標準編號:	GB/T 13625-2018
中文名稱:	核電廠安全級電氣設備抗震鑒定
英文名稱:	Seismic qualification of safety class electrical equipment for nuclear power plants
中標分類:	F65    核電廠核島
行業分類:	GB    國家標準
ICS分類:	27.120.10 27.120.10    反應堆工程 27.120.10
發布機構:	國家市場監督管理總局、中國國家標準化管理委員會
發布日期:	2018-05-14
實施日期:	2018-12-1
標準狀態:	valid
替代舊標準:	GB/T 13625-1992 核電廠 安全系統 電氣設備 抗震鑒定
翻譯語言:	英文
文件格式:	PDF
中文字符數:	45000 字
翻譯價格(元):	4500.0
交付時間:	付款后 1 個工作日

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. This standard is developed in accordance with the rules given in GB/T 1.1-2009. This standard replaces GB/T 13625-1992 Seismic qualification of electrical equipment of the safety system for nuclear power plants, and the following main technical changes have been made with respect to GB/T 13625-1992: —— relevant contents are added for damping (see Clause 6 and Annex A); —— the requirement is modified for TRS low frequency band so that the low-frequency displacement of the test device shall not be too large (see 8.6.3.2); —— related contents are added for power spectral density envelope (see 8.6.3.2.1); —— the seismic qualification approach combining analysis and test is added (see Clause 9); —— the guidelines for seismic qualification using seismic experience data of reference equipment (see Annex G). This standard was proposed by China National Nuclear Corporation. This standard is under the jurisdiction of the National Technical Committee 30 on Nuclear Instruments of Standardization (SAC/TC 30). The previous edition of this standard is as follows: ——GB/T 13625-1992. Seismic qualification of safety class electrical equipment for nuclear power plants 1 Scope This standard specifies the implementation method and documentation requirements of seismic qualification for verifying that safety level electrical equipment can perform its safety function during and/ or after an earthquake. This standard is applicable to seismic qualification of safety level electrical equipment in nuclear power plants, including any interface components or equipment whose failure will have harmful effects on the performance of safety system. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 12727 Qualification of safety class electrical equipment for nuclear power plants 3 Terms and definitions For the purpose of this document, the following terms and definitions apply. 3.1 broadband response spectrum response spectrum that describes motion in which amplified response occurs over a wide (broad) range of frequencies 3.2 coherence function comparative relationship between two times histories. It provides a statistical estimate of how much two motions are related, as a function of frequency. The numerical range is from zero for unrelated, to +1.0 for related motions 3.3 correlation coefficient function comparative relationship between two time histories. It provides a statistical estimate of how much two motions are related, as a function