预应力混凝土梁桥系统失效树分析

针对预应力混凝土梁桥,采用失效树的方法进行系统可靠性分析。运用全局临界强度分枝-约界准则识别结构系统主要失效模式,以JC法计算各主要失效模式的可靠指标,采用Ditlevsen上下界公式分析结构体系的失效概率。以某汉江公路大桥为例,分析了失效树图形,研究了主要失效模式的可靠指标、失效概率及桥梁结构体系可靠性。与实桥运营状态的对比分析表明,上述理论分析较好地预测了实际的结构行为,能用于桥梁结构安全性及可靠性分析评估。     

Structural health monitoring of bridges with piezoelectric AE sensors

Monitoring the health of structures using acoustic emission technique offers many advantages such as early and quick detection of damage in real-time inexpensively. This paper is concerned with health monitoring of infrastructure hardware like highway bridges using this technique for timely intervention preventing catastrophic failure. Both experimental and numerical investigations were undertaken to determine the effectiveness and applicability of the method in the case of bridge superstructures. Three types of representative bridge girders of steel, reinforced concrete and prestressed concrete were designed, fabricated and monitored in the laboratory for structural integrity under cyclic loads with the help of an acoustic emission sensor system. After laboratory work, wavelet and Fourier transform techniques were applied to the recorded signals for de-noising and to diagnose the damaged state of the structure. Finally the locations of the cracks were determined by using the artificial neural network (ANN) approach.     

Visual Inspection of Highway Bridges

The Federal Highway Administration recently conducted an investigation to assess the reliability of visual inspection of highway bridges as implemented by state departments of transportation. The study focused on routine and in-depth inspection, the two most prevalent forms of visual inspection of bridges. Because visual inspection is a highly subjective nondestructive evaluation technique, the results of these bridge inspections can be highly variable and are dependent on many factors. This study included the completion of 10 bridge inspection tasks by 49 practicing state bridge inspectors. With regard to routine inspections, this study showed that condition ratings are assigned with significant variability. Specifically, approximately 68% of condition ratings are within 1 rating point of the average. The results of the in-depth superstructure inspections indicated that these inspections are not likely to detect and identify the specific types of defects for which this inspection procedure is sometimes prescribed. Specifically, widespread defects such as those normally noted during a routine inspection are likely to be noted; however, local deficiencies, such as crack indications, are unlikely to be detected. The results of the deck delamination survey indicate that the accuracy of this type of inspection is relatively poor, with few inspection teams providing results that could be considered to accurately portray the condition of the deck.     

预应力混凝土桥梁时变效应分析的钢筋约束影响系数法

系统地提出了预应力混凝土桥梁结构中钢筋对徐变和收缩时变效应的约束影响系数的概念,并给出了影响系数的计算公式,籍此提出了时变效应分析的钢筋约束影响系数法,建立了一套理论公式,可计算时变的钢筋和混凝土应力、应变及梁体竖向变形。不仅适用于静定桥梁结构,亦适用于超静定桥梁结构,可计算时变结构内力重分布。计算式物理意义明确,使用方便;理论分析与试验结果比较表明,公式具有较高的计算精度。     

预应力高强轻骨料混凝土连续刚构桥的试验研究

强度等级在CL40以上的高强轻质混凝土(HSLWC)应用于大跨度桥梁结构,具有减轻自重,有效降低结构内力,增大跨度,减少桥墩数量等优点。以云南安宁至楚雄高速公路14号达连坝段公路桥为原型,按照1/4比例设计了一个3跨预应力高强轻骨料混凝土连续刚构桥,其桥面结构采用CL50混凝土,进行了多种荷载工况的试验研究。结果表明,预应力高强轻骨料混凝土连续刚构桥具有较好的受力性能,1倍和1.5倍等效车队荷载通过时,各项指标均满足规范要求;2倍等效车队荷载通过时,部分指标不满足使用要求,但桥梁表现出了较好的延性;在严重超载情况下,桥梁虽破坏严重,但仍可保持较好的承载力水平且不会发生跨塌。     

