Fatigue stress monitoring and analyses for steel box girder of Runyang Suspension Bridge

The monitoring of fatigue stress of steel bridge is a key issue of bridge health monitoring and safety assessment. This paper aims to find out the strain history features of the girder components of Runyang Suspension Bridge (RYSB) under vehicle and environmental loading during its first year of service based on the strain-history data recorded by structural health monitoring system installed in the bridge. The fatigue stress spectrums of steel box girders under normal traffic load, heavy trucks and typhoon loads were studied as well as the correlation between varying strain and temperature based on real-time monitoring of temperature histories. The results show that, monitoring on local strain in health monitoring systems of RYSB can effectively provide the information on fatigue stresses. The range of the equivalent fatigue stress on the monitoring location of the bridge is currently low, mainly due to varying traffic loading and temperature. There exists significant correlation between varying temperature and mean value of fatigue stress. Effect of the passing of heavy trucks on bridge fatigue is quite significant since the value of the cumulative fatigue damage generated by heavy trucks is 10 to 100 times larger than that by normal traffic. Therefore, the effect on fatigue cumulative damage due to heavy trucks or overloaded vehicles needs to be monitored and paid much attention to. __________ Translated from Journal of Southeast University (Natural Science Edition), 2007, 37(2): 280–286 [译自: 东南大学学报(自然科学版)]     

高速公路钢桥在地震荷载下的疲劳评估

在概率论的前提下,运用线弹性断裂力学的方法研究高速公路桥钢梁在地震荷载作用下的疲劳特性。第一部分介绍的疲劳破坏是由经过桥面的重型卡车的车辆荷载引起;第二部分介绍的疲劳破坏由地震荷载引起。两种类型的破坏都使用线弹性断裂力学方法进行分析,并计算了最初裂缝发展的时间。考虑到在桥梁的使用年限里通常不同时考虑疲劳效应和地震效应,提出的方法能更好地理解桥梁由疲劳引起的逐渐破坏现象,并对如何延长地震区众多钢桥梁的疲劳寿命提出一些建议。     

Fatigue assessment of highway steel bridges in presence of seismic loading

In this study a LEFM (Linear Elastic Fracture Mechanics) approach is used in a probabilistic context to evaluate the fatigue reliability of steel girder highway bridges in the presence of seismic loading. In the first part the fatigue damage is related to the traffic load produced by heavy trucks crossing the bridge; the second part deals with the fatigue damage related to seismic loading. Both damage typologies are analyzed using linear elastic fracture mechanics principles, and the time required for an initial crack propagation is calculated. Taking into account that the correlation between fatigue effects and seismic actions is not usually considered in the literature, this method could enable a better understanding of progressive damage phenomena due to fatigue related problems, and could give some new insights for increasing the remaining fatigue life of a large number of steel bridges in seismic zones.     

基于微塑性应变的钢箱梁疲劳损伤及仿真分析

随着大跨度桥梁服役时间的不断增加,交通量持续增长以及负荷严重等因素,车辆对桥面系结构的冲击效应将越加提高。作为大跨度桥梁主要受力构件的钢箱梁,将直接承受车轮荷载的作用,焊接区域应力集中效应尤为显著。本文设计了典型的钢箱梁构件,并进行了疲劳加载试验。研究表明,在形成裂纹的初始时期,裂纹发展速度最快且形成微小裂纹,即试件的损伤快速积累阶段,其后疲劳损伤稳定发展,最终损伤急剧增加乃至试件破坏。本文提出的三阶段疲劳累积损伤公式及空间有限元分析方法可供工程设计参考。     

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.     

基于马尔可夫链的钢箱梁正交异性板疲劳状态分析

为对正交异性板U肋的剩余强度退化规律进行研究,引入马尔可夫过程理论,以特大跨径钢箱梁悬索桥--西堠门大桥为工程背景展开研究。首先分析西堠门大桥钢箱梁长期应变监测数据的时频特征,应用小波分析分离出环境温度变化所引起的桥面板结构应力波动,再对小波变换系数在不同尺度上选择合适的阈值来消除由环境随机激励和测量噪声引起的低幅值应力变异;采用雨流计数法对车辆荷载作用下的应变监测数据进行统计分析,得到疲劳应力范围并设定6个疲劳应力区间;然后由U肋对接部位的典型S-N曲线计算得到其强度从初始状态至最终状态的转移概率,并根据Palmgren-Miner线性疲劳累积损伤理论构造出连接部位易损点区域强度演变的状态转移概率矩阵;最后利用初始状态的概率分布向量和状态转移概率矩阵,得出大桥运营阶段不同时刻对应的剩余强度值,给出U肋连接部位的强度退化轨迹。结果表明：所建立的疲劳状态分析模型可以考虑构件强度退化过程中各状态的相关性,能够根据车流量变化来预测正交异性板U肋疲劳状态随桥梁服役时间的变化规律,从而可实现钢箱梁正交异性板U肋的服役性能评估。     

