Close
About
FAQ
Home
Collections
Login
USC Login
Register
0
Selected
Invert selection
Deselect all
Deselect all
Click here to refresh results
Click here to refresh results
USC
/
Digital Library
/
University of Southern California Dissertations and Theses
/
Behaviour of hipped roof dwellings in response to wind forces: A comparitive study of thatch against conventional roofs
(USC Thesis Other)
Behaviour of hipped roof dwellings in response to wind forces: A comparitive study of thatch against conventional roofs
PDF
Download
Share
Open document
Flip pages
Contact Us
Contact Us
Copy asset link
Request this asset
Transcript (if available)
Content
BEHAVIOUR OF HIPPED ROOF DWELLINGS IN RESPONSE TO WIND FORCES: A COMPARITIVE STUDY OF THATCH AGAINST CONVENTIONAL ROOFS by Shina Mehta A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF BUILDING SCIENCE August 1992 UMI Number: EP41428 All rights reserved INFORMATION TO ALL U SE R S T he quality of this reproduction is d ep en d en t upon the quality of the cop y subm itted. In th e unlikely ev en t that the author did not sen d a com plete manuscript and there are m issing p a g es, th e s e will b e noted. A lso, if material had to be rem oved, a note will indicate the deletion. Dissertation Publishing UMI E P 41428 Published by ProQ uest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQ uest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United S ta tes C od e P roQ uest LLC. 7 8 9 E ast E isenhow er Parkway P.O . Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 use ©ARCHITECTURE APPROVAL FOR FINAL TYPING This thesis, written by . ,.,£h\n*.. Mdfoy. under the direction o f h .................. Thesis Committee, and approved by all its members, has been presented to and accepted by the Dean o f The School o f Architecture, and is ready fo r final typing, in partial fulfillment o f the requirements fo r the degree of A ta V te /: .c * f. Dean Date &/*/0*- > \ j f s * ^ 2 . M 4 9 & 3 7 5 7 J /.# £ THESIS'/COMMITTEE Chairman V . ' < n r C O C i S O c n < 1,59 < • * » > » * 2S 5 S O tv n f Sm itherTi C a lifo rn ia S rh n n I n f A rrhitertnr** W a tt H a ll 904. I nc AtktaW C a lifo rn ia Qnn«Q.09Q1 ^91 74.0.9793 I?ov ^91 74.0.«ftfi ACKNOWLEDGEMENTS ii I am grateful to the School of Architecture, University of Southern California for giving me an opportunity to carry out this work. My deepest respects and thanks to Prof. G. G. Schierle, Prof. Pierre Koenig, and Prof. Dimitri Vergun for their valuable guidance and time. My special thanks to Prof. Pierre Koenig without whose help and cooperation none of this would have been possible, and to Prof. Goetz Schierle not only for his guidance for this work but for his support and help in the entire duration of this program. My deepest heartfelt respects to my Mother and Father who gave me an opportunity to come to the other side of the world and carry out this work, and also to Srinivas Rao who laid the foundations to this work. TABLE OF CONTENTS iii I Introduction 1.1 Introduction 1 13 Understanding Cyclones 2.0 Understanding Cyclones 3 2.1 Cyclones in the North Indian Oceans 5 2.2 Movement of Cyclones and Coastal Affects 9 2.3 Storm Wave 13 2.4 Hurricane Prediction and Preparedness: A Brief History 14 HI Cyclone Management: A Discussion 3.0 Cyclone Management: A Discussion 16 3.1 Cyclone Planning and Management 17 3.2 Emergency Shelters 20 3.3 Notes from the ARTIC Seminar 21 3.3.1 Temporary S helter 21 3.3.2 Permanent Housing 23 3.4 Analysis 23 3.5 Rural Settlements 28 IV Case Study: The Andhra Cyclone 4.0 The Andhra Cyclone 31 V The Hipped Roof: An Empirical Study 5.0 The Hipped Roof: An Empirical Study 35 5.1 Objectives of the Study 35 5.2 Methodology 35 5.3 Assumptions 38 5.4 Configuration 38 5.5 Opening Variations 46 5.6 Nature of Overhang 5.7 Permeability and Nature of Roof 5.8 Thatch Roof Dwellings 5.8.1 Construction 5.8.2 Behaviour 5.9 Failure of a Thatch Roof Dwelling 5.9.1 Simulation Model 5.10Graphic Computer Simulation Selected Bibliography Appendix A Analytical Graphs for Opening Variations Appendix B Excerpts from Study done by Srinivas Rao Appendix C Bamboo B .l Introduction to Bamboos B.2 Physical Characteristics B.2.1 Dimensions B.2.1 Splitting B.2.3 Durability B.2.4 Moisture Content B.2.5 Weight B.2.6 Strength B.3 Uses of Bamboo in Building Construction B.3.1 Tensile Strength B.3.2 Compressive Strength B.3.3 Diagonal Tenson Reinforcement B.3.4 Bond B.3.5 Permissible Stresses B.4 Earthquake Resistant Construction Appendix C Conversion Table From In. of H2O to psf. 1 CHAPTER I 1.1 Introduction Shelter is a man's basic need. Those who live through the torrential rains, the cold nights and the scorching heat of midday in tropical and subtropical regions know that shelter is as important there as in arctic and temperate climates. A man's home is still the center of family activities; providing facilities for cooking, sleeping, personal hygiene, and protection from animals and the elements. It is this shelter which is the destruction and also in many cases the causes of more destruction of life and property. To make the shelter per the lifestyles of the dwellers, climate, and geographical location is true Architecture and not the other way around. When the geographic location is on a coast which is subject to severe cyclones every year, then the climate becomes an important factor in the lifestyles and shelters of the people. This is the story in areas of Bangladesh, and West Bengal, Orissa, Andhra Pradesh, Tamil Nadu, in coastal east India. Any attempt to tackle this problem, all three issues mentioned above, culture, climate, and geographic location must be considered equally and understood properly. What is happening today is contrary to the above. These issues have been discussed in a study done by Srinivas Rao. This study is a continuation of the work done by Rao (Summarized in Appendix B) and is intended as a reference guide to carry out further research in specific issues and to stimulate interest among people to undertake further studies in this task which may save millions, year after year. It is my sincere 2 attempt to see that this work along with Rao's work acts as a thumb rule guide for actual construction. Details for construction and some data about the properties and uses of bamboo have also been compiled to aid in reference. This is accomodated in Appendix C. CHAPTER H 3 2.0 Understanding Cyclones A Cyclone is climatic disturbance or a phenomenon. Climate, by the very nature of the word, implies longevity. We attribute a permanence to climate by relating climate as a particular property of a geographic location. But climate, like the geographic location, is in a state of flux, however, at perhaps a much faster rate than the geological changes that cause changes in location. The implication of permanence to climate is therefore erroneous and should be corrected to imply the various temporal scales of change (Ferrar, 1976: 43-44) Climate changes as a function of the following natural phenomenon: * The orientation of the earth with respect to the solar system (the tilting axis) * The interaction of the earth with the interstellar space (influence of meteor dust). * The internal action of the earth (volcanic dust). * The more timely but less familiar sea-air tele-connections that cause moving * perturbations. * Anthropogenic effects(Ferrar, 1976:43-44). The nature of wind is complicated and depends among other things on: * The difference in heating of the surface of the earth by the sun; * The differences in absorption of this heat by different areas of the earth, especially as between land and water; 4 * Natural obstacles to the free flow of the wind such as continents and mountains; * The rotation of the earth. If the surface winds in a cyclonic whirl exceed 120 km per hour (64 knots, 75 mph or Beaufort force 12) this storm is called a hurricane in the western Atlantic, a typhoon in the western Pacific or sometimes just a cyclone (in the Indian Ocean). In order to obtain simple guidelines for better design against strong winds, a brief description of those characteristics of tropical storms that may have an impact on the design compiled by Rao is reproduced here. All tropical storms/cyclones develop....... the rotation of the vortex in counter-clockwise direction in the northern hemisphere. over water whose temperature exceeds 27 C (80 F). in areas of relatively low pressure. approximately between latitudes 5 and 30 in both hemispheres. between July and October in the northern hemisphere. speeds > 120km/hr with diameters of 15km. in the early stages and 80- 250km when fully developed. an effective area of impact measures a diameter of 800km. winds > 160km/hr near the center, sometimes up to 320km/hr. speeds of disturbance > 160km/hr, with the rate of movement of 15-30 km/hr. a tendency to drift westward with the prevailing trade wind after maturity and also come under influence of westerlies @ 30, when there is a curve with an increase in the speed pf 80-100 km/hr. a tendency to lose intensity and strength when striking land (more so if rugged — even small islands) reducing to about 50 km/hr. within 24- hours. rising wind speeds toward the innermost portion and abruptly changing to light breezes to calm winds in the center called the "eye", with a diamter of about 25 km.(see figure (i)). a reduction in the atmospheric pressure (60-100 millibars) with a rise of the water level, called the 'storm surge'. This, along with the wind driving sea water inland(when the cyclone approaches the land), hard-breaking waves and the astronomical tide may raise the water level by about 5-14 meters (Rao, 1991:77-78). 2.1 Cyclones in the North Indian Oceans* Cyclones in the North Indian oceans are not infrequent. In these parts of the world, cyclones are called depressions, cyclonic storms or severe cyclonic storms depending on whether the maximum wind speed is less than 34 knots, between 34 konts and 47 knots, and greater than 47 knots respectively. On the average about 13 cyclones of all intensities form in the Bay of Bengal per annum, while only two cyclones occur in the Arabic Sea. The total number * All the Data and Tables on "Cyclones in the North Indian Oceans" is from "Seminar Report: Problems & Lessons from the Andhra Pradesh Cyclone", published by ARCTIC, Vijayawada (A .P., India). Figure (i) is compiled and reproduced from Sinnamon and van't Loo's "Cyclone-resistant Rural Primary School Construction - A Design Guide", published by UNESCO. A tf .A WITH W IN D S P E E D S t X C l & D I M O 1 2 0 K M pte hoc*. AREA WITH HEAVY RAIN FALL D IR LC TtO N OF UHND w CHARACTERISTIC FEATURES OF A NORTHERN-HEM ISPHERE CVCLONIC STORM SBCTiON THL PHLMOME.KIOW O f W /IMD RAINFALL AND AIR FLOW IN A CYCLONIC STORM EYE O F THE STORM o w z , MAIM AK.EAS OF ORIGIN AMD MAIN T FAC ICS OF TROPICAL CYCLONES h (km) Eye wall ^ 0 25 200 500 K (km) F igure (i) Structure of a hurricane. 7 CYCLONIC DISTURBANCES (CD)CYCLONIC STORMS (CS) AND SEVERE CYCLONIC S T O R M S ( S C S ) THAT HAVE OCCURRED IN THE BAY OF BENGAL AND ARABIAN S EA IN DIFFERENT MONTHS IN HUNDRED YEARS ( 1 8 7 7 - 1 9 7 6 ) JAN 5 FEB MAR APR MAY JUN JUL AUG js E P I OCT NOV DEC 1 I ... .. 1 ...................... B A Y OF B E N G A L C D 1 G 4 S 2 a 8 3 Jl 2 7 18 2 , 3 0 20 5 178 1 4 5 77 13 3 5 c s* 5 1 4 20 4 3 42 48 30 4 4 7 G 8 8 4 2 4 4 9 5 C 5 1 1 2 3 3 2 4 7 3 1 G 29 4 3 18 1 G 5 A R A B I A N S E A C D 5 - 1 8 3 3 4 O 1 G 4 1 G 4 5 4 3 1 1 1 3 7 C S* 2 - - G 23 20 S I ^ 7 22 2 G G 1 1 9 SC 5 - -- — 4 14 3 1 I - • 2 t O . 18 2 G O * C S - CYCLONIC STORMS INCLUDING SEVERE CYCLONIC STORMS. F ig u re (ii) of cyclones of all intensities or cyclonic diaturbances as well as cyclonic storms and severe cyclonic storms occured in the last one hundred years in the Bay of Bengal and Arabian Sea are given month wise in figure (ii). In the Bay of Bengal the frequency of cyclonic disturbances is maximum in the month of September and least in February. On the other hand in the frequencies of cyclonic and severe cyclonis storms show double maxima. The primary maximum is in November while secondary maximum is in May. However, it should be noted that the frequency in October is higher than that in May. About 60% of the cyclones in the pre-monsoon (April-May) and 50% in the post-monsoon (October-November) seasons develop into intense systems while only 20% in the monsoon sesson (July-August-September) become intense. The disparity in the proportion of more intense systems is much greater. In the Arabian Sea the frequencies of cyclones of all intensities as well as that of intense systems show double maxima of equal magnitude - one in May-June and the other in October-November. The former maximum is due to the cyclones that originate in the Arabian Sea itself while the latter is mainly due to redevelopment of Bay cyclones in the Arabian Sea after crossing peninsular India. It may also be noted that unlike the Bay of Bengal, a greater percentage of these disturbances, about 60% on the average over the year, are intense cyclones. The cyclonic activity is least in the months of February, March and August. 