考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析

基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。     

预应力混凝土桥梁徐变分析的全量形式自动递进法

首先将预应力混凝土桥梁中考虑收缩、徐变影响的任意时刻混凝土应力、应变关系在持荷时段内写成代数形式,引入内力平衡方程及变形协调条件后,提出了计入截面上钢筋位置、配筋率、预应力钢筋松弛、混凝土弹性模量随时间变化等影响的徐变效应分析的全量形式自动递进法,并建立了计算式,适用于任何形式的收缩、徐变特性表达式;基于建立的全量形式公式,可方便地求解任意时刻混凝土、钢筋的应力与应变和梁体竖向变形。理论分析与试验结果比较表明,公式可方便地控制计算精度,直至给出满意的结果。将计算式编程后极易与目前桥梁设计中常用的杆系有限元软件接口,进行可靠的徐变分析。     

A systematic analysis and design approach for single-span FRP deck/stringer bridges

There is a concern with worldwide deterioration of highway bridges, particularly reinforced concrete. The advantages of fiber reinforced plastic (FRP) composites over conventional materials motivate their use in highway bridges for rehabilitation and replacement of structures. In this paper, a systematic approach for analysis and design of all FRP deck/stringer bridges is presented. The analyses of structural components cover: (1) constituent materials and ply properties, (2) laminated panel engineering properties, (3) stringer stiffness properties, and (4) apparent stiffnesses for composite cellular decks and their equivalent orthotropic material properties. To verify the accuracy of orthotropic material properties, an actual deck is experimentally tested and analyzed by a finite element model. For design analysis of FRP deck/stringer bridge systems, an approximate series solution for orthotropic plates, including first-order shear deformation, is applied to develop simplified design equations, which account for load distribution factors under various loading cases. An FRP deck fabricated by bonding side-by-side box beams is transversely attached to FRP wide-flange beams and tested as a deck/stringer bridge system. The bridge systems are tested under static loads for various load conditions, and the experimental results are correlated with those by an approximate series solution and a finite element model. The present simplified design analysis procedures can be used to develop new efficient FRP sections and to design FRP highway bridge decks and deck/stringer systems, as shown by an illustrative design example.     

Service life prediction of structural systems using lifetime functions with emphasis on bridges

In order to adequately handle the huge increase in traffic over the past three decades, most North American and European countries invested enormous funds in building highway networks. Nowadays, most of these networks are complete or close to completion. The biggest challenge highway agencies and departments of transportation face is the maintenance of these networks, keeping them safe and serviceable, with limited funds. The use of consistent measures of safety is fundamental for the development of optimum strategies for bridge maintenance. The analysis of safety on a component basis is a gross approximation of the real system performance of a bridge. In this paper, a model using lifetime functions to evaluate the overall system probability of survival of existing bridges, under maintenance or no maintenance, is proposed. In this model, bridges are modeled as systems of independent and/or correlated components. The proposed model is applied to an existing bridge located in Denver, Colorado, and the optimal maintenance strategy of this bridge is obtained in terms of service life extension and cumulative maintenance cost.     

汶川地震公路桥梁易损性研究

研究发现汶川地震Ⅵ度区和Ⅶ度区内公路桥梁震害调查数据相对于更高烈度区的调查情况不够全面详实,特别是完好桥梁的数据偏少,因此,基于这些原始调查数据生成的经验易损性曲线就会和实际的地震易损性有偏差。针对这一问题,利用高烈度区域内桥梁调查数量与烈度区分布面积的比例关系对低烈度区域的桥梁调查数量进行了补充。基于补充后的桥梁震害数据,得到了汶川地震公路桥梁的经验易损性曲线,并分析了桥型和桥梁规模对易损性的影响。     

