322 M.J. Wesolowsky et al. 40.2 Vibration Criteria A method for defining vibration criteria for human comfort uses the root mean square (RMS) velocity response of each onethird-octave band from 1 to 80 Hz [1]. For sensitive equipment, this criterion may also be expressed in one-third octave bands, or other formats, including power spectral densities, peak-to-peak levels, etc. Over the past 25 years, generic vibration criteria (VC) have been developed which provide frequency-dependent sensitivities for various classes of equipment, and these are applied as performance criteria. These VC curves are internationally accepted as a basis for designing and evaluating the performance of vibration sensitive equipment and the structures that support them. The VC curves currently range from Workshop (least stringent) to VC-G (most stringent). As a point of reference, most laboratories target at least VC-A (50 m/s) as an uppermost vibration condition. The VC curves were originally based on the ISO 2631-2 (1989) [2] base curve for human response to whole-body vibration, which is considered the threshold of human perception, but have since evolved. The ISO base curve is often referred to as the ISO—Operating Room criteria of 100 m/s which is not as stringent as VC-A. The above-noted VC are specified in terms of RMS velocities each one-third octave band. The VC curves are beneficial where manufacturers’ specifications are non-existent, incomplete, where specific equipment has not yet been selected, or as an alternative when manufacturer-supplied specifications prove to be inaccurate. 40.3 Case Study #1: Construction Zone of Influence Case Study #1 involves a new patient tower addition for a large existing hospital. As such, parts of the existing hospital will be demolished and re-built, while the rest of the hospital will continue to stay in operation. The hospital has vibration-sensitive areas throughout the facility, although the main area of concern is the DI suite where the Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scanners are installed. Simulated construction-vibration testing was carried out to determine whether or not construction activities can be expected to cause vibration levels within the hospital that would exceed the equipment’s vibration limits. Two types of tests were conducted: (1) vibration propagation into buildings; and (2) vibration propagation with distance. The main purpose of these tests was to develop zone of influence lines to determine just how close to the hospital that construction activities could be conducted while allowing for continued operation of the vibration-sensitive equipment. To measure the vibration propagation into buildings, three uni-axial accelerometers were set-up to obtain tri-axial acceleration data at various outside and inside locations of the hospital buildings. Accelerometers were placed in the MRI and CT scanner rooms as well as an X-ray room. Measurement rooms were purposely chosen to be in different wings of the hospital, as every wing was built at a different time (with some wings dating back to the year 1929) and had different structural systems. To simulate construction activities, a backhoe/excavator with a bucket was used to strike the pavement repeatedly approximately 100 times, where the time between strikes ranged from 1 to 3 s. The striking location was in the hospital’s parking lot in closest proximity to the DI equipment. The measured VC levels are shown in Table 40.1 and show that at all sensitive areas, the vibration levels exceeded the required VC curves. As these vibration levels were for one exterior impact location, a second set of tests were conducted to determine the reduction of vibration with distance. This would allow for vibration levels to be estimated anywhere on the future construction site. This testing was conducted in the parking lot (and future site of the new patient tower) and was completed with three different pieces of construction equipment: excavator with a bucket, caisson driller and a vibratory roller (see Fig. 40.1). Tri-axial accelerometers were placed at 5, 10, 15, 20 and 120-m distances from the construction source. The first construction simulation used the excavator with bucket to strike the ground repeatedly. The second simulation consisted of using a caisson driller to drill a hole approximately 1 m in diameter and 3 m deep. Finally, the third simulation consisted of a vibratory roller Table 40.1 Measured VC levels during excavator test Roomtype VC measured VC limit Exceeds X-ray Office (ISO) Operating theatre (ISO) Yes MRI VC-A Manufacturer-provided (analogous to VC-B) Yes CTscanner VC-A Manufacturer-provided (analogous to VC-B) Yes Chemistry lab Residential night (ISO) Operating theatre (ISO) Yes
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