Load Test Analysis and Research on Long-Span Concrete Continuous Rigid Frame Bridge

Based on the as-built load test of a large bridge,this paper introduces the procedure of the prestressed concrete continuous rigid frame bridge load test.Numerical analysis of the bridge was carried out by simulating and establishing a finite element model,and comparative analysis was carried out with the measured values.The results show that the calculated values were basically consistent with the measured values,which showed that the establishment method of the model was reasonable,and the mechanical performance of the bridge met the service requirements of the designed live load.

Fatigue Safety Assessment of Concrete Continuous Rigid Frame Bridge Based on Rain Flow Counting Method and Health Monitoring Data

The fatigue of concrete structures will gradually appear after being subjected to alternating loads for a long time,and the accidents caused by fatigue failure of bridge structures also appear from time to time.Aiming at the problem of degradation of long-span continuous rigid frame bridges due to fatigue and environmental effects,this paper suggests a method to analyze the fatigue degradation mechanism of this type of bridge,which combines long-term in-site monitoring data collected by the health monitoring system(HMS)and fatigue theory.In the paper,the authors mainly carry out the research work in the following aspects:First of all,a long-span continuous rigid frame bridge installed with HMS is used as an example,and a large amount of health monitoring data have been acquired,which can provide efficient information for fatigue in terms of equivalent stress range and cumulative number of stress cycles;next,for calculating the cumulative fatigue damage of the bridge structure,fatigue stress spectrum got by rain flow counting method,S-N curves and damage criteria are used for fatigue damage analysis.Moreover,it was considered a linear accumulation damage through the Palmgren-Miner rule for the counting of stress cycles.The health monitoring data are adopted to obtain fatigue stress data and the rain flow counting method is used to count the amplitude varying fatigue stress.The proposed fatigue reliability approach in the paper can estimate the fatigue damage degree and its evolution law of bridge structures well,and also can help bridge engineers do the assessment of future service duration.

Application of Long-Span Continuous Bridge Technology in Bridge Construction

In order to promote the rapid development of urbanization in our country,it is necessary to improve the construction level and technology of bridge engineering.For long-span continuous bridge technology,it has the characteristics of wide application range,various applicable conditions,and short construction period.Therefore,it is necessary to pay attention to the application of long-span continuous bridge technology.This article mainly analyzes its application in bridge construction,hoping to provide some reference for future use.

Stability Analysis of Long-Span Continuous Rigid Frame Bridge with Thin-Wall Pier

During cantilever cast in construction of high-pier and large-span continuous rigid frame bridges, structural stability in the longest cantilevered stage is very important. Based on a practical design case of a large-span continuous rigid frame bridge in Wuhan, the longest span stability coefficient is calculated with linear-buckling and nonlinear-buckling methods, respectively. The influences of both geometrical nonlinearity and the dual nonlinearity of material and geometry are considered. Numerical results indicate that the nonlinear solution is necessary to stability analysis because linear buckling loads are much higher than those of nonlinear buckling. Thus, the edge fiber yield criterion is more convenient and faster than ultimate loading criterion when estimating nonlinear stability of structure, and can be used easily in the initial engineering design.

Time-varying Reliability Analysis of Long-span Continuous Rigid Frame bridge under Cantilever Construction Stage based on the Monitored Strain Data

In general,the material properties,loads,resistance of the prestressed concrete continuous rigid frame bridge in different construction stages are time-varying.So,it is essential to monitor the internal force state when the bridge is in construction.Among them,how to assess the safety is one of the challenges.As the continuous monitoring over a long-term period can increase the reliability of the assessment,so,based on a large number of monitored strain data collected from the structural health monitoring system(SHMS)during construction,a calculation method of the punctiform time-varying reliability is proposed in this paper to evaluate the stress state of this type bridge in cantilever construction stage by using the basic reliability theory.At the same time,the optimal stress distribution function in the bridge mid-span base plate is determined when the bridge is closed.This method can provide basis and direction for the internal force control of this type bridge in construction process.So,it can reduce the bridge safety and quality accidents in construction stages.

Research on controlling long-term performance by tensioning post tendon of long-span continuous rigid-frame bridges

The problems like cracking of the girder in the mid-span and the ever-increasing vertical deflection appear during the long term usage of the long-span continuous rigid-frame bridge.Post-tension tendon with reserved duct can increase the pre-stress of the main beam effectively,and decrease the long term span deflection in order to improve the performance of the girder.At the same time,the proper tension position is very crucial to optimise the stress distribution of the bridge and control the deflection increase.Combining with practical engineering,the authors analyze the influence of different positions of post-tension tendon(including top-,weband bottom plate tendons)on the stress and deflection of the main beam,and find out the optimal position of post tendon.