Damage due to heavy traffic on three RC road bridges

An investigation of the damage caused by road traffic on three reinforced concrete bridges was performed. This study was performed with a focus on the determination of the damage induced by heavy vehicles in relation to the damage caused by average everyday traffic. A damage model based on fatigue of reinforcement bars was employed. The stress cycles in the reinforcement bars were determined using measurements of the crack widths under traffic loading. Stress cycles were analyzed using the Rainflow Method and Miner’s Rule was employed to gain a measurement for the damage. Monitoring systems were installed on each of the three bridges and operated for several weeks continuously to collect input data for the damage model. Computer software was developed to process the monitoring data in the sense of the damage model. The described methodology was developed and used for the first time in the described project.Heavy traffic was shown to cause a disproportionate high portion of the overall damage on all three bridges. The obtained results indicated that the damage caused by singular events, such as the passage of a heavy vehicle, in relation to the damaging effects of every-day traffic differed significantly between the considered bridges. For one of the bridges the greatest damage from singular traffic events was computed for passages of special transport vehicles. The same bridge was also found to display the highest damage by a single passage in relation to average everyday traffic. Passages of short and heavy trucks with four and five axles were identified as the most detrimental traffic events on the other two bridges.     

Schädigung einer schlaff bewehrten Betonbrücke durch Verkehrsbelastung

Evaluation of Damage Due to Traffic on a Reinforced Concrete Bridge An investigation of the damage caused by road traffic on a reinforced concrete bridge was performed. Focus was given to damage induced by extra‐heavy vehicles. A damage model based on fatigue of reinforcement bars was employed. The stress cycles in the reinforcement bars were determined using measurements of the crack widths under traffic loading which were analysed using the rainflow method and Miner's rule. A monitoring system was mounted and used for seven weeks continuously to collect input data for the damage model. Computer software was developed to process the monitoring data in the sense of the damage model. The results indicate that a singular passage of an extraheavy vehicle over the investigated bridge causes damage equivalent to the damage caused by one day of average weekly traffic. The described method was developed and used for the first time in the described project.     

Fatigue analysis of long-span suspension bridges under multiple loading: Case study

Long-span suspension bridges are often subject to multiple types of dynamic loads, especially those located in wind-prone regions and carrying both trains and road vehicles. Fatigue assessment shall be performed to ensure the safety and functionality of the bridges. This paper proposes a framework for fatigue analysis of a long-span suspension bridge under multiple loading by integrating computer simulation with structural health monitoring system. By taking the Tsing Ma Bridge in Hong Kong as an example, a computationally efficient engineering approach is first proposed for dynamic stress analysis of the bridge under railway, highway and wind loading. The fatigue-critical locations are then determined for key bridge components, and databases of the dynamic stress responses at the critical locations are established. The time histories of dynamic stresses induced by individual loading during the design life of the bridge are generated based on the databases. The corresponding stress time histories due to the combined action of multiple loading are also compiled. Finally, fatigue analysis is performed to compute the cumulative fatigue damage over the design life of 120 years. The results indicate that it is necessary to consider the combined effect of multiple loading in the fatigue analysis of long-span suspension bridges.     

黑龙江呼兰河大桥的光纤光栅智能监测技术

对光纤光栅波长变化与应变的关系进行了理论分析,并通过材料试验和等强度梁试验加以验证;研究了光纤光栅的布设工艺,并在黑龙江省呼兰河大桥预应力箱形梁的施工过程中成功地布设了12个光纤光栅应变传感器与3个温度传感器;布设的传感器监测了预应力箱形梁张拉过程的钢筋应变历程,以及箱形梁静载试验的钢筋应变增量与分布;大桥建成后,利用布设的光纤光栅应变和温度传感器对呼兰河大桥进行了阶段性运营监测,监测了车辆荷载下的应变历程和大桥温度变化过程。监测结果表明埋入的光纤光栅可以方便地监测汽车的流量及其可能的疲劳损伤,为桥梁结构的健康诊断提供依据。一年多的考验表明,光纤光栅的稳定性与耐久性满足钢筋混凝土桥梁结构长期健康监测的要求,性能明显优于传统的电阻应变片。     

Multi-scale fatigue damage prognosis for long-span steel bridges under vehicle loading