of time delay. The numerical range is from zero for unrelated, to +1.0 for related motions 3.4 critical seismic characteristics design, material, and performance characteristics of an equipment item that provide assurance that the item will perform its required function under seismic loads 3.5 cutoff frequency frequency in the response spectrum where the ZPA asymptote begins. This is the frequency beyond which the single-degree-of-freedom (SDOF) oscillators exhibit no amplification of motion and indicate the upper limit of the frequency content of the waveform being analyzed 3.6 damping energy dissipation mechanism that reduces the amplification and broadens the vibratory response in the region of resonance. It is usually expressed as a percentage of critical damping. Critical damping is defined as the least amount of viscous damping that causes a SDOF system to return to its original position without oscillation after initial disturbance. 3.7 earthquake experience spectrum; EES response spectrum that defines the seismic capacity of a reference equipment class based on earthquake experience data 3.8 flexible equipment equipment, structures and components whose lowest resonant frequency is less than the cutoff frequency on the response spectrum 3.9 inclusion rules rules that define the bounds of equipment included in a reference equipment class based on an acceptable range of equipment physical characteristics, dynamic characteristics, and functions for which seismic ruggedness has been demonstrated by experience data 3.10 independent items components and equipment that (a) have different physical characteristics or (b) experienced different seismic motion characteristics, e.g., different earthquakes, different sites, different buildings, or different orientations/locations in the same building 3.11 narrowband response spectrum response spectrum that describes the motion in which amplified response occurs over a limited (narrow) range of frequencies 3.12 natural frequency frequency(s) at which a body vibrates due to its own physical characteristics (mass and stiffness) when the body is distorted in a specific direction and then released 3.13 operating basis earthquake; OBE earthquake that could reasonably be expected to occur at the plant site during the operating life of the power plant considering the regional and local geology and seismology and specific characteristics of local subsurface material Note: For the vibratory ground motion produced by the earthquake, those features of the nuclear power plant, necessary for continued operation without undue risk to the health and safety of the public, are designed to remain functional. 