2.2 Movement of Cyclones and Coastal Affects Tropical cyclones move generally to the west-northwest initially and northeastward later. This change in direction of movement is called recurvature. Tropical cyclones, therefore being of oceanic origin generally hit the east coast of the continents.If the recurvature takes place over the ocean a cyclone would hit the southern of western coasts. The usual attacks of tropical cyclones in the Bay of Bengal and Arabian Saea are presented in figure (iii). Cyclones in the Bay during April and May generally move more nothward and take recurvature over the central latitudes of the Bay. They effect the North Orissa, Bengal, Bangladesh. During the monsoon season a series of low pressure systems come from the Far East and develop into cyclones over the head of the Bay and move west-northwestward affecting mainly the Orissa coast. In October and November cyclones either form or develop over the southeastbay of the Bay of Bengal and some of them move west-northwestward and cross the peninsular coast, some show a tendency to recurve over the west central part of the Bay and cross the central and northern parts of the east coast of India, while some take a complete recurvature over the Bay and effect the Bangladesh and upper Burma coasts. In December also cyclones form over the southeast Bay and some west- northwestward affecting the southern peninsula; while some recurve and hit the Burma coast. In January and early summer, occasional cyclones affect the extreme south of peninsular India. M *r S E P T E M B E R J U L Y N O V E K S E R U SUAL TRACKS OF TOPICAL CYCLONES IN THE NORTH (NOiAN SEAS. Figure (iii) o 1 1 Cyclones in May and June form over the east Arabian Sea and move mainly north-northwestward. Some of them recurve and effect the Kutch and Gujarat coasts. In the post-monsoon season some of the Bay cyclones cross the peninsular India and redevelop over the Arabian Sea. Some of them recurve and affect the northern parts of the west coast of India. However, the number of cyclones that effect the west coast is very small compared to the number that hit the east coast. The number of cyclonic and severe cyclonic storms that have crossed the east coast in different latitudes in different months during a period of one hundred years (1877-1976) is given in figure (iv). The total number of storms that have crossed the east coast, including part of Bangladesh, is 327; out of which 100 were severe cyclonis storms. The frequency is highest over north Orissa and Bengal in the latitude belt 21-22 degrees N where the length of the coast is also longest. Nearly one-third of the total cyclonic storms and one- fourth of severe cyclonic storms affect this part of the coast. Most of the activity is confined to the period June to September. A second maximum occurs in the vicinity of Machilipatnam (Bandar) in the latitude belt 16-17 degrees N. On the average the frquency works out to one cyclonic storm for every five years and one severe cyclonic storm for every 17 years. A third maximum is present south of Madras in the latitude belt 12-12 degrees N. In fact the frequency is large and fairly uniform over most of the peninsular coast (10-14 degrees N). 12 SEVERE CYCLONIC ST O R M S/C Y C L O N IC STORM S INCLUDING SEVERE CYCLONIC STORMS THAT CROSSED THE EAST COAST OF INDIA IN DIFFERENT LATITUDE BELTS IN HUNDRED Y E ARS 0 8 77 - 19 7 6 ) A ND THE AVERAGE RECURRING PERIOD OF A SEVERE CYCLONIC STORM. a v ETr a c L . R E C U H U IN C PERI --Q D _Q F _A . (5 C 5 )_ L A T - 2 3 - OEC AUG S E P OCT NOV JA N -E D MAR APR MAY JU N J U t - 2 2 /n o - 21 - % 2 -2 0 24 -19 -10 20 -17 22 50 20 - 1 3 - \ l I -1 2 / 2 50 50 TOTAL 1° % 27 F ig u r e (iv ) 13 There is practically no storm activity on the east coast, south of 18 degrees N during the monsoon season while in the post-monsoon season it spreads to the whole of the coast making any part of the coast vulnerable to cyclonic damage. 2.3 Storm Wave The principal dangers from a cyclone are gales and strong winds. Water piles up against the coast, hence storm surges occur to the right of the places where a cyclone hits the coasts. When the cyclone is a very intense one, the surge is very strong and occurs close to the center where the winds are strongest. The magnitude of the surge or tidal wave also depends on the coastal configuration, the near shore bottom topography as well as the speed and direction of motion of the cyclone. A cyclonic storm in favourable areas can cause a tidal wave of more than lm height, while a severe cyclonic storm can cause a wave of more than 3.5m. Tidal waves caused by cyclonic storms of severe intensity are devastating in some areas. It is found that it is not just these phenomenon themselves but their interaction with human settlements that constitutes disaster. The rehabitilation of economic life and restoration of the civic and social life need staggering resources and the damages to these are found to be large. The vulnerable community is generally able and willing to tolerate flooding to some extent after having come to terms with the problem after years of experience. Nevertheless, the intensification of the flood plains occupation and its growing importance to 14 the social and economic welfare of a region have added new dimensions, and there is an increasing demand for protection in these areas. 2.4 Hurricane Prediction and Preparedness: A Brief History For centuries hurricanes have caused great destruction. There was always an attempt made by man to somehow know beforehand when a hurricane or a cyclone was going to hit. In ancient times probability predictions and astrological predictions were done in order to meet these needs. Today however, due to modern science and positivistic attitude of the modern people, there is less faith and belief in these practices. The first hurricane warning system was setup in 1898. A fleet of ships stationed off the American coast. But for decades meteorologists had no way to track storms far out at sea. During World War II, American ships in the pacific were caught unaware and battered by typhoons. 1944 saw a whole new era in hurricane tracking using a powerful new tool-the radar. Military cruisers began flying into hurricanes to determine their strength and direction. While better tracking could save lives it could not protect vulnerable coast lines from spiralling property damage. In the early 1960's scientists believed they had an answer. It was wondered "if only the force of the hurricane winds could be reduced, the death toll and damage could be greatly lessened." The way was "Project Storm Fury", an active assault on the hurricane. It was a joint project of the U.S. Department of Commerce and the U.S. Department of Defense. A fleet of planes would drop Silver Iodide into hurricane clouds, ice crystals would form disrupting the storms delicate heat balance and sapping its strength. But there seemed to be too many assumptions involved and the project saw no succesful results. Henceforth scientists returned to the age old method of hurricane tracking. Today sattelites give us pictures showing the location of the hurricane at various points in time. But the possible track it may follow is still left for the human mind to comprehend. CHAPTER n i 16 3.0 Cyclone Management: A Discussion India is the seventh largest country in the world. It is well marked off from the rest of Asia by mountains and the Sea, which give the country a distinct geographic entity. Bounded by the great Himalyas in the north, it stretches southwards and at the Tropic of Cancer, tapers off into the Indian Ocean between the Bay of Bengal on the east and the Arabian Sea on the west. It covers an area of 1,284,087 miles (32,87,263 sq.km). Lying entirely in the northern hemisphere, the mainland extends, between latitudes 8 4' and 37 6' north and longitudes 68 7' and 97 25' east and measures about 2009 miles (3,214 km) from north to south between the extreme latitudes and about 1833 miles (2,933 km) from east to west between extreme longitudes. It has a land frontier of about 9500 miles (15,200 km). The total length of the coastline of the mainland, Lakshadweep group of Islands and Andaman and Nicobar group of Islands is 4698 miles (7,516.5 km). There are 550,000 villages in India, with their prime occupation being agriculture. Natural disasters such a floods, cyclones, earthquakes cause large scale destruction to houses year after year in different parts of India. Floods . / pose serious problems in thickly populated states like Uttar Pradesh, Assam, j Bihar and West Bengal. The coastal districts of Andhra Pradesh, Tamil Nadu, \ * \ West Bengal, Orissa, etc., are susceptible to cyclones and storms. Hundreds \ I have lost their lives due to cyclones in India and property of unaccountable \ value has been lost. The loss of life and property in the coastal areas of the sub- 17 continent are caused by the direct and indirect effects of the high winds and the excessive rains. The winds cause buildings to be severely damaged or even to collapse. In addition, their are sometimes short circuits in the electrical system which start fires. Government has, in the past, adopted several strategies to counter this. 3.1 Cyclone Planning and Management In 1985, the attention of the Planning Commission was drawn towards housing and land use in disaster prone areas. It was decided that there was a need for evolving guidelines for ensuring proper land use in disaster prone areas j to minimise the damage and destruction and for evolving designs of low cost J houses which would be better resistant to the effects of natural calamities. The i working Group on Flood/Cyclone Management set up by the Planning j i Commission under the aegis of the Ministry of Agriculture and Rural j Development in connection with the formulation of the 7th Five Year Plan had j ! suggested that suitable designs for structures built in vulnerable areas J | particularly the coastal regions and cyclone shelters be developed. In pursuance 1 of this recommendation, the Ministry of Urban Development (the then Ministry V j of Works and Housing)set up a development Group (Task-Force) on Housing in J Disaster Prone Areas to go into various aspects of the problem and make / suitable recommendations in the matter. The Group after review and revision formulated these terms of reference: (i) study and analyse type of damage and destruction caused to houses j and small buildings due to natural disasters and review the technical measures including cost-effective construction techniques, methods and designs evolved by Research Institutes for putting up houses and small buildings that are more resistant to natural disasters and to indicate areas of further research . (ii) identify and suggest appropriate construction techniques, designs, building codes, methods, planning procedures, etc., to build new houses that are more resistant to natural disasters and to strengthen existing houses and small buildings that are considered deficient in this regard. (iii) formulate guidelines for siting and relocation of new houses with a view to framing suitable building regulations in areas prone to natural disasters. (iv) suggest specific areas for research and development work for housing in disaster prone areas. (v) evolve strategy for implementation of technology for housing in disaster prone areas including transfer of technology, dissemination of technical information, training etc. Such strategies, plans, and proposals have been carried out in various parts of the country. The approach adopted by the Government is extremely objective and far from reality. Even if it is made to be feasible it is seldom without affecting the other dimensions of life of that particular geographical area. In the previous study done by Rao, the philosophical, theoritical and practical inappropriateness of these methods in India was discussed at great lengths and it is suggested that the reader gets acquanted with the critical 19 reasoning behind rejecting this objective approach. The critical argument presented against this approach of the Government requires knowledge of Rao's discussion. This argument indroduces the basis of feasibility of the empirical know-how gathered in relation to wind effects on structures in the following chapters. Everyone is aware that the problem of Natural disasters exists, especially of cyclones in coastal India. For thousands of years it has existed and humankind has tried to fight, escape, or bow to it. There have been numerous factors involved in tackling this problem. The primary concern of any medicine, following a thorough diagnosis, is to have minimal or no side affects. Similar should be the case with this problem. Most solutions adopted today are such that they directly or indirectly affect, disrupt, mould, or strangle the natural process of evolution of that particular society or region. It is often to the extent that in course of time the very lifestyles, convictions, attitudes and also the political economy of the region is severly affected. This has been happening through the ages, both intentionally and some unintentionally. Solutions for such complex problems are often sought by a group or groups of highly qualified individuals who are "specialists" in that particular field (as a result of the current educational trend). These people are so specialized these days that aspects other than those concerned directly to their field of "specialization" are not visible to their qualified eyes and even if they do, it is not usually within their "scope". In fact solutions such as making concrete cyclone shelters in India are one of the root causes of the continued foreign debt (See Rao, 1991). The Government with a team of UN experts and other local specialists proposed concrete cyclone shelters in areas where they have never lived, for the people whom they have never known, let alone the aspects of language and culture. This chapter would very informally mention the work that has been already carried out by the Government and other agencies, and analyzing them critically, it shall lay groundworks upon which this empirical study would be based. 