Multi-scale damage analysis for a steel box girder of a long-span cable-stayed bridge

Accurate evaluation of the effect of possible damage in critical components on the dynamic characteristics of a structure is of critical importance in developing a robust structural damage identification scheme for a long-span cable-stayed bridge. The strategies of finite element (FE) modelling of a long-span cable-stayed bridge for multi-scale numerical analysis are first investigated. A multi-scale model of the Runyang cable-stayed bridge is then developed, which is essentially a multi-scale combination of a FE model for modal analysis of the entire bridge structure and FE sub-models for local stress analysis of the selected locations with respect to the substructuring method. The developed three-dimensional global-scale and local-scale FE models of Runyang cable-stayed bridge achieve a good correlation with the measured dynamic properties identified from field ambient vibration tests and stress distributions of a steel box girder measured from vehicle loading tests, on the basis of which the effectiveness of some damage location identification methods, including a modal curvature index, a modal strain energy index and a modal flexibility index, are evaluated. The analysis results show that the effect of the simulated damage in various components of the steel box girder on the dynamic characteristics of a long-span cable-stayed bridge should be properly considered in structural damage analyses using multi-scale numerical computation.     

重载列车作用下桥墩-桩基竖向动荷载特性试验研究

为探明大轴重、长编组和高密度重载列车作用下桥墩和桩基承台顶的动荷载特性,开展不同车速和轴重条件下的桥墩-桩基体系竖向动荷载响应现场试验。分析桥墩动荷载曲线的时域、频域特征,采用Kolmogorov法对动荷载幅值进行正态性检验,建立列车参数与动荷载频域特征的联系;基于3σ原则对不同敞车作用下的动荷载特征值(均值、均幅值和均峰值)进行统计,结合实测数据建立重载列车作用下的墩顶动力系数计算公式,并提出墩顶和桩基承台顶的荷载谱公式及其参数取值。结果表明:动荷载响应在时域上可分为快速增加,周期波动和快速衰减3个阶段,在频域上服从倍频规律和幅值调制效应,0～5Hz频段激振对动荷载起控制作用;动荷载幅值服从正态分布,动荷载均峰值和振动能量沿墩身衰减明显,动荷载均值和均峰值随轴重增大而增大,均幅值随轴重的增加而减小;建议采用φ=1+0.0045v计算墩顶动力系数,采用三角级数式拟合桥墩荷载谱效果显著。研究成果可为重载列车作用下桩基的长期承载变形性状及环境振动评估的研究提供关键参数和可靠检验样本。     

Einsatz von multiplen Schwingungstilger‐Systemen an schlanken Fußgängerbrücken

The Application of Multiple Tuned Mass Damper Systems at slender footbridges. While for standard footbridge only a few vibration modes are within the critical footfall frequency range and hove to be considered for the dynamic design, lightweight structures dis‐play multiple modes in that frequency range. Furthermore the modal masses are very little so also the smaller load components for the excitation of higher harmonic vibration modes can become significant to assess the vibration susceptibility. Various observations have been made during experimental tests of these structures and will be introduced in this contribution using the example of a canopy walk structure and a stress ribbon bridge. To understand the observed effects at such continuous dynamic systems for pedestrian loading, numerical calculations have been performed for which a similar lightweight structure has been modelled and pedestrian loading was simulated with several footfall frequencies. Similar to the experimentally investigated structures it was found that the multimodal dynamic response of the bridges strongly depends on the pedestrian loading (footfall frequency). Experimental tests have shown, that the application of a Tuned Mass Damper System to dampen only the critical mode that is within the footfall frequency range is not sufficient to reduce the multi‐modal dynamic response of the lightweight bridge structures under pedestrian so the occurring accelerations remain below certain comfort levels. Therefore the concept of Multiple Tuned Mass Dampers was introduced to the bridge structure and its practicability was investigated.     

Nothing-on-road bridge weigh-in-motion considering the transverse position of the vehicle

Bridge weigh-in-motion (BWIM) is a technology that uses the bridge as a weighing platform to estimate vehicle weights. Previous research has shown that ignoring the transverse position (TP) of vehicles may lead to significant identification errors of vehicle weight for BWIM systems. However, the traditional method to identify the vehicle’s exact TP requires using axle detectors on the road surface. Aiming at achieving the nothing-on-road (NOR) BWIM, this paper proposes a novel NOR BWIM algorithm that is able to identify the vehicle’s TP and axle weights using only the weighing sensors. Numerical simulations are conducted using three-dimensional vehicle and bridge models and the proposed algorithm was used to identify the vehicle’s TP and axle weights. The results show that the proposed algorithm can successfully identify the vehicle’s TP and that the identification accuracy of axle weights and gross vehicle weight is significantly improved after considering the vehicle’s TP. The effects of the road surface condition, the vehicle speed, the vehicle width, and different measurement stations on the identification accuracy are investigated. The proposed algorithm is then verified by a field study and the results indicate that the proposed algorithm can achieve acceptable identification accuracy in practice.     

