Effectiveness of sliding isolators with variable curvature in near‐fault ground motions

Recent studies have revealed that a sliding isolator with variable curvature (SIVC) can mitigate the resonance phenomenon likely to occur in seismic response of a conventional friction pendulum system (FPS) isolator due to its constant isolation frequency. The present study simulates four SIVC isolators and an FPS to find the optimum range of initial isolation period and coefficient of friction and employ them in comparing the effectiveness of SIVC in different peak ground acceleration (PGA) scales of near‐fault earthquakes. Velocity‐dependent coefficient of friction and modified viscoplasticity model have been used to simulate nonlinear friction force of the isolators. Results indicate identical performance of all SIVC isolators in PGA scales up to 0.4 g. When subjected to PGA scales from 0.4 g to 1.0 g, polynomial friction pendulum isolator (PFPI) and variable curvature friction pendulum system (VCFPS) reduce base displacement greatly, while conical friction pendulum isolator (CFPI) and variable frequency pendulum isolator (VFPI) show amplified responses. However, in mitigating structural acceleration, performance of CFPI and VFPI, unlike PFPI and VCFPS, which perform poorly, is excellent. Thus, in a strong near‐fault earthquake, PFPI and VCFPS or CFPI and VFPI can be chosen based on whether reduction of base displacement or super‐structural acceleration is the main concern of designer, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Finite element formulations and theoretical study for variable curvature friction pendulum system

The friction pendulum system (FPS), a type of base isolation technology, has been recognized as a very efficient tool for controlling the seismic response of a structure during an earthquake. However, previous studies have focused mainly on the seismic behavior of base-isolated structures far from active earthquake faults. In recent years, there have been significant studies on the efficiency of the base isolator when subjected to near-fault ground motions. It is suggested from these studies that the long-duration pulse of near-fault ground motions results in significant response of a base-isolated structure. In view of this, an advanced base isolator called the variable curvature friction pendulum system (VCFPS) is proposed in this study. The radius of the curvature of VCFPS is lengthened with an increase of the isolator displacement. Therefore, the fundamental period of the base-isolated structure can be shifted further away from the predominant period of near-fault ground motions. Finite element formulations for VCFPS have also been proposed in this study. The numerical results show that the base shear force and story drift of the superstructure during near-fault ground motion can be controlled within a desirable range with the installation of VCFPS. Therefore, the VCFPS can be adopted for upgrading the seismic resistance of the structures adjacent to an active fault.     

Assessment of sliding‐rubber isolator effect in progressive collapse of bridges under two scenarios

In this study, performances of 2 types of bridges, with and without seismic isolation, are addressed in 2 damage analysis scenarios, where, in the first, the side column and, in the second, the middle column are removed from the bridge piers. The performance was assessed using nonlinear dynamic analysis, and the time history and maximum structural responses were evaluated. Initially, sliding‐rubber isolators were designed according to AASHTO guide specifications, and then the bridges were modeled in OpenSees software package. Additionally, the coefficient of friction for the isolator was considered as a variable due to sudden removal of the columns and the consequent changes in the sliding velocity and axial forces. The results indicate that use of seismic isolation systems caused an increase in all maximum structural responses except that of the base shear. Considering the frictional performance of the isolators, slides in the deck are not caused by yielding of seismic isolators, and the reason for permanent displacements of the deck may be attributed to bridge instabilities in the first scenario. However, decrease in the horizontal stiffness results in increased maximum permanent displacement. In the first scenario, uplift of the deck occurred in the case of isolated bridge.     

