城市桥梁地震碰撞反应研究与发展

地震时城市桥梁会因邻跨之间的碰撞而发生灾害.本文从桥梁碰撞的模拟模型、发生条件、影响因素、碰撞对桥梁抗震性能的影响以及防止碰撞的措施等方面,对国内外有关城市桥梁碰撞地震反应研究的成果进行了系统的总结和分析,得出以下结论：桥梁碰撞是多因素共同作用所导致的,并使得桥梁的地震反应更加复杂、呈现非线性;要准确评价桥梁地震碰撞反应需要建立更精确的模拟模型;选择合理的邻跨间距和支座宽度以及安装合适的消能减震装置,可有效地减小桥梁的地震碰撞反应.     

地震作用下隔震简支梁桥碰撞反应的振动台试验

由地震引发的碰撞是影响桥梁地震反应以及造成桥梁破坏的重要因素。本文对地震作用下隔震简支梁桥的碰撞反应进行了振动台试验。设计制作1个两跨简支的隔震梁桥模型,试验研究了梁间隙、邻梁质量比、隔震支座类型等参数对桥梁碰撞反应的影响。试验结果表明邻梁间隙、邻梁质量比、隔震支座类型等参数对桥梁的碰撞反应有着显著的影响。邻梁间隙越大,碰撞次数越少;邻梁质量比越大,撞击力越大。铅芯橡胶支座比板式橡胶支座耗能能力更强,可以有效降低邻梁之间的撞击力甚至避免碰撞发生。从而为桥梁防碰撞设计提供了可靠的试验依据。     

地震作用下公路桥梁碰撞的半主动控制研究

针对地震作用下公路桥梁的碰撞问题,采用接触单元法模拟桥梁之间的碰撞作用,并在此基础上研究了采用磁流变阻尼器的公路桥梁碰撞的半主动控制方法。通过对某公路桥梁的数值模拟发现,地震作用下桥梁之间的相互碰撞,将大幅增加桥梁的绝对加速度响应。采用磁流变阻尼器的半主动控制系统能够较好地降低结构的地震响应和消除地震作用下的碰撞。     

空间多点地震作用下桥梁结构碰撞响应振动台试验研究

地震造成的桥梁上部结构碰撞及落梁破坏在历次大地震中基本都能观察到,以往的研究大多数局限于地震作用下桥梁碰撞响应的数值模拟研究,相关的试验研究还不多。此外,这些研究中也少有考虑空间多维多点地震动作用引起的桥梁上部结构更大的异向振动。本文采用振动台台阵系统,对空间多维多点地震作用下相邻桥梁结构碰撞响应进行试验研究。试验设计制作了几何缩尺比为1∶6的桥梁模型,研究比较了空间多点激励以及摇摆基础与固定基础两种基础形式对试验模型地震碰撞响应的影响。介绍了试验模型的设计制作、传感器布置,给出了试验结果及模型桥梁碰撞破坏情况。试验结果表明,地震动的空间变异性不能忽视,较大的碰撞力会引起桥梁伸缩缝处混凝土严重的局部破坏,相比于固定基础,摇摆基础能有效降低墩的破坏程度,但提高了上部结构的碰撞及落梁风险。     

行波输入下连续梁桥纵向墩梁相对位移碰撞效应分析

结合多跨连续梁桥的结构特点,提出了一种能模拟联间碰撞行为的连续梁桥碰撞分析模型.用非线性时程方法对行波输入下连续梁桥的地震碰撞反应进行了参数分析.结果表明:相邻联的周期比对短周期联位移的碰撞效应较大,考虑地震行波输入时伸缩缝处的碰撞效应可能会大幅度增大墩梁的相对位移,从而增大了地震作用下发生落梁的风险;墩梁相对位移随滑动支座摩阻系数的增大而减小.最后提出用一个碰撞效应增大系数来考虑连续梁桥相互碰撞对墩梁相对位移的影响,利用碰撞效应增大系数的概念为连续梁桥防止落梁的设计提供了一个新的思路.     

