Simulation of floor response spectra in shake table experiments

Among several different experimental techniques, used to test the response of structures and to verify their seismic performance, the shake table testing allows to reproduce the conditions of true effects of earthquake ground motions in order to challenge complex model structures and systems. However, the reproduction of dynamic signals, due to the dynamics of the shake table and of the specimen, is usually imperfect even though closed‐loop control in a shake table system is used to reduce these errors and obtain the best fidelity reproduction. Furthermore, because of the dynamic amplifications in the specimen, the signal recorded at desired locations could be completely different from the expected effect of shake table motion. This paper focuses on the development of practical shake table simulations using additional ‘open loop’ feedforward compensation in form of inverse transfer functions (i.e. the ratio of the output structural response to an input base motion in the frequency domain) in order to obtain an acceptable reproduction of desired acceleration histories at specific locations in the specimen. As the first step, a well‐known global feedforward procedure is reformulated for the compensation of the table motion distortions due to the servo‐hydraulic system. Subsequently, the same concept is extended to the table‐structure system to adjust the shake table input in order to achieve a desired response spectrum at any floor of the specimen. Implementations show how such a method can be used in any experimental facility. Copyright © 2010 John Wiley & Sons, Ltd.     

Pile group response to liquefaction-induced lateral spreading: E-Defense large shake table test

This paper presents the results of a large-scale shake table test at E-Defense facility on a pile group located adjacent to a gravity-type quay wall and were subjected to liquefaction-induced large ground displacements. Extensive liquefaction-induced large ground lateral spreading displaced the quay wall about 2.2 m and damaged the pile foundation. The pile foundation consisted of a six-pile group which supported a footing and a superstructure model. Large lateral soil displacements were measured by several sensors such as inclinometers and the results favorably agreed with the directly observed deformations. Soil lateral displacement decreased as the distance from the quay wall increased landward. The piles were densely instrumented and the measured bending strain records were able to explain the damage to the piles. Lateral pressures of the liquefied soil exerted on the piles were measured using earth pressure (EP) sensors. The application of two design guidelines (JRA [1] and JSWA [2]) for estimation of liquefaction-induced lateral pressure on piles is discussed and their advantages and shortcomings are addressed. Furthermore, two simplified methods (Shamoto et al. [3] and Valsamis et al. [4]) are employed to predict the extent of liquefaction-induced large ground displacements and they are compared to the measured deformations. Finally, their accuracy for predicting the liquefaction-induced lateral displacements is evaluated and practical recommendations are made.     

地震动作用下刚体扭转效应的振动台模拟试验

2008年汶川地震中江油市太白公园曲径桥上的石雕发生转动破坏现象,本文对这一转动现象进行了振动台模拟试验。模拟试验结果表明:① 在振动台三向加载1.5倍的汶川地震江油台记录的平动加速度后,模型的转动情况与实际观测的石雕转动情况比较一致;② 石雕的转动与石雕的非对称性、地震动输入角度和地震动的竖向作用有关;③ 加载竖向地震动作用后,石雕模型会发生摇摆现象,说明竖向地震动是造成模型扭转现象的重要原因,这也说明在分析相似震害现象时竖向地震动作用不可忽视。      

Deterministic and probabilistic floor response spectra

The paper presents a comparative study for computing floor response spectra (FRS) for complex structures. For the purpose of validation and evaluation of the methods for practical application, a systematic comparison of two concepts, classical deterministic and probabilistic, was carried out as an example of a nuclear power plants structure. The deterministic method utilizes time history analyses compatible with the prescribed design response spectrum. The probabilistic method uses an analysis of random vibrations for defining the probabilistic FRS influenced by random seismic soil movement. The seismic input is a power spectral density function (PSDF) compatible with the design response spectrum. The probabilistic approach based on PSDF provides satisfying FRS with far less effort and time consumption needed for calculation.     

