Effect of vehicle weight on natural frequencies of bridges measured from traffic-induced vibration

Recently,ambient vibration test(AVT)is widely used tu estimate dynamic characteristics of large civil struc- tures.Dynamic characteristics ean be affected by various envirnnmental factors such as humidity,intensity of wind,and temperature.Besides these environmental conditions,tire mass of vehicles may change the measured valnes when traffic-in- duced vibration is used as a source of AVT tor bridges.The effect of vehicle mass on dynamic characteristics is investigated through traffic-induced vibration tests on three bridges;(1)three-span suspension bridge(128m+404m+128m),(2) five-span continuous steel box girder bridge(59m+3@ 95m+59m),(3)simply supported plate girder bridge(46m). Acceleration histories of each measurement location under normal traffic are recorded for 30 minutes at field.These recor- ded histories are divided into individual vibrations and are combined into two groups aceording to the level of vibration;one by heavy vehicles such as trucks and buses and the other by light vehicles such as passenger cars.Separate processing of the two groups of signals shows that,for the middle and long-span bridges,the difference can be hardly detected,but,for the short span bridges whose mass is relatively small,the measured natural frequencies can change up to 5.4%.

Maximum Probabilistic and Dynamic Traffic Load Effects onShort-to-Medium Span Bridges

The steadily growing traffic load has resulted in lots of bridge collapse events over the past decades, especiallyfor short-to-medium span bridges. This study investigated probabilistic and dynamic traffic load effects on shortto-medium span bridges using practical heavy traffic data in China. Mathematical formulations for traffic-bridgecoupled vibration and probabilistic extrapolation were derived. A framework for extrapolating probabilistic anddynamic traffic load effect was presented to conduct an efficient and accurate extrapolation. An equivalent dynamicwheel load model was demonstrated to be feasible for short-to-medium span bridges. Numerical studies of twotypes of simply-supported bridges were conducted based on site-specific traffic monitoring data. Numerical resultsshow that the simulated samples and fitting lines follow a curve line in the Gumbel distribution coordinate system. Itcan be assumed that dynamic traffic load effects follow Gaussian distribution and the extreme value follows Gumbeldistribution. The equivalent probabilistic amplification factor is smaller than the individual dynamic amplificationfactor, which might be due to the variability of individual samples. Eurocode 1 is the most conservative specificationon vehicle load models, followed by the BS5400 specification. The D60-2015 specification in China and ASSHTOspecification provide lower conservative traffic load models.

How Do Water Filled Traffic Barriers Shake a Suspension Bridge?

The present study stems from the realization that the general problem relating to the analysis of wind-induced vibrations in suspension bridges still requires significant attention.Sidewalk railings,overhaul tracks,and deflectors are known to largely affect such dynamics.Here,the influence of a row of water-filled traffic barriers on the response of a sample suspension bridge is investigated numerically.It is shown that the existence of water barriers causes flow separation and non-negligible vortices with respect to the condition with no water barriers.The vortex shedding frequency at the far end is around 41.30 Hz,relatively close to the real vibration frequency.It is also shown how different incoming angles of attack can change the flow field around the bridge cross-section and the vortex detachment frequency.

A cellular automaton model for a bridge traffic bottleneck

A cellular automaton （CA） model is proposed in this paper to analyze a bridge traffic bottleneck. The simulation results with this model show that there are several phase transitions in the traffic average density, velocity and flow for each lane under a periodic boundary condition. An unstable phase in the traffic average density and velocity for the upstream and downstream lanes of the bridge is shown in a range of initial traffic densities. The critical points of the phase transitions and the phenomenon of the unstable phase found in the simulation are also explained with the mean-field theory.

Durability of Bridge Expansion Joints with Perforated Dowels Under Traffic Impact Loading

In design phases, expansion joints are required to have movement capacity, bearing capacity for static and dynamic loading, watertight, low noise emission and traffic safety. On the basis of the fact that failure due to dynamic loading is the main reason for the observed damages, attention is focused on the bearing capacity for dynamic loading governed by impact, because it differs from the static loading. In this study, from the viewpoint of durability, experimental studies for dynamic behavior were conducted for aluminium alloy expansion joints with perforated dowels. The validity of the perforated dowels against traffic impact loading was confirmed by both experimental and numerical studies.

Comparative analysis of cast-in-place post-tensioned and steel-concrete composite bridge bent caps

The complexity of the IH-635 Managed Lanes Project, located in Dallas County, Texas, posed several technical and constructive challenges, leading to the adoption of solutions different from the traditional. Two alternative solutions for the pier cap on one of the bridge crossings over IH-35E in the IH-635 project were analyzed in this case study, a cast-in-place post-tensioned concrete cap and an innovative prefabricated steel-concrete com- posite cap. The approach was to use an estimation of direct costs for material and labor and consideration of con- struction time schedules. A supplementary numerical modeling confirmed that both alternatives behave elasti- cally under imposed loads. The direct cost of material and labor for the two alternatives were close. However, the composite alternative required 13 days less construction time, resulting in substantial cost savings from traffic closing in the very busy traffic corridor. Traffic closing costs were substantially higher than the direct costs, especially for the post-tensioned cap. The quantification of the benefits allows more confidence in the utilization of the composites caps, leading to faster completion of bridge projects and substantial economic savings.

