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. Hurricane Katrina was one of the strongest and most expensive storms to make landfall 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, Hurricane Georges 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 Hurricane Keith of 2000, Hurricane Iris of 2001, Hurricane Richard of 2010, Hurricane Earl 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 (Hurricane Hattie 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 Hurricane Irma 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 Central America, 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 Caribbean Sea, 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.