Effect of train dynamics on seismic response of steel monorail bridges under moderate ground motion

This study is intended to investigate the seismic response of steel monorail bridges using three‐dimensional dynamic response analysis. We particularly consider monorail bridge–train interaction when subjected to ground motion that occurs with high probability. A monorail train car with two bogies with pneumatic tires for running, steering and stabilizing wheels is assumed to be represented sufficiently by a discrete rigid multi‐body system with 15 degrees of freedom (DOFs). Bridges are considered as an assemblage of beam elements with 6 DOFs at each node. Modal analysis is used for dynamic response analysis under moderate earthquakes. The seismic response of an advanced monorail bridge that adopts a simplified structural system and composite girders is investigated through comparison with seismic responses of a conventional bridge. The acceleration response of a monorail train is also calculated to investigate the effect of structural types of bridges on the train's dynamic response during earthquakes. Results show that the seismic responses of the advanced bridges are greater than those of the conventional monorail bridge because of the simplified structural system and increased girder weight that is attributable to composite girders of the advanced bridge. Moreover, the train on the advanced bridge shows greater dynamic response than that on the conventional bridge. Observations reveal that the dynamic monorail train system acts as a damper on the monorail bridge. That fact shows that the existing design, which considers a train as additional mass, yields a conservative result. Copyright © 2006 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.     

地震作用下曲线梁桥双向碰撞作用影响分析

碰撞作用直接影响到桥梁不同构件的地震响应,是桥梁抗震研究中一直关注的问题。针对地震作用下曲线梁桥因主梁面内转动而发生主梁与切向桥台和径向挡块碰撞的现象,以1座3跨预应力混凝土连续梁桥为例,采用非线性时程分析方法,对曲线连续梁桥的双向碰撞作用影响进行研究,并分析了不同减撞措施的效果。结果表明:考虑双向碰撞作用后,下部结构响应有明显增加,主梁转动现象变得复杂,曲线梁桥地震响应分析中应通过建立精细化模型来考虑主梁双向碰撞作用的影响;在切向桥台处设置限位拉锁装置能起到较好的减轻双向碰撞作用的影响,以及采用减隔震设计后,减撞效果更明显,桥梁抗震性能明显改善,但合理减撞措施设计参数应结合曲线梁桥约束体系及结构设计参数进行体系分析确定。     

伸缩缝刚度对大跨度悬索桥动力特性的影响

伸缩缝作为大跨度桥梁与引桥之间的重要连接构件,其抗推刚度及可能存在的变异性对主桥及引桥动力特性的影响不可忽略。本文建立了大跨度悬索桥及引桥的有限元模型,采用弹簧单元模拟加劲梁与引桥箱梁之间的伸缩缝,分析伸缩缝刚度对悬索桥及引桥自振特性及其地震响应的影响规律。分析结果表明:伸缩缝刚度对加劲梁的横弯振型、竖弯与纵飘耦合振型的频率有明显的影响;伸缩缝刚度的变化会导致加劲梁与引桥的振型相互耦合,同时这些振型的频率发生相应的突变,当伸缩缝刚度较大时,加劲梁两个竖弯与纵飘的耦合振型解耦成为独立的竖弯和纵飘振型;当引桥与悬索桥加劲梁的纵飘振型发生耦合时,在纵向和竖向地震作用下的悬索桥及引桥的地震响应达到最小。伸缩缝刚度对悬索桥动力特性影响的分析可为悬索桥的模态参数确认、损伤识别、抗震性能分析提供有价值的借鉴。     

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。     

Shaking table tests of a reinforced concrete bridge pier with a low-cost sliding pendulum system

After the occurrence of various destructive earthquakes in Japan, extensive efforts have been made to improve the seismic performance of bridges. Although improvements to the ductile capacities of reinforced concrete (RC) bridge piers have been developed over the past few decades, seismic resilience has not been adequately ensured. Simple ductile structures are not robust and exhibit a certain level of damage under extremely strong earthquakes, leading to large residual displacements and higher repair costs, which incur in societies with less-effective disaster response and recovery measures. To ensure the seismic resilience of bridges, it is necessary to continue developing the seismic design methodology of RC bridges by exploring new concepts while avoiding the use of expensive materials. Therefore, to maximize the postevent operability, a novel RC bridge pier with a low-cost sliding pendulum system is proposed. The seismic force is reduced as the upper component moves along a concave sliding surface atop the lower component of the RC bridge pier. No replaceable seismic devices are included to lengthen the natural period; only conventional concrete and steel are used to achieve low-cost design solutions. The seismic performance was evaluated through unidirectional shaking table tests. The experimental results demonstrated a reduction in the shear force transmitted to the substructure, and the residual displacement decreased by establishing an adequate radius of the sliding surface. Finally, a nonlinear dynamic analysis was performed to estimate the seismic response of the proposed RC bridge pier.     

强震区非对称连续梁桥地震响应及性能评价

为研究高烈度地区不等跨连续梁桥的抗震性能，依托某高速公路上一座主跨为（40+60+35）m的典型不等跨连续梁桥，建立其动力分析有限元模型，获得该桥的模态特性。在E1概率和E2概率两种地震水平作用下，同时采用反应谱分析和时程分析法，对不等跨桥梁结构的地震响应进行分析。最后根据桥墩验算截面的弯矩-曲率关系曲线，探讨该桥梁的抗震性能。研究结果表明：动态时程反应分析与反应谱分析所得的结果基本吻合，由于反应谱分析假定结构线弹性状态而时程反应分析考虑了材料的弹塑性，在E2概率水平下，两者个别响应值有较大差别；由于反应谱法是对各阶模态下最大响应的组合，动态时程反应分析是同一时刻各地震波引起的结构响应的组合，因而时域和频域计算结果会存在一些误差，频域结果偏于保守；E1、E2概率地震作用下，主桥桥墩检算截面仍然在弹性范围内工作，满足弹性设计要求。     

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.     

