PD 6698
PD 6698
PD 6698
PUBLISHED DOCUMENT
© BSI 2009
ICS 91.120.25
Publication history
First published July 2009
Contents
Foreword ii
Introduction 1
1 Scope 1
2 Normative references 1
3 Assessing 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 1998‑1: General rules,
seismic actions and rules for buildings 7
8 Additional 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 1998‑5: Foundations,
retaining structures and geotechnical considerations –
Assessment of liquefaction 17
11 Additional advice specific 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 1998‑4, BS EN 1998‑5 and BS EN 1998‑6,
with cross‑references to relevant (sub)clauses of PD 6698 19
Bibliography 22
List of figures
Figure 1 – Seismic 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 considered 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, masts 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.
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Foreword
Publishing information
This Published Document is published by BSI and came into 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.
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 alternative 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.
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Introduction
When there is a need for guidance on a subject that is not covered
by the Eurocode, a country can publish documents containing
non‑contradictory complementary 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 1998‑1:2004, BS EN 1998‑2:2005, BS EN 1998‑4:2006,
BS EN 1998‑5:2004 and BS EN 1998‑6:2005.
1 Scope
This Published Document provides non‑contradictory 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 subject 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 structures 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 undated 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 structures 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 1998‑5:2004, 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 chimneys
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Figure 1 Seismic hazard map of 475 year return period Peak Ground Acceleration (PGA) on rock
(redrawn from Musson and Sargeant [1])
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Figure 2 Seismic hazard map of 2 500 year return period Peak Ground Acceleration (PGA) on rock
(redrawn from Musson and Sargeant [1])
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6.1 Introduction
BS EN 1998‑1, Clause 3, recommends response spectrum shapes, the
ordinates of which are multiplied by the design PGA ag to produce
a design spectrum. Where ag has been selected from Figure 2, as
discussed in Clause 5, a response spectrum shape is needed to define a
response spectrum for design purposes. The shapes recommended by
BS EN 1998‑1, Clause 3, depend on the profile of the soil underlying
the site in question. 6.2 and 6.3 discuss the appropriateness for UK
conditions of the soil profiles and the corresponding spectral shapes
recommended by BS EN 1998‑1.
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7.1.1 General
It is suggested that seismic design is not required for buildings
classified by BS EN 1990:2002, Table B1, as being in consequence
class CC1 or CC2. Following the discussion of 3.5, buildings classified
as consequence class CC3 do not necessarily require explicit seismic
design, but should be assessed to see if that need applies.
Booth and Skipp [3] propose a screening procedure for establishing
whether CC3 buildings warrant an explicit seismic design, and outline
suggested methods of preliminary and final design in cases where
it is found to be warranted. Consequence class CC3 corresponds to
importance classes 3 and 4 in BS EN 1998‑1 and other Eurocodes.
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7.6.1 General
Instances where the UK National Annex to BS EN 1998‑1 modifies
the recommended values for steel buildings are discussed in the
following subclauses.
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tension. This could overestimate the residual load for slender braces,
and underestimate it for stocky braces. The UK National Annex
therefore proposes the following.
γ
pb
*Nb,Rd λ ( )
γ pb =
Npl,Rd
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Table 1 Examples of bridges with high consequence of failure where seismic design might need to
be considered
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stiff soils (soil types A, B and C). However, they should be checked for
the looser soil types D and E where the length of continuous bridge
deck exceeds the recommended value of Llim. This is because, in softer
soils, seismic ground motions have relatively longer periods, involving
larger displacements for a given acceleration level, and shorter
wavelengths than apply to stiffer soils. Therefore, where soft soils are
present, differential movements between bridge supports are more
likely to give rise to significant effects.
BS EN 1998‑2, 3.3(1)P, requires that all bridges with continuous
decks are checked for spatial variability where they are supported
on more than one ground type. The simplified method proposed in
BS EN 1998‑2, 3.3(4) to (7), will usually be adequate, and the more
sophisticated methods given in BS EN 1998‑2, Annex D, are unlikely to
be required.
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Bibliography
Standards publications
For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including
any amendments) applies.
BS EN 1473, Installation and equipment for liquefied natural gas –
Design of onshore installations
BS EN 1993, Eurocode 3 – Design of steel structures
BS EN 1996‑1, Eurocode 6 – Part 1: Design of masonry structures
BS EN 14015, Specification for the design and manufacture of site
built, vertical, cylindrical, flat bottomed, above ground, welded, steel
tanks for the storage of liquids at ambient temperatures and above
BS EN 14620‑1:2006, Design and manufacture of site built, vertical,
cylindrical, flat bottomed, above ground, welded, steel tanks for the
storage of refrigerated liquefied gases with operating temperatures
between 0 °C and −165 °C – Part 1: General
Other publications
[1] MUSSON R. and SARGEANT S. Eurocode 8 seismic hazard zoning
maps for the UK. British Geological Survey Seismology And
Geomagnetism Programme Technical Report Cr/07/125. Research
Report for the Institution of Civil Engineers. January 2008.
[2] GIARDINI, D. 1999. The Global Seismic Hazard Assessment
Program (GSHAP) – 1992/1999. Annali di Geofisica, Vol. 42,
957‑976. www.seismo.ethz.ch/GSHAP
[3] BOOTH E. and SKIPP B. Establishing the necessity for seismic
design in the UK. Research Report for the Institution of Civil
Engineers. January 2008.
[4] IStructE/AFPS. Manual for the seismic design of steel and concrete
buildings to Eurocode 8. Institution of Structural Engineers,
London. 2009.
[5] ELGHAZOULI, A. Y. “Seismic Design Procedures for Concentrically
Braced Frames”, Proc. Instn. Civ. Engrs., Structures and Buildings,
156 (2003), 381‑394.
[6] GOGGINS, J. M. BRODERICK, B. M., ELGHAZOULI, A. Y. and
LUCAS, A. S. “Experimental Cyclic Response of Cold‑Formed
Hollow Steel Bracing Members”, Engineering Structures, 27(7),
(2005), 977‑989.
[7] GREAT BRITAIN: The Building Regulations 2000, as amended,
SI 2000, No. 2531, London: The Stationery Office.
[8] GREAT BRITAIN: The Building Standards (Scotland) Regulations
1990, as amended, SI 1990, No. 2179, London: The Stationery
Office.
[9] NORTHERN IRELAND: The Building Regulations (Northern
Ireland) 2000, SR 2000, No. 389, London: The Stationery Office.
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