a possibility of moderate damages or more. The critical parameters of connection with the orthogonal walls, adequate shear resisting wall area, regularity in height and current condition play a major 105

Earthquake resilience of Pol houses in Ahmedabad

role in determining the possible damage. The case had masonry walls till the second floor supporting the roof unlike the other two cases where the walls were of timber. The approach of constructing higher masonry walls signifies the structural understanding of the creators, as the width is larger for better support masonry was chosen over complete timber structure.

0

No Damage

1

Slight

2

Moderate

3

Substantial to Heavy

4

Very Heavy

5

Destruction

Figure 103 Mean damage grade v/s Intensity - Vulnerability graph for case 3, Source Author

Conclusion – From the vulnerability analysis using GNDT method of the three cases above it can be stated that •

The seismic resilient vernacular typology – pol houses, have inherent earthquake resistant features as when analyzed for ‘good condition’ the damage grade is low/slight for all the cases. It is these inherent features which defines the structural integrity of pol houses.

•

The current condition parameter – if the structures are not maintained in good condition the damage significantly increases between the intensities V and VII, because the vulnerability curves for good and poor conditions diverges in all the cases. Hence the conservation state is one of the most critical parameters that would determine the damage grade. It is important to conserve and restore the materials for the structure, because the condition can significantly change the situation of vulnerability.

•

The critical parameters and the conservation measures are explained in the next chapter (Chapter 6).

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Earthquake resilience of Pol houses in Ahmedabad

5.3 Comparative Analysis of Pol houses and Pombalino structures Randolph Langenbach in his article the ‘earthquake resistance architecture in the Himalayas’ writes that – “Their resilience was proven by their survival, and so they inspired the design and mandatory use of the Gaiola - technology that became such a compelling part of Lisbon’s subsequent rebirth.”

All over the world, there are vernacular typologies that have survived earthquakes and eventually developed a local seismic culture but were not “designed”. The Pombalino structures are the first recorded/designed earthquake-resilient building, after the Lisbon earthquake of 1755. The design of structures was based on the traditional framing system known as “Gaiola”.

When the other vernacular seismic resilient typologies from Italy, Greece, Iran, Pakistan, and Turkey were studied (refer literature review), structurally the pol houses are found similar to the Hatil typology found in Turkey. But when studied at the wholistic and settlement level there are parallels between the Pombalino structures and pol house settlement. Also, it is important to identify the earthquake-resistant features in a pol house while comparing it with the ‘designed’ earthquake resistant structures as no records mention that pol houses were designed as seismic resilient.

A comparative analysis would help to corelate the conservation issues faced by both the typologies and would help in formulating the strengthening and conservation measures as discussed in the case study 2 (Chapter 4, section 4.3.1).

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Parameter Settlement pattern

Pombalino structures

Pol houses

Pombalino Houses

Pol Houses

Lanes

Lanes

The houses share common orthogonal masonry walls. They are grouped together in a grid plan.

The houses share common orthogonal masonry walls. the planning of settlement is organic.

World heritage

Historic city of Lisbon is on tentative Old city of Ahmedabad is a world world heirtage list (UNESCO, 2017) heritage city (UNESCO, 2016)

Age

Dates to 1755.

Seismic resilient Design

Materials

The settlement pattern is evident from the sultanate period (15th century).

Designed as a seismic resistant There are no records available which structure post the great Lisbon mentions about the seismic resistant earthquake. design. Hence considered as nondesigned structures. The good performance in 2001 Bhuj earthquake highlights the seismic resilient properties.

Timber frames and masonry Timber and masonry

Figure 104 Timber frame, Source (Cardoso, Lopes , & Bento , 2004)

-

Figure 105 Timber lacing, Source - (Modan, 2006)

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Parameter Structure

Pombalino structures Composite structure with predominant masonry on ground floor and timber frame cage with masonry infill on the floors above.

Timber frame gaiola

Pol houses Composite structure with predominant masonry with timber lacing on ground floor. The floors above have timber partition walls.

Timber lacing, beam and columns

Masonry wall adjoining the other house Complete masonry structure with vaults

Figure 106 Pombalino structure, Source Author

Number floors Roof structure Floor

of 3 to 4 floors

Masonry wall adjoining the other house

Figure 107 Pol house structure, Source Author

3 to 4 floors

Sloping roof with timber joists and clay tiles as roof covering.

Timber floor with joists and floorboards. The floor diaphragm is only breaking for the staircase well.

Floorboards

Sloping roof with timber joists and tiles as roof covering.

Composite floor with timber joists, floorboards, and brick bat coba. The floor diaphragm breaks for the courtyard.

Brick bat coba

Timber joists

Figure 108 Pombalino flooring detail, Source - Author

Timber joists

Floorboards

Figure 109 Pol house flooring detail, Source Author

Type of walls Stone or brick masonry with the Flat brick masonry with rubble core rubble core and lime mortar. and mud lime mortar.

