大跨度公铁两用斜拉桥公路桥面铺装层受力特点分析

为研究适合于大跨度公铁两用斜拉桥的公路桥面铺装复合结构及其控制荷位和力学指标,以武汉天兴洲大桥为例,采用有限元方法,首先建立整桥结构三维模型,计算列车荷载作用下的公路桥面力学响应,然后截取最不利梁段建立公铁两用斜拉桥公路桥面铺装复合结构模型,并以列车荷载作用下的整桥计算结果等效为复合结构模型强制位移边界条件,最后计算公路车辆荷载作用下的铺装结构力学响应,得到铺装层的控制荷载和力学指标。分析表明,考虑列车荷载作用后,公路车辆荷载中心位于纵向加劲肋一端正上方位置为公路铺装体系的横向控制荷位;考虑列车荷载作用后的铺装层最大横向拉应力峰值比不考虑列车荷载时增加了18%,给公路桥面铺装层纵向裂缝的控制、结构设计和材料试验提出更高的要求。     

System reliability models for bridges

There is a need for efficient bridge evaluation procedures. A considerable number of existing bridges in the United States require repair and/or replacement. Accurate estimate of the current strength and the remaining life time is essential for optimum distribution of the available limited resources. The major parameters which determine the structural performance are random variables. Statistical models of load and resistance can be derived from the test data, observations and analysis. For bridge members the reliability can be calculated using this available data, observations and analysis. considerable discrepancy between the reliability level of individual members and the overall bridge reliability. Due to load sharing and redundancies, the actual load-carrying capacity often exceeds the theoretical value. System reliability methods allow us to reveal an actual safety reserve in the structure. This paper summarizes the practical bridge reliability models. Using a special sampling technique, the reliability is evaluated for typical girder bridges.     

#br# 我国钢管混凝土拱桥应用现状与展望

共收集到截止2015年1月的已建和在建的钢管混凝土拱桥413座（跨径不小于50m）。统计分析表明,钢管混凝土拱桥在我国修建的数量不断增多、跨径不断增大。从行业分布来看,在公路、城市桥梁中的应用仍是主体,在铁路尤其是高速铁路中的应用不断增多。在结构体系方面,上承式、中承式、拱梁组合式、飞鸟式和下承式刚架系杆拱5大类,仍为主要应用的桥型,占总数的85%。在截面形式方面,以圆钢管混凝土为基本单元组成的单圆管、哑铃形和桁式是应用的主流。提篮拱被应用于各种桥型,尤其是大跨度铁路桥。无风撑拱主要应用于120m跨径以下的桥梁,且以斜靠拱和拱梁组合桥为主,截面多采用横向刚度较大的形式。拱肋的材料强度不断地提高,钢管以Q345钢为主,混凝土以C40、C50为主。虽然对桥面系强健性的重视在不断提高,然而强健性好的整体式和具有加劲纵梁的悬吊桥面系的应用还不够普及。钢管拱的架设方法仍以支架法、悬臂法和转体法3种为主,其中悬臂拼装法应用最多,适用跨径最大范围也最广。     

Reliability-based strength limit state for steel railway bridges

Railway bridges require special attention to provide safe and economical service. To assess the reliability of a structure, all critical parameters need to be specified. Load and resistance are random in nature; hence, the probabilistic approach is the best method for accurate evaluation of the performance of a bridge. In this study, identification of critical parameters was conducted on a typical through-plate girder, riveted, open deck railway bridge. This type of structure is a weakest link system. In such a system, the failure of one component can lead to failure of the entire structural system. This research involved identification of the basic load and resistance parameters and the development of analytical procedures for modelling the structural behaviour. The finite element method (FEM) was used to investigate the structural performance characteristics of the evaluated bridge. A three-dimensional structural model was developed to determine stress distribution in the members and connections. Based on the results of FEM analysis, the reliability indices were calculated for critical components.     

