Chapter 1

Introduction

1.1 General Background Semi-engineered buildings are often considered to be those built in an organized fashion with materials which are processed or engineered for the most part, but which include little or no formal structural engineering input during the design and construction stages. These structures along with non-engineered buildings are thought to constitute the majority of buildings typically built on an annual basis, particularly in developing countries. Even in developed countries such as the United States of America, semi-engineered residential buildings are very prevalent and often fare the worst after experiencing the effects of hurricanes. This is evidenced in the aftermath of the numerous storms that have ravaged the southern coast of the United States over the years. was one of the strongest and most expensive storms to make in the United States of America in recent history. The storm killed over 1,300 people and caused the destruction of thousands of homes in the states of Mississippi and Louisiana (FEMA April 2006). Of the buildings destroyed, the great majority was determined to be single family dwellings. Similarly, made landfall in Puerto Rico on September 21, 1998 and caused substantial damages to residential buildings. During this storm, it is reported that the majority of building losses were in “all-wood” residential buildings. The structural performance of buildings constructed of concrete and masonry, however, performed well, while those with timber framed roofs saw substantial failures (FEMA March 1999). Contrary to this, properly built “semi-engineered buildings” have often survived the effects of significant hurricanes, including many that were observed by the au- thor after major wind events such of 2000, of 2001, Hurricane Richard of 2010, of 2016 and most recently Hurricanes

1 (a) Semi-engineered roofs intact after a (b) Entire building shifted from its original major hurricane position as a result of a moderate hurricane

Figure 1.1: Semi-Engineered Buildings After Extreme Windstorms ( of 1961 and Hurricane Iris of 2001) Photos by D. Dawson and C. Johnson taken from thinkquest.org

Irma and Maria of 2017. Noteworthy is the fact that many of the observed failures are as a result of the breakdown of connections of the roof framing systems more so than actual failure of the main framing components themselves. Such behaviors have reinforced the belief that one of the key to the successful performance of such roof structures subjected to extreme wind storms is indeed the configuration and makeup of the joints more so than the general member sizes and arrangements of the main structural components of the roof. With this fundamental premise, it is rea- sonable to assume that data can be gathered from a particular area that represents typical roof construction details; and be combined with engineering principles to develop an analytical tool that can be used to estimate the structural vulnerability of a particular semi-engineered roof system to extreme wind loads. While it is appreciated that such a tool would not replace rigorous engineering methods to perform structural analysis, such a tool could indeed replace or sup- plement current risk assessment methods that are probability based or those that are based on field experiences of local engineers. Additionally it is also appreciated that semi-engineered buildings are not constructed with any rigorous quality control processes that would guarantee a certain level of quality or consistency. Nonethe- less, the development of such a protocol, that can assist in the rapid evaluation of semi-engineered roof systems is the aim of the research. In Figure 1.1 the image to the left shows semiengineered roofs intact after a major hurricane. The image to 2 (a) Significant roof damage caused by (b) Total roof failure along with collapse of extreme winds the reinforced masonry and concrete building frame as a result of extreme winds

Figure 1.2: Semi-Engineered Buildings After of 2017 (Photo by Author in September 2017 British Virgin Islands ,Tortola) the right shows the entire building shifted from its original position as a result of a moderate hurricane. Figure 1.2 shows Semi-Engineered Buildings After Hurricane Irma of 2017. The image on the left shows significant roof damage caused by extreme winds. The image to the right shows total roof failure along with collapse of the reinforced ma- sonry and concrete building frame as a result of extreme winds. These photos were taken by the author in September 2017 at British Virgin Islands (Tortola) after the on field post storm damage assessment. Material types and techniques utilized in the construction of semi-engineered buildings are typically dependent on factors such as local availability, construction traditions, and economic considerations. In many parts of the United States for instance, residential buildings are often mass produced timber framed structures which are clad with various forms of facades such as stucco and other non-structural systems. In Mumbai on the other hand, the more substantial residential buildings are predominantly of multi leveled rein- forced concrete structures with reinforced concrete roofs; while in the Caribbean and much of , a combination of reinforced concrete and concrete masonry structures with timber framed roof is often the system of choice for semi- engineered and engineered residential buildings. Nonetheless, the east coast and to a lesser extent the west coast of India, the south-east coast of the United States, and virtually the entire Caribbean and Central American regions are all highly pop- ulated with semi-engineered residential buildings which are all susceptible to the