3.14 power spectral density; PSD mean squared amplitude per unit frequency of a waveform, and it is expressed in g2/Hz versus frequency 3.15 prohibited features design details, materials, construction features, or installation characteristics that have resulted in seismic induced failure or malfunction of the equipment to maintain its structural integrity and perform its specified function at earthquake or test excitations with defined seismic capacity 3.16 qualified life period of time, prior to the start of a design basis event (DBE), for which the equipment was demonstrated to meet the design requirements for the specified service conditions 3.17 reference equipment equipment used to establish a reference equipment class 3.18 reference equipment class a group of equipment sharing common attributes as defined by a set of inclusion rules and prohibited features 3.19 reference site site containing equipment or items used to establish a reference equipment class 3.20 required response spectrum; RRS response spectrum issued by the user or the user's agent as part of the specifications for qualification or artificially created to cover future application 3.21 resonant frequency frequency at which a response peak occurs in a system subjected to forced vibration. This frequency is accompanied by a phase shift of response relative to the excitation 3.22 response spectrum plot of the maximum response, as a function of oscillator frequency, of an array of SDOF damped oscillators subjected to the same base excitation 3.23 rigid equipment equipment, structures and components whose lowest resonance frequency is greater than the cutoff frequency on the response spectrum 3.24 safe shutdown earthquake; SSE earthquake that is based upon an evaluation of the maximum earthquake potential considering the regional and local geology and seismology and specific characteristics of local subsurface material Note: Some certain structures, systems, and components need to remain their functions under the maximum vibratory ground motion caused by the earthquake. These structures, systems and components are those necessary to ensure the following requirements: a) Integrity of the reactor coolant pressure boundary; b) Capability to shut down the reactor and maintain it in a safe shutdown condition; c) Capability to prevent or mitigate the consequence of off-plant irradiation accidents. 3.25 seismic capacity highest seismic level for which required adequacy has been verified 3.26 sine beats continuous sinusoid of one frequency, amplitude modulated by a sinusoid of a lower frequency 3.27 stationarity condition that exists when a waveform is stationary and when its amplitude distribution, frequency content, and other descriptive parameters are statistically constant with time 3.28 test experience spectra; TES test-based response spectra that define the seismic capacity of a reference equipment class 3.29 test response spectrum; TRS response spectrum that is developed from the actual time history of the motion of the shake table 3.30 transfer function complex frequency response function that defines the dynamic characteristics of constant parameter linear system Note: For an ideal system, the transfer function is the ratio of the Fourier transform of the output to that of a given input. 