在氯侵蚀和混凝土碳化环境下用时变可靠度和预后验决策优化桥梁检修制度

基于作者用Monte Carlo法和回归分析法开发的计算在氯侵蚀和混凝土碳化情况下混凝土梁的抗力退化随机过程的软件,用Bayes公式和桥梁检查结果更新桥梁退化状态,考虑桥梁检修的货币收益或更一般的能反映业主的财政承受能力和风险规避心理的效益函数,用预后验决策分析法给出了桥梁检查的期望效益,并以期望效益最大来优化桥梁检修制度。用北京一座混凝土梁桥为例,考虑恒载随机变量和两个Poisson随机过程活载作用下跨中抗弯承载能力极限状态,以设计基准期内任意时段的时变结构可靠度不低于桥梁设计规范的目标可靠度为条件,对这种桥梁检修制度进行优化。结果表明:用效益函数优化时,业主的财政承受能力和风险规避心理能给出明显不同的桥梁检修制度。     

Reliability evaluation and optimisation of imperfect inspections for a component with multi-defects

In this paper, a model is developed to evaluate the reliability and optimise the inspection schedule for a multi-defect component. The model uses a non-homogeneous Poisson process (NHPP) method in conjunction with a delay time approach. The inspections are designed to detect any defects in the component, however it can be imperfect. The defect is a definable state before a functional failure happens to the component. Occurrences of defects are assumed to follow an NHPP and a defect will be minimally repaired if it is identified during an inspection. It is shown that the failures occurring in an interval of inspection will also follow an NHPP. The situation of imperfect inspections and non-constant inspection intervals are considered. An algorithm is presented to optimise the intervals of inspections in order to maximise the reliability of the component, and the properties of the algorithm are shown. A numerical example with parametric study is given to show the performance of the model and the algorithm.     

双幅桥面桥梁三分力系数的气动干扰效应研究

双幅桥面桥梁在风的作用下,上下游两桥面之间会产生气动干扰效应。分别采用测力法和测压法对某双幅桥面桥梁三分力系数的气动干扰效应进行了一系列的节段模型风洞试验研究。结果表明:双幅桥面阻力系数的气动干扰效应不容忽视。与单幅桥面相比,下游桥面的阻力系数降低较多,上游桥面的阻力系数略有降低。上下游桥面升力系数和升力矩系数的气动干扰效应不明显。     

曲线梁桥地震响应的简化分析方法

曲线梁桥的平面不规则性引起的弯扭耦合效应,导致了地震响应的复杂性。对弹性支座上的刚性桥面系统建立了具有刚度偏心的简单曲线梁桥模型,给出了自振特性和地震响应的简化计算方法。通过数值模拟比较,系统地分析了各种影响因素及其对曲线梁桥动力响应的影响规律和计算图表,可以在抗震初步设计中参考使用。     

Field performance of an FRP slab bridge

Fiber reinforced polymer (FRP) composite decks are new to bridge applications and hence not much literature exists on their in-service performance. The in-service performance, and impact and dynamic characteristics of the first fiber reinforced polymer composite bridge superstructure built in New York State in late 1998 are documented in this paper. Test data indicate that the superstructure and the shear-key are structurally performing well. The average impact factor was about 0.3. Observed low strains and deflections, compared to those predicted at the design stages, show room for optimization of the deck design to make these more cost-effective in the future. Higher modal damping values were observed and reflect the vibration absorbing capacity of FRPs. Several delaminations were found during visual inspections and the wearing surface was replaced once. For future applicability of FRPs for bridge deck applications, these issues affecting the long-term durability should be resolved.     

基于健康监测系统的大跨多荷载桥梁的 疲劳可靠度评估

考虑到火车、汽车与风荷载的长期作用以及多荷载的随机性,评估大跨多荷载桥梁的疲劳可靠度是一项富有挑战的任务。该研究基于健康监测系统提出了大跨多荷载悬索桥的疲劳可靠度分析框架,并应用到香港青马大桥。首先,定义了疲劳可靠度的极限状态函数,基于监测数据建立火车、汽车与风荷载的概率模型。基于概率模型和蒙特卡洛模拟方法,利用疲劳关键位置上多荷载的每日随机应力响应,估计每日应力幅m次方之和的概率分布。假设交通保持不变,可确定在给定时段内应力幅m次方之和的概率分布。最终得到桥梁不同疲劳关键位置不同时间点的疲劳失效概率。结果表明,在目前的交通状态下,青马大桥的疲劳健康状况可保持良好。     

