LNG储气罐的地震设计反应谱_英文_

� 第 47卷 � 第 4期 2008年 � 7月 中山大学学报 (自然科学版 ) ACTA� SCIENTIARUM � NATURALIUM � UNIVERSITAT IS� SUNYATSENI Vo l� 47� No� 4 Jul�� 2007 � Seism ic Response Spectrum of LNG Storage Tanks * LIUH ao 1 , ZHANG Ya�fang2, WU T ie�sheng3 ( 1. H alcrow Ch ina, H ongKong, China; 2. Schoo l o f C iv il Eng ineering, Guang zhouUn iversity, Guangzhou 510006, Ch ina; 3. Ha inan Se ism ic Bureau, H aikou 570100, China) Abstrac t: Up to now, in M a in land of China, the re is no appropriate codes su itab le for low tem pera ture LNG sto rage tanks, though it could be referred to GB50191- 93, GB50011- 2001, SH 3068- 95 and e tc. Bo th Un ited S tates and Europe standards and codes can be, therefo re, applied as references. A s a project instance, an eva luation on seism ic design requ irement for Tang shan LNG pro ject, Caofe id ian Island, Boha i Bay, Ch ina is presented, show ing tha t the defin ition of OBE ( Opera ting Basis Earthquake) and SSE ( Sa fe Shutdown E arthquake) appropriate fo r LNG pro ject. K ey words: se ism ic assessment; LNG sto rage tanks; design spectrum CLC num ber: TE88� � Docum ent code: A� � Artic le ID: 0529�6579 ( 2008) 04�0128�05 1� Introduction Now adays typical LNG term ina ls have above ground storage tanks w ith capacities rang ing from 160 000 m 3 to 180 000 m 3 ; capacities o f 200 000 m 3 are under p lann ing. In the case o f a conta inment fail� ure, the econom ic damagew ould be substantia l and the danger to life, property and env ironment co rrespond ing� ly grea.t Consequent ly, storage tanks for liquefied ga� ses at low temperature require most advanced design and construction techn iques to ensure that the po tent ia l risk invo lved is reduced to am in imum. Large�scale LNG storage tanks have a fundamenta l natura l period of about 2 to 3 H z, depend ing on their shape and geometry, and are more or less w ithin the range of max imum excitation o f typica l severe earth� quakes. They w ill in fact be subjected tomuch stronger accelerations than the ground beneath them. In addi� t ion, the slosh ing period o f the liqu id inside the tank depends on its actua l con ten,t and could vary in a re la� t ive large range. This increases also the comp lex ity o f the design. A ccording to prev ious experience and his� to rica l accident records, earthquake is considered to be a determ inant factor for the safety requ irement of LNG sto rage tanks [ 1- 2] . A seism ic eva luation w as carried out for an LNG term ina,l in Cao feidian Island, BohaiBay, China. The seism ic response spectrum, as part of this study, is summarized in paper. The analysis in the paper is most ly complied w ith NFPA 59A, NEHRP FEMA450 and IBC 2006 [ 3- 5] , and is also referred to EN 1473, EUROCODE, CSA and nat iona l regu lat ions and codes ofm ainland o f China [ 6- 8] . U p to now, in M a inland o f China, there is no appropriate codes suitable for low temperature LNG sto rage tanks, though it could be re� ferred to GB50191- 93, GB50011- 2001, SH3068 - 95 and etc. Both Un ited States and Europe standards and codes can be, therefore, referred to. The d iffer� ence is that in reg ionalmap for spectral param eters, the def ined value of probab ility of ex ceedance, and part icu� lar design concept /m ethod. Th is ana lysis is major based onUS codes, consid� ering that a) there are some updates in US codes based on research after the earthquakes in Lom a Prieta ( 1989, M 7�0 ) and N orthridge ( 1994, M 6�7), and b) the ex isting attenua tion relationsh ip o f spectral seis� m ic param eters, app lied in mainland o fCh ina, are de� rived from w estern and centra lU nited States S ite Back� ground [ 9 - 14] . 