Parametric earthquake response of torsionally coupled buildings with foundation interaction

A study is made of the effect of soil-structure interaction on the coupled lateral and torsional responses of asymmetric buildings subjected to a series of historical free-field earthquake base motions. It sh shown that for particular classes of actual buildings the equivalent rigid-base responses are significantly increased for structures founded on medium-stiff soils, and hence the assumption of the major building codes that a conservative estimate of response is obtained by considering the structure to be fixed rigidly at its base is shown to be inconsistent with the presented dynamic results. It is shown that foundation interaction produces greatest amplification of torsional coupling effects for structures subjected to a particular class of European strong-motion earthquake records, identified by similarities in their spectral shape, for which the vibrational energy of the ground motion is distributed approximately uniformly over the range of frequencies which are of interest for real structures. It is recommended that provision be made in the torsional design procedures of building codes for the increase in the coupled torsional response due to soil-structure interaction as indicated in this study. Such provision should be based on the results of comprehensive parametric studies employing a wide selection of earthquake records and accounting for expected variations in localized soil conditions.     

Mechanism and bounding of earthquake energy input to building structure on surface ground subjected to engineering bedrock motion

The mechanism of earthquake energy input to building structures is clarified by considering the surface ground amplification and soil–structure interaction. The earthquake input energies to superstructures, soil–foundation systems and total swaying–rocking system are obtained by taking the corresponding appropriate free bodies into account and defining the energy transfer functions. It has been made clear that, when the ground surface motion is white, the input energy to the swaying–rocking model is constant regardless of the soil property (input energy constant property). The upper bound of earthquake input energy to the swaying–rocking model is derived for the model including the surface ground amplification by taking full advantage of the above-mentioned input energy constant property and introducing the envelope function for the transfer function of the surface ground amplification. Extension of the theory to a general earthquake ground motion model at the engineering bedrock is also made by taking full advantage of the above-mentioned input energy constant property.     

Parallel finite element modeling of earthquake ground response and liquefaction

Parallel computing is a promising approach to alleviate the computational demand in conducting large-scale finite element analyses. This paper presents a numerical modeling approach for earthquake ground response and liquefaction using the parallel nonlinear finite element program, ParCYCLIC, designed for distributed-memory message-passing parallel computer systems. In ParCYCL1C, finite elements are employed within an incremental plasticity, coupled solid-fluid formulation. A constitutive model calibrated by physical tests represents the salient characteristics of sand liquefaction and associated accumulation of shear deformations. Key elements of the computational strategy employed in ParCYCL1C include the development of a parallel sparse direct solver, the deployment of an automatic domain decomposer, and the use of the Multilevel Nested Dissection algorithm for ordering of the finite element nodes. Simulation results of centrifuge test models using ParCYCLIC are presented. Performance results from grid models and geotechnical simulations show that ParCYCLIC is efficiently scalable to a large number of processors.     

深厚软弱地基上桩箱基础高层建筑地震反应特性数值模拟

根据土体—结构体系整体分析方法，以某26层桩箱基础框架—剪力墙高层建筑为例，探讨了深厚软弱地基与输入地震动特性对桩箱基础高层建筑地震反应的影响。通过数值模拟，得到以下结论：地震作用下高层建筑的地震反应与建筑物的地基条件与输入的振动特性等因素有关。一般地，SSI效应使上部结构的绝对加速度反应减小，但当输入加速度峰值较低时，建筑物部分楼层的绝对加速度反应有可能增大。在给定的输入地震动作用下，SSI效应使上部结构的楼层相对位移增大，但也可能存在减小的情况。分析结果表明：SSI效应对深厚软弱地基上桩箱基础高层建筑地震反应有很大的影响，在此类建筑的抗震分析中考虑SSI效应的影响是必要的。     

桩-土-结构相互作用弹塑性地震反应分析

采用动力有限元时程分析方法，以多高层框架结构为对象，研究了水平地震作用下桩-土-结构相互作用时上部结构弹塑性动力特性和规律。结果表明，弹塑性分析和弹性分析引起的结果有较大的差异；考虑弹塑性相互作用后柱的剪力、轴力和弯矩在不同的楼层有放大现象，按折减方法来考虑相互作用并非总是安全的，柱的剪力、轴力、弯矩和等效应力的折减系数沿楼层变化曲线不尽相同，应引起注意。     

