内罐影响下LNG储罐外罐地震响应分析

为了考虑内罐在不同方向地震动时对LNG(液化天然气)储罐外罐的影响,对有内罐和无内罐情况下LNG储罐外罐进行了地震响应分析。结果表明:有内罐时地震响应比无内罐时小,内罐的存在对LNG储罐抗震有好的影响;竖向地震波对结构振动的影响不能忽视。     

Evaluation of the earthquake performance of anchored wine tanks during the San Juan,Argentina, 1977 earthquakexs

This paper details the damage sustained by a number of wine tanks during the San Juan, Argentina, 1977 earthquake. The available ground motion information is used to compare the actual tank performance with that predicted. Two of the tanks examined were located quite near the two accelerographs that recorded the ground motion in the city of San Juan for the main shock. An empirical attenuation formula which describes the intensity of the shaking was derived for this earthquake and used in a quantitative evaluation of the performance of a number of other tanks. By correlating and comparing the observed performance of the anchors and what was predicted we see the predictions are upheld by the actual damage. When the anchoring system failed during the earthquake the tanks were rendered effectively unanchored. Consequently, the state of stress that results from their base uplift was then examined in conjunction with the tank wall stability approach proposed by the author, and seen to give results consistent with the observed tank wall performance.     

水平地震激励下储罐液体晃动与提离分析

在考虑地基与储罐相互作用的情况下,采用有限元法对储罐在水平地震荷载作用下的液面晃动及储罐提离反应进行了分析。结果表明:罐内液体的晃动是长周期运动,其周期受地震动影响。无论是小体积罐还是大体积罐,在一定的地震烈度下均可以发生提离,而且储罐发生提离的时刻大多数是在地震动的峰值过后的一段时间内。大体积的储罐的提离明显小于小体积的罐。底板提离区域为月牙形。     

竖向地震作用对储液罐地震响应的影响分析

地震作用下大型储液罐的安全问题日益引起重视。基于ANSYS软件建立储罐液体耦合有限元模型,考虑罐底非线性接触效应,以El-Centro南北向和竖直向记录地震波为输入,研究水平激励以及水平和竖向同时激励两种工况下储罐的动力响应。研究结果表明,两种工况下靠近罐底1.2m处均发生了"象足"变形,竖向激励下水平相对位移增加了14%。竖向激励使得罐壁环向应力和轴向压应力均有不同程度的增加。竖向地震激励对液面的竖向晃动影响较小。储液罐底板在地震作用下发生了竖向提离和永久滑移,竖向激励时增长幅度均在10%左右。同时罐体基底剪力在竖向地震作用下也有所增大。储罐抗震设计时应考虑竖向地震分量的影响,研究结论可为立式储罐的抗震设计提供一定的参考和依据。     

Evaluation of sheet pile-ring countermeasure against liquefaction for oil tank site

The evaluation of a countermeasure against liquefaction which uses a sheet pilering for oil tank sites is presented. The simulation of earthquake responses observed at tank sites with and without sheet pile-ring is first performed to validate the three-dimensional finite element numerical model. Using the numerical model, liquefaction analysis is performed and the excess pore water pressure generated in the soil and the settlement of tank are investigated. The comparison of two- and three-dimensional models is also conducted to assess the applicability of two-dimensional analysis. The results show that the numerical model could simulate the observed earthquake responses of tank-ring-soil system, and that the excess pore water pressure and the settlement of the tank could be significantly reduced using a sheet pile-ring. The two-dimensional analysis proves to be capable of representing the main features of the dynamic response of the three-dimensional tank-ring-soil system.     

A strong motion database for the chiba seismometer array and its engineering analysis

A three-dimensional seismometer array was installed in the Chiba Experiment Station of the Institute of Industrial Science, University of Tokyo in 1982. The array system consists of 44 three-component accelerometers densely placed both on the ground surface and in boreholes. A complementary system for the measurement of ground and buried pipe strains was also installed at the same site. The array system has been successfully in operation, and more than 160 earthquakes have been recorded. Considering a wide use of these seismograms, the Chiba array database has recently been created comprising twenty-seven major events. This paper describes the Chiba array system and its strong motion database. Results of engineering analysis using the selected records are also presented.     

