Effect of near-fault earthquake on bridges: lessons learned from Chi-Chi earthquake

The objective of this paper is to describe the lessons learned and actions that have been taken related to the seismic design of bridge structures after the Chi-Chi, Taiwan earthquake. Much variable near-fault ground motion data was collected from the rupture of Chelungpu fault during the Chi-Chi earthquake, allowing the seismic response of bridge structures subjected to these near-fault ground motions to be carefully examined. To study the near-fault ground motion effect on bridge seismic design codes, a two-level seismic design of bridge structures was developed and implemented. This design code reflects the near-fault factors in the seismic design forces. Finally, a risk assessment methodology, based on bridge vulnerability, is also developed to assist in decisions for reducing seismic risk due to failure of bridges. Director of Center for Research on Earthquake Engineering. Supported by: the Science Council, Chinese Taipei, under grant no. SC 90-2211-E-002-028.     

A comparative study between China and U.S. on seismic design philosophy and practice of a long span arch bridge

This paper presents the first of a series of case studies on the seismic design of long span bridges （cable-stayed bridges, suspension bridges and arch bridges） under a cooperative research project on seismic behavior and design of highway bridges between the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University and the Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo. The objective of this series of case studies is to examine the differences and similarities on the seismic design practice of long span bridges in China and the U.S., to identify research needs and to develop design guidelines beneficial to bridge engineers in both countries. Unlike short to medium span bridges, long span bridges are not included in most seismic design specifications, mainly because they are location dependent and structurally unique. In this paper, an available model of a steel tied half through arch bridge with a main span of 550m in China is discussed. Analysis is focused on comparisons of the seismic responses due to different ground motions. Seismic design criteria and seismic performance requirements for long span bridges in both countries were first introduced and compared, and then three near field earthquake records with large vertical components were selected as the excitations to examine the seismic behavior and seismic vulnerability of the bridge. Results show that （1） the selected near field ground motions cause larger responses to key components （critical sections） of the bridge （such as arch rib ends） with a maximum increase of more than twice those caused by the site specific ground motions; （2） piers, longitudinal girders and arch crowns are more vulnerable to vertical motions, especially their axial forces; and （3） large vertical components of near field ground motions may not significantly affect the bridge＇s internal forces provided that their peak acceleration spectra ordinates only appear at periods of less than 0.2s. However, they may have more influence on the longitudinal displacements of sliding bearings due to their large displacement spectra ordinates at the fundamental period of the bridge.     

胜利黄河公路大桥震害预测研究

桥梁是生命线工程的重要组成部分,对桥梁作出符合实际的震害预测意义重大。以胜利黄河公路大桥为例,介绍了经验统计法、规范校核法、Push-over方法、大跨度桥梁定性和定量分析等桥梁震害预测方法。分别用Push-over(推倒分析)法和大跨度桥梁定性与定量相结合的震害预测方法对胜利黄河公路大桥进行了震害预测评价。     

铁路梁式桥地震灾害损失评估

针对铁路桥梁地震灾害评估中多因素影响问题,结合铁路桥梁地震灾害的复杂特点和各结构层次的震害表现形式,从桥面系、上部结构和下部结构3个方面构建铁路梁式桥地震灾害评估指标体系.基于改进的层次分析法计算了各评估指标的权重,以桥梁承灾系统为研究主体,运用多级综合模糊理论,建立铁路梁式桥震害评估模型.结合汶川地震中一座铁路混凝土...     

近断层地震动作用下钢筋混凝土桥墩的抗震性能

通过对满足规范延性要求的12根典型钢筋混凝土桥墩试件的线性和非线性地震反应分析，指出在近断层地震动作用下满足延性需求与延性能力比小于1.0的桥墩仍可能发生严重破坏和倒塌，若考虑桥墩的地震损伤性能，允许的延性需求与延性能力比不宜超过0.6-0.8。讨论了桥墩延性抗震设计中强度折减系数Rμ和设计基底剪力系数BSC取值问题。     

Enhancing resilience of highway bridges through seismic retrofit

The present study evaluates seismic resilience of highway bridges that are important components of highway transportation systems. To mitigate losses incurred from bridge damage during seismic events, bridge retrofit strategies are selected such that the retrofit not only enhances bridge seismic performance but also improves resilience of the system consisting of these bridges. To obtain results specific to a bridge, a reinforced concrete bridge in the Los Angeles region is analyzed. This bridge was severely damaged during the Northridge earthquake because of shear failure of one bridge pier. Seismic vulnerability model of the bridge is developed through finite element analysis under a suite of time histories that represent regional seismic hazard. Obtained bridge vulnerability model is combined with appropriate loss and recovery models to calculate seismic resilience of the bridge. Impact of retrofit on seismic resilience is observed by applying suitable retrofit strategy to the bridge assuming its undamaged condition prior to the Northridge event. Difference in resilience observed before and after bridge retrofit signified the effectiveness of seismic retrofit. The applied retrofit technique is also found to be cost‐effective through a cost‐benefit analysis. First order second moment reliability analysis is performed, and a tornado diagram is developed to identify major uncertain input parameters to which seismic resilience is most sensitive. Statistical analysis of resilience obtained through random sampling of major uncertain input parameters revealed that the uncertain nature of seismic resilience can be characterized with a normal distribution, the standard deviation of which represents the uncertainty in seismic resilience. Copyright © 2013 John Wiley & Sons, Ltd.     

