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Week4-Strong_Grnd_Motions_S11

Week4-Strong_Grnd_Motions_S11 - CE 316 Geotechnical...

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Click to edit Master subtitle style § CE 316 Geotechnical Earthquake Engineering § Strong Ground Motions § 11
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§ Strong Ground Motions Microseismic activity Strong ground motion Measurements of these motions: (3 translation & 3 rotation) Commonly acceleration time history is recorded at discrete points, e.g., t = 0.02sec.
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§ Strong Ground Motions
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§ Strong Ground Motions -0.2 -0.1 0 0.1 0.2 Acceleration (g) -15 -10 -5 0 5 10 15 Velocity (in/s) -6 -4 -2 0 2 4 6 0 5 10 15 20 25 30 35 40 45 Time (sec) Displacement (in) -0.2 -0.1 0 0.1 0.2 Acceleration (g) -15 -10 -5 0 5 10 15 Velocity (in/s) -6 -4 -2 0 2 4 6 0 5 10 15 20 25 30 35 40 45 Time (sec) Displacement (in) Yuerba Buena Island (rock) Treasure Island (soil)
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§ Ground Motion Parameters Amplitude Frequency Content Duration Often a combination of these 3 parameters are used to describe the strong ground motion.
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§ How Do We Measure Motions? Seismographs Accelerographs Force Balance (suspended mass) Piezoelectric Geophones (velocity transducers) Digital common today Seismoscopes
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§ Ancient “Seismograph” 2000 years old. The post inside will fall on the direction earthquake happen; on that direction the dragon will spit out a bead into the mouth of the frog. "Zhang Heng seismograph" Replicas
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§ Modern Seismograph
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§ Seismographs Seismographs are designed so that slight earth vibrations move the instruments; The suspended mass (M) tends to remain at rest, and its recording stylus records this difference in motion; Spring absorbs some of the motion and causes the mass to lag behind actual motion. http://neic.usgs.gov/neis/seism ology
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§ Modern Seismograph
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§ Seismograph Response 2 2 2 2 (1 ) (2 ) g u u β β ξβ = - + Displacement Response Ratio: At frequencies way above the natural frequency this ratio is 1.
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