1、BRITISH STANDARD BS 7527-2.6: 1991 IEC 721-2-6: 1990 Classification of environmental conditions Part 2: Environmental conditions appearing in nature Section 2.6 Earthquake vibration and shockBS7527-2.6:1991 This British Standard, having been prepared under the directionof the General Electrotechnica
2、l Standards PolicyCommittee, was publishedunder the authority ofthe Standards Board and comesinto effect on 29 November 1991 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference GEL/15 Special announcement in BSINews July 1991 ISBN 0 580 20170 8 Committee
3、s responsible for this British Standard The preparation of this British Standard was entrusted by the General Electrotechnical Standards Policy Committee (GEL/-) to Technical Committee GEL/15, upon which the following bodies were represented: Directorate of Telecommunications EEA (the Association of
4、 Electronics, Telecommunications and Business Equipment Industries) Electronic Components Industry Federation Ministry of Defence National Supervising Inspectorate Society of Environmental Engineers Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date
5、CommentsBS7527-2.6:1991 BSI 08-1999 i Contents Page Committees responsible Inside front cover National foreword ii Introduction 1 1 Scope and object 1 2 Normative reference 1 3 General 1 4 Seismic scales 2 5 Description of the seismic environment by response spectra 2 6 Earthquake zone map 2 Figure
6、1 Acceleration record of the San Fernando Valley earthquake (1971) 4 Figure 2 Model for composing a basic response spectrum 5 Figure 3 Basic response spectrum of the San Fernando Valley earthquake (1971) (Figure 1) for damping values 0, 2, 5 and 10% (curves from top to bottom) 6 Figure 4 Example of
7、required response spectrum 7 Figure 5 Zones of earthquake activity 8 Table 1 Earthquake intensity levels 3 Table 2 Approximate RICHTER scale magnitude 3 Publication(s) referred to Inside back coverBS7527-2.6:1991 ii BSI 08-1999 National foreword This Section of BS7527 has been prepared under the dir
8、ection of the General Electrotechnical Standards Policy Committee. It is identical with IECPublication721-2-6:1990“Classification of environmental conditions Part2:Environmental conditions appearing in nature. Earthquake vibration and shock”, published by the International Electrotechnical Commissio
9、n (IEC). For the purposes of this British Standard, any references to IEC page numbers in the text should be ignored. Other Parts of this British Standard are as follows. Part 1: Environmental parameters and their severities; Part 2: Environmental conditions appearing in nature; Section 2.1: Tempera
10、ture and humidity; Section 2.2: Precipitation and wind; Section 2.3: Air pressure; Section 2.4: Solar radiation and temperature; Section 2.5: Dust, sand, salt mist; Section 2.7: Fauna and flora; Part 3: Classification of groups of environmental parameters and their severities; Section 3.0: Introduct
11、ion; Section 3.1: Storage; Section 3.2: Transportation; Section 3.3: Stationary use at weatherprotected locations; Section 3.4: Stationary use at non-weatherprotected locations; Section 3.5: Ground vehicle installations; Section 3.6: Ship environment; Section 3.7: Portable arid non-stationary use. T
12、he Technical Committee has reviewed the provisions of ISO 6258:1985, to which reference is made in the text, and has decided that they are acceptable for use in conjunction with this standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of British
13、 Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross references International Standard Corresponding British Standard BS 7527 Classification of environmental conditions IEC 721-1:1990 Part 1:1991
14、 Environmental parameters and their severities (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated.
