采用二维梁修正模型的钢梁-混凝土板组合桥梁的承载力分析

通过试验对钢梁-混凝土板组合桥梁的结构鉴定、基于修正模型的承载力、承载力对分析模型的敏感性进行分析。基于振型、频率、振型阶次等动力性能及静力变形,建立修正模型。用二维梁模型成功模拟了纵梁间横向荷载传递机理、扭转变形及斜桥影响。算得的承载力结果与三维有限元分析接近,而简化的一维杆模型误差却很大。在模型修正的不同阶段,将模型参数分组,这样能提高收敛速度和成功率。虽然可认为横向支撑不参加工作,但在承载力分析中它们却是临界杆。横向支撑的破坏改变了纵梁间的传力机理,可能导致内梁的过早破坏。     

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.     

Behavior of instrumented prestressed high performance concrete bridge girders

A comprehensive monitoring of the behavior of four prestressed high performance concrete (HPC) bridge girders, with higher compressive strength, during construction and while in-service, is presented. The monitoring program covered instrumentation and monitoring of a series of four girders during the casting operation, after construction, under the effects of traffic and thermal loads, as well as under controlled load conditions. Information regarding transfer length, prestress loss, heat of hydration, compressive strength, modulus of elasticity (MOE), modulus of rupture (MOR), creep, shrinkage, coefficient of thermal expansion, and chloride permeability of the concrete used is obtained and presented. Furthermore, the in-service monitoring and controlled load tests and details regarding thermal expansion, bridge stiffness, and load distribution factors are also presented. This paper provides details of testing of the concrete properties and field instrumentation of the bridge girders as well as a discussion of service level monitoring and controlled load testing. Comparisons are made between experimental and theoretical results.     

斜靠式拱桥侧倾失稳临界荷载解析解

以新型空间拱桥——斜靠式拱桥为研究对象,提出斜靠式拱桥发生侧倾失稳时主拱肋与稳定拱肋间横撑切向和径向受力模型,基于Ritz法,构造桥梁各主要构件的变形能、外力势能以及吊杆非保向力势,首次推导出斜靠式拱桥侧倾失稳临界荷载的解析解,并通过与有限元计算结果比较,验证该解析解计算公式的正确性。进一步分析稳定拱肋、吊杆非保向力、以及主拱肋与稳定拱肋间横撑对斜靠式拱桥侧倾失稳临界荷载的影响。研究结果表明:①增设稳定拱肋可使桥梁侧倾失稳临界荷载提高1.6～1.8倍左右,同时随着稳定拱肋倾角的增加,临界荷载呈增大趋势;②受吊杆非保向力以及桥面系的影响,桥梁侧倾失稳临界荷载可提高约3.5倍左右;③横撑的径向抗弯刚度对斜靠式拱桥侧向失稳临界荷载影响较大。     

Analysis of Bridge Condition Rating Data Using Neural Networks

Currently bridges are evaluated using either a visual inspection process or a detailed structural analysis. When bridge evaluation is conducted by a visual inspection, a subjective rating is assigned to a bridge component. With analytical evaluation, the rating is computed based on the load applied and the resistance of the bridge component. There have been several attempts to correlate the subjective rating to the analytical rating. The conventional statistical analyses, as well as methods based on fuzzy logic, have not been very successful in providing a clear relationship between the two rating systems. This paper describes the application of neural network systems in developing the relation between subjective ratings and bridge parameters as well as that between subjective and analytical ratings. It is shown that neural networks can be trained and used successfully in estimating a rating based on bridge parameters. The specific application problem for railroad bridges in the commuter rail system in the Chicago metropolitan area is presented. The study showed that a successful training of a network can be achieved, especially if the input data set contains parameters with a diverse combination of intercorrelation coefficients. When the relationship between the bridge subjective rating and bridge parameters was investigated, the network had a prediction rating of about 73%. The study also investigated the relation between the subjective and analytical rating. In this case, the prediction rate was about 43%. Compared with conventional statistical methods and the fuzzy‐logic approach, the neural network system had a much better performance ratio in establishing the relation between the bridge rating and bridge parameters.     