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Earthquake resilience of Pol houses in Ahmedabad

Parameter Conservatio n issues

Pombalino structures Pol houses • Lack of maintenance • Lack of maintenance • Increase in number of floors • Insensitive demolition and reconstruction • Insensitive changes in the existing structure.

• Use of incompatible materials for reconstruction and repair • Cracks due to ground water works level change.

• Damaged roof leading to • Damaged roof leading to water infiltration. water infiltration.

Figure 111 Pol house conservation state, Source - Sarjan Dalal 2020 Figure 110 Pombalino building state, Source - (Carlos, et al., Lisbon: Downtown’s reconstruction after the 1755 earthquake, 2015)

5.4 Analysis of restoration projects In the restoration of Tankshal ni haveli, the front part was retained and restored the way it is. The rear part was completely a new construction in R.C. The floor height was maintained as deciphered from the remains of the previous timber floors. However, the structure was restored as two separate structures which would act as separate entities during a seismic event. As mentioned by Ar.Khushi Shah (site in charge for the project) the main rationale for choosing modern R.C. material was the adjacent building which was constructed in R.C. Also, the archival records that mentioned the original planning of the structure were missing.

The front portion flooring was stabilized by using R.C. in place of original brick bat coba.

The presence of new R.C. flooring would change the floor diaphragm, and there is a possibility of wall peeling due to outward thrust, during a seismic event. For example, as Ferruccio Feerrigni in his study of retrofitting of the traditional structures explains the 110

Earthquake resilience of Pol houses in Ahmedabad

phenomenon where the floors were retrofitted as R.C. that resulted in complete collapse of the masonry walls. (Figure114)

Figure 112 "peeled" walls in Italy due to change of floors to R.C. Source - (Ferrigni, Vernacular architecture: A paradigm of the local seismic culture, 2015)

The roof of the front structure was rebuilt as wooden truss. The original roof structure was a partial truss which was not supporting the rafters effectively.

Currently Tankshal ni haveli is again vacant from past six to seven years due to issues of ownership. Lack of maintenance would make a restored structure vulnerable to damage in near future.

In the restoration of Deewanji ni haveli the approach for critically understanding the structure is evident, as there is addition of columns, post tensioning of masonry walls and reconstruction of floors. The addition of column will redistribute the loads from upper floors and will prevent further sagging of the beam. Post tensioning in the masonry walls would cause compression and increased stiffness. The increased compression would help by increasing the shear strength of the material.

The change of floors from brick bat coba to concrete foam would reduce the floor weight but is still an experiment, in terms of durability and seismic performance. There is a possibility of wall peeling in the masonry walls. Also, the reduction of load will be accompanied by some (limited) upheaval of the structure. More importantly, reduced dead 111

Earthquake resilience of Pol houses in Ahmedabad

loads can be beneficial as the inertial mass will reduce, and hence the earthquake effects.

But precompression available due to the deadloads, can be beneficial in load-bearing walls, and contributes to shear resistance. On the capacity side, reduction of dead loads will imply reduction of resistance also.

5.5 Survey Analysis of Pol house residents

Figure 113 Disaster management cycle. Source -. Arun Menon

The telephonic survey was conducted with the residents of pol (refer chapter 3). The situation of pandemic was a limitation in conducting an ample number of interviews. The current data analysis is based on detailed telephonic interviews from 20 residents of Mandvi ni pol and around along with the observations from the NIDM workshop.

Memory and damage – The disaster management cycle (figure 115) has been understood by many researchers around the world, the cycle reflects the position of measures till the next disaster (earthquake) occurs. The event of earthquake has an immediate response through safety evaluation followed by short term counter measures like erecting temporary supports for 112

Earthquake resilience of Pol houses in Ahmedabad

the structures, which leads to the reconstruction phase. As the time passes the damaged structures are repaired, which is termed as the mitigation process. The reconstruction phase is followed by the capacity building phase which includes strengthening of structures through vulnerability assessment, that prepares the settlement/structures for a future disaster. The time cycles of the processes and measures are dependent on the occurrence of disasters (earthquakes). It is this time which has been corelated with the development of local seismic culture by Ferrigni as explained in Chapter 1. Sir Bernard Feildon in his book ‘Between Two Earthquakes’ describes – “Each earthquake must become another significant chapter in our growing body of knowledge. Repair and reconstruction after the last earthquake have to be studied. Lessons must be learned continually, and we must always be aware that we live Between Two Earthquakes.”

For the residents of Ahmedabad, the only earthquake to learn from is the Bhuj earthquake of 2001, which demonstrated the seismic resilient nature of the traditional pol houses. The earthquake before 2001 was in 1819 AD, which was 180 years before.