3 effects of extreme wind storms. The fundamental problem that must be address is the fact that the millions of people that do occupy these non-engineered and semi- engineered buildings are vulnerable and are affected by the effects of wind storms on an annual basis, yet with proper evaluation and moderate modifications to the detailing of many of these structures, their abilities to resist extreme wind storms can be enhanced significantly. This will ultimately save lives and properties. 1.2 Nature of Windstorms In the East Pacific Ocean, Atlantic Ocean, and , tropical cyclones are generally referred to as hurricanes. In the Western Pacific region they are more often referred to as typhoons, and simply cyclones in the areas surrounding the In- dian Ocean. Wind flow in hurricane and cyclone systems follows a counter clockwise rotational pattern in the Northern Hemisphere and a clockwise rotational pattern in the Southern Hemisphere. Due to their nature, the life spans of tropical cyclones range from as little as several hours to as much as several weeks, and are often more predictable in intensity and path than other natural hazards such as tornadoes and earthquakes. Nevertheless, even with the availability of fairly accurate path predic- tion computer models and reasonable knowledge of their damage potential, scores of towns and villages across the globe are still adversely affected by these events on an annual basis. Table 1.1, illustrates the severity of the impact of some of the most

Table 1.1: Dangerous Cyclones of The Past

Year Location Casualties

7 October, 1737 Bengal, India Over 300,000 10 October, 1780 Caribbean Islands 20,000 to 30,000 5 October, 1864 Calcutta, India 50,000 to 70,000 1876 Bengal India 200,000 1881 Haiphong, Vietnam 300,000 6 June 1882 Bombay, India Over 100,000 16 October 1942 Bengal, India Over 35,000 28 May, 1963 Bangladesh 22,000 May 1965 Bangladesh 35,000 to 40,000 13 November 1970 Bangladesh 500,000 to 1,000,000 (taken from Thinkquest.org)

4 damaging cyclones of the past. Notable is the fact that the great majority of these listed events have developed in the Indian Ocean near very significant population centers. Tropical cyclones are classified by various scales such as the Saffir-Simpson Scale, the Beaufort’s Scale and Japan’s Meteorological Agency’s Scale. Table 1.2 illustrates the Saffir-Simpson Scale which was originally developed in the 1970’s by Herbert Saffir and Robert Simpson (FEMA, July 2000 [2]). The wind velocities shown in the table are based on an averaging time of 1 minute at 33 feet above open water and typically referred to as “Sustained Wind Speeds”. It is important to note that 1 [mph 1.609 km/hr] (1 minute average) is approximately equivalent to 1.25 mph [2.011 km/hr] (3 seconds average). Table 1.3, illustrates an approximate relationship

Table 1.2: Saffir Simpson Scale

Hurricane Sustained Wind Damage Category Velocities Potential

1 74-95 mph Minimal (33-42.5 mps) 2 I 96-110 mph Moderate (43 - 49 mps) 3 I 111-130 mph Extensive (49- 58 mps) 4 I 131-155 mph Extreme (58 - 69 mps) 5 I 155 mph Catastrophic (69 mps)

between the scale utilized by the Regional Specialized Meteorological Center in New Dehli and the Saffir-Simpson Scale. Adjustments have been made to account for the fact that one scale allows for a 1 minute averaging time while the other is based on a 10 minute averaging time. The averaging time adjustment is based on the Krayer-Marshall correlation curve developed in 1992. Unlike tropical cyclones, tornados are essentially violent cyclonic events that typically span from thunderstorm systems to the ground and produce wind loads similar to that of tropical cyclones with the exception that load levels can be much more significant, load duration shorter and the wind patterns may differ due to the much smaller diameter of the system. Another key difference between the tropical cyclones and tornadoes is the source of their power. Tornados are fueled by thunder- 5 Table 1.3: Approximate Comparisons of Scales (Averaging time adjusted to 1 min)