地震作用下简支梁桥非线性碰撞分析

采用能量原理建立了能考虑梁薄壁特性的桥梁上部结构梁段单元动力分析模型,利用非线性接触单元Kelvin碰撞模型,考虑非线性支座的滞回特性(采用W en模型),选择适合不同场地条件的地震波,以京港澳高速公路孟姜女河桥(3跨简支梁桥)为例,进行了桥梁结构纵向碰撞非线性地震响应分析。计算结果表明,随着地震波强度的增加,桥梁上部结构碰撞次数明显增加,结构响应峰值均有所增大;跨间碰撞发生对地震响应值影响较大;伸缩缝间距大小及各跨长度比变化对跨间碰撞效应影响很大;结构碰撞响应对输入地震波具有较强的频谱敏感性;桥梁碰撞计算时桥台铅芯橡胶支座不能简单按简支约束处理。所得结论可供桥梁抗震设计参考。     

高架桥梁的地震碰撞和落梁分析及其控制

高架桥梁是城市交通网络的连接枢纽,在国内外历次大地震下高架桥梁都遭受了严重破坏。本文针对高架桥梁在地震作用下的碰撞和落梁,阐述了一维纵向碰撞以及扭转碰撞分析中所涉及的相关问题,并针对高架桥梁碰撞的磁流变阻尼器(MR)半主动控制以及采用形状记忆合金(SMA)限位器的落梁控制进行了研究。     

地震作用下桥梁防碰撞及防落梁措施研究综述

桥梁作为生命线工程的重要组成部分,一旦在地震中发生破坏,会造成巨大的经济损失和社会损失。地面上相邻的桥跨结构由于其动力特性存在差异及地震动输入的空间变化特性,地震发生时会引起相邻桥跨间的非同向振动,当桥跨间预留的间隙不能满足彼此的相对位移时就会发生相互碰撞,间隙过大时很容易引起落梁。针对相邻桥跨间的碰撞和落梁问题,对历次大地震中与碰撞和落梁相关的震害进行了回顾,介绍了纵桥向各种防碰撞与防落梁措施的研究现状,主要包括限位器、阻尼限位装置、模数式伸缩缝、减震装置以及组合限位装置五个方面。同时通过对研究现状的分析对以上各种防碰撞与防落梁措施的优点和缺点分别进行总结,进而对有待进一步研究的问题进行了展望。     

人字形曲线梁桥振动台试验研究

为研究人字形曲线桥梁在地震输入下的地震反应特性,按1/20的几何比例设计制作了一座人字形曲线桥模型,进行了单向和多向输入下的振动台试验。研究了人字形桥梁结构在地震作用下的震害现象,以及多向输入对梁跨中及邻梁碰撞响应的影响。结果表明:梁体和桥墩主要表现为以弯曲裂缝为主的破坏模式,墩梁相对位移随着地震烈度的增大而增大;梁跨中加速度响应在三向和双向输入下都较单向输入为大,双向和三向输入都会使邻梁间的相对位移较单向输入时增大,更容易使结构发生碰撞;人字形桥梁结构地震响应不但与地震波输入方向有关,且与输入地震波的频谱特性和结构的形式及自身特性有关。     

地震序列下落梁震害的防灾设计分析

地震的发生具有丛集的特征,主震发生之后通常伴随余震,主震震级越高其余震震级亦越高,对结构的破坏越大.桥梁结构作为重要交通枢纽工程,其在整个地震序列发生时应能确保通行.为得到桥梁结构在地震系列作用下的响应,选用集集地震序列对桥梁进行地震响应分析,结果显示结构在主震作用下发生落座,余震时有发生落梁的可能,对结构设置连梁装置,验证其在地震序列中的防落梁效果.结果显示连梁装置可有效减小桥梁上、下部结构相对位移,同时可提高结构整体性,使各桥墩平均分配地震力,并能在地震序列中有效防止落梁震害的发生.     

高墩梁桥的地震冲撞效应及其应对策略初探

国内外多次地震表明了高墩桥梁的地震冲撞破坏现象,针对目前国内大量兴建的高墩梁桥,有必要研究高墩梁桥地震冲撞效应和减轻桥梁地震冲撞破坏的应对策略。本文根据高烈度震区的1座高墩梁桥建立全桥的空间有限元模型,并在墩-梁结合部伸缩缝处采用非线性接触单元模拟相邻梁间的冲撞行为,同时考虑了下部支座的影响;考虑不同的强震动输入,采用非线性时程分析方法,研究了高墩梁桥的地震冲撞效应及减轻冲撞的有效措施。研究结果表明:本文采用的冲撞力学模型能够合理地模拟地震作用下结构的冲撞现象;冲撞行为对结构的地震反应影响复杂;地震动特性对冲撞效应影响显著;调整伸缩逢宽度或设置弹簧-阻尼限位装置可有效缓解结构间的冲撞效应。     