同时考虑速度和轴跨比影响时铁路钢桥的影响因子的确定

传统桥梁设计方法中,把交通荷载处理为静载乘以影响因子。依据现行规范,该因子仅是跨度或一阶自振频率的函数。分析各种参数对钢桥动力响应的影响,包括:速度、火车轴距、车轴数、桥跨度,并研究影响因子。计算了火车速度100～400km/h,轴距13～20m,桥跨度10,15,20,25m情况下的动力响应和影响因子。动力分析表明,大多数情况下,算得的影响因子高于相关规范中的值。影响因子随火车速度、火车轴距和桥跨度之比而变化,而车轴数仅在共振时产生影响。给出了速度、车轴距、桥跨度与影响因子的关系。     

中低速磁浮列车-桥梁系统竖向耦合振动#br# 理论分析与试验验证

为探讨中低速磁浮列车-桥梁系统竖向动力相互作用特性,文章将中低速磁浮列车进行两种方式的简化,考虑PID主动悬浮控制系统,基于模态叠加法,建立2种类型的中低速磁浮列车-桥梁系统竖向耦合振动分析模型。随后基于长沙中低速磁浮运营线桥梁动载试验,对建立的2种仿真模型进行对比与验证。基于仿真模型2,以不同梁高的桥A、桥B、桥C为研究对象,对中低速磁浮列车-桥梁系统耦合振动特性进行分析。研究表明：将磁浮列车简化为均布荷载的方式能较为准确的模拟实际状况;桥梁刚度的减小会导致作用于车辆和桥梁上的电磁悬浮力增大,使得车体和桥梁的动力响应变大;磁浮列车低速运行时悬浮力频谱分布较离散,而正常速度运行时较集中;中低速磁浮列车-桥梁系统竖向存在着由电磁悬浮力自身频率引起的共振现象,该共振频率较低。     

Control mode selection for modal control of long-span arch bridge

For seismic control of arch bridge, a model reduction of long-span arch bridge was implemented based on modal analysis. As for the critical mode selection, an approach based on the maximum modal displacement was presented. This approach takes into consideration the effect of external seismic excitation and is more reasonable than only considering dynamic bridge characteristics based on a modal contribution ratio. The time domain and frequency domain analysis method were used to verify the simplified model of the Nimu arch bridge in Tibet as an example. The numerical results show that the method of maximal modal displacement better analyze long-span arch bridge when multisupport seismic excitation must be considered. The reduced-order system also is more in line with the performance of the original model.     

Control mode selection for modal control of long-span arch bridge

For seismic control of arch bridge, a model reduction of long-span arch bridge was implemented based on modal analysis. As for the critical mode selection, an approach based on the maximum modal displacement was presented. This approach takes into consideration the effect of external seismic excitation and is more reasonable than only considering dynamic bridge characteristics based on a modal contribution ratio. The time domain and frequency domain analysis method were used to verify the simplified model of the Nimu arch bridge in Tibet as an example. The numerical results show that the method of maximal modal displacement better analyze long-span arch bridge when multisupport seismic excitation must be considered. The reduced-order system also is more in line with the performance of the original model.     

A multidisciplinary approach for fatigue assessment of a steel–concrete high-speed railway bridge on Sesia river

Steel–concrete composite bridge solutions have been more and more exploited in the new high-speed (HS) lines of European railway networks. New design solutions, introduced during a period of quick expansion for railway networks, amplified open problems related to dynamic effects, train–bridge interaction phenomena, fatigue loadings, structural modelling, fatigue life and comfort. In this article, results obtained by long-term dynamic monitoring of Sesia viaduct, a medium span double-box composite bridge of the new Italian HS network, are described and analysed. Structural modal properties were determined in order to evaluate the real-time dynamic behaviour and its correlation with environmental conditions. A suitable numerical procedure was then implemented in order to identify typology, length and velocity of trains crossing the bridge, to evaluate the intensity of deck vertical accelerations as a function of train speed and to obtain a reliable evaluation of real traffic spectra. A final fatigue assessment on welded connections was executed evaluating fatigue spectra by the aforementioned real traffic spectra and assuming S–N curves obtained by suitably executed experimental tests.     