Aseismic roof isolation system: analytic and shake table studies

Presented are the features of a roof isolation system that is proposed as a device to reduce the seismic response of buildings. Presented also are the details of and results from analytical and experimental studies conducted with a small-scale laboratory model to assess the feasibility and effectiveness of such a device. The roof isolation system entails the insertion of flexible laminated rubber bearings between a building’s roof and the columns that support this roof, and the installation of viscous dampers that are connected to the roof and a structural element below the roof. It is based on the concept of a damped vibration absorber and on the idea of making the roof, rubber bearings, and viscous dampers respectively constitute the mass, spring, and dashpot of such an absorber. The model considered in the analytical and experimental studies is a 2·44-m high, five-storey, moment-resisting steel frame, with a fundamental natural frequency of 2·0 Hz. In the experimental study the frame is tested with and without the proposed roof isolation system on a pair of shaking tables under a truncated version of one of the accelerograms from the 1985 Mexico City earthquake. In the analytical study, the frame is also analysed with and without such a system and under the same ground motion except that the ground motion accelerations are properly magnified to study the effec tiveness of the roof isolation system when the frame is stressed beyond its linear range of behavior. It is found that the suggested device effectively reduces the seismic response of the frame, although the extent of this reduction depends on how large its non-linear deformations are. Based on these findings, it is concluded that the proposed roof isolation system has the potential to become a practical and effective way to reduce earthquake damage in low- and medium-rise buildings. Copyright © 1999 John Wiley & Sons, Ltd.     

振动台试验模型地震反应的HHT研究

Hilbert-Huang Transform(HHT)是一种新的适用于非线性、非平稳信号,且具有自适应性的数据处理方法．本文简要介绍了一座45层钢筋混凝土框架结构及其振动台试验模型概况. 利用HHT分析了模型结构在不同烈度地震中的反应记录,得到了Hilbert时频幅值三维分布和Hilbert边际谱．Hilbert谱得到记录能量集中分布的频段与时间范围,捕捉到信号变化的主要特征. Hilbert边际谱曲线形状和峰值频率值随着地震烈度的升级而发生了相应变化,而且所有的结果图形体现出相同的规律性,预示着Hilbert边际谱在土木工程结构安全评价中的应用前景．      

Seismic response of nonstructural components in case of nonlinear structures based on floor response spectra method

This paper investigates the response of nonstructural components in the presence of nonlinear behavior of the primary structure using floor response spectra method (FRS). The effect of several parameters such as initial natural frequency of the primary structure, natural frequency of the nonstructural components (subsystem), strength reduction factor and hysteretic model have been studied. A database of 164 registered ground acceleration time histories from the European Strong-Motion Database is used. Results are presented in terms of amplification factor and resonance factor. Amplification factor quantifies the effect of inelastic deformations of the primary structure on subsystem response. Resonance factor quantifies the variation of the subsystem response considering the primary structure acceleration. Obtained results differed from precedent studies, particularly for higher primary structure periods. Values of amplification factor are improved. Obtained results of resonance factor highlight an underestimation of peak values according to current design codes such as Eurocode 8. Therefore a new formulation is proposed.     

弹塑性位移谱法的振动台模型试验验证

弹塑性位移谱法求解结构在指定强度地面运动作用下的位移需求是一种简便合理的方法。本文将弹塑性位移谱法就具体地震波计算的楼层位移需求、层间位移角需求与一比例为1／10的12层钢筋混凝土模型框架振动台试验结果作了比较。设计的12层钢筋混凝土模型框架结构在振动台上经历了7种强度等级地震波的作用,输入峰值加速度依次为：0．090g、0．258g、0．388g、0．517g、0．646g、0．775g和0．904g。求出了弹塑性位移谱法计算的楼层位移和层问位移角需求与振动台试验结果的比值,研究了二者比值的均值及方差沿楼层的分布情况。结果表明：弹塑性位移谱法的计算结果与振动台得到的位移需求值吻合较好,在基于性能的抗震设计中具有较好的应用前景。     

Substructure shake table test method using a controlled mass: formulation and numerical simulation

This study proposes a new substructure shake table test method that allows for experimental investigation of the lower portion of structures while the upper part is numerically analyzed. Compatibility conditions are derived to ensure that the dynamic characteristics of the substructured system are equivalent to the reference entire structure. This method utilizes controlled masses to incorporate interface forces from the computational substructure to the experimental substructure. A feasible implementation procedure for the interface force compatibility is developed using a series of conversions and signal processing. For validation of the capabilities and limitations of the proposed substructure method, numerical simulations are performed using detailed models including dynamics of the controlled mass systems. Results from the numerical simulations showed that the proposed substructure method produced comparable results to the reference entire simulations. The average error between top floor displacements produced by substructured and entire responses for earthquake inputs was 7.1%. Numerical studies showed that the substructure method has potential to serve as an alternative to shaking table tests of entire structures. Copyright © 2012 John Wiley & Sons, Ltd.     

