IEEE 60980-344-2020 pdf free download – Nuclear facilities – Equipment important to safety – Seismic qualification.
5 General discussion of earthquake environment and equipment response
5.1 General This clause provides background information on earthquake behaviour and on the performance of equipment during simulated seismic events. Numerical values provided are typical and illustrative and should not be considered as standards. The flowchart provided in Figure G.1 illustrates the establishment of the seismic conditions from the earthquake to the equipment being qualified.
5.2 Earthquake environment
Earthquakes are initiated by rupture and slippage along geologic faults. Earthquakes produce three-dimensional (3D) random ground motions that are characterized by simultaneous but statistically independent horizontal and vertical components. The ground motion is typically broadband random and produces potentially damaging effects over a frequency range of 1 Hz to the cutoff frequency of the response spectra. The cutoff frequency is generally between 32 Hz and 50 Hz for a building structure subjected to an earthquake with the exception of hard rock regions of the Central and Eastern U.S. and other parts of the world which may experience energy content up to 1 00 Hz. The cutoff frequency may be greater if additional vibration induced loads are combined with seismic loads. The strong motion portion of the earthquake may last from 1 0 s to 1 5 s, although the complete event may be considerably longer and produce a horizontal ground acceleration from 0,1 g to 0,6 g or higher. Duration of strong motion is dependent upon ground soil type, distance from the fault, energy released by the rupture, and slippage along a geological fault.
5.3 Equipment on foundations
The vibratory level of the ground motion (both horizontal and vertical) can be amplified or attenuated in foundation-mounted equipment. For any given ground motion, the alteration depends on the natural frequencies of vibration (soil, foundation, intermediate structure and equipment), the stiffness, the mass and the geometry of the building and intermediate structures and the damping mechanisms (damping coefficient may depend on frequencies considered). The broadband response spectra that typically describe the ground motion indicate that multiple-frequency excitation predominates.
5.4 Equipment on structures
The ground motion (horizontal and vertical) can be filtered by intervening building structures to produce amplified or attenuated narrowband motions within the structure. The dynamic response of equipment on structures can be further amplified or attenuated to an acceleration level many times more or less than that of the maximum ground acceleration, depending upon the equipment damping and natural frequencies. The narrowband response spectra that typically describe a building floor motion indicate that single-frequency excitation can be predominant. Filtering of in-structure motion can occur in flexible piping systems. For components mounted away from piping supports, the resultant motion can be predominantly single frequency in nature and centered near or at the resonant frequency of the piping system. This resonance condition can produce the most critical seismic load on components mounted on the pipe line.
5.5 Interfaces and adverse interactions
Some equipment may have interfaces in an electrical or mechanical way or located in close proximity to each other. Seismic qualification of equipment shall consider installation features (e.g., support assembly and anchorage) and the potential for adverse seismic interactions (such as falling of overhead components, proximity impacts, differential displacements, spray, flood, or fire). If two pieces of equipment have mechanical or electrical interfaces, the effect of differential relative displacement of both equipment induced by earthquake shall be evaluated by considering resulting constraints at interface level and by proving (through analysis and/or test) there is no impact to performance function(s) required during and/or after seismic conditions. This demonstration may rely on specific test modalities (methods and procedures).IEEE 60980-344 pdf download.