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  15 The seismic design of ambienttemperature storage tanks This Chapter describes the most commonly used method ofdesigning verticalcylindricalliquidstorage tanks for seismic loadings- This method is taken from API 650 Appendix E. Some indications of the srcins of the various methods of calculation and the formulae used are orovided. The equivalentdesign sections of BS 2654 and the forthcoming Euronorm are a lso described. Contents: 15.1 lntroduction 15.2 The API 650 _approach '15.2.'1 The basic seismic data15.2.2 The behaviour of the pmduct liquid '15.2.3 The overtuming moment15.2.4 Resistance to overluming '15.2.5 Shell comDression15.2.5.1 Unanchored tanks 15.2.5.2 Anchored tanks 15.2.6 Ailowable longitudinal compressive stresses 15.2-7 Slosh height and freeboard considerations15.2.8 Other conditions arjsing from seismic loadings 15.3 The BS 2694 approach 15.4 The prEN 14015 approach 15.5 References STORAGE TANKS & EQUIPMENT 263  15 The seismic design of ambient temperature stoftge tanks 15.1 lntroduction The design of liquid storage tanks to resist seismic loadings is a subject which is taken very seriously these days. Despite the collapse of a large steel water tank during the Long Beachearthquake of 1933, nothing was done to provide a framework of rules for the seismic design of liquid containing tanks until af-ter the Alaska earthquake of 1964. This seismic event causedwidespread damage and subsequent fire to a large number of petrochemical fuel tanks. The site contained a numberoftanks of different sizes, different proportions and filled to different lev- els with products with different specific gravities at the time that the earthquake struck. The study of the levels of damage sus-tained by the various tanks allowed the various theories relating to seismic design to be tested. The Alaska event is described in References 15.1 and 15.2.Two further seismic events involving damage to storage tanksalso contributed evidence to the discussions. These were the '1971 San Fernando and the 1974 Lima Peru eafthquakes de-scribed in References 15.3 and 15.4 The credit for the production of a workable and user friendly set of rules for the safe design of liquid storage tanks to enablethem to resist seismic loads owes a lot to the document com-monly known as TID 7024 (Reference t5.5) and to the work ofWozniakand Mitchell (Reference 15.6). The proposalsgiven in this paper by Wozniak and Mitchell were adopted with minorchanges as Appendix E ofAPl 650 (Refe rence 15.7). Appendix L of API 620 (Reference 75.8) uses the same design method BS 2654 (Reference 75.9) has borrowed the same rules, al- though not the seismic zones from the UBC, (The AmericanUniform Building Code). This Chapter devotes most of iis efforts to the seismic design of ground based ve(ical cylindrical tanks as these form the largemajority of ambient tanks. TID 7024 provides some guidanceon the design of rectangular and elevated tanks.The seismic design of liquid containing storage tanks has been a popular subject for study over the years and there are hun-dreds of articles and papers covering work which has been car-ried out. lt is proposed to include in this Chapter only the mostimmediately relevant references. lf more are required, then ref-erence to chapter 6 of Philip Myers' book ( Refercnce 15.10)will provide a list of 61 papers and reference to these in turn shou ld Figure 15.1 Selsmic zone map ofthe lJnited StatesFrom the Unifam Building Code 264 STORAGE TANKS & EQUIPMENTproduce sufficient material for even the most enthusiastic stu-dent of this subject. 