2� Regional Tectonic Late Quaternary deformation o f continentalA sia is distributed over a vast reg ion, and inc ludes a fu ll spec� trum o f deform ationa l sty les and structural o rientations. * 收稿日期: 2008- 06- 06 基金项目: 国家自然科学基金资助项目 ( 50778046) 作者简介: 刘浩 ( 1966年生 ), 男, 博士, 高级工程师; E�m a i:l L iu�H ao� hk@ gm a il� com � 第 4期 刘 � 浩等: LNG储气罐的地震设计反应谱 Much, if no t a l,l of the deform ation can be attributed to the co llision and subsequent penetration of the Indian plate w ith respect to Eurasia. H ima layan Fronta lA rc, is the consequence of such co llision. The North�China block, is one the e ldest continen tal tecton ic wh ich can be back to A rchaean and early Proterozoic. Its evo lve� ment inc ludes three rough stages, i�e. base crystalliza� t ion, covering deve lopment and crack expansion. From the Tert iary epoch, the tecton ic o fNo rth�Ch ina plateau has no obv ious changes; the princ ipal compression stress is in NEE�SWW direct ion, almost horizonta,l w hile the second stress is nearly vertica.l The studied LNG p lant is located in the interface ofHuangye concave and Chengn ing uplif,t and th is re� gion is extension of an important active se ism ic fau lt be lt ( see Fig�1) . F ig� 1� Epicentre map in the prox im ate o f Caofe id ian Island � P lain area; � Sea area; � Qua ternary Contour ( 100m ); �Early Qua ternary fault; � Ex- Quaterna ry fault; �Nor� m al fau lt; � Insidious fau lt; � P ipeline and the LNG plant The LNG plant is located in the edge of Boha i Bay, an area most ly be longs to shallow o ffshore pla in and /or bottom land. There are four large sca le fau lts ex� ist in its prox imate, all are in the orientation of NW to NE and are submerged in the seaw ater. They are, Laobao Fault ( F1), Paogezhuang Fault ( F2) , Shabe i Fault ( F3) and Shanan Fau lt ( F4) . Among them, the Shabe i fault is the c losest one to the site. How ever, the site borehole logs show that the Quaternary stratum is basica lly continuous and no obv ious large fau lts w ere identified, w hich imp lies that the chance of strong earthquakes part icularly for th is site is sm al.l The seism ic activ ity in the prox im ity o f the studied LNG plant is re lative ly w eak in the pas,t as there are no h istorical earthquake record of M I > 4. 9. A fter years o f 1970, there are tota l 39 earthquake records o f M I 1�0~ 4�9, among which, 4 in a range o fM I 3�0~ 3�9 and 8 in M I 4�0~ 4�9. Small earthquakes w ere unevenly distributed in the prox im ate o f the site, re la� t ive ly more in the north�western and south�eastern are� as. 3� Seism ic Design Objectives The ob ject ive o f seism ic design for bu ild ing struc� tures, in ma inland of China, could be described as � less damage under common earthquake, repairable under medium earthquake and sustainab le under sever earthquake�. In technical language, w hen the first lev� el earthquake ( probab ility exceedance is of 63% for a 50 years occurrence period ) is me,t the structures shou ld remain operab le. The structures cou ld be de� signed in an elastic response spectral range w ith an e� lastic analysis. When the second level earthquake ( probability ex ceedance is of 63% for a 50 years oc� currence period) is m e,t the structures are under ine� lastic range. How ever, th is inelast ic deformat ion and / or structural damage shou ld be contro lled in a repaira� b le leve.l For the third leve l earthquake ( 2% ~ 3% for 50 years), a large ine lastic deformat ion of the struc� tures is allow able but the structure should be st ill under contro l to avo id comp lete ly co llapse. Regarding to the design for LNG facilities, its combust ible, explosive and co rrosive natures and the sever consequence o f its leakage shou ld a lso be consid� ered. Further to that the impacts to the surrounding popu lation, economy, and transportat ion netw ork in the event o f a catastroph ic event are a lso important facto rs. The above ment ioned ob ject ive is, there fore, consid� ered no t be adequate fo r a LNG pro jec.t According to NFPA 59A [ 1] , se ism ic category I components and structures should rema in operab le w hen under or after an OBE, and in fact this OBE level is approx ima tely same to the second earthquake level o fCh ina standard. W hen a SSE is me,t seism ic category I components and structures could be designed in the ine lastic range. The primary fac ilities cou ld be safe shutdow n during and af� ter SSE. 4� Seism ic Response Spectrum Peak horizontal ground acceleration on bedrock on the study site is summarized in Tab le 1. Tab� 1� Peak g round acce lera tion va lue based on bedrock ( g al) P robability o f ex ceedance 50 years 10% 50 years 2% 100 years 1% PGA 143� 6 262� 2 382�2 129 中山大学学报 (自然科学版 ) 第 47卷 � The design response spectrum under OBE, fo r probab ility o f exceedance o f 10% , in an average 50 years occurrence period, is show n in F igure 2. The 5% damped design response spectrum under SSE ( fo r an average 2 475 and 5 000 occurrence period) , corre� spond ing to probab ility o f exceedance of 2% and 1% respective ly, in an average 50 years occurrence period, are show n in figure 3 and 4. In F igure 5, the spec� trum s derived from GB50011 - 2001 are presented fo r comparison. One can find thema jo r difference is in the range of long period. � � Fo r easy reference, seism ic spectra l dynam ic parameters are listed in T able 2. � � F ig�5� Compar ison of design response spectrum and ones der ived from GB50011- 2001 Tab� 2� Peak hor izonta l ground acceleration and param ete rs o f des ign spec trum Probab ility of exeedance Am ax / ga l T1 /s T2 / s �m � 50years 10% 160 0� 15 0� 55 2� 5 1� 1 50yea rs 2% 255 0�2 0� 80 2� 5 1� 1 50yea rs 1% 330 0�2 0� 9 2� 5 1� 2 5� D iscussion on response spectrum Because the se ism ic eva luation w orks inm ainland of China shou ld be carried out by the au thorized institu� tes, th is report w ill on ly present som e discussions on the updated research resu lts o f LNG storage tanks and other se ism ic category I structures and components. 5�1� The attenuation re la tionsh ip It is a cruc ial procedure for sett ing up the attenua� t ion re lationsh ip fo r seism ic spectra l parameters. U sual� ly, this relationsh ip is quite localized andma jor derived from the attenuat ion re lationsh ip of a selected reference district. Th is is based on a fundamenta l assumpt ion that the attenuat ion relat ionship o f the intensity in d ifferent areas and a ll spectra l parameters fo llow s sim ilar law s. Refer to the study of Yu Yanx iang [ 14] , up to now, most internal site se ism ic hazard evaluat ion w orks are st ill based d irectly on the attenuation re la tionship de� rived by Huo Junrong, w hich is actua lly the relat ion� sh ip o f site intensity to the spectral parametric attenua� t ion re lationsh ip of W estern U nited S tates. However, there are som e tw o ex tra po ints shou ld be c larified: ( a) the reco rds of sever earthquakes used byHuo Jun� rong w ere before 1996 and ( b) The attenuat ion of ac� celerator spectrum data recorded by the o ld simu lated earthquake recorder is no t re liable in the long response period range ( T > = 3s). In fac,t the recorded accel� erator spectrum drops too quick ly in the long response period, even faster then the one in low period, w hich does no t consist w ith modern observation of strong earthquakes. 130 � 第 4期 刘 � 浩等: LNG储气罐的地震设计反应谱 5�2� Differences of des ign spectrum based on dif� fe rent codes A s per ASCE 7, if the proposed sto rage tanks are not founded on Foundat ion C lass A or B as FEMA [ 4] , shear w ave velocity d istr ibution o f corresponding so il strata shou ld be measures through boreholes, thus the response characterist ic cou ld be eva luated. However, if the above m entioned data is absen,t accord ing to FE� MA [ 4] or IBC 2006 [ 5] , spectral response acceleration values, correspond ing to T = 0�2s and 1�0s, should be obtained from reg iona lmax imum considered earthquake (MCE ) g round motionm ap, and then T0 and Ts cou ld be determ ined. Then accord ing to the c lassification o f the site so il shou ld a lso be considered. In addit ion TL can be determ ined from ano ther reg ional spectral pa� rametersm ap particular for long period. In ma in land o f Ch ina, PGA and se ism ic natura l period g roup can be determ ined from the nation pub� lished spectra l parameters m ap. The site period w ill then be obta ined from th is natura l period group and the site condition. Se ism ic acce leration response curves versus peri� od, derived from FEMA [ 4] and GB50011 - 2001 [ 13] , are presented in F igures 6 and 7, respectively. The difference in the long period range is obv ious, although in GB 50011 - 2001 [ 13] , some improvement had been