铁路钢桥环氧沥青柔性保护层受力控制指标值研究

研究轨道高低动态不平顺引起的列车随机动荷载作用下铁路钢桥柔性保护层的力学行为。采用有限单元法,建立高速列车-轨道-柔性保护层-桥梁耦合体系有限元模型,其中轨道体系采用一次梁(单层)轨道模型和离散支撑体系。将轨道高低不平顺作为列车随机动荷载的激励源输入,通过典型铁路钢桥面系算例分析可见,轨枕两侧、纵肋上方及轨枕下方对应的保护层区域较易出现开裂破坏;钢板和保护层之间较容易发生横向剪切滑移;考虑轨道高低动态不平顺的柔性保护层力学响应明显大于静载计算结果。研究成果表明铁路钢桥柔性保护层设计时应重点考虑轨道随机不平顺的影响。     

考虑轨道不平顺全概率分布的车桥随机分析方法

轨道不平顺是车桥耦合系统最主要的激励之一,其高维的随机性导致车桥耦合确定性计算模型不能精确反映实际系统动力响应的离散性。为了完整地反映实际线路中的轨道不平顺信息,文章建立一种适用于车桥耦合随机系统分析的轨道不平顺随机场模型,模型在包含了轨道谱概率、幅值、波长、相位等信息的基础之上,尽可能地减少了参数数量,通过与实测数据对比,该模型的有效性得以验证。此外,将该轨道不平顺随机场模型作为三维车 线 桥耦合时变计算模型的激励源,引入概率密度演化方法,对该耦合系统动力指标的统计特性及动力可靠度进行分析。结果表明,该轨道不平顺随机分析模型产生的空间序列较好地表征了平稳随机过程的谱表达;概率密度演化方法相对于蒙特卡洛方法有着更高的计算效率;不同的动力指标有着不同的均值、均方差、可靠度特征。     

Impact of track irregularities and damping on the fatigue damage of a railway bridge deck slab

The structural response of reinforced concrete slabs in railway bridges is strongly influenced by local dynamic effects and, therefore, detailed calculations of internal forces have to be performed for a realistic fatigue assessment. In this context, this paper discusses the influence of track irregularities and modal damping coefficients in the dynamic response and fatigue behaviour of a railway bridge deck slab. For that purpose, track irregularities were measured (at different instants of time) and damping coefficients were determined based on acceleration records for passing trains in a real bridge. The bridge behaviour was calculated using a train–bridge interaction methodology, considering calibrated numerical models of the viaduct and the train. The fatigue damage was quantified through the linear damage accumulation method. This methodology allowed to understand the way track irregularities and damping coefficients affect the magnitude of applied bending moments and fatigue damage in the slab.     

Vibration of railway bridges under a moving train by using bridge-track-vehicle element

During the last two decades, much attention has been paid to various vibration problems associated with railways. They include the dynamic response of railway bridges and railway tracks at grade under the action of moving trains. However, studies on the role of track structures on the vibration of railway bridges are rather limited. In this paper, a new element called bridge-track-vehicle element is proposed for investigating the interactions among a moving train, and its supporting railway track structure and bridge structure. The moving train is modelled as a series of two-degree-of-freedom mass-spring-damper systems at the axle locations. A bridge-track-vehicle element consists of vehicles modelled as mass-spring-damper systems, an upper beam element to model the rails and a lower beam element to model the bridge deck. The two beam elements are interconnected by a series of springs and dampers to model the rail bed. The investigation shows that the effect of track structure on the dynamic response of bridge structure is insignificant. However, the effect of the bridge structure on the dynamic response of the track structure is considerable.     

Study on the safe value of multi-pier settlement for simply supported girder bridges in high-speed railways

This paper presents a method to analyse the influence of multi-pier settlement on the train–track–bridge coupled dynamic system, and to determine the safe value of the continuous multi-pier settlement for simply supported girder bridges in Chinese high-speed railways. Firstly, the mapping relationship between the multi-pier settlement and the rail deformation is derived theoretically. Then, taking the superposition of the rail deformation and the track random irregularity as excitation, the variations of vehicle dynamic indices are analysed based on the train–track–bridge dynamic interaction theory. Further, the relationships between the pier settlement and the change amounts of vehicle dynamic indices are obtained. The multi-pier settlement safe value is determined according to the limits of vehicle dynamic indices. Results show that the rail deformation caused by multi-pier settlement agrees well with the settlement data. When passing through the 32.6 m-long simply supported girder bridge with multi-pier settlement, the train suffers a low-frequency excitation. Only considering the influence of pier settlement, the settlement value difference between two adjacent piers should be less than 26.3 mm at China’s highest operation speed of 350 km/h from the perspective of dynamics, which is much larger than the pier settlement limit in the current code for Chinese high-speed railways.     