15.2 The API 650 approach 15.2.1 The basic seismic data Before the task ofdesigning a particular storage tank for a seis- mic event can start, it is necessary to have some idea of the ap- propriate set of seismic criteria which are to be applied. Thedefinition ofthe appropfiate seismic design datia for a particular site location and geology is a complex business. This can be seen in Chapter 26 which deals with low temperature tank de- sign where the subject of seismic design is considered in a greater level of detail.For ambient tanks it is usual to adopt a simpler approach and this is reflected in the rules provided in API 650 Appendix E. This Code allows tvvo aporoaches to the selection of the seis-mic design criteria:Firstly it takes as its starting point the American Uniform Build- ing Code (UBC) (Reference 15.11).fhis document divides theUnited States of America into seismic zones ranging from zone 0 (no seismic event to be considered)to zone 4 (the most oner- ous seismic event). This is illustrated as Figure 15.1.ltalso pro-vides guidance regarding the appropriate seismic zones for lo- cations outside the USA. This tabulation is shown in Figure 15.2. The UBC approach is to express an earthquake event as a horizontal acceleration which can be applied to the structurein any direction.The second approach has more in common with the practices for low temperature tanks. By agreement between the pur-chaser and the manufacturer, the horizontal accelerations may be determined from site specific response spectra produced bythe purchaser. The accelerations should not be less than thosederived from the use ofthe UBC. Forthe impulsive component of the liquid and the tank and roof self-weighb, the valuesshould be based on 2% damping, and for the convective com-ponent ofthe liquid, should be based on 0.5% damping. Unless the tanks are in some way special, this more exacting approachis rarely adopted. -\ l''r-Tt  1 5 The seismic design of ambbnt temperature sto@ge tanks t.oc6lion AFRICAAlgeria Alge.OrarBdtin G8borone B'rrundiBujumbt'ra Douala Cap€ Verde Cantral African RcpublicBatrguiChad Ndjrmcna Congo Brazavillc Djibouti EgvPlCair0Pod SaidEquatorial CuineaMalaboEtbiopia Gabon Libreville Gatubia Banjul Ghana CuiDea Bissau Conaky Ivory Coasl Abidjan Kenys Nairobi L€sotho UberiaLibya Tripoli Wi€elirs AFB Malagisy RcpublhThna ariveBlantyreLilongw€Zonba Seismic Zone Locaton Mali Banako MaudtaDia NornkchottMaurillus Pon lruis Port Lyautcy P.abqt TangrerMozambiqueMaputo Nigcr NiameyNig€ria Iba&n Kaduna llgos R€public of RwandaKiCali scrcd DakarSeychetles Sonalia Mogadishu South Africa Cap€ TownDulbanNaralTanzania Dar es Salaam Zanzibtl TogoTunisia Turis Ugadarial|Ipal ' Uppervolta OuSado gou z,j,ir. BrkavuKi$hasatubumbashi 7ar$ia Lukasa Zimbrbwe Hardrc (srlisbury) ASTA Afghribran &bd 30003000000 3 2A2A2Ao 33 0 0 t 00 2A2A I 2A2A 03 S€l8nlc Zone STORAGE TANKS & EQUIPMENT 265 0 0 0 I 2A 3 2A 0000 3 2A 1 2A2A2A 2A I t3 2A 03 0 2A ZA3 Figure 15.2 Tabulation of tho seismic zones woddwide - pagg t Fromthe Uniform Buildino Code  15 The seismic design of ambientlewenfiJre slorage fanksLocttlon Bib|3ir MBnamrBangladcsh BIuneiBandu Sci Begiunn B rmt Mandalay RangooD China B6ijirg Chctrgdu ' Guangzhou Nenjing aiogdto ShaoShiSbenB|{t|t 'tbiwmAtl Tihrva xisrggangcypro6 Nicosr:a India Bor|bryCalqna Madr3l Ncw DclhiIndorcsh BendungJakrnaMedatrSursbrya lmn Islbiar ShirazTabrizTehmn I' q aaghdad Bisra lsrael llaifa Fukuoka Ilrzi(e AFB Mis8v,,a AIB Naha, Okinewa ft*a/Kobe SapporoTokyo Jord tr Korca KimhrcKwanAi KuNeil Kuwiii Figure 15.2 Tabulalion of the seismic zone6 worldwide - pags 2 From the Unltom Bulldlng Code 266 STORAGE TANKS & EQUIPiIENT Lao6 0 VllirtidD Irbdiron 3 Bdifill Maley6is I IOah LumFrr N.P3l K'btnandu otlla \ Pddsran ftlth.bad Ksncni hiorc Qatrr DohaSrudi AnbiaAl Balh Dhr$r Jiild. Khnis Mwl|arf Riysdh Sing.poi All Soulh Ydncn Adr[ Cily Sri btrk. Colodbo Syri. Aloppo Dimrs€rs Thailand BrIgko* ChiuB irri SongllllaTn ftcy lsnir Isi'rbul Kal nluJselUnil€d Arab En ntes Abu Dhabi DubaiHo Chi Minh (Saigor) Y€Detr Aran RepublicSanal AT'I,ANTIC OCEAN AREAAtl Bcrtnudt AI CARTBBEAN SEA hlruna Islsods AI Cubr AI Domiricar nepublic Sanlo DoninSo Frcndr Wbsl lndi€s Ma iniquc Grensda Sli Geolgcs Sa|amlozone Locellon SstEmlc Zdao 1 .3 1 2A I 2A .{0 I I 2A I 0 I 3033 I 2A 0 I 2A2A 4300 0 I 33 '32A2A 3 2A 2A 32A I 44 1 3 l 3 l 3 3433 7 II 0 I 133
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