Damage alarming for bridge expansion joints using novelty detection technique based on long-term monitoring data

Damage alarming and safety evaluation using long-term monitoring data is an area of significant research activity for long-span bridges. In order to extend the research in this field, the damage alarming technique for bridge expansion joints based on long-term monitoring data was developed. The effects of environmental factors on the expansion joint displacement were analyzed. Multiple linear regression models were obtained to describe the correlation between displacements and the dominant environmental factors. The damage alarming index was defined based on the multiple regression models. At last, the X-bar control chart was utilized to detect the abnormal change of the displacements. Analysis results reveal that temperature and traffic condition are the dominant environmental factors to influence the displacement. When the confidence level of X-bar control chart is set to be 0.003, the false-positive indications of damage can be avoided. The damage sensitivity analysis shows that the proper X-bar control chart can detect 0.1 cm damage-induced change of the expansion joint displacement. It is reasonably believed that the proposed technique is robust against false-positive indication of damage and suitable to alarm the possible future damage of the expansion joints.

Design of Bridge Expansion Joints with Perforated Dowels Under Impact Loading

The expansion joints are expected to have movement capacity, bearing capacity for static and dynamic loading, water-tightness, low noise emission and traffic safety. In particular, the failure due to impact loading is the main reason for the observed damages. The problem of dynamic behavior of the expansion joints is so complex that we shall focus our attention on the impact factor for vehicle load that is governed by traffic impact. In order to overcome this difficulty, the cantilever-toothed aluminum joint (finger joint) is one of the promising joints under impact loading. In this study, from the viewpoint of design methodology, numerical studies for impact behavior were conducted for aluminum alloy expansion joints with perforated dowels. The design impact factor for the expansion joints with the perforated dowels against traffic impact loading was examined by using numerical simulations.

Damping Identification of Bridges Under Nonstationary Ambient Vibration

本研究着重于使用非平稳的环境振动数据来识别桥梁的阻尼比。我们通常使用基于输入信号的静态白噪声假设的运行模态分析(OMA)来识别使用中的桥梁的阻尼比。然而,大多数桥梁在使用时通常会受到非平稳激励,而违反这种基本假设会导致阻尼识别的不确定性。为了处理非平稳性,根据测量的响应来计算幅度调制函数,以消除由非平稳输入引起的整体趋势。采用自然激励技术(NExT)-特征系统实现算法(ERA)估算平稳过程中的阻尼比。为了提高基于OMA的阻尼估计的准确性,在提取的平稳过程和非平稳数据之间进行比较分析,以评估消除非平稳性的效果。在信号平稳化后,第一竖向模态的阻尼比的平均值和标准偏差会减小。

THE EFFECT OF THE NEW EURASIAN CONTINENTAL BRIDGE ON THE EASTERN COASTAL AREAS OF CHINA

This article has discussed the effects on the eastern coastal areas of China brought by the new Eurasian Continental Bridge when it was joined up from Chinese coastal harbour Lianyungang to Rotterdam Harbour in Holland.The effects will be discussed from f

Study on the Girder-End Displacement of a Suspension Bridge Based on Field Measurements

The load-response correlation is a great concern for the management and maintenance agency of bridges. Based on both the load test data and the long-term structural health monitoring data, this study aims to characterize the variation in the girder-end longitudinal displacement of a long-span suspension bridge, i.e., the Zhaoyun Bridge in Guangdong Province of China. The load test provides a valuable chance to investigate the structural deformation in high loading levels, while the structural health monitoring system records the real-time, in-site, and long-term measurements in the normal operational stage of bridges. During the load test, the movement direction of the main girder is found to depend on the relative position of the center of gravity of the girder and the loading vehicles. However, over the period of normal operation, the quasi-static displacement at the ends of the main girder along the bridge axis is dominated by the temperature variations, rather than the traffic loading. The temperature-induced deformation is considerable so it should be filtered out from the structural total responses to highlight the live load effects or the anomalies of the bridge. As a case study, the temperature-displacement baseline model of the Zhaoyun Bridge is established and then utilized to identify the erroneous measurements in the structural health monitoring system. This paper serves as a reference for the structural behavior interpretation and performance evaluation of similar bridges.