Categorization Wind Speed Categorization Wind Speed in mps in mps

Cyclonic Storm 21 - 30 Severe Cyclonic Storm 31 - 40 Category 1 33 - 42 Very Severe Cyclonic 41 - 75 Category 2 43 - 49 Storm - Category 3 49 - 58 - Category 4 58 - 69 Super Cyclone Storm Above 75 Category 5 Above 69

storm systems and tropical cyclones by warm open waters of the tropics. As such, cyclones tend to lose power when over major significant land masses. In fact, small short-lived tornadoes are often spawned from larger cyclones. Such tornadoes were observed by residents interviewed by the author during the period when Hurricane Irma made landfall over Tortola in 2017. Due to the unpredictability and short life cycle of tornadoes they are not gauged using scales utilized for tropical cyclones. The Fujita Scale as illustrated in Ta- ble 1.4 is a very popular qualitative scale that categorizes tornadoes based on actual damages caused. The scale is used as an after-event gauge as wind velocities in tornadoes are very difficult to measure directly on a routine basis. Due to this issue and the fact that tornadoes are not common within the zones examined, they are not addressed within the research. 1.3 Nature of Semi-Engineered Buildings A significant amount of work has been done in the area of wind engineering and the design of buildings to resist loads from extreme wind storms. As such it is not the intention to “re-invent the wheel” in any form. However, semi-engineered buildings are by nature built without significant engineering input, and similarly, little has been done to evaluate the performance of these buildings under loads caused by extreme wind storms. Furthermore, little information is also available on the roofs of these buildings, which are generally the most vulnerable major component of semi-engineered buildings. The matter of estimating the structural capacities of existing semi-engineered roof systems is particularly difficult considering the fact that these buildings may vary drastically in construction details and material types from one locality to an- other. Yet it seems vitally important for us to understand and appreciate the struc-

6 Table 1.4: The Fujita Scale

Category Details Extent of Damage

F0 Light Chimneys are damaged, tree branches are broken, shallow-rooted trees are toppled. F1 Moderate Roof surfaces are peeled off, win- dows are broken, some tree trunks are snapped, unanchored manufac- tured homes are overturned, at- tached garages may be destroyed F2 Considerable Roof structures are damaged, man- ufactured homes are destroyed, de- bris become airborne, large trees are snapped or uprooted. F3 Severe Roof and some walls are tom from structures, some small buildings are destroyed, unreinforced masonry buildings are destroyed, most trees in forests are uprooted. F4 Destructive Wellconstructed houses are de- stroyed, other houses are lifted from foundations and blown some distances, cars are blown some distances, large debris become airborne. F5 Incredible Strong framed houses are lifted from foundations, reinforced con- crete structures are damaged, auto- mobile sized debris become airborne, trees are completely debarked.

tural effectiveness of these systems against impending wind loads that are so often responsible for loss of property and life.

7 Semi-engineered and non-engineered structures constitute the majority of build- ings across the country of . These building types are in fact very similar to those predominant in the Caribbean and much of Central America. In fact, the building cultures for many of the countries in this region have their roots in the Colonial era with traditional influences from tradesmen from European countries such as the United Kingdom, France and Spain. In more recent times, however, the United States has also influenced the way buildings are built within the region. However, the construction methods most often employed in the area today are still significantly different from those methods often utilized in the United States for the construction of the typical mass produced housing developments. Non-engineered buildings across Belize take various forms. These ad-hoc struc- tures, which are informally constructed with little or no technical input and with materials for which their structural characteristics are often not readily known, are not only influenced by the locality in which they are built but also by ethnic tradi- tions of the builders. The Mayan Indians of the rural south for example, traditionally construct small residential huts of un-sawn timber frames with joints tied with vines. These structures are routinely clad with various forms of thatch or wood which are crudely sawn by semi-modern means such as with chain saws. The Mestizos of the rural North tend to use un-sawn wood frames sealed with a stucco of white lime. Remarkably, many of these structures do survive the effects of extreme winds. In recent times, however, engineered materials and components are slowly being used as substitutes for some of the traditional systems. With the exception of what is classified as temporary housing, the majority of residential buildings currently being constructed in the country of Belize are semi-engineered. These include those built by low-middle income to upper-middle income families as well as a limited amount of lower income and upper income families. In fact, the 2010 Population and Housing Census of Belize revealed that as much as 80% of all residential units in the country are constructed of sheet metal roofs (Statistical Institute of Belize, 2011 [3]) which are typically cold formed steel sheets supported on sawn timber framing. Mumbai and other parts of India are highly populated with both semi-engineered and non-engineered buildings. The non-engineered buildings in the areas examined under the research work were found to be primarily “temporary structures” built with absolutely no intention to resist anything more than the frequent gale that may be experienced every so often. It is for this and other practical reasons that the research conducted by the author focused on semi-engineered buildings where the variations in methods and details are not as vast and the overall performances are more predictable. Figure 1.3 and Figure 1.4 shows examples of non-engineered