既有铁路钢筋混凝土梁桥动态可靠性评估

介绍了既有桥梁结构的动态可靠性分析方法,提出了桥梁的恒载概率模型、活载概率模型及抗力概率模型,并对可靠度计算方法中的验算点法进行了介绍。以一座既有铁路钢筋混凝土梁桥为工程背景,计算了该桥的活载效应统计参数、恒载效应统计参数及抗力统计参数等,利用验算点法计算了桥梁结构构件的可靠度指标,又采用PNET方法分析了整个桥梁体系的可靠性,最后给出了桥梁的可靠性评估结果。结果显示动态可靠性评估应用于铁路钢筋混凝土梁桥可以得到较好的评估结果。     

体外预应力加固刚构桥及锚固分析

随着交通量的增加和荷载等级的不断提高,旧桥加固问题愈加突出。为研究大跨度刚构桥体外预应力加固后的结构性能以及锚固块空间应力分布情况,采用有限元程序ANSYS分别对主跨160 m连续刚构桥加固后的承载能力和边跨锚固块的空间应力进行了分析。分析结果表明,体外预应力加固能有效地提高结构的承载能力、改善结构性能,应用于大跨度连续刚构桥梁加固是有效可行的;同时指出,锚固区箱梁中的主要拉应力存在于箱梁边缘及转向孔边缘。分析结果可为同类桥梁的加固提供参考。     

Das Erdevicki Structural System – ein innovatives Seiltragsystem für Brücken‐ und Dachkonstruktionen

The Erdevicki Structural System – a new structural system for bridge and roof design. The Erdevicki Structural System has been developed in Vienna 1995. It represents an innovative alternative to suspension and cable state structures. The Structural System consists of a main single span girder element, top and bottom tension chords, diagonal compression struts and vertical tension elements connecting the diagonals to the girder. Relative short distances between the joints of the tension chords enable economical application of tension rods, very good vibration characteristics as well as good utilization of tension capacity from the applied elements. The basic system structural approach is to reduce the main girder positive moments. It is possible to reduce girder moments to virtually any level desired by the designers.     

板桁组合结构受力分析

对板桁组合结构受力特征进行了分析,揭示了其桥面板荷载的分布规律,提出了板桁组合体系主梁的简化模型方法,针对不同形式的桥面板对荷载传递路径及大小进行了分析,得出了一些有意义的结论。     

Time-variant reliability profiles for steel girder bridges

Evaluation of existing steel bridges becomes more important due to natural aging, increasing load spectra, deterioration caused by corrosion, and other problems. In the result, bridge structures exposed to aggressive environmental conditions are subjected to time-variant changes of resistance. Therefore, there is a need for evaluation procedures for an accurate prediction of the load carrying capacity and reliability of bridge structures, in order to make rational decisions about repair, rehabilitation, and expected life-cycle costs. The objective of this paper is to develop time-variant reliability models for steel girder bridges. Traditional methods based on deterministic analysis do not reveal the actual load carrying capacity of the structure. The proposed approach is based on reliability analysis of components and structural systems. The study involves the selection of representative structures, formulation of limit state functions, development of load models, development of resistance models for corroded steel girders, development of the reliability analysis method, reliability analysis of selected bridges, and development of the time-dependant reliability profiles including deterioration due to corrosion. The results of the study can be used for a better prediction of the service life of deteriorating steel girder bridges, and development of optimal reliability-based maintenance strategies.     

Proof load testing for bridge assessment and upgrading

Bridge deterioration with time and ever increasing traffic loads raise concerns about reliability of aging bridges. One of the ways to check reliability of aging bridges is proof load testing. A successful proof load test demonstrates immediately that the resistance of a bridge is greater than the proof load. This reduces uncertainty in the bridge resistance and so increases the bridge reliability. The paper considers a reliability-based calibration of intensities of proof loads for aging bridges to verify either an existing or increased load rating taking into account possible bridge deterioration. Intensities of proof loads are calibrated based on a consistent target reliability index. The influence of test risk, dead to live load ratio, and uncertainties associated with dead and live loads and bridge resistance is considered. The results presented in the paper relate to short and medium span bridges.     

Measured behavior of a curved composite I-girder bridge

Current techniques for the rating of horizontally curved composite steel girder bridges often use approximate methods of linear elastic analysis based on the assessment of individual straight girders with altered properties to account for member curvature. This paper summarizes measured versus computed results from a field test with heavy live load conducted on a multi-span, horizontally curved composite steel I-girder bridge in Duluth, Minnesota. Eight 320 kN (72,000 lb) trucks were placed on the bridge in 43 static and 13 dynamic loading configurations, and the results were compared to those obtained from linear elastic grillage analyses. Stresses up to 75% of the girder yield stress were obtained in the bridge, whose design was controlled by strength, thus representing some of the largest stresses ever achieved in an instrumented curved steel girder bridge, and behavior is described in the girders, diaphragms, lateral wind bracing, deck, bearings, and fatigue details. Grillage analyses are developed and used to corroborate the results and assess the accuracy of these procedures for load rating of bridges.     

