Breeze Strength Lacked Charging on Structures - Essay Example

Wind loading on Buildings Windstorms Definition There are various types of windstorms that do exist in the world today. A windstorm can be defined as a storm with very strong winds or with strong wind gusts though without rain or with little rain. A windstorm can come in a variety of ways all with a variety of names. A dust storm is a very big wind storm where large and diverse clouds of dust are swept over a large geographical area. A tempest is a windstorm that is very violent and also accompanied by rain, hail or snow. A squall is a violent windstorm that occurs for a brief time period but is also accompanied b hail, rain or snow. In this section of the paper, there will be a description of tropical cyclones, typhoons, hurricanes and tornadoes. In the paper, there will be information on the scales of severity. Facts on windstorms There is a wide ranging phenomenon that is referenced by the term windstorm. Some of the most common event will be looked into in this section. Tropical cyclones are violently rotating windstorms that form over tropical water that has a temperature of over 260C and in a location of between 5-150 latitude. A typical cyclone is experienced when the winds assume a large gale force of a minimum 34 knots or 117km/h. These winds are referred to using different names in different place. In the United States, the Caribbean, Pacific and Central America, they are called hurricanes. In the Bay of Bengal, they are called cyclonic storms; tropical cyclones in south India, Australia and the south Pacific and typhoons in East Asia and Northwest Pacific. The tropical cyclones first occur as thunderstorms that due to the spinning of the earth revolve in a clockwise direction in the southern hemisphere and anti clockwise in the northern hemisphere. The storms span about 2000km and can be up to 10 km high. In the organization of the storm, there is formation of “an eye” at the center which is calm and clear at the center. Surrounding the eye is a dense cloud ring called the “eye wall” which is a dense cloud ring and marks the belt of the strong winds. The eye spans a width of at least 10 km and up to 50km. The tropical cyclones are persistent can take days. They gain the energy with which they get powered from the warmth of the tropical waters. Due to this fact, they loose the energy as they move into the landmasses. A sandstorm is a wind that carries sand in the air with formation of a low cloud at near ground level. A typical sandstorm will reach a height of 15 meters. It contains sand particles of an average size of 0.15mm – 0.30mm and moves at speeds of about 10 miles per hour. At a certain critical speed, the sand grains roll ahead along the surface of the ground. When the speeds of the wind are high, the grains move through a process called saltation where they are lifted slightly and then pushed forward making them to move in a hopping motion. Dust storms form in semi arid areas where s mall particles of dust are blown into the air by wind. Due to their small physical size, they are drifted aloft by the wind and suspended in the air. A tornado is a violent rotating air column that extends from a thunderstorm to the ground. Very violent tornadoes can cause widespread destruction with the speeds of wind being up to 500km per hour. The paths of these tornadoes vary from one to 50 miles length. They are at times accompanied by large hailstones that that are from a diameter of 10cm moving at 150km/hr. tornadoes form with some intense and heat. The tornadoes can be so destructive and are often accompanied by flash floods, large hails and lightning. Shamal winds Shamal winds have acquired their names from the Arabic world the name meaning north. The winds are predominant in the summer months of May to July. Shamals are northwesterly winds that blow over Iraq and the Arab Peninsula. They are most prevalent during the transition from the winter to the spring season. This trend is seasonal and is characterized as a combination of two weather systems that are separate: the “sub tropical jet stream” from the southern Arabian Peninsula and a “polar front jet stream” from the European continent. When the systems get close to each other, they create some weather that is more dynamic giving rise to the shamal winds. Shamals occur as a result of very strong northwest winds that infiltrate into the Persian Gulf from the Turkish mountains and Iraq from the northeastern side and Saudi Arabian plains from South West. The winds causing the Shamals are strongest in the spring to summer period; the shamals are also persistent in this period too. The close proximity of the two streams erstwhile stated are the main promoters of the dry fronts and the cold fronts that make up the shamals. The strong winds basically form in front of the shamals and behind the shamals. The shamals last between 3-5 days. Due to the intensity of the sandstorms, the shamals usually halts both air and ground movement. This is mainly due to the depth of the dust and sand that cannot allow movement and visibility. There are winter and summer shamals; summer shamal occurs when cold air passes over the Turkish mountains which have got some cool air which then sends the sand and the dust aloft. The winter shamal happens due to high pressure over the Arabian Peninsula after a cold front passes causing some low pressure to be maintained in the East of the Persian Gulf. This happens to cause very strong winds that last up to five days. The events of these winds are as a result of the climate and the topography of the region. The heat that is over the Afghan and the Pakistan region that occurs as a result of the monsoon circulations creates low pressure areas in the Zagros Mountains of Iran. When these low pressure zones interact with high pressure zones in North Saudi Arabia, there is an enhancement of some flow features in the Arabian Gulf. This is increased to a higher extent by the topography of Saudi Arabia which is below 2000m in some areas. Wind damage in Australia There are various cyclones that have hit Australia but this section of the paper will highlight some of the recent cyclones than have occurred. In 2005, Cyclone Ingrid occurred as a category 4/5 disaster. The cyclone crossed the far coast of North Queensland somewhere near Lockhart River. It started as category 4 and rose to category 5 on the Northern territory. It then weakened and later build again at the Kimberly Coast (Kamenev, 2011). There were sea swells that occurred causing a boat to capsize and kill five at Papua New Guinea. In 2006, Cyclone Larry, a category 4 cyclone hit north Queensland close to Innisfail. 