Experimental study on dynamic load magnification factor for ballastless track-subgrade of high-speed railway

The magnitude of dynamic load produced by high-speed trains depends on many factors, of which train speed is the most critical one. However, it is quite difficult to determine the effect of train speed on dynamic load using the theoretical methods due to the complexity of the interaction between vehicle and track-subgrade. Thus large-scale model test has gradually become an important approach for studying dynamic responses of ballastless track-subgrade of high-speed railway. In this study, a full-scale model of ballastless track-subgrade was constructed in accordance with the design and construction standards for Shanghai–Nanjing intercity high-speed railway line firstly. Then, the dynamic strain of slab and the dynamic earth pressure of subgrade were measured by conducting single wheel axle excitation test. In addition, the relationship between the dynamic load magnification factor (DLF) and the train speed was obtained. Finally, the DLF of track-subgrade under different train speeds was proposed, similar to that given by German Railway Standard.     

Moving train loads identification on a continuous steel truss girder by using dynamic displacement influence line method

This paper presents a dynamic displacement influence line method for moving load identification on bridge. The finite element model of Poyang Lake continuous truss bridge-train systems is established and the dispersed modal shapes are acquired by modal analysis. Multi-axle moving train loads are identified with simulated annealing genetic algorithm by minimizing the errors between the measured displacements and the reconstructed displacements from the identified moving loads. In the identification process, the dynamic displacement influence line technique is used to calculate the time history displacement responses of the bridge to avoid solving equations of motion of the bridge repetitively. Several important parameters of the bridge-train system are discussed to investigate their effects on the proposed method. The results demonstrate that the proposed method is an accurate and efficient method for moving train load identification on complex bridges.     

大跨斜拉桥环境模态频率识别的最大熵法研究

大跨斜拉桥结构的振动特性随环境与运营条件的变化表现出时变的特征。本文对润扬大桥斜拉桥结构的实测加速度响应信号采用复模态指示函数法(CMIF法)进行了模态参数识别,在此基础上采用最大熵法对实测模态频率的不确定性进行了分析。分析结果表明,环境温度的变化对斜拉桥模态频率的影响是长期性的趋势,而交通荷载和风荷载对模态频率的影响则由于荷载的非平稳性呈现瞬时的颤动变化。采用最大熵法较好地改善了润扬大桥斜拉桥的环境模态频率识别效果,有效地减少了实测模态频率因车辆和风荷载随机因素影响的变异性。     

Structural performance evaluation of a precast prefabricated bridge column under vehicle impact loading

In this study, the numerical analysis method was proposed to analyse the structural behaviour of bridge columns under various impact loading conditions. A parametric study of vehicle impact simulation was carried out to determine the impact loading-time functions. According to the impact simulation results, five-point piecewise linear approximation is proposed and validated. The proposed loading function was applied to the material nonlinear finite element analyses of two different types of bridge piers, the cast-in-place reinforced concrete bridge columns and the prefabricated bridge columns, which were designed under the same loading conditions. The dynamic performances of the considered bridge piers are compared using the results of dynamic numerical analyses. Also, the static design loadings of a vehicle crash defined in the Korean bridge design code and AASHTO LRFD Bridge Design Specifications were applied to analyse the results of the dynamic analyses of the piers.     

路面谱激励下的运营桥梁结构的响应分析

基于运营桥梁结构中不同路谱激励样本的差异,分别计算了特定样本下,车速变化时桥梁结构、运营车辆的位移、速度、加速响应。采用标准路面等级的功率谱密度,运用余弦叠加方法,模拟了不同样本的各等级路面谱激励;采用直接积分的方法,计算了加入路面随机激励后的车桥振动的微分方程,分析了不同路面等级、不同车速下系统的响应。结果表明：随机相位角、功率谱密度等级分别影响路面谱激励的样本形状和幅值大小,不同随机样本具备相同统计特征;对于系统的响应曲线,路面平整度等级对幅值影响相对显著,车速变化对形状影响相对显著;根据算例中不同路面平整度等级的计算结果,给出了相应的工程建议。     

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.     