3.31 zero period acceleration; ZPA acceleration level of the high-frequency, unamplified portion of the response spectrum Note: This acceleration corresponds to the maximum peak acceleration of the time history used to derive the response spectrum. 4 General discussion of earthquake environment and equipment response 4.1 Earthquake environment Three-dimensional (3D) random ground motion caused by earthquakes may be characterized by simultaneous but statistically independent horizontal and vertical components. The strong motion portion of the earthquake may last from 10 s to 15 s, although the complete event may be considerably longer. The ground motion is typically broadband random and produces potentially damaging effects over a frequency range from 1 Hz to the cutoff frequency of response spectrum. 4.2 Equipment on foundations The vibratory nature of the ground motion (both horizontal and vertical) can be amplified or attenuated in foundation-mounted equipment. For any given ground motion, the amplification or attenuation depends on the system’s natural frequencies (soil, foundation, and equipment) and the damping dissipation mechanisms. The typical broadband response spectra that describe the ground motion indicate that multiple-frequency excitation predominates. 4.3 Equipment on structures The ground motion (horizontal and vertical) may be filtered by intervening building structures to produce amplified or attenuated narrowband motions within the structure. The dynamic response of equipment on structures may 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 components can predominate. Similar filtering of in-structure motion may occur in flexible piping systems. For components mounted away from supports, the resultant motion may be predominantly single frequency in nature and centered near or at the resonant frequency of the piping system. This resonance condition may produce the most critical seismic load on components mounted on the line. 4.4 Simulating earthquake 4.4.1 General 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 history; 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. The simulated seismic motion is usually supplied by the user or the user’s agent as a part of the specifications. 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 shall be specified or accounted for in some other appropriate manner. 4.4.2 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 response spectrum can indicate the frequency content and the peak value of the input motion (namely the ZPA). It should be pointed out that the response spectrum cannot provide 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 corresponding appraisal technical requirements document); c) The dynamic response of any specific equipment. 