15、This will be indicated in the amendment table on the inside front cover.BS7527-2.6:1991 BSI 08-1999 1 Introduction This part of IEC721is intended to be used as background material when selecting appropriate severities of parameters relating to earthquakes for product application. Severities given in
16、 IEC721-1 should be applied. More detailed information may be obtained from specialist documentation, some of which is given in the bibliography in ISO6258:1985, Nuclear power plants Design against seismic hazards. 1 Scope and object This part of IEC721 deals with environmental conditions appearing
17、in nature, and in particular related to earthquake vibration and shock. Its object is to define some fundamental properties and quantities for characterization of earthquakes as background material for the severities to which products are liable to be exposed during storage and use. Accelerations gi
18、ven are for ground surface conditions only. Conditions related to structures are referred to but restricted to general case descriptions. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this part of IEC721. At the time
19、of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this part of IEC721 are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers
20、of currently valid International Standards. IEC 721-1:1990, Classification of environmental conditions Part 1: Environmental parameters and their severities. 3 General Influences from earthquakes are vibrations which may be modelled as stochastic processes, and can affect products and provide stress
21、 in many ways. This clause is intended to provide information on earthquake behaviour, and on the dynamic performance of products during earthquakes. Numerical values given are typical and illustrative but should not be considered as standard. 3.1 Earthquake origin and propagation An earthquake occu
22、rs when stresses have accumulated to such a degree that they cause the breaking of the earths crust. These instabilities are located in areas known as active seismic zones, in connection with a series of geological accidents such as troughs, oceanic ridges, mountain ranges, volcanoes, ocean trenches
23、, tectonic faults. The sudden breaking releases potential energy deformation which will spread from the hypocentre in the form of three typical basic waves with different speeds: longitudinal volume waves which compress and expand the rock in the propagation direction; transversal waves which shear
24、the rock by distortion, perpendicular to the propagation; surface waves which are a combination of the two previous ones and subject to surface limit conditions. 3.2 Earthquake behaviour Earthquakes produce random ground motions which are characterized by simultaneous but statistically independent h
25、orizontal and vertical components. A moderate earthquake may persist for15s to30s; a severe earthquake for60s to120s. In general, the strong part with the highest ground acceleration may last up to10s. The typical broadband random motion has its maximum energy over a frequency range from1Hz to35Hz,
26、and produces more damaging effects from1Hz to10Hz. Usually the vertical component of the ground motion is assumed to be between 67 % and100% of the horizontal below3,5Hz and equal to the horizontal above3,5Hz. NOTEMaximum acceleration is commonly used in design to reflect earthquake “strength” at a
27、particular site. 3.3 Products on foundations The typical broadband spectra which describe the ground motion indicate that multiple frequency excitation predominates. The vibration nature of the ground motion (both horizontal and vertical) can be magnified in foundation-mounted products. For any give
28、n ground motion, the magnification depends on the characteristic frequencies of vibration of the system (soil, foundation and product) and on the mechanism of damping.BS7527-2.6:1991 2 BSI 08-1999 3.4 Products in buildings and structures The ground motion (mainly horizontal) may be filtered and ampl
29、ified by intervening building structures to produce fluctuating sinusoidal floor motions. The typical narrowband spectra which describe a building floor motion indicate that single frequency excitation can predominate. The dynamic response of floor-mounted products may reach an acceleration many tim
30、es that of the maximum ground acceleration, depending on the system damping and characteristic frequencies of vibration. The magnification and bandwidth depend on the dynamic response characteristics of each building and product structure. Products sensitive to frequencies ranging from5Hz to8Hz are
31、most likely to be affected. 4 Seismic scales In seismology, earthquakes are classified with the aid of various scales according to their intensity or magnitude. Intensity scales (e.g. the modified MSK scale or MERCALLI CANCANI SIEBERG scale) are determined empirically and classify earthquakes in deg
32、rees of intensity according to their effects (seeTable 1). Magnitude scales (e.g. the RICHTER scale) are based on recorded values and assess the seismic energy released at the source of an earthquake. These scales may roughly correspond with certain values of ground acceleration; their use for estab