大型结构地震反应值模拟中的波动输入

解耦的时域有限元数值模拟技术在考虑土－结构相互作用的大型结构地震反应分析中的应用日趋成熟。为完善其中的波动输入技术，本提出 了一种波动输入时步数值模拟的简便方法，替换对自由场的频域计算，从而使结构反应分析可以完全通过时步数值模拟实现。同时，通过数值实现，对这一实施方案的有效性进行了检验。     

桩-土-结构相互作用地震反应分析

从桩-土-结构在地震作用下的受力分析出发，考虑平面应变假设，用有限元法(FEM)建立相互作用系统的模型。文中用地震动反演法处理土层的动力放大现象，用读入刚度单元来处理不同类型单元交界处的连续问题。最后，结合实际工程进行相互作用体系的地震反应计算，得出了一些有用的结论。     

不同底面积与埋深的结构-土体系地震反应分析

对结构-土相互作用体系中结构基础底面积和结构基础埋深对体系地震反应的影响进行了研究.基于有限元分析方法建立了结构-土相互作用三维计算模型,通过改变结构底面积及基础埋深在不同地震动下进行了地震反应分析.结果表明,考虑相互作用时,在同一种地震动作用下,结构顶层总位移及基础转动随着结构底面积的增大而明显减小,上部结构本身位移在总位移中所占比例随着底面积的增加而增大;底面积相同,结构顶层总位移及基础转动均随着埋置深度的增大而减小,上部结构本身位移在总位移中所占比例随着埋置深度的增加而增大.比较不同特性的地震动,不同底面积及埋深结构顶层总位移、基础转动、基础平动和结构自身位移的变化规律趋势相同.     

On the sensitivity of bridge seismic response with local soil amplification

The paper presents a numerical sensitivity study of the local site effects on structural response. Following a recently developed model of spatial coherency and a concept of a simple site coefficient the local site effects are modelled as filtrations of excitation processes with a frequency shift. An analysis of a bridge response with supports founded on different soils is carried out. The joint effects of dynamic response and pseudostatic motion are considered. Two types of response are analysed: longitudinal and transverse. The differences between dynamic displacements and force responses are pointed out. © 1998 John Wiley & Sons, Ltd.     

Seismic response of underground utility tunnels: shaking table testing and FEM analysis

Underground utility tunnels are widely used in urban areas throughout the world for lifeline networks due to their easy maintenance and environmental protection capabilities. However, knowledge about their seismic performance is still quite limited and seismic design procedures are not included in current design codes. This paper describes a series of shaking table tests the authors performed on a scaled utility tunnel model to explore its performance under earthquake excitation. Details of the experimental setup are first presented focusing on aspects such as the design of the soil container, scaled structural model, sensor array arrangement and test procedure. The main observations from the test program, including structural response, soil response, soil-structure interaction and earth pressure, are summarized and discussed. Further, a finite element model (FEM) of the test utility tunnel is established where the nonlinear soil properties are modeled by the Drucker-Prager constitutive model; the master-slave surface mechanism is employed to simulate the soil-structure dynamic interaction; and the confining effect of the laminar shear box to soil is considered by proper boundary modeling. The results from the numerical model are compared with experiment measurements in terms of displacement, acceleration and amplification factor of the structural model and the soil. The comparison shows that the numerical results match the experimental measurements quite well. The validated numerical model can be adopted for further analysis.     

Modeling the dynamic process of tsunami earthquake by liquid-solid coupling model

Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock     

A centrifuge study of the influence of site response,relative stiffness,and kinematic constraints on the seismic performance of buried reservoir structures

The seismic performance of underground reservoir structures depends on the properties of the structure, soil, and ground motion as well as the kinematic constraints imposed on the structure. A series of four centrifuge experiments were performed to evaluate the influence of site response, structural stiffness, base fixity, and excitation frequency on the performance of relatively stiff reservoir structures buried in dry, medium-dense sand. The magnitude of seismic thrust increased and the distribution of seismic earth pressures changed from approximately triangular to parabolic with increasing structural stiffness. Heavier and stiffer structures also experienced increased rocking and reduced flexural deflection. Fixing the base of the structure amplified the magnitude of acceleration, seismic earth pressure, and bending strain compared to tests where the structure was free to translate laterally, settle, or rotate atop a soil layer. The frequency content of transient tilt, acceleration, dynamic thrust, and bending strain measured on the structure was strongly influenced by that of the base motion and site response, but was unaffected by the fundamental frequency of the buried structure (f_structure). None of the available simplified procedures could capture the distribution and magnitude of seismic earth pressures experienced by this class of underground structures. The insight from this experimental study is aimed to help validate analytical and numerical methods used in the seismic design of reservoir structures.     