Liquefaction mitigation using secant piles wall under a large water tank

Two-dimensional and three-dimensional numerical models were developed to evaluate the effectiveness of a foundation perimeter wall on the mitigation of the effects of liquefaction in a 64 m diameter, reinforced-concrete water tank. The seismic response of the tank was evaluated in terms of differential settlements induced by an actual earthquake recording by comparing the situations with and without a mitigation strategy consisting of 20 m-long, 1 m-diameter secant piles wall. Although the mitigation strategy did not significantly reduce the liquefaction-induced settlements, it enforced a relatively homogeneous distribution of these settlements, leading to less structural damage.     

山西地区Ms〉4．0地震地倾斜资料异常变化特征

2009-2010年山西地区相继发生4次Ms〉4．0地震,着重对地震前地倾斜资料的异常变化进行分析,汲取地倾斜数字资料中的地震前兆信息,从而为准确利用临汾地震台地倾斜资料,分析预报地震提供依据。     

大型储液罐摩擦摆基底隔震控制分析

针对弹性钢制圆柱储液罐,基于Haroun-Housner模型,将连续流体质量等效为3种集中质量,分别为:对流质量、脉冲质量和刚性质量,与这些集中质量连接的相应刚度取值依赖于储罐壁和流体质量.在水平地震激励下,在储罐底部加摩擦单摆支座,给出了简化的液体 - 储罐-隔震支座的力学分析模型,建立了摩擦摆支座基底隔震体系的振动控制方程,并利用Newmark逐步积分法对控制方程进行了数值求解,研究了摩擦摆支座基底隔震的储液罐地震反应,验证了FPB隔震的有效性.     

地震作用下立式储液罐罐壁"象足"变形仿真分析

基于ANSYS软件建立了考虑液体晃动和罐底提离立式储液罐有限元模型,分别进行了水平地震和竖向地震作用下罐壁"象足"变形分析.分析表明:立式储液罐罐壁"象足"变形主要是由罐壁纵向压应力超过临界应力而产生的局部屈曲破坏,并非强度破坏.因罐底提离导致的罐底与基础反复撞击加大了作用在罐壁上的应力,使罐壁底部"象足"变形不断发展,最终导致罐壁撕裂.在完全相同地震加速度作用下,水平地震作用比竖向地震作用罐壁更早更容易进入屈曲状态,产生"象足"变形.     

地震作用下立式储液罐罐壁“象足”变形仿真分析

基于ANSYS软件建立了考虑液体晃动和罐底提离立式储液罐有限元模型,分别进行了水平地震和竖向地震作用下罐壁“象足”变形分析。分析表明:立式储液罐罐壁“象足”变形主要是由罐壁纵向压应力超过临界应力而产生的局部屈曲破坏,并非强度破坏。因罐底提离导致的罐底与基础反复撞击加大了作用在罐壁上的应力,使罐壁底部“象足”变形不断发展,最终导致罐壁撕裂。在完全相同地震加速度作用下,水平地震作用比竖向地震作用罐壁更早更容易进入屈曲状态,产生“象足”变形。     

Seismic analysis of a LNG storage tank isolated by a multiple friction pendulum system

The seismic response of an isolated vertical, cylindrical, extra-large liquefi ed natural gas (LNG) tank by a multiple friction pendulum system (MFPS) is analyzed. Most of the extra-large LNG tanks have a fundamental frequency which involves a range of resonance of most earthquake ground motions. It is an effective way to decrease the response of an isolation system used for extra-large LNG storage tanks under a strong earthquake. However, it is diff icult to implement in practice with common isolation bearings due to issues such as low temperature, soft site and other severe environment factors. The extra-large LNG tank isolated by a MFPS is presented in this study to address these problems. A MFPS is appropriate for large displacements induced by earthquakes with long predominant periods. A simplifi ed fi nite element model by Malhotra and Dunkerley is used to determine the usefulness of the isolation system. Data reported and statistically sorted include pile shear, wave height, impulsive acceleration, convective acceleration and outer tank acceleration. The results show that the isolation system has excellent adaptability for different liquid levels and is very effective in controlling the seismic response of extra-large LNG tanks.     