10,000 homes were damaged and farmers were greatly affected by the effects of this cyclone. The most affected area was Silkwood where 99% of the homes were damaged. Some of the extreme damages that were recorded were collapse of high voltage transmission towers along Palmerstone Highway. Estimations by the Federal Government stood at $1.5 billion. There was no loss of lives and no serious fatalities were reported (Kamenev, 2011). There have been other cases which have however been slight and with little impact such as high overnight winds in Victoria. The most recent wind damage to hit the country is cyclone Yasi. This stormed slammed various towns including Mission Beach, Cardell and Tully with the speeds of winds raging up to 280km/hr (CBCnews, 2011). The storm toppled power lines and uprooted trees making over 180, 000 homes to go without power in Queensland. The estimates of the damage caused by cyclone Yasi were $5.6 billion. At least one person went missing though there were no other serious fatalities or deaths as a result of the cyclone. Large scales of crops were also devastated by the winds (CBCnews, 2011). The most affected area was the coastal region as the other people were mainly affected by the flooding. Effects of winds on high rise buildings The nature and the impact that is caused by wind loading on a built environment are very essential in determining the design of tall buildings. Up until the recent times, it has been practiced typically that vertical distribution of the wind profiles in full scale that are modeled for testing of boundary layer wind tunnel have some focus on those wind profiles that have a behavior that is synoptic (Holmes, 2006). In the examination of wind loading, it is typical to have mean wind profile applied for a given range of return periods when examining the impact of wind loading. Various effects have been considered in the following paragraph. The section will consider the effects as evidenced by shamal winds against synoptic winds (Holmes, 2007). Cladding pressures in times of synoptic winds are higher as compared to the shamal case with the latter being up to three times higher. There are high base moments and the floor by floor distribution of loads is high. The building acceleration at the highest floor that can be occupied is higher when the buildings get exposed to synoptic events (Aurellius et al., 2006). The impact of wind profiles on high rise buildings can be looked at using the “wind tunnel modeling technique”. In this, design parameters that depend on large return periods like base moments, cladding pressure and load distributions greatly affected the design of the buildings. In looking at the case highlighted and in consideration of the design for tall buildings, synoptic events have a high cause for consideration in the process of designing of tall buildings due to wind loading (Aurellius et al., 2006). Wind pressures are differently experienced on claddings as compared to structures in high rise buildings. The differences that are realised on pressures that are induced by wind surfaces of buildings are not uniform and get unsteady due to the varying properties of cladding. Pressures that result to production of loads on structures are of a higher average figure than those on a window panel. Wind pressure information required for design is derived using wind tunnel tests for structures and also for cladding. For the structures, characteristics of the flow are modeled rightly (Dalgliesh, 1974). Wind pressure measurements on buildings at full scale can give results that are pertinent for modeling for the sake of design. Wind pressure fluctuations on the cladding are as a result of fluctuating speed of the wind as well as the direction of the wind. These values impact on wind turbulence. Fluctuating wind pressures have a big effect on the pressures on the structure loading (Standen et al., 1971). References Aurellius et al. (2006) “The impact of Shamal winds on tall building design in the Gulf Region” Retrieved from http://login.dm.gov.ae/wps/wcm/connect/93e05a8049ddc3c08063ef85e0561914/WindSe minar-seminarpaper.pdf. Dalgliesh, W. (1974) “Comparison of model/ full scale wind pressures on a high rise building” Journal of Industrial Aerodynamics 1: 55-66. CBCnews (2011) “Cyclone Yasi weakens after slamming Australia” Retrieved 07.09.2011 from http://www.cbc.ca/news/world/story/2011/02/03/australia-cyclone-yasi.html. Holmes, J.et al (2007), A forensic study of the Lubbock-Reese downdraft of 2002, Part 1: Storm Characteristics, 12th International Conference on WindEngineering, Cairns, Australia. Holmes, J. (2007), A forensic study of the Lubbock- Reese downdraft of 2002, Part 2: Running Mean Wind Speeds and Turbulence, 12th International Conference on Wind Engineering, Cairns, Australia. Holmes, J. (2006), Review of Extreme Thunderstorm and Shamal winds in the Arabian Gulf Region, Report prepared for BMT Fluid Mechanics, September. Kamenev, M (2011) “Australia’s worst cyclones: timeline”. Australian Geographic Retrieved 07.09.2011 from Feb, 4, 2011< http://www.australiangeographic.com.au/journal/timeline-australias-worst-cyclones.htm> Standen, N., W.A. Dalgliesh and R.J. Templin (1971), “A wind tunnel and full-scale study of turbulent wind, pressures on a tall building”, Proc. 3rd. Int. Conf. on Wind Effects on Buildings and Structures,Tokyo, Part 11: 199-209. Vickery, B.J, (1965) “On the flow behind a coarse grid and its use as a model of atmospheric turbulence in studies related to wind loads in buildings”, National Physical Laboratory Aero Report 1143. Read More