Fatigue damage prognosis for long-span steel bridges is of the utmost importance in bridge maintenance and management. In this study, a multi-scale fatigue damage prognosis algorithm is developed to calculate the trans-scale fatigue damage accumulation of newly-built long-span steel bridges under vehicle loading. The necessity and procedure of establishing a multi-scale finite element (FE) model of a newly-built long-span bridge for fatigue damage prognosis are first introduced. The future vehicle loading on the bridge is forecasted using the recorded weigh-in-motion (WIM) data and the agent-based traffic flow micro-simulation method. Then, the multi-scale fatigue damage prognosis algorithm is developed based on the multi-scale FE model and using the future vehicle loading. Finally, the proposed algorithm is applied to a newly-built long-span cable-stayed bridge for the time period from 2010 to 2020. The results show that the macro-scale fatigue damage accumulation and micro-scale short crack evolution of the critical components of the bridge can be simultaneously predicted and visualized. The proposed algorithm can be used as a numerical tool for fatigue damage prognosis of steel bridges where (or near where) WIM station is installed.     

Statistical analysis of online strain response and its application in fatigue assessment of a long-span steel bridge

This paper covers reliability assessment of the fatigue life of a bridge-deck section based on the statistical analysis of the strain–time histories measured by the structural health monitoring system permanently installed on the long-span steel bridge under study. Through statistical analysis of online strain responses in the frequency domain using multiple linear regression, a representative block of daily cycles of strain history is obtained. It is further assumed that all cycles of online strain response during bridge service are repetitions of the representative block. The rain-flow counting method is then used to determine the stress spectrum of the representative block of daily cycles. The primary assessment of fatigue life at a given value of failure probability is undertaken for the sample component in a bridge-deck section by using the classification of details for welded bridge components and the associated statistical fatigue model provided by the British Standard BS5400. In order to evaluate bridge fatigue at any value of failure probability, a modified probability model is proposed based on BS5400. The fatigue life of the considered component in the bridge-deck section is then evaluated for some other values of probability of failure which are not included in BS5400 by use of the modified probability model. The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.     

Remaining fatigue life of steel railway bridges under enhanced axle loads

In this study, various fatigue damage models proposed by researchers have been briefly discussed and found that the models are problem specific and their efficacy needs to be checked for high cyclic fatigue cases such as in railway bridges. Towards this, field studies were conducted to obtain the strain responses from a steel bridge during the passage of scheduled trains and test train formation with enhanced axle loading. Instrumentation was carried out at critical locations to obtain the responses from the girder. Three different scenarios have been considered to avoid the influence of noise. Further, numerical simulation of the bridge subjected to train loading at different speeds was carried out using ANSYS to obtain synthetic data of strain response from the validated finite element model. Analysis was carried out for normal as well as for futuristic speed of the trains. Responses obtained from field measurements as well as from numerical investigations were used to calculate the damage indices. Based on the damage indices, remaining fatigue life of the bridge was evaluated. The present study can be helpful in assessing the health condition of the railway bridges and to check the suitability of further increase in axle load or speed of trains.     

模块型桥梁伸缩缝疲劳试验研究

模块型桥梁伸缩缝 (MBEJ)由于其伸缩变形能力大、密封防潮性能优良 ,越来越引起世界的广泛关注并被工程界所接受。模块型桥梁伸缩缝在使用过程中要经历数百万次的车轮疲劳循环荷载的作用 ,因此疲劳性能就成为评价模块型桥梁伸缩缝的一个最重要的力学性能指标。利用MTS疲劳试验机和设计加工的加载设备 ,同时施加伸缩缝在工作过程中可能承受的垂直和水平荷载 ,对标准模块型桥梁伸缩缝产品试件进行了静载和先后两次 2 0 0万次不同荷载幅值的疲劳试验。试验结果表明 ,伸缩缝中心梁和支撑梁的残余应变随疲劳循环次数的增加而增加 ,而荷载幅值的提高将在很大程度上提高累计残余应变的增长速率。     

Measured behavior of a curved composite I-girder bridge

Current techniques for the rating of horizontally curved composite steel girder bridges often use approximate methods of linear elastic analysis based on the assessment of individual straight girders with altered properties to account for member curvature. This paper summarizes measured versus computed results from a field test with heavy live load conducted on a multi-span, horizontally curved composite steel I-girder bridge in Duluth, Minnesota. Eight 320 kN (72,000 lb) trucks were placed on the bridge in 43 static and 13 dynamic loading configurations, and the results were compared to those obtained from linear elastic grillage analyses. Stresses up to 75% of the girder yield stress were obtained in the bridge, whose design was controlled by strength, thus representing some of the largest stresses ever achieved in an instrumented curved steel girder bridge, and behavior is described in the girders, diaphragms, lateral wind bracing, deck, bearings, and fatigue details. Grillage analyses are developed and used to corroborate the results and assess the accuracy of these procedures for load rating of bridges.     