Design of a d_(33)-mode piezocomposite electricity generating element and its application to bridge monitoring

The piezoelectric effect is used in sensing applications such as in force and displacement sensors.However,the brittleness and low performance of piezoceramic lead zirconate titanate(PZT) often impede its applicability in civil structures which are subjected to large loads.The concept of a piezocomposite electricity generating element(PCGE) has been proposed for improving the electricity generation performance and overcoming the brittleness of piezoceramic wafers.The post-curing residual stress in the PZT layer constitutes a main reason for the PCGE's enhanced performance,and the outer epoxy-based composites protect the brittle PZT layer.A d33-mode PCGE designed for bridge monitoring application was inserted in a bridge bearing to provide a permanent and simple weigh-in-motion system.The designed PCGEs were tested through a series of tests including fatigue and dynamic tests to verify their applicability for monitoring purposes in a bridge structure.A simple beam example was presented to show the applicability of the proposed bridge bearing equipped with the PCGE for adequately measuring the traffic loads.

典型钢桥面铺装体系生命周期碳足迹分析

为了量化钢桥面铺装体系的碳排放量,应用基于过程的生命周期评价方法分析了钢桥面铺装体系的生命周期碳足迹.从材料生产、施工建造、运营管理、维修养护、废弃处置和运输6个过程构建了钢桥面铺装体系碳排放的生命周期清单数据库,采用国际平整度指数建立铺装层行驶质量衰减下的碳排放预估模型,利用SMUO仿真软件进行交通延误仿真获取相关参数以建立交通延误的碳排放模型,建立了相应的碳足迹量化框架和模型,同时对下层EA(环氧)+上层SMA(沥青玛蹄脂)典型铺装体系进行了实例分析.结果表明,维修养护和运营管理阶段贡献了碳排放总量的近80%,交通延误导致的额外碳排放约达到了碳排放总量的24%,固化剂、喷砂除锈等材料或施工工艺也分别贡献了碳排放总量的8.11%和5.42%.

实测车流作用下大跨悬索桥吊索疲劳性能分析

为研究车辆长期作用下悬索桥吊索的疲劳性能,以南京栖霞山长江大桥为工程背景,利用该桥动态称重系统的实测数据,采用有限混合分布拟合了车辆荷载模型.然后,基于时间权重矩阵模拟了桥面多车道随机车流,并基于Ansys计算了随机车流作用下的桥梁动力时程响应.在上述基础上,获取了大桥短吊索、长吊索和限位吊索3组典型吊索的应力时程,并采用名义应力法对其疲劳性能进行分析.结果表明:在随机车流作用下,大部分时间段内吊索应力波动较为平稳;各吊索应力变化趋势与车流量的变化密切相关,短吊索、长吊索以及限位吊索的最大应力幅分别为40、30和25 MPa;在车辆荷载的长期作用下,短吊索的疲劳可靠度显著低于长吊索与限位吊索.

桥梁预拱度对行车舒适性的影响及桥面线形调整

为研究成桥预拱度对连续刚构桥行车舒适性的影响,以多座主跨跨径为110~200 m的连续刚构桥为研究对象,首先,采用滤波白噪声法建立桥面时域模型,并与按余弦曲线设置的成桥线形叠加模拟成桥后的桥面不平度;其次,采用MATLAB/Simlink搭建车辆-桥面系统模型,以加速度均方根值(RMS)作为桥梁边跨、中跨桥面的行车舒适性评价指标,以最大瞬态振动值(MTVV)作为边跨峰值处短时内的行车舒适性评价指标;最后,分析采取经验法按照余弦曲线设置成桥预拱度的桥梁其跨径和设计时速对边、中跨RMS值的影响,以及成桥预拱度取值对边跨3L/8处MTVV值的影响。研究结果表明:在边跨、中跨处RMS值均小于0.315 m/s^(2),说明采取经验法按照余弦曲线设置成桥预拱度并不影响中跨处的行车舒适性;在边跨3L/8处MTVV值在短时内存在大于0.345 m/s^(2)的情况,说明在边跨峰值处短时内会产生一定不舒适感。提出了一种基于桥面铺装层施工优化边跨3L/8处和边墩墩顶桥面线形的方法,改善了边跨的行车舒适性。

震后RC桥墩竖向承载力最优工程需求参数的选取方法

桥墩结构的震后竖向承载力是评估梁式桥梁震后通行功能的重要指标,但其难以测量。为了快速定量地评估桥梁结构的震后通行能力,对评估梁式桥梁结构震后竖向承载力的最优工程需求参数(EDP)进行了系统地研究。首先选取与墩柱残余侧移和损伤相关的5个EDPs,通过对考虑了材料不确定性的RC桥墩进行Pushover分析和动力时程分析得到5个EDPs,进一步对震后的桥墩进行Pushdown分析获取震后竖向承载力。然后采用回归模型对所选EDPs与震后竖向承载力损失比的关系曲线进行回归分析,选取竖向承载力损失比关系曲线的最优回归模型为在ln(x)-y坐标系中的正态累积函数模型,进一步通过最优EDP评价准则对评估竖向承载力损失比的5个EDPs进行评价分析。评价结果表明:当考虑震后可计算性时,峰值侧移率最优;当考虑震后可测性时,残余侧移率最优;当考虑余震时,改进的Park-Ang指标最优。通过选取的最优EDP可以建立桥梁结构功能指标与抗震性能指标之间的联系,为进一步发展和完善桥梁结构的抗震韧性评估和设计提供参考。