When the speeds of the wind are high, the grains move through a process called saltation where they are lifted slightly and then pushed forward making them to move in a hopping motion. Dust storms form in semi arid areas where s mall particles of dust are blown into the air by wind. Due to their small physical size, they are drifted aloft by the wind and suspended in the air. A tornado is a violent rotating air column that extends from a thunderstorm to the ground. Very violent tornadoes can cause widespread destruction with the speeds of wind being up to 500km per hour.

The paths of these tornadoes vary from one to 50 miles length. They are at times accompanied by large hailstones that that are from a diameter of 10cm moving at 150km/hr. tornadoes form with some intense and heat. The tornadoes can be so destructive and are often accompanied by flash floods, large hails and lightning. Shamal winds Shamal winds have acquired their names from the Arabic world the name meaning north. The winds are predominant in the summer months of May to July. Shamals are northwesterly winds that blow over Iraq and the Arab Peninsula.

They are most prevalent during the transition from the winter to the spring season. This trend is seasonal and is characterized as a combination of two weather systems that are separate: the “sub tropical jet stream” from the southern Arabian Peninsula and a “polar front jet stream” from the European continent. When the systems get close to each other, they create some weather that is more dynamic giving rise to the shamal winds. Shamals occur as a result of very strong northwest winds that infiltrate into the Persian Gulf from the Turkish mountains and Iraq from the northeastern side and Saudi Arabian plains from South West.

The winds causing the Shamals are strongest in the spring to summer period; the shamals are also persistent in this period too. The close proximity of the two streams erstwhile stated are the main promoters of the dry fronts and the cold fronts that make up the shamals. The strong winds basically form in front of the shamals and behind the shamals. The shamals last between 3-5 days. Due to the intensity of the sandstorms, the shamals usually halts both air and ground movement. This is mainly due to the depth of the dust and sand that cannot allow movement and visibility.

There are winter and summer shamals; summer shamal occurs when cold air passes over the Turkish mountains which have got some cool air which then sends the sand and the dust aloft. The winter shamal happens due to high pressure over the Arabian Peninsula after a cold front passes causing some low pressure to be maintained in the East of the Persian Gulf. This happens to cause very strong winds that last up to five days. The events of these winds are as a result of the climate and the topography of the region.

The heat that is over the Afghan and the Pakistan region that occurs as a result of the monsoon circulations creates low pressure areas in the Zagros Mountains of Iran. When these low pressure zones interact with high pressure zones in North Saudi Arabia, there is an enhancement of some flow features in the Arabian Gulf. This is increased to a higher extent by the topography of Saudi Arabia which is below 2000m in some areas. Wind damage in Australia There are various cyclones that have hit Australia but this section of the paper will highlight some of the recent cyclones than have occurred.

In 2005, Cyclone Ingrid occurred as a category 4/5 disaster. The cyclone crossed the far coast of North Queensland somewhere near Lockhart River. It started as category 4 and rose to category 5 on the Northern territory. It then weakened and later build again at the Kimberly Coast (Kamenev, 2011). There were sea swells that occurred causing a boat to capsize and kill five at Papua New Guinea. In 2006, Cyclone Larry, a category 4 cyclone hit north Queensland close to Innisfail. 10,000 homes were damaged and farmers were greatly affected by the effects of this cyclone.

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