Integrating reliability and structural health monitoring in the fatigue assessment of concrete bridge decks

The overall objective of this article is to demonstrate how the concepts of reliability and structural health monitoring (SHM) can be integrated to create bridge assessment and decision systems. The steel-free concrete bridge deck system was chosen as a specific case study providing tangible focus for the research. The bridge assessment model therefore focused on fatigue cracking issues associated with wheel loads due to heavy truck traffic. The bridge assessment model required five components: a vehicle load model, a fatigue damage accumulation model, a residual strength model, a reliability model and an SHM decision model. Each of these components is discussed within the article with specific reference to previous research on steel-free bridge deck systems. The proposed model is used to develop a decision threshold for monitoring the oldest steel-free bridge deck in service.     

考虑屈曲效应的混凝土柱纵筋低周疲劳性能和变形能力研究

屈曲导致的局部塑性应变集中将使钢筋损伤加重,并提前断裂.传统低周疲劳损伤模型(如Coffin-Manson模型,简称C-M模型)中未考虑屈曲效应的影响,这将高估屈曲钢筋的低周疲劳寿命.为研究屈曲对钢筋疲劳寿命的影响,完成了30个原状钢筋试件考虑屈曲的循环加载试验,得到了钢筋断裂时的极限塑性平均应变的测量结果,分析了局部...     

高家花园大桥挠度长期监测数据分析

通过对高家花园大桥长期监测数据的分析,掌握大桥挠度与温度、车辆荷载等作用的变化规律,并初步确定大桥挠度的变化规律。对桥梁结构状态监测系统采集的温度、车流量及重车、挠度监测数据采用时间序列相关分析和小波分析,重点研究了桥梁跨中处挠度变化主要与温度、车辆荷载之间的关系。分析结果表明,桥梁跨中处挠度与温度具有较好的相关性,而挠度的波动主要是由重车引起的。分析结果为高家花园大桥和类似连续刚构桥的安全状态评估提供了技术支持。     

Separation and extraction of bridge dynamic strain data

Through comparing the measured data of dynamic strains due to loading and temperature by the stain gauge and temperature sensor at the same location, the information in the strain data was divided into three parts in the frequency domain by using the defined index named power spectral density (PSD)-ratio index. The three parts are dominated respectively by temperature varying, stresses, and noises and thus can be distinguished from the determined the separatrix frequencies. Also, a simple algorithm was developed to separate the three types of information and to extract the strain caused mainly by structural stresses. As an application of the proposed method, the effect of strain deformation and noises on the fatigue assessment was investigated based on the separated data. The results show that, the determined values of separatrix frequencies are valuable for the monitoring data from other bridges. The algorithm is a multiresolution and hierarchical method, which has been validated as a simple and effective method for data analyses, and is suitable for the compression and preprocessing of the great amount monitoring data and easy to be integrated into the structural health monitoring (SHM) soft system. The strain due to temperature varying attributes a little to the errors of fatigue assessment; however, the noises or random disturbance existed in the monitoring data have much responsibility for the errors, and the main reason is that the random disturbance shifts the real strain/stress amplitude picked up by real structural stress or strain.     

Separation and extraction of bridge dynamic strain data

Through comparing the measured data of dynamic strains due to loading and temperature by the stain gauge and temperature sensor at the same location, the information in the strain data was divided into three parts in the frequency domain by using the defined index named power spectral density (PSD)-ratio index. The three parts are dominated respectively by temperature varying, stresses, and noises and thus can be distinguished from the determined the separatrix frequencies. Also, a simple algorithm was developed to separate the three types of information and to extract the strain caused mainly by structural stresses. As an application of the proposed method, the effect of strain deformation and noises on the fatigue assessment was investigated based on the separated data. The results show that, the determined values of separatrix frequencies are valuable for the monitoring data from other bridges. The algorithm is a multiresolution and hierarchical method, which has been validated as a simple and effective method for data analyses, and is suitable for the compression and preprocessing of the great amount monitoring data and easy to be integrated into the structural health monitoring (SHM) soft system. The strain due to temperature varying attributes a little to the errors of fatigue assessment; however, the noises or random disturbance existed in the monitoring data have much responsibility for the errors, and the main reason is that the random disturbance shifts the real strain/stress amplitude picked up by real structural stress or strain.