大跨度桥梁钢桥面板跨尺度疲劳损伤评估方法

大跨度斜拉桥正交异性钢桥面板的顶板与纵肋焊接构造细节在车辆荷载作用下易产生疲劳损伤进而导致服役性能降低、影响行车安全。为评估大跨度桥梁钢桥面板的疲劳性能,提出基于细观损伤力学的大跨度钢桥疲劳损伤跨尺度评估方法;推导了基于细观损伤力学的钢桥面板疲劳损伤演化模型,在此基础上,结合实测交通数据,实现了基于Monte-Carlo法的随机车流模拟;最后,将提出的方法应用于一座大跨度三塔斜拉桥。研究结果表明,大跨度斜拉桥钢桥面板体系焊缝周围区域的累积疲劳损伤程度明显高于桥面板体系的其他部位;顶板与纵肋焊接构造细节的疲劳损伤累积呈现明显的非线性,预测的疲劳寿命远小于Miner线性疲劳损伤累积准则的结果。

复杂艰险山区高速铁路慢行病害特征与治理

针对我国西南复杂艰险山区高速铁路建设与运营中路基、桥梁和隧道出现导致列车运行速度减慢的病害(慢行病害),依托南昆、沪昆、西成高铁3条复杂艰险山区高速铁路运营期间监测与补充勘察资料,分析不同慢行病害的危害方式与变形破坏特征,研究高速铁路慢行病害产生的原因,提出治理方案。研究得出结论:地层岩性、地形地貌、构造应力环境、气候降雨、岩体结构条件等多重因素造成复杂艰险山区高速铁路出现路基基底上拱、斜坡桥梁位移、隧道基底上拱、隧道混凝土腐蚀等慢行病害,针对不同慢行病害提出多种治理方案。研究成果可为复杂艰险山区高速铁路工程建设、运营维护提供借鉴。

高铁箱梁桥顶板纵向加筋对其声振特性的影响

伴随着高速铁路箱梁桥的大规模建设,列车经过时引起的高架桥低频声辐射问题已成为限制其发展重要因素之一。为了缓解列车经过箱梁桥时的声辐射问题,有必要开展桥梁降噪措施研究。以高速铁路箱梁桥为研究对象,对箱梁桥顶板增设纵向筋板,采用多体系统动力学软件UM及有限元-边界元方法建立车辆-轨道-桥梁耦合动力学模型和声学预测模型,对原结构箱梁桥和加筋板箱梁桥的振动加速度、辐射声功率、线性声压级和声场分布等进行分析,研究顶板纵向加筋对箱梁桥声振特性的影响。研究结果表明:增设纵向筋板后箱梁桥各个板件振动加速度都明显减小,在顶板处减幅最大;增设纵向筋板后箱梁桥的辐射声功率和声压级明显降低,降噪效果良好;其对桥上声场的降噪效果好于桥下和桥侧声场。

随机车载激励下大跨度悬索桥中央扣振动控制研究

大跨度悬索桥车流荷载作用下振动响应明显,关键构件疲劳损坏直接影响结构服役状态及运营安全。为改善大跨度悬索桥结构振动响应,基于有限元模拟对柔性中央扣及刚性中央扣振动控制效应开展研究,分析了中央扣对结构模态特性的影响,并基于考虑参数相关性及车流参数聚类特征的随机车流模拟方法,分析了车流荷载下的中央扣振动控制效应及其对吊索钢丝寿命影响。研究结果表明:中央扣主要对悬索桥的反对称竖弯频率及一阶扭转频率存在影响,随着柔性中央扣数量的增加结构振动频率有所提升,刚性扣的提升效果与三柔性中央扣接近。车流作用下中央扣可显著减小梁端位移、梁端累计位移及缆梁相对位移,随柔性中央扣数目的增加,控制效率有所提升但提升效果逐渐减小。刚性中央扣对梁端位移及梁端累计位移的控制效果与三柔性扣索接近,其对缆梁相对位移的控制效果好于柔性中央扣。吊索钢丝的疲劳寿命与弯曲应力响应的变化趋势一致,长吊索整体弯曲应力水平相对较小,中央扣对其钢丝寿命影响不明显。短吊索钢丝疲劳寿命则大幅提升,但柔性中央扣数量的增加提升效果有限,刚性中央扣提升效果与三柔性扣索接近。