飞机在预应力桥梁上降落过程的数值模拟分析

将现有高等级公路直线段应急改成飞机跑道是特殊情况下维持空运保障能力的有效途径之一,但公路直线段包含的中小跨径桥梁将会影响飞机起降。针对目前高等级公路中广泛存在的13 m与10 m跨径的标准多跨简支预应力梁桥梁,运用有限元分析软件LS-DYNA分析了预应力桥梁的初始状态及飞机在预应力桥梁上着陆时对桥梁的冲击响应,据此得到了高等级公路13 m和10 m跨径的桥梁在飞机直接着陆情况下的动力响应。计算表明13m跨径的预应力桥梁承受某型飞机直接降落相对冒险,所得到的有关结论可供今后在高等级公路直线段中选择应急飞机跑道路段参考。     

Durability of CFRP cables exposed to simulated concrete environments

One of the main causes of structural deficiency in concrete bridges is the deterioration of the constituent materials. Some transportation agencies have started exploring the use of carbon fiber reinforced polymers (CFRP) as a corrosion-resistant alternative to steel prestressing materials for longer lasting concrete bridge structures. To implement CFRP in prestressed concrete bridge structures with more confidence, an understanding of the challenges pertaining to durability under in-service environmental conditions is essential. This paper explores the effects of temperature with alkaline and alkaline/chloride solutions on material properties over time, in the context of reinforced and prestressed concrete structures for transportation applications. The durability testing yielded several key findings: (1) higher temperatures accelerate degradation, (2) moisture sorption was the primary process responsible for the observed degradation, with plasticization and microcracking as the controlling mechanisms leading to fiber–matrix interfacial debonding, and (3) a relaxation-based analytical model was implemented to predict residual properties after environmental exposure, showing promising agreement with experimental data.     

既有预应力空心板桥加宽设计的荷载横向分布计算方法

既有预应力空心板桥加宽时,一般将新旧空心板连接起来共同工作,荷载横向分布系数是该类型桥加宽设计的关键问题之一.该文根据铰接板法的基本假定,应用力法原理推导出了铰接板法的一般力法方程,可用于空心板截面、间距和材料属性等均不同的任意铰接空心板桥的荷载横向分布影响线计算.编制程序求解了荷载横向分布影响线、横向分布最不利位置和横向分布系数,对一座普通空心板桥和一座加宽空心板桥进行了计算分析.通过对比原规范与现行规范中相应汽车荷载,提出了旧桥加宽后各板最大横向分布系数允许值,以该值为标准校核各板横向分布系数计算值可以确定需要加固的空心板.通过对比各板横向分布系数值的变化,确定了需要增强横向联系的空心板.     

公路斜交梁桥地震易损性模型研究

采用增量动力分析方法建立公路斜交梁桥地震易损性模型并开展易损性简化计算方法研究。依据不同的墩柱形式、支承形式及新旧规范将公路斜交梁桥分成8种桥型,统计桥梁结构参数并采用随机抽样方法确定其相应取值,依此装配生成240个基准桥梁样本,同时进行斜交角度变换建构新的桥梁样本。基于增量动力分析方法对相同斜交角下桥梁样本进行分析并建立易损性模型,重点研究斜交角与易损性参数之间的关系。研究发现:易损性模型中位值大致随斜交角的增加而减小,对数标准差则呈相反趋势。以计算得到的易损性模型参数为样本,拟合提出适用我国斜交梁桥的中位值修正系数公式,同时给出对数标准差的建议值,进一步总结公路斜交梁桥地震易损性简化计算方法,结果可为后续斜交梁桥地震风险评估及加固规范修订提供参考依据。     

现有混凝土桥梁的时变可靠度分析

在研究现有混凝土桥梁抗力和荷载的时变性的基础上,建立了现有桥梁的时变可靠度计算模型,并采用自适应重要抽样法计算时变可靠指标。同时,对变量进行了参数敏感性分析。研究结果对于科学、经济地制定桥梁维修计划和方案具有重要意义。     

Seismic retrofit of existing highway bridges in Japan

This paper presents the current technical developments for seismic design and seismic retrofit of existing highway bridges in Japan. At first, the histories of the past seismic design codes, past seismic evaluation investigation, and past seismic retrofit practices for highway bridges are described. Then the damage caused by the 1995 Hyogo-ken Nanbu Earthquake and the lessons learned from the earthquake are briefly described. Finally, the seismic retrofit program after the Hyogo-ken Nanbu Earthquake is described with emphasis on research and development as well as field practice of the seismic retrofit of existing reinforced concrete highway bridges such as single column bent, wall-type pier, and multicolumn bents.     