The specific interviews with the people who have experienced the earthquake of 2001, it was evident that today still there is a generation which has the exact memory of the event.

People were able to clearly describe the event and survival of the pol houses (figure 116).

They are aware of the inherent earthquake resistant properties in a pol settlement. From the survey it was evident that the houses which were abandoned in 2001, were the only houses that completely collapsed. There were only minor damages like cracks in wall.

Residents could come out of their houses while their houses were swaying due to earthquake, unlike the R.C. construction where people lost their lives due to sudden collapse of the entire structure.

Reconstruction – In the interviews conducted and the NIDM survey report it has been found that complete reconstruction with I sections as beams and columns, was the only suggested option for maintaining the house. Some people were guided by local contractors to demolish the house and reconstruct it. Due to lifestyle changes many people have sold their traditional houses or given to tenants. People are aware of the heritage grading, but owners of the graded structures do not know the process of restoration. Lack of money for repairing the

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house was identified as the major reason for complete reconstruction. Out of 20 interviews, it was one house which was being maintained with the traditional materials.

Heritage che! – When people explain about the construct of pol houses there is a strong association of pride with it. People recognize the historicity of the houses; they appreciate the intricate unique carvings and the good quality imported wooden beams, but the lack of awareness and funds limit them to maintain it.

Other hazards – Fire hazards were the major threat identified in the interviews and NIDM report. The main cause for the fire hazards is short circuiting in houses which are now converted to go downs. Another cause was the use of cigarettes by the go down night watchmen. Use of styrofoam as a false ceiling material is another major cause of fire hazard.

What next? – The survey conducted for the research is preliminary and beyond the scope of this thesis, it is required that extensive on ground primary survey is done to understand the issues and culture which can be then implemented at policy level. However, when the survey observations are correlated (figure 116) it is evident that ‘value’ for the heritage exists but the provisions, awareness, and funds for preserving the heritage lack.

Today the memory and experience of 2001 exists but as the region does not fall in the high seismic zone with frequent occurrence of earthquakes, the experience and knowledge will be lost soon. It is this experience and memory of survival of these old houses which has potential to manifest in the conservation of heritage of Ahmedabad and importantly preservation of vernacular techniques.

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Earthquake resilience of Pol houses in Ahmedabad

Figure 114 Representation of survey observations, Source – Author

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Earthquake resilience of Pol houses in Ahmedabad

6. Conclusions The chapter aims to draw inferences from the analysis (chapter 5) based on the four case studies (chapter 4) and their interrelations. It also attempts to correlate the principles of conservation, authenticity, and integrity with seismic retrofitting and structural strengthening. The chapter concludes with the way forward and scope of the GNDT method and other approaches that systematically (Qualitative and Quantitative) assess the structural materials, configuration, details and state of maintenance to understand the vulnerability of pol houses at the settlement level.

6.1 Critical structural health parameters The vulnerability assessment using the GNDT method highlighted four parameters that are critical for the structural health of the pol houses, hence any conservation/restoration of pol house must not compromise on these critical parameters identified. The four critical parameters are as follows – 1. Shear wall area of orthogonal walls and masonry cross walls, quality of the material.

2. Orthogonal connections 3. Height regulation 4. Conservation state The other crucial parameters are floor structure, courtyard structure, and roof connections.

The floor structure is composite (timber and bricks), due to which the behaviour is partially deformable during a seismic event. It is recommended that until and unless there is major damage the flooring material should not be altered. It should be assured that the courtyard has an independent structural system, and if not tie members and columns can be introduced. The typology demands a better connection for the roof system, which can be assured by a truss.

Figure 117 summarizes the critical parameters with the specific construction details and the possible defects.

As mentioned in the analysis the pol houses have inherent structural features that contribute to their good seismic performance. These inherent features are determined by the critical parameters. Post identification it is important to formulate the conservation as

116

Earthquake resilience of Pol houses in Ahmedabad

well as strengthening technique to be adopted by accessing the conservation principles such as authenticity (refer section 6.2).

The critical parameters in this research are determined at the individual level. It is also important to study the structures collectively at the settlement level, which is a complex study and beyond the scope of this research. The vulnerability and structural understanding can be established by analysing the changes such as construction in R.C. between two traditional timber houses or by a change in façade projection (Figure 118)

117

Earthquake resilience of Pol houses in Ahmedabad

Figure 115 Identification of critical parameters and possible strengthening measures, Source - Author

118

Earthquake resilience of Pol houses in Ahmedabad

Damages due to lack of Alignment

Damages due to height changes in a row.

Damages in the corner house Figure 116 Damages at settlement level, Base source - (Polimi, 2010)

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Earthquake resilience of Pol houses in Ahmedabad

6.2 Authenticity and Strengthening The discussion here correlates the aspects of authenticity with the structural parameters.