3.2 Emergency Shelter Regarding the need for emergency shelter, most people believe that all victims affected by the disaster need some protection from the elements immediately from the event. During the Andhra Cyclone of 1977, It was seen that options vailable for the construction of emergency shelter differed in the tidal wave affected and the wind affected areas. In the wind affected area almost all people (an estimated 90%) provided their own emergency shelter. Specific examples of how people found some emergency shelter included the use of temples, churches, schools, and public buildings; using salvaged materials and partially collapsed buildings; or moving temporarily to nearby villages. These observations made during the Andhra Cyclone leads to the conclusion that before helping agencies embark on a program of providing emergency shelter, they should better understand how people are providing for themselves. In the tidal wave affected area the total destruction of the villages and the fact that most building materials are washed away leads most people to believe that emergency shelter has to be provided from outside sources. The types of emergency shelters that are brought to notice generally are tents, 21 individual family structures of bamboo and palmyra leaves, and large communal structures also of bamboo and palmyra leaves. 3.3 Notes from the ARTIC seminar During a seminar on "Problems and Lessons from the Andhra Pradesh Cyclone" conducted by the Appropriate Reconstruction Training and Information Centre (ARTIC) in August, 1978 at Vijayawada, INDIA, it was noted that tents had very limited use. primarily by volunteers. In some villages it was found that the people preferred the communal shelters immediately after the disaster, but it was generally agreed that for a variety of social reasons single family structures were preferred. It was noted that the most common type of emergency shelter used was built by the residents themselves of bamboo nad palmyra leaves. Of all those used, this type of construction, and the method of doing it yourself, proved to be the most acceptable. The bamboos were left uncut so that they could be reused afterwards in the reconstruction of permanent houses. After discussing the different types of shelters provided it was the consesus of the participants that, as a general rule, outside agencies can best help to provide emergency shelter by distributing local building materials. 3.3.1 Temporary shelter The definition of "temporary shelter" was debated at some length, but the term was generally agreed to mean those structures which were built for the community to serve as interim shelters until replaced by permanent houses. Confusion arose from the fact that some agencies have classified the traditional 22 house as "temporary", although most participants thought that traditional houses should be defined as "permanent". The discussion of whether traditional houses were permanent or temporary lead the group to conclude that there was a difference in perception of the traditional house, as between villagers and the helping agencies. Villagers accepted the houses as permanent for they lasted many years although they were prone to wind damage. Many outside agencies, on the other hand saw traditional houses as having only a short life. Participants agreed that while most of the temporary shelters provided by agencies were appreciated by the majority of recipients, the temporary shelters provided may not always have been needed. Participants felt that if agencies had not promised to provide housing, the victims in many cases , would have rebuilt themselves without outside help. Examples were noted of villages which had not received temporary houses but which of their own initiative had rebuilt traditional-style houses. Examples were also given of villages which had not received temporary shelters, but in which the victims remained, apparently without initiative, in the emergency shelters provided initially. However, it was noted that this was due to the fact that the victims believed that they would not receive a promised concrete (pukka) house if they rebuilt of their own or accepted any alternative agency. The major lesson that was learnt from this was that the most effective way of providing temporary shelter was by providing locally known building materials, and by encouraging people to rebuild, improving their houses as best they could within the constrainsts imposed by their limited economic means. 23 3.3.2 Permanent housing As mentioned above the term "permanent housing" was used both for the rebuilding of traditional structures and for the construction of concrete houses. It was accepted that "pukka housing" should refer to concrete houses. In evey discussion group, participants suggested that the many promises by agencies to provide pukka housing in fact retarded a return to normality. Because of the promise that concrete housing would be built and given away free, people did not assume responsibilty for solving their own shelter needs. They believed that any action on their part might prevent them from getting the promised house. They simply waited for the outside agency to provide for them. The promise of pukka housing, reported to have come initially from a few voluntary agencies, set off a series of decisions in other agencies which could not be reversed for fear of losing face. Therefore, housing made immediately after the disaster, without time to assess the likely impact of intervention, caused serious long term problems. 3.4 Analysis In the notes from the seminar it is seen that a concern for self made shelter with available materials is realised. But unfortunately the definitions of temporary housing and permanent housing suffer a serious deficiancy of appropriateness and feasibility. In the past ventures by Governmental and other agencies to provide permanent housing (concrete in this context) have failed miserably. To understand this we must look at an example. 24 We shall look into the case of the Tultuli Hydro-Electric Project on the river Wainganga in Gadchiroli district of north-eastern Maharashtra, central India. The proposed dam was to have a submergence area of several hundred square kilometers. Hundreds of villages were in this submergence area. The people in that area are rural and are completely self sufficient with their major occupations being agriculture, handloom, handicrafts, etc. The villages had developed over several centuries and are models of perfection for that particular climate, geographic location, and culture. The Government built modern concrete and brick houses with all the modern amenities for their rehabilitation. To the dismay of the Government not even a single family or person agreed to move to the so thought "superior" housing. Millions of Rupees were wasted not only on the houses but for the whole project itself which was indefinitely postponed and popularly believed to be cancelled. One wonders at the reason for such a choice of these people. The problem lies with the educated elite who are the decision makers in India who little understand the values of these villagers. According to cost benefit analysis the economists still argue that their decision was correct and are therefore convinced that the villagers are being foolish. One must understand that accepting that offer would have moulded their very lifestyles which is the foundation of their culture. The meaning of progress for them is completely different. Similar is the case with cyclone shelters and schemes proposed by the government. In the following pages there are reproductions of some such schemes proposed by the Government. 25 c YcLoN eLje R I I V jaicn S|*m •navwp Ft9 * tj J fm tj Flfft, Syrtil «*rHS f L » » * a « « a * 7 4 * S v r t / r w * i . K 'M jH A * V * A > < * 4 ® JW|UM,U * K rc^ F aa *»• • c L a * » » « i ty * H * % u c h A * u « i q r . * 1 *. Figure (v) 26 £X£Lqmjz. . . . S h e L j e r /cmctiUftfn) 5cA \.B :iT otV ulc«l .t © 9 & * r * i V f i - f i H P W P F L o o f t / f l ^ f , -P L a N H IH G : F I oor Ar b a i . . . 0 0oo . . . . sat lift' (A«iA « = 1 :S |A J M » a « V J <Lft J*fMS3JA&L • A -c.c Framid e*H*n»c[-(o«. -clAooma i F fO nc © U *n h v w h ». j S i » A r . f • n t 1 , *x>,ooo. Figure (vi) 27 1 C Y c L o N E _ £ i i £ l j - & R - ScaLi L. t»ch« afrit; I u u j U U j UU I I 1 s 1 — — la2zq-_£U^A0^a_ -K ll'-o '— * t— «i*'---) . — (» -V ~ G p y o W H P FI o o r / F i ^ s j F I oqr { > L a,h H ¥ 1 G » - Floon Ahra< • *(* (t> 7o iy-Tl- M.IKJH A * * * ' «. . . (M 2 • • Pt»C.C<F AAMC D C o * » T a u c tio n * • C U t> 0 !» « » fcRtCH A (A (O N A y> . * B(. f,24»< , 0 9 0 * Figure (vii) 28 This study tries not to introduce new ways of living and building but tries to put back on track the derailed train of evolutionary construction. We shall try to briefly introduce the essence of Rural settlements. 3.5 Rural Settlements A typical village layout is irregular with no particular pattern or module (the term used very often by architects and forms the basis of design) and yet the cluster is so finely well knit with every use of space being appropriate without any deliberate attempt to incorporate the "positive" and "negative" spaces. It evolves out of its own and develops as and when required thus emerging with a distinguishing character of its own. Every concern is given to small yet essential feature for its existence considering the caste, culture , economy, social status etc. of that particular place. Out of this emerges the humbleness, innocence and intimacy of the village folk rarely found in so called planned towns and cities. Little does one realize the conciousness for cleanliness and their concern for it, for the simple reasons that it is a preconceived idea that all disasters root out from the unhygienic conditions prevailing here. Unlike urban areas land use planning measures which evolve avoiding mixing of residential functions with the productive ones and isolating by open spaces, regulating density of building and systems of connected open spaces would be disastrous. The majority of houses in the villages are traditional types which have evolved over a long period of time in response to the basic needs of the family, and to the climate, and can be built with locally and readily available natural (in 29 modem terms "cheap" building materials). They are constructed with a timber and bamboo frame, palm leaf roof, and mud walls. There are usually a few brick houses. During cyclones the traditional houses usually collapse, or the main posts break at ground level due to decay caused by termites and wet rot. During these periods the people take refuge in the temple which has always withstood the greatest of cyclones. Most villages have temples built out of stone on the highest ground, usually a hill. Most temples in coastal Orissa and Andhra Pradesh are out of Laterite. The practise of building temples has been discontinued in most places due to much publicized authenticity of modem materials. The age old skills of temple building are slowly dieing. The people build their houses almost every year, and this is itself a part of their annual activity. This enhances the health and hygiene in the village, keeps up the skill of building alive through generations and evolves organically year after year, generation after generation. Little effort is done today to understand the lifestyles of these villagers. Today to overcome problems, several simple low cost techniques with the help of locally available materials have been introduced and it has been realized that whatever it be, the ancient building code "Vastushastra" is of utter importance. Efforts have been made to retain the character of the traditional house but unfortunately