Effects on accidents of periodic motor vehicle inspection in Norway

An extensive programme of periodic motor vehicle inspection was introduced in Norway after 1995, when the treaty between Norway and the European Union (EU) granting Norway (not a member of the EU) access to the EU inner market took effect (The EEA treaty). This paper evaluates the effects on accidents of periodic inspections of cars. Trucks and buses were not included in the study. Negative binomial regression models were fitted to data on accidents and inspections created by merging data files provided by a major insurance company and by the Public Roads Administration. Technical defects prior to inspection were associated with an increased accident rate. Inspections were found to strongly reduce the number of technical defects in cars. Despite this, no effect of inspections on accident rate were found. This finding is inconsistent with the fact that technical defects appear to increase the accident rate; one would expect the repair of such defects to reduce the accident rate. Potential explanations of the findings in terms of behavioural adaptation among car owners are discussed. It is suggested that car owners adapt driving behaviour to the technical condition of the car and that the effect attributed to technical defects before inspection may in part be the result of a tendency for owners who are less concerned about safety to neglect the technical condition of their cars. These car owners might have had a higher accident rate than other car owners irrespective of the technical condition of the car.     

Optimal load rating-based inspection planning of corroded steel girders using Markov decision process

Steel girder bridges are vulnerable to corrosion. To maintain their safety above a predefined target level, the load rating can be computed from the inspection results and guide the following maintenance actions. Optimizing inspection and maintenance based on load ratings has substantial practical and economic relevance. Load rating-based strategies can be categorized based on whether the inspection interval and replacement criteria are fixed or flexible. Existing studies focus on fixed inspection intervals throughout the service life. In general, their results are not optimal for inspection planning. To reduce life-cycle cost, aged steel girders may be inspected and repaired in an adaptive manner. To this end, a method based on Markov decision process (MDP) is proposed to compare the life-cycle cost of four load rating-based policies (i.e. uniform or adaptive non-uniform inspection interval, and fixed or adaptive replacement threshold). Load rating-based inspection planning is formulated as MDP and the optimal plans are obtained using dynamic programming. The conventional approach to discretize states cannot accurately approximate the non-stationary deterioration process, while state augmentation is successful in doing this but will increase computational cost. A comparison of two approaches is made to investigate their effects on life-cycle cost. A bridge girder under corrosion attack is used as an illustrative example. The results show that the load rating-based plan with an adaptive non-uniform inspection interval and fixed replacement threshold obtained using the state augmentation technique can be near-optimal.     

An inspection model for a process with two types of inspections and repairs

This paper considers a problem often met in practice. A production process may be subject to two types of deteriorations. The first is a shift in product quality caused by minor process defects that may be identified and rectified by routine inspections and repairs. The second is a major defect caused by a major mechanical or electrical problem that can be observed only when the defect has led to a breakdown of the process or the defect is revealed by a major inspection followed by an appropriate major repair action at the time of the inspection. We formulated an inspection model for the above problem and aimed at optimising the inspection intervals for both types of inspections. A numerical example is given to demonstrate the applicability and solution procedure of the model.     

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.     

斜拉桥参数振动有限元分析与半主动控制

采用有限单元法分析了斜拉桥的非线性参数振动问题,验证了在一定的频率范围内斜拉索与桥面板会发生参数共振;提出了应用形状记忆合金(SMA)对斜拉桥的参数振动实施半主动控制,并数值模拟了其控制效果,结果表明,斜拉桥参数振动的SMA半主动控制,不仅能大幅度地降低斜拉索和桥面板的振动,而且能有效地抑制斜拉桥参数共振的发生。     

Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design values to determine if the tendon is performing below expectations. The focus of this paper is the characterization of the relationship between ultrasonic wave velocity and stress level in prestressing tendons. Measurements were made to determine constants that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular waveguides for ultrasonic waves, are evaluated.     

大跨度斜拉桥结构横向消能减震设计方法

桥梁消能减振技术是通过在桥梁结构上合理设置耗能装置来增加结构阻尼、吸收地震等其它外界因素作用下的振动能量,减小结构的振动反应.本文结合杭州湾大桥工程南航道桥,提出在斜拉桥主梁与过渡墩、辅助墩之间沿横向设置粘滞阻尼器,来控制大跨桥梁的横向地震反应.分析表明,采用阻尼消能减震技术,不仅可有效地减少大跨桥梁的横向地震反应,而且还可同时限制桥面横向温度变形,保护伸缩缝.     