8 buildings found in both Belize and on West Coast of India.

(a) (b)

Figure 1.3: Non-Engineered Buildings Built by the Mayan Indians of Southern Belize

Semi-engineered buildings, which include buildings build with little no direct engineering input, but with engineered components are very common in Belize, the wider Caribbean, and much of the West Coast of India. These buildings are routinely built of light-weight pitched roof systems with various forms of roof decking. The most common form of roof decking utilized in Belize is the traditional cold formed galvanized roof sheets with a sinusoidal profile also called corrugated galvanized iron (CGI). More recently galvalume panels, which are aluminum and zinc coated steel sheets with an industrial or “R” profile is very popular. In the parts of West Coast India covered by the research, the roof deck of semi-engineered single family residential buildings were found to be primarily of a locally manufactured clay tile (Mangalore), corrugated asbestos sheets, and corrugated steel sheets (CGI) similar to those found in Belize. In both areas, concrete slabs are also often used in the construction of the more upscale buildings. The roofs of semi-engineered buildings in Belize as shown in Figure 1.5, are most often constructed with trusses of timber and less frequently of concrete beams and slabs. Walls are also primarily of concrete masonry with or without reinforcement. These are generally rendered with a cement plaster internally and externally, which add to their flexural capacities. Multileveled buildings are often built of reinforced concrete frames. The range of windows and doors are also limited in range and includes a few types of aluminum louvers and in- frequently timber battens and timber louver windows. In more prominent buildings, single hung aluminum and glass windows are sometimes favored. Other components 9 (a)

(b)

Figure 1.4: Non-engineering Buildings in West Coast India

10 (a) (b)

Figure 1.5: Typical Semi-engineered Buildings in . such as doors are often of solid timber but more commonly of paneled timber. In the areas inspected in India, pitched roof systems of semi-engineered buildings were primarily found to be of two types. These include timber framed and metal framed systems. Routinely, spans were found to be relatively small and the roof structures comprise of simple spans as opposed to truss systems which were found to be more common in Belize. Walls in these areas were found to be primarily of bricks rendered on both sides, and in a few cases concrete masonry were found. Reinforced concrete frames are apparently used occasionally. Figure-1.5 illustrate some of the more prevalent semi-engineered building forms found in Belize. 1.4 Need for a New Protocol Prior to , which made landfall in Florida in 1992 , vulnerability assessment in areas such as Florida was done by the actuarial method and lost estimation was based historical claims data (Ed Rappaport, 1993 [4]). These models proved significantly inadequate after the effects of Hurricane Andrew were realized which lead to the development of a new approach. The new approach included the development of a new building code, and the Florida Public Hurricane Loss Model (FPHLM). One of the objectives of the new model was to predict hurricane risk in the state of Florida (Jean-Paul Pinelli, Gonzalo Pita and Kurt Gurley, September 2010 [5]). The new model moved away from the purely actuarial approach of the past and included an engineering component that considers the physical characteristics of the building stock of the subject area. The engineering component of the model makes