设置负刚度装置的大跨长联连续梁桥地震反应分析

为完善大跨长联连续梁桥的减震和隔震技术,提出将负刚度装置引入某带有摩擦摆支座隔震的大跨长联连续梁桥中组成新型减震和隔震系统。基于CSIBridge软件建立全桥有限元模型,负刚度装置采用弹性多段线模拟,摩擦摆支座采用双线性恢复力模型,输入7条地震波进行了非线性时程分析,考查了新型减震和隔震系统下桥梁结构的地震反应,探究了负刚度系统对大跨长联隔震连续梁桥地震反应的影响。研究结果表明：在大跨长联隔震连续梁桥上布置负刚度装置后,梁体加速度及支座位移可被有效降低,近场地震动下的墩底内力也有明显减小。负刚度装置可有效提高大跨长联摩擦摆支座连续梁桥的抗震性能,负刚度装置也适用于大跨长联隔震连续梁桥。     

Numerical simulations of a highway bridge structure employing passive negative stiffness device for seismic protection

A new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

海底地震动作用下近海桥梁地震响应研究

以某近海大桥引桥段连续梁桥为工程背景,建立考虑海底地震动特性和腐蚀效应的近海桥梁地震反应分析模型。采用增量动力分析方法分析腐蚀效应以及海底地震动作用对近海桥梁地震响应的影响。研究结果表明:腐蚀效应与海底地震动作用都会不同程度影响近海桥梁结构的抗震性能。其中:腐蚀效应会增大近海桥梁的破坏指标,降低最大墩底剪力和弯矩值,从而降低桥梁的抗震性能;海底地震动作用会增大近海桥梁的破坏指标及最大墩底剪力、弯矩值;在2种因素耦合作用下,桥梁的抗震性能将会进一步降低。     

考虑竖向地震作用的拱式廊桥的地震响应分析

本文以某大型商业拱式廊桥工程实例为依托,利用有限元软件分别建立了整桥模型和不考虑上部建筑结构的桥梁模型以及不考虑下部桥梁结构的建筑模型,并计算了各自的自振动力特性,在此基础上通过反应谱方法分析了同时考虑水平地震作用和竖向地震作用的廊桥主拱圈和上部建筑结构柱的地震响应以及不同模型计算结果的差异,以此研究桥梁结构与建筑结构的耦合作用,为廊桥的抗震设计或分析提供一定的参考依据。     

多维地震输入下曲线匝道桥梁伸缩缝碰撞响应

针对曲线匝道桥梁伸缩缝地震碰撞破坏现象,依托某市多层互通式立交体系中一座独立、单支、多联、曲线、箱梁匝道桥,用Kelvin接触单元模拟了伸缩缝处地震和碰撞效应,建立了全桥空间动力分析模型。利用非线性时程分析法,分别输入单维(X方向、Y方向)和多维共8种地震动工况,分析了曲线匝道桥梁伸缩缝的地震碰撞响应差异。结果表明:曲线匝道桥梁由于曲率的影响,不同方向地震动响应存在耦合效应,其伸缩缝碰撞响应的最不利值应考虑多维地震输入工况,并用碰撞力和碰撞位移双指标控制伸缩缝的地震碰撞响应。     

在役公路梁式桥综合震害等级预测研究

为客观预测在役公路梁式桥综合震害状况,考虑在役桥梁在运营期存在的病害问题,从压力和承压两方面建立在役公路梁式桥综合震害预测评价指标体系。以桥梁作为承灾体,建立在役公路梁式桥综合震害物元可拓模型,运用熵权法进行赋权,确定桥梁的综合震害状况。以一座在役梁式桥为例,运用上述模型确定算例的综合震害状况。研究结果表明,该桥的综合震害等级为Ⅲ级,破坏等级中等,且根据结果分析影响桥梁震害程度的主要影响因素;该模型通过对多个指标关联系数的综合分析来评价在役梁式桥的综合震害等级,极大地提高了该模型评估的准确率及可靠性,为桥梁震害等级的预测提供一定的参考,对提升桥梁综合抗震能力具有积极意义。     

大跨径钢筋混凝土拱桥抗震性能分析

结合跨径220米的许沟大桥结构设计,通过对全桥有限元模型动力分析和通车动载试验,对钢筋混凝土拱桥全桥动力特性进行分析,并选用50年超越概率为3%的人工地震波和E l Centro波(调整至7度)进行时程分析。根据抗震分析的结果分析控制截面地震内力,并结合通车动载试验结论,对许沟大桥抗震性能做出综合评价,对大跨径钢筋混凝土拱桥抗震设计提出合理建议。     

