Dynamic finite element model updating of prestressed concrete continuous box-girder bridge

The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .

Lifetime Reliability Analysis of Flexural Cracking for Prestressed Concrete Bridge

Time-dependant reliability is analyzed for the flexural cracking of prestressed concrete bridges under service limit state. The limit state function and random variables are derived from Chinese highway bridge design specifications. For deterioration of structural performances, chloride-induced reinforcement corrosion is emphasized. Through integrating first order reliability method （FORM） and time discretized approach, the time-variant reliability is evaluated. For illustrative propose, the reliability of a typical simply supported prestressed concrete beam is exemplified.

Evaluation method research on prestressed concrete bridges

Considering the construction features of prestressed concrete bridge, the comprehensive evaluation method about the bridge damage conditions are studied. Particular attentions are paid on establishing a multi-level evaluation model for damaged prestressed concrete bridge, and the evaluation indices of the model as well as the rating standards are defined in the model. A normal relative function about the evaluation indices of each element is developed to calculate the relative degree, and for each element which is no sub-level elements. When evaluating the elements in sub-item level or index level of the model, the weights of elements that are pertained to one element are adopted, taking account of their deterioration degree. At the same time, the damage conditions of bridge are characterized by relative degree, element evaluation scale and structural technology mark of bridge,so it agrees with Code for Maintenance of Highway Bridges and Culvers.

Seismic Analysis for Rigid-Framed Prestressed Reinforced Concrete Bridge in Tianjin Light Railway

The seismic analysis of a rigid-framed prestressed concrete bridge in Tianjin Light Railway is performed. A 3-D dynamic finite element model of the bridge is established considering the weakening effect caused by the soft soil foundation. After the dynamic characteristics are calculated in terms of natural frequencies and modes, the seismic analysis is carried out using the modal response spectrum method and the time-history method, respectively. Based on the calculated results, the reasonable design values are finally suggested as the basis of the seismic design of the bridge, and meanwhile the problems encountered were also analyzed. Finally, some conclusions are drawn as: 1) Despite the superiority of rigid-framed prestressed concrete bridge, the upper and lower ends of the piers of the bridge are proved to be the crucial parts of the bridge, which are easily destroyed under designed earthquake excitations and should be carefully analyzed and designed; 2) The soft soil foundation can possibly result in rather weakening of the lateral rigidity of the rigid-framed bridge, and should be paid considerable attention; 3) The modal response spectrum method, combined with time-history method, is suggested for the seismic analysis in engineering design of the rigid-framed prestressed concrete bridge.

Degradation process assessment of prestressed concrete continuous bridges in life-cycle

To accurately evaluate the degradation process of prestressed concrete continuous bridges exposed to aggressive environments in life-cycle,a finite element-based approach with respect to the lifetime performance assessment of concrete bridges was proposed.The existing assessment methods were firstly introduced and compared.Some essential mechanics problems involved in the degradation process,such as the deterioration of materials properties,the reduction of sectional areas and the variation of overall structural performance caused by the first two problems,were investigated and solved.A computer program named CBDAS(Concrete Bridge Durability Analysis System) was written to perform the above-metioned approach.Finally,the degradation process of a prestressed concrete continuous bridge under chloride penetration was discussed.The results show that the concrete normal stress for serviceability limit state exceeds the threshold value after 60 a,but the various performance indicators at ultimate limit state are consistently in the allowable level during service life.Therefore,in the case of prestressed concrete bridges,the serviceability limit state is more possible to have durability problems in life-cycle;however,the performance indicators at ultimate limit state can satisfy the requirements.

Weakening effect of vertical prestress ducts on web sections in prestressed concrete box girder bridges

Based on experimental study result of two simply supported beams,which were prestressed by vertical tendons,the research on the weakening effect of vertical prestress ducts on web sections of prestressed concrete box girder was carried out. The test result shows that in the condition without grouting into the ducts,the cracking load is evidently lower than that with full grouting,and stirrup stress and principal tension stress at the surface of concrete will increase obviously. Meanwhile,the finite element analysis has been done to the test beams. The research is consistent with the analysis of finite element. The research tells that strengthening the detection and management for the vertical prestress grouting quality have an important meaning to prevent cracking of the prestressed concrete box girder bridge and provide one theoretical and testing basis for analyzing the cracking reason of such bridges.

Unified analogue method of effective prestress for post-prestressed tendon

In order to obtain the present effective prestress and its longitudinal distribution of prestressed tendon during the process of inspection and evaluation, a unified analogue method was put forward. Based on the theory for calculating instantaneous prestress loss of the tendons with complicated geometry, a universal numerical model was established. Therefore, the distribution of effective prestress could be simulated after recognizing the nominal coefficients of prestress loss with the obtained stress data of objective steel tendon. The numerical simulation results of a full-length tendon of a three-span continuous beam bridge show that the relative errors between the calculated value and the value in the code are within 5%, which meets the requirement for engineering application.