Seismic analysis of long-span continuous rigid frame bridges in cold regions:a case study of Bridge 1 in north of international tourism resort in Changbai Mountain

It is helpful to improve the seismic design theory of long-span continuous bridges for studying the seismic performance of each cantilever construction state.Taking the Bridge 1 in the north of Changbai-Mountain international tourism resort as an example,the authors studied it in shutdown phase and the cantilever construction process,established the simulation model by using Midas / civil,and analyzed time-history of each construction stage for the bridge.The study shows that long-span bridge cantilever construction in northeastern China can be divided into two-year tasks for construction(suspending in winter).It is needed to think about seismic stability of the cantilever position in shut-down phase of winter.The effect of longitudinal vibration is the most disadvantageous influence to bridge,and its calculation results can provide reference for seismic design of similar bridges in the future.

Longitudinal force in continuously welded rail on long-span tied arch continuous bridge carrying multiple tracks

Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.

Numerical analysis of dynamic response of vehicle–bridge coupled system on long-span continuous girder bridge

To systematically study the vehicle-bridge coupled dynamic response and its change rule with different parameters, a vehicle model with seven degrees of freedom was built and the total potential energy of vehicle space vibration system was deduced. Considering the stimulation of road roughness, the dynamic response equation of vehicle-bridge coupled system was established in accordance with the elastic system principle of total potential energy with stationary value and the ＂set-in-right-position＂ rule. On the basis of the self-compiled Fortran program and bridge engineering, the dynamic response of long- span continuous girder bridge under vehicle load was studied. This study also included the calculation of vehicle impact coefficient, evaluation of vibration comfort, and analysis of dynamic response parameters. Results show the impact coefficient changes with lane number and is larger than the value calculated by the ＂general code for design of highway bridges and culverts （China）＂. The Dieckmann index of bridge vibration is also related to lane number, and the vibration comfort evaluation is good in normal conditions. The relevant conclusions from parametric analyses have practical significance to dynamic design and daily operation of long-span continuous girder bridges in expressways. Safety and comfort are expected to improve significantly with further control of the vibration of vehicle-bridge system.

Analytical Research on Deformation Monitoring of Large Span Continuous Rigid Frame Bridge during Operation

Based on a large span continuous rigid frame bridge in Chongqing of China, the main pier vertical displacement and deviation, the bridge deck alignment and the expansion joint deformation are analytically researched during operation. Firstly, the monitoring content and method of the large span continuous rigid frame bridge are clearly stated. Secondly, by finite element software Midas Civil, the relevant deformation values of the bridge are calculated. Thirdly, in practice, the relevant deformation values of the bridge are measured. Finally, the measured values in practice are compared with the calculated ones by the finite element software Midas Civil, finding that the former is less than the latter, and it can be concluded that the bridge is basically in the normal working condition. In this paper, the analytical research on the deformation monitoring can provide the basis for similar bridges, which has good practical significance.

Maintenance Management Research of a Large-span Continuous Rigid Frame Bridge Based on Reliability Assessment by Using Strain Monitored Data

When the bridge components needing maintenance are the world problem at present,and the health monitoring system is considered to be a very help­ful tool for solving this problem.In this paper,a large number of strain data acquired from the structural health monitoring system(SHMS)installed on a continuous rigid frame bridge are adopted to do reliability assessment.Firstly,a calculation method of punctiform time-dependent reliability is proposed based on the basic reliability theory,and introduced how to cal­culate reliability of the bridge by using the stress data transformed from the strain data.Secondly,combined with“Three Sigma”principle and the basic pressure safety reserve requirement,the critical load effects distribu­tion function of the bridge is defined,and then the maintenance reliability threshold for controlling the unfavorable load state which appears in the early operation stage of this type bridge is suggested,and then the combi­nation of bridge maintenance management and health monitoring system is realized.Finally,the transformed stress distribution certifies that the load effects of concrete bridges practically have a normal distribution;as for the concrete continuous rigid frame bridge with C50 strength grade concrete,the retrofit reliability threshold should be valued at 6.13.The methodology suggested in this article can help bridge engineers do effective maintenance of bridges,which can effectively extend the service life of the bridge and bring better economic and social benefits.