11 certain simplifying assumptions about the make-up of the various building types and the details of these buildings in the area and does not consider specific structural details of each individual building. The Florida Public Hurricane Loss Model was developed based on surveys done on building typology across the state of Florida and provides a more accurate and relevant alternative to the actuarial method. However, this and other similar models are not adoptable to other areas such as Belize or India for that matter. Addition- ally, the building stock of Belize and other developing countries by their nature include a much higher percentage of residential buildings that are semi-engineered and non-engineered; and the fact of the matter is that the vulnerability levels of these buildings are not well known by the insurance companies, the local emergency management organizations, or the home owners themselves. Hurricane Irma, that devastated the Caribbean in 2017 with winds speeds amongst the highest ever recorded in the Atlantic and Caribbean, has been a reminder of the desperate need for us to better understand the characteristics and vulnerability lev- els of our building stock. The vulnerability protocol developed under the research work offers a unique opportunity towards that need and allows for the vulnerability assessment of individual buildings within the study area that currently does not exist. 1.5 Aim and Objectives of the Study The aim of the research is to develop an engineering based protocol to assess the vulnerability of semi-engineered building roofs against high wind velocities in a rapid and site-friendly manner specific to the study area. The study area is comprised of the country of Belize and the coastal town of Alibag, India.

12 In order to achieve the research aim the following objectives have been estab- lished:

1. Understand the building stock and construction culturein terms of the types of buildings that we have and the methods and materials used to construct the roof systems.

2. Identify and close gaps that exist in parameters in the study areas necessary to conduct mass vulnerability assessments and for the development of the protocol.

3. Catalog and analyse relevant data of the building stock such as the varia- tions in these building roof types, their physical geometries, and other details that affects the structural performance of a given roof system under wind loads.

4. Develop the vulnerability protocol based on the engineering-based ap- proach that allows for the structural assessment of these systems under wind loads in a way that is not nearly as time consuming as the rigorous conven- tional approach would provide a reasonable level of accuracy for the intended purpose.

5. Streamline the protocol by making the assessment protocol user friendly and more importantly site-friendly for practical industry use.

6. Validate Protocol by comparing results of a case study using the assessment protocol compared with results determined by the traditional engineering ap- proach.

• Objective No. 1 : Understand the Building Stock and Constriction Culture Understanding the building stock is a necessary step to any of the approaches to vulnerability assessment. Much of the information necessary to understand the building stock and construction culture of the study areas was gathered from post-storm assessments, field inspections and industry knowledge. Addi- tionally, literature review of historic events and post-storm damage assessment reports provides a wealth of information in this regard. This objective is also closely tied to the second objective that follows.

• Objective No. 2 : Identify and Close Gaps

13 It was clear from the onset of the research and the execution of Objective no. 1 that there are certain gaps that exist in the industry of the study areas that are necessary to perform a structural evaluation of semi-engineered roof and to develop the proposed protocol. This, for obvious reasons was more significant in the main study area of Belize. This is illustrated by the fact that the vulnerability assessment that is done in the main study area by the local insurance companies for example, is currently a simple broad based estimation of vulnerabilities based on historic performances of the building stock and location of the individual buildings relative to the coastline. As such, it was necessary to close these gaps in order to establish an engineering- based protocol that is suitable for use in practice as indicated in Table 1.5. Table 1.5: Research Gaps and Proposed Strategy

General Data Specific Data Gap Proposed Method Gap to Close Gap Quantitative Qualitative Building Typol- Range of Building Types Physical Surveys Visual Surveys ogy and Configura- (Main Area) tion of Existing Build- Range of Building Types Physical Surveys Visual Surveys ing Stock (Secondary Area) Range of Roof Types Physical Surveys Visual Surveys (Main Area) Range of Roof Types Physical Surveys Visual Surveys (Secondary Area) Deck Type Physical Surveys Visual Surveys (Main Area) Deck Type Physical Surveys Visual Surveys (Secondary Area) Construction Roof Framing Types Physical Surveys Visual Surveys Details (Main Area) Roof Framing Types Physical Surveys Visual Surveys (Secondary Area) Range of Foot-print Physical Surveys Visual Surveys Dimensions (Main Area) Range of Roof Angles Physical Surveys Visual Surveys (Main Area) Range of Roof Angles Physical Surveys Visual Surveys (Secondary Area)