基于WFI动三轴试验仪的小型土箱震动台试验系统研制

为开展模型地基土动力特性的试验研究,开展了小型土箱振动台试验系统的研制.该系统由WFI动三轴试验仪的控制平台、气压供应系统、气压动力设备和伺服控制数据采集系统与自行设计制作的承台及支撑导向系统、小型土箱、信号调理变换器组装而成.经过性能检测,该系统台面具有较好的单向平稳振动性能,并能通过位移控制实现地震动输人,小型土箱...     

Generation of floor response spectra including oscillator-structure interaction

A method is presented for generating floor response spectra for aseismic design of equipment attached to primary structures. The method accurately accounts for tuning, interaction and non-classical damping, which are inherent characteristics of composite oscillator-structure systems. Modal synthesis and perturbation techniques are used to derive the modal properties of the composite system in terms of the known properties of the structure and the oscillator. Floor spectra are generated directly in terms of these derived properties and the input ground response spectrum using modal combination rules that account for modal correlations and non-classical damping. The computed spectra, in general, are considerably lower than conventional floor response spectra due to the effect of interaction. They provide more realistic and economical criteria for design of equipment. The method is accurate to the order of perturbation and is computationally efficient, as it avoids time-history analysis and does not require numerical eigenvalue evaluation of the composite oscillator-structure system. The results of a parametric study demonstrate the accuracy of the method and illustrate several key features of floor response spectra.     

低频振动台主要性能指标测试分析

为了更好满足地震计的振动测试需求,对振动台的波形失真度、横向运动比、台面不均匀度及稳定性等主要性能指标进行了测试分析.测试结果表明:该振动台具有较好的低频振动特性.利用低频标准套组对该振动台和中国计量科学研究院标准振动台进行比对分析,测试结果存在较小偏差.     

基于振动台模型试验的高落差埋地管道地震响应研究

为研究高落差埋地管道的地震响应,进行了高落差埋地管道振动台模型试验和有限元数值模拟,探讨管道径厚比、管道倾角、地震波入射角、地震动峰值加速度和管道埋深对高落差埋地管道地震响应的影响规律。试验结果与数值模拟结果符合较好。研究结果表明,在入射角0°的地震波作用下,高落差埋地管道轴向应变峰值随着管道径厚比的增大而增大;在一定管道倾角范围内,管道轴向应变峰值随着管道倾角α的增大而增大;当地震波入射角度从0°变化到60°时,管道上下表面的轴向应变减小,侧面的轴向应变增大;管道应变随着地震动峰值加速度和管道埋深的增加而增大;相同地震作用下,管道最大轴向应变出现在下弯管1/3处附近。     

Shake‐table test performance of an inertial force‐limiting floor anchorage system

A new floor connecting system developed for low‐damage seismic‐resistant building structures is described herein. The system, termed Inertial Force‐Limiting Floor Anchorage System (IFAS), is intended to limit the lateral forces in buildings during an earthquake. This objective is accomplished by providing limited‐strength deformable connections between the floor system and the primary elements of the lateral force‐resisting system. The connections transform the seismic demands from inertial forces into relative displacements between the floors and lateral force‐resisting system. This paper presents the IFAS performance in a shake‐table testing program that provides a direct comparison with an equivalent conventional rigidly anchored‐floor structure. The test structure is a half‐scale, 4‐story reinforced concrete flat‐plate shear wall structure. Precast hybrid rocking walls and special precast columns were used for test repeatability in a 22‐input strong ground‐motion sequence. The structure was purposely designed with an eccentric wall layout to examine the performance of the system in coupled translational‐torsional response. The test results indicated a seismic demand reduction in the lateral force‐resisting system of the IFAS structure relative to the conventional structure, including reduced shear wall base rotation, shear wall and column inter‐story drift, and, in some cases, floor accelerations. These results indicate the potential for the IFAS to minimize damage to the primary structural and non‐structural components during earthquakes.     

多层建筑结构水平剪扭-竖向地震反应的智能复合隔震控制

本文在提出了“碟形弹簧-橡胶隔震垫”和MR阻尼器组合而成的智能复合隔震系统的基础上，建立了智能复合隔震系统对多层建筑结构“水平剪扭-竖向”地震反应控制的设计计算方法。提出了智能复合隔震系统对建筑结构水平地震反应的模糊半主动控制策略和对建筑结构竖向地震反应的被动控制方法。以一个五层框架结构为例进行了仿真分析。分析结果表明，本文提出的智能复合隔震系统是一种十分简单和有效的隔震系统。它可克服建筑结构常规隔震系统的两个主要缺点，有效地抑制多层建筑结构的多维地震反应。     

Experimental characterization,modeling and identification of the NEES‐UCSD shake table mechanical system

This paper proposes a simple conceptual mathematical model for the mechanical components of the NEES‐UCSD large high‐performance outdoor shaking table and focuses on the identification of the parameters of the model by using an extensive set of experimental data. An identification approach based on the measured hysteresis response is used to determine the fundamental model parameters including the effective horizontal mass, effective horizontal stiffness of the table, and the coefficients of the classical Coulomb friction and viscous damping elements representing the various dissipative forces in the system. The effectiveness of the proposed conceptual model is verified through a comparison of analytical predictions with experimental results for various tests conducted on the system. The resulting mathematical model will be used in future studies to model the mechanical components of the shake table in a comprehensive physics‐based model of the entire mechanical, hydraulic, and electronic system. Copyright © 2007 John Wiley & Sons, Ltd.     

三维隔震系统振动台实验研究

针对目前隔震体系尚不能减小竖向地震反应的缺陷,提出并研制了采用碟形弹簧的竖向半主动隔震装置。竖向半主动隔震装置是由碟形弹簧和外套油缸组成的,且由电磁阀控制油缸内油体与外接蓄油箱内油体间的油路,可实现竖向半主动隔震控制,提出了竖向隔震控制的半主动策略,结合水平隔震支座可实现三维隔震。通过振动台地震模拟实验,验证了三维隔震体系的效能,该研究对高烈度地区隔震技术的改善具有应用参考价值。     

Generation of lateral and rotational floor response spectra by an alternative approach

A procedure is described to compute the lateral and rotational floor response spectra of an asymmetric reactor building structure without a time history analysis. The spectral values obtained by filtering the prescribed ground motion first through the structure and the resulting lateral-rotational motions through simple oscillators are equal to the maximum lateral-rotational responses of the structure developed when the order of filtration is reversed. Based on the preceding concept a deterministic method is presented to construct the lateral-rotational floor response spectra utilizing the response spectrum technique.     

Shaking table test and dynamic response prediction on an earthquake-damaged RC building

This paper presents the results from shaking table tests of a one-tenth-scale reinforced concrete (RC) building model. The test model is a protype of a building that was seriously damaged during the 1985 Mexico earthquake. The input ground excitation used during the test was from the records obtained near the site of the prototype building during the 1985 and 1995 Mexico earthquakes. The tests showed that the damage pattern of the test model agreed well with that of the prototype building. Analytical prediction of earthquake response has been conducted for the prototype building using a sophisticated 3-D frame model. The input motion used for the dynamic analysis was the shaking table test measurements with similarity transformation. The comparison of the analytical results and the shaking table test results indicates that the response of the RC building to minor and the moderate earthquakes can be predicated well. However, there is difference between the predication and the actual response to the major earthquake.     

Predominant period and equivalent viscous damping ratio identification for a full‐scale building shake table test

The predominant period and corresponding equivalent viscous damping ratio, also known in various loading codes as effective period and effective damping coefficient, are two important parameters employed in the seismic design of base‐isolated and conventional building structures. Accurate determination of these two parameters can reduce the uncertainty in the computation of lateral displacement demands and interstory drifts for a given seismic design spectrum. This paper estimates these two parameters from data sets recorded from a full‐scale five‐story reinforced concrete building subjected to seismic base excitations of various intensities in base‐isolated and fixed‐base configurations on the outdoor shake table at the University of California, San Diego. The scope of this paper includes all test motions in which the yielding of the reinforcement has not occurred and the response can still be considered ‘elastic’. The data sets are used with three system identification methods to determine the predominant period of response for each of the test configurations. One of the methods also determines the equivalent viscous damping ratio corresponding to the predominant period. It was found that the predominant period of the fixed‐base building lengthened from 0.52 to 1.30 s. This corresponded to a significant reduction in effective system stiffness to about 16% of the original stiffness. The paper then establishes a correlation between predominant period and peak ground velocity. Finally, the predominant periods and equivalent viscous damping ratios recommended by the ASCE 7‐10 loading standard are compared with those determined from the test building. Copyright © 2017 John Wiley & Sons, Ltd.