地震作用下高速铁路车-轨-桥系统安全研究进展

桥梁占线比高、列车运行密度大及地震带分布范围广,使得我国高速铁路桥梁面临巨大的潜在地震威胁。目前地震下的高速铁路桥梁及桥上行车安全相关规定不够详细具体,地震下安全防控尚未将列车、轨道、桥梁作为一个大系统进行安全设防,亟待开展系统研究保障地震下高速铁路桥梁结构及桥上行车安全。针对高速铁路轨道 桥梁系统结构特性,首先介绍地震作用下高速铁路轨道 桥梁系统破坏特征和损伤机理研究现状,然后从震后高速铁路桥上轨道不平顺状态劣化机理、地震作用下高速铁路列车 轨道 桥梁系统动力分析、地震作用后桥上行车安全分析及基于性能的高速铁路桥梁抗震设计方法等几个方面阐述现有研究进展及现有研究的不足,最后针对地震下高速铁路列车 轨道 桥梁系统多状态多水准多防线安全防控急需开展系统研究的问题进行展望。     

Seismic vulnerability assessment of a Californian multi-frame curved concrete box girder viaduct using fragility curves

Seismic response of multi-frame curved viaducts has been proved to be very complex due to typically inherent irregularities identified in this class of bridge structures such as deck in-plane curvature, altitudinal irregularity and deck discontinuity. The discontinuity provided by the expansion joint has made this class of bridges prone to catastrophic damages caused by multiple collisions between adjacent frames during both torsional and translational modes of responses as well as deck unseating at the expansion joints. This paper presents the seismic response of a Californian multi-frame curved concrete box girder viaduct, considering four different radii of curvature and five altitudinal coefficients, using fragility curves. Fragility curves are developed by considering different sources of uncertainties related to earthquakes, structural geometries and material properties. The full nonlinear time-history analyses are performed utilising 3-D numerical bridge models generated in OpenSees finite element platform. The results show that bridge vulnerability increases with increasing irregularity in bridge plan and elevation. It is observed that bridge components and system fragility show different sensitivity to each type and level of irregularity for each damage state. In addition, the obtained results can be used to aid seismic retrofit prioritisation, financial loss estimation, pre-earthquake planning and design improvement processes.     

列车运行引起高架桥群桩基础地面振动分析

采用半解析数值方法分析列车运行引起高架桥群桩基础地面振动,研究合理设计桩基减小地面振动。半解析数值模型包括列车–轨道模型、高架桥模型、群桩模型。列车轨道模型中采用多质点弹簧–阻尼模型模拟列车,采用美国功率谱描述轨道随机不平顺,使用Euler梁模拟钢轨,采用Hertzian非线性公式描述轮轨接触,采用振型分解法求解轮轨作用力。铁路高架桥采用弹性支座简支梁模拟,采用传递系数矩阵和群桩影响因子分析桥墩下群桩的动力阻抗,根据桥墩的动力平衡方程求得桥墩–地基相互作用力,采用Green函数求得弹性半空间地面振动。研究铁路高架桥下群桩参数对地面振动的影响,分析不同桩长、桩直径、桩间距和轨道不平顺条件下地面振动速度1/3倍频程的大小。结果表明:轨道不平顺对桥墩作用力有较大影响,对小于6 Hz的地面振动影响较小,对大于6 Hz的地面振动影响较大。合适调整桥梁跨度与车速组合可减小地面振动。车速小于260 km/h时,桩径对地面振动影响较小;车速大于260 km/h时,增加桩径可减小地面振动。适当增加桩间距可避开振动增大区、减小地面振动随车速的增加。合理设计桩长可减小地面振动的增大区域。     

A new accelerated-replacement method and full-scale test of a new superstructure for existing OSPG railway bridges

Existing open-steel-plate-girder (OSPG) railway bridges in Korea are so old that they can no longer provide the desired ride quality when trains pass over them due to loss of integrity. In addition, existing bridges do not have ballast, thus impacts from passing trains are delivered directly to piers and abutments. The damage that accumulated is one of the main causes of cracks in pier concrete. To cure this problem, replacement of the existing bridges is required. However, since they are still in service, conventional construction methods cannot be used for their replacement. A new method is necessary to quickly replace the existing bridges in a way that does not disturb the existing train schedule. In this study, a new accelerated-replacement method is proposed using a newly developed crane-vehicle which possesses cranes able to lift a replacement bridge, and which is able to travel on existing train tracks. This study also addresses the design and manufacture of a new bridge deck appropriate for accelerated-replacement construction. Finite element analyses and experimental tests were conducted to estimate the performance of the new bridge deck. The analyses included a static load case and dynamic analysis at various train speeds. The experimental tests included static loading and modal tests to capture the fundamental natural frequency and damping ratio of the bridge deck, and a dynamic amplification test. The results of this study can be used for practical replacement of aged existing open-steel-plate-girder bridges and to improve the integrity and ride quality of railway bridges in Korea.     