already made. Furthermore, compared to the European codes, the w idth of the upper platform ( 0�1s ~ Tg ) in China is narrow er than in Europe. When the period is lager than Tg, the curve drops faster than one in Europe codes. A s a consequence, for stiff structures w ith short period, seism ic load w ith Ch inese Codes should be rel� atively higher [ 11- 13] ; w hile for the structuresw ithm edi� um or long period, the se ism ic load w ith Ch inese codes w ou ld be relatively smaller. A s a summ arizat ion here, in F igure 5, it is shown that the design spectrum is generally low er than the spectrum derived from GB50011- 2001 in the range o f long period [ 13] . The possible reasons have been dis� cussed th is section. F ig�6� D iagram o f response spectrum, FEMA 450. F ig�7� D iagram o f response spectrum, GB50011- 2001 Fo r structures o f LNG storage tanks, the natura l period cou ld be re lative ly long due liquid slosh ing, the response spectrum in the range o f long to very long pe� riod is quite crucial to the design. From the view o f safety, based on the ex isting design spectrum prov ided, the facto r of safety in this long period should be in� creased. O therw ise, further study on this feature shou ld better be imp lemented. F ig� 8� Ca lculated design response spectrum. 6� Conclusion Considering the characteristics of the possible structura l natura l period and the slosh ing period o f the liqu id, there m ight be a r isk in the range o f long to very long period ( T= 8~ 9s, for slosh ing design), for the Code Spectrum could be low er than expected. The recommendation is that the amplificatory factor in the same range would be better increased o therw ise a more detailed study should better be conducted. In Figure 8, the design response spectrum for studied LNG site, is recommended as appropriate. References: [ 1] � 49 CFR Pa rt 193. L iquefied Natural Gas Fac ilities: F ed� era l Sa fety S tanda rds[ C]. 2004. [ 2] � API 620. Design and Construction o f La rge[ R ] . W e lded, Low P ressure Sto rage Tanks, 2007 ed. 2007. [ 3] � NFPA 59A. Standa rd for the Production[ R ]. Sto rage and H andling of L ique fied Na tura lGas ( LNG ), 2005. [ 4] � NEHRP. Recomm ended P rov isions fo r se ism ic regulations for new buildings and other structures( FEMA450) [ C ]. Building Se ism ic Safety Counc i,l 2003. 131 中山大学学报 (自然科学版 ) 第 47卷 � [ 5] � Interna tiona l Bu ild ing Code. Internationa l Code Council ( fo rme rly BOCA, ICBO, and SBCC I) [ C ]. 01 - M ar- 2006. [ 6] � European No rm EN 1473. Insta llation and equ ipm ent fo r lique fied natura l gas - Design of onshore insta llations [ C] . 2005 draft. [ 7] � Eurocode 8. Des ign of Struc tures fo r Ea rthquake Resist� ance[ C] . F ina lD ra ft 2001. BSI London, 2001. [ 8] � CSA Z276, L iquefied natura l gas. ( LNG ) - produc tion [ C] . Storage and H and ling C anad ian S tandard Assoc ia� tion, 2001. [ 9 ] � ABDOUN T. M ode lling of seism ica lly induced latera l spreading of mu lti- layered so il and its effect on pile foundations[ D ]. Rensse laer Po ly technic Institute, T roy, NY, USA, 1997. [ 10] � BORCHERDT R D. Estim ates of site - dependent re� sponse spectra fo r design ( M ethodology and Justifica� tion) [ J]. Ea rthquake Spectra, 1994, 10: 617- 653. [ 11] � GB 50223- 95. C lassified standa rd o f earthquake fortifi� cation of bu ildings[ S]. 1995 [ 12] � JT J 304 - 2003. Design regu lation o f LNG Jetty [ S ]. 2003. [ 13] � GB 50011 - 2001. Code fo r seism ic design of bu ildings [ S]. 2001. [ 14] � YU Y X, WANG S Y. A ttenuation re lationship of pectra l acce lera tion on bedrock for the eastern and western Ch i� na area[ J]. T echn iques of Se ism icH aza rd P revention, 2006( 1): 3( Ch inese). LNG储气罐的地震设计反应谱 刘 � 浩 1, 张亚芳 2, 吴铁生 3 ( 1. 合乐中国, 香港; 2. 广州大学土木工程学院, 广东 广州 510006; 3. 海南省地震局, 海南 海口 570100) 摘 � 要: 对于液化天然气储罐, 关注的重点往往是安全性与经济考量之间的怎样取得一个平衡, 就大陆的石化工程而言, 依据怎样的 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 既满足社会对工程安全的期待值, 又符合液化天然气储罐的结构特点和场地特征, 一直是个重要的课题。 重点介绍了对于液化天然气储罐这类结构的在设计中的运行基准地震水平 ( OBE) 和安全停机地震水平 ( SSE) 的确定。 以曹妃店岛的 LNG项目为例, 介绍了液化天然气储罐所采用的地震设计反应谱。 关键词: 地震评估; 液化天然气储罐; 地震设计反应谱 中图分类号: TE88 132