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The Effect of a Building’s Shape on
Wind/Load Sheer |
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Researched by Azalea K.
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The purpose of this experiment was to determine the effect of a building’s shape on wind load/sheer,
I became interested in this idea when I saw reports about the huge hurricanes that damaged many homes in Florida and the Caribbean. I wondered if the shape of a building affected its ability to avoid damage.
The information gained from this experiment could help the people in hurricane or tornado areas build safer structures.
My first hypothesis was that the geodesic dome would withstand wind load better than the gable and hip roofs. It would create less drag in a wind tunnel.
My second hypothesis was that the hip roof would be the building that exerted the second least amount of drag.
I based my hypothesis on the fact that the nose of an airplane is rounded and airplanes fly fast through the air. This means that air must skim off the nose allowing less drag. I thought that this might be the same with roofs, the air would skim off them not allowing wind power to destroy or severely damage the house.
The constants in this study were:
- The speed of the wind
- The size of building
- Materials used in building
- Time tested
- Wind tunnel used
- Spring scale to measure force
The manipulated variable was the shape of the buildings.
The responding variable was the force of drag exerted on the buildings by strong wind.
To measure the responding variable I used a wind tunnel with a spring scale inside of it to find drag force.
QUANTITY |
ITEM DESCRIPTION |
| 1 | wind tunnel |
| 1 |
geodesic dome model |
| 1 | hip roof building model |
| 1 | gable roof building model |
| 1 | room to conduct experiment |
| 1 | low friction car |
| 3 | spring scales (n) |
1. Reserve time to use the school’s wind tunnel
2. Get the materials for three building models, approximately 10x10x15 cm. The building models were built out of one sheet (8x4feet) of exterior grade 1/4 inch plywood. Each one of the three bases was 10x10cm and was glued together and made with 90-degree angles.
3. Build a dome on one of the 10x15cm square bases based on the geodesic model. The dome is made of a square “flat” roof on which sit two reinforcement “ribs” creating four segments. Then, 20 triangular pieces of heavy, single-ply construction paperboard (specifically an old shirt box) are glued into the four 5 piece geodesic design segments. The basic format for the building, as well as complete directions for building a geodesic dome, are at http://architecture.about.com/library
4. Build a hip roof building approximately 10x10x15cm, where the triangular hip sides have a 30-degree slant and the other 10cm sides have a 50-degree slant.
5. Build a gabled-roof building approximately 10x10x15cm, where the gabled sides are perpendicular to the ground and the slanting sides are at about 50-degrees.
6. Take the models to the wind tunnel. Attach a spring scale to a low friction car and a wind tunnel connection.
7. Place one of the completed buildings on the low friction car in the wind tunnel.
8. Start the wind tunnel at 25 miles an hour.
9. Measure how the wind load affects the drag on each of the buildings.
10. Conduct several trials with each model. Record results in journal.
11. Finally, average results for each building
The original purpose of this experiment was to determine the effect of building shape on wind load/sheer.
The results of the experiment were that the geodesic dome exerted the least amount of drag. The geodesic dome averaged 35.0 grams, The hip roof averaged 44.4,, and the gable roof averaged 105.6.
See my table and graphs
My first hypothesis was that the geodesic dome would exert the least amount of drag. My second hypothesis was that a hip roof would exert the second least amount of drag.
The results indicate that these hypotheses should be accepted. Because, the geodesic dome exerted the least amount of aerodynamic drag (35.0g). Then the hip roof at 44.4g, and finally the gable roof at 105.6g.
Because of the results of this experiment, I wonder if the strength of the wind would affect the general results.
If I were to conduct this project again I would make sure that these trials were fairer by keeping the dimensions of each building type more equivalent. I would attach the model buildings to the frictionless car so the building was much lower to the ground. (The car would then be inside the building.) I would do many more trials for each building. I would modify the wind tunnel so the airflow was truer and less swirly.
