IEEE 344-2013 pdf download

IEEE 344-2013 pdf download.IEEE Standard for Seismic Qualification of Equipment for Nuclear Power Generating Stations.
4.4 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 of equipment subcomponents can predominate. Similar filtering of in-structure motion can occur in flexible piping systems. For components mounted away from 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 line.
4.5 Simulating the earthquake
The goal of seismic simulation is to reproduce the postulated earthquake environment in a realistic manner. The form of the simulated seismic motion used for the qualification of equipment by analysis or testing can be described by one of the following functions:
a) Response spectrum
b) Time histoiy
c) Power spectral density (PSD)
The simulated seismic motion may be generated for the foundation, floor of the building, or substructure upon which the equipment is to be mounted. It is supplied by the user or the user’s agent as a part of the specifications for that equipment (see Clause 11) or generated by others for generic applications.
Because of the directional nature of seismic motion and the filtered output motion of building and equipment structures, the directional components of the motion and their application to the equipment should be specified or accounted for in some other appropriate manner.
4.5.1 Response spectrum
The response spectrum provides information on the maximum response of single-degree-of-freedom
(SDOF) oscillators as a function of oscillator frequency and damping when subjected to an input motion.
The frequency content and the peak value of the input motion, that is, the ZPA, are indicated.
It is important to recognize that the response spectrum does not supply the following information:
a) The waveform or time history of the excitation that produced it
b) The duration of motion (this shall be defined in the qualification specification)
c) The dynamic response of any particular equipment
4.5.2 Time history
A time history displays the earthquake-induced motion (usually in terms of acceleration) as a function of time. The simulated motion is derived from existing or artificially generated earthquake records. For application at any floor, the time history record generated includes the dynamic filtering and amplification effects of the building and other intervening support structures.
4.5.3 PSD function
The mean squared amplitude per unit frequency of the vibratory motion is characterized in terms of the PSD as a function of frequency.
NOTE—Although the rcsponsc spectrum and the PSD function do not define the exact wavcfom or duration of the excitation, they are valuable tools. They enable significant frequency-dependent properties of the motion to be seen at a glance from one curve. The PSD provides information regarding the excitation directly without including the effects on an array of SDOF oscillators as is done for the response spectrum. As a result, the PSD allows application of relationships between excitation and response by way of the transfer functions for linear systems.
4.6 Support structure and interactions
Seismic qualification of equipment requires consideration of installation features, such as (a) the seismic adequacy of the supporting structure (support assembly, structure, anchorage, floors, walls, or foundation), and (b) the potential for adverse seismic interactions (such as falling of overhead components, proximity impacts, differential displacements, spray, flood, or fire).
5. Seismic qualification approach
The seismic qualification of Seismic Category I equipment shall demonstrate an equipment’s ability to perform its required safety function(s) during and/or after the time it is subjected to the forces resulting from a safe shutdown earthquake (SSE). For equipment being qualified by test and having more than one safety function, more than one SSE may be required to demonstrate satisfactory performance of all the safety functions. In addition, the equipment shall withstand the effects of a number of operating basis earthquakes (OBEs) [see 7.5, 8.1.5.2, item b) in 10.2.3.1, and 10.31 prior to the application of an SSE. The most commonly used methods for seismic qualification are contained in this standard.