An experimental study on after-fracture redundancy of continuous span two-girder bridges

This paper presents the results of an experimental test and numerical analysis of the after-fracture redundancy of two-girder continuous span bridges. Two test specimens that are commonly composed of two steel-plate girders and concrete deck have a fractured section in one of the two girders, which is artificially set up by making an entire cut along the web and bottom flange of the girder. To demonstrate the effect of bottom lateral bracings on the after-fracture redundancy of two-girder bridge system, one of the two test specimens includes a lateral bracing system between the girder bottom flanges but the other does not. The bend-loading test was conducted on the bridge specimens up to the collapse state. The test results revealed that the ultimate bending behaviors of the bridge specimens are considerably different from each other and the load carrying capacity could be increased as much as 20% when the bottom lateral bracings are installed. The numerical analysis of the test specimens indicates that the bottom lateral bracings play a substantial role in the load redistribution process from the severely fractured girder to the intact girder, making a considerable contribution to the load-carrying capacity of the after-fracture two-girder bridges. In the last part, the after-fracture redundancy was quantitatively evaluated for a prototype example bridge and some conclusions were drawn.     

Concept and requirements of sustainable development in bridge engineering

The concept of sustainability is described in this paper using a single sustainable principle, two goals of sustainable development, three dimensions of sustainable engineering, four sustainable requirements and five phases of sustainable construction. Four sustainable requirements and their practice in China are discussed in particular. The safe reliability of bridges is first compared with the events of bridge failure in China and in the rest of the world and followed by structural durability, including the cracking of concrete cable-stayed bridges, deflection of concrete girder bridges and fatigue cracks of orthotropic steel decks. With respect to functional adaptability, lateral wind action on vehicles and its improvement are introduced regarding a sea-crossing bridge located in a typhoon-prone area. The Chinese practice of using two double main span suspension bridges and a twin parallel deck cable-stayed bridge is presented in discussing the final sustainable requirement: capacity extensibility.     

Reliability assessment of cable-stayed bridges based on structural health monitoring techniques

This paper presents the reliability analysis approach of long-span cable-stayed bridges based on structural health monitoring (SHM) technology. First, the framework of structural reliability analysis is recognised based on SHM. The modelling approach of vehicle loads and environmental actions and the extreme value of responses based on SHM are proposed, and then models of vehicle and environmental actions and the extreme value of inner force are statistically obtained using the monitored data of a cable-stayed bridge. For the components without FBG strain sensors, the effects and models (extreme values) of dead load, unit temperature load, and wind load of the bridge can be calculated by the updated finite element model and monitored load models. The bearing capacity of a deteriorated structure can be obtained by the updated finite element model or durability analysis. The reliability index of the bridge's critical components (stiffening girder in this study) can be estimated by using a reliability analysis method, e.g. first order reliability method (FORM) based on the models of extreme value of response and ultimate capacity of the structure. Finally, the proposed approach is validated by a practical long-span cable-stayed bridge with the SHM system. In the example, reliability indices of the bridge's stiffening girder at the stage after repair and replacement after 18 years of operation, and the damaged stage are evaluated.     

Reliability-based condition assessment of deteriorating concrete bridges considering load redistribution

A wide variety of models have been proposed for estimating the reliability of highway bridges. For reinforced concrete bridges subjected to environmental attack, time-variant reliability methods have to be used. In this study, the condition of reinforced concrete girder bridges is assessed using a time-variant system reliability approach in which both load and resistance are time-variant quantities. Several system models are considered, including failure of any girder (series system) and failure of a specified number of adjacent girders (series-parallel system). Adaptive importance sampling is used to determine the cumulative-time system failure probability. An existing reinforced concrete T-beam bridge located near Pueblo, Colorado, is investigated. The influence of resistance degradation and post-failure load redistribution is included. A comparison of reliability estimates for several system models is given, including the influence of correlation among initial girder strengths. The results can be used as a guide for the selection of system models for bridge reliability analysis, identification of critical girders in a bridge system, and for the development of optimal reliability-based maintenance strategies for reinforced concrete highway bridges.     