波形或桁架式钢腹板的预应力钢混组合桥主梁的安全性能和使用性能评估

在许多国家,预应力混凝土箱梁被认为是中等跨径(30～50m)混凝土梁最有效的结构形式。但是当混凝土梁的单跨长度超过50m时,相对钢梁,混凝土箱梁自重问题成为其最大约束。因此,在韩国,中等跨径桥梁主要采用钢箱梁。在20世纪,研究者们多次尝试提高预应力混凝土箱梁结构的有效性,最终采用混凝土-钢混合梁以减轻结构自重。但是,混合桥采用不同类型钢腹板及不同连接形式,会引起结构安全性能和使用性能的变化。为了全面了解钢腹板梁及钢腹板连接形式的性能,对5根带腹板的预应力混凝土梁进行静力荷载试验。这5根试件中,有2根混合梁采用波形钢腹板,而另3根采用桁架式钢腹板。结果显示:通过加强钢腹板与预应力筋的连接节点,可以改善使用性能相关问题(开裂荷载和挠度)及安全性能相关问题(刚度和极限承载力)。     

Analytical prediction of transfer length in prestressed self-consolidating concrete girders using pull-out test results

While self-consolidating concrete (SCC) is comparable to conventional concrete (CC) in terms of strength, the comparability of SCC’s bond to steel is less well-defined. A keen understanding of SCC’s bond strength is essential to advance SCC within the prestressed concrete industry. This study presents an analytical method for predicting the transfer length of steel strands in prestressed girders using pull-out test results. The experimental data from a series of 56 pull-out tests is utilized to derive bond stress–slip relationships for 12.7 mm steel strands embedded in SCC and CC. Modification factors are used to correlate pullout bond stresses to transfer bond stresses in prestressed members, and the modified relationships are integrated in three-dimensional finite element models to predict transfer lengths in prestressed SCC girders. The analytical predictions correlate well with experimental results and transfer length requirements of current US design codes.     

基于荷载试验的大跨钢拱桥承载能力评估

为了解大跨钢拱桥的力学特性,评价其实际承载能力,以厦门五石桥为工程背景,对该桥的动静态力学性能进行了有限元数值分析和动静载试验研究.试验与分析结果表明:静载作用下,该桥拱肋、主梁的应力和变形试验校验系数均在正常范围内,弹性工作性能良好,具有足够的强度和刚度;钢主梁剪力滞效应比较明显,顶底板纵向应力沿横断面近似呈V形分布;动载作用下,结构动态放大系数处于正常范围,结构动力性能良好.     

工字形复合曲线梁桥的性能研究

目前在计算水平弯曲的复合钢梁桥时,通常采用一种近似方法,即单个直梁的线弹性分析法,其中具有可变参数以考虑构件曲率。归纳了明尼苏达州德卢斯的一个具有较重活荷载的多跨水平弯曲工字形复合钢梁桥的现场试验数据和计算结果。将8个320kN的卡车以43种静力加载和13种动力加载的方式放置在桥上,并将试验结果与线弹性梁格分析中得到的结果进行对比。桥被设计为由强度控制,梁的应力达到了屈服应力的75%,有些部位甚至达到了最大应力,同时,对梁、隔板、水平抗风支撑、桥面板、轴承的性能和疲劳特性进行了描述。采用梁格分析以验证这些方法对于计算梁桥承载能力的有效性和准确性。     

Field investigation of ultra-high performance concrete shear key in an adjacent box-girder bridge

Adjacent box girders are widely used in short to intermediate span bridges in several states because they make bridges quick and easy to build. However, the strength and serviceability of this type of bridge can frequently be compromised by the reductions in efficiency of load transfer and shear resistance due to joint degradation at the shear keys. Because of its superior mechanical properties and improved durability, ultra-high performance concrete (UHPC) has been proposed as an alternative grout material to eliminate shear key degradation. In this project, a single-span adjacent box-girder bridge was instrumented and monitored to investigate the performance of the UHPC shear keys under truck loads. The parameters of primary importance to shear key performance were identified from the response data. A finite element (FE) model of the bridge was developed to evaluate the efficiency of the load transfer mechanism at the UHPC joints. The UHPC shear key and transverse shear reinforcement bars fully transferred the load through the joints due to high bond strength of UHPC. The maximum relative displacement for all load cases was 0.151?mm (0.00594 in.) insufficient to cause damage to the UHPC shear key interface.     

