Damped resonant appendages to increase inherent damping in buildings

It is demonstrated that the addition of a tuned mass-spring-dashpot system with a relatively small mass and a high damping ratio can be an effective way to increase the inherent damping characteristics of buildings and reduce, thus, their response to earthquake excitations. The demonstration is based on a theoretical formulation and on numerical and experimental studies that confirm this formulation. In the theoretical formulation, it is shown first that, if certain conditions are satisfied, the damping ratios in two of the modes of the system that is formed by a building and an appendage in resonance are approximately equal to the average of the corresponding damping ratios of the building and the appendage. Based on this finding, it is then shown that an attached appendage with a high damping ratio and tuned to the fundamental frequency of a building may increase the damping ratio in the fundamental mode of the building to a value close to half the damping ratio of the appendage. In the numerical study, the response of a ten-storey shear building is analysed under two different earthquake ground motions with and without the proposed resonant appendages. Appendages with damping ratios of 20 and 30 per cent are considered. In this study, it is found that under one of the ground motions the maximum displacement of the building's roof is reduced 30 per cent with the appendage with 20 per cent damping and 39 per cent with the one with 30 per cent damping. Similarly, with these two appendages the building's base shear is reduced 31 and 41 per cent, respectively. In the experimental study, a wooden three-storey structural model is tested in a shaking table with and without an appendage designed and constructed to have a damping ratio of 53-5 per cent. The test is conducted under random and sinusoidal base excitations. In the shaking table test under random excitation, the attached appendage reduces the response of the model 38-6 per cent, while in that under sinusoidal vibration 45-2 per cent.     

Seismic energy dissipation for cable-stayed bridges using passive devices

This study assesses analytically the effectiveness, feasibility and limitations of elastic and hysteretic damping augmentation devices, such as elastomeric and lead–rubber bearings, with respect to the dynamic and seismic performance of cable-stayed bridges. This type of bridge, which has relatively greater flexibility, is more susceptible to undesirable vibrations due to service and environmental loadings than are conventional bridges. Therefore, damping is a very important property. Supplementary damping devices based on the plastic deformation of lead and steel are proposed at critical zones, such as the deck–abutment and deck–tower connections, to concentrate hysteretic behaviour in these specially designed energy absorbers. Inelastic behaviour in primary structural elements of the bridge can therefore be avoided, assuring the serviceability of these cable-supported bridges. Analytically, three-dimensional modelling is developed for the bridge and the damping devices, including the bridge geometrical large-displacement non-linearity and the local material and geometric non-linearities of the energy dissipation devices. The effects of various modelling and design parameters of the bridge response are also studied, including the properties, modelling accuracy and location of the devices along the bridge superstructure. It is shown that an optimum model of the seismic performance of the bridges with these passive control devices can be obtained by balancing the reduction in forces along the bridge against tolerable displacements. Appropriate locations and hysteretic energy dissipation properties of the devices can achieve a significant reduction in seismic-induced forces, as compared to the case with no dampers added, and relatively better control of displacements. In addition, proper selection of the location of the passive control systems can help redistribute forces along the structure which may provide solutions for retrofitting some existing bridges. However, caution should be exercised in simulating the device response for a reliable bridge structural performance. Moreover, while seismic response of the bridge can be significantly improved with added dampers, their degree of effectiveness also depends on the energy absorption characteristics of the dampers.     

考虑阻尼器极限状态的耗能减震体系 斜拉桥抗震性能分析

在大震或特大震下,黏滞阻尼器可能因某个极限状态的出现而发生破坏。现有在斜拉桥上设置黏滞阻尼器的研究多集中在阻尼器的参数优化上,很少考虑到阻尼器失效对斜拉桥抗震性能的影响。针对这一问题,以某三塔斜拉桥为背景,利用OpenSees平台建立斜拉桥有限元模型和可以考虑承载力及行程极限的黏滞阻尼器模型;分析黏滞阻尼器的阻尼系数和阻尼指数对斜拉桥地震响应的影响,确定阻尼器参数的取值;对不安装阻尼器、安装不考虑极限状态及考虑极限状态阻尼器等多种工况的斜拉桥进行非线性时程分析,对比各工况斜拉桥的地震响应。分析结果表明,在大震下,考虑极限状态阻尼器的耗能能力及减震效果将显著降低;不考虑阻尼器达到极限状态后失效的情况将高估耗能减震设计斜拉桥的抗震能力。     