考虑支座摩擦滑移及结构碰撞的非规则人字形桥梁地震响应分析

针对非规则人字形桥梁在地震作用下灾变严重的问题,以一座非规则人字形桥梁为研究对象,建立其空间分析模型,研究综合考虑支座摩擦滑移、结构碰撞对非规则人字形桥梁地震响应的影响。结果表明:邻梁间的碰撞作用可使得桥梁墩顶位移及内力相比不考虑时有所减小,但同时也使梁体产生了较大的加速度脉冲效应;当考虑支座摩擦滑移和结构碰撞时,固定墩墩顶位移和邻梁相对位移峰值有一定程度增大,然而对梁体加速度脉冲效应结果影响并无统一规律;纵向地震波作用下,非规则人字形桥梁不仅存在顺桥向的碰撞,横桥向的碰撞响应也不容忽视。非规则人字形桥梁进行抗震设计计算时应选取符合实际情况的计算模型,考虑支座摩擦滑移及结构间的碰撞。     

Implications of seismic pounding on the longitudinal response of multi-span bridges-an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes. The consequences of pounding include damage to piers, abutments, shear keys, bearings and restrainers, and possible collapse of deck spans. This paper investigates pounding in bridges from an analytical perspective. A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior, to study the seismic response to longitudinal ground motion. Pounding is implemented using the contact force-based Kelvin model, as well as the momentum-based stereomechanical approach, Parameter studies are conducted to determine the effects of frame period ratio, column hysteretic behavior, energy dissipation during impact and near source ground motions on the pounding response of the bridge. The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7. Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact, especially for elastic behavior of the frames. Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion. Finally, it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records.     

Implications of seismic pounding on the longitudinal response of multi-span bridges - an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes. The consequences of pounding include damage to piers, abutments, shear keys, bearings and restrainers, and possible collapse of deck spans. This paper investigates pounding in bridges from an analytical perspective. A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior, to study the seismic response to longitudinal ground motion. Pounding is implemented using the contact force-based Kelvin model, as well as the momentum-based stereomechanical approach. Parameter studies are conducted to determine the effects of frame period ratio, column hysteretic behavior, energy dissipation during impact and near source ground motions on the pounding response of the bridge. The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7. Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact, especially for elastic behavior of the frames. Representation of stiffness degradation in bridge columns is cssential in capturing the accurate response of pounding frames subjected to far field ground motion. Finally, it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records.     

Experimental study of a highway bridge with shape memory alloy restrainers focusing on the mitigation of unseating and pounding

This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study.     

Reduction of pounding effects in elevated bridges during earthquakes

Pounding of adjacent superstructure segments in elevated bridges during severe earthquakes can result in significant structural damage. The aim of this paper is to analyse several methods of reduction of the negative effects of collisions induced by the seismic wave propagation effect. The analysis is conducted on a detailed three‐dimensional structural component model of an isolated highway bridge. The results show that the influence of pounding on the structural response is significant in the longitudinal direction of the bridge and significantly depends on the gap size between superstructure segments. The smallest response can be obtained for very small gap sizes and for gap sizes large enough to prevent pounding. Further analysis indicates that the bridge behaviour can be effectively improved by placing hard rubber bumpers between segments and by stiff linking the segments one with another. The experimental results show that, for the practical application of such connectors, shock transmission units can be used. Copyright © 2000 John Wiley & Sons, Ltd.     

Modelling three‐dimensional non‐linear seismic performance of elevated bridges with emphasis on pounding of girders

Unseating of bridge girders/decks during earthquakes is very harmful to the safety and serviceability of bridges. Evidence from recent severe earthquakes indicates that in addition to damage along longitudinal direction, lateral displacement and rotation of bridge girders caused by pounding to adjacent girders can also lead to unseating. To simulate this effect, 3D modelling of the dynamic performance of whole bridge structures, including pounding, is needed strongly. This paper presents a 3D model that is practically suitable to precisely analyse pounding between bridge girders. Experiments have been conducted to verify the proposed pounding model. The 3D non‐linear modelling of steel elevated bridges is also discussed. A general‐purpose dynamic analysis program for bridges, namely dynamic analysis of bridge systems (DABS) has been developed. Seismic analyses on a chosen three‐span steel bridge are conducted for several cases including pounding as a case study. The applicability of the proposed pounding model is illustrated by the computations. The effects of poundings on the response of bridge girders are discussed and the computation results are given. Copyright © 2002 John Wiley & Sons, Ltd.