Sunday, November 30, 2008

Structural Engineering for Kids 3 - The 3 Little Pigs and the Big Bad Wolf - Lessons on Wind Loads

Remember the story of the Three Little Pigs and the Big Bad Wolf? This is a story where kids will learn the importance of designing structures against external forces such as wind due to typhoons and hurricanes. The big bad wolf wants to eat the pigs. And to do that he must be able to destroy each pig’s house by blowing on the house. The big bad wolf represents external wind forces that a house must resist. So to protect themselves, the pigs have to build their own houses. Pig 1 built a house of hay. Pig 2 built a house of twigs, while Pig 3 built a house of stone. And you all know the story’s ending, the big bad wolf’s strong blowing power destroyed the houses of hay and twigs, but not the house of stone. Structural engineers must design structures against wind loads. Codes like the National Structural Code of the Philippines (NSCP) specifies wind zones with corresponding basic wind speeds in determining the design wind loads. For example, Metro Manila belongs to Zone II with a basic wind speed of 200 kph, while the Northeastern parts of Luzon and Visayas under Zone I have a speed of 250 kph. According to the Outdoor Advertiser's Association after the Typhoon Milenyo in 2006 struck Metro Manila, they designed their billboards for 120 kph (PDI Oct. 1, 2006) and this is less than 200 kph. The toppled billboards due to Typhoon Milenyo showed us what will happen to structures not designed, constructed and maintained properly against wind forces. Photo courtesy of Engr. Willy Lopez (DPWH): Fallen billboard due to Typhoon Milenyo 2007

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