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.     

A numerical investigation on the fire response of a steel girder bridge

The response of bridges subject to fire is an under researched topic despite the number of bridge failures caused by fire. Since available data shows that steel girder bridges are especially vulnerable to fire, this paper delves into their fire response by analyzing with a 3D numerical model the response of a typical bridge of 12.20 m span length. A parametric study is performed considering: (1) two possibilities for the axial restraint of the bridge deck, (2) four types of structural steel for the girders (carbon steel and stainless steel grades 1.4301, 1.4401, and 1.4462), (3) three different constitutive models for carbon steel, (4) four live loads, and (5) two alternative fire loads (the hydrocarbon fire defined by Eurocode 1 and a fire corresponding to a real fire event). Results show that restraint to deck expansion coming from an adjacent span or abutment should be considered in the numerical model. In addition, times to collapse are very small when the bridge girders are built with carbon steel (between 8.5 and 18 min) but they can almost double if stainless steel is used for the girders. Therefore, stainless steel is a material to consider for steel girder bridges in a high fire risk situation, especially if the bridge is located in a corrosive environment and its aesthetics deserves special attention. The methodology developed in this paper and the results obtained are useful for researchers and practitioners interested in developing and applying a performance-based approach for the design of bridges against fire.     

锚箱式索梁锚固结构受力特性研究Ⅰ:理论模型

对于大跨度钢箱梁斜拉桥而言,需通过索梁锚固结构实现斜拉索与主梁之间的荷载传递。该结构传递荷载大、传力机理复杂、局部应力集中问题突出,是大跨度钢斜拉桥的关键结构和构件之一。以典型的超大跨度斜拉桥——苏通大桥锚箱式索梁锚固结构为研究对象,通过理论研究与试验研究相结合的方法对于锚箱式索梁锚固结构的受力特性进行了研究。研究表明:理论模型与试验结果基本吻合,采用理论研究与模型试验相结合的研究方法对于锚箱结构的传力机理进行研究是可行的;锚箱结构各主要受力构件的受力特性存在较大差异;各关键受力构件均存在不同程度的应力集中,其中钢箱梁腹板、锚箱顶板和底板的应力集中问题较为突出。     

Shear strength of horizontally curved steel I-girders — finite element analysis studies

This paper presents the results of finite element analysis (FEA) studies of four curved steel I-girder shear components tested experimentally in previous research, as well as parametric extensions of these tests. These studies focus on the influence of horizontal curvature on the maximum strength of transversely stiffened members with web slenderness D/t_w approximately equal to the largest value permitted in AASHTO [AASHTO LRFD bridge design specifications. 3rd ed. In: 2005 Interim Provisions, Washington (DC): American Association of State and Highway Transportation Officials; 2004], and with panel aspect ratios of d_o/D=1.5 and 3.0. These ratios are larger than previously considered in experimental tests of curved I-girders with similar or larger slenderness. The girders studied have subtended angles between their bracing locations of L_b/R=0.05 and 0.10, and web panel d_o/R values ranging from 0.03 to 0.10. The FEA models incorporate the measured material stress-strain relationships and section dimensions from the physical tests, detailed modeling of the test boundary conditions, residual stresses due to flame cutting and welding, and initial geometric imperfections in the form of buckling mode shapes. The load transfer mechanisms of the test girders are investigated via elastic buckling and full nonlinear analyses. The parametric studies are performed to investigate the effects of residual stresses and geometric imperfections, the behavior of equivalent straight girders, and the influence of reduced flange size on the peak shear capacity and moment-shear interaction.     

Finite element modelling of plate girders with web openings

This paper is concerned with a finite element model to predict the behaviour and ultimate load of plate girders with web openings. The finite element package is used to model the plate girders with web openings. Accuracy of the model is assessed by applying it to plate girders tested earlier by other researchers. Comparison of analytical results with the available experimental results for yielding patterns, ultimate load values and load–deflection relationships show good agreement between the finite element and experimental results thus validating the accuracy of the proposed model. The proposed finite element method was extended to carry out a parametric study. The study covered parameters such as web slenderness and flange stiffness.     

