Agenda - Council - 02/26/2019 - Laserfiche WebLink

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Vibration Introduction to Vibration Ground -borne vibration is the transmission of energy through the earth. The low level noise often generated by vibration, caused by the movement of room surfaces and contents, is termed "ground -borne noise." Vibration, although not typically an issue of environmental concern, could be destructive to buildings and furnishing when excessive and/or an annoyance at lower levels. The evaluation presented here is taken from guidelines develop by the FTA (Transit Noise and Vibration Assessment, Harris Miller Miller & Associates, 1995). Vibration consists of rapidly fluctuating motions with an average motion of zero. There are several different methods that are used to quantify vibration amplitude. In the case of human response to vibration, the root mean square (rms) amplitude is used to describe the smoothed vibration amplitude. The root mean square of a signal is the average of the squared amplitude of the signal calculated, typically, over a one (1) second period. The rms in the United States is normally described in inches per second. In addition, decibel notation is another common notation that acts to compress the range of numbers required to describe vibration. In contrast to airborne noise, ground -borne vibration is not a phenomenon that most people experience every day. The background vibration velocity level in residential areas is usually 50 VdB (vibration decibels) or lower, well below the threshold of perception for humans, which is around 65 VdB. In the U.S., the RMS vibration velocity level in VdB is typically measured relative to 10-6 inches/second. Most perceptible indoor vibration is caused by sources within buildings such as operation of mechanical equipment, movement of people or slamming of doors. Typical outdoor sources of perceptible ground -borne vibration are construction equipment, steel wheeled trains, and traffic on rough roads. If the roadway is smooth, the vibration from traffic is rarely perceptible. Table 24.7 illustrates common vibration sources and the human and structural response to ground -borne vibration. The range of interest is from approximately 50 VdB to 100 VdB. Background vibration is usually well below the threshold of human perception and is of concern only when the vibration affects very sensitive manufacturing or research equipment. Electron microscopes and high resolution lithography equipment are typical of equipment that is highly sensitive to vibration. Location of these businesses within the RTC site, should they occur, will be encouraged well away from the railroad tracks. 23/24-7