大跨斜拉桥的近断层地震响应及减震控制

近断层地震长周期成分丰富,存在速度大脉冲效应;而大跨度斜拉桥一般采用半漂浮体系或漂浮体系,所以固有频率较低。为了研究大跨度斜拉桥在近断层地震作用下的反应规律及减震措施,利用ANSYS软件分析了某半漂浮体系的大跨斜拉桥在近断层地震作用下的时程响应,并对其减震控制方法进行了探讨。研究表明,大跨度斜拉桥的近断层地震响应随着PGV/PGA值的增大而增大,且增大幅度较大,近场脉冲效应较为显著;对于近断层地震作用,不建议采用塔梁弹性连接装置作为主梁纵漂的减震措施,而采用参数适宜的铅挤压阻尼器和粘滞阻尼器则均能获得很好的减震效果;由于大跨度斜拉桥的近断层地震反应较大,应提高其支座的设计允许位移。     

A simplified design method for metallic dampers used in the transverse direction of cable-stayed bridges

The aseismic design of cable-stayed bridges in the transverse direction with newly proposed metallic dampers that can accommodate both longitudinal and transverse movement of the deck has recently been considered. This work focuses on developing a simplified method to design an appropriate metallic damper. The seismic performance of cablestayed bridges with different damper stiffness, main span lengths, tower shapes and types of deck in the transverse direction are investigated. The transverse displacement of the deck of a cable-stayed bridge increases significantly with the increment of the damper stiffness, which proves that the design of the damper stiffness is crucial. A simplified model considering the damper stiffness, cable system and tower in the transverse direction is developed to evaluate the period and lateral displacement of a complicated cable-stayed bridge. Based on the simplified model, a design method is proposed and assessed using two cable-stayed bridges as examples. The results show that metallic dampers can be designed with high efficiency, and the optimal ductility of the damper can be selected.     

超大跨度斜拉桥考虑行波效应的地震动随机响应研究

斜拉桥地震反应不同于其它桥型,具有明显的空间耦合效应.利用有限元理论对苏通长江公路大桥的空间抗震性能进行分析,重点研究行波效应对结构响应的影响,并与一致激励计算的结果进行比较,为大跨度斜拉桥抗震分析采用随机方法提供了一定的参考依据.研究结果表明,行波效应对斜拉桥结构内力有显著的影响,大跨度斜拉桥抗震性能分析必须考虑行波效应.而行波效应的影响与结构自身动力特性、视波速、构件位置及研究响应类型(位移与内力)相关.     

飘浮体系斜拉桥纵向抗震计算的单塔模型

通过全桥模型计算结果与单塔模型计算结果的对比,讨论了集中质量在塔上锚固区处堆聚位置,定义了一个结构动力特性和结构地震反应的修正系数,提出了飘浮体系斜拉桥塔纵桥向地震反应计算的单塔模型。多个工程实例的分析结果表明,采用单塔模型的典型误差在15%左右,精度可以满足工程抗震设计的要求,使桥塔的抗震计算得到简化。     

摩擦摆支座在矮塔斜拉桥中减震效果研究

矮塔斜拉桥有着良好的受力性能与美观性能,因此抗震设计对矮塔斜拉桥至关重要.摩擦摆式减隔震设计能够将桥梁上部结构与下部结构分离,从而延长结构的自振周期和摩擦耗能机理来降低和耗散传递到桥梁上部结构的能力.本文以靖远金滩黄河大桥(100+168+100)m矮塔斜拉桥为分析模型,利用摩擦摆式减隔震支座对矮塔斜拉桥的墩身进行减隔...     

Morison方程中动水阻力项对桥梁桩柱地震反应的影响

深水桥梁地震反应计算时,当采用Morison公式考虑水的作用时,增加了一个附加惯性项和一个附加阻尼项,其中附加阻尼项是非线性的。由于非线性附加阻尼项的存在,给采用反应谱方法求解桥梁的地震反应带来不便。讨论了非线性阻尼项对一般桥梁桩、墩结构地震反应的贡献,得到的结论是阻尼项的贡献很小,可以忽略。从而水中桥梁地震反应的计算就得到了很大的简化。     

基于粘滞阻尼器的元江大桥减震设计方案

为了提高大跨度桥梁的抗震性能水平,基于粘滞阻尼器的结构减震控制技术成为专家学者研究的重点和工程设计人员首先考虑的抗震设防措施。现有成果主要集中在大跨度公路斜拉桥的研究和应用,在山区的非规则高墩钢桁连续梁桥研究的较少。以云南省元江大桥为例,采用Midas/civil建立弹性分析的有限元模型,对元江大桥进行了动力特性分析。采用快速非线性时程分析方法对粘滞阻尼器参数进行了优化分析,并且总结了粘滞阻尼器参数对高墩连续梁桥的减震作用规律。最后,通过有控和无控结构的地震动响应对比分析,评价了安装阻尼器后的结构主控部位的减震效果。结果表明:减震控制提高了结构的安全性。     

