Nonlinear Stability Analysis of Long Span Continuous Rigid Frame Bridge with Thin Wall High Piers

By utilizing the current finite element program ANSYS, two types of finite element models (FEM), the beam model (BM) and shell model (SM), are established for the nonlinear stability analysis of a practical rigid frame bridge—Longtanhe Great Bridge. In these analyses, geometrical and material nonlinearities are simultaneously taken into account. For geometrical nonlinearity, updated Lagrangian formulations are adopted to derive the tangent stiffness matrix. In order to simulate the nonlinear behavior of the plastic hinge of the piers, the multi lines spring element COMBIN39 is used in the SM while the bilinear rotational spring element COMBIN40 is employed in the BM. Numerical calculations show that satisfying results can be obtained in the stability analysis of the bridge when the double coupling nonlinearity effects are considered. In addition, the conclusion is significant for practical engineering.

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.

Experimental investigation on seismic performance of rigid frame tied-arch bridge with split-piers

A novel seismic design method, namely split-pier seismic design, is proposed. A vertical gap and connect elements are set in split-piers. The lateral stiffness of piers is reduced by cracking of the connect elements under severe earthquake, and the seismic response of bridges is reduced by avoiding the site predominant periods. A model of tied-arch rigid frame bridge with split-piers was designed. Seismic performance was investigated by pseudo-static experimentation on the scale model, The failure process of split-piers, the hysteresis characteristic and the effect of split-piers on the superstructure are presented. Results show that the split-pier has better seismic performance than common ductile piers do.

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.

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.

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.

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.

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.

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.

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。

三水河特大桥桥墩温度场及温度效应研究

为研究温度效应对连续刚构桥空心薄壁墩受力行为的影响,以(98+5×185+98)m变截面预应力混凝土连续刚构桥——三水河特大桥主桥为背景,通过现场温度场测试,研究桥墩垂直温度场和水平温度场的分布规律,并以实测温度场为依据,选取对桥墩刚度影响较大的桥墩高度、顺桥向宽度和壁厚作为关键参数,分析整体均匀温度T和梯度温度ΔT对空心薄壁墩受力的影响。结果表明:实测桥墩垂直温度场随着墩高的变化分布差异较小,水平温度场受日光照射影响较大,桥墩夏季的梯度温度值约为冬季的2倍。墩高对桥墩温度应力的影响基本呈反比关系,顺桥向宽度对墩底温度应力的影响呈线性增长趋势,壁厚与温度应力呈反比关系。对于长联刚构桥,为减小桥墩的温度效应,建议边主墩高度不宜小于60 m,桥墩顺桥向宽度宜尽量减小,桥墩壁厚宜取80~100 cm。

钢筋混凝土薄壁空心高墩塑性铰长度计算方法

针对我国现行抗震设计规范尚未明确给出钢筋混凝土(RC)薄壁空心高墩塑性铰长度计算方法的问题,首先收集整理了既有RC桥墩塑性铰长度计算方法以及试验数据,分析影响塑性铰计算长度的主要因素;同时对实际桥梁工程采用的RC薄壁空心墩构造参数进行统计归纳.在验证有限元建模方法准确性后,采用ABAQUS软件建立了高度为40~120 m的8种典型RC薄壁空心高墩的精细化有限元模型,并开展非线性推覆分析,得到不同高度桥墩的等效塑性铰长度.最后讨论不同塑性铰长度计算方法的适用性,发现Eurocode 8规范的计算公式精度最高,可用于计算RC薄壁空心高墩的塑性铰长度.

风屏障透风率对强风作用下重载铁路刚构-连续梁车桥耦合振动响应的影响

为探究风屏障透风率对强风作用下重载铁路刚构-连续梁车桥耦合振动的影响,先通过节段模型风洞试验获取桥上设置0%,20%,40%,60%和无风屏障5种不同透风率风屏障时车桥系统的三分力系数,再根据弹性系统动力学总势能不变原理建立风-车-桥耦合振动仿真计算分析模型,对不同车速下重载货运列车通过设置不同透风率风屏障刚构-连续梁桥开展风-车-桥系统动力学仿真计算与分析研究。结果表明:在列车上桥初期,桥梁横向位移峰值随透风率的增大而明显减小,而当列车运行趋于满布桥梁时,桥梁的横向位移峰值随透风率的增大变化不明显;列车的动力响应峰值随风屏障透风率的增大而增大,相比于满载编组列车,空载和轻重混编编组列车的动力响应对风屏障透风率的变化更加敏感。综合桥梁动力响应和列车走行安全性评价指标(脱轨系数和轮重减载率),该桥梁应设置40%透风率的风屏障。