Behaviour of liquid storage tanks with VCFPS under near-fault ground motions

Earthquake response of slender and broad liquid storage steel tanks isolated with variable curvature friction pendulum systems (VCFPSs) is investigated under near-fault motions. The tanks isolated with VCFPS are idealised with three-degrees-of-freedom associated with convective, impulsive and rigid masses. The frictional forces mobilised at the interface of the VCFPS are assumed to be velocity independent. The governing equations of motion of isolated tank are derived and solved in the incremental form using Newmark's method. For comparative study, the seismic response of liquid storage tanks with the VCFPSs is compared with that of same liquid storage tanks isolated using the friction pendulum systems (FPSs). The seismic response of isolated liquid storage tanks is also compared with that of the non-isolated tanks. Further, a parametric study is carried out to critically examine the behaviour of liquid storage tanks isolated with the VCFPSs. The important parameters considered are the friction coefficient of VCFPS, the fundamental period at the centre of the sliding surface of VCFPS and the tank aspect ratio. It is observed that under near-fault ground motions, the VCFPS is quite effective in controlling the seismic response, viz. the base shear, the sloshing displacement and the impulsive displacement, of liquid storage tanks.     

Base‐isolated structures with selective controlled semi‐active friction dampers

This paper investigates effectiveness of selective control strategy in hybrid base isolation systems including isolators and semi‐active variable friction (VF) dampers. According the selective control strategy, VF dampers are activated just if the displacement at the isolators exceeds the threshold value. The slip‐force control is based on the values of floors' accelerations and velocities. By controlling the slip‐force magnitude in the VF dampers, effective energy dissipation can be achieved in a seismic event. Activation of dampers according to the selective control strategy allows high‐energy dissipation by minimum energy required for adjusting the slip‐force. Performance of a multi‐storey frame with a base isolation system and VF dampers under various earthquake records was obtained numerically using originally developed MATLAB routines. Seismic response of the analysed structure with the selective controlled system was compared with that when the VF dampers were active during the whole earthquake. It is shown that adjustment of the slip‐force in a selective manner allows additional reductions in peak displacements and accelerations of the structure. The results also demonstrate that this control strategy yields reduction of the base displacement without increasing the peak base shear forces. Copyright © 2009 John Wiley & Sons, Ltd.     

摩擦摆隔震结构的地震响应分析

基于摩擦摆（FPS）及其隔震剪切型结构的振动微分方程，进一步研究了该系统的振动形态。通过改变摩擦摆的摩擦系数和滑道半径，分析二者对结构隔震效果的影响。结果说明：摩擦系数对结构层间位移、基底剪力以及基底滑移量均有较大的影响；滑道半径对基底滑移量有较大影响，但对层间位移和基底剪力影响不大。     

Seismic performance of column supporting single-layer reticulated domes with friction pendulum bearings

The friction pendulum bearing (FPB) has been widely studied as an effective dry friction sliding isolation device, due to its self-limit and self-reset capability. The refinement finite element models of FPB were applied to column supporting single-layer reticulated domes. The seismic performances of these structures with FPBs were systematically analyzed by finite element software LS-DYNA. Numerical results illustrate that the optimal friction coefficient of FPB increases with increasing earthquake intensity and the optimal range of friction coefficient locates between 0.025 and 0.15. The seismic effects of single-layer reticulated domes with FPBs are strengthened with the increase of curvature radius, while isolation effect of FPBs has no obvious change as the curvature radius exceeds 1.5 m. Additionally, the parameter selection principles of friction pendulum bearings for column supporting single-layer reticulated domes are given by means of investigating the force of the slider of FPBs and dynamic analysis of single-layer reticulated domes with FPBs.     

昆明新国际机场主航站楼A区隔震效能分析

昆明新国际机场主航站楼A区为复杂大跨钢-混凝土组合结构,位于抗震设防烈度为8度的昆明市,经多方论证最终对该结构采用了基础隔震技术,建成后它将成为目前世界上最大的单体隔震建筑。本文采用ANSYS有限元程序建立结构分析模型,模型主要由非线性杆单元、壳单元和非线性的隔震单元组成。首先介绍了隔震方案的论证过程及隔震支座的布置对结构隔震效能的影响,然后介绍了用于时程分析的地震波的选取过程,最后通过多遇和罕遇烈度下的弹性时程分析,研究了该结构的变形、内力和隔震效果。计算结果表明,该结构不仅可以实现小震下"降一度"的减震目标,还可以满足大震下隔震层最大剪切位移的控制指标,隔震层的设计是合理的,结构在隔震后的抗震性能是可以满足要求的。     