大跨度桥梁结构多级地震响应研究

大跨度桥梁结构在地震发生时其支承点受到的地震动激励均不相同,使得在多级地震中其桥梁结构对于地震的响应程度也不同。通过分析多级地震作用下,水中结构的运动引起桥梁墩部周围水体辐射波浪运动对桥梁结构的影响,分析大跨度桥梁墩-水耦合边界。基于反应谱理论,计算大跨度桥梁结构承受的地震力最大值,得出多级地震响应曲线,以分析其多级地震响应;并以某地六跨桥为例,以多级地震下桥梁的位移、剪力、弯矩等响应时程为指标进行分析,得出有效结论。     

高强钢筋ECC-RC复合桥梁地震易损性分析

考虑高强钢筋、ECC等高性能材料在桥梁工程中的推广应用,针对普通钢筋混凝土桥墩抗震性能相对较差的情况,研究高强钢筋ECC-RC复合桥墩的桥梁抗震性能。通过OpenSees平台建立普通RC桥墩桥梁、ECC-RC复合桥墩桥梁及高强钢筋ECC-RC复合桥墩桥梁非线性有限元模型,采用增量动力法和"能力需求比"分析方法建立桥梁各构件及系统的地震易损性曲线,探讨高强钢筋及ECC对桥梁抗震性能的影响。研究表明:ECC-RC、高强钢筋ECC-RC复合桥墩及其桥梁系统的地震易损性均有改善,且高强钢筋ECC的改善效果更显著,高强钢筋ECC-RC复合桥墩支座的地震易损性有所降低,高强钢筋及ECC的应用有助于提高桥墩和桥梁系统抗震性能和安全性,特别是在中震及大震作用下这一现象更加明显。     

大跨度斜拉桥地震响应非线性时程分析

以有限元分析理论为基础,结合某大跨度斜拉桥工程实例,利用ANSYS软件建立有限元模型,通过修正后的El Centro波分别考虑横向、竖向及纵向输入,采用时程分析方法对其进行地震反应分析.计算分析表明:考虑几何非线性后,结构的内力和位移响应明显增大,且对主梁和索塔内力与位移的影响程度及规律也不尽相同,须区别对待分析.同时表明该桥抗震性能良好,地震荷载不控制设计.由此得出结论,对于斜拉桥这类柔性体系, 不可忽视结构几何非线性的影响.     

地震动空间效应对大跨度桥梁非线性地震响应的影响

由于大跨度桥梁的桥墩间距离较大,其地震响应分析应考虑地震动输入的空间效应。本文建立了多点激励下大跨度桥梁地震响应分析方法,采用损伤塑性本构模型模拟混凝土材料特性,考虑地震动空间效应对大跨度连续刚构桥进行非线性地震响应分析,从而分析地震动空间效应对大跨度桥梁地震响应的影响。研究表明:考虑行波激励或多点激励时桥梁地震响应较一致激励而言有所差异,考虑地震动空间效应时可能会夸大或减小桥梁结构的动力响应;多点激励时桥梁地震响应会随视波速的改变而变化。由此得出结论,对于大跨度桥梁地震响应分析应合理的考虑地震动空间效应。     

考虑冲刷作用效应桥梁桩基地震易损性分析

冲刷造成桩周土体的剥蚀将会削弱土体对桩基的侧向支撑能力,冲刷效应会对桥梁桩基的地震易损性产生影响,因此有必要对冲刷和地震共同作用下桥梁桩基的易损性进行研究。利用SAP2000软件建立三维桥梁有限元模型,通过非线性时程分析得到桥梁桩基地震响应峰值。采用概率性地震需求分析方法,建立不同冲刷深度下桥梁桩基地震易损性模型,在地震易损性函数假设为对数正态分布函数的基础上,通过回归分析得到概率模型中的参数,进而得到不同冲刷深度下桥梁桩基在不同破坏状态所对应的地震易损性曲线,并分析冲刷深度对桩基破坏概率的影响。研究结果表明:随着冲刷深度的增加,桥梁桩基在地震作用下的破坏概率显著增加。     

5跨连续中承式钢管混凝土拱桥抗震性能分析

钢管混凝土拱桥由于桥型优美在城市桥梁中得到广泛应用,对某正在设计的5跨连续巾承式钢管混凝土拱桥进行了动力特性和抗震性能分析,根据该桥的结构特点,建立了’该桥的空间有限元分析模型,计算桥梁的自振特性,基于反应谱方法计算了该桥在横向、纵向水平地震反应,计算结果表明：该桥拱肋的面外刚度相对较小,在桥梁振动中首先出现拱肋的面外振动;桥梁的竖向振动表现为拱肋与桥面的整体竖向振动,其基频明显比拱肋面外振动大;主拱肋的轴力由横桥向地震动控制,其他内力由纵桥向地震动控制;地震作用对弯矩的影响较大,故主拱的内力计算应考虑地震力的影响;在设计计算中除常规关键点应作为控制点外,内外拱连接处也应作为控制点。计算结果已为该桥的抗震设计提供了参考。