14 Table 1.5 continued from previous page General Data Specific Data Gap Proposed Method Gap to Close Gap Quantitative Qualitative Performance Deck Fastener Types Physical Load Visual Obser- Data Tests vations, (Both Areas) and Literature Re- view Deck Fastener Analytical Post Storm Configuration Computations Observations (Both Areas) Details of Framing Joints -do- -do- (Both Areas) Fastener Failure Modes -do- -do- (Both Areas) Capacities with various -do- -do- Roof Deck Types (Main Area) Head Loss with -do- -do- Various Deck Gauges Withdrawal -do- -do- from various Wood Types Wood densities -do- -do- Failure Modes with -do- -do Various configurations Truss Joints -do- -do-

• Objective No. 3: Catalog and Analyze Relevant Data The third objective of the research includes the cataloging and analysis of the data collected. This includes the development of charts, graphs and ta- bles from the data collected and those otherwise available that are necessary to facilitate the protocol as well as the establishment of capacity thresholds. Table 1.6 outlines the various forms of cataloging that was done under this objective.

• Objective No. 4 : Develop a Vulnerability Protocol The development of the protocol necessary for the vulnerability assessment of semi-engineered building roofs in the study areas is the forth research ob- jective. The development of the protocol requires a number of steps, most of which are captured in the previously listed objectives. Specifically the protocol requires the following:

15 Table 1.6: Presentation of Data Form

Data Type Catalogue Form

Building Types ( Both Areas) Pie Charts, Photos Roof Deck Types Pie Charts Roof Framing Types Pie Charts Local Wood Densities Result Tables And Graphs Floor Plans Auto Cad Drawings Cross Sections Auto Cad Drawings Deck/Fastener Capacities Table Of Results Fas Tener Capacities (Withdrawal) Table Of Results And Graphs Joint Capacities Tables And Graphs Pressure Distributions On Various Forms Tables And Graphs From Analytical Results

1. Conduct literature review and surveys as outlined above to capture the range of variables that would be contained in the typical semi-engineered building roof. 2. Establish the limitations based on observations made in the surveys and literature review. 3. Identify data and information gaps necessary for the structural evaluation of a typical semi-engineered roof system as outlined above. 4. Conduct tests and analyse collected data in order to close the gaps. 5. Based on the range of building forms, locations, roof angles, roof types determine pressure distributions on the various roof surfaces based on varying wind velocities. 6. Develop pressure-velocity tables for the range of roof variations being considered. 7. Based on the results of the literature review, analytical computations and load tests results develop load tables to facilitate the protocol. 8. Develop detailed protocol to conduct the evaluation of a typical semi- engineered roof system based on the input parameters typical of the study areas.

• Objective No.5 : Streamline the Protocol This objective of the research is to streamline the protocol such that the pro- cess can be done by a mid-level technician in a rapid manner. Additionally the objective includes provisions to make the protocol site-friendly. These objectives were satisfied by the development of a mobile app. 16 • Objective No.6 : Validation of Protocol The final objective of the re- search include a validation of the protocol using a comparison analysis of the results produced by the protocol against an analysis done using the traditional engineering approach.

1.6 Layout of the Thesis This thesis presents a summary of the work done on the performance of semi- engineered building roofs when subjected to extreme wind loads. The thesis is made up of six main chapters and an appendix. The first chapter is the Introduc- tion and provides a general background of the research area including windstorms and semi-engineered buildings. The introductory chapter also sets out the aim and objectives of the research and the layout of the thesis. Chapter 2 provides a brief background of the risk assessment industry and elab- orates on other key publications that are relevant to the research. Chapter 3 includes the research Formulation and Approach and examines the effects of windstorms on buildings. The chapter also presents an overview of the research and its limitations and provides details of the field observations and surveys, as well as an overview of the evaluation approach. Chapter 4 includes details of the data collected and the results of analysis con- ducted. It includes observations made in the two study areas as well as a tertiary area of the British Virgin Islands following two significant hurricanes in 2017. The chapter also presents samples of the various tables and charts developed from the data gathered. Chapter 5 provides comprehensive background details of the assessment proto- col. It also includes a validation of the assessment protocol which is achieved by conducting a case study using the traditional engineering method. Results of both methods are compared and examined. The final chapter of the thesis includes con- clusions and recommendations and provides scope for future work. The Appendices which follows provides references, samples of drawings prepared of sample buildings surveyed and photos of post storm damages.

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