利用流固耦合模型模拟地震和海啸全过程

海底地震引起的海啸过程在力学上是一个流固耦合问题。地震引起的海底变形会影响流体的运动,流体运动会影响地震引起的海底变形。海啸的数值模拟,通常采用浅水波控制方程,把地震引起的海底变形作为海啸波动的边界条件或初始条件,不考虑它们之间的相互作用。本文采用势流体的流固耦合有限元方法模拟了地震和海啸的全过程。地震过程的模拟与地震位错模型不同,在位错模型中,断层的位错是事先指定的;而在本文中,首先形成自重作用下的初始应力场,然后通过断层材料的突然软化引起的错动,模拟地震震源的动力学过程。模拟结果显示,在海面除了可以看到大振幅的海啸波外,还可以发现体波震相和面波震相。在600 km的海面震中距上,它们要比海啸波早到48分钟,在此处面波的最大平均振幅可达0.55 m,是相同震中距海底面波最大平均振幅的2倍。因此,海啸预警信息在海面可以比在地表更早地得到。海啸波的传播速度在水深3 km的开阔海面是175.8 m/s,它要比理想长波理论预测的大,其平均振幅为2 m,波长可达32 km. 到达大陆架后其速度、波长都减小,在岸边可以激起10 m高的巨浪,水平方向深入陆地达53 m。震中附近海面和地震断层上的最大垂直加速度分别为5.9 m/s2和16.3 m/s2,后者是前者的2.8倍。由此看来,海水是很好的减震器。海啸波的加速度到达岸边会衰减10倍。与加速度不同,海面震中处的振动速度为3.2 m/s, 是海底震源处的1.4倍。震源处的最大位移小于震中海面的最大位移, 其差就是海啸波源的振幅。值得注意的是,海底地震的最大位错在震后23 s达到,不是发生在断层滑动的开始。      

Prediction of the maximum credible ground motion in Singapore due to a great Sumatran subduction earthquake: the worst‐case scenario

Although Singapore is located in a low‐seismicity region, huge but infrequent Sumatran subduction earthquakes might pose structural problems to medium‐ and high‐rise buildings in the city. Based on a series of ground motion simulations of potential earthquakes that may affect Singapore, the 1833 Sumatran subduction earthquake (M_w=9.0) has been identified to be the worst‐case scenario earthquake. Bedrock motions in Singapore due to the hypothesized earthquake are simulated using an extended reflectivity method, taking into account uncertainties in source rupture process. Random rupture models, considering the uncertainties in rupture directivity, slip distribution, presence of asperities, rupture velocity and dislocation rise time, are made based on a range of seismologically possible models. The simulated bedrock motions have a very long duration of about 250 s with a predominant period between 1.8 and 2.5 s, which coincides with the natural periods of medium‐ and high‐rise buildings widely found in Singapore. The 90‐percentile horizontal peak ground acceleration is estimated to be 33 gal and the 90‐percentile horizontal spectral acceleration with 5% damping ratio is 100 gal within the predominant period range. The 90‐percentile bedrock motion would generate base shear force higher than that required by the current design code, where seismic design has yet to be considered. This has not taken into account effects of local soil response that might further amplify the bedrock motion. Copyright © 2002 John Wiley & Sons, Ltd.     

多维地震输入下首都机场航站楼T3反应谱分析

首都机场航站楼(T3)下部为混凝土和钢混合框架,上部为复杂的双曲面形双层扁网壳,长960 m,宽780 m,为超大体量大跨度复杂空间钢结构体系。本文采用SAP2000有限元软件,对其进行了单维和多维地震输入下的反应谱分析,研究了单维和多维地震输入对构件内力、节点位移和地震总剪力的影响;研究了多维地震输入下地震响应值与按规范地震组合公式计算所得地震响应值的关系;研究了模态提取数目和质量参与系数的关系,CQC法中参与组合的模态数目与结构地震响应的关系。研究表明,采用振型分解反应谱法时,模态频率越高,对结构内力的影响越小,对于对结构影响较小的高频模态,可以忽略其对结构的影响;根据单维和多维地震反应的对比分析,对超大跨度复杂钢结构宜进行三维地震输入的反应谱分析。另外,本文提出了一种新的地震效应组合方法,可替代多维地震反应分析,并弥补现行规范的不足。     

