A new seismic isolation system and its feasibility study

<正>This paper introduces a new seismic isolation system called a periodic foundation(PF),where inclusions are periodically arranged.The PF is different from traditional base isolation in that it causes a fundamental frequency shift in the structure,thus reducing its response and generating a frequency gap.If the frequency contents of a seismic wave fall into the gap,it can not propagate in the foundation.Thus,it will exert no influence on the structure above.A systematic study of the band of frequency gap for a 2D PF is conducted.The influence of physical and geometrical parameters such as density and elastic modulus as well as filling fraction of the PF and its materials on the band of frequency gap are investigated, and a design with a frequency gap as low as 2.49-3.72 Hz is achieved.This band of frequency gap corresponds well to the design spectra in earthquake engineering.Numerical simulations of a six-story frame structure with different foundations demonstrate that a proposed PF can greatly reduce the seismic response of an isolated structure.This investigation shows that PFs have great potential in future applications of seismic isolation technology.     

Three-dimensional seismic isolation bearing and its application in long span hangars

Based on the seismic response characteristics of space frame structures,a new type of seismic isolation bearing defined as a three-dimensional seismic isolation bearing(3DSIB) is developed in this paper.The bearing offers excellent properties such as multi-dimensional seismic isolation,reasonable rotation capability,good ability to resist lifting load,uncoupled stiffness in horizontal and vertical directions,etc.In the 3DSIB,the horizontal dimension is designed by combining the Teflon sliding device and helical spring,while the vertical dimension is developed by introducing disk springs or helical springs.The mathematical model of the 3DSIB was established and its performance with the critical parameters was tested on a shaking table.Furthermore,the 3DSIB was applied in a 120 m span hangar structure and simulated using SAP2000 software to evaluate its performance in practical structures.The performance of the structures with and without 3DSIB was compared.It is shown that the hangar structure with 3D bearings achieves a better performance.The axial force and acceleration response of the structures with 3DSIB are effectively reduced,while the displacement response of the bearing is within the predetermined range.     

Feasibility of reducing three-dimensional wave energy by introducing periodic foundations

A new seismic isolation foundation called the periodic foundation is proposed, which can be described as a three-dimensional typical cell consisting of a high density core, a soft coating and a concrete matrix. Utilizing the attenuation zones (AZs) resulted by the periodicity of the foundation, the mechanism of this new seismic isolation system is different from the traditional ones. The seismic waves with the frequencies in the AZs cannot propagate across the foundation. Thus, the seismic responses on the top surface of the periodic foundation can be reduced significantly. In this paper, the dispersion curves of the three-dimensional three-component (3D–3C) periodic foundations are analyzed by the finite element method (FEM). The influencing factors such as physical and geometrical parameters of the typical cell are investigated. In order to verify its feasibility, a three-dimensional (3D) soil-foundation finite element model is analyzed, and the frequency zones of seismic attenuations are consistent with the AZs. The periodic foundation can greatly reduce the seismic response, which implies that the periodic foundation has a great potential application on seismic isolation.     

A parametric study of seismic behavior of roller seismic isolation bearings for highway bridges

A roller seismic isolation bearing is proposed for use in highway bridges. The bearing utilizes a rolling mechanism to achieve seismic isolation and has a zero post‐elastic stiffness under horizontal ground motions, a self‐centering capability, and unique friction devices for supplemental energy dissipation. The objectives of this research are to investigate the seismic behavior of the proposed bearing using parametric studies (1) with nonlinear response history analysis and (2) with equivalent linear analysis according to the AASHTO guide specifications, and by comparing the results from both analysis methods (3) to evaluate the accuracy of the AASHTO equivalent linear method for predicting the peak displacement of the proposed bearing during an earthquake. Twenty‐eight ground motions are used in the studies. The parameters examined are the sloping angle of the intermediate plate of the bearing, the amount of friction force for supplemental energy dissipation, and the peak ground acceleration levels of the ground motions. The peak displacement and base shear of the bearing are calculated. Results of the studies show that a larger sloping angle does not reduce the peak displacement for most of the parametric combinations without friction devices. However, for parametric combinations with friction devices, it allows for the use of a higher friction force, which effectively reduces the peak displacement, while keeping a self‐centering capability. The AASHTO equivalent linear method may underestimate the peak displacement by as much as 40%. Vertical ground motions have little effect on the peak displacement, but significantly increase the peak base shear. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of the seismic performance of expansion double spherical seismic isolation bearings for continuous girder bridges

The development of an expansion double spherical seismic isolation (DSSI) bearing by modifying the fixed DSSI bearing is described in this paper.The expansion DSSI bearing is characterized by its good ...     

Wigner-Ville分布及其在地震衰减估计中的应用

地震信号的衰减一般是在频域内利用信号功率谱的统计性质进行表征。但是,传统的基于傅立叶变换的功率谱估计方法的分辨率较低,使得衰减估计的精度较低。Wigner-Ville分布是一种重要的Cohen类时频分布,它具有一系列的优良性质,如时频边缘分布性质、好的时频聚集性等。这些性质对信号的时频分析具有重要意义。因此,Wigner-Ville分布为地震信号的衰减估计提供了新的手段。本文首先介绍了Wigner-Ville分布以及能够减少或消除交叉项影响的平滑Wigner-Ville分布,然后,提出了一种基于Wigner-Ville分布的衰减估计方法。在这一方法中,利用Wigner-Ville分布得到的瞬时能量谱中高频段的能量下降速率度量衰减。将这一方法应用到塔中地区奥陶系礁滩相碳酸盐岩储层预测,结果表明,基于Wigner-Ville分布的衰减能够有效地检测出礁滩相带和泻湖区域之间衰减特性的差异。     

Improved numerical analysis for ultimate behavior of elastomeric seismic isolation bearings

Elastomeric isolation bearings consist of multiple rubber layers with their top and bottom surfaces bonded to steel plates to restrict compressive deformation. Deformation constraints result in a variation of elastic modulus over the cross section of the rubber layers. In this paper, we describe a normalized compression modulus distribution on a circular rubber pad. The compressive and bending moduli of the rubber pad can be reproduced by applying the distribution to a series of axial springs. We also present a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to large shear deformation and high compressive load. The mechanical model consists of a series of multiple shear springs at midheight and a series of axial springs at the top and bottom interfaces of the bearing. Simulation analyses of bearing tests were conducted to validate the proposed model. The analyses demonstrated that a model for circular lead-rubber bearings can successfully capture the influence of the axial load magnitude on the bearing shear behavior. The new model can simulate much more realistic behavior than prior models based on a uniform modulus assumption.     

Coupling behavior of shear deformation and end rotation of elastomeric seismic isolation bearings

This paper presents a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to combined end rotations and shear deformation. The mechanical model consists of a series of axial springs at the top, mid‐height and bottom of the bearing to vertically reproduce asymmetric bending moment distribution in the bearings. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing and the imposed shear deformation. Static bending tests under various combinations of vertical load and shear deformation were performed to identify the mechanical characteristics of bearings. The test results indicate that bearing rotational stiffness increases with increasing vertical load but decreases with increasing shear deformation. Simulation analyses were conducted to validate the new mechanical model. The results of analyses using the new model show very good agreement with experimental observations. A series of seismic response analyses were performed to demonstrate the dynamic behavior of top‐of‐column isolated structures, a configuration where the end rotations of isolation bearings are typically expected to be larger. The results suggest that the end rotations of elastomeric bearings used in practical top‐of‐column isolated structures do not reduce the stability limit of isolation system. Copyright © 2016 John Wiley & Sons, Ltd.     

地震信号的复地震道分析及应用

复地震道分析又称三瞬分析,该分析方法可将反映地震信号局部变化情况的地震波的瞬时振幅、瞬时相位和瞬时频率等信息分离开.本文应用Hilbert变换求解虚地震记录,用复地震道分析方法求取"三瞬"信息,并用该方法计算了理论合成地震记录的瞬时振幅、瞬时相位和瞬时频率,获得了较好的效果.同时,本文也利用该方法对某区块实际地震资料进行了处理,结果表明,复地震道分析方法获得的"三瞬"信息可反映地震信号的局部变化,有助于进行地震薄互层分析,并能提高数据的解释精度.     

跨断层隔震管道管端与土体相互作用分析

断层错动是造成埋地管道破坏的重要因素之一,因此,跨断层埋地管道在断层错动下的破坏机制、模型设计与参数分析和管道抗断层措施一直是生命线工程的前沿问题。对跨断层管道内力分析取得的成果较多,比较经典的是Newm ark-Hall方法、Kennedy方法和王汝梁方法,后来又出现基于壳模型的有限元分析方法。现有的管道抗断层措施具有其优点的同时亦有其不足。本文基于壳模型的有限元动力数值模拟,对一种管道跨断层隔震措施进一步研究,考虑管端与土体相互作用计算隔震管段的断层错动响应。计算结果表明拉应变容易在土中的管段传递,相比较而言,压应变不容易在土中的管段传递;最大拉应变降低比较多,最大压应变降低比较少。根据分析结果,对跨断层隔震管段边界条件的选取提出建议。     

Copula joint function and its application in probability seismic hazard analysis

A mature mathematical technique called copula joint function is introduced in this paper, which is commonly used in the financial risk analysis to estimate uncertainty. The joint function is generalized to the n-dimensional Frank’s copula. In addition, we adopt two attenuation models proposed by YU and Boore et al, respectively, and construct a two-dimensional copula joint probabilistic function as an example to illustrate the uncertainty treatment at low probability. The results show that copula joint func...     

Seismic isolation of buildings with sliding concave foundation (SCF)

In this paper, a new base isolation system, namely the sliding concave foundation (SCF), is introduced and the behaviour of the buildings using such a system is theoretically investigated. A building supported on the new system behaves like a compound pendulum during seismic excitation. The pendulum behaviour accompanied by the large radius of foundation curvature shifts the fundamental period of the system to a high value (e.g. more than 8sec), in a frequency range where none of the previously recorded earthquakes had considerable energy. This results in a large decrease in the structural responses. Since small friction forces are essential on the contact surfaces, PTFE sheets can be used as sliding surfaces. Although the pure frictional sliding systems have the same efficiency as the SCF, in reducing the responses of the superstructure, the main advantage of the new system is a significant decrease in sliding displacement. The performance of the SCF subjected to a number of harmonic and non‐harmonic base excitations is studied and its ability to reduce the structural responses is examined. Some numerical examples are solved for a single‐degree‐of‐freedom (SDOF) structure and the responses are compared with the responses of the same SDOF structure on a fixed base or a pure frictional sliding support system. The comparisons confirm the effectiveness of the new system. Copyright © 2002 John Wiley & Sons, Ltd.     

联结(copula)函数在概率地震危险性分析中的应用

介绍了一种成熟的已广泛应用于金融领域的估计不确定性的方法——copula函数方法, 并推广了n重的Frankrsquo;s copulas; 在实际应用中, 本文采用了俞言祥和美国西部由Boore等人给出的两个衰减模型, 针对其中存在的模型不确定性以及它们之间的相互依赖性, 构造出概率意义上联合的copula分布函数, 并将其应用于实例分析. 结果表明, 对比于传统逻辑树中所用的线性结合方法, copula将两者带来的概率分布写成一个联合概率分布, 能够很好地考虑双方不尽相同的意见. 另外, 由于copula函数可采用各种各样的边际分布函数来获得联合概率分布, 且在金融风险投资评估已有大量的应用, 因此在现代地震危险性评估中将有着广泛的前景.      

不同减隔震措施下平板支座抗震性能试验研究

为探究不同减隔震措施对短边距混凝土网架平板支座的抗震性能和破坏模式的影响,分别针对不同混凝土边缘距离以及采用不同减隔震措施的四个平板支座缩尺试件进行拟静力加载试验,对平板支座破坏模式、滞回曲线、箍筋应变进行分析。试验结果表明:平板支座的运动伴随着平动和转动。当混凝土边距不足时,边缘混凝土在压剪作用下,会发生冲切破坏。开长孔支座能较好的释放水平位移,并且对锚栓约束较弱,使其受力较小,从而减轻了边缘混凝土的受力。对采用橡胶垫板的支座,混凝土边缘未发生破坏,原因是橡胶垫具有良好的变形能力,可以释放支座的位移和转角,使得边缘混凝土受力较小。因此,针对混凝土边缘距离较短的平板支座节点,为防止混凝土发生边缘破坏,可采用开长孔支座,但需要对孔长进行合理的设计。采用橡胶垫支座也可避免混凝土发生边缘破坏,橡胶垫板可按照我国相关设计规范进行设计。     

A mechanical model for elastomeric seismic isolation bearings including the influence of axial load

For the purpose of predicting the large‐displacement response of seismically isolated buildings, an analytical model for elastomeric isolation bearings is proposed. The model comprises shear and axial springs and a series of axial springs at the top and bottom boundaries. The properties of elastomeric bearings vary with the imposed vertical load. At large shear deformations, elastomeric bearings exhibit stiffening behavior under low axial stress and buckling under high axial stress. These properties depend on the interaction between the shear and axial forces. The proposed model includes interaction between shear and axial forces, nonlinear hysteresis, and dependence on axial stress. To confirm the validity of the model, analyses are performed for actual static loading tests of lead–rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Seismic response analyses with the new model are also conducted to demonstrate the behavior of isolated buildings under severe earthquake excitations. The results obtained from the analyses with the new model differ in some cases from those given by existing models. Copyright © 2008 John Wiley & Sons, Ltd.     

新型单自由度基础隔震体系简化计算方法研究

本文建立了一种新型的单自由度体系基础隔震结构实用设计方法，该方法考虑了上部结构的变形、简便，合理，可靠，与传统抗震设计方法概念比较接近，便于在工程应用中推广。     

地震波衰减反演研究综述

对地震波衰减的研究经过近五十年的发展已经取得了不少进展.本文简述了地震波的衰减机制、有关衰减的基本理论以及影响地震波衰减的主要因素,重点概括了地震波衰减的反演方法,最后预测了地震衰减研究的发展趋势.     

层间隔震结构计算模型的简化分析

本文通过对层间隔震结构整体动力性能及时域反应的分析，用模态综合方法建立了该结构计算分析简化模型。该模型合理、可靠，为建立实用设计方法、推广层间隔震结构的应用提供了有效途径。     

摩擦隔震结构中不同摩擦力模型在地震作用下结构响应分析

本文选用两种摩擦力模型来分析隔震结构的地震响应，运用newmark方法推导了隔震结构采用库仑摩擦力模型在地震作用下结构响应的计算公式。并编程计算了实例，进行了综合分析，得出质量比、摩擦系数对隔震效果的影响；并给出在其他结构参数相对稳定的条件下，滑移面摩擦系数的取值范围。     

An alternative approach for the seismic rehabilitation of existing RC buildings using seismic isolation

Usually, buildings with seismic isolation are designed to comply with an operational building performance level after strong earthquakes. This approach, however, may limit the use of seismic isolation for the seismic rehabilitation of existing buildings with low lateral strength or substandard details, because it often requires invasive strengthening measures in the superstructure or the use of expensive custom‐made devices. In this paper, an alternative approach for the seismic rehabilitation of existing buildings with seismic isolation, based on the acceptance of limited plastic deformations in the superstructure under strong earthquakes, is proposed and then applied to a real case study, represented by a four‐storey RC frame building. Nonlinear response‐time histories analyses of an accurate model of the case‐study building are carried out to evaluate the seismic performances of the structure, comparing different rehabilitation strategies with and without seismic isolation. Initial costs of the intervention and possible (future) repair costs are then estimated. Based on the results of this study, values of the behavior factor (i.e. response modification factor) higher than those adopted in the current codes for base‐isolated buildings are tentatively proposed. Copyright © 2015 John Wiley & Sons, Ltd.