Mechanistic quantification of RC bridge damage states under earthquake through fragility analysis

Risk assessment of infrastructure systems plays an increasingly important role in their plan, design, maintenance, retrofit and life-cycle cost evaluation taking into consideration their vulnerability to natural, technological and terrorist hazard. This paper develops a mechanistic model for seismic damageability of concrete bridges in the form of fragility curve in such a way that the model can be calibrated with the empirical fragility curves constructed on the basis of the damage data from the 1994 Northridge earthquake. As often observed from this and other destructive earthquakes, bridges are one of the most vulnerable components of a highway network system subjected to earthquake ground motion. For this reason, bridge damageability information in a succinct from as fragility curve is needed to pursue the seismic risk assessment of a highway networks consisting of as large as thousands of bridges that can be affected by a high magnitude earthquake with in and near the service area of the network.     

钢筋混凝土矩形空心桥墩抗震性能

针对钢筋混凝土(RC)矩形空心桥墩基于性能抗震设计所需要的性能量化参数和抗震性能问题,该文对高宽比、轴压比、纵向和横向配筋率不同的12个约束良好的RC矩形空心桥墩,开展了恒定轴力作用下的水平循环荷载试验研究,并把试验观测到的桥墩主要损伤状态与工程设计参数联系起来,以满足基于性能抗震设计所需要的量化指标。在此基础上,基于OpenSees软件平台,采用纤维模型对试件体桥墩的滞回性能进行数值模拟,模拟结果与试验数据吻合良好。结果表明:使用累积概率曲线,可以较好地把混凝土开裂和剥落等主要损伤状态与混凝土压应变和纵向钢筋拉应变等工程极限状态联系起来,为基于性能的桥梁抗震设计提供量化指标。试件体桥墩的延性系数在3.71~8.29,等效粘滞阻尼比在0.19~0.31,延性系数和耗能指标均满足结构抗震设计要求。该横向配筋构型的RC矩形空心桥墩,可以作为当前我国公路桥梁抗震设计细则(JTG/T B02-01-2008)矩形空心截面横向配筋构型的一种补充。     

Application of multiple assessment items optimization method to determining the repair ranking of existing reinforced concrete bridge system

Abstract

The D. (Degree) E. (Extent) R. (Relevancy) evaluation method is widely used to assess the damage states of existing reinforced concrete (RC) bridges in Taiwan. The present study is first to distinguish between relevancy (R^a, a = 1.5, 2) and non‐relevancy (R^a, a= 1) for the repair ranking of the existing RC bridge system to be assessed. The multiple assessment items optimization method was mainly applied to seek the optimum repair ranking. The five existing RC bridges, i.e. Chi‐jou, Lan‐yang, Dah‐jea, Dah‐duh and Dah‐an in Taiwan are chosen as practical examples. The results show that when each bridge is judged to be non‐relevant by the system, the repair ranking predicted by the D.E.R. evaluation method is correct. Nevertheless, when the bridge system has one or more one important bridge, the repair ranking predicted by the D.E.R. evaluation method is not accurate. The proposed method may be remedied the defect of the D.E.R. evaluation method to predict the repair rankings of existing RC bridge system.     

预应力混凝土箱梁桥竖向预应力孔道对腹板截面

以两片安装竖向筋试验简支梁为基础,进行了预应力混凝土箱梁桥竖向预应力孔道对腹板截面削弱的研究,试验表明在不灌浆情况下梁开裂荷载提前,箍筋应力、混凝土表面主拉应增加明显,同时对试验梁进行了有限元分析,试验结果与有限元分析一致。研究表明加强竖向预应力灌浆质量的检测与管理对防止预应力混凝土箱梁桥的开裂有重要意义,同时为分析这类桥的开裂原因提供了理论与试验依据。