these things sound more theoretical and in practicality, are no way near these "written" statements in all the reports carried out by foreign agencies who have a bare minimum of understanding of the complexities involved as regards the cultural and social aspects and the problems faced by an 30 average Indian family. The unintended effects of the so-called relief operations are least realized. CHAPTER IV 31 4.0 The Andhra Cyclone On November 13th 1977, a depression developed in the southeast part of the Bay. It moved westward and developed into a cyclonic storm by the 15th in the south central Bay (Figure (ix)). It further intensified into a severe cyclonic storm and moved into the southeast Bay by the 16th and showed a tendency to recurve. It did not , however, recurve but altogether changed its course from a west-northwesterly direction to a north-northwesterly direction. It crossed the Andhra Pradesh coast approximately at 16 degrees N-81 degrees E on the evening of the 19th and therafter it quickly dissipated. A ship caught in the cyclone reported a central pressure of 940 mb on the 17th but at the time of crossing the coast the central pressure appeared 980 mb. Machilipatnam reported a sustained surface wind of 67 knots at 17:30 hours I.S.T on the 19th. The eye of the storm appeared on the radar at Madras from the 17th night. The eye was nearly circular and had a diameter of about 37.5miles (60km). From the 19th morning there was a gradual decrease in the rain-area but a well defined circular eye wall continued to appear till noon. Therafter the echoes around the eye started gradually breaking. The cyclone moved at a speed of about 11 knots on the morning of the 19th but in the afternoon was reduced to 8 knots. Being a cyclone of high intensity, it caused a tidal wave of more than 10 ft (3m) height. The concavity 32 and the flatness of the near-shore sea-bottom to the east of the mouth of Krishna river added to the intensity of the tidal wave. The cyclone caused untold misery to lives and property. Approximately 7.1 million people in 2302 villages were affected. In the Krishna District alone the death toll was estimated over 10,000, besides loss of 2.31 million cattlle and 45.000 other live stock. The aftermath of the cyclone was that 4 million people were rendered homeless and 11,600 dead. 690,000 houses were destroyed or damaged. About 86,000 huts were compeletly washed away and crops comprising 1,184,000 acres of paddy, banana, tobacco, chillies, sudarcane, etc. worth Rs.450 crores in all were lost. Communication - railways, roadways, telephones, electrical installations, canals, etc. and storage buildings suffered substantial damage. The estimated cost of reconstruction and rehabitilation was of order of 300 million US $. More recently, the cyclone storm with wind speeds upto 150 miles per hour on May 9th and 10th 1990 resulted in huge loss of public and private property, though timely evacuation of about 650,000 people resulted in the human death toll being contained to less than a thousand. The damaged caused in single and multi-family houses, single/double storey apartment houses, small shopping centers and other such buildings can be summarized as follows. 1. The most vulnerable points in such buildings are: connection at the intersection of two walls, between walls and foundations, between wall and roofs and attachment of cladding or sheathing to wall or frames. 33 2. Rafters failed due to failure of anchorage in uplift or at connection details with the wall. 3. Roof coverings consisting of asbestos cement, clay tiles, asphalt shingles and mangalore tiles suffered great damage. 4. Walls failed due to their incapability to resist gravity as well as lateral loads. 5. Openings in walls create stress concentrations which may be critical particularly at the corners of the openings. 6. The projections at the eave levels are especially vulnerable to excessive upward pressure. 7. Buildings with flat roofs suffered excessive wind damage 8. Orientation of building is important. It was seen during the Andhra cyclone that one set of buildings survived, whereas the buildings at 90 degrees to this set collapsed. 9. Buildings that were located in valleys or surrounded by trees survived during cyclones except damages caused by uprooted trees. 10. Most of the RC cantilever sun shades collapsed. 11. Ancient stone masonry temples survived the Andhra cyclone of 1977. 12. People sought shelter in schools and Panchayat buildings, but in several cases such buildings proved to be very harmful because the rising column of water acted like a piston and blocked off air at the ceiling. This choked people to death. In some cases the buildings exploded. 13. A circular or a square plan constrained by L/W and H/W ratio was seen to have offered excellent survival probability compared to oblong or any other shape which exposes more surface area. 34 14. Roof coverings were the first casualty of the cyclone, but where such roof coverings were rigid, strong, well anchored and secured to the support, the walls on which they rested were damaged. 0 0 ° 6 0° Z O 2 0 Z O OF ZO 6 5* 7 0° O O * 9 5° TAMILNADU/ KARNATAKA AND ANDHRA PRADESH CYCLONIC S T O R M S OF. N O V E M B E R 1 3 7 7 . Figure (ix) CHAPTER V 35 5.0 The Hipped Roof: An Empirical Study Based on earlier studies conducted on the behavior of different Roof forms, the hipped roof was selected for further study. The idea was to test a thatched hipped roof as against conventional ones. Based on earlier observations, both in the testing laboratories as well as on the sight, the following was hypothesized: The Thatch Hipped Roof acts as a very efficient wind energy dissipator unlike any other conventional hipped roofs which resist wind forces by storing it as potential energy causing immense destruction when released. 5.1 Objectives of the Study * To evaluate the physical response of hipped thatch roofs under wind forces against other conventional hipped roofs. * To layout guidelines for construction in terms of configuration, and inter dependency of roof, walls, openings, overhang, and other such variables. * To carry out a study that is economically, socio-culturally, scientifically, and histo-graphically cogent and feasible. 5.2 Methodology The methodology adopted is predominantly empirical, using model testing in a wind tunnel based on philosophical groundworks laid down in the earlier studies. 36 As far as the roof of dwelling unit is concerned the factors influencing it's response to high winds depend mainly on the form which is defined by its elements and its material. Their are numerous variables between these two characteristics of a roof, namely: * the proportions of the element with respect to one another. * porosity (or permeability) of an element which may also be a function of the material. * the overhang of the roof which may depend on the nature of the overhang and also the nature of its material. * the interaction of one element form with another (wall with a ro o f) which may involve another variable as their material. All the above points have been brought together in the Figure (x) below which shows the scope of this study and also the study which was carried out earlier to some extent. .<H Ksis»^O O Fig;:»H » .M X M M X X X X X N X M M X . a .X K M X a a K a X H K X K .. .MKMVMBMKX*MBBBBX I « * a*MaMMB■M■XXXK. .X X X X X X M X X X X X M X K X X X I* X X X M X X X X X M X X X X X X . a « H X M K X M M X M M * M M M M W M . ■ «xaan > ax > IK K < «a a K X f c * 4 « X « IIX 1 IIIK )l)IX X X 1 |« « ll)'lir " - ’X M a X X M X X K X M N I X M H K M A * . DRM -«**»**x*aa*ax*xKMKXKxxxx*..< XKXMMXMMMMMMMKXMMxSaaxKaMaMK** *•****>«« a aa a a a a* a a» a a a a aa a a a * ,.aB£22222£2252222222222222££*2£*, '">l « » < x 2 S x £ S k 52S2S2£22222S222£22222S5^|8 .a*;222S52222"K*****-— I :3«r35555;55j«5^^ . x a n x m x t x a a i i , I 1 — x a a i — — ■ ■ !! I ■ — i1 .1 i . .... 1 1 * » 1 1 . »«»»«*» ■ a aa a a v 1 «j* a a ax xx ' c k n k m k x k m n m n x x ■ xaxaaxa dilslLE LE M E N TS js KaaMMaaxaiSr* ••*aa-'.;:x*xwaa» MxaxKBaaaxx* <axx.| -a a a a* a » aaaaaaaaaaa* «aaa:l > » a > » vxaaaa xaaaa <««al — • i l l i S l i ______ i ::::::::::5 "IN TER AC TIO N m i m .................JO IN TS MATERIAL POROSITY OVERHANG TYPE MATERIAL C overed in p r e c e e d in g stu d y by Reo To be c o v e r e d in t h is stu d y Figure (x) • C onceptual d iagram of S c o p e of th e study. 151 37 The study was found to be considerably complex. Since, it not only had to deal with innumerable variables but also had to keep an eye out for their interdependency. This later was realized to be more important than the variables themselves. The Figure (xi) shows a chart of the variables that were studied. HIPPED ROOF DWELLINGS I I ROOF WALL HEIGHT OPENING VARIATIONS 2.0 2.5 ANGLE OPENINGS NATURE OVERHANG LENGTH NATURE 20 STIFF FLUTED 40 45 (Concrete, Timber, (Thatch) Asbestos, G.I Sheets, etc.) Figure (xi) 38 5.3 Assumptions * In all the tests carried out, the material was mainly plexiglass unless otherwise stated. * Throughout the length of this study, emphasis was laid on relative dimensions of the walls, roofs, and overhangs rather than their actual sizes. The term "unit" throughout the study does not point to a specific unit, but it suggests the values that are relative and representing only ratios with respect to one another. However, ideally, 1 unit may be equal to 3.28 ft (1 meter). * Considering that 1 unit equals 1 meter, the scale of the model (unless otherwise stated was 1.6 inches = 3.28 feet (1 meter). * All tests were carried out under an average wind speed of 37m/hr (60km/hr). * All the readings were taken by means of a Manometer measuring Pressure in I n c h e s of W a te r C o lu m n (A table for conversion of Pressure in I n c h e s o f W a te r C o lu m n to Relative Velocity in M ile s p e r H o u r and Pressure in P o u n d s p e r S q u a r e F e e t is provided in Appendix D). 5.4 Configuration In this part of the study, different Wall heights of 1.5, 2.0, and 2.5 with their respective plans to be 5 x 5 units square were studied and tested with varying Roof angles of 20, 25, 30, 35, and 45 degrees respectively with each one (See Figure (xii)). In all cases, unless otherwise stated the depth of the overhang is 1.0 unit deep on all sides. 39 3 0 Figure (xii) 40 The walls are higher in relation to the depth of the overhang, which happens to be 2.5 in our case, the wind ignores the overhang to a great extent. The relative depth of the overhang being small the winds acts similar to how what it behaved on a flat roofed building with similar walls. Thus, high suctions s appears towards the windward side of the wall and decreases toward the leeward one (see Figure(xiii), (a) and (b)). It is similar not only near the overhang by which uplift can be determined but also on the rest of the wall. Another interesting and important deduction from this phenomenon is that, in case of such ratios between the overhang and the walls their is very little effect of the change in roof angle on the the uplift on the eaves. Now let us consider the dwellings with wall heights comparable to the depth of the overhang, which is 1.5 in our case. If we visualize the cross-section near the overhang we would notice that the three planes of the overhang, the wall, and the ground create a sort of a triangular channel. The wind ricochets off these planes repeatedly to create strong eddies Thus, as we can see in Figure (xiv), (a) and (b) that, although the behaviour of the wind is radically different in the earlier case and this one, both create high negatives near the eaves on the walls; one due to flat surface parallel to wind direction creating high suctions and the other due to the triangular channel creating the turbulence with high negatives. We see (Figure (xv)) that therefore, both the values of the pressure on the walls do not differ much (only about 2%). One can imagine that the turbulence in the lower walled dwelling depends on the acuteness of the triangle which itself can be adjusted by changing the angle of the roof. The turbulence would thus be more when the lO c v l * KjoDnno Figure (xiii) Figure (xiv) 4 ^ I n ) M A X . PRESSURE (Inches o f Water Column) 43 CHANGE IN MAX. PR E SSU R E ON WALLS DUE TO VARYING ROOF ANGLES AND WALL HEIGHTS 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 30 20 25 Wall Ht. 1.5 ---------1--------- Wall Ht. 2.0 — — Wall Ht. 2.5 ROOF ANGLE (Degrees) Figure (xv) 44 angle of the roof is 45 degrees than when it is 30 degrees. Considering this logic one can expect a case when the overhang angle offers no turbulence, which ofcourse would again result in high suctions as seen in the first case. Therefore it is possible to find out a point in which, due to the angle of the roof, the wind ricochets off of the overhang only once or twice and thus avoiding both the high suctions and the high turbulences. In the tests that were carried out it was found that until the angle of the roof 30 the turbulence remained the same. But, after that we see a 10% decrease in the pressures at the eaves on the walls (uplift) when the angle is reduced to the 25 degrees, and a substantial reduction of 20 % when the angle is further narrowed to 20 degrees. Thus speaking of uplift the angle of 20 degrees seemed to be the most appropriate. The case of the roof however, is quite different as we can see on the graph (Figure (xvi)). The 30 degree angled roofs by far behave the best of the lot, among which the one with wall height as 1.5 is the best. The angle of 20 degrees with wall heigth 1.5 which acted so well in our earlier experiment does not perform as well with its roof suctions. Taking the unit to be a meter which fits the actual scale of most dwellings in coastal Andhra Pradesh, an angle of 20 degrees with a wall height of 1.5 meters does not give enough head room at the center apart from acting as a flat roof when it comes to roof suctions. The pressures at the roof then were taken as critical rather than below the overhang which result in uplift, the reason for this shall be discovered as we proceed in our study. Thus, the dwelling unit with a roof angle of 30 degrees, wall height of 1.5 units, with a square plan of 5 x 5 units, and with an overhang of 1 unit deep M A X . PRESSURE (Inches o f Water Column) 45 CHANGE IN MAX. P R E SSU R E ON ROOFS DUE TO VARYING ROOF ANGLES AND WALL HEIGHTS Wall Ht. 1.5 — i— Wall Ht. 2.0 — *6— Wall Ht. 2.5 35 30 25 20 ROOF ANGLE (Degrees) 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 Figure (xvi) 46 was considered as a standard and as an optimum hipped roof dwelling configuration in all the tests that were carried thereafter. This would be termed as standard module hence forth in this study. 