PDF - Seismic Design Of Spherical Liquid Storage Tanks.pdf

of 18

Please download to get full document.

View again

All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
PDF
18 pages
1 downs
15 views
Share
Description
COMPDYN 2011 III ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis, V. Plevris (eds.) Corfu, Greece, 26–28 May 2011 SEISMIC DESIGN OF SPHERICAL LIQUID STORAGE TANKS (COMPDYN 2011) Matthias Wieschollek 1 , Maik Kopp 1 , Benno Hoffmeister 1 and Markus Feldmann 1 1 Institute for Steel Structures RWTH Aachen University 52074 Aachen, Germany e-mail: wieschollek@stb.rwth-aachen.de Keywords: Spherica
Tags
Transcript
   COMPDYN 2011 III ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis, V. Plevris (eds.) Corfu, Greece, 26–28 May 2011 SEISMIC DESIGN OF SPHERICAL LIQUID STORAGE TANKS (COMPDYN 2011) Matthias Wieschollek  1 , Maik Kopp 1 , Benno Hoffmeister 1  and Markus Feldmann 1   1  Institute for Steel Structures RWTH Aachen University 52074 Aachen, Germany e-mail: wieschollek@stb.rwth-aachen.de Keywords:  Spherical Liquid Storage Tanks, Industrial Structures, Behaviour Factor, Sloshing Effect, Seismic Design, Earthquake Engineering. Abstract:  Spherical storage tanks are widely used for various types of liquids, including haz-ardous contents; consequently these storage tanks must be adequately designed for seismic actions. While very detailed and specific seismic design rules for cylindrical tanks are provided by  several codes, such rules are missing for spherical tanks. This paper describes the results of a  survey on existing European and American Codes with regard to their applicability to spheri-cal liquid storage tanks and provides comparison of design outcomes according to these codes. The investigations were performed on an example of an existing spherical tank which was selected to be representative for the current practice. The studies comprised numerical  FE modelling and calculation as well as simplified models for the estimation of the dynamic  properties of the tank structure. The applicability of behaviour factors was discussed based on proposals made by Eurocode 8. Particular attention was paid to the influence of sloshing effects for which no guidance is given in the codes. The sloshing effects were investigated ac-cording to the current state of the art based on available publications.  Finally the resistance of the tank was compared to the action effect determined from the Eu-ropean and American codes. The comparison of action effects obtained with and without con- sideration of sloshing effects showed a rather important influence of these effects on the final results.  M. Wieschollek, M. Kopp, B. Hoffmeister and M. Feldmann 2 1   INTRODUCTION The contribution describes the results of an investigation of a representative example of a spherical liquid storage tank subjected to seismic actions. The aim of the study was to verify the applicability of existing European and American codes to spherical tanks although no par-ticular design rules for this kind of tanks – neither for the determination of loads nor for the detailing – are provided by the considered codes. Furthermore the influence of sloshing ef-fects was investigated according to the current state of the art [9]. 2   OBJECT OF INVESTIGATION 2.1   Dimensions and load cases The research focused on a spherical pressure vessel (material S 355) with the dimensions given below, see Figure 1. The spherical tank was supported by twelve vertical legs without additional bracings between them. Figure 1: Spherical pressure vessel with 12 columns (inner diameter of the sphere  D  I   = 19.9 m )   The numerical investigation considered the following load cases: ▪   self-weight of the structure (columns and sphere) (total weight m = 879 t  ); ▪   operating load (density  ρ   = 522kg/m³  , filling height h  p  = 18.1m , weight m = 2104t  ); ▪   seismic load ( a  g   =   0.24 g ≈   2.4 m/s²  ) 2.2   Seismic actions In order to compare European and American standards the value of the response accelera-tion S  d   for T   B   ≤   T ≤   T  C   according to EN 1998-1:2010 (3.13) [1] was selected to be equal to S  a  for T  0   ≤   T ≤   T  S   according to ASCE/SEI 7-05 (11.4-5) [4] (see Figure 2). However, the behav-iour factor q is not taken into account at this point (q = 1). ( )  ⎥⎦⎤⎢⎣⎡⎟⎟ ⎠ ⎞⎜⎜⎝ ⎛ −⋅+⋅⋅= 32q5.2T T 32S aT S   B g d   (according to EN 1998-1 (3.13)) (1)  M. Wieschollek, M. Kopp, B. Hoffmeister and M. Feldmann 3  ⎟⎟ ⎠ ⎞⎜⎜⎝ ⎛ ⋅+⋅= 0 6.04.0 T T S S   DS a  (according to ASCE/SEI 7-05 (11.4-5)) (2) T  B  (T  0   ) T  C   (T  S   ) T  D  (T  L  )S d   (S a  ) 3224.0  ⋅⋅ S  g   g  24.0   Figure 2: Elastic response spectrum according to EN 1998-1 [1] and ASCE/SEI 7-05 [4] To consider similar ground conditions for both standards comparable locations were as-sumed (ground type C   according to EC 8, part 1 [1] complies with site class C   according to ASCE 7 [4]). The model for the determination of the fundamental period T  1  was divided into the follow-ing sub-systems: ▪   ground and foundation (soil-structure interaction effects are not considered here); ▪   spherical pressure vessel structure; ▪   fluid, sloshing response, etc. 2.3   Fundamental period of the spherical pressure vessel structure The fundamental period of the tank structure including maximum filling and neglecting sloshing effects was determined as follows (see Figure 3): ▪   using FEM-calculations, fundamental period was determined to T  1  = 1.54 s ; ▪   using a strut-and-tie model (single equivalent load in center of gravity) T  1  = 1.56 s.   XZY IsometrieRF-DYNAM 2007FA11. Eigenform - 0.64878HzuFaktor für Verformungen: 3.50Maxu: 1.0,Minu: 0.0[-] ZXY LF3: ErsatzsteifigkeituMaxu:21.1,Minu:0.0[mm] Figure 3: Ascertainment of the fundamental period T  1  based on FEM model (left) and strut-and-tie model (right)  M. Wieschollek, M. Kopp, B. Hoffmeister and M. Feldmann 4  3   SELECTION OF A BEHAVIOUR FACTOR 3.1   Basis of the behaviour factor In the seismic design of structures the behaviour factor q  (or response modification factor  R ) represents the dissipation capability of the structure. This dissipation capability depends on the structural type and the type of the construction (e.g.: concrete, steel, composite …). The upper limit value of q  depends on the ductility class. EC 8, part 1 [1] differentiates between three ductility classes. Structures with small dissipation capability belong to the low ductility class (DCL). Structures belonging to DHM (medium ductility class) or DCH (high ductility class) have to fulfil minimum requirements with regard to plastic deformability (e.g. rotation capacity of the cross-sections) and with regard to detailing (e.g. capacity design of connec-tions). In the following medium ductility class (DCM) was supposed for the steel tanks under investigation.   For structures in Europe basic seismic design rules, including seismic actions, are provided  by Eurocode 8 Part 1. In the USA basic rules and seismic actions are provided e.g. by ASCE 7 [4]. With regard to tank structures EN 1998-4 [2] applies in Europe. The American stand-ards API 620 [5] and API 650 [6] are used for the design of ground supported tanks including earthquake. Table 1 shows a compilation of references to the behaviour factor q  respectively response modification factor  R  available the European and American standards.   Behaviour factor q Response modification factor R EN 1998-1, chap. 6.3 (steel buildings)  ASCE/SEI 7-05, tab. 12.2 1 (general systems)  EN 1998-4, chap. 2.4 (general)  ASCE/SEI 7-05, tab. 15.4 2 (nonbuilding struc-tures) EN 1998-4, chap. 3.4 (silos)  API 650, tab. E 4 (ground supported, liquid storage tanks) EN 1998 -4, chap. 4.4 (tanks)  API 620, tab. L 1Q and L1 R (ground supported, liquid storage tanks) UBC 1997, Volume 2, tab. 16 N (general systems) UBC 1997, Volume 2, tab. 16 P (nonbuilding struc-tures) Table 1: References of behaviour factor and response modification factor 3.2   Behaviour factor q  according to European standards The provisions given by EC 8 for the application of behaviour factor q  to spherical tanks are of limited precision. For elevated tanks EN 1998-4 [2], Chap. 4.4 refers to Chap. 3.4 (silos) where the application of behaviour factor q  for an inverted pendulum (see Figure 4) is rec-ommended. Basic definitions of an inverted pendulum system are given in EC8 Part 1. The following definitions given by Eurocode 8 are of interest for assessment of the behaviour fac-tors of spherical elevated tanks: ▪   EN 1998-1 5.1.2 (1): Inverted pendulum systems – system in which 50% or more of the mass is in the upper third of the height of the structure, or in which the dissipation of energy takes place mainly at the base of a single building element.  NOTE: One-storey frames with column tops connected along both main directions of the building and with the value of the column normalized axial load  ν d  exceeding 0,3 nowhere, do not belong in this category.
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks