Robustness of base‐isolated high‐rise buildings under code‐specified ground motions

The robustness of base‐isolated high‐rise buildings is investigated under code‐specified ground motions. Friction‐type bearings are often used in base‐isolated high‐rise buildings to make the natural period of those buildings much longer. While additional damping can be incorporated into every story in passive controlled structures with inter‐story type passive members, that can be incorporated into the base‐isolation story only in the base‐isolated building. This fact leads to the property that, as the number of stories of the building becomes larger, the damping ratio reduces. This characteristic may cause some issues in the evaluation of robustness of base‐isolated high‐rise buildings. The purpose of this paper is to reveal the robustness of base‐isolated high‐rise buildings. A kind of inverse problem for the target drift in the base‐isolation story is formulated in order to determine the required quantity of additional viscous damping. It is demonstrated numerically that, as the base‐isolated building becomes taller, the damping ratio becomes smaller and the ratio of the friction‐type bearings in the total damping becomes larger. This may lead to the conclusion that base‐isolated high‐rise buildings have smaller robustness than base‐isolated low‐rise buildings. Copyright © 2007 John Wiley & Sons, Ltd.     

宿迁市府苑小区综合楼隔震分析

宿迁市府苑小区综合楼位于 8度区 ,设计基本地震加速度值为 0 3 0 g ,为 6层底部框架砌体结构 ,平面呈三折线形。工程采用基础隔震技术进行结构设计 ,隔震层由橡胶隔震支座、滑移支座、粘滞消能器组成。对隔震体系空间模型的时程分析表明 :采用基础隔震措施可显著降低上部结构的地震作用 ;设置粘滞消能器能较好地解决降低上部结构的地震作用和限制隔震层位移之间的矛盾 ,有效地消除结构的扭转效应     

粘滞阻尼器连接的相邻隔震与非隔震建筑地震反应分析

针对隔震结构在地震作用下隔震层位移较大,可能会与相邻非隔震结构之间产生碰撞问题进行了分析,采用简化模型对隔震与相邻非隔震结构之间布置粘滞阻尼器的减震控制的工作机理进行了研究。建立了隔震与相邻非隔震结构之间布置粘滞阻尼器减震控制的数值仿真分析模型,研究了粘滞阻尼器的阻尼系数、布置位置以及隔震结构隔震层刚度对结构顶点位移的影响。结果表明:随着阻尼器阻尼系数和隔震结构隔震层刚度的增加,隔震结构顶层位移也随之增大,阻尼器布置位置越靠近隔震层,相邻非隔震结构顶层位移控制效果越明显。     

Los Angeles City Hall

This paper describes the Los Angeles City Hall building and a unique seismic strengthening program. Four hundred and sixteen high damping rubber bearings, 90 flat sliding bearings and 64 viscous dampers have been installed as part of the seismic rehabilitation. The building is a 460 feet tall steel frame with unreinforced masonry infill. The rehabilitation consists of installing high damping rubber bearings at its base supplemented with nonlinear viscous dampers. This paper describes various aspects of the project including the development of seismic performance goals, identification of inherent seismic deficiencies of the existing building, evaluation of alternative strengthening schemes, the final design process and construction issues. Copyright © 2000 John Wiley & Sons, Ltd.     

宿迁市人防指挥大楼隔震设计方法研究

宿迁市人防指挥大楼位于地震高烈度区,钢筋混凝土框架-剪力墙结构,地上13层,高48.9m。该工程采用基础隔 震技术设计,为我国目前最高的隔震建筑之一。隔震层布置在地下室顶板和±0.00楼面之间,由橡胶隔震支座、滑移支座 和粘滞阻尼器组成,共采用了53只橡胶隔震支座、12只滑移支座,沿结构的两个主轴方向共设置4只非线性粘滞阻尼 器。分析结果表明,采用基础隔震措施可显著降低上部结构的地震作用;设置粘滞消能器能较好地解决降低上部结构地震 作用和限制隔震层位移之间的矛盾。在本工程中采用基础隔震技术,具有明显的技术经济效益。     

宿迁市府苑小区综合楼隔震结构设计

宿迁市府苑小区综合楼采用基础隔震技术进行结构设计 ,现介绍其设计要点 ,包括地下室、隔震层、上部结构的设计等 ,着重阐述结构布置方案与隔震支座、滑移支座、消能器的连接构造等。     

Evaluation of coupling–control effect of a sky‐bridge for adjacent tall buildings

In this study, the coupling–control effect of a sky‐bridge for adjacent tall buildings has been investigated. To this end, two building structures of 42‐ and 49‐stories connected by a sky‐bridge and constructed in the Seoul, Korea, were used. Earthquake excitations and wind load data obtained from wind tunnel tests are employed for numerical simulation. Lead rubber bearings and linear motion bearings were used for the connectors between the sky‐bridge and the example buildings. Several types of connector configurations were investigated to find an appropriate configuration for the tall buildings considered. The displacement and acceleration responses of the coupled buildings, and the reactions of the bearings and member forces of the sky‐bridge were evaluated in comparison with the uncoupled buildings. Numerical results demonstrated that the sky‐bridge could effectively increase the damping ratio of the coupled tall buildings, resulting in decreased dynamic responses. In addition, it was shown that the coupling–control effect of the sky‐bridge could be significantly improved by using additional viscous dampers. The connection system and configuration proposed in this study had been applied to the construction of the sky‐bridge for the example structures. Copyright © 2010 John Wiley & Sons, Ltd.     

基础隔震结构高宽比限值研究

本文研究目的是得到隔震结构在各种工况下的高宽比限值,这对隔震结构设计是必要的。橡胶隔震支座不能产生拉应力和隔震支座压应力不超过容许值是保证隔震结构在强震中不产生倾覆的充分条件。基于这两个条件,本文推导了隔震结构高宽比限值的显式并给出了针对不同建筑类别、不同设防烈度、不同场地条件和不同隔震层阻尼比的高宽比限值。在支座的轴力计算中,考虑了水平地震作用、竖向地震作用和重力荷载代表值的共同影响以及荷载的最不利组合。研究发现,当控制条件为支座不产生拉应力时,高宽比限值随隔震结构周期的增加而增加;当控制条件为支座压应力不超过容许值时,高宽比限值随隔震结构周期的增加而减小。因此,存在一个临界周期使高宽比限值取得极大值。研究还发现,存在一个最大的隔震结构周期使高宽比限值等于零或隔震层位移超过容许值。将隔震结构的周期与临界周期和最大隔震周期比较,就可以得到相应高宽比限值的表达式。     

Notes and comments on the energy cost of building construction

The energy cost for construction of new homes is about one million Btu/ft², and higher for commercial buildings, confirming Stein's estimate of 1.3 million Btu/ft². A home, constructed under ASHRAE Standard 90 - 75, will consume 150 000 – 250 000 Btu/ft² annually, so its construction uses as much energy as about five years of operation. For a commercial building, the times are comparable.     

Simplified procedures for seismic design verification and evaluation of lead rubber bearing base‐isolated buildings based on free‐vibration response

Base isolation has seen widespread application to buildings and infrastructures over the past four decades. However, there is a lack of methods for assessing the performance of a base‐isolated structure at the end of construction and during its service life. To this end, simplified methods are developed for verifying isolation design and evaluating seismic demands of rubber‐bearing‐supported base‐isolated buildings based on their free‐vibration response, which could be obtained using field (on‐site) testing. The base isolation layer consists of lead rubber bearings (LRBs) and linear natural rubber (LNR) bearings. For design verification purposes, analytical solutions are provided to benchmark the free‐vibration response of base‐isolated buildings, considering the general case of a multilinear hysteretic isolation response representing multiple LRBs with distinct mechanical specifications. In seismic demand evaluation, seismic capacity of an isolation system is estimated using free‐vibration response of various amplitudes that cover a range of expected seismic intensity of interest. Seismic demands are obtained when capacity coincides with an earthquake response spectrum at a compatible damping level. Procedures are developed for the potential use of snap‐back tests and verified using experimental and numerical data.     

房屋建筑中间层隔震研究

房屋建筑隔震的新体系 中间层隔震不同于基底隔震。本文通过SAP2 0 0 0程序对某工程二层框架平台上多塔楼与平台间隔震与不隔震的对比分析 ,探讨了中间层隔震的隔震效果     

基础隔震建筑简化软碰撞保护与变刚度保护的对比分析

基础隔震建筑通过设置隔震支座来保护上部结构不受损坏,但在长周期或强烈地面运动作用下会使隔震支座变形过大而导致隔震支座失稳破坏。在这种情况下,需增设保护装置作为第二道防线,以减小隔震层的变形,使之限制在允许的范围内,同时上部结构层间剪力不明显增大。本文主要对比分析了两种保护措施:①简化后的软碰撞保护;②变刚度保护。通过对其原理、力学模型以及工程实例的研究,选取了恰当的参数并进行了地震反应分析。     

Dynamic characteristics and viscous dampers design for pile‐soil‐structure system

A series of large‐scale shaking table tests are conducted on tall buildings with and without energy dissipation devices on soft soils in pile group foundations, representing pile‐soil‐structure interaction (PSSI) system and the corresponding fixed‐base situations. The superstructure is a 12‐story reinforced concrete (RC) frame. The dynamic characteristics of the test models show that the frequencies decrease and the damping ratio increase in PSSI system by comparison with the fixed‐base structures. The mode shapes of PSSI system are different from that under fixed‐base condition, and the mode shapes of structure without dampers change greater than that with energy dissipation devices under various white noises. An improved method for structural dynamic characteristics, considering the impedance function of piles, is developed to address the issue of modal parameters with PSSI effect. In addition, the structural dynamic parameters of the large‐scale shaking table tests are identified using the modification method and other regulation methods, demonstrating that the improved approach is highly accurate and effective. Subsequently, a design procedure for viscous dampers of structures with PSSI effect is presented based on the dynamic characteristics of the system. Finally, the dynamic responses of the structure with viscous dampers in the practical engineering are decreased effectively, indicating the good performance of designed viscous dampers. The numerical results also show that the damping efficiency of interstory drift is larger than the acceleration and interstory shear force. Therefore, the improved modal parameters method, validated through a series large‐scale shaking table tests, is applicable for identifying dynamic characteristics of pile‐soil‐structure with energy dissipation devices system. The design procedure of viscous dampers, proved by a reinforced concrete frame structure located on a practical Shanghai soft site, can be employed to design the viscous dampers considering seismic PSSI effect.     

基础隔震建筑中应用变刚度保护装置的地震反应分析

长周期的地面运动会使隔震建筑物发生类共振而导致隔震支座失稳破坏。在这种情况下,可以利用附加的弹簧改变建筑物的周期,减小隔震层的变形,使之限制在允许的范围内,同时使上部结构的层间剪力不明显增大。按照多质点结构分析模型推导了不发生附加、右侧附加、左侧附加弹簧的运动方程,编制了相应的分析程序。通过对模型实例分析,论证了变刚度保护装置在限制支座大变形中的作用,讨论了在工程设计中如何选取变刚度保护装置的适宜参数。     

Coordinative similitude method considering overturning effect for scale model testing of structures with rubber bearings

Generally, when a prototype is scaled down to a scale model, all parameters of the scale model should be designed to satisfy the similitude criteria. For a base‐isolated structure with rubber bearings, however, it is technically difficult to obtain small‐sized rubber bearings with the first shape factor satisfying the similitude criteria. This distortion affects the similitude ratio of the vertical stiffness of the bearings and, thus, influences the similitude ratio of the horizontal response of the structure because of the overturning effect. To solve this problem, a coordinative similitude method is proposed for scale model testing of structures with rubber bearings by adjusting configuration of the isolators to match the similitude ratio of the overturning stiffness of the isolation layer. A full‐scale and two 1/3 scaled bearings were designed and tested, and their similitude relations were evaluated. Test results of the model bearings were extrapolated to the OpenSEES model of a conventional model building and a coordinative building designed based on the conventional similitude method and the coordinative similitude method, respectively. A comparison between seismic responses of two model buildings against the prototype building indicates that the coordinative similitude method has significantly larger accuracy than the traditional similitude method.     

Seismic behaviour of asymmetric base isolated structures with various distributions of isolators

The paper tries to contribute to a better understanding of the behaviour of base isolated asymmetric structures. Numerous variants of originally symmetric four storey RC frame building isolated by a simple lead rubber bearing base isolation system with various distributions of isolators were considered as test examples. The symmetrical structural variant and appropriate LRB bearing properties were designed according to Eurocode 2 and 8. The asymmetric variants were produced by shifting the centre of mass CM toward one side of the building. Additional “torsionally unrestrained” and “torsionally restrained” sub-variants of each building variant were obtained by changing the mass distribution, while total mass sum remained unchanged. For the base isolation system we have considered six different distributions of bearings characterized by the position of the centre of isolators CI in respect to the centre of mass CM of the superstructure. Two symmetric (Uniform and Peripheral distribution) and four asymmetric distributions of isolators (called CI = CM, CI = CM/2, CI = ?CM/2 and CI = ?CM) were included in the analyses. The paper analyses the positive and negative effects of different bearing distributions to the displacements and rotations of the superstructure as well as to the base isolation system and tries to determine the most favourable distribution of isolators that is able to balance the effects of introduced eccentricities. The results obtained by 3D nonlinear dynamic analyses are presented as an average of maximums for ten selected ground motions and three different scalings. They indicate that all six considered distributions of bearings, however differently, substantially reduce the unfavourable torsional effects, which are with different extent transferred from the superstructure to the base isolation system. It was further observed that CI = CM distribution, favoured by common building codes, is best only for accommodating the torsional effects in the base isolation system. A significantly different conclusion was found observing the nonlinear behaviour of the superstructure, where CI = CM distribution might cause more damage in the flexible side frames.     

橡胶垫隔震支座结构高宽比限值研究

本文对叠层橡胶垫隔震结构的高宽比限值进行了研究,导出了实用的简化计算公式,分析了地震动峰值、场地条件、隔震层刚度、上部结构刚度(反映了上部结构类型)、橡胶垫的布置等因素对隔震结构高宽比限值的影响及其变化规律。给出了不同条件下具有统计意义的隔震结构高宽比限值的定量范围,并提供了提高隔震结构高宽比的有效方法,得出了一些具有实际意义的结论,为工程计算与设计提供了方法和依据。本文结果可供编制有关规范和规程参考。     

并联组合基础隔震体系的简化计算方法及试验分析

对并联组合基础隔震体系的周期和阻尼比进行了分析,并对其影响因素进行了讨论,同时提出了计算该种结构体系的简化计算方法.通过对某工程实例所采用的滑板支座及橡胶隔震支座进行了静力试验,获得其隔震性能参数,并应用SAP2000进行了该工程多遇与罕遇地震下的弹性时程分析计算,结果表明罕遇地震下上部结构仍处于弹性工作状态,且简化方法的计算结果与该结果比较接近,能够满足工程设计的要求.     

Analysis of a high‐rise steel structure with viscous damped outriggers

Damped outriggers for tall buildings draw increasingly attentions to engineers. With a shaking table test, two models of a high‐rise steel column‐tube structure are established, one with outriggers fixed to the core and hinged at the columns, whereas the other's cantilevering outriggers are connected to columns by viscous dampers. According to their dynamic properties, five earthquake waves are selected from the Ground Motion Database of Pacific Earthquake Engineering Research Center (PEER), and two artificial waves are generated by software SIMQKE_GR. Under various peak ground accelerations (PGAs), nonlinear time‐history analysis is applied to compare structural elastic seismic responses, including accelerations, inter‐story drifts, base shear force, damper's response and additional damping ratios. It is concluded that under minor earthquakes, accelerations, inter‐story drifts and base shear force of structure with damped outriggers are larger than or nearly equal to those of the one with fixed outriggers, and the viscous dampers hardly work. But as PGA increases, the contrary situation happens, and the effect of viscous dampers is enhanced as well. The additional damping ratio reaches around 4% under mega earthquakes. Copyright © 2013 John Wiley & Sons, Ltd.     

Analytical and Numerical Study of a Smart Sliding Base Isolation System for Seismic Protection of Buildings

The seismic response of a single–story steel building frame with a smart base isolation system is evaluated. The isolation system consists of sliding bearings combined with an adaptive fluid damper. The damping capacity of the fluid damper can be modulated in real time based on feedback from the earthquake ground motion and superstructure response. The adaptive capabilities of the fluid damper enable the isolation system displacement to be controlled while simultaneously limiting the interstory drift response of the superstructure. This paper concentrates on the development of analytical models of the smart isolation system and control algorithms for operation of the system. In general, the results from numerical simulations demonstrate that, for disparate earthquake ground motions, the smart isolation system is capable of simultaneously limiting both the response of the isolation system and the superstructure.