Uncertainty quantification and seismic fragility of base-isolated liquid storage tanks using response surface models

Seismic response of base-isolated liquid storage tank is represented using response surface model (RSM) to consider the uncertainty in the isolator parameters. The effectiveness of RSM to represent the probability distributions of the peak seismic response quantities of the base-isolated liquid storage tank is studied in the framework of Monte Carlo (MC) simulation. Broad and slender configurations of the tanks isolated by lead–rubber bearing (New Zealand – NZ system) characterized with non-linear force-deformation behavior is considered in the present study. The influence of the uncertain isolator parameters on the seismic response of the base-isolated liquid storage tanks is investigated. Subsequently, seismic fragility of the base-isolated liquid storage tanks is evaluated using the RSM based MC simulation. The RSM estimates the non-linear seismic response of the base-isolated liquid storage tanks with sufficient accuracy. It is observed that the uncertainties in the isolator parameters significantly influence the peak response quantities of the base-isolated liquid storage tanks. The effectiveness of the base isolation technique, in terms of the reduced probability of failure, is observed by comparing the fragility curves for the fixed-base and base-isolated liquid storage tanks. It is also observed that increase in the isolation time period decreases the probability of failure for the base-isolated liquid storage tanks. It is concluded that the peak ground acceleration (PGA) of the earthquake ground motion can be included in the RSM to reduce the computational efforts for seismic fragility analysis.     

An efficient framework for the reliability-based design optimization of large-scale uncertain and stochastic linear systems

This paper is focused on the development of an efficient reliability-based design optimization algorithm for solving problems posed on uncertain linear dynamic systems characterized by large design variable vectors and driven by non-stationary stochastic excitation. The interest in such problems lies in the desire to define a new generation of tools that can efficiently solve practical problems, such as the design of high-rise buildings in seismic zones, characterized by numerous free parameters in a rigorously probabilistic setting. To this end a novel decoupling approach is developed based on defining and solving a limited sequence of deterministic optimization sub-problems. In particular, each sub-problem is formulated from information pertaining to a single simulation carried out exclusively in the current design point. This characteristic drastically limits the number of simulations necessary to find a solution to the original problem while making the proposed approach practically insensitive to the size of the design variable vector. To demonstrate the efficiency and strong convergence properties of the proposed approach, the structural system of a high-rise building defined by over three hundred free parameters is optimized under non-stationary stochastic earthquake excitation.     

Empirical approaches to estimate the nonlinear dynamic responses of earth-core rockfill dams subjected to earthquake ground motions

This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.     

Model test study on the dynamic response of the portal section of two parallel tunnels in a seismically active area

A model test of the portals of two parallel tunnels is carried out to learn about the dynamic response of tunnel liner and the interaction between surrounding rock and liner in earthquakes. The experiment results show that: first, when the seismic acceleration traverses the model material, the low-frequency segment of seismic acceleration is magnified and the high-frequency segment of seismic acceleration is attenuated; second, the horizontal shear failure of the surrounding rock is caused by the interaction between the surrounding rock and the tunnel liner, and the cracks in the surrounding rock grow nearly in the same direction, however, because of the different constraints on the tunnel liner by the surrounding rock outside the tunnel, the destruction degree is different; third, the liner cracks of the left tunnel with short length appear mainly at the left tunnel entrance, the cracks of right tunnel with large length appear mainly at the right tunnel entrance and the tunnel cross-section nearly which is in the same vertical plane with the left tunnel portal, and the liner cracks are distributed mainly on the closer side of two liners between the two holes; finally, in the same vertical testing cross-section, the liner maximal strain at the inner sides between two tunnels is greater than outer sides. In addition, the cross-section maximal strain on the right tunnel decreases with the increasing distance between the tested cross-section and a reference vertical plane containing the left tunnel portal.     

