汶川大地震简支梁桥落梁震害与设计对策

总结了5.12汶川大地震中简支梁桥落梁震害及主要影响因素,发现除地震山体滑坡等地质灾害外,断层地表破裂、近断层地震动效应、桥台胸墙冲切破坏、防落梁构造措施单一及桥梁体型复杂等因素都是引起简支梁桥落梁震害的重要原因。提出了简支梁桥防落梁设计的基本理念及相关技术方案要点为允许墩梁间发生滑移,以降低桥墩承受的地震惯性力,以及盖梁提供允许的最大滑移长度及支座支承宽度,再辅助挡块或拉索限位器等共同防止落梁发生。最后结合现行规范,以拉索限位器为例给出了简支梁桥防落梁设计方法。     

Energy dissipating restrainers for highway bridges

Recent destructive earthquakes have demonstrated the vulnerability of highway bridges to collapse due to excessive movement beyond the available seat widths at expansion joints. This paper investigates the efficacy of using energy dissipating restrainers at expansion joints for preventing collapse of highway bridges in the event of a severe earthquake. The restrainer consists of a nonlinear viscous damper and an elastic spring connected in parallel or in series. Two-dimensional finite element analysis using bilinear hysteretic models for bridge substructure joints and nonlinear gap elements for expansion joints is performed on example bridges with one or two expansion joints. The analytical study demonstrates that the energy dissipating restrainers are effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints, without significantly increasing ductility demands in the bridge substructures.     

Experimental and analytical study on pounding reduction of base‐isolated highway bridges using MR dampers

Pounding between adjacent superstructures has been a major cause of highway bridge damage in the past several earthquakes. This paper presents an experimental and analytical study on pounding reduction of highway bridges subjected to earthquake ground motions by using magnetorheological (MR) dampers. An analytical model, which incorporates structural pounding and MR dampers, is developed. A series of shaking table tests on a 1:20 scaled base‐isolated bridge model are performed to investigate the effects of pounding between adjacent superstructures on the dynamics of the structures. Based on the test results, the parameters of the linear and the nonlinear viscoelastic impact models are identified. Performance of the semiactive system for reducing structural pounding is also investigated experimentally, in which the MR dampers are used in conjunction with the proposed control strategy, to verify the effectiveness of the MR dampers. Structural responses are also simulated by using the established analytical model and compared with the shaking table test results. The results show that pounding between adjacent superstructures of the highway bridge significantly increases the structural acceleration responses. For the base‐isolated bridge model considered here, the semiactive control system with MR dampers effectively precludes pounding. Copyright © 2009 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.     

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。     

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.     

梁桥搁置长度的计算方法比较

梁桥的搁置长度是在桥梁上下部结构之间产生大的相对变位时，为防止上部结构脱落而需要确保的梁端到下部结构边缘的距离。通过修改桥梁参数，对计算梁桥搁置长度的反应谱法和静力法进行对比，分析2种方法产生差异的原因。研究表明，静力法不需考虑桥墩延性系数的变化和阻尼系数的影响，计算简单，适合于设计使用。     

Relative displacement response spectra with pounding effect

To avoid unseating of a deck, an adequate seat width must be provided. The seat width is basically determined from maximum relative displacement between two bridge segments. Under a strong ground excitation, pounding between two decks may occur at a joint. The pounding will affect the response of two bridge segments. This research is conducted to investigate the effect of pounding on the relative displacement between two adjacent bridge segments. A simplified analytical model of two linear single‐degree‐of‐freedom systems is employed. To take into account the pounding, the laws of conservation of momentum and energy are applied. The analytical results are represented in the form of relative displacement response spectra with pounding effect. It is found that due to the pounding the relative displacement can be amplified, resulting in the requirement of a longer seat width to support a deck. The formulation of normalized relative displacement response spectra is presented together with an application example. It is found that the seat width determined from the relative displacement response spectra with pounding effect becomes close to the value specified in the Japanese design specifications for structures with large difference of natural periods. Copyright © 2001 John Wiley & Sons, Ltd.     

Required separation distance between decks and at abutments of a bridge crossing a canyon site to avoid seismic pounding

Major earthquakes in the past indicated that pounding between bridge decks may result in significant structural damage or even girder unseating. With conventional expansion joints, it is impossible to completely avoid seismic pounding between bridge decks, because the gap size at expansion joints is usually not big enough in order to ensure smooth traffic flow. With a new development of modular expansion joint (MEJ), which allows a large joint movement and at the same time without impeding the smoothness of traffic flow, completely precluding pounding between adjacent bridge decks becomes possible. This paper investigates the minimum total gap that a MEJ must have to avoid pounding at the abutments and between bridge decks. The considered spatial ground excitations are modelled by a filtered Tajimi‐Kanai power spectral density function and an empirical coherency loss function. Site amplification effect is included by a transfer function derived from the one‐dimensional wave propagation theory. Stochastic response equations of the adjacent bridge decks are formulated. The effects of ground motion spatial variations, dynamic characteristics of the bridge and the depth and stiffness of local soil on the required separation distance are analysed. Soil–structure interaction effect is not included in this study. The bridge response behaviour is assumed to be linear elastic. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