Bridge condition modelling and prediction using dynamic Bayesian belief networks

The development of a condition-based deterioration modelling methodology at bridge group level using Bayesian belief network (BBN) is presented in this paper. BBN is an efficient tool to handle complex interdependencies within elements of engineering systems, by means of conditional probabilities specified on a fixed model structure. The advantages and limitations of the BBN for such applications are reviewed by analysing a sample group of masonry bridges on the UK railway infrastructure network. The proposed methodology is then extended to develop a time dependent deterioration model using a dynamic Bayesian network. The condition of elements within the selected sample of bridges and a set of conditional probabilities for static and time dependent variables, based on inspection experience, are used as input to the models to yield, in probabilistic terms, overall condition-based deterioration profiles for bridge groups. Sensitivity towards various input parameters, as well as underlying assumptions, on the point-in-time performance and the deterioration profile of the group are investigated. Together with results from ‘what if’ scenarios, the potential of the developed methodology is demonstrated in relation to the specification of structural health monitoring requirements and the prioritisation of maintenance intervention activities.     

Bridge dynamics and aerodynamics: design and practical requirements for high structural performance and safety

Abstract

Bridge dynamics and aerodynamics have been in many cases overlooked in the design stages and consequent low behaviour performance and safety margin have been not rarely observed and detected by means of structural monitoring of the bridge soon after it is brought into full service. In this paper, a selection of important issues regarding design and practical requirements for a high structural performance of main components of conventional and cable-stayed bridges are pointed out and discussed briefly. The paper encompasses sections describing some relevant aspects regarding the numerical and physical modelling of the structural system and the mathematical modelling of the dynamic and aerodynamic loads. Special attention is given to the dynamic interaction between vehicles and structures of roadways and railway bridges and also to the aeroelastic analyses of bridges′ behaviour and their consequent implications on the structural performance of a bridge during its service life. Case examples of actual bridges subjected to dynamic forces produced by the traffic of heavy vehicles and by the wind action are explored to depict the main sources of problems which in some cases caused structural misbehaviour. Some practical measures to improve the behaviour and performance of bridge structures are outlined.     

Dynamic analysis of three-dimensional bridge–high-speed train interactions using a wheel–rail contact model

A formulation of three-dimensional dynamic interactions between a bridge and a high-speed train using wheel–rail interfaces has been developed. In the interface, contact loss is allowed, the vertical contact is represented by finite tensionless stiffness and the lateral contact is idealized by finite contact stiffness and creepage damping. Such stiffness and damping are nonlinearly dependent on normal contact force. The relative rotations of a wheelset to the rails about its vertical and longitudinal axes are included. Bridge eccentricities and deck displacement due to torsion are accounted for in bridge deck modeling. A numerical algorithm using separate integrations for bridges and trains, and iterations for interface compatibilities is established. A case study of a ten-car train passing over a two-span continuous bridge at various speeds and rail irregularity wavelength ranges is analyzed. The responses of the bridge, car-bodies and wheelsets are investigated for their behavior, acceptability and relations with the wavelengths. Analytical and numerical evaluations of resonant speeds are in good agreement, and the exit span vibration is more amplified than the entrance one at those speeds. The computed relative displacements of all wheelsets to the rail facilitate an explicit assessment for derailment risk.     

钢筋混凝土框架结构竖向不规则参数的概率评估

采用蒙特卡罗模拟方法分析钢筋混凝土(RC)框架结构竖向不规则参数的抗震控制效果。以底层和中间层竖向楼层承载力和刚度不规则的5层和10层RC框架结构为分析对象,考虑地震动输入的随机性,通过非线性动力时程分析确定结构的最大层间位移角,并分析其随竖向不规则系数变化的规律和超越极限状态水准的失效概率。分析结果表明：楼层竖向承载力和刚度不规则对结构最大层间位移角的影响较大,最大层间位移角随竖向不规则系数的减小而增大,底层不规则较中间层不规则的影响大,承载力不规则较刚度不规则的影响大;竖向不规则对结构地震反应超越极限状态水准的失效概率有显著的影响,失效概率随竖向不规则系数的减小而增大,竖向不规则系数越小失效概率越大;承载力不规则系数为0.7和刚度不规则系数为0.8可作为竖向不规则参数的抗震控制点。     

Vereinfachte Methoden zur Berechnung der dynamischen Antwort von Eisenbahnbrücken bei Zugüberfahrt

Simplified methods to calculate the dynamic response of railway‐bridges under crossing trains. In this paper, two different methods to calculate the dynamic response of single‐span bridges under moving forces are presented. The work is focused on beam bridges with constant cross‐section in underdamped condition. In the first method, referred to as “Impulse‐method”, the effective impulse resulting from the load is approximated by simple analytical functions. The bridge is modelled as a single degree of freedom system by means of modal analysis. For this simplified system describing bridge and load, closed analytical formulae to calculate the dynamic response can be set up. The “Impulse‐method” is exemplified by the HSLM‐A1 load train given in Eurocode 1 (EC1). In the second method the response spectrum analysis widely used in earthquake engineering is adopted for the present problem. The calculation of response spectra for beam bridges under the HSLM‐A load models is demonstrated. An example shows how this method is deployed.     