PSC Bridge Subjected to Combined Post Tension and Post Compression—A Case Study

Starting from the ideas of Conventional Post Tensioning we present a heuristic argument of advantages of combined actions of post compression along with post tensioned technique for a PSC member through a Design Example. Our aim was to assess the characterization of a pre stressed member if it was?to be under the Load effects of post compressing a bar with post tensioned method through hydraulic jacks as the reinforcements in the tensioned zone of conventional PSC bridge were to be compressed in order to induce internal tensile stress similar to internal compressive stresses developed due to conventional post tensioned design. The results ultimately concluded that post compressing a Slender bar by a pre stressing force in the compression zone by a value equal to 0.1?-?0.7 times the pre stressing force in the tension zone would eventually lead to cancelling out of tensile and compressive stresses, thereby forming the desired section which is comparatively smaller in size but can account for sustainability. The anchorage at the top end was?provided by special slender steel rods to eliminate the compressive stresses. All the dead loads?were?counteracted by the action of prestress and the bridge section was able to carry only live load which is deduced through examples in the article.

简支变结构连续小箱梁桥负弯矩区UHPC-NC组合桥面板抗裂性研究

针对当前简支变结构连续小箱梁桥负弯矩区钢束易堵孔、运营中桥面开裂病害等问题,提出一种无负弯矩钢束的UHPC-NC组合桥面板结构。以一座3×30 m简支变结构连续小箱梁桥为研究对象,以正常使用极限状态梁体不开裂为控制准则确定UHPC合理构造尺寸,对所提出的负弯矩组合桥面板结构进行1∶2的缩尺模型试验。试验显示:裂缝首先出现于UHPC-NC交界面处的普通混凝土部分,随后逐渐向UHPC层沿伸,且C50混凝土开裂、梁体破坏对应的截面弯矩分别为3 520,9 152 kN·m(考虑1∶8弯矩缩尺比),大于正常使用极限状态、承载能力极限状态梁体截面弯矩3 300,5 838 kN·m,即该组合桥面板结构满足小箱梁的抗裂与承载能力要求。基于试验结果建立精细化有限元模型,采用参数分析法研究UHPC厚度对梁体开裂荷载、极限承载力等方面的影响。结果表明:梁体开裂弯矩主要由UHPC上覆层厚度决定,相较于普通钢筋混凝土梁,5 cm厚的UHPC上覆层可将梁体开裂弯矩提高28.9%,7.5 cm厚的UHPC上覆层可将梁体开裂弯矩提高41.6%;在配筋率不变的情况下,增大UHPC层厚度对梁体承载力无显著提升。综合考虑梁体受力性能以及施工便利性,建议背景工程UHPC厚度取10 cm。

PPC斜拉桥主梁多状态疲劳及疲劳后静力性能试验研究

为研究大跨径部分预应力混凝土(PPC)斜拉桥主梁的抗疲劳性能,进一步探究混凝土斜拉桥主梁采用部分预应力设计的可行性及合理性,制作了斜拉桥缩尺节段模型,并对主梁采用部分预应力设计,开展4轮共4×250万次主梁具有不同初始损伤及带裂缝工作状态下的疲劳试验;疲劳试验结束后,以4种不同主梁裂缝宽度(0.1mm、0.2mm、0.3mm和0.5mm)为控制工序,反复加载一定倍数的等效活载至主梁裂缝宽度逐步达到0.5mm,以全面研究PPC斜拉桥主梁多状态疲劳后的受力性能。试验结果表明:在等效设计疲劳荷载作用下,主梁无初始损伤时,体系刚度基本无退化,主梁最大裂缝宽度预损伤分别为0.1mm、0.2mm时,跨中截面体系刚度下降量仅为3.35%、4.44%,且未发现裂缝张开;主梁带裂缝工作状态下,跨中截面体系刚度平缓下降7.46%,上峰值静载下,裂缝数量及高度略有增加,但卸载后裂缝均闭合,说明PPC斜拉桥具有良好的抗疲劳性能;疲劳后主梁大损伤静载试验中,主梁裂缝平稳发展,各工序反复加载过程中,主梁挠度、裂缝状态及斜拉索索力均具有较好的恢复能力,当主梁最大裂缝宽度为0.5mm时,荷载达到了7.49倍活载,斜拉桥体系仍然具有较大的剩余承载力。该文试验研究结果表明混凝土斜拉桥主梁采用部分预应力设计具有工程应用的可行性。