汶川地震余震记录及紫坪铺面板堆石坝余震反应研究

对汶川地震后紫坪铺面板堆石坝台阵余震记录进行了分析,研究实测余震地震动频谱特性等基本特征。选择有代表性的坝址基岩台站记录到的余震地震动作为大坝地震动输入,对紫坪铺大坝进行了三维动力有限元分析,并将计算得到的坝体加速度放大倍数与不同坝高台站的监测数据进行了对比。研究结果表明：实测余震地震动加速度反应谱在短周期部分有一定波动,在周期稍长时随周期增加而衰减,符合地震动反应谱的基本特征;综合实测大坝反应、数值计算结果以及以往实测相关资料,本次紫坪铺大坝余震实测结果反映了土工构筑物反应的一般规律。     

智利地震钢筋混凝土高层建筑震害对我国高层结构设计的启示

2010年2月27日在南美洲智利发生的8.8级大地震,造成了钢筋混凝土高层建筑的严重破坏,这是近年来现代钢筋混凝土高层建筑经历的最大地震,引起了国内外工程设计人员的广泛关注.以智利高层建筑结构体系特点入手,分别介绍了智利地震中钢筋混凝土剪力墙高层建筑、立面收进复杂高层建筑、连体复杂高层建筑、带消能减震支撑超高层建筑、带...     

天地基综合观测的东日本大地震电离层异常分析

介绍了地震电离层前兆的主要特性,并给出了掩星电离层电子密度峰值位置的标高估计技术。利用天地基电离层观测数据,综合分析了2011年3月11日日本9.0级大地震发生前的电离层异常变化,发现地震前3天内电离层f0F2异常扰动、相对垂直总电子含量(VTEC)扰动以及电子密度峰值处标高(Hs)增加等多种异常现象。分析了地磁活动和太阳活动等因素后,认为其可能与地震有一定关联,表明电离层异常变化对于地震短期预报具有重要参考意义。     

汶川地震灾后重建地区的人口容量分析

Assessment of population carrying capacity is a key task in the reconstruction planning of areas struck by disasters, in which the precision of estimation is required. This study developed a decision-making model for estimating the population capacity of the in-volved townships and cities in the 2008 Wenchuan Earthquake based on the assessment of the suitability for reconstruction of the areas. Through analysis, arable land resources were argued to be the critical constraint of population capacity in these areas. Then, the spatial differentiations of the post-quake development conditions across different regions were ana-lyzed with respect to their natural environments, socio-economic development and quake damages. The expected levels of urbanization, family incomes and income structures, output levels of land, and the reliance of agricultural population on arable land were estimated by different regions. With these parameters, the population capacities of the involved townships and cities in three scenarios were estimated. The total population capacity of the entire areas is abundant compared with the actual post-quake population; however, the status of over-population substantially varies across space. It was suggested to put the emphasis of post-quake resettlement policy on those counties where earthquake had been the main causes of over-population. In the Full Recovery Scenario, three mountain counties were identified including Wenchuan, Beichuan and Maoxian, with a total over-population of about 100,000 people.     

Influence of longitudinal structural connectivity on seismic performance of three-hinged precast arch culverts

The hinge type of precast concrete arch culvert was introduced to Japan from France in the 1990s in consideration of the saving of labor, shortening of the construction period, and high quality control of the concrete members. However, due to the 2011 off the Pacific Coast of Tohoku Earthquake (March 11, 2011), the three-hinged precast arch culverts that had been constructed in Japan at the beginning of the period when precast arch culverts were firstly introduced, suffered damage, which spoiled their serviceability. According to the extent of the damage and the type of culverts that were damaged, the longitudinal structural connectivity of the culverts was assumed to be one of the possible reasons for the reported damage mechanism. Therefore, the objective of this paper was to clarify how strongly the longitudinal structural connectivity influenced the longitudinal seismic behavior of the three-hinged arch culverts. To achieve this objective, an elasto-plastic finite element analysis was conducted with an analytical model that could capture the characteristics of the damaged culverts. Simultaneously, a penalty method with the bi-linear spring model was applied as a solution to the contact-impact problems of the precast segmental arch members. As a result, it was found that the weaker longitudinal structural connectivity in the damaged culverts allowed the torsional displacements of the arch members to induce critical damage to the arch members, namely, edge defects in the arch crown and concrete foundation. The numerical results proved the unignorable influence of the longitudinal structural connection on the possible damage to three-hinged arch culverts.