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Disclaimer: The purpose of this forum is to collect comments and suggestions for the upcoming revision of Eurocode 8. SECED does not assume any liability for any posts or comments placed in the forum by its users.

× EC8 Part 4 is one of the three parts of EC8 specifically devoted to non-building structures (the others being Part 2: Bridges and Part 6: towers, masts and chimneys). It is a section of EC8 which may be of direct relevance for application in the UK, because of the possible need to consider the seismic resistance of tanks and pipelines for high consequence of failure petrochemical installations, even in the very low seismicity environment of the UK.

The forum is open for comment on any aspect of Part 4, but three may in particular be considered, as follows.

a) General principles
Are the rules for performance requirements and safety levels sufficiently clear and practical? Do they cater sufficiently for the needs of the UK, as well as regions of higher levels of seismicity?

b) Ductility and q factor rules
Are the q factors for tanks and silos appropriate? For example, are they sufficiently conservative, or over-conservative, do they accord with the most recent research, do they allow for all current methods of construction, or innovative systems?

c) Detailed analysis
The dynamic analysis of tanks and silos is highly complex. Much analytical research has been carried out, over a period of almost half a century, on tanks, but little has been done for silos, which however do fail quite frequently in earthquakes. Part 4 has a long informative annex, giving analytical results for tanks (but not silos), but this does not extend to expressions for tank wall bending moments. The appendix is not particularly easy to use; the New Zealand tanks guide of 2009 (which it is understood will shortly to be upgraded to a more official NZ standard) is (in this author's experience) easier to apply and is more comprehensive.

There is also a short informative annex on the analysis of buried pipelines.

Should (and can) more be added on the seismic response of silos? What should be done to the informative annexes on tanks and on buried pipelines? Are the bibliographies in those annexes as up-to-date and informative as they could be?

Edmund Booth

Appendix A

3 months 3 weeks ago #96 by Colin Robertson
The EDF entity Septen has identified a problem with formulae in EN 1998-4 with regard to the impulsive time period and flexible impulsive height expressions for pools and tanks. They have recommended that the code Appendix A formulae shall be used, but with the following modification: the impulsive time period and flexible impulsive height expressions are replaced by the ones from NZSEE Guidelines (Seismic Design of storage tanks: recommendations of a study Group of the New Zealand Society for Earthquake Engineering, December 1986) as the NZ standard is closely aligned with the EN1998 philosophy. The RCC-CW code that has evolved from the ETC-C has already incorporated this change.
Is the code committee aware of this issue and do they agree with Septen’s view and the solution, for example does the 2009 update to the NZSEE Guidelines use the same formulae?

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