面向未来的高性能桥梁结构研发与应用

为从根本上解决混凝土桥、钢桥及钢 混凝土组合桥中的共性技术难题,并提升桥梁结构的性能与品质,笔者团队以超高性能混凝土（UHPC）为基础,研发了面向未来的高性能桥梁结构体系。介绍了笔者团队研发的4类高性能桥梁结构:①钢-超高韧性混凝土（STC）轻型组合桥面结构,其中的STC是钢桥面专用的UHPC;②钢 UHPC华夫板轻型组合桥梁结构;③单向预应力UHPC薄壁连续箱梁结构;④全预制快速架设UHPC城市桥梁结构。通过大量静力和疲劳试验,掌握了各类UHPC桥梁结构的基本受力性能,并建立了计算理论和设计方法。列举了钢 STC轻型组合桥面结构已推广应用于中国的17座钢桥,涵盖了梁桥、拱桥、斜拉桥和悬索桥等各类基本桥型,典型应用包括湖南岳阳洞庭湖二桥等重大工程。到目前为止,各实桥运营状态良好,钢 STC未出现任何病害问题。综合而言,高性能桥梁结构有望突破现有桥梁中的技术瓶颈,具有广阔的应用前景。     

我国20 m预应力T梁桥承载能力可靠度分析

为了准确掌握我国20 m预应力T梁桥承载能力可靠度,基于我国公路钢筋混凝土及预应力混凝土桥涵设计规范(JTG 3362—2018),利用大型结构有限元分析软件Midas-civil建立了公路-Ⅰ级设计荷载作用下20 m预应力T梁全桥三维有限元模型,分析了最不利工况下桥梁的内力,并基于承载能力极限状态可靠度方法,计算了该类桥梁的承载能力可靠度,与美国和欧洲的可靠度计算值进行了比较。结果表明:我国20 m预应力T梁桥恒载最大弯矩为1516.7 kN·m,活载产生的最大弯矩为1386.4 kN·m,我国的活载效应值和美国基本一致,欧洲的活载效应较大;活荷载效应值对桥梁结构可靠度计算结果影响较大,我国20 m预应力T梁桥可靠度指标β为5.478,大于我国规范值约17%,高于美国的4.43,但低于欧洲的7.25。     

Experimental investigation of double composite twin-girder railway bridges

A railway bridge with a double composite section has been proposed to enhance the structural performance of existing twin-girder bridges, because the governing design parameter of railway bridges is flexural stiffness. The concrete deck in negative moment regions is neglected in the design of continuous composite bridges assuming the concrete slab has no resistance to tension. Therefore, the flexural stiffness of the composite section in the negative moment region is reduced, resulting in an increase of the depth of the steel section. In this study, push-out tests on lying studs and mixed stud shear connection with lying and vertical studs were performed to investigate the behavior of the shear connection in the double composite section. In addition, the static strength of the shear connection was evaluated. This study focuses on continuous two girder bridge models of 5m-5m span length with the proposed double composite section. From the static tests on the bridge models, several design considerations were investigated including the effective width, shear connection, and ultimate strength of the double composite section. Based on the test results, design guidelines and innovative twin-girder bridges were suggested.     

无背索斜拉桥的概念、设计与施工

长沙市洪山大桥是一座无背索斜拉桥,该类型桥梁的受力特性与常规斜拉桥有较大的不同,造成其设计和施工的特殊性。归纳国内外已建和在建的无背索斜拉桥的一般情况,详细论述其塔梁平衡关系和索、塔倾角的取用准则,根据优化塔、索造价和降低塔重偏差对塔身受力的影响来可以得到塔的合理倾角。进一步介绍洪山大桥的主梁类型和截面型式、若干构造细节和施工过程,分析研究表明钢-混凝土组合脊骨梁更能够适应无背索斜拉桥的受力特点,并具有造价和技术优势;主跨两端特殊的构造设计可以保证塔梁结合部和主跨-辅助跨过渡段的传力平顺;施工中采用桥面预压工艺可以有效改善桥面板横桥向受力状态。     

下穿式斜拉-拱组合结构体系桥:深圳燕罗人行桥

燕罗人行桥桥长136.0m,桥宽11.5 m,主跨108.0 m,矢跨比1/11.74。桥梁设计首创了“下穿式斜拉-拱组合结构体系”,相较于常规的上承式拱桥,该组合结构体系显著改善了主拱的受力,降低了拱脚的水平力,提高了主拱的刚度。燕罗人行桥由主拱、主梁、桥塔、主索、背索、竖向撑杆、圆管立柱和基础等组成,采用水中少（量）支架施工。