隔震曲线梁桥不同等级地震的振动特性模拟分析

曲线桥梁抗震特性模拟分析对于曲线桥梁隔震、减震有着重要意义。基于隔震曲线桥梁设计过程中的特点,通过非线性水平弹簧单元对铅芯橡胶支座双向非线性的能力进行模拟,根据SAP2000科学选择强震观测地震波,并考量曲线桥梁本身存在的特性对桥梁振动特性产生的影响,针对隔震曲线桥梁在不同等级地震下振动特征进行模拟分析,其中,通过隔震曲线桥梁铅芯橡胶支座模型的构建和梁桥不同等级地震计算模型、输入地震波与传感器量测等步骤得到的模拟结果为:不同地震波与加速度峰值输入过程中,地震动较小下的支座水平刚度比较大,且结构相对稳定;地震幅值增大时,桥梁支座水平刚度减小,且支座的恢复力位移滞回变化曲线面积比较大,能够更多地将地震输入能量消散掉,减小能量不断向曲线桥梁上方传递的速度,可有效减轻地震反应,起到隔震的效果。     

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,…     

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。     

强震下斜交桥地震反应与减隔震性能分析

针对斜交桥在破坏性地震中发生破坏和损伤的突出问题,采用铅芯橡胶支座(LRB)进行隔震和滞回耗能。基于OpenSees平台建立了不同斜度的传统非隔震和全桥采用LRB隔震的4跨斜交连续梁桥动力分析模型,沿2个水平方向输入远场地震动和具有向前方向性效应、滑冲效应以及无速度脉冲效应的近断层地震动,并进行非线性时程计算,研究桥墩和挡块的损伤状态、主梁旋转度、碰撞力与斜交桥斜度的关系以及LRB对斜交桥抗震性能的影响。结果表明:向前方向性效应和滑冲效应的脉冲型地震动作用下的斜交桥地震反应和损伤明显大于无速度脉冲近断层和远场地震动作用; 采用LRB隔震后,明显降低了固定墩的地震损伤,桥墩位移减震率可达到50%以上; LRB隔震桥主梁与挡块的间隙宜结合桥梁的地震风险和设计位移进行确定。     

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations (PGA). The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.     

A simple non-linear model for the investigation of the effects of the gap closure at the abutment joints of short bridges

Closure of the gap at the abutment joints of bridges has been the source of extensive damage during the 1971 San Fernando and more recent earthquakes. In this paper a model for the investigation of the effects of this gap closure is presented and analysed. The focus of the model is the representation of the non-linear response of the bridge abutments, the foundation and the columns. The model is used for the investigation of the response of a short bridge located in California.     

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。     

高速铁路桥梁-桥墩-桩基础-地基耦合系统的地震反应

高速铁路中的桥梁常采用灌注桩基础以控制沉降,地震作用是桩基础的设计工况之一。建立桥梁-桥墩-桩基础-地基为一体的耦合系统非线性三维数值分析模型,以典型地震波为输入,考虑上部结构和基础的共同工作、土-结构动力相互作用、材料非线性和土层对桩的侧阻及端阻作用,开展三向地震作用下的动力有限元计算,并对地基主要土层压缩模量、桩体材料弹性模量、桩径和桩长进行参数敏感性分析。计算结果表明:现行的桩基础设计方案能有效控制地震荷载作用下桥梁的变形;地震过程中的不同时刻,桩侧阻发挥程度不同且不可忽略,以单纯的梁单元模拟桩的动力学行为的适用性值得商榷;桩长和地基主要土层压缩模量对桥梁地震反应影响最大,桩体材料弹性模量的影响次之,桩径的影响最小。     

Numerical analysis on seismic response of Shinkansen bridge-train interaction system under moderate earthquakes

This study is intended to evaluate the influence of dynamic bridge-train interaction (BTI) on the seismic response of the Shinkansen system in Japan under moderate earthquakes. An analytical approach to simulate the seismic response of the BTI system is developed. In this approach, the behavior of the bridge structure is assumed to be within the elastic range under moderate ground motions. A bullet train car model idealized as a sprung-mass system is established. The viaduct is modeled with 3D finite elements. The BTI analysis algorithm is verified by comparing the analytical and experimental results. The seismic analysis is validated through comparison with a general program. Then, the seismic responses of the BTI system are simulated and evaluated. Some useful conclusions are drawn, indicating the importance of a proper consideration of the dynamic BTI in seismic design.     

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.     

Seismic behavior of a post-tensioned integral bridge including soil–structure interaction (SSI)

Current practice usually pays little attention to the effect of soil–structure interaction (SSI) on seismic analysis and design of bridges. The objective of this research study is to assess the significance of SSI on the modal with geometric stiffness and seismic response of a bridge with integral abutments that has been constructed using a new bridge system technology. Emphasis is placed on integral abutment behavior, since abutments together with piers are the most critical elements in securing the integrity of bridge superstructures during earthquakes. Comparison is made between analytical results and field measurements in order to establish the accuracy of the superstructure–abutment model. Sensitivity studies are conducted to investigate the effects of foundation stiffness on the overall dynamic and seismic response of the new bridge system.     

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.