1、raising standards worldwide NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BSI British Standards WB9423_BSI_StandardColCov_noK_AW:BSI FRONT COVERS 5/9/08 12:55 Page 1 PD 6698:2009 PUBLISHED DOCUMENT Recommendations for the design of structures for earthquake resistance to BS
2、EN 1998 This publication is not to be regarded as a British Standard. PD 6698:2009 PUBLISHED DOCUMENT Publishing and copyright information The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2009 ISBN 978 0 580 61346 3 ICS 91.120.25 The following BSI
3、reference relates to the work on this standard: Committee reference B/525 Publication history First published July 2009 Amendments issued since publication Date Text affected BSI 2009 i PD 6698:2009 PUBLISHED DOCUMENTContents Foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Assessing
4、the need for seismic design of structures within the UK 2 4 Seismic hazard in the UK 3 5 Limit states and choice of associated design ground motions in the UK 6 6 Choice of response spectrum 6 7 Additional advice specific to BS EN 19981: General rules, seismic actions and rules for buildings 7 8 Add
5、itional advice specific to BS EN 1998 2: Bridges 12 9 Additional advice specific to BS EN 1998 4: Silos, tanks and pipelines 16 10 Additional advice specific to BS EN 19985: Foundations, retaining structures and geotechnical considerations Assessment of liquefaction 17 11 Additional advice specific
6、to BS EN 1998 6: Towers, masts and chimneys 18 Annexes Annex A (informative) List of clauses subject to National Choice in BS EN 1998 1, BS EN 1998 2, BS EN 19984, BS EN 1998 5 and BS EN 1998 6, with crossreferences to relevant (sub)clauses of PD 6698 19 Bibliography 22 List of figures Figure 1 Seis
7、mic hazard map of 475 year return period Peak Ground Acceleration (PGA) on rock 4 Figure 2 Seismic hazard map of 2 500 year return period Peak Ground Acceleration (PGA) on rock 5 List of tables Table 1 Examples of bridges with high consequence of failure where seismic design might need to be conside
8、red 12 Table A.1 BS EN 1998 1: General rules, seismic actions and rules for buildings 19 Table A.2 BS EN 1998 2: Bridges 20 Table A.3 BS EN 1998 4: Silos, tanks and pipelines 20 Table A.4 BS EN 1998 5: Foundations, retaining walls and geotechnical considerations 20 Table A.5 BS EN 1998 6: Towers, ma
9、sts and chimneys 21 Summary of pages This document comprises a front cover, an inside front cover, pages i to ii, pages 1 to 24, an inside back cover and a back cover.PD 6698:2009 ii BSI 2009 PUBLISHED DOCUMENTForeword Publishing information This Published Document is published by BSI and came into
10、effect on 31 July 2009. It was prepared by Subcommittee B/525/8, Structures in seismic regions, under the authority of Technical Committee B/525, Building and civil engineering structures. A list of organizations represented on these committees can be obtained on request to their secretary. Informat
11、ion about this document This Published Document is a background paper that gives noncontradictory complementary information for use in the UK with the following parts of BS EN 1998, Design of structures for earthquake resistance, and their UK National Annexes: Part 1: General rules, seismic actions
12、and rules for buildings; Part 2: Bridges; Part 4: Silos, tanks and pipelines; Part 5: Foundations, retaining walls and geotechnical considerations; Part 6: Towers, masts and chimneys. It is not planned to issue a UK National Annex or Published Document to BS EN 1998 3, Assessment and retrofitting of
13、 existing buildings, because it is considered that little use will be made of this part for buildings in the UK. Presentational conventions The word “should” is used to express recommendations of this Published Document. The word “may” is used in the text to express permissibility, e.g. as an altern
14、ative to the primary recommendation of the clause. The word “can” is used to express possibility, e.g. a consequence of an action or an event. Contractual and legal considerations This publication does not purport to include all necessary provisions of a contract. Users are responsible for its corre
15、ct application. Compliance with a Published Document cannot confer immunity from legal obligations. BSI 2009 1 PD 6698:2009 PUBLISHED DOCUMENTIntroduction When there is a need for guidance on a subject that is not covered by the Eurocode, a country can publish documents containing noncontradictory c
16、omplementary information that supports the Eurocode. This Published Document provides just such information and has been cited as a reference in the UK National Annexes to BS EN 19981:2004, BS EN 19982:2005, BS EN 1998 4:2006, BS EN 19985:2004 and BS EN 1998 6:2005.1 Scope This Published Document pr
17、ovides noncontradictory complementary information for use in the UK with BS EN 1998 1:2004, BS EN 1998 2:2005, BS EN 1998 4:2006, BS EN 1998 5:2004 and BS EN 1998 6:2005, and their UK National Annexes. This Published Document gives background information and some additional guidance on the clauses s