基于WIM的典型城市桥梁车辆荷载状况分析

基于安装在杭州石祥路留石高架上的动态称重系统（WIM）采集的交通流和车辆荷载数据,通过对交通流量、车辆构成、轴重、车辆总重等进行分析,获取了其概率统计特性及分布规律,建立了轴载谱和车辆总重谱,并与相关文献、规范进行了比较。结果表明：一天中各时段的交通流量具有很强的潮汐规律性;2.86%的车辆轴重超过了10 t的超载标准,最大的单轴重量达39.5 t,最大车辆总重达115 t,后半夜车辆恶性超载严重;2轴车车辆总重表现为单峰分布,3轴以上车辆的总重均表现为多峰分布,5轴车和6轴车的总重表现为3峰分布;轴重大的车辆主要是超载的2轴、3轴车辆,这部分车辆对桥梁等基础设施的危害较大。这些车辆荷载特征的获取有助于区域既有桥梁安全性的合理评估,为超重车辆治理和桥梁安全管理提供帮助。     

Dynamic stress analysis for fatigue damage prognosis of long-span bridges

For fatigue damage prognosis of a long-span steel bridge, the dynamic stress analysis of critical structural components of the bridge under the future dynamic vehicle loading is essential. This paper thus presents a framework of dynamic stress analysis for fatigue damage prognosis of long-span steel bridges under the future dynamic vehicle loading. The multi-scale finite element (FE) model of the bridge is first developed using shell/plate elements to simulate the critical structural components (local models) and using beam/truss elements to simulate the rest part of the bridge (global model). With the appropriate coupling of the global and local models, the multi-scale FE model can accurately capture simultaneously not only the global behavior in terms of displacement and acceleration but also the local behavior in terms of stress and strain. A vehicle traffic load model is then developed for forecasting the future vehicle loading based on the recorded weigh-in-motion (WIM) data and using the agent-based traffic flow microsimulation. The forecasted future vehicle loading is finally applied on the multi-scale model of a real long-span cable-stayed bridge for dynamic stress analysis and fatigue damage prognosis. The obtained results show that the proposed framework is effective and accurate for dynamic stress analysis and fatigue damage prognosis.     

Modeling of Traffic Excitation for System Identification of Bridge Structures

Abstract:   In long-term health monitoring of bridge structures, system identification is often performed based only on the system output (bridge vibration responses) because the system input (traffic excitation) is difficult to measure. To facilitate the identification of the bridge properties, traffic excitation is commonly modeled as spatially uncorrelated white noise. A physical model of a stationary stream of vehicles (moving loads) arriving in accordance with a Poisson process, traversing an elastic beam, shows that the traffic excitation is spatially correlated. Employing the dynamic nodal loading approach, this spatial correlation results in a frequency-dependent excitation spectrum density matrix, and shifts the response spectra obtained from those excited by spatially uncorrelated white noise. It is shown that the application of system identification techniques based on the conventional excitation model may result in misleading structural properties. Hence, this study further proposes an output-only gray-box identification technique for bridge structures, in which knowledge about the nature of the traffic excitation, such as its spatial correlation, is implanted into an autoregressive-moving-average (ARMA) model. The identifiability of the ARMA model so constructed is assured and the feasibility of the proposed identification technique is demonstrated by a numerical example.     

A filtering-based bridge weigh-in-motion system on a continuous multi-girder bridge considering the influence lines of different lanes

A real-time vehicle monitoring is crucial for effective bridge maintenance and traffic management because overloaded vehicles can cause damage to bridges, and in some extreme cases, it will directly lead to a bridge failure. Bridge weigh-in-motion (BWIM) system as a high performance and cost-effective technology has been extensively used to monitor vehicle speed and weight on highways. However, the dynamic effect and data noise may have an adverse impact on the bridge responses during and immediately following the vehicles pass the bridge. The fast Fourier transform (FFT) method, which can significantly purify the collected structural responses (dynamic strains) received from sensors or transducers, was used in axle counting, detection, and axle weighing technology in this study. To further improve the accuracy of the BWIM system, the field-calibrated influence lines (ILs) of a continuous multi-girder bridge were regarded as a reference to identify the vehicle weight based on the modified Moses algorithm and the least squares method. In situ experimental results indicated that the signals treated with FFT filter were far better than the original ones, the efficiency and the accuracy of axle detection were significantly improved by introducing the FFT method to the BWIM system. Moreover, the lateral load distribution effect on bridges should be considered by using the calculated average ILs of the specific lane individually for vehicle weight calculation of this lane.     

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.