双座串联大跨度斜拉桥粘滞阻尼器参数分析

以双座串联大跨度斜拉桥-珠海洪鹤大桥为背景,根据桥梁自振特性及场地效应,生成了三组人工波,采用纵向+2/3竖向的地震作用组合输入方式,通过非线性时程分析,系统的研究了粘滞阻尼器对双座串联大跨度斜拉桥减震性能的影响。同时为了确定粘滞阻尼器的最优参数,对粘滞阻尼器的阻尼系数C和速度指数α进行了参数敏感性分析。结果表明:设置纵向粘滞阻尼器能够显著减小双座串联斜拉桥的纵向位移响应,减小主梁在串联处发生碰撞的概率,同时改善主塔塔底结构受力情况,具有良好的耗能减震效果。综合考虑安全性、适用性和经济性等方面,最后给出针对洪鹤大桥的最优粘滞阻尼器参数:速度指数α为0.3,阻尼系数C为3 000kN/（m/s）^0.3。     

高烈度区深水斜拉桥动水效应及抗震体系研究

位于高烈度区的深水斜拉桥在地震下不仅会受到强震的作用,还会受到附近水体的作用,结构抗震要求高,选择合理的抗震体系非常重要.以云南格巧高速双河特大桥为工程实例,分析动水作用对斜拉桥地震响应的影响及其与地震强度的关系,在此基础上对斜拉桥的纵、横向抗震体系展开研究并给出合理建议.结果表明,动水作用会增大索塔塔底内力和结构整体位移响应,且对剪力的影响最大;动水对结构各响应的放大作用随地震强度增加呈现出增减不一的变化趋势,抗震设计时应分别考虑各级地震下的动水效应;索塔、辅助墩和桥台处均设置黏滞阻尼器等阻尼约束的纵向协同抗震体系能够最有效减小墩、塔底纵向内力及结构纵向位移,建议作为斜拉桥纵向抗震体系; 斜拉桥横向推荐采用索塔处设置固定约束、墩台处设置钢阻尼器等弹塑性约束的组合约束体系,该体系能同时降低墩、塔底横向内力,并有效控制结构整体横向位移响应.     

Ambient vibration survey of the fatih sultan mehmet (second Bosporus) suspension bridge

Ambient accelerations due to dynamic excitation by wind and traffic were measured on the deck, towers, cables and hangers of the Fatih suspension bridge. From these measurements it was possible to obtain natural frequencies, mode shapes and damping ratios for vertical, lateral, torsional and associated modes in the deck and tower up to a maximum of 2 Hz. The objective of the test was to validate the mathematical modelling used in seismic analyses of the bridge. The agreement between the experimental and theoretical modes was acceptable for vertical modes below 1 Hz, and for torsional modes, but it was difficult to identify the lateral modes due to low levels of response. The dynamic behaviour of this bridge and two other major European suspension bridges is discussed in relation to the differences in loading and structural design.     

斜拉桥地震破坏的计算研究

地震曾破坏了大量的桥梁结构。然而，尽管目前世界上斜拉桥数目正以指数函数规律增长，但还没有任何斜拉桥经历过强地震，斜拉桥可能的地震破坏形式、破坏机理还是一个有待探索的领域。本文对本世纪几次大地震中严重破坏的桥梁进行损坏部分的震害原因分析，总结出一般桥梁结构地震破坏机理及破坏形式。利用大型结构分析程序ＭＳＣ／ＮＡＳＴＲＡＮ，对斜拉桥地震反应特征进行了分析，并在综合考虑结构地震反应的三维性、行波效应、非     

Effects of ground motion spatial variability on the response of cable-stayed bridges

In order to extend our knowledge of the performance of long-span bridges under earthquake loading the effects of spatial variability of ground motion on the structural response of cable-stayed bridges are studied; the result can be useful to practising bridge engineers. The multiple-support excitation analysis is described, and two three-dimensional models representing the modern and future trends in cable-stayed bridge design are utilized to shed some light on salient features of the seismic response characteristics of these modern bridges. In addition, models of steel- and concrete-design alternates of an existing bridge are considered. Differential ground motion records (obtained from dense instrument arrays) are used as synchronous and non-synchronous support motions; in addition, non-dispersive seismic waves travelling along the bridge are considered. The bridge response to non-uniform ground motion is compared to its response to uniform input. An overview of the unique dynamic characteristics of these cable-supported bridges is also presented. Finally, the study, which was used in the seismic design of several existing cable-stayed bridges in U.S. and Canada, indicates that the response quantities may increase substantially from the non-uniform input ground motion, especially for more rigid bridges and for bridges having different dynamic properties of the local soils at the supporting points, but the degree of increase depends upon the specific problem, in particular upon the aspects of span length, rigidity and structural redundancy. Thus, the response to non-uniform input ground motion should be examined for these bridges.     