33、lishing test values is limited. The relationship between the modified MERCALLI scale and ground acceleration is given inTable 1 as approximations. The acceleration levels given in Table 1 are for ground surface conditions. The relationship between the modified MERCALLI scale and the acceleration lev
34、el on products can only be approximated on account of the following factors: the soil or rock conditions (including water saturation); the proximity to the earthquake activity; the conditions of the structure or base of the product. An approximate indication of the relationship between an intensity
35、scale and a magnitude scale is given inTable 2 where the RICHTER magnitude scale has been aligned with Table 1. It should be observed that the relationship between the scales is limited by the following effects: the soil or rock base at the location; the focal depth of the earthquake; the duration o
36、f the earthquake activity. 5 Description of the seismic environment by response spectra 5.1 Response spectrum A commonly accepted design description of the seismic environment specially for testing is the use of response spectra. In a response spectrum the maximum response of a family of oscillators
37、, each having a single degree of freedom with fixed viscous damping, is represented as a function of the characteristic frequency of these oscillators when subjected to the acceleration of the ground movement caused by the earthquake. (It may be noted that a response spectrum is not a spectrum in it
38、s real meaning.) InFigure 1 an example of an acceleration record (natural time history) of a real earthquake is given. Figure 2 shows a model for composing a response spectrum. The response to the initiating vibration amplitude of oscillators with a fixed characteristic frequency f ri(i =1ton) and c
39、onstant damping is registered. The response amplitude of an oscillator will be all the greater the longer and stronger it is excited at its characteristic frequency. 5.2 Basic response spectrum If a ground motion time history has been recorded at the site of an earthquake, or near it, this is used t
40、o establish a response spectrum. By controlled shape changes one may deduce a basic response spectrum which reflects the seismic excitation of the earthquake (Figure 3). A representative number of basic response spectra determined from different earthquakes describes the anticipated seismic stress f
41、or the site or a area. 5.3 Required response spectrum An enveloping curve around the basic response spectra is termed a required response spectrum because it marks the limits of vibrational requirements made on an item to which the latter may be exposed at a given site or area during earthquakes. Di
42、fferent implementations of products at a certain site may lead to the use of different corrected required response spectra according to the behaviour of their support (building structure, floor, or enclosure, etc.). This spectrum (Figure 4) indicates the relationship between the frequency, amplitude
43、 (displacement, velocity or acceleration) and damping for testing purposes. 6 Earthquake zone map The different zones of earthquake activity as indicated in Table 1 are shown on the world map inFigure 5.BS7527-2.6:1991 BSI 08-1999 3 Table 1 Earthquake intensity levels Modified MERCALLI scale Approxi
44、mate acceleration level Seismic zone Table 2 Approximate RICHTER scale magnitude m/s 2 See note 1 Not felt 2 0 0 2 2 Felt by persons at rest or on upper floors 1 2 3 Hanging objects swing Light vibrations 2 3 4 Vibrations as from heavy trucks Windows and dishes rattle Standing cars rock 3 4 5 Felt o
45、utdoors Sleepers awakened small objects fall Pictures move 1 4 5 6 Felt by everybody Furniture displaced Damage: broken glassware, merchandise falls off shelves, cracks in plaster 5 6 7 Felt in moving cars Loss of balance while standing church bells ring Damage: broken chimneys and architectural orn
46、aments, fall of plaster, broken furniture, widespread cracks in plaster and masonry, some collapse in abode houses 3 2 5 7 8 Steering trouble in moving cars Tree branches broken off Cracks in saturated soils Destruction: elevated water tanks, monuments, abode houses Severe to mild damage: brick cons
47、tructions, frame houses (when unsecured to foundation), irrigation works, embankments 3 and 4 6 8 9 “Sand craters” in saturated city sands Landslides. Cracking ground Destruction: unreinforced brick masonry Severe to mild damage: inadequately reinforced concrete structures, underground pipes 5 7 9 1
48、0 Widespread landslides and soil damage Destruction: bridges, tunnels, some reinforced concrete structures Severe to mild damage: most buildings, dams, railway tracks 8 or more 11 Permanent ground distortion 12 Almost total destruction NOTEThe assigned zone indicates the expected occurrence of the i
49、ntensity level during a 50-year period (seeFigure 5).BS7527-2.6:1991 4 BSI 08-1999 a = acceleration t = time Figure 1 Acceleration record of the San Fernando Valley earthquake (1971)BS7527-2.6:1991 BSI 08-1999 5 a = initiating acceleration amplitudef = frequency A a= amplitude of response acceleration k i= stiffness D i= dampingM i= mass f ri = natural frequency of distinct oscillatorst = time Figure 2 Model for composing a basic response spectrumBS7527-2.6:1991 6 BSI 08