4.4.3 Time history A time history displays the earthquake-induced motion (usually in terms of acceleration) as a function of time. The simulated motion in seismic qualification test is derived from existing or artificially generated earthquake records. For any floor, the time history generated includes the dynamic filtering and amplification effects of the structures and other intervening support structures. 4.4.4 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 response spectrum and the PSD function do not define the exact waveform 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. 4.5 Supporting structure and interactions Seismic qualification of equipment requires consideration of installation features, such as: a) The seismic adequacy of the supporting structure (supporting assembly, structure, anchorage, floors, walls or foundation); b) The potential for adverse seismic interactions (such as falling of overhead components, proximity impacts, differential displacements, spray, flood, or fire).

Foreword i 1 Scope 2 Normative references 3 Terms and definitions 4 General discussion of earthquake environment and equipment response 5 Seismic qualification approach 6 Damping 7 Analysis 8 Testing 9 Combined analysis and testing 10 Experience 11 Documentation Annex A (Informative) Recommended damping ratio of typical electrical equipment in seismic analysis Annex B (Informative) Statistically independent motions Annex C (Informative) Test duration and number of cycles Annex D (Informative) Fragility testing Annex E (Informative) Measurement of ZPA Annex F (Informative) Frequency content and stationarity Annex G (Informative) Method of seismic qualification with reference to experience data

核電廠安全級電氣設備抗震鑒定 1范圍 本標準規定了為驗證安全級電氣設備在發生地震期間和(或)地震后能執行其安全功能而進行的抗震鑒定的實施方法及其文件要求。 本標準適用于核電廠安全級電氣設備的抗震鑒定，包括其故障會對安全系統的性能產生有害影響的任何接口部件或設備。 2規范性引用文件 下列文件對于本文件的應用是必不可少的。凡是注日期的引用文件，僅注日期的版本適用于本文件。凡是不注日期的引用文件，其最新版本(包括所有的修改單)適用于本文件。 GB/T 12727核電廠安全級電氣設備鑒定 3術語和定義 下列術語和定義適用于本文件。 3.1 寬頻帶反應譜broadband response spectrum 描述在寬頻范圍內產生放大反應運動的反應譜。 3.2 相干函數 coherence function 表征兩個時程在頻域上的相互關系。相干函數給出了兩個運動統計上的相關程度，為頻率的函數。其數值范圍從0～+1.0，其中完全不相關運動為0，完全相關運動為+1.0。 3.3 相關系數函數 correlation coefficient function 表征兩個時程在時域上的相互關系。相關系數函數給出兩個運動統計上的相關程度，是以時間延遲為自變量的函數。其數值范圍從0～+1.0，其中完全不相關運動為0，完全相關運動為+1.0。 3.4 關鍵抗震特性critical seismic characteristics 能夠確保設備在地震載荷作用下執行要求功能的設計、材料和性能特性。 3.5 截止頻率cutoff frequency 反應譜中零周期加速度漸近線開始處的頻率。單自由度振子的頻率在超過該頻率后將不再放大輸入運動，這是所分析波形的頻率上限。 3.6 阻尼damping 一種在共振區域中減少放大量和拓寬振動反應的能量耗散機理。阻尼通常以臨界阻尼的百分數來表示。臨界阻尼定義為單自由度系統在初始擾動后來經振蕩回復到其原來位置的最小黏性阻尼值。 3.7 地震經驗譜earthquake experience spectrum；EES 根據地震經驗數據來確定表征參考設備抗震能力的反應譜。 3.8 柔性設備 flexible equipment 最低共振頻率小于反應譜截止頻率的設備、構筑物和部件。 3.9 范圍規則 inclusion rules 根據經驗數據已證明為耐震設備的物理特性、動態特性和功能的可接受范圍來確定參考設備組的規則。 3.10 獨立物項 independent items 具有不同的物理特性或經受不同的地震運動特性[例如，不同的地震、不同的廠址、不同的構筑物，或同一構筑物的不同方向和(或)位置]的部件和設備。 