An equivalent SDOF system model for estimating the response of R/C building structures with proportional hysteretic dampers subjected to earthquake motions

For the purpose of estimating the earthquake response, particularly the story drift demand, of reinforced concrete (R/C) buildings with proportional hysteretic dampers, an equivalent single‐degree‐of‐freedom (SDOF) system model is proposed. Especially in the inelastic range, the hysteretic behavior of an R/C main frame strongly differs from that of hysteretic dampers due to strength and stiffness degradation in R/C members. Thus, the proposed model, unlike commonly used single‐spring SDOF system models, differentiates the restoring force characteristics of R/C main frame and hysteretic dampers to explicitly take into account the hysteretic behavior of dampers. To confirm the validity of the proposed model, earthquake responses of a series of frame models and their corresponding equivalent SDOF system models were compared. 5‐ and 10‐story frame models were studied as representative of low‐ and mid‐rise building structures, and different mechanical properties of dampers—yield strength and yield deformation—were included to observe their influence on the effectiveness of the proposed model. The results of the analyses demonstrated a good correspondence between estimated story drift demands using the proposed SDOF system model and those of frame models. Moreover, the proposed model: (i) led to better estimates than those given by a single‐spring SDOF system model, (ii) was capable of estimating the input energy demand and (iii) was capable of estimating the total hysteretic energy and the participation of dampers into the total hysteretic energy dissipation, in most cases. Results, therefore, suggest that the proposed model can be useful in structural design practice. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake

Nonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake.     

Input and system identification of the Hualien soil–structure interaction system using earthquake response data

This paper presents an input and system identification technique for a soil–structure interaction system using earthquake response data. Identification is carried out on the Hualien large‐scale seismic test structure, which was built in Taiwan for international joint research. The identified quantities are the input ground acceleration as well as the shear wave velocities of the near‐field soil regions and Young's moduli of the shell sections of the structure. The earthquake response analysis on the soil–structure interaction system is carried out using the finite element method incorporating the infinite element formulation for the unbounded layered soil medium and the substructured wave input technique. The criterion function for the parameter estimation is constructed using the frequency response amplitude ratios of the earthquake responses measured at several points of the structure, so that the information on the input motion may be excluded. The constrained steepest descent method is employed to obtain the revised parameters. The simulated earthquake responses using the identified parameters and input ground motion show excellent agreement with the measured responses. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of surface topography on seismic ground response in the Egion (Greece) 15 June 1995 earthquake

The Greek coastal town of Egion on 15 June 1995 was shaken by a strong, small epicentral distance, earthquake that caused heavy damages to buildings and loss of life. The damages were concentrated in the central elevated part of the town whereas the flat coastal region remained almost intact. This non-uniform distribution of damage is studied in this article in terms of surface topography effects by conducting seismic response analyses of a simplified 2-D profile of the town. A dynamic finite element code implementing the equivalent-linear soil behavior (FLUSHPLUS) was used for the analyses and it was found that the step-like topography amplified greatly the intensity of motion without affecting its frequency content. The analyses showed that the motion recorded by an accelerograph installed at the center of the town is in agreement with the computed values; they also indicated a particularly intense amplification close to the crest of the steep slope, where a multi-story RC residential building partially collapsed. In contrast, the level of motion was found to be low at the flat coastal zone of the town where the earthquake damages were insignificant. It is concluded that the characteristic surface topography of the town played an important role in modifying the intensity of base motion.     

Nonlinear response of surface soil and NTT building due to soil–structure interaction during the 1995 Hyogo-ken Nanbu (Kobe) earthquake

The 1995 Hyogo-ken Nanbu (Kobe) earthquake brought about enormous damage to structures in the Hanshin and Awaji areas. In this paper the importance of investigating the relationship between ground motion and structural damage is pointed out.

Strong seismic motion was observed at the NTT (Nippon Telegraph and Telephone) Building during this earthquake. The structural damage to this building was relatively slight. In order to evaluate the relationship between ground motion and structural damage, it is necessary to assess the effects of the soil–structure interaction. In this study, the seismic response of the building and of the surface soil were evaluated by means of a nonlinear soil–structure interaction analysis using FEM.

It was found that, the nonlinearity of surface soil near the building had a great effect on the soil–structure interaction, especially the rocking of the building.