Identification of critical parameters is not enough to proceed with the decision of intervention. Hence, concluding the thesis without addressing on the core concept of authenticity would be incomplete. The discussion here aims to introduce the way forward for approaching the conservation project.

Many scholars and researchers have interpreted and refined the concept of authenticity from the NARA document of 1994. According to Jukka Jokhilehto – “Authenticity can be understood as a condition of the heritage resource, and can be defined in the artistic, historical and cultural dimensions of this resource. These dimensions can be seen in relation to the aesthetic, structural and functional form of the object or site, in relation to its material and technology, as well as in relation to its physical and socio-cultural context.”

Authenticity is based on the concept of truthfulness while conserving a structure. It can also be understood as the manifestation of the values associated with the heritage structure. The set of authenticity criteria is defined by 5 parameters (Alho, Morais, A., Mendes, J., & Galvão, A. ) – 1. Material/substance 2. Design 3. Worksmanship 4. Function/use 5. Setting However structurally the authenticity is function of three elements (Attar, 1991)1. Authenticity of materials 2. Authenticity of construction system 3. Authenticity of construction methods The important discussion that emerges here is how much ‘change’ while conserving the structure is ‘authentic’, which respects the values associated. The question is more significant when the intervention is structural like strengthening the existing elements.

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Materials

The material used in original or period construction Basic elements of historic property

Ability of structure to carry its own weight and other imposed loads

Strength Construction System

Authenticity

Assemblage of materials that combine one or more building elements and ultimately a complete structure

Structure

Durability Construction Methods

Techniques, tools and process used to prepare and assemble material and systems.

Function of the useful life of a material or system over time

Figure 117 Functions of authenticity and strength and durability, Reference source - (Attar, 1991)

Any conservation program will include certain degree of intervention30. For structural intervention there are four broad categories in order of increasing intervention – 1. Stabilisation 2. Consolidation 3. Restoration 4. Reconstruction

Figure 118 Stability v/s Authenticity graph, Source - (Attar, 1991)

The theoretical graph here represents the relation between stability and authenticity. The point of intersection is the ideal condition for balancing the two, which is restoration zone.

However, this approach is introduced here to highlight the fact that while doing structural 30

Intervention - Intervention is the physical work per- formed on an historic property as part of its conservation program. It can be as simple as routine mainte- nance or as complex as complete re- construction.

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restoration it is equally important to analyse the concept of authenticity for the particular structure. Impact assessment forms are used to roughly help the conservation architects and engineers for the same. (Appendix 2) Hence it is important that both the concepts are studied together before any intervention.

6.3 Vulnerability Assessment at settlement level The introduced rapid visual survey using GNDT methodology for pol house typology is a construct for both at individual as well as settlement level for assessing the damage for a specified intensity, the cases here are pilot project examples for executing the vulnerability analysis. The method can be used at the pol settlements to determine and critically schedule and plan the conservation strategies for protecting the structures. The vulnerability assessment could be then corelated with the grades of the structures for executing the interventions. GNDT is one of the methods that has been adapted, more appropriate rapid visual assessment approach suitable for pol houses can be evolved with further research.

Figure 119 Vulnerability assessment at settlement level (conceptual), Source – Author

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Earthquake resilience of Pol houses in Ahmedabad

6.4 Overall conclusion and way forward The good performance of pol houses in 2001 was an experience learning of the seismic resistance characteristics. The study identifies those critical structural parameters responsible for the good performance, therefore the health of theses parameters should not be compromised during the conservation process. The comparative analysis highlighted the strengthening measures which reduces the vulnerability. The introduced methodology of vulnerability assessment for the pol houses is a way forward towards a new direction in research that can eventually determine the “preparedness” of Ahmedabad, a world heritage city, which is the driving research question of the study. The survey analysis addressed the on-ground issues and the earthquake memory in the residents of the old city. It also pointed towards the contradiction between the high value association and complete reconstruction. As the onsite visit was a limitation with the study due to the covid19 pandemic, the future researches must conduct intensive surveys to correlate the conservation methodology and concerns that the residents have, only then structured policy level decisions can be established.

The topic of earthquake resilience of pol houses has been studied through qualitative, quantitative, comparative, approach, and survey-based analysis in brief. The study has the potential for onsite survey of structures, damage assessment, vulnerability mapping at settlement level, development of conservation guidelines, disaster mitigation strategies, policy level changes, structural modelling for pol houses and community awareness.

The research also establishes the significance of the multidisciplinary approach for structural conservation, by bridging the gap between the numerical calculations and architectural drawings. It put forwards the importance of structural understanding for a conservation architect.

So, “will the pol houses survive” is completely in our approach of understanding the vulnerability!

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