5.5 Opening Variations In cyclones one of the greatest dangers is the explosion of buildings to the extreme differencial of pressure within the building to that of the outside. This results due to many factors like the gushing effect of wind, the sudden change in wind direction due to local turbulences, the sudden drop in the barometric pressure as low as 1000 mb. Unable to cope up with the rate of change of pressure the building explodes or implodes. The adjustment of the building with this change in pressure depends on the nature of its openings. In our next experiment we examined the effect of all possible combinations of doors as well as windows with the standard module (see Figure (xvii)). Each of these combinations were tested under eight different orientations. Results are plotted on graphs (Appendix A, Figures (i) through (xvii)). Lets try to analyze for combination A1 (Figure (xviii)) which has only one door. Notice that when the door-side is facing the wind direction the external pressure is 16-18% greater than the internal pressure whereas when the wind blows perpendicular to the face of the door-side the external pressure stays the same but the internal pressure shoots up and becomes as high as 100% greater than the external pressure. Now, sudden changes in wind directions is not very uncommon in cyclones. In the event of such a change lets try to see m r n w m m m n v m i A1 tp - (P .T w . Z-W * Jt> .1 N . X P .i-W H tX H W . tp.W Figure (xvii) 2 .W .1D . PRESSURE (Inches o f Water Column) 48 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 ORIENTATION (Degrees) Figure (xviii) what would happen. Lets assume that in a cyclone the external pressure is 30 psf and the wind is blowing into the door-side. In that case we would know that the internal pressure can be as much as 24 psf. The next moment due to some local turbulence the wind direction changes by 90 degrees. We know that the external pressure would not have changed but the internal pressure would have gone up to as high as 60 psf. This means that before the change in wind direction the building was being crushed by the greater external pressure with 6 psf whereas after the change in the direction the building would be trying tear away with pressure of 30 psf. But to reach form state 1 to state 2 the internal pressure has to push outward every component of the building with a pressure of 36 psf and all this would happen within a split second, causing the building to explode. Thus one can now easily make out that this combination is probably the worst. Based upon the above discussion one can deduce a few basic thumb rules for determining the best out of the 20 combinations. 1. The graphs should be as parallel as possible thereby showing consistant behaviour in all directions 2. The graphs should be as flat as possible 3. The graphs should be as close as possible thereby showing lower difference in pressures. Looking closely at all the combinations it is clear that B4 (Figure (xix)) having 4 windows, one on each side, is the best. One may argue that combination A5 (Figure (xx» to be a close contender. However, only 10-12% more pressure differential may mean a lot when dealing with winds up to 100 miles per hour or more. PRESSURE (inches o f W ater Column) 50 0.5 Int. Pressure 0.45 Ext. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) 4 D . Figure (xix) PRESSURE (Inches o f W ater Column) 51 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) f a f a < 0 ^ f a f a f a f a Figure (xx) 52 An immediate question arises; how can there be only windows on all four sides? well, one of them could be a door with two shutters, somewhat similar to what are called as dutch doors. 5.6 Nature of overhang In this test the effect of fluting the overhang and the effect of change in width of the flutes was to be determined. The aim of this test was to find out whether fluting as norrow as that of the palm leaves are better to reduce the pressures on the walls as against broader ones which may be made artificially. The model was constructed out of plexiglass and the overhang was made out of thin transparent plastic have approximately similar stiffness as that of palm leaves. The results from the previous test, i.e., four windows on four walls was to be used in every test that was to be carried out henceforth. Four different combinations were considered (Figure (xxi), (A) through (D)). It was found that the thinner the fluting the lower the pressures were (see Figure (xxii)). This behaviour was probably due to the fact that thinner once being very slender offer very little resistance thereby letting most of the wind escape through and thus avoiding the high pressures on the walls (see Figure (xxiii)). 53 Figure (xxi) MAX. PRESSURE @ EAVES 54 A O V E R H A N G LENGTH 1. TYPE SO LID B-OVERHANQ LENGTH 0 .5 . TYPE S O U O R H A N G LEN G TH 1. TYPE 8 R O A O ST R IA T IO N S V ERH A N G LEN G TH 1. N A R R O W S T R IA T IO N S 0.35- i l TYPE OF OVERHANG Figure (xxii) Figure (xxiii) 56 5.7 Permeability and nature of roof In this test four configurations of thatch roof were considered. The variable here was number of layers of thatch (Figure (xxiv)). One can see that if the size of the dwelling is kept constant then, as the number of layers increase, the length of the thatch itself increases. Also, with this increase the number of rafters on the roof increase, thereby increasing its overall stiffness. The model in this case was also constructed out of plexiglass with the rafters out of modelling wood and the thatch out of transparent plastic. Unfortunately there was too much of approximation in this experiment and the results did not show considerable promise. The thatch simulation was too flat and 2-dimensional and therefore was not as dynamic as the actual thatch would have been. It was however impossible to undertake this test using actual thatch due to constraints of time and available resources . However, of all the four combinations tried out, the one with three layers of thatch showed greatest potential of equalizing internal and external pressures. But if the room size is to be kept at 5 m (16.4 ft.) square then the length of the thatch of combination (d) would have to be not less than 1.7 metres (5.57 ft.). Now, where in the world can we find a palm leave which has that length. Based on the above observation it is clear that the size of thatch can change very little in our case and that with increase in number of layers of thatch would mean an increase in the size of the dwelling itself. A size of lm (3.28 ft.) is not very uncommon in palm leaves. For 3 layers of thatch, the dwelling size would be approximately 2.6 m x 2.6 m (8.528 ft. x8.528 ft.) 57 For 4 layers of thatch, the dwelling size would be approximately 3.5 m x 3.5 m (11.48 ft. x 11.48 ft.) For 5 layers of thatch, the dwelling size would be approxiamtely 4.3 m x 4.3 m (14.1 ft. x 14.1 ft.) For 6 layers of thatch, the dwelling size would be approximately 5.2 m x 5.2 m (17.1 ft. x 17.1 ft.) 58 * I Figure (xxiv) 59 5.8 Thatch roof dwellings 5.8.1 Construction The thatch roof dwellings are usually made of 5 materials - mud, straw, palm leaves, bamboos, and bamboo or coconut fibres/ropes. Bamboo for the posts, purlins, rafters, etc., palm leaves for the thatch, bamboo fibres or ropes for fastening all these members (see Appendix C for typical details), and mud mixed with straw for the walls. Typical construction is shown in Figure (xxvii) and (xxviii). The species of bamboo used in the construction is Bambusa arundinacea known locally as Veduru (in Telugu), whose culms are 25-30 metres (80-100 ft) long and 15-20 cms (6-8 inches); thick walled; commonly rather crooked; only moderately strong and durable to very durable; lower branches very thorny. Other physical and structural characteristics are described in Appendix B. There are a variety of ways to thatch a roof some of the common ways not only in India but in most parts of the world, are shown in Figures (xxv) and (xxvi)* . The most commonly used form of thatch in east coastal India and especially in Andhra Pradesh is the Split Stalk Thatch (See Figure (xxv)). The Stick Thatch also is used to some extent. * The source o f all the sketches on thatch roofed dwelling construction (Figures (xxv) through (xxviii)) are form, Easton's edited Shelter. Shelter Publications, Inc., 1990. Reproduced without permission 60 S titc h at b a tto fn o f first (butch on low est thatching hat ten. The second layer m ust overlay the stitching o f the first row and include th e to p section o f the underneath layer in the actual stitch. It is b e tte r to have each layer held b y three row s o f stitching. The stitching o f every/ row m ust be co m p letely covered b y th e fre e ends o f the n e x t layer above it. Truro? )\v^\Ilpitf r * V J | - t W G ood m eth o d for 2-3* long pliable m aterial such as reeds. G ather into sheaves 1 " thick. 13cnd b u tt end over batten, twist a few stra n d s ' around the sheaf to hold tight. Slide along b atten . This looks good from inside, is good w eather p rotection. Im p o rta n t th at long free ends overlap 2 or 3 rows below . D o not bunch tightly — leave W* b etw een bcnt-ovcr ends. w / C , Fl-AmsH t o ' M - ' - n + u L + = . r^e& icn-e f=t^=>/sa c n y , h a k o , \ e > " % l'’T H lC + c. . rk u e > c u t e y e "Tt+FM FUAT W wipe, '/ a . " U P N C t I.ay the lhatching material xoith th e b u tts tow ards the r o o f and the low er en d on the lowest, batten. Secure owe end o f th e sew ing material w ith a tim b er hitch to the thatching batten, thread the t/ther end through the eye. of the thatching needle and sew in th e ordinaryr manner to the thatching batten. To avoid holes where the sewing m ay ten d to b unch the . thatching together, pass the needle through the thatch at the angle indicated in the sketch and push thatch over th e crossing o f the stitches. r£ < ^ IlC 3 ^ T 3VS^ciryFS. Sim ple and quick. C ut fronds during full m oon. Weave stalks b etw een battens. ~ Jtf ' / M i l l li/ll Tied 2 ’ apart. Tic stick sil one end, put iluuch underneath, tie o th er end. Follow same principles as w ith sinow thatching. 7 a Figure (xxv) 61 Weave together tliusly, then overlap as w ith o th er m ethods. > 1 i.i.rfri,.. Neat and efficient for certain m aterials. Make im sure m aterial will n o t curl w hen it dries. 'J&k s e w n r^jps£,e - m p-t c t * h i W fr CIWVM TH/*T<SH Figure (xxvi) 62 1 . | First a circle w ith a d iam eter o f 9 to 2 0 ft. is ! draw n at the building site. F'ucalyptus poles are placed in the g round at o n e yard o r so intervals along the circum ference. T h e poles should h e long enough so that at least 7 or 8 feet o f th e pole is above the ground. N ex t th e center pole is set. It should he tall enough to give the ro o f an angle o f at least 50". % . N ow tiic walls are filled w ith upright poles set close together anti stuck in rhc ground. R ope is used to tic supports to th e side o f the wall. G reen w o o d is used for ease in bending. N ow the ro o f su p p o rts are attached 1 fo o t from th e to p o f the center pole anti ex ten d ab o u t tw o feet past the to p of the wall. 'This helps shed rain aw ay from the wall. 