Using orthogonal pairs of rollers on concave beds (OPRCB) as a base isolation system—part I: analytical,experimental and numerical studies of OPRCB isolators

A somehow new isolating system is introduced for short‐ to mid‐rise buildings. It does not need high technology for manufacturing and is not costly, contrary to other existing systems like lead‐rubber bearing or friction pendulum bearing systems. Each isolator of the proposed system consists of two Orthogonal Pairs of Rollers on Concave Beds (OPRCB). Rolling rods installed in two orthogonal directions make possible the movement of the superstructure in all horizontal directions. The concave beds, in addition to giving the system both restoring and re‐centring capabilities, make the force–displacement behaviour of the isolators to be of hardening type. The results of the studies on the specifications of the proposed isolating system and its application to buildings can be presented in two parts. Part I relates to the analytical formulations and the results of experimental and numerical studies of the system's mechanical feature, including its dynamical properties, and part II focuses on the effectiveness of the proposed isolation system in seismic response reduction of low‐ to mid‐rise buildings. In part I of the work, presented in this paper, at first general features of the OPRCB isolator are explained and the analytical formulation, governing its dynamic motion, is derived and discussed in detail. Then, the results of experimental and numerical investigations, including the lateral load displacement relationship of the OPRCB isolators under various vertical loads, obtained by both Finite Element Analyses (FEA) and laboratory tests are presented (FEA results have been verified by the laboratory tests). Finally, responses of some Single Degree of Freedom (SDOF) systems, isolated by OPRCB devices, subjected to simultaneous effect of horizontal and vertical ground motions, are presented and compared with responses of their fixed‐base counterparts. Based on the numerical calculations, it is observed that the oscillation period of the isolated SDOF system is independent of its mass, the initial amplitude of its free vibration response and the value of rolling resistance coefficient. With regard to seismic response reduction it is seen that the amount of absolute accelerations in the SDOF systems, isolated by OPRCB devices, can be reduced drastically in comparison with the fixed‐base systems. Results also show that if the rollers and cylindrical beds are made of high‐strength steel materials, the system can be used effectively under the vertical loads of about the axial forces of ground floor columns in ordinary buildings up to 14 storeys. Copyright © 2010 John Wiley & Sons, Ltd.     

滑移摩擦型隔震结构考虑竖向地震作用影响的分析

摩擦滑移型隔震支座具有较好的减震效果和经济性能,越来越多地应用于结构隔震.这种支座屈服力取决于滑动摩擦力,与摩擦系数和支座竖向压力有关.地震动是多维的,本文考虑双向地震动,分析了采用摩擦滑移型支座隔震的质量块、基础隔震结构和顶层隔震结构,在不同摩擦系数和地震烈度情况下竖向地震作用对结构水平地震反应的影响.计算表明,在大摩擦系数、高烈度情况下,竖向地震作用对基础隔震和设备隔震有一定影响,建议考虑竖向地震作用的影响;而在小摩擦系数时则可忽略.并且,适当的屈服后刚度可以减小竖向地震作用的影响.     

复摩擦摆支座应用于楼面隔震研究

对复摩擦摆支座在楼面隔震中的应用进行了研究.在长期使用过程中,隔震楼板的上部质量可能发生较大变化,考虑到摩擦摆支座自身隔震周期与上部质量无关的特性以及复摩擦摆支座相较于单曲面摩擦摆支座更好的隔震效益,因此推荐复摩擦摆支座用作楼面隔震支座.为控制隔震楼板相对结构楼面的位移,可通过提高复摩擦摆支座的摩擦系数或附加粘滞阻尼器而实现.以一工程实例为背景,对比研究粘滞阻尼器+低摩擦系数复摆支座方案与高摩擦系数复摆支座的隔震效果,发现前一方案 可以保证不同加速度水平作用下隔震楼面的隔震效果,是一种较好的隔震配置组合.     