Introduction Through the ages hurricanes have torn apart thousands of people’s homes, leaving them shelter less, starving, and cold. As a result people in high hurricane risk areas, like on the US south east coast, have been searching for a house that they can build which will stay intact when exposed to hurricane force winds. Aerodynamics Aerodynamics is the study of the forces acting on an object as it moves through air or other fluid. Aerodynamics act on airplanes, sailboats, or other objects that move through the air. Aerodynamics affect the motion of objects. The Wright brothers studied aerodynamics before building the first successful airplane. Aircraft manufacturers use aerodynamics principles in designing aircraft. Architects use aerodynamics to build skyscrapers and other buildings. Engineers also use aerodynamics to build automobiles. Most principles of aerodynamics relate to the two basic aerodynamic forces called lift and drag. Lift is an aerodynamic force made by the motion of an airfoil through the air. Drag is also an aerodynamic force that resists forward motion of objects. The shape of an object influences amount of drag exerted by it. For example a geodesic dome might exert a different amount of drag than a hip, or gable roof. Geodesic Domes Most of the time a geodesic dome is shaped like a hemisphere and made up of triangles. All triangles have two faces, one viewed from inside and one viewed outside of the geodesic dome. A geodesic design uses many triangles to create a very strong spherical structure. This structural shape encloses the most amount of space using the least amount of material, therefore making a dome very economical and earth-friendly. There are no equilateral triangles in this structure although it is not immediately visible. Geodesic domes use three lengths of edges and two types of triangles. Since airplane architects and engineers use cone shaped noses on their planes to make them cut down on wind resistance, the same concept might apply to a cone or sphere shaped house. Wind Power The energy in wind comes indirectly from the sun. Air above is warmed or cooled by contact with earth’s surface, making high and low pressure areas that cause air streams to flow horizontally from region to region making wind. The strongest winds occur mostly in coastal areas. In wind the amount of energy produced depends on speed. The German firm Messer Schmitt-Boelkin - Blohm estimated that 170,000 potential wind sites could make up to 20 million kilowatts of energy per year. Hurricanes and tornadoes cause lots of devastation and poverty each year. Lives, houses, property, and money are lost every time a tornado or hurricane hits. These tragedies are due to powerful forces made by wind. In the year 1900 a hurricane killed approximately 6,000 people in Galveston, Texas. Also in 1989 Hurricane Hugo hit the West Indies and the southeastern U.S. causing $7 billion in damage, and $5 billion in South Carolina. A hurricane is a whirling storm anywhere from 200-300 miles in diameter, the wind is 75 miles per hour or more. Hurricanes have many destructive powers. A wall cloud area blows 130-150 miles per hour. Hurricanes cause many floods. Tornadoes are often present in hurricane clouds. Summary Studies of wind power or home design can determine which design you should buy or build if you live in a hurricane force wind risk zone. Because of the large amount of destruction caused by hurricanes each year the people and the government lose billions of dollars each year. Geodesic domes are environmental, as well as cheap. In order to save money we should have more people live in geodesic domes. |
Brown, Warren. “Windmills.” Alternative Sources of Energy 1994. Blake, Trevor. “How to Build a Geodesic Dome Model http://architecure.about.com/library/cdome.htm Insurance Council, Florida. “Key Facts from Florida’s 2004 Hurricane Season” P.O. Box 13686 Tallahassee, FL 32317-3686 2004. Plotkin, Allen “Aerodynamics” The World Book Encyclopedia 1998 Wendland, Wayne M. “Hurricane” The World Book Encyclopedia 1991 |
I would like to thank the following people for helping make my project possible:
- My parents for pushing me to keep going and for helping me make my building models.
- My friends for making my work seem easier with their humor and sense of fun.
- Mr. Newkirk for being an excellent teacher, supporter, and motivator.
- Mrs. Helms for being an awesome helper and answering our questions no matter how weird they might seem.
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