'Hie supports can be ex ten d ed even farth er and used as a ty p e o f veranda. More su p p o rts arc added to the roof. These again arc o f green w ood and tied w ith rope. Nov/ it is tim e to put on the roofing m aterial. S um batit, a straw ty p e grass is used. It is th a tc h e d or tied. This w ork is d o n e from th e to p d o w n , w orking carefully to insure a good roof. A p o tte ry jar is added over the top of the cen ter pole b o th as a decoration anil to help shed w ater from the center of the roof. Now an adobe plaster o f straw and m u d is put on the wall. A fter the plastering is finished, a d o o r is built and installed and tw o small holes are put in the wall to allow sunlight to co m e in. N ow w ith th e outside finished it is tim e to w ork the inside. This is d one according to the use. It can he used as living quarters, kitchen, stable, or storage. M any tim es it is used for all four anil therefore m ust be partitioned accordingly. Figure (xxvii) Figure (xxviii) 64 5.8.2 Behaviour The aim throughout this study has been not only to study the behaviour of thatch roofs but also to compare it conventional roofs. This comparision is done taking the character of any conventional roof which is stiff compared to the thatch which is fluted. All comparison is based on this central point since it is this character that distinguishes the thatch from other roofs. Let us try to understand how a conventional roof works ( please refer data from Rao's study included in Appendix B). In case of the conventional roof, as shown in Figure (xxix), The windward side of the roof has pivot action slightly above the joint of the wall and the roof, about this axis the roof has a tendency to fly away. Its tendency to rotate counter-clockwise due to uplift at the eaves and positive pressure at the apex lifts roof up and the drag force helps pull the roof away. The leeward side of the roof is totally subject to suction, which, combined with the drag force, tries to pull it away from the structure. On top of these two forces there is, in most cases, high internal pressure built up compared to the external pressure which is also pushing the components of the building out. This tremendous differential adds to the other forces. One can imagine what would happen if this dwelling has one door and the wind direction changes which, as we discussed earlier, is not too uncommon in cyclones. We can see that neither the characteristics of the material nor its strength is of much help in reducing the forces. Such dwellings actually help in increasing the forces. Designing for these forces in the name of high technology and modernization, I am sure one would agree now, would be foolish. Rgure (xxix) C \ Figure (xxx) C \ 67 Looking now at the dwelling with the thatch roof as shown in Figure (xxx) we see that the uplift force is absorbed due to the dynamic behaviour of the thatch (see also Figure (xxiii)). The lifting up of the thatch causes the wind flow to be deflected upward which causes a slight suction causing the next layer of thatch to lift up which in turn deflect the wind upwards again resulting in suction and therefore the next layer of thatch on top. This action finally reaches to apex of the roof at which point of time all the layers of thatch would be up. Given the openings under the leaves, air starts passing through the roof which cuts off the suction action, causing the leaves to lift up. So, the leaves fall back on to place,which in turn starts the whole cycle of uplift of each layer and so forth. Meanwhile on the other side (leeward) the leaves tend to straighten due to the suction and drag force of the wind during the uplift of the leaves on the windward side. During the passing through wind phase of the windward side the leeward side behaves similar to what it did in the first phase, only this time the leaves are being pushed from inside. This dynamic behaviour of the thatch roof is unsurpassed by any other material. This behaviour copes not only with regular with wind forces as seen above but also the pressure differential between the inside and outside. 5.9 Failure of a thatch roof dwelling The intention of all the empirical data accumulated was to see that the dwelling failure becomes as predictable as possible. We have already discussed that the intention was to make the dwelling reduce the pressures it would be subject to, as much as possible. But after a certain point, in the event of severe 68 cyclone they would fail. The aim here is to make it fail in such a way that -(1) In the process of failure it must not have the potential to cause harm to people, animals, or other property, and (2) It fails in a way that rebuilding after the cyclone is easy and fast. A few tests were carried out to achieve this goal. First the normal standard module was tested again but this time its wall corners were rounded off (since it would be such in mud construction) as shown in Figure (xxxi). It was noted that the pressures were lessened by as much as 8-10%. During failure we do not want the walls to fail first since this would make the whole structure collapse. The best way to do it would be to see that the wall only melts away during the storm surge. But this obviously is not within our control. Then we thought that there was only one way which would be to see that the structure would not collapse even if the wall collapses. Till now we have tried to reduce pressures on the wall as much as possible by optimizing its height to width ratio; reducing forces near the eaves of thatched overhang; putting optimal openings; and rounding off the corners. We had an idea. What if the posts are not embedded within the wall but are outside or inside of the line of the framing. This is not a fool proof solution but surely it reduces the probability when we see that the failure would be caused not only due to the wind but also due to seepage of rain water and flooding. We tested our standard module with the rounded off wall corners but this time with the four posts on the outside of the wall (see Figures (xxxii) and (xxxiii)). To our astonishment the pressures on the walls parallel to the wind direction were further reduced by about 5-6%. This was truelly a bonus for our efforts. Figure (xxxi) Figure (xxxii) Figure (xxxiii) 72 5.9.1 Simulation Model for Failure Having accumulated all the above data it was time to test it out using the actual material. A model was made using bamboo and palm leaves. The intention was to see how the thatch behaves and fails. The failure of the wall was not taken into account since it was difficult to simulate the properties of the wall at such a small scale. Hence around the bamboo posts a sheet of plexiglass was kept with windows in the center to simulate the wall (see Figure (xxxiv)). The wall was not intended to give any form of stiffness to the rest of the structure but was to behave only in the interest of the aerodynamics of the space within. Figure (xxxiv) HiFperp R //F * / H I ft, X , 73 5.10 Graphic Computer Simulation During the course of this study we found it difficult to visualize the effect of such varying pressures on the wall. This forced us to develop a computer program in LISP which would run within AutoCAD. This program at the moment takes a wall from our standard module and prompts for 44 pressure point along a grid work. It then calculates the actual negative and positive pressures on the wall, given the external static pressure had draws a deformed wall as though it were a soap bubble fully elastic and therefore taking the shape of the stresses in 3-D (see Figure (xxxv)). Figure (xxxv) ^ 74 SELECTED BIBLIOGRAPHY Easton, Bob. in his Edited, Shelter. Shelter Publications, Inc., Bolinas, California., 1990. Ferrar, Terry A. The Urban Costs of Climate Modification , A Wiley- Interscience Publication, New York-London-Sydney-Toronto, 1976. Government of Andhra Pradesh., (Revenue Department), Community Cyclone Shelter Construction Programme for Cyclone Prone Coastal Areas of Andhra Pradesh. Government Central Press, Hyderabad, 1980. Government of India., (National Buildings Organization and UN Regional Housing Centre ESCAP), "Cyclones," Housing in Disaster Prone Areas - Report of the Development Group. Government of India Press, Faridabad, 1988. Jamieson, Keith K. "Traditional Housing" Seminar Report: Problems and Lessons from the Andhra Pradesh Cyclone. Organized and Published by Appropriate Reconstruction Training and Information Centre (ARTIC), Vijayawada, A .P., India. Mackey, S. Finney, C. and Okubu, T. Philippines: The Typhoons of October and November 1970. Paris. UNESCO, May 1971. (Serial no. 2387/RMO RD/SCE). Mathur, G. C. and Lai, A K. Cyclone Damage and Rehabilitation with Reference to Housing and Human Settlements. Asia Pacific Symposium on Wind Engineering, December 5-7, 1985, University of Roorkee, Roorkee, India. Olgyay, Victor. Design with Climate. Princeton University Press, Princeton, 1963. Rao, Srinivas M. V. Masters Thesis: From Nescience to Science, and Beyond: A Critical Investigation of 'Building1 in Cyclone Prone Areas.. School of Architecture, USC, 1991. Sinnamon, Ian T. and G. A. van't Loo. Cyclone-resistant Rural PrimarvSchool Construction - A Design Guide. , Bangkok, UNESCO Regional Office for Education in Asia, 1977. 75 Sinnamon, Ian T, Natural Disasters and Educational Building Design: An Introductory Review and Annotated Bibliography for the Asian Region. Bangkok, 1976 Subbaramayya, I, and Ramanadhan, R. "Cyclones and Cyclone Warnings" Seminar Report: Problems and Lessons from the Andhra Pradesh Cyclone. Organized and Published by Appropriate Reconstruction Training and Information Centre (ARTIC), Vijayawada, A .P., India. APPENDIX A PRESSURE (Inches o f W ater Column) 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 45 90 135 180 225 270 315 360 ORIENTATION (Degrees) A Z tv. Ext. Pressure Int. Pressure Figure (i) 78 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 S 0.25 £ 0.2 UJ § 0.15 L U 0.1 CL. 0.05 ORIENTATION (Degrees) onon<>nOG Figure (ii) PRESSURE(lnches o f water column 79 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15— 0.1 0.05 45 90 Ext. Pressure Int. Pressure ORIENTATION(Degrees) O o ^ ^ ^ ^ ^ ^ Figure (iii) PRESSURE (Inches o f W ater Column) 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 90 45 ORIENTATION (Degrees) Figure (iv) PRESSURE (Inches o f Water Column) 81 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 135 180 225 270 315 360 ORIENTATION (Degrees) '1 Z Y t* Figure (v) PRESSURE (Inches o f Water Column) 82 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15- 0.1 0.05 45 90 Ext. Pressure — i— Int. Pressure ORIENTATION (Degrees) Figure (vi) 3>W- PRESSURE (Inches o f Water Column) 83 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 ° 45 90 135 180 225 270 315 360 ORIENTATION (Degrees) n 2.W. Figure (vii) Ext. Pressure Int. Pressure PRESSURE (Inches o f Water Column) 84 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) IP -IW . Figure (viii) PRESSURE (Inches o f W ater Column) 85 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) ODOEiOnOE ^ Figure (ix) PRESSURE (Inches o f W ater Column) 86 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) Figure (x) PRESSURE (Inches o f Water Column) 87 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 ° 45 90 135 180 225 270 315 360 ORIENTATION (Degrees) O n o o ^ f c p - t w . Figure (xi) Ext. Pressure Int. Pressure PRESSURE (Inches o f W ater Column) 88 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 90 135 180 225 270 315 360 45 ORIENTATION (Degrees) Ext. Pressure Int. Pressure 1 x > .z w . Figure (xii) PRESSURE (Inches o f W ater Column) 89 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15- 0.1 0.05 45 90 Ext. Pressure Int. Pressure ORIENTATION (Degrees) O E Figure (xiii) P i 1 t x » W . PRESSURE (Inches o f Water Column) 90 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 ORIENTATION (Degrees) P t HtXHW. Figure (xiv) PRESSURE (Inches o f Water Column) 91 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 45 90 Ext. Pressure Int. Pressure ORIENTATION (Degrees) F ig u r e (xv) PRESSURE (Inches o f W ater Column) 92 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 90 45 ORIENTATION (Degrees) 2 -p . 2.W Figure (xvi) PRESSURE (Inches o f Water Column) 93 0.5 Ext. Pressure 0.45 Int. Pressure 0.4 0.35 0.3 0.25 0.2 0.15- 0.1 0.05 45 90 ORIENTATION (Degrees) ZVtAD - Figure (xvii) APPENDIX B Note: The la st colum n indicates the ratio of th e Side to the H eight of the wall. Conf. # Plan Roof Angle Wall S : Ht. Conf. 01 Square Gable 3 0 ' 5 : 1.5 Conf. 02 Square Gable 3 0 ' 5 : 2.5 Conf. 03 Square Gable 45" 5 : 2.0 Conf. 04 Square H ipped 45" 5 : 2.0 Conf. 05 Square H ipped 30" 5 : 2.0 Conf. 06 C ircular Conical 30" 5 : 2.0* * Wall length of 5 denotes length of the side of the sq u are in which the circular plan is inscribed. E ach of th ese w ere tested for all possible o rien tatio n s. The figures in the following pages show sh ad ed are as m arking equal p ressures (Isobars). 