带限位装置的摩擦隔震结构动力特性及地震反应分析

提出了一种新型基础隔震模型,即带限位装置的摩擦隔震体系 (S- LF);基于此隔震模型,利用 Poincare映射法研究地面谐运动下 S- LF结构的运动特征;并利用高精度的精细时程积分法,通过对地震作用下 S- LF动力响应的计算,绘制了上部结构最大加速度反应谱和基底最大滑移量反应谱,并研究了各种结构参数对隔震的影响;通过与恢复力摩擦隔震系统 (R- FBI)和纯摩擦力滑移隔震系统 (P- F)的比较表明, S- LF的隔震性能优于 P- F和 R- FBI;最后通过对计算实例的分析发现,地震作用下 S- LF结构的层间最大剪力和最大绝对加速度反应分布较一般传统结构有很大区别。     

摩擦摆隔震支座在地震反应中的影响分析

本文以一座7层框架结构作为研究对象,运用有限元分析软件SAP2000,对摩擦摆基础隔震结构进行地震反应分析,输入地震波EI-Centro波,通过调整摩擦摆支座的摩擦系数,分析在不同的摩擦系数下结构的周期、基底位移、楼层加速度的影响变化,表明随着支座摩擦系数的增大,结构自振周期逐渐变小,楼层的滑动位移反应也呈减小的趋势,但楼层加速度反应会逐渐变大,为滑移隔震技术应用到实际工程提供了参考依据。     

Seismic response of shear‐core with sliding support to bi‐directional ground excitation

To study the effectiveness of a sliding support for the isolation of structures from damaging ground motion, the model of a shear‐core supported on a sliding foundation and subjected to random ground motion in two orthogonal directions is considered here. A fictitious spring model is adopted to deal with the discontinuous nature of the sliding structural system. The rigid friction force deformation characteristics of the sliding support are modelled as elasto‐plastic with high elastic stiffness. The sliding support is assumed to remain in the elastic state during non‐sliding and is treated as plastic during the sliding state. An incremental numerical scheme for the solution of a multi‐degree‐of‐freedom system is used for solving the time history responses. The responses (the absolute value of the acceleration of the top of the wall, and the bending moment at the base of the wall), are calculated under various important parametric variations. The result presented here are of interest in the area of the vibration isolation of important structural systems. Copyright © 1999 John Wiley & Sons, Ltd.     

Probabilistic seismic risk assessment of modified pseudo-negative stiffness control of a base-isolated building

Pseudo-negative stiffness (PNS) control of a base-isolated structure, which has a large damping ratio at the isolation level, is used to suppress isolator displacement without large force transmission to the superstructure during extreme earthquakes. However, potential increases in floor acceleration in the superstructure are induced by the large damping ratio, especially for low-to-moderate seismic input level. In consideration of structural functionality and safety, a modified PNS (MPNS) control scheme based on the ‘ideal isolation control principle’ is proposed, considering different seismic intensity levels. The effect of the MPNS control is investigated from three aspects, namely floor acceleration, inter-storey drift and isolator displacement within a probabilistic performance-based seismic engineering framework. Comparisons are made between MPNS control, conventional PNS control and passive damping control. A benchmark base-isolated building is used as a case study. In the seismic performance evaluation, the seismic intensity measures for different response parameters are optimised. An extensive parametric study is also conducted to identify the optimal control parameter to conform to the ideal isolation control principle. Results demonstrated that the MPNS control is an effective solution to the challenging problem of improving structural functionality at low seismic intensity, as well as structural safety from collapse at extreme seismic intensity.     

非线性基础隔震结构复振型反应谱设计方法

采用铅芯橡胶支座、弹性滑板支座或摩擦摆支座的基础隔震结构,在利用反应谱方法进行设计时,需要考虑支座的非线性特征.在传统非线性振动分析平均方法或慢变振幅法中引入激励随机性,以等效线性系统和原非线性系统势能和阻尼耗能相等为原则,提出了基于能量平衡的随机等效线性化方法.在该方法中,等效刚度和等效阻尼系数表达为振动幅值的期望,...     