Non-linear earthquake-response analysis of long-span cable-stayed bridges: Applications

The dynamic non-linear behaviour of three-dimensional long-span cable-stayed bridges under seismic loadings is studied. The cases of multiple-support as well as uniform seismic excitations of these long and flexible structures are considered. Different sources of non-linearity for such bridges are included in the analysis, as outlined in the companion paper. In this accompanying analysis a tangent stiffness iterative procedure is utilized to estimate the non-linear seismic response. Numerical examples are presented in which a comparison between a linear earthquake-response analysis (based on the utilization of the tangent stiffness matrix of the bridge at the dead-load deformed state which is obtained from the geometry of the bridge under gravity load conditions) and a non-linear earthquake response analysis using the step-by-integration procedure is made. In these examples two three-dimensional bridge models representing recent and future trends in cable-stayed bridge design are utilized. The study sheds some light on the salient features of the seismic analysis and design of these long contemporary bridges. In addition, parameters affecting the seismic response of these bridges are discussed: other factors considered are non-linearity, uniformity and spatial variation of ground motion inputs and structural configuration.     

Effects of seismic isolation on the seismic response of a California high‐speed rail prototype bridge with soil‐structure and track‐structure interactions

With the launch of the high‐speed train project in California, the seismic risk is a crucial concern to the stakeholders. To investigate the seismic behavior of future California High‐Speed Rail (CHSR) bridge structures, a 3D nonlinear finite‐element model of a CHSR prototype bridge is developed. Soil‐structure and track‐structure interactions are accounted for in this comprehensive numerical model used to simulate the seismic response of the bridge and track system. This paper focuses on examining potential benefits and possible drawbacks of the a priori promising application of seismic isolation in CHSR bridges. Nonlinear time history analyses are performed for this prototype bridge subjected to two bidirectional horizontal historical earthquake ground motions each scaled to two different seismic hazard levels. The effect of seismic isolation on the seismic performance of the bridge is investigated through a detailed comparison of the seismic response of the bridge with and without seismic isolation. It is found that seismic isolation significantly reduces the deck acceleration and the force demand in the bridge substructure (i.e., piers and foundations), especially for high‐intensity earthquakes. However, seismic isolation increases the deck displacement (relative to the pile cap) and the stresses in the rails. These findings imply that seismic isolation can be promisingly applied to CHSR bridges with due consideration of balancing its beneficial and detrimental effects through using appropriate isolators design. The optimum seismic isolator properties can be sought by solving a performance‐based optimum seismic design problem using the nonlinear finite‐element model presented herein. Copyright © 2016 John Wiley & Sons, Ltd.     

大跨度斜拉桥横桥向减震研究

斜拉桥在横桥向采用塔-梁、墩-梁固结的约束体系,导致其整体刚度增加,地震惯性力增大,给边墩及其基础的抗震设计造成困难。分别采用位移相关型(方案1)和速度相关型(方案2)两类减震装置对一座斜拉桥的横桥向进行了减震研究。方案1在边墩-主梁间设置位移相关型减震装置,并对其屈服荷载进行了参数分析;方案2对速度相关型减震装置的安装位置和数量进行了优化分析,并对其参数取值进行了参数分析;对横桥向固结体系和减震体系的地震反应进行了对比。结果表明:地震作用下两类减震装置发生滞回变形,延长了结构在横桥向的周期,有效降低了边墩的地震剪力和弯矩反应;横桥向墩-梁间的相对位移会增大,可通过减震装置参数的选取将其控制在合理的范围内;塔底的地震剪力和弯矩反应变化不明显。2种方案均可用于斜拉桥横向减震。     

Vehicle effects on seismic response of a simple‐span bridge during shake tests

Presence of vehicles on a bridge has been observed many times during past earthquakes. Although in practice, the engineers may or may not include the live load contribution to seismic weight in design, current bridge design codes do not specify a certain guideline. A very limited research has been conducted to address this issue from design point of view. The focus of this research is to experimentally assess the effect of a vehicle on the seismic response of a bridge through a large‐scale model. In this scope, a 12‐meter long bridge, having a one lane deck with concrete slab on steel girders, has been shaken under five different ground motions obtained from recent earthquakes that occurred in Turkey, in its transverse direction, both with and without a vehicle on top of the deck. The measured results have indicated that top slab transverse acceleration and bearing displacements can reduce up to 18.7% in presence of a vehicle during seismic tests, which is an indication of reduction in substructure forces. The main reason for the reduction in seismic response of the bridge in the presence of live load can be ascribed to the increase in damping of the system due to mass damper‐like action induced by the vehicle. This beneficial effect cannot be observed in vertical seismic response. Copyright © 2014 John Wiley & Sons, Ltd.