Effect of concrete creep on pre-camber of continuous rigid-frame bridge

The effect of concrete creep on the pre-camber of a long-span pre-stressed concrete continuous rigid-frame bridge constructed by cantilever casting method was investigated.The difference of creep coefficients calculated with two Chinese codes was discussed.Based on the calculations,the pre-camber of a pre-stressed concrete continuous rigid-frame box bridge was computed for construction control purpose.The results show that the short-term creep coefficient and long-term creep coefficient calculated with the CC-1985 are larger than those calculated with the CC-2004,while the medium-term creep coefficient calculated with the CC-1985 is smaller than that calculated with the CC-2004.The difference of creep deformation calculated with these two codes is small,and the influences of concrete creep on the pre-camber for most of the segments are negligible.The deflections and stresses of the box girder measured during the construction stages agree very well with the predictions.

Dynamic Reliability Assessment of Heavy Vehicle Crossing a Prototype Bridge Deck by Using Simulation Technology and Health Monitoring Data

Overloads of vehicle may cause damage to bridge structures,and how to assess the safety influence of heavy vehicles crossing the prototype bridge is one of the challenges.In this report,using a large amount of monitored data collected from the structural health monitoring system(SHMS)in service of the prototype bridge,of which the bridge type is large-span continuous rigid frame bridge,and adopting FEM simulation technique,we suggested a dynamic reliability assessment method in the report to assess the safety impact of heavy vehicles on the prototype bridge during operation.In the first place,by using the health monitored strain data,of which the selected monitored data time range is before the opening of traffic,the quasi dynamic reliability around the embedded sensor with no traffic load effects is obtained;then,with FEM technology,the FEM simulation model of one main span of the prototype bridge is built by using ANSYS software and then the dynamic reliability when the heavy vehicles crossing the prototype bridge corresponding to the middle-span web plate is comprehensively analyzed and discussed.At last,assuming that the main beam stress state change is in the stage of approximately linear elasticity under heavy vehicle loads impact,the authors got the impact level of heavy vehicles effects on the dynamic reliability of the prototype bridge.Based on a large number of field measured data,the dynamic reliability value calculated by our proposed methodology is more accurate.The method suggested in the paper can do good for not only the traffic management but also the damage analysis of bridges.

Field Load Test Based SHM System Safety Standard Determination for Rigid Frame Bridge

The deteriorated continuous rigid frame bridge is strengthened by external prestressing. Static loading tests wereconducted before and after the bridge rehabilitation to verify the effectiveness of the rehabilitation process. Thestiffness of the repaired bridge is improved, and the maximum deflection of the load test is reduced from 37.9 to27.6 mm. A bridge health monitoring system is installed after the bridge is reinforced. To achieve an easy assessmentof the bridge’s safety status by directly using transferred data, a real-time safety warning system is createdbased on a five-level safety standard. The threshold for each safety level will be determined by theoretical calculationsand the outcomes of static loading tests. The highest risk threshold will be set at the ultimate limit statevalue. The remaining levels, namely middle risk, low risk, and very low risk, will be determined usingreduction coefficients of 0.95, 0.9, and 0.8, respectively.

考虑墩-梁碰撞效应的连续刚构桥系统易损性与概率地震风险性分析

为研究连续刚构桥主梁与过渡墩碰撞效应对其地震系统易损性和概率地震风险性的影响,以一座主桥跨径为(120+220+120)m的连续刚构桥为研究背景,通过模拟实际施工过程以获得真实成桥内力状态,基于等效荷载法建立考虑该内力状态的动力弹塑性分析模型,采用Hertz-damp接触模型考虑包括主梁与过渡墩碰撞在内的伸缩缝处碰撞效应。选取90条具有速度脉冲的脉冲型近断层地震动沿纵桥向输入,通过时程分析解释了墩梁碰撞过程和破坏机理;采用增量动力分析法,建立考虑桥墩和支座权重系数的全桥复合系统易损性曲线,并与一阶界限法串联模型下限和并联模型上限系统易损性曲线进行对比,将场地危险性函数与易损性函数卷积,建立概率地震风险曲线,考察桥梁系统易损性、概率地震风险性及墩梁碰撞效应的影响。结果表明,若忽略过渡墩与主桥梁体的碰撞效应,将会低估过渡墩的位移反应3~5倍,低估其地震风险性概率120%;当地震动强度为0.2g~0.6g时,轻微破坏和中等破坏的损伤概率被低估了35%~80%;地震动强度为0.6g~1.5g时,严重破坏和完全破坏分别被低估13%~68%和15%~59%。