Nonlinear sloshing in a floating‐roofed oil storage tank under long‐period seismic ground motion

A hybrid analytical and FEM is proposed to investigate the nonlinear sloshing in a floating‐roofed oil storage tank under long‐period seismic ground motion. The tank is composed of a rigid cylindrical wall and a flat bottom, whereas the floating roof is treated as an elastic plate undergoing large deflection. The contained liquid is assumed to be inviscid and incompressible, and the flow is assumed to be irrotational. The method of analysis is based on representation of the liquid motion by superposing the analytical modes that satisfy the Laplace equation and the rigid wall and bottom boundary conditions. The FEM is then applied to solve the remaining kinematic and dynamic boundary conditions at the moving liquid surface coupled with the nonlinear equation of motion of the floating roof. This requires only the discretization of the liquid surface and the floating roof into finite elements, thus leading to a computationally efficient and accurate method compared with full numerical analysis. As numerical examples to illustrate the applicability of the proposed method, two oil storage tanks with single‐deck type floating roofs damaged during the 2003 Tokachioki earthquake are studied. It is shown that the nonlinear oscillation modes with the circumferential wave numbers 0, 2 and 3 caused by the finite liquid surface elevation as well as the membrane action due to large deflection of the deck produce excessively large stresses in the pontoon, which may cause the catastrophic failure of pontoon followed by the submergence of the roof. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil amplification based on seismometer array and microtremor observations in Chiba,Japan

Soil amplification characteristics of earthquake ground motion were investigated in terms of peak ground acceleration and transfer function based on the Chiba array observation records. The amplification of peak ground acceleration occurred mostly at the top soft layer and was similar for the three components. The effects of non-linear response of soil deposits on the transfer function were examined. Transfer functions calculated by ensemble average were close for the two horizontal components while those obtained from a smoothing operation were generally different. Both the transfer functions from the ensemble average and the smoothing operation underestimated the gain factor around the natural frequencies. A two-step smoothing procedure was proposed and a rotary spectrum was used to improve the estimation of the transfer function. Microtremors were observed at the locations of the boreholes where seismometers are buried. The power spectrum and spatial coherency of the microtremors were compared with those of the earthquake ground motion. Emphasis was placed on the wavetypes which dominated the peaks in the power spectra.     

基于阻尼器反力墙体系的特大型LNG储罐控制研究

特大型液化天然气（LNG）储罐的固有频率通常介于2~10 Hz之间,处于大部分地震运动的频率范围之内。在过去的几十年中,许多事故已经证明,储罐在地震作用下很容易遭破坏。使用隔震支座来减少储罐的地震作用已经被证明是非常有效的,但对于特大型LNG储罐,其连接组件对隔震层层间位移有严格限制,尤其是在软土场地中,桩水平抗力与隔震层位移是一对矛盾,普通隔震系统会在隔震层产生较大位移,导致特大型LNG储罐连接组件的设计非常困难。因此提出了一种由环形阻尼器反力墙、粘滞阻尼器以及安装于基桩顶端的隔震支座组成的新型隔震系统,反力墙独立设置于地基中,不与桩基连接,罐底的部分剪力直接向反力墙传递。以容量为16万m3的特大型LNG储罐为例,建立多自由度集中质量简化模型,以层间位移、桩基剪力作为性能指标进行了评价分析。结果显示,新型隔震系统对特大型LNG储罐隔震层位移及桩基剪力的控制非常有效。     

Orientation error estimation of buried seismographs in array observation

Array observation is an efficient tool to investigate various characteristics of earthquake ground motion. However, seismographs used in arrays may involve unexpected errors in their orientations. Methods of orientation error estimation were developed in three-dimensional space by comparing recorded ground motions at a reference point with those at a checking point. A maximum cross-correlation method and a maximum coherence method were proposed and their accuracy was demonstrated. The earthquake ground motions recorded in the Chiba array and in two other arrays were used in numerical examples. Non-trivial orientation errors were detected for all these arrays. The cross-correlation coefficients and the coherence values between two points increased significantly by correcting the estimated orientation errors.     