18、ubject to National Choice in these parts of BS EN 1998. This document only covers the United Kingdom and does not consider conditions applicable to British Overseas Territories, where seismological and other aspects might be very different. It is restricted to considerations for the design of new st
19、ructures within the scope of BS EN 1998 1, BS EN 1998 2, BS EN 1998 4, BS EN 1998 5 and BS EN 1998 6 to resist seismic actions.2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For u
20、ndated references, the latest edition of the referenced document (including any amendments) applies. BS EN 1990:2002, Eurocode Basis of structural design BS EN 1991 1 5:2003, Eurocode 1: Actions on structures Part 1-5: General actions Thermal actions BS EN 1998 1:2004, Eurocode 8 Design of structure
21、s for earthquake resistance Part 1 General rules, seismic actions and rules for buildings BS EN 1998 2:2005, Eurocode 8 Design of structures for earthquake resistance Part 2 Bridges BS EN 1998 4:2006, Eurocode 8 Design of structures for earthquake resistance Part 4 Silos, tanks and pipelines BS EN 1
22、998 5:2004, Eurocode 8 Design of structures for earthquake resistance Part 5 Foundations, retaining walls and geotechnical considerations BS EN 1998 6:2005, Eurocode 8 Design of structures for earthquake resistance Part 6 Towers, masts and chimneysPD 6698:2009 2 BSI 2009 PUBLISHED DOCUMENT3 Assessin
23、g the need for seismic design of structures within the UK3.1 Function, location and form of structure The UK National Forewords to BS EN 1998 1 and BS EN 1998 5 state the following: “There are generally no requirements in the UK to consider seismic loading, and the whole of the UK may be considered
24、an area of very low seismicity in which the provisions of EN 1998 need not apply. However, certain types of structure, by reason of their function, location or form, may warrant an explicit consideration of seismic actions.” 3.2 to 3.4 discuss in turn how the function, location and form of a structu
25、re in the UK affect the need for seismic design.3.2 Influence of function For most engineered and non engineered structures in the UK, natural hazards, such as wind, flood, ground movements due to moisture change, and extreme temperatures, pose a substantially higher risk of injury and economic loss
26、 over the lifetime of a structure than the risk posed by earthquakes. However, in some cases the function of a structure is such that failure due to very low probability events, including earthquakes, might need to be considered. At least four such categories of structure can be distinguished, as fo
27、llows. 1) Structures where failure poses a large threat of death or injury to the population. Examples include nuclear power plants and major dams (both of which are explicitly outside the scope of BS EN 1998) and certain petrochemical installations, such as liquid natural gas (LNG) storage tanks an
28、d high pressure gas pipelines (which are within the scope of BS EN 1998). 2) Structures which form part of the national infrastructure and the loss of which would have large economic consequences. An example is a major bridge forming a transportation link vital to the national economy. 3) Structures
29、 whose failure would impede the regional and national ability to deal with a disaster caused by a major damaging earthquake. 4) Strengthening or upgrading of historic structures forming an important part of the national heritage. In many cases, structures could fall into more than one category; for
30、example, the seismic failure of a busy estuarial bridge might cause extensive human casualties, affect the regional or national economy and also impede the flow of disaster relief into the area affected by the earthquake. In some cases, UK legislation requires an explicit consideration of seismic de
31、sign for certain types of infrastructure. In other cases, seismic considerations have been widely applied, even in the absence of legislation, for example in the assessment of major dams and in the contractual specifications for the design of major bridges. There might be other cases where the owner
32、 of a structure decides that an explicit seismic design is required for economic or other reasons; the local BSI 2009 3 PD 6698:2009 PUBLISHED DOCUMENT level of seismic hazard and the particular sensitivity of the structure to seismic excitation (as discussed in 3.3 and 3.4) are likely to influence
33、that decision.3.3 Influence of location The location of a structure affects the regional seismic hazard, which varies significantly across the UK, as discussed in Clause 4; that is, the earthquake ground motions for a given annual probability of exceedence are significantly greater in some parts of