斜拉桥非对称V形钢塔-混凝土基座结合部构造设计优化

某空间异型斜拉桥主塔钢柱与斜撑在底部形成非对称V形结构,钢构件轴线严重偏离下部混凝土基座顶面垂线,给结合部构造设计带来困难。目的 为了确定所采用构造方案中的众多参数,缓解塔柱到基座的刚度陡变,降低结合部各部件的应力最大值,方法 基于精细化非线性有限元模拟,通过改变参数取值,对多种典型工况下各部件的应力进行分析、对比、验算,对于锚杆设置这一参数的影响,还研究了承压板与混凝土基座之间的界面应力。结果 研究结果表明:张拉1~4号索的施工极端工况和平面内外弯矩绝对值相加最大的使用工况最为关键,基座混凝土主拉应力常起控制作用,塔根应力比较接近规范限值;加厚承压板、适当提高混凝土强度有利于控制锚箱钢板和基座混凝土应力;原方案锚箱中部纵横向钢板作用很小;锚杆布置位置合理远比数量重要,弯矩作用下受拉侧施加预应力能够起到有益作用。结论 最终优化方案大量减少了锚箱钢板块数和锚杆根数,预应力分布也更合理。研究结果兼顾安全、适用和经济,对相关工程具有借鉴意义。

体外预应力UHPC无腹筋梁抗剪性能试验研究

为研究体外预应力超高性能混凝土(Ultra-high Performance Concrete,UHPC)无腹筋梁的抗剪性能,设计了3片体外预应力UHPC无腹筋梁,剪跨比分别为1.44、2.56、3.67,采用四点加载的方式进行抗剪性能试验,获得了试验梁的荷载-位移关系、荷载-应变关系、破坏形态以及极限抗剪承载力。试验结果表明:体外预应力UHPC无腹筋梁的抗剪破坏方式均表现为脆性破坏,随着剪跨比的增大,试验梁破坏形态依次表现为斜压破坏、剪压破坏、剪拉破坏;剪跨比越大,斜裂缝的数量越少、倾角越小,试验梁的极限抗剪承载力越小,且减小趋势变缓。基于极限平衡法推导了体外预应力UHPC无腹筋梁的抗剪承载力计算公式,验算了14片无黏结预应力UHPC梁的抗剪承载力,该公式适用性良好。

受损PPC斜拉桥主梁灌缝加固后疲劳性能试验研究

为进一步研究受损部分预应力混凝土(PPC)斜拉桥主梁裂缝灌浆加固后的疲劳性能,对受较大疲劳及静力损伤的PPC斜拉桥节段缩尺模型主梁进行裂缝灌浆加固,并开展疲劳及疲劳后静载试验研究。研究结果表明:在疲劳荷载作用下,灌浆裂缝未重新开裂,在疲劳加载初期(约20万次),结构体系刚度下降较快,后期下降较平缓;250万次疲劳加载后,主梁L/4、L/2和3L/4截面处的结构体系刚度分别降低12.83%、9.48%、13.62%,较原主梁第4轮疲劳加载下结构体系刚度下降幅度大,但疲劳结束时结构体系刚度仍然比原主梁第4轮疲劳加载初始结构体系刚度大;对裂缝进行灌浆处置能有效恢复PPC斜拉桥主梁的抗裂强度及结构体系刚度;随着荷载增大,灌浆裂缝逐步张开,但最大裂缝宽度对应位置发生转移,同时不断有新裂缝产生,且裂缝分布区域范围增大,环氧树脂胶的作用极大地延缓了裂缝宽度的增大,提高了主梁的抗裂性能;环氧树脂胶不仅能修复混凝土裂缝界面,同时能有效恢复钢筋与混凝土间的黏结滑移损伤;对受严重损伤的PPC斜拉桥主梁仅进行裂缝灌浆处置后,主梁仍然具有良好的抗疲劳性能,同时,其疲劳后的抗裂性能及刚度也得到较大恢复。