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。

耐震时程法在大跨连续刚构桥纵向抗震性能评估中的应用

采用简化方法对大跨连续刚构桥的抗震性能进行高效和准确的评估,在该类桥梁的设计和加固改造时是非常必要的。耐震时程法作为一种评估桥梁抗震性能的简化方法,只需要一次时程分析就可以实现桥梁从完好到倒塌的全过程分析。为研究耐震时程法在评估大跨连续刚构桥纵向抗震性能的适用性与精确性,本文以一座大跨波形钢腹板连续刚构桥为研究对象,基于中国公路桥梁抗震设计规范设计反应谱,生成3条耐震加速度时程曲线作为地震输入,同时选择16条天然地震动进行增量动力分析,对比研究了该连续刚构桥地震响应特征。研究结果表明:耐震时程分析结果处于增量动力分析结果的包络线之内,耐震时程法中位值与增量动力分析结果的均值曲线吻合较好,因此,耐震时程分析方法可以作为大跨连续刚构桥抗震性能评估的一种高效率方法。

高铁大跨双肢墩连续刚构桥减震系梁地震易损性分析

为了解地震作用下减震系梁对高铁大跨双肢墩连续刚构桥的减震效果,以某主跨180 m的山区高铁双肢墩连续刚构桥为背景,分别建立采用钢筋混凝土(RC)系梁、2种新型减震系梁(可屈服钢系梁与斜交筒式黏弹性阻尼器系梁)方案的全桥有限元模型,对比分析不同系梁方案下的结构损伤、桥面平顺性指标等。结果表明:2种新型减震系梁均不会在地震作用下出现负刚度,新型减震系梁方案较RC系梁方案能有效降低系梁和主墩的结构损伤概率,主墩最大压应变降低83.3%;但减震系梁对震后桥面平顺性指标无明显改善,需采用更具针对性的技术措施。

高速铁路跨度250 m级连续刚构桥长波不平顺控制研究

连续刚构桥随着跨度增加,其收缩徐变、温度等引起的桥面变形随之增加,导致轨道长波不平顺加剧,进而可能对列车走行性产生不利影响。以一座试设计主跨250 m高速铁路连续刚构桥为研究对象,建立有限元模型,依据规范检算桥梁的强度和刚度,同时计算由于混凝土收缩徐变、温度效应等引起的桥面附加变形。采用“车-线-桥”动力仿真软件分析由于桥面附加变形导致的轨道长波不平顺对列车动力响应的影响。选用中点弦测法作为评价指标,通过相关性分析选出最优弦测长度,最后计算出最优弦长下连续刚构的桥面变形和等效不平顺限值。研究结果表明:横、竖向桥面附加变形均出现在桥梁的跨中截面;当附加变形增加到1.9倍,列车以速度350 km/h通过连续刚构时,车辆的竖向加速度首先达到限值1.3 m/s^(2);采用弦长为60 m的中点弦测法与车辆响应匹配性最好,适用于评价连续刚构的长波不平顺;连续刚构的桥面附加变形和等效不平顺60 m弦中点弦测值分别为7.2 mm和14.5 mm,对应限值建议分别为7 mm和14 mm。

大跨连续刚构桥梁腹板施工裂缝成因分析研究

广西某连续刚构桥在悬臂浇筑施工时箱梁腹板产生了斜向裂缝。为剖析这些裂缝的产生原因,避免该类施工缺陷,通过现场深入调查,对裂缝成因开展了相应的理论分析,借助ABAQUS有限元软件对主要影响因素进行模拟,从而揭示了斜裂缝的病因,基于计算结果提出了一系列的改善措施。计算结果表明:当竖向预应力张拉滞后箱梁腹板的竖向拉应力值超过原混凝土的抗拉强度设计值(即2.51 MPa)会导致箱梁腹板开裂;为防止张拉竖向预应力过程中腹板开裂,建议第一次张拉量应超过设计荷载的60%以上,应在施工下一节段前及时将竖向预应力完全张拉防止预应力的损失;混凝土弹性模量值对箱梁腹板受拉也有较大影响,为降低开裂风险,应保证混凝土龄期在7 d以上再进行张拉。