Buckling of cylindrical liquid-storage tanks under earthquake loading

The earthquake response behaviour of a cylindrical wine storage tank similar to many that were damaged in Livermore, California during the January 1980 earthquake was studied on the University of California shaking table. Tests of the 9.5 ft diameter by 20 ft high tank, with simulated earthquake accelerations up to 0.95 g, induced buckling patterns similar to those observed after the actual earthquake. Observed peak axial compression stresses in the test tank wall were substantially higher than those assumed in typical design standards, demonstrating the need for further study of the buckling problem in tanks free to uplift during earthquake excitation.     

随机有限断层法合成地震动的研究与应用

目前很多研究者采用随机有限断层模型预测地震动并被证明是可行的.本文运用随机有限断层地震动叠加合成方法,模拟了1988年肃南5.7级地震,与实际记录进行对比分析,发现：用有限断层方法模拟得到的峰值加速度以及峰值加速度出现所对应的特征时刻与真实记录较为吻合;比较模拟的地震动反应谱和实际记录的加速度反应谱,总体上在工程感兴趣的频段内,有限断层方法拟合的结果基本能满足实际工作的需要.为进一步开拓该方法在工程应用中的前景,以兰州市柴家峡水电站为例,将此理论方法应用于缺乏强震记录地区的近场地震动估计中,模拟分析了马衔山北缘活动断裂发震时在坝址区产生的地震动特征,其近场合成结果与1125年兰州7.0级地震的烈度分布符合较好,可供工程抗震设计参考使用.     

芦山地震地震动上下盘效应研究

2013年4月20日的芦山7.0级地震是继2008年5月12日汶川8.0级特大地震之后,发生在龙门山断裂带上的又一次大震级逆冲型地震.与汶川地震相比,芦山地震的发震断层没有地表出露,断层的滑动角更大,其逆冲性质更强烈.本文挑选了芦山地震中断层距小于200km的45条强震动记录,基于地震动衰减关系进行统计分析,对比了上盘和下盘台站地震动参数相对于衰减关系的对数残差.结果表明：芦山地震的上下盘效应明显,近断层上盘地震动的高频成分要高于同断层距的下盘;上盘地震动衰减要明显快于下盘.地震动衰减关系用简单的一个距离参数很难描述近场断层尺寸效应的影响,也很难模拟地震动上下盘效应.因此,在近场强地面运动模拟中,应多考虑有限断层模型,以模拟断层的尺寸效应.     

Tank damage during the may 1983 coalinga earthquake

The magnitude M = 6-5 Coalinga earthquake of 2 May 1983 caused intense ground shaking throughout the epicentral region. Unanchored cylindrical ground supported tanks located at six sites within this oil producing area were damaged; damages included elephant's foot buckling at the base of three moderate sized tanks, joint rupture and top shell buckling in one large old rivetted tank, bottom plate rupture of a relatively new welded tank and damage to the floating roofs of 11 tanks. Also oil spilled over the top of many tanks and secondary damages occurred in pipe connections, ladders, etc. In this paper an estimate is made of the intensity of ground motion at each of the tank sites, based on strong motion records made during the main shock and the strongest aftershock. Then response parameters specified by current codes are correlated with the damages observed at each tank site. Based on this comparison, it is concluded that current U.S. practice under-estimates the sloshing response of tanks with floating roofs and does not adequately address the uplifting mechanism of unanchored ground supported tanks.