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Engineering impacts on buildings
To begin the series on the impact a hurricane has on engineering, we will look at structural engineers and the work they do with buildings and tunnels in anticipation of hurricanes. Structural engineers, as the name designates, work with the structures of things such as buildings and determine what shapes, materials and designs will most benefit that particular project.
To just build a square building that stands in the path of hurricane winds, is not the most aerodynamic design. It instead acts as a wall and blocks the path of the air. In a Cat 5 hurricane where winds can hit 155 mph or more, the pressure caused by that wall can reach up to 65 pounds per square foot (450 kPa). As a hurricane passes over however, winds are not just coming in one direction. Instead they pummel the building from all sides and challenge the integrity of the design. Also, as wind tries to escape the wall it rushes around the corners of the building and creates small cone shaped spirals which can create suction force nearly twice that of the wind pressure. As sheets or bits of building start to come off it only increases the vulnerability of the building and increases the area that the wind can attack. Hurricanes however are not solely comprised of wind; they also have a lot of rain and sometimes even hail, as well as numerous amounts and sizes of debris. These can weigh down low quality roofs and erode foundations of building fairly easily. As water levels rise, flooding can simply push buildings from their foundations.
Engineering from the top
Structural engineers, in conjunction with mechanical and electrical engineers, are constantly finding new ways to improve building design and better manage any large scale effects from hurricanes. One simple thing that structural engineers have put onto many buildings in the areas most commonly affected by hurricanes is a parapet roof design. A parapet is basically a low wall that is designed to combat wind towards the top of a building so that a roof does not take the attack full on. The problem is many parapets lead to flooding on roofs because they either block the water or the rain gutters that it allows are too narrow to do any good in a hurricane. An external gutter was then designed to work with a parapet but it was determined that unless absolutely necessary, a gutter should be avoided. Today, most parapet roof designs are located on commercial buildings where the roof actually acts as a large drain allowing the water to be carried down the piping system that either runs through the building, along with the other plumbing or through the outside wall where it is allowed to drain into the storm runoffs. While this type of roof can lessen the effects of extreme wind, a hurricane that creates large amounts of water quickly, can result into water pooling up upon the roof which will eventually cave in under the weight. When it comes to more traditional or residential buildings, engineers determined that the slope of a building’s roof can have a very large impact on how well it will reduce impact during a hurricane. To combat the rain a large slope is desired, around 14 degrees to allow for quicker run off of water. On the other hand, a low slope is desired, around 8 degrees to reduce the profile and increase the aerodynamics in the wind. These are some of the calculations that need to be taken into effect when designing traditional style structures. On smaller buildings it is more common to have the higher sloped roof because the wind speeds are typically slower and less violent at lower altitudes. On taller buildings where a high roof would drastically increase the area that the wind is able to attack, engineers will typically design a roof closer to 8 degrees so that they are less likely to be torn apart from the onslaught of wind.
Engineering tools play their part
Many factors are taken into consideration when structures are being designed. The surrounding areas such as the landscape, as well as other structures play a major role in building design. Engineers will use a plethora of tools that include computer aided design (CAD) for design drawings, finite element analysis (FEA) for material and stress analysis and computational fluid dynamics (CFD) for aerodynamic and flow dynamics. As we continue this discussion on engineering practices and designs in the wake of disasters, we will look into how other disciplines are utilized and the roles they have in lessening the effects of hurricanes.
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