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。     

Seismic performance of bridges with novel SMA cable-restrained high damping rubber bearings against near-fault ground motions

This study presents a novel type of shape memory alloy (SMA) cable-restrained high damping rubber (SMA-HDR) bearing, which is particularly suited to near-fault (NF) regions where the pulsing effect potentially exists in the ground motions. The working mechanism of the bearing is first described, followed by an experimental investigation on a full-scale SMA-HDR bearing specimen. The test results confirm the efficient restraining effect offered by the SMA cables, which contribute to 65% and 24.4% of the lateral load resistance and total energy dissipation, respectively, prior to the initial fracture of the SMA cables. The failure of the cables is initiated near the end grip where moderate stress concentration exists at this region. Following the experimental study, the numerical modeling strategy for the bearing is discussed, and a case study is then presented, demonstrating the application of the SMA-HDR bearings in the Datianba #2 highway bridge, a real project that first adopts the proposed bearings in the world. A simplified design process is introduced for the bridge with novel SMA-HDR bearings to mitigate the potential damage during strong earthquakes especially the NF ones. The system-level analysis on the prototype bridge shows that the novel SMA-HDR bearings equipped with ten 7×7×1.2 SMA cables in each bearing could reduce the average maximum bearing displacement (MBD) by nearly 30% compared with the conventional bridge with HDR bearings. The application of the novel SMA-HDR bearing can significantly alleviate the pounding effect, especially under the NF earthquakes. The presence of the SMA cables tends to increase the maximum force response of the piers, but this effect is minor and under control.     

形状记忆合金橡胶对高架桥梁碰撞减震效果的试验研究

地震作用下,高架桥梁相邻主梁间的碰撞会引起结构位移和加速度响应增大、应力提高,导致混凝土开裂、脱落和伸缩缝被挤压破坏,甚至引发桥梁落梁和倒塌等,因此采取减轻或者避免桥梁结构在地震作用下碰撞的措施显得尤为必要。设计制备了具有变形自恢复能力的形状记忆合金橡胶碰撞缓冲器,通过桥梁地震碰撞的振动台试验,研究了形状记忆合金橡胶缓冲器对桥梁碰撞的控制效果,提出了碰撞缓冲器吸能效率和结构自身耗能控制率指标。研究表明,形状记忆合金橡胶碰撞缓冲器具有稳定的吸能效率,能够大幅度降低桥梁结构碰撞加速度和碰撞力,这对于提高城市交通网络的地震安全性能具有重要意义。     

Parametric study on performance of bridge retrofitted by unseating prevention devices

1 Introduction Structural retro?t techniques (Roberts, 2005), such as restrainers, concrete shear keys, steel jackets, CFRPshells, base isolators, or dampers have been widely studied and implemented in actual structures based on the experiences learned from past earthquakes. In the Chi-Chi earthquake (EERI, 2001), the damage to simply-supported PCI girder bridges provided a different view from which to examine the function of a rubber bearing system for simply- supported bridges (NCREE,…     

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.     

双向地震作用下互通式斜交桥梁地震响应及碰撞效应分析

斜交桥梁由于其不规则的结构形式使其受力规律与规则桥梁相比具有特殊性和复杂性,在地震作用下梁体的平动与转动存在弯扭耦合效应,导致结构动力响应分析复杂。针对斜交桥梁的结构特点,建立包含桩土相互作用的三维有限元模型,在考虑水平双向地震作用下,采用反应谱法及时程分析法对京包高速公路某互通式斜交桥梁进行地震反应分析。结果表明:互通式简支斜交桥梁的地震响应受地震动输入方向的影响较大,在考虑碰撞效应后,碰撞涉及结构部位的地震位移显著增加,地震内力也出现较大差异,即说明在斜交桥梁抗震设计时有必要适当考虑地震动输入方向和梁端与墩台及相邻梁端的碰撞效应。     

A phenomenological contact‐element model considering slight non‐uniform contact for pounding analysis of highway bridges under seismic excitations

Impact stiffness is an important parameter of the contact‐element models for the analysis and prediction of the pounding responses of highway bridges subjected to seismic excitations. This paper presents a pounding experiment to investigate the inconsistencies between the theoretical and experimental values of the impact stiffness both for the linear impact model and Kelvin impact model presented in literature. The analysis of the impact acceleration and acoustic emission signals indicates that accelerometer performance and the non‐uniform pounding are two important factors that affect the pounding responses. Based on this observation, a phenomenological contact‐element model is proposed based on the actual contact state of highway bridges during the impact. To evaluate the effectiveness of the proposed impact model, a numerical simulation is subsequently conducted. A comparison of the results indicates that the proposed impact model can effectively predict the pounding responses of highway bridges. Copyright © 2015 John Wiley & Sons, Ltd.     

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。     

桥梁限位器抗震设计方法研究

本文建立了两跨简支梁桥和五跨多跨刚架桥两结构模型，针对限位器的种类、刚度、强度、安装位置，输入地震动等进行了大量工况下的数值模拟研究。研究表明限位器与柱（框架）的刚度比在0.5-2之间较优。将现有的限位器设计方法应用于两算例结构，对现有限位器设计方法进行了比较研究。     

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。