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%。

不等高双薄壁墩结构参数对连续刚构桥力学行为影响分析

对于因地形和地貌原因而使双薄壁墩连续刚构桥相邻桥墩高度相差较大的情况,设计常采用不等高双薄壁墩。相比常规双薄壁墩,不等高双薄壁墩结构设计及优化可供借鉴和参考的成果不多。以某不等高、不等厚双薄壁墩预应力混凝土连续刚构桥为工程依托,基于有限元数值分析方法,改变低墩壁厚和墩间距,针对结构恒载作用、最大悬臂状态稳定及结构自振,采用单因素分析方法研究薄壁墩结构参数对连续刚构桥结构力学行为影响。结果表明:恒载作用下,低墩壁厚对主梁根部弯矩影响很小,对跨中弯矩影响相对较大;增大双肢间距可明显降低主跨跨中、根部弯矩。低墩稳定安全系数对壁厚更敏感;墩参数变化不改变失稳模态。随着低墩壁厚和间距增加,结构自振频率增大,壁厚、双肢间距影响结构一阶振动模态,且壁厚对一阶自振影响最显著。分析结论可供不等高双薄壁墩连续刚构桥结构设计和优化参考。

多跨连续刚构桥合龙顶推方案优化

为了能更好地减少多跨连续刚构桥成桥后期各个桥墩墩顶的纵桥向水平位移和结构附加内力,提出由中到边合龙依次顶推的优化方案,作出了相应的计算图示且推导了相关的理论计算公式,同时根据顶推力理论计算公式的需要,推导了变截面的主梁和桥墩的抗弯惯性矩的理论计算公式,以某六跨连续刚构桥为例,建立有限元模型,通过理论计算公式和有限元模型分别计算了优化方案的顶推力数值并进行了对比分析,验证合龙优化方案顶推力理论计算公式的有效性,然后将由边到中的原合龙顶推方案和先中后边的优化合龙顶推方案作对比,验证合龙优化方案的合理性。结果表明:相较于原方案,使用优化方案虽然增加了顶推次数,但是其每次顶推力的数值较原方案中一次顶推力的数值都有大幅减少,从而能够有效地减少顶推处的局部应力水平;优化方案能更好地调控各个墩的变形,尤其是距离主梁中点较远的桥墩,因此优化方案对墩顶的纵向水平位移和墩底的弯矩改善效果更加明显;优化方案理论计算公式计算得到的顶推力数值相比于使用有限元模型推算的顶推力数值偏大,但总的来说相差不大,满足实际工程的要求;不同的顶推方案主要的影响是桥墩的变形与内力,顶推施工对成桥后主梁的收缩徐变以及线形的影响不大。

甘溪特大桥空腹三角区施工阶段受力分析

甘溪特大桥是主跨300 m的空腹式连续刚构桥,空腹三角区上弦箱梁采用可伸缩部分立柱后支配合挂篮悬浇,下弦箱梁采用全斜拉扣挂法配合挂篮悬浇。为分析采用该施工方法在三角区临时结构体系中的受力特性,总结三角区临时结构体系施工过程中受力变化规律,验证施工方法的有效性,并提出临时扣索和支撑立柱的最佳解除时机,采用有限元结构分析软件模拟全桥施工过程。结果表明:采用该工法施工,结构受力满足规范要求。三角区施工过程中,已施工的上、下弦箱梁以受压为主,受下一节段混凝土浇筑、立柱支顶、扣索张拉等工序影响,其间会出现短暂轻微受拉状态。三角区合龙完成时,箱梁截面以受压为主,局部存在轻微受拉。全桥合龙后三角区箱梁为全受压状态,较三角区合龙状态压应力增加明显。临时扣索、立柱拆除后,上、下弦箱梁出现了明显的应力重分布,但仍为全受压状态。临时扣索索力峰值均出现在三角区合龙完成前,三角区合龙后总体呈下降趋势,临近拆除前有所回升。后方临时立柱在施工过程中支撑力总体呈下降趋势,前方立柱呈上升趋势,临近拆除前立柱支撑力增幅均较大。经比选,推荐全桥合龙后先拆立柱、再拆扣索。

连续刚构箱形-双薄壁组合式主墩及其刚度匹配设计方法

文章针对因受到建设条件制约而不得不采用主墩高度相差较大的连续刚构桥梁,应用箱形-双薄壁组合式桥墩作为主墩结构,提出了对应的主墩刚度匹配设计方法,并对刚度计算过程进行了推导,得到了组合式桥墩墩顶顺桥向抗推集成刚度的计算公式,用实桥计算示例对提出的主墩设计和传统设计的结果进行了对比。结果表明,文章提出的箱形-双薄壁组合式主墩刚度匹配设计方法能有效地避免主墩高度差引起的内力不均匀分配问题,从而改善高、低主墩连续刚构桥梁在温度、制动力等水平荷载下的力学表现,提高结构的抗震性能。