3.11 窄頻帶反應譜narrowband response spectrum 描述一個有限(窄帶)頻率范圍內產生放大反應運動的反應譜。 3.12 自振頻率natural frequency 物體在特定的方向上受到變形然后釋放時，由于其自身的物理特性(質量和剛度)使物體發生振動的頻率。 3.13 運行基準地震operating basis earthquake；OBE 結合地區和當地的地質和地震情況以及當地地層材料的具體特性，在電廠正常運行壽期內可合理預期在廠址會發生的地震。 注：對于該地震產生的地震動，那些需繼續運行而不對公眾的健康與安全產生過度風險的核電廠設施可以保持其功能。 3.14 功率譜密度power spectral density PSD 一個波形每單位頻率的均方幅值，用g2/Hz與頻率的關系表示。 3.15 禁止特征prohibited features 在規定抗震能力的地震或試驗激勵下，會導致設備發生結構完整性及功能失效或異常的詳細設計、材料、結構特征或安裝特性。 3.16 鑒定壽命qualified life 證明設備在設計基準事件(DBE)之前對于規定的使用工況能滿足設計要求的時間期限。 3.17 參考設備 reference equipment 用于建立參考設備組的設備。 3.18 參考設備組reference equipment class 由范圍規則和禁止特征確定的一組具有相同屬性的設備。 3.19 參考廠址reference site 具有確定參考設備組設備或物項的廠址。 3.20 要求反應譜required response spectrum；RRS 由用戶或其委托人在鑒定技術要求文件中規定的反應譜，或人工生成能夠覆蓋將來應用的反應譜。 3.21 共振頻率resonant frequency 受到強迫振動的系統中出現反應峰值處的頻率。該頻率下，反應相對于激勵有相位差。 3.22 反應譜response spectrum 一組單自由度(SDOF)有阻尼振子在受相同基礎激勵情況下最大反應與振子頻率的關系曲線。 3.23 剛性設備 rigid equipment 最低共振頻率大于反應譜截止頻率的設備、構筑物和部件。 3.24 安全停堆地震safe shutdown earthquake；SSE 結合地區和當地的地質和地震情況以及當地地層材料的具體特性，對可能的最大地震作出評估后確定的一個地震。 注：在該地震產生的最大地震動下一些特定的構筑物、系統和部件需保持其功能。這些構筑物、系統和部件對保證下列要求是必需的： a)反應堆冷卻劑壓力邊界的完整性； b)使反應堆停堆并維持反應堆在安全停堆狀態的能力； c)防止或減輕廠外輻照事故后果的能力。 3.25 抗震能力 seismic capacity 經過驗證的設備所能經受的最大地震水平。 3.26 正弦拍波sine beats 幅值受較低頻率正弦波調制的某一頻率的連續正弦波。 3.27 穩定性stationarity 波形是穩定時，其幅值分布、頻率成分和其他特征參數不隨時間而變化。 3.28 試驗經驗譜test experience spectra；TES 確定參考設備組抗震能力的、基于試驗的反應譜。 3.29 試驗反應譜test response spectrum；TRS 由地震臺面運動的實際時程得到的反應譜。 3.30 傳遞函數transfer function 一個用來確定常系數線性系統動態特性的復頻響應函數。 注：對于一個理想系統，傳遞函數為輸出與給定輸入的傅里葉變換之比。 3.31 零周期加速度zero period acceleration；ZPA 反應譜高頻、未被放大部分的加速度水平。 注：該加速度相當于用來推導反應譜的時程的最大峰值加速度。 4地震環境和設備反應概論 4.1 地震環境 地震產生的三維隨機地而運動可用同時發生且統計上相互獨立的水平和垂直分量來表征。雖然整個地震事件可能持續較長的時間，但其強震持續時間可能僅10 s～15 s。地面運動是典型的寬頻帶隨機運動，在1 Hz至反應譜截止頻率的頻率范圍內可能產生破壞作用。 4.2基礎上的設備 對安裝在基礎上的設備，地面運動(水平和垂直)的振動特性可能被放大或衰減。對于任何給定的地面運動，放大或衰減取決于系統(土壤、基礎和設備)的自振頻率和阻尼耗散機理。地面運動大都采用寬帶反應譜進行描述，說明多頻激勵起了主導作用。 4.3結構上的設備 地面運動(水平和垂直)可因相關結構的濾波作用而在結構中產生放大或衰減的窄帶運動。結構上設備的動態反應加速度則會得到進一步的放大或衰減，可達最大地面加速度的數倍或若干分之一，具體取決于設備的阻尼和自振頻率。通常采用窄頻帶反應譜來描述構筑物的樓面運動，表明對設備部件的單頻激勵起主導作用。構筑物運動中的類似濾波作用在柔性管道系統中也會發生。對于不在支承上安裝的部件，最終的運動可能是以管系共振頻率(或其附近)為主的單頻。這種共振條件會對安裝在管線上的部件產生最苛刻的地震載荷。 4.4模擬地震 4.4.1概述 地震模擬的目的是用可行的方式復現假定的地震環境。采用分析或試驗方法鑒定設備時所用的模擬地震運動，可由下列任何一種形式給出： a)反應譜； b)時程； c)功率譜密度(PSD)。 可為基礎、構筑物樓面或安裝設備的子結構生成模擬地震運動。這些模擬地震運動通常由用戶或其委托人在設備規格書中規定。 由于地震運動的方向性以及構筑物和設備結構濾波后輸出運動的方向性，運動的方向分量及其對設備的作用應加以規定，或以其他適當的方式進行說明。 4.4.2 反應譜 反應譜給出了單自由度振子在給定輸入運動下的最大反應信息，它是振子頻率和阻尼的函數。反應譜能給出輸入運動的頻率成分和運動峰值(即零周期加速度)。 需要指出的是反應譜不能提供下列信息： a)產生反應譜的激勵波形或時程； b)運動持續時間(這應在相應的鑒定技術要求文件中規定)； c)任何特定設備的動態反應。 4.4.3時程 地震引起的運動(通常為加速度)隨時間變化的函數即為時程。抗震鑒定試驗時所模擬的運動來自實際或人工產生的地震記錄。對任一樓面，所生成的時程包括了構筑物和其他中間支承結構的動態濾波和放火效應。 4.4.4功率譜密度函數 功率譜密度表征某一運動參數單位頻率內振動幅值的均方值，它是頻率的函數。 注：盡管反應譜和功率譜密度函數不能確定確切的激勵波形或持續時間，它們依然是有用的工具，能從一根曲線上得到運動的重要頻率特性。功率譜密度直接給出了關于激勵的信息，但并來像反應譜那樣考慮激勵對一組單自由度振子的作用。因此，利用線性系統的傳遞函數理論，可以根據功率譜密度確定激勵和反應之間的關系。 4.5支承結構和相互作用 設備抗震鑒定需考慮安裝特性，如： a)支承結構(支承組件、結構、錨固件、樓面、墻或基礎)抗震適用性； b)有害的地震相互作用可能性(如上部部件的跌落、鄰近的撞擊、不同的位移、噴淋、水淹或火災)。 