并联基础隔震体系地震反应特征与隔震层参数的优选

本文在大量工程算例仿真分析的基础上,较为系统地研究了典型并联基础隔震结构地震反应的一般特征,探讨了并联基础隔震体系隔震层参数的合理选择问题。研究表明,在一定限度内,增加隔震层回复刚度几乎不会改变上部结构的最大层间剪力,但对隔震层最大滑移位移和残留位移却有非常显著的限制作用,隔震层回复刚度的参与不改变结构地震反应的频谱特性。为限制隔震层位移,在保证不增大上部结构最大层间剪力的前提下,应尽量增加隔震层回复刚度;隔震层屈服剪力的取值则需兼顾隔震效果与隔震层滑移位移。     

Seismic response control of base‐isolated buildings using multiple tuned mass dampers

Seismic response of a base‐isolated building equipped with single tuned mass damper (STMD), multiple tuned mass dampers (MTMDs), and distributed multiple tuned mass dampers (d‐MTMDs) under real earthquake ground motions is investigated. Numerical study is carried out using analytical models of five‐, 10‐, and 15‐storey base‐isolated buildings equipped with the STMD, MTMDs, and d‐MTMDs. The buildings are modeled as shear‐type structure with a lateral degree of freedom at each floor level, and the buildings are isolated using the laminated rubber bearing, lead‐core rubber bearing, friction pendulum system, and resilient‐friction base isolator. The coupled differential equation of motion for the buildings are derived and solved in the incremental form using Newmark's step‐by‐step method of integration. From the numerical study conducted, it is concluded that installing a tuned mass damper at each floor level of a base‐isolated building reduces the structural response in terms of top floor acceleration and bearing displacement. It is found that installing the MTMDs and d‐MTMDs are significantly beneficial in reducing top floor acceleration as compared with the STMD. Further, almost comparable reduction in the bearing displacement could be obtained by installing the STMD, MTMDs at top, and d‐MTMDs in the base‐isolated buildings. The d‐MTMDs are more beneficial as compared with the STMD and MTMDs as otherwise huge controller mass can now be divided and distributed on different floor levels.     

摩擦摆支座恢复力模型研究

采用微分连续模型模拟摩擦摆支座的单向和双向耦合恢复力，表明其可以较好地描述恢复力的非线性特征和双向耦合效应。由计算分析可以看出，考虑双向耦合作用与未考虑双向耦合作用的滞回曲线有较大差别，因而，支座应采用双向耦合恢复力模型以考虑双向耦合作用对结构地震反应和支座性能的影响。     

碟簧-单摩擦摆三维隔震(振)装置力学性能及隔震(振)效果研究

碟簧-单摩擦摆三维隔震(振)装置(3DFPS)由碟簧竖向隔振单元和单摩擦摆水平隔震单元组成,可以实现环境激励工况下建筑结构的竖向隔振与地震工况下的水平隔震。为了研究3DFPS的力学性能及隔震(振)效果,制作了足尺的3DFPS试件,并对其进行压剪试验。结果表明：3DFPS的竖向性能与水平向性能相互独立,竖向隔振单元与水平隔震单元可独立设计;通过在叠合碟簧间加入0.03mm聚四氟乙烯(PTFE)薄膜可以减小碟簧间摩擦,使小位移下的循环加载刚度更接近大位移下的单调加载刚度。对采用3DFPS和固接到地面的平面框架结构进行有限元弹性时程分析,研究此装置在水平地震与竖向地铁振动激励下的隔震(振)效果。结果表明：三维隔震(振)装置可使水平地震下结构响应减少80%以上,使地铁振动激励下楼面竖向加速度响应减小61%;碟簧竖向压缩变形对结构在水平地震下的响应没有明显的影响。