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~ I <br />i~ <br /> <br />I <br />All buildings are characterized by a single natural fundamental <br />frequency. This means that, as with a pendulum or a tuning fork, <br />there is one dominant frequency at which a particular building will <br />vibrate depends primarily upon its height. Tall buildings are more <br />flexible and vibrate at low frequencies. Low-rise structures, <br />being stiffer, vibrate at higher frequencies. <br />When the frequency of a ground vibration wave matches the <br />structure's natural frequency, the ground motion will be amplified <br />within the structure. According to the USBM, the natural frequency <br />of typical residential structures ranges between 4 and 12 hertz. <br />Thus, it is within this range that the vibration limits recommended <br />by the USBM are most stringent. <br />By applying the computerized RSVP technique to the data obtained in <br />this survey, both the ground particle velocity and response <br />characteristics of residential structures are considered over a <br />wide range of frequencies. The results are then related to the <br />USBM velocity versus frequency curve discussed previously, and are <br />plotted on the analysis sheets at the end of this report. <br />Ground vibration is measured as a particle velocity in units of <br />inches per second. Below is an excerpt from "Explosives and Rock <br />Blasting" by Atlas Powder Company: <br />Type of Structure <br />Houses <br />Concrete Blocks <br />Cased Drill Holes <br />Mechanical Equipment <br />Prefabricated Metal <br />Building on Pad <br />Type of Damage Particle Velocity at <br />Which Damage Starts <br />Plaster Cracking <br />Cracks in Blocks <br />Horizontal Offset <br />Shafts Misaligned <br />Twisted Metal, <br />Cracked Pad <br />2.0 <br />8.0 <br />15.0 <br />40.0 <br />60.0 <br />inches/second <br />inches/second <br />inches/second <br />inches/second <br />inches/second <br />7 <br />