4.3.11 Pressure Isobars 4.3.11.1 Conf. 01 0.08 Test 1 -Side A (Isobar) (AH n u m bers in -vc. in c h e s o f water colum n) i L . & D £ F <sj j V figure 8 97 iw m W<VWW('! 0 .3 7 0 .5 2 0 .3 9 • I: I 0 .3 4 0 .4 0 0 .3 6 0 .4 0 0 .3 9 0 .3 8 0 .4 4 0 .4 6 ° ' 33:io !3 l1 ;;;f. T est 1-Side B /F (Isobar) (All n u m bers in - v e . in c h e s o f water colu m n) figure 9 41 Test 1-Side C (Isobar) (A ll num bers in -vc. in c h e s of water colu m n) 4.3.11.6 Conf. 06 M /i- c * ri 6-tet figure 4 8 p ( 7 A e o 0 ♦ I ❖ £ - f - - $ L 135 100 225 270 315 3G0 ORIENTATION (D egrees) PRESSURE (Inches of W ater Column) o o o o O o & f o £ O 3 . P w 100 PRESSU RE (Inches of W ater Column) PRESSURE {Inches of Water Column) 102 0 . 05 Conf.01 0 . 7 5 C onf.02 C onf.03 -E3- C on(.04 0 . 6 5 0 . 5 5 C onf.05 - A - C onf.06 ,X 0 . 3 5 0 . 2 5 0 . 0 5 135 100 22 5 270 ORIENTATION (D egrees) 3 15 ■3 6 0 figure 51 figure 52 * □ ❖ * 135 180 225 270 315 360 ORIENTATION .{Degrees) PRESSURE (Inches of W ater Colum n) v O O nJ, o O i o o PRESSURE (Inches of Water Colum n) 104 0.05 0 . 7 5 0 . 6 5 0 . 5 - 0 . 4 5 0 . 2 5 0 . 0 5 90 135 100 225 27 0 315 ORIENTATION (D egrees) i i ------ Conf.01 C onf.02 C onf.03 -O- C onf.04 — K- C onf.05 -A- C onf.06 figure 5 3 105 0 . 8 5 Conf.01 —f— C onf.02 0 . 7 5 Conf.03 0 . 6 5 0 . 3 5 - U J 135 180 ORIENTATION (D egrees) 270 315 figure 54 PRESSURE (Inches o f Water Colum n) 106 0 . 05 0 . 7 5 0 . 6 5 0 .5 5 0 .3 5 0 . 1 5 45 90 225 315 135 100 2 70 C onf.01 C onf.02 C onf.03 ■ £ 3 — C onf.04 - X - Corif.05 -•A - C onf.06 ORIENTATION (D egrees) ”1 ( ! i r r i — i ____ - & ■ i figure 55 PRESSURE (Inches o f Water Colum n) 107 0.05 - m - Conf.01 0 . 7 5 Conf.02 C onf.03 0 . 6 5 C onf.04 - - X - C onf.05 0 . 5 5 C onf.06 0 . 4 5 0 . 3 5 X* 31 5 360 225 270 90 135 ORIENTATION (D egrees) fig u re 5 6 PRESSURE (Inches ol Water Column) 108 0 . 8 5 C o n f .01 8 0 .7 5 C onf.02 - 7 * * - C onf.03 C onf.04 7 0 . 6 5 6 0 . 5 5 C onf.05 5 0 . 4 5 .4 0 . 35 3 0.25 0 . 2 0 . 1 5 .1 --- 0.05 0 3 1 5 36 0 45 22 5 90 135 1 80 2 7 0 ORIENTATION (D eg rees) figure 5 7 4 .3 .1 3 Conclusion 4.3.13.1 Inferences 1. In case of a G able Roofed U nit it w as seen th a t the highest p ressu res are reached w hen the gable side is bn the leeward side of the u n it with the wind cutting diagonally across. I 2. Regarding the bottom corners of the wall (intersection of two walls and the connection to the foundation), It was found th at the pressure slightly dropped when the condition changed from a gable wall to a non-gable wall - w ith the p ressu res a ttain in g peak levels w hen the wall is parallel to the wind direction. The wall of the Conical Roofed U nit however, behaved in a m uch b etter way w ith it’s peak levels being 10-20% lower th an the o th ers’. It’s peaks are reached a t points which are parallel and perpendicular to th e d irectio n of the wind (in terestin g ly b o th p re s s u re s are approxim ately the sam e). 3. It is interesting to note that when the wall height was reduced to 2 .0 /2 .5 to 1.5 the pressures were greatly uniform and stabilized apart from being slightly lower. 4. At the center of the walls however, the p ressu res were found to be m uch more uniform and stabilized th an any other p art of the wall. 110 5. However, in case roofs center, extreme highs resulted, especially in the surfaces which were parallel to the wind direction. 6. As regards the apex of the roof, highs were recorded at the leeward side with the wind blowing diagonally across. 1 figure 5 8 figure 59 i l l figure 60 112 113 figure 62 115 4.3.13.2 Recommendations: With the plan of the units as 5 units side square, the following ‘th u m b rule’ recom m endations are made. 1. Any Roof Angle >30° and <25° not recom m ended. Suggested Angle- 30°. 2. Any wall with a relative height of >2.0 is highly discouraged. » Highly recom m ended relative height- 1.5 units. 3. High predictability forms are recom m ended. 4. R ecom m ended form s- * Conical Roof with 30° angle and relative Wall height 1.5 units. — The highest recom m ended configuration. * Hipped Roof is highly recom m ended only if wall is < 1.5 units and roof angle is 30° Note: Increase in wall proportions form 1.5 to 2.0 can cause a considerable difference. 5. It is recom m ended th a t the apex of conical roofs and hipped roofs be rounded off. 6. The intersection of the walls also to be rounded off. 7. All the openings to be located at the denter of the walls. 4.3.13.3 Sim ulation Model Seeing th e above p o s tu la te s it w as decided th a t all the requirem ents of rounding of apex, dissipating th e tu rb u len ces at the eaves, eq u alizin g in te rn a l a n d e x te rn a l p r e s s u r e s to p rev en t explosion, ro unding off of walls being the n a tu ra l characteristics of m ud and thatch, m u st be tested. THATZU OUT Of- P A 1 . M L^Y' CS - /M ain . Fram e' m m o o m PE-|NfT30EF>V / W AU^ ^ s. Y iM £ ..m :.-a fi^ p ^ L >. . ... MDp.+GYf$m:^v^:-u : :::M figure 63 117 Based on the resu lts from the tests an d from predom inantly existing building types in coastal India, A scale model (1"=2' approx.) out of Palm leaves. Bamboo, Bamboo Ropes, Mud, etc. w as made. The sketches in figure.63 illustrate the m aterial and m ethod of construction of the model. The model was later subjected to a wind speed of 85 miles per I hour. In m aking the model, the following assu m p tio n s were m ade, 1. It w as assum ed that, aerodynamically. only the shape, size, and the n a tu re of surface of the wall would m atter. Neither the composition of the wall m aterial nor the stru c tu ra l properties of the wall were of significance. 2. it w as a ssu m e d th a t the p re ssu re in creases linearly with the increase in the wind speed 4.3.13.4 Observations: The behavior of the roof was extremely dynam ic. As the wind speed reached 60 m iles per hour, the leaves opened u p on the w indw ard side and letting the wind pass through the leaves on the leeward side acting as outlets (see figure 64). The tu rb u len ces at the eaves and the problem of uplift due to eaves (overhang) w as totally elim inated due to the dynam ic behavior of the palm leaves. 118 i At extremely high winds, the leaves cut loose and blow away as h arm less objects. Once they arc away, the rafters cease to take any load due to absence of surface area (see figure 65). The relatively short ration of height to length of the m ud wall reduces it's chances of collapse over being w ashed away, leaving the fram ew ork in tact for faster rebuilding. This however, could not be J tested in the wind’ tunnel (see figure 65). It is recom m ended th a t hill site temples (out of stone) be given more encouragem ent as cyclone shelters rath er th an building schools i o ut of concrete, j ! Fine tuning in thatch construction should also be revitalized by the G overnm ent today. figure 64 figure 65 APPENDIX C B .l Introduction to Bamboo | Bamboo and reeds are the oldest and the chief building materials in rural j areas and villages throughout India. Bamboo and reed construction is popular for good reasons: the material is plentiful and cheap, the villager can build his own house with simple tools, and there is a living tradition of skills and ( methods required for construction. This tradition has been augmented in recent j years by experiments carried out principally in India, Indonesia, the Philippines | I and Columbia. The bamboo and reed housing is easily built, easily repaired, i P well-ventilated, sturdy and earthquake-resistant. Deterioration by insects, rot fungi and fire is the chief drawback of bamboo and reeds as a building material. Many buildings of untreated bamboo must be replaced every two or three years. Most bamboo houses have no interior toilets , indoor water supply, or cooking facilities. It is easy to speculate j about the relation between the absence of these facilities and the rapid deterioration. I i Improving the material properties and construction techniques for j I bamboo buildings would be a giant step towards improving the standards of j comfort for millions of rural dwellers in India. j This study has two purposes. The first is to acquaint the government, ministries of housing, regional housing authorities, village and community development officers, rural aid societies, building co-operatives, building contractors and the villagers themselves with new or not well known techniques of bamboo building construction. The techniques may be directly transferable or may be only an indication of possibilities. 122 The second purpose is to stimulate additional research on improving the properties of bamboo as a building material and on improving the techniques of building construction with bamboo. B.2 PHYSICAL CHARACTERISTICS. B.2.1 Dimensions: Bamboo and reed culms vary in height and diameter. Some bamboos and reeds grow to a height of 36 meters, and others are no more than shrubs. The diameter varies from 1 to 30 centimeters. The variability between species is far greater that the variability within the species.The variability makes difficult the mechanization of processing and fabrication. When the supply of culms is very large, this variability may be partially overcome by careful selection and grading. Where nodes or rings are very prominent, they will interfere with close fitting construction. The prominent node can be dressed to size but more commonly the use dictates the selection, and these culms are not used for close fitting construction. B.2.2 Splitting: Bamboo and reeds have a tendency to split easily, this tendency is particularly pronounced in the internodes, which have a lower coefficient of shear than the nodes. Wherever possible cuts in the culms should be made just beyond the node to minimize splitting. The splitting tendency precludes the use of nails, screws or pegs unless pilot holes are drilled beforehand. Often, 123 splitting is preceded by cracking. Cracking is usually controlled by air or kiln drying. B.2.3 Durability: Bamboos are highly susceptible to destruction by wood eating insects, fungi and fire. Within the culm, the middle and tip portions are less resistant than the bottom portion. There is also a considerable variation in durability from species to species. The durability of untreated bamboo is, however in general short. Bamboo posts embedded in the ground are destroyed in six months to two years. Bamboo stored above the ground gave , in tests, a useful life of 22 to 41 months. Bamboo under cover and not in contact with the ground may last from two to seven years. B .2.4 Moisture content: Owing to anatomical changes caused by drying, the moisture content of bamboo has a great influence on its treatability with preservatives. Freshly cut bamboo with high moisture content is far easier to treat with the boucherie process than dry bamboo. Moisture content in bamboo decreases with the height of the culm from the ground. It also varies with the age of the culm and the season. Older culms (6 to 9 years) contain less moisture than the younger (3 to 4 years) ones. The youngest culms (6 months to 1 year) show the highest moisture content. The differences due to age, however are not as great as the differences due to the seasons. 124 B .2.5 Weight: Bamboo and reed are light in weight compared to construction timber. The specific gravity of bamboo varies from about 0.5 to 0.79 with a median of about 0.65. This would make the weight of bamboo 648 kg/m^. The volume weight is about 130-180 kg/m^. B .2.6 Strength: The modulus of elasticity of mature air dried culms range from 125,000 to 195,000 k g/cm ^ with an average value of about 160,000 kg/cm^.One kiln- dried species reaches a value of 225,000 kg/m^. green culms generally fall below 100,000 kg/cm ^ . Tensile tests on one of the common species produced an amazing strength parallel to grain of 2,629 kg/cm^. This compares favourably with the allowable tensile stress on ASTM A36 structural steel of 1,375 k g /cm ^ . Of course, this high tensile strength of bamboo cannot be used to full advantage, in, say, bamboo-reinforced concrete since bamboo would fail in shear long before its full tensile strength was developed. It is, therefore, advisable to take the modulus of rupture to represent the tensile strength for design purposes. The modulus of rupture of bamboo varies from 900 to 1700 kg/ctn^ or an average of 1,300 kg/cm^. The compressive strength parallel to grain varies from 315 to 725 kg/cm^ or an average of 520 kg/cm^. 