某在役重载铁路32 m预应力混凝土T梁后装声屏障适应性分析

随着我国货运铁路重载扩能运输的发展,大轴重、长编组引起的噪声污染日趋严重,后装声屏障已成为减小噪声污染的主要措施之一,但通过扩能改造提升的在役重载铁路桥梁原设计时并未考虑后装声屏障对桥梁结构的影响。为研究在重载铁路桥梁上后装声屏障的适应性,以在役铁路桥梁主梁型32 m简支T梁(专桥-2059A)为研究对象,采用数值模拟与结合现场实测桥梁现状分析的方法,基于不同荷载组合作用,开展T梁加装声屏障后主梁、声屏障与桥梁连接的位置及道砟槽板适应性分析,并对T梁翼缘板及声屏障结构的潜在薄弱位置进行破坏分析。研究结果表明:T梁加装声屏障后,主梁纵向强度受梁体L/8~L/4处抗剪控制,其中梁体L/8处抗剪安全系数为1.70,小于规范要求值1.80;声屏障与桥梁连接位置安全储备不足,其中,在最不利荷载组合作用下,挡砟墙钢筋应力超过容许值1.25倍、裂缝宽度超过容许值0.54 mm;道砟槽板在最不利荷载组合作用下,其钢筋应力安全储备剩余23.2%、裂缝宽度比规范容许值小0.07 mm。综合考虑3种分析,该类型T梁不宜后装声屏障;在最不利情况下,T梁及声屏障结构破坏顺序依次为预埋化学锚栓处、挡砟墙处、声屏障立柱与水平杆交接处、道砟槽板变高度处、翼缘板根部处。

深中通道泄洪区非通航孔桥主梁设计

深中通道泄洪区非通航孔桥总长6.05 km,分布于伶仃洋大桥及中山大桥2座通航孔桥两侧。泄洪区非通航孔桥采用等跨连续梁布置,4~6跨一联。主梁设计过程中,首先进行110、120、130 m三种跨径方案比选,确定采用最经济的110 m跨径方案。然后针对结构形式,提出预应力混凝土梁、钢-混组合梁和钢箱梁3种方案,从力学性能、经济性和施工风险等方面综合考虑,最终推荐采用钢箱梁方案。钢箱梁采用外形简洁流畅的封闭式断面,有利于后期维养;考虑全线景观效果,主梁高度取4 m,高跨比为1/27.5;横隔板间距取2.5 m,采用实腹式横隔板和框架式横肋的组合式设计,使箱室内部通透性更好;钢箱梁采用Q420qD钢和Q345qD钢2种材料。钢箱梁施工采用适合海上长大桥梁的大节段预制+现场拼装的施工方案。

大跨径预应力混凝土连续梁桥加固研究进展

基于我国危旧桥改造需求多、病害情况复杂给桥梁加固提出的挑战,需把握桥梁加固国内外的研究现状,为未来深入研究和工程应用提供参考。结合大跨径预应力混凝土连续梁桥主要加固手段的基本原理,对各加固手段的优点、局限性及适用对象进行分析,系统梳理近两年来的最新研究成果,并对未来发展进行了展望。

PC连续箱梁桥的日照温度效应及合龙温度研究

以云南省某大跨径预应力混凝土连续箱梁桥为工程背景,研究其日照温度效应以及合龙温度的确定。使用ANSYS数值模拟混凝土箱梁的温度场,结合实测值验证其可靠性,并拟合相应的指数型温度梯度曲线;使用Midas研究日照温度模式对混凝土箱梁桥施工中和成桥下的内力和位移影响;基于年温差效应对合理合龙温度进行研究,并针对非设计合龙温度下的合理施工提出相应的改善措施。结果表明,温度场计算理论得出的数据同实测值吻合较好;拟合出指数型的升温和降温模式下的温度效应公式,尤其是对最大悬臂状态的下挠影响显著,最大下挠值达21.6 mm;结构因整体升温或降温产生的横向位移值比竖向位移值大,升温22℃时,最大纵向位移值为-31.2 mm;合龙温度为10℃时,对主梁结构的受力最好,同时升温带来的结构上挠值对结构长期变形有利。

预应力技术在桥梁工程施工中的应用研究

预应力技术可提高工程的耐久性和抗裂性,具有较强的实践价值。文章阐释了预应力施工技术的基本原理和应用优势,从混凝土构件施工、梁段预制、受弯构件施工等方面探究了预应力施工技术在道路桥梁施工技术中的具体应用,分析了预应力施工技术应用于桥梁施工技术出现的问题,并提出了相应的施工质量控制措施。

桥梁顶升施工有限元分析

山东省青岛市辽阳路桥是一座预应力混凝土连续箱梁桥。为实现与新建桥梁的衔接,现需该桥的46#桥梁顶升655~1218mm。利用ANSYS软件建立46#桥梁有限元计算模型,分析其在同步顶升工况、千斤顶失效工况下,顶升至最高点时所需的最大顶升力以及箱梁桥和分配梁的受力和变形情况,以确保桥梁顶升过程中的安全性。结果表明桥梁在两类工况下,均具有较大的安全储备,可保障桥梁顶升过程中的安全可行性。研究成果可为其他同类型桥梁顶升施工工程提供案例参考。