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• Forces within the Earth are constantly bending and straining the thin crust we call home. • Most earthquakes occur within the earth’s upper crust, 15 miles below us. • Major earthquakes that occur in heavilypopulated areas with tall buildings can result in tremendous destruction, injuries, and death! A Large Boat on a House? • Seismic waves cause tremors (shaking). • Primary waves move fast with a push-pull action. They show up on a seismograph as a smooth line. • Secondary waves are slower but cause the most damage to structures. They show up as jagged up and down lines. • The “focus” is the point in the Earth where the earthquake started. • The “epicenter” is the point on the Earth’s surface directly above the focus. Damage is usually greatest at the epicenter. • Most earthquakes leave a crack called a “fault line”. Magnitude • In 1935 American Seismologist Charles Richter came up with a 1-10 scale to measure an earthquake’s “magnitude”. • Each single number increase in magnitude, like 6.0 to a 7.0, is 10 TIMES more powerful than the lower number. Worst Earthquake in History • January 23, 1956, Shensi, China 8.0 on the Richter Scale 830,000 deaths Worst Earthquake in America • 1906, San Francisco • 7.9 on the Richter Scale • 3,000 deaths Worst Earthquake in Idaho • October 28, 1983, near Challis • 6.9 on the Richter Scale • 2 deaths Question Why such a difference in deaths? • China: 800,000 (8.0) • San Francisco: 3,000 (7.9) • Idaho: 2 (6.9) Structures must survive: • Compression • Tension • Shearing • Torsion • Bending • Every building has its own “resonance”, where the shaking of the ground matches the shaking of the building. • Resonance results in maximum damage. • In this chart, a 10 story building that shakes back and forth once every one second will likely be shaken apart. FACT: Most earthquakes shake between .5 and 2 seconds per cycle, making 5-20 story buildings the most vulnerable! Building Heights & Natural Frequency Building Height Typical Natural Period 2 story .2 seconds 5 story .5 seconds 10 story 1.0 second 20 story 2.0 second 30 story 3.0 second 50 story 5.0 seconds Speakers Boy Required: • Earthquake Tester • Tower block base • Foundation block • 1/8” welding rod • 4 Pitsco dragster wheels • Engineers, architects, and scientists are working together to learn how to design and build earthquake-resistant buildings. • Most deaths have been caused by faulty construction or poor building site. • Poor countries with no or limited building codes, tend to see much more damage than countries like America. Brick vs. Framed • Brick buildings tend to crumble quickly in an earthquake compared to those built with wood or steel frames. • The best defense against a strong earthquake is to build a structure that will move WITH the earthquake and absorb most of the destructive energy. • Steel and concrete-reinforced steel are the best solutions for large buildings. • To design and build a scale 20 story building (if full size would measure 40’ x 40’ at its base) that will be able to withstand an earthquake without damage. • Such a building would weigh 1.5 million TONS, so your building will include weighted floor plates that will be equal to that weight, to scale. EXAMPLE • • • • • • • • • • • Green structure glue, white glue, or hot glue 20’ of 1/8” x 1/8” balsa wood Graph paper Pins or tape Cardboard or wood board Cutting board Hobby knife Foundation block Tower base Wooden floor plates Waxed paper 1. Draw one side of your building actual size on graph paper. 2. Plan how to best use your 20’ of balsa! 3. Your skyscraper MUST be at least 20” tall. 4. Lay waxed paper over your drawing. 5. Lay pieces of balsa wood over your drawing, mark with a pencil, and cut to length. 6. Glue balsa together but NOT to the waxed paper. 6. Once dry, position your first wall vertical. 7. Glue the bottom of your first wall to the foundation block. Wooden Floor Plates 8. It is suggested that you glue wooden floor plates to the first building side every 10cm (4”) from the BOTTOM of the foundation block. 4” 9. Build a second side and glue it opposite the first side. 10. Add additional sides or bracing until you’ve used all of your balsa (or less, if desired). Requirements • • • • 20” tall Foundation glued to base. No more than 20’ of balsa wood. Each floor must have enough headroom for a 2” tall army man to stand freely without touching anything but where he is standing. • Glue should not be visible. • No wax paper 1. The earthquake tester allows us to record an earthquake sequence. 2. An earthquake sequence will be pre-recorded for your shaking pleasure. 3. The first team will insert a bolt, nut, and washers to each floor above the foundation block. 4. The first team will then place six (6) army men, one on each floor, without touching anything but the floor plates. 5. The tower will be tested until any floor fails. 6. You may stop the quake anytime after 10CPS. 7. The highest setting the building endured will be recorded. 8. The number of army men that remain on its original floor will be recorded and you receive 5pts for each. 9. You will receive an extra two feet of balsa wood after each test. 10. Other towers will experience the exact same earthquake sequence. CONSTRUCTION QUALITY (Amount of glue, correct dimensions, square, plumb) 30/40/50 points. • • • • DAY 1: One washer per floor (5 ounces total) 5 cycles per second (CPS) before failure = 5pts. 10 CPS before failure = 10pts. 20 CPS before failure = 20pts. (70pts. possible at this point + 5pts for each army man still on a floor. Day 1 Total Points: _____ + Construction Quality = ______ Day 2: Five washers per floor (25 ounces total) 5 CPS before failure = 5pts. 10 CPS before failure = 10pts. 20 CPS before failure = 15pts. (85pts. possible at this point + 5 pts for each army man still on a floor. Day 2 Total Points: _____ + Day 1 Total Points = ______ Day 3: Ten washers per floor (50 ounces total) 5 CPS before failure = 5pts. 10 CPS before failure = 10pts. (100 points possible) 20 CPS before failure = 20 pts. (110pts possible + 5 pts for each army man still on a floor. Day 3 total points + Day 2 total points = __________. _________ TOTAL / 100 POINTS