刚构-连续组合桥梁冲击系数多因素灵敏度分析

为了研究影响冲击系数的显著性因素,以某刚构-连续组合桥梁为依托工程,采用三轴二分之一车辆模型,基于通用程序建立了车桥耦合振动有限元分析模型,考虑了车桥频率比、桥面不平整度、车体质量、车辆阻尼比、行车速度、车辆行驶方式、桥梁刚度、桥跨布置和下部结构计算模式等9个影响因素,通过正交试验表研究了该桥在诸因素下结构控制截面的挠度（位移）、弯矩冲击系数,并开展了冲击系数的敏感性因素分析。结果表明,现有规范计算此类桥梁的冲击系数值偏小;车桥频率比、桥面不平度及车辆行驶速度是影响该类桥梁冲击系数的敏感性因素,研究成果为将冲击系数定义为多因素的函数表达式指明了方向     

Velocity Constants for Ultrasonic Stress Measurement in Prestressing Tendons

Abstract

There is currently widespread use of high-strength steel tendons for prestressing and post-tensioning of concrete structures and as suspension cables for long-span bridges. Tendons normally consist of one or more seven-wire, helically wound steel strands or solid rods. There are more than 130,000 prestressed bridges in the United States that contain these tendons, and approximately 3,000 new bridges are constructed each year. The prestressing tendons are critical structural elements because the forces in the tendons counteract tensile stresses in the concrete that result from loads acting on a bridge. The tendons are frequently inaccessible for visual inspections and there is currently no accepted nondestructive evaluation technique to assess the condition of these tendons. The goal of this research is to examine ultrasonic stress measurement techniques for the condition assessment of prestressing tendons. This information could be used to compare the actual force in the tendon with its design values to determine if the tendon is performing below expectations. The focus of this paper is the characterization of the relationship between ultrasonic wave velocity and stress level in prestressing tendons. Measurements were made to determine constants that relate the change in ultrasonic velocity to the change in stress. The effects of dispersion in prestressing tendons, which act as circular waveguides for ultrasonic waves, are evaluated.     

平行双箱梁桥面颤振稳定性试验研究

在建的佛山平胜大桥和设计中的青岛海湾桥红岛航道桥方案分别是具有平行双箱梁的独塔自锚式悬索桥和独塔斜拉桥，对两座桥梁的单、双桥面弹性悬挂节段模型风洞试验结果表明双桥面之间存在不可忽略的气动干扰效应，从而使桥梁在单、双桥面状态时的颤振临界风速不同。以平胜桥主梁节段模型为基础的一系列风洞试验研究表明，平行双箱梁桥面主梁的颤振临界风速与两桥面之间的距离有关系，双桥面的颤振临界风速随两桥面之间距离D值的增大而增加。与单桥面状态相比较，平行双箱梁桥面的颤振导数也有相应的变化，且这种变化和两桥面之间的距离D也有关系。     

Inspection procedures in manufacturing processes: recent studies and research perspectives

Quality inspections are performed in almost every production system to prevent nonconforming products from reaching final customers or end users. Quality inspections are typically performed referring to specific inspection procedures, depending on the production process. Two general inspection paradigms may be identified: online inspection and offline inspection. These are differentiated by the way in which inspections are made. The paper presents a recent survey on new studies on inspection procedures for both paradigms. The main novelty of the study is the identification of new research perspectives in such a highly explored field. New schemes of analysis allow highlighting the research areas which are not adequately covered by the literature. A brief examination of some bibliometric aspects is also proposed.     

上承式钢板梁桥空间振动计算分析

本文提出了列车、上承式钢板梁桥空间振动的有限单元分析模型，采用计算机模拟方法，计算了列车提速后通过32m上承钢板梁板的空间振动响应，检算该桥是否具有足够的刚度及良好的运营平稳性，所得结果与实测资料相符，可供决策部门参考。     

Evaluation of effective flange width by shear lag model for orthotropic FRP bridge decks

In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section with a reduced width of deck in relation to center-to-center spacing of stringers, over which the longitudinal normal stresses are assumed to be uniformly distributed, which is termed as effective flange width. It is defined in the AASHTO specifications primarily for concrete slabs and has inherent applicable limitations because of its empirical nature. This paper provides an analytical shear lag model for effective flange width for orthotropic bridge decks, applicable to various materials including Fiber-Reinforced Polymer (FRP) and concrete decks. To verify this solution, a Finite Element (FE) parametric study is conducted on 44 simply-supported FRP deck-on-steel girder bridges. The results from the shear lag model correlate well with the FE results. The accuracy of this model is further verified by close correlations with an existing empirical solution. It is also illustrated that the shear lag model, with the introduction of a reduction factor, can be applied to predict effective flange width for FRP deck-on-steel girder bridges with partial composite action, by favorable comparisons between the analytical and testing results for a T-beam section cut from a one-third scaled bridge model, which consists of an FRP sandwich deck attached to steel girders by mechanical connectors.