125 The culm has a tubular structure stiffened at intervals at cross wall of the nodes which prevents it from buckling and collapse. The disposition of the nodes is significant in the bending strength of bamboo, but it is not a good material in its crushing strength. In static bending tests, specimens with a node at the loading point show a higher strength but lower stiffness than those having the load point between two nodes. Owing to its greater wall thickness, the base portion of the culm is significantly stronger in the modulus of rupture and allows a greater fibre stress at the elastic limit, in both the green and dry conditions. There is hardly any difference in the compressive strength between the base portion, the middle and the top. The modulus of elasticity is generally lower for the bottom portion. In splints of bamboo, the compressive strength of the outer layers from the culms is higher than the inner layers, following the difference in specific gravity. Bamboo splints with and without nodes, when tested in static bending gave higher values when the face nearest the periphery was in compression. B.3 USES OF BAMBOO IN BUILDING CONSTRUCTION B.3.1 Tensile strength: The ultimate tensile strength of some species of bamboo in direct tension is about the same as that of mild steel at its yield point. On an average it varies from 1,400 kg/cm^ to 2,800 kg/cm^. it was this high value that attracted the attention of investigators for the use of bamboo in reinforcement for concrete. However, as already indicated, the results of their investigations showed that in practice it is not possible to make use of the complete tensile strength of 126 bamboo when it is embedded in concrete as reinforcement. Poor bond strength between bamboo and concrete and the low modulus of elasticity of bamboo are the main factors that prevent the effective exploitation of the high tensile strength of bamboo as tensile reinforcement in concrete members. The modulus of elasticity of bamboo is slightly higher in direct tension than in flexure and compression. This value ranges from 1-5 x 10^ kg/cm^ to 2 x 105 kg/cm^, which is almost the same as 1:2:4 concrete. This suggests that bamboo as reinforcement in concrete does not contribute anything to reducing the deflection or preventing cracks at loads near the ultimate failure figure for a f member in which no bamboo is only about one twentieth of that of mild steel. This low elasticity value of bamboo decreases correspondingly the value for modular ratio (m) of concrete and bamboo so that bamboo reinforcement does not help in increasing the moment of inertia (I) of a bamboo reinforced section over that of an unreinforced one. This means that bamboo reinforcement unlike steel, will not contribute to reduce deflection when used as reinforcement. Therefore, the span/depth ratio should be such that the total section will take care of the deflection. Reasons for cracking before the ultimate failure are deflections, bond slippage, shrinkage, and swelling of the bamboo and also deferential thermal expansion between bamboo and concrete. From these it may be concluded that effective methods must be developed to overcome the limitation of bamboo as a reinforcing material. 127 B.3.2 Compressive strength: The load capacity of bamboo reinforced beams increases with increasing strength of the concrete for a given section, the average ultimate direct compressive strength of bamboo varies from 400 to 700 kg/cm^. The corresponding value of 1:2:4 concrete is 158 kg/cm^. The effect of bamboo as a compressive reinforcement does not seem to have been studied. The use of bamboo in doubly reinforced concrete members may result in increasing the load capacity. B.3.3 Diagonal tension reinforcement: Studies have been made of the effect on diagonal tension of using bamboo dowels spaced vertically and also bending the upper rows of j longitudinal reinforcement. Both increase the load capacity and the combination j proves better. But even after providing the above type of reinforcement, J ultimate failure may occur owing to diagonal tension stresses, more effective j ways of reinforcing this zone of the member must be developed. This can probably be achieved by using steel stirrups. Bamboo can be more effectively used in slabs than in beams because shear failure generally does not occur in slabs B.3.4 Bond: An important disadvantage of bamboo as reinforcement is its tendency, if already seasoned, to absorb a large amount of water present in the wet concrete, resulting in initial swelling and subsequent shrinkage as the concrete 128 dries out. This phenomenon results in the development of longitudinal cracks in the concrete, which lower the capacity of the members, and in poor bond formation between the concrete and the reinforcement. The cracks are more where the percentage of bamboo reinforcement is high. Green bamboo used as reinforcement also shrinks as the concrete dries out , and the bond strength is poor. A remedial measure adopted to overcome the high water absorption and swelling of bamboo embedded in concrete is the application of a water repellent coating. Seasoned bamboo splints treated with one brush coat of asphalt emulsion or coal-tar gives more bond strength than do seasoned untreated and unseasoned ones, concrete reinforced with treated bamboo developes greater load capacities than that reinforced with untreated bamboo. Excess of asphalt on the surface of the bamboo splints is, however, harmful; it lowers the bond between the concrete and the bamboo. Poor adhesion of bamboo to concrete may be overcome by coating the air dry bamboo strips with lead in varnish. Three coats of forty percent solution of rosin in alcohol and a subsequent coat of white lead also prevents water absorption but the coatings get disturbed while the concrete is being rodded and cracks develop in the concrete. A mixture of 80/100-grade bitumen and kerosene in the ratio 4:1 may be used for the same purpose. Soaking the bamboo in a 50:50 mixture of linseed oil and turpentine is also reported to be satisfactory. Bond stress between untreated bamboo and concrete has been found to range from zero to 13 kg/cm^. About 50 percent increase in bond stress may be obtained by treating bamboo with coal tar/asphalt emulsion, bond stress values 129 range from 4 to 24 kg/cm^ for treated bamboo. Bamboo specimens with node developed higher bond stresses than those without, because of the uneven surface of the former. B.3.5 Permissible stresses: Since the actual stress developed in bamboo when it is used as reinforcement is far less than in direct tension tests, permissible stresses should be based on the actual test results obtained on bamboo reinforced members. Based on the observed tensile stresses in bamboo in concrete, a safe tensile stress of 350-420 kg/cm^ may be used in design. However, design values not in excess of 210-280 kg/cm^ should usually be used if the deflection of the member is to be kept under 1/360 of the span length. Permissible bond stress of 3.5 kg/cm^ has been recommended for bamboo as compared to 6 kg/cm^ for mild steel in 1:2:4 concrete. B.4 Earthquake resistant construction: Earthquake forces that a building has to withstand are proportional to its weight and are predominantly horizontal. The heavier the building the more likely it is to get damaged during an earthquake. Lightweight material such as bamboo and reeds, with a high strength/weight ratio, are therefore preferred in regions where earthquakes occur. Experience in the different seismic regions of the world has shown that a house built of bamboo, properly lashed together, is earthquake resistant. In this respect bamboo is somewhat superior to timber. It has the capacity to absorb 130 more energy and shows large deflection before failure occurs. A bamboo frame structure therefore yields readily to vibrations and contortions of the earth during an earthquake and does not readily collapse, even if such a mishap were to occur, loss of life and property is not large because it is a light structure, the use of bamboo as a specific earthquake material has not been developed in comparison to timber, steel and concrete, nevertheless, the principles applied to a timber structure could be applied to bamboo structures also. In bamboo frame j j structure construction details should be adopted at the joints of the framing j j members and wall panels so that the structure as a whole behaves as one unit against earthquake forces. Experience in India shows that a closed frame construction should be adopted with horizontal connecting members for the columns at foundation level. Walls and partitions should be provided with diagonal braces and anchored properly to the vertical and horizontal struts. Observations on the framed structures during earthquakes in Assam have led to j ! the conclusion that the superstructure should rest on a foundation of masonry, j j Small one storey buildings may rest on firm ground, however, in large buildings, the posts should be attached to the foundations by means of pins or straps, bolts and nuts. Bamboo board, matting and plastered matting walls and reed slab walls, being light flexible, are suitable for seismic areas. Experience in Columbia has shown that the bajaraque wall construction, which is more massive than wattle and daub but less massive than rammed earth or adobe, is earthquake resistant. Load-bearing adobe and heavy mud walls, which fail under relatively slight tensile or bending force, are the first to fall during a seismic vibration. It is 131 recommended that a bamboo lattice should be used in mud walls to strengthen them. Brick masonry walls also have a poor resistance to earthquake shocks, especially when a weak mortar such as mud is used. In ancient Babylonia and Ur, reeds embedded in asphalt appear to have been used as horizontal reinforcement in brick walls. Vertical steel reinforcement is now specified for brick masonry walls at corners and junctions. Vertical steel at doorjam bs and a lintel band are also recommended. The use of bamboo splints or reeds in place of steel in these places should prove beneficial, especially in single storey houses. ] | A false ceiling should be tied rigidly to the roof. Plaster on the ceiling should be avoided or kept to a minimum thickness. Light roofing materials are advantageous in reducing the inertia force at the top of a building. Bamboo tile, bamboo shingle, and thatch are satisfactory roof coverings in this respect. 132 o I I J o in t s used i n b u ild in g w it h bamboo • a h ) i i u - j J o in t s u sed in b u ild in g v;ith bamboo 134 DETAIL - . - M i DETAIL C D E T A IL B DETAIL D J o in t s u sed in b u ild in g w ith bamboo 135 IQ i .J / / J o in t s u sed in b u ild in g w ith bamboo J C I J o in ts u sed i n b u ild in g v i t h bamboo APPENDIX D 138 Conversion for Pressure in I n c h e s of W a te r C o lu m n to Relative Wind Velocity in M ile s p e r H o u r and Pressure in P o u n d s p e r S q u a r e F e e t. In. H 2 0 M iles/Hr. lbs/sq.ft. 0.1 14.47 0.5 lk 0.2 20.47 1.037 0.3 25.07 1.556 0.4 28.94 2.074 0.5 32.36 2.593 0.6 35.45 3.112 0.7 38.29 3.630 0.8 40.93 4.148 0.9 43.42 4.667 1.0 45.76 5.180
Linked assets
University of Southern California Dissertations and Theses
Conceptually similar
PDF
A cross-ventilation study on a building with skip-stop corridors
PDF
Return to the moon: MALEO, Module Assemby in Low Earth Orbit: A strategy for lunar base build-up
PDF
A passive cooling system for residential buildings in the Eastern Province desert in Saudi Arabia
PDF
Vibration reduction using prestress in wood floor framing
PDF
Computer modelling of cumulative daylight availability within an urban site
PDF
From nescience to science and beyond: A critical investigation of 'building' in cyclone prone areas
PDF
Emergency shelter study and prototype design
PDF
Passive cooling methods for mid to high-rise buildings in the hot-humid climate of Douala, Cameroon, West Africa
PDF
A proposed wood frame system for the Philippines
PDF
A passive solar heating system for the perimeter zone of office buildings
PDF
Investigation of sloshing water damper for earthquake mitigation
PDF
Statistical analysis of the damage to residential buildings in the Northridge earthquake
PDF
Investigation of seismic isolators as a mass damper for mixed-used buildings
PDF
Computer aided design and manufacture of membrane structures Fab-CAD
PDF
Computer aided form-finding for cable net structures
PDF
Eccentric braced frames: A new approach in steel and concrete
PDF
The response of high-rise structures to lateral ground movements
PDF
A computer teaching tool for passive cooling
PDF
A proposal for the Indian National Lighting Code
PDF
Computer aided design and analysis of anticlastic membranes and cable nets
Asset Metadata
Creator
Mehta, Shina
(author)
Core Title
Behaviour of hipped roof dwellings in response to wind forces: A comparitive study of thatch against conventional roofs
Degree
Master of Building Science
Degree Program
Building Science
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
engineering, architectural,OAI-PMH Harvest
Language
English
Contributor
Digitized by ProQuest
(provenance)
Advisor
Schierle, G.G. (
committee chair
), Koenig, Pierre (
committee member
), Vergun, Dimitri (
committee member
)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c17-784038
Unique identifier
UC11347959
Identifier
EP41428.pdf (filename),usctheses-c17-784038 (legacy record id)
Legacy Identifier
EP41428.pdf
Dmrecord
784038
Document Type
Thesis
Rights
Mehta, Shina
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
engineering, architectural