34、the UK than others, although everywhere the hazard is very low by international standards. Location also affects the local influences on seismic hazard; in particular, the effect of superficial soil deposits in modifying seismic ground motions.3.4 Influence of structural form All structures possess
35、some degree of earthquake resistance, and this is greatly enhanced by regulatory requirements to provide measures enhancing robustness, such as peripheral ties in buildings and detailing to increase ductility, and by the provision of wind resistance. In many cases, these are considered to provide su
36、fficient protection against seismic actions in the UK. However, certain features might result in designs that are satisfactory for resisting wind but are vulnerable to seismic loading. Examples of such seismically unsatisfactory features in building structures are open and relatively weak ground sto
37、reys, very heavy roof masses and large eccentricities between centres of mass and stiffness. Examples for bridges are bridge decks on bearings which provide poor lateral restraint, and concrete bridge piers which are poorly confined by transverse reinforcement.3.5 Decision on seismic design It is th
38、e responsibility of the designer to establish whether statutory or other considerations require an explicit seismic design. In the absence of statutory requirements or contractual specifications, structures classified by BS EN 1990:2002, Table B1, as being in consequence classes CC1 or CC2 are unlik
39、ely to warrant seismic design, provided they are adequately designed for non seismic design conditions. For structures in consequence class CC3, the need for an explicit seismic design should be considered, although in many cases examination of the consequences of failure, location and structural fo
40、rm will indicate that an explicit seismic design is not warranted. Specific advice for the design of buildings, bridges, and silos, tanks and pipelines is given in Clauses 7, 8 and 9 respectively.4 Seismic hazard in the UK An assessment of the seismic hazard in the UK was carried out at the British
41、Geological Survey by Musson and Sargeant 1, for the purposes of preparing the UK National Annex to BS EN 1998 1 and this Published Document. Figure 1 and Figure 2 show the seismic hazard maps that resulted from this exercise. Note that Figure 1 corresponds to the definition of a gRin BS EN 1998 1 fo
42、r the recommended reference return period of 475 years.PD 6698:2009 4 BSI 2009 PUBLISHED DOCUMENT Figure 1 Seismic hazard map of 475 year return period Peak Ground Acceleration (PGA) on rock (redrawn from Musson and Sargeant 1) Comparison of the peak ground acceleration (PGA) values shown in Figure
43、1 with PGA values found worldwide (see, for example, GSHAP 2) shows that seismic hazard in the UK is very low by international standards. The recommended definition of a very low seismicity region in BS EN 1998 1 is an a gRvalue of less than 0.04 g for a 475 year return period; application of the Eu
44、rocode is not required in such regions. It can be seen from Figure 1 that only a very small part of Wales exceeds this recommended value and Musson and Sargeants study 1 found no values exceeding 0.08 g. The zoning of the whole BSI 2009 5 PD 6698:2009 PUBLISHED DOCUMENT of the UK as an area of very
45、low seismicity given in the UK National Forewords to BS EN 1998 1 and BS EN 1998 5 therefore essentially accords with the definition of very low seismicity recommended by the Eurocode. It may be observed, however, that the Eurocode provides an alternative definition of very low seismicity regions as
46、 those where the product a gRS(i.e. the design PGA on soil) exceeds 0.05 g; this represents the PGA at the reference return period after allowing for the amplifying effects of soil on the bedrock motions. It is likely that a rather larger area of the UK would exceed the “very low” seismicity thresho
47、ld on this definition, but the area would still be relatively small. Figure 2 Seismic hazard map of 2 500 year return period Peak Ground Acceleration (PGA) on rock (redrawn from Musson and Sargeant 1)PD 6698:2009 6 BSI 2009 PUBLISHED DOCUMENT5 Limit states and choice of associated design ground moti
48、ons in the UK Booth and Skipp 3 demonstrate that the values of return periods and importance factors recommended in the main body of BS EN 1998 are inappropriate for an area of very low seismicity such as the UK, and are too small for the no collapse requirement defined in BS EN 1998 1, 2.1(1)P; the
49、refore, alternative advice is provided in the UK National Annexes. This is summarized as follows. In cases where an explicit seismic design is considered warranted for a consequence class CC3 structure (see 3.5), it is recommended that the mapped acceleration values of Figure 2 for a 2 500 year return period are used for selection of the design PGA a g , where a g= g I a gRa g , g Iand a gRare defined in BS EN 1998 1, 3.2.1(3). Effectiv