5抗震鑒定方法 5.1 概述 設備的抗震鑒定應證明在承受由一個安全停堆地震產生的作用力期間和(或)之后設備執行其安全功能的能力。另外。在承受安全停堆地震之前，設備應承受若干運行基準地震的作用。 5.2抗震鑒定技術條件 抗震鑒定需明確規定被鑒定設備的技術條件，具體詳見第11章。 應明確規定抗震要求的技術條件至少包括：持續時間、頻率范圍和加速度值。提供這些數據信息的可以是： a)以功率譜密度(頻率的函數)表示的振動運動； b)地震強震部分的持續時間； c)設備安裝點上的要求反應譜，要求反應譜必需包括主水平軸和垂直軸的數據，以及不同阻尼比(如2％、5％和7％)的數據； d)設備安裝點(樓板或構筑物)上的最大加速度與重要頻率的關系曲線或時程曲線。 對于運行基準地震(OBE)和安全停堆地震(SSE)，其反應譜的形狀和幅值均可能不同。故為了對試驗件進行鑒定，應知道這些地震水平所相應的加速度譜。技術條件應說明所用反應譜的合理性。 5.3 常用抗震鑒定方法 常用的抗震鑒定方法通常有四種： a)通過分析來預測設備性能； b)在模擬地震條件下對設備進行試驗； c)采用試驗和分析相結合的方法來鑒定設備； d)通過使用經驗數據來鑒定設備。 上述每一種方法，或其他證明合理的方法均適用于驗證設備的抗震性能。選擇適用的鑒定方法至少需考慮以下因素： a)設備結構的類型、尺寸、形狀和復雜程度； b)是通過(設備)可操作性，還是僅僅通過結構完整性驗證安全功能； c)結論的可靠性。 被鑒定的設備應能夠證明在地震期間和(或)之后能執行其安全功能。要求的安全功能不僅取決于設備本身，還取決于設備在系統和電廠中的作用。地震期間的安全功能可能與地震之后所要求的安全功能相同，也可能不同。例如，可能要求某一電氣設備在地震期間不誤動作，或在地震期間和之后都能執行能動功能，或可能要求它在地震期間保持完好而在地震之后要求執行能動功能，或是上面這些要求的任意組合。而對另一設備，可能只要求在地震期間和之后保持結構完整性。這些給定要求應是明確的，并且對安全功能的定義應作為設備鑒定技術要求文件的一部分給出。驗證所選用的鑒定方法符合要求是用戶和(或)委托方的職責。 當設備安全功能要求證實設備在地震期間的可運行性時，應在鑒定模擬的強震運動持續部分進行。 作為總的鑒定大綱的一部分，抗震試驗應按GB/T 12727或其他適用標準指明的順序進行，并注意按相關標準中所討論的試驗裕度來確定和考慮顯著的老化機理。在這些導則中，應證明設備在其整個鑒定壽期中能執行其安全功能，包括在鑒定壽期末發生安全停堆地震期間和(或)之后的功能可運行性。 6 阻尼 6.1概述 阻尼是系統中多種能量耗散機理的統稱。實際上，阻尼取決于許多參數，如結構系統、振型、應變、法向力、速度、材料、連接方式和滑動量。按線性振動理論，簡化假設為阻尼是純黏性的，或與運動部件的相對速度成正比。因此，當涉及一個實際系統的阻尼值時，通常假定它是等效于黏性或是線性的。通常這是采用線性分析理論方法來描述具有某種程度非線性的實際硬件性能的一種簡化方法。 對于由許多部件組成的設備，阻尼常常不是單一值，阻尼與設備的每一個部件都有關系，從螺栓連接或焊接結構到材料性質。在確定設備阻尼值時，通常給出典型值的范圍。由于在多數情況下，設備、構筑物、部件各振型的阻尼值是不同的，因此在分析中常常在所研究的頻率范圍內采用一個綜合的阻尼值。 6.2 阻尼測量 6.2.1 概述 線性振動理論表明有許多測量阻尼的方法。應特別注意實際系統與理論模型之間的對應關系。例如，幾乎不可能找出設備中與模型集中質量單元嚴格一致的精確位置。一些計算模態阻尼的方法，如Q值法，完全依賴于單自由度的假設。 注：Q值是單自由度振子傳遞函數幅值的峰值，與阻尼比存在如下關系：Q=0.5ξ-1。通過測量半功率帶寬可確定Q=fn/Δf，其中fa為共振頻率，Δf為半功率帶寬。 由于設備中各點的反應通常由振型向量和每個振型的參與因子確定，所以直接由在設備中任何點上測得的最大共振反應峰值和正弦掃描輸入激勵幅值計算阻尼通常是不可接受的。為估計阻尼，常用下列方法，但也可采用其他證明是合理的方法。這些方法假設在設備中能激勵起單一振型，且運動傳感器安裝在非零運動位置上。任何情況下都應仔細考慮，針對不同的反應幅值是否存在明顯的阻尼非線性。 6.2.2通過測量衰減來確定阻尼 等效黏性阻尼可通過記錄特定振型的衰減率進行計算。這個方法通常稱作對數衰減法。 6.2.3通過測量半功率帶寬確定阻尼 以慢速正弦掃描激勵設備，測量設備中任意要求位置的反應并繪制成頻率函數的曲線。從這些反應曲線上，與每個振型有關的阻尼可通過測量其半功率點處相應共振峰的寬度進行計算。這個方法常稱為半功率帶寬法。 6.2.4通過曲線擬合法確定阻尼 用正弦掃描、隨機或瞬態激勵對設備進行激振，并通過反應獲得相應的傳遞函數。利用數學模型對實際頻率反應數據(傳遞函數)進行擬合，即能得到各階頻率下的模態阻尼。這種曲線擬合通過平滑處理能去除噪聲或小的實驗誤差。 6.3 阻尼的應用 6.3.1 分析中阻尼的應用 分析中，為預計設備對地震運動的反應建立設備的數學模型，該模型中所用的阻尼值需對應于設備中實際的能量耗散，以便能精確地預估反應。另一個方法是用一個保守的線性阻尼值來得到保守的反應。在任何情況下，都需要知道具體設備的阻尼范圍和非線性的性質及它們對反應的影響。合適的阻尼值可從試驗或其他經證明是合理的來源獲得。 實際阻尼本質上是非線性的。在大多數設備中，由于如材料內摩擦或部件之間連接處的內摩擦，或庫侖型滑動摩擦等因素，實際阻尼是反應幅值的函數。對分析而言，可采用線性阻尼進行近似，但需注意阻尼實際上是隨反應增加而變化的。 一般來說，對結構系統的主要處理方法是假定阻尼是黏性的。然而，某些機柜或殼體可能表現出非黏性阻尼的特征，分析中對此需加以關注。 除非另有規定，分析中典型的電氣設備阻尼比推薦值可參見附錄A。 6.3.2試驗中阻尼的應用 試驗中，可使設備經受由要求反應譜(RRS)所確定的人工模擬地震運動時程來鑒定設備。反應譜通過一組單自由度有阻尼振子的峰值反應來確定地震運動。由于振子是假設的，在用于試驗的要求反應譜中可采用任何可行的阻尼值，例如5％，并且不需要與設備的實際阻尼相一致(注意與分析中使用的要求反應譜的區別，分析時采用的阻尼值應與實際設備相對應)。在8.6.1中給出了在選擇可接受的試驗運動中要求反應譜(RRS)和試驗反應譜(TRS)的應用。對于反應譜中的阻尼值，有下列關系： a)在比較要求反應譜和試驗反應譜時，兩個反應譜的阻尼應相同； b)在不同阻尼下比較要求反應譜和試驗反應譜時，則需考慮以下情況： 1)當試驗反應譜的阻尼大于要求反應譜且滿足8.6.1中的準則時，這種情況是保守的，鑒定結果可以接受； 2)當試驗反應譜的阻尼小于要求反應譜的阻尼時，則應進行進一步的評估。一種可能性是對試驗運動進行重新分析以產生一個可接受阻尼值的試驗反應譜，并應用a)或b)的1)中給出的準則。