Seismic analysis

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GUR 7383
ISSN 1018-5593
Commission of the European Communities
BENCHMARK EXERCISE
ON MAJOR HAZARD ANALYSIS
VOL. 3 - SEISMICS
Blow-up from microfiche original ;
Commission of the European Communities
BENCHMARK EXERCISE
ON MAJOR HAZARD ANALYSIS
VOL. 3 - SEISMICS
Edited by:
G. DROGARIS, G. SOLOMOS, A. AMENDOLA
Commission of the European Communities
Joint Research Centre
Institute for Systems Engineering and Informatics
Ispra Establishment
I-21020 Ispra (VA)
FINAL REPORT
Directorate-General
Science, Research and Development
Joint Research Centre
PARL EUROP. Biblioth.
N.C.EUR 13898 EN
CI. Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of then is responsible for the use which might be made of the following
information
Catalogue number: CD-NA-13898-EN-C
© ECSC — EEC - EAEC, Brussels - Luxembourg, 1992 Ill
ABSTRACT
As a part of the Benchmark Exercise on Major Hazard Analysis, a seismic
analysis of ammonia storage plant has been also performed by the fol­
lowing four participating groups:
1. C.S.R. : Consultant - Denmark.
2. TECHNICAt United Kingdom.
3. TNO : Research Centre - The Netherlands.
4. NCSRDhe - Greece.
This volume contains the description of this seismic project, the data
and information on which the seismic analysis has been based, compari­
son of the results and the main conclusions.
The final reports of the participants are also included. EXECUTIVE SUMMARY
The overall objectives and the description of the Benchmark Exercise on
the Major Hazard Analysis Project have been already given in Vol. 1.
As a part of this exercise a seismic analysis of the plant under con­
sideration has been performed by the following participating groups:
1. C.S.R. : Consultant - Denmark'*'.
2. TECHNICAt United Kingdom.
3. TNO : Research Centre - The Netherlands.
4. NCSRDhe - Greece.
Whereas for a more comprehensive description of the results of this
exercise reference shall be made to the main report, the general
conclusions are highlighted herebelow. These conclusions represent the
results of the discussions of the participating experts.
General
- Even though the application of a full stochastic approach (Seismic
input and material properties) in a risk study is desirable, in this
study there are gaps of knowledge which dictate the employment of
conservative and/or simplifying assumptions.
Seismic Source
- Site recorded accelerograms or their corresponding spectra could
describe better particular seismic conditions for a specific site
provided that an adequate number of them is available. Due to lack of
this data the more conservative approach of using widely accepted
design earthquake response spectra is followed. Furthermore, due to
the recording practice for accelerograms (mainly recording on rock
surfaces), there are still difficulties with reference to the proper
application (subsoil filtering effect, position of application of the
accelerogram for a specific construction).
- Accurate description of soil/structure interaction largely depends on
the availability of adequate data. Limited knowledge of the
earthquake propagation mechanism in huge structure does not permit
the formulation of a general guide on the use of smoothing of the
seismic excitation by averaging due to the size of the structure.
(*) Participated in the Benchmark Exercise only for the seismic analysis is in collaboration with
the RISOE Research Centre. VI
Method of Seismic Analysis
- Finite element discretization is generally accepted as the most accu­
rate method for a seismic study of complex structures and there are
techniques available to reduce the extent of time consuming
calculations. Due care has to be paid in order for the users to keep
the physical insight of the problem and hence to not overlook
critical situations.
Seismic Impact on the Specific Structure
- There was a common agreement that the inner metal tank is the most
critical component of this specific structure in case of an earth­
quake whereas foundations, piles and the outer concrete shell should
not be substantially affected.
- The study of this specific structure showed that there is a need for
more research and for the development of easily workable methods in
the following areas:
. Effect of pile differential movement in case of an earthquake on
the structure.
. Impact of dynamic fluid/structure interactions both on the inner
metal tank and on the outer concrete tank, should the inner metal
tank fail.
. Hitting of the concrete outer shell by the inner metal tank due to
differential movement.
. Tackling buckling problems at the base of the inner metal tank.
. Effect of impact of inner metal tank against the concrete slab fol­
lowing a base uplift in a rocking motion.
(Note that the last three points mainly refer to the case that the
inner metal tank is not anchored on the concrete slab).
- Accurate seismic risk calculations would require due consideration
of:
. The uncertainties in the failure criteria (incorporation of deter­
ministic failure modes in a probabilistic risk assessment, yield
strength distribution, stress distribution, etc.).
. The effect of the variability of the filling height.
This is especially important when the contribution of the seismic
source to the overall risk of the installation (taking all potential
sources into consideration) is not negligible. VII
ACKNOWLEDGMENT
The collaboration of the plant owner and the plant personnel is grate­
fully acknowledged. Without it the project would have not been
possible.
Furthermore the contribution of the following colleagues from SER/MTR
sector has to be acknowledged:
- S. Contini for the project coordination and his contribution at the
start of the seismic analysis exercise.
- P. Wiederstein and G. Francocci for their valuable assistance in the
organization and the documentation of the project.
Finally the constructive comments of Mr. V.A. Pinto and Mr. A. Youtsos
are kindly acknowledged.