Cyclic response of RC continuous span bridges with irregular configuration in longitudinal direction

Cyclic response of a class of reinforced concrete bridges with different degrees of irregularity in longitudinal direction has been investigated. Eighteen bridge configurations have been identified from regular to the so-called highly irregular models. The geometric irregularity in this class of bridges is assumed to vary with the height of the piers. Using non-linear fibre-based analytical models, the cyclic response curves have been generated for theindividual piers of each of these 18 bridge models. Discussions have been made about the imposition of the displacement ductility demand of the piers versus the bridge regularity. Comparison of the cyclic response curves shows that the most vulnerable bridges are the irregular ones, and a high level of damage and ductility demand is expected for the short piers of this class of bridges.     

Effect of linearized contact spring in track dynamic system

In recent years, a number of researches into dynamic characteristics of the noise and vibration in the railway have been performed. Since the high frequency vibration, which occurs in the irregularity(roughness) of the wheel and rail running surfaces, causes the track noise in railway system, analytic study with measurement of the vibration for the wheel and rail is needed. So, the algorithm and program for the vibration analysis in the track system were developed as a part of the analytic study. In this study, evaluation for the effect of the linearized contact spring in track dynamic system was studied with the developed program. In addition, analytical study for the comparison between hysteretic and viscous damping in this system was performed. The result shows that both the linearized contact spring stiffness and damping of track system are important factors in track dynamic analysis model.

     

列车荷载对桥梁及桩基下边坡的动力作用

研究了车辆荷载对桥梁及桩基下的边坡的动力作用,以李子沟特大桥为计算示例,建立了桥梁上下部、基础–边坡两个三维体系动力分析模型,采用大型工程分析软件ANSYS分析了大跨高墩桥梁在列车荷载作用下由于轨道不平顺引起的动力响应,以及对桩基下边坡产生的安全和稳定影响,并采用预应力锚索加固,以保证边坡的稳定性。     

Static strain energy and dynamic amplification factor on multiple degree of freedom systems

Many references and design codes propose the use of a dynamic amplification factor applied to the static response of a structure for estimating its dynamic response. This is the case of the present recommendations on cable stayed bridges or other references for evaluating the dynamic effects produced by the accidental loss of a segment during the cantilever construction of a precast concrete bridge. This paper deals with the dynamic amplification factor of multiple degree of freedom systems under the action of a rectangular pulse load of infinite duration. A theoretical study of the possible maximum values that the dynamic amplification factor can reach has been carried out, establishing the relation between this factor and the strain energy of the system under the load statically applied. This relation allows us to determine if the dynamic amplification factor can exceed the value of 2.0 and to derive a simple method for comparing the dynamic effects of different pulse loads. Finally, a numerical example illustrates this method applied to determine which rectangular pulse load, produced by the accidental loss of a segment of a bridge, can produce a larger and a smaller dynamic amplification factor on a cantilever precast segmental bridge under construction. In this example, the possible maximum dynamic amplification factor obtained has been 3.24.     

Effect of vertical structural irregularity on seismic design of tall buildings

Many tall buildings are practically irregular as an entirely regular high‐rise building rarely exists. This study is thus devoted to assessing the approach and coefficients used in the seismic design of real‐life tall buildings with different vertical irregularity features. Five 50‐story buildings are selected and designed using finite element models and international building codes to represent the most common vertical irregularities of reinforced concrete tall buildings in regions of medium seismicity. Detailed fiber‐based simulation models are developed to assess the seismic response of the five benchmark buildings under the effect of 40 earthquake records representing far‐field and near‐source seismic scenarios. The results obtained from a large number of inelastic pushover and incremental dynamic analyses provide insights into the local and global seismic response of the reference structures and confirm the inferior local response of tall buildings with severe vertical irregularities. Due to the significant impacts of the severe irregularity types on the seismic response of tall buildings, the conservative code approach and coefficients are recommended for design. It is also concluded that although the design coefficients of buildings with moderate irregularities are adequately conservative, they can be revised to arrive at more consistent safety margins and cost‐effective designs.