A hybrid experimental-numerical approach for load rating of reinforced concrete bridges with insufficient structural properties

This article presents a non-destructive approach for load rating of reinforced concrete bridges without structural plans. The approach is found on a hybrid method, which employs vibration and live load testing coupled with numerical simulation and model updating techniques, to converge on estimate of unknown structural parameters. The material properties of bridge and the amount of reinforcing steel for calculating the bending capacity of a bridge are determined through model updating results and nondestructive approaches. The updated model is then employed to determine load effects for calculating load rating factors, and these results are combined with live load test result to arrive at the bridge capacity, and ultimately the load rating. The method is validated by testing a skewed reinforced concrete slab bridge for load rating purposes. The bridge was instrumented with accelerometers and strain gages, and the responses of the bridge under vibration and quasi-static tests were measured. Results demonstrated that the proposed method is capable of determining the bridge capacity and load rating factor with good accuracy, and not only can be used for load rating of concrete bridges without structural information, but also can be useful in condition assessment of existing concrete bridge with available as-built information.     

Modal Flexibility Analysis of Cable-Stayed Ting Kau Bridge for Damage Identification

Abstract:   The cable-stayed Ting Kau Bridge has been permanently instrumented with more than 230 sensors for long-term structural health monitoring. In this article, the feasibility of using the measured dynamic characteristics of the bridge for damage detection is studied. Making use of a validated three-dimensional (3D) finite element model (FEM), modal flexibility matrices of the bridge are constructed using a few truncated modes and incomplete modal vectors at the sensor locations. The relative flexibility change (RFC) between intact and damage states is then formulated as an index to locate damage. The applicability of this flexibility index for damage location in the cable-stayed bridge is examined by investigating various damage scenarios including those at stay cables, longitudinal stabilizing cables, bearings and supports, longitudinal girders and cross girders, and taking into account measurement noise in modal data. The influence of two ambient factors, that is, temperature change and traffic loading, on the damage detectability is also analyzed by approximately considering an equivalent alteration in the material and structural behaviors. It is revealed that in the absence of ambient effects the RFC index performs well for locating damage of different severities in single-damage cases. In multi-damage cases the RFC index may provide false-negative identification for damage at the members with low sensitivity. Eliminating ambient effects is requisite for reliable detection of damage at stay cables and cross girders. The capability of the RFC index for locating damage at cross girders is significantly dropped in the presence of measurement noise.     

Experimental study on inelastic mechanical behaviour of composite girders under hogging moment

Negative bending moments acting on the support regions of continuous composite girders generate tensile stresses in the concrete slab and compressive stresses in the lower steel profile. As a result, the mechanical behaviour of these girders becomes strongly nonlinear, which needs special study. In this paper, static experimental tests on four half-scale models of steel and concrete composite girders with different shear connectors such as studs and Perfo-Bond Strips (PBLs) under hogging moments are cautiously conducted in order to investigate the reduction of flexural stiffness and the inelastic behaviour after cracking. In the test results, crack development, crack widths and strains of the composite section before and after cracking were observed. The crack width evaluation methods based on design codes for steel and concrete composite girders under negative bending moment were compared. Crack widths should be controlled appropriately within an allowable value in the slab under service load. The strains in reinforcing bars obtained through the static tests agreed well with the values calculated through the application of the existing tension stiffening theory. The test specimens could be assumed to be a full composite section until the ultimate state on the basis of load and slip relationship results of shear connectors. It follows that analytical and experimental studies can be served as a basis for the design of continuous composite bridges.     

LRB曲线桥震致碰撞效应的非线性分析方法

发展了一种适用于体元模拟联间轴向正面碰撞效应的束缚面型碰撞单元(Constraint-sur face Impact Element,CIE);基于柔度法给出了不同以往文献中碰撞单元刚度的计算取值,该取值不仅理论合理且在物理角度可解释其合理性.将该方法应用于广州潮汕机场航站楼高架桥的震致碰撞分析.箱梁采用壳单元模拟,伸缩缝位置设有CIE,桥墩与箱梁间设置隔震单元模拟铅芯橡胶隔振支座(Lead-rubber Bearing,LRB),采用通过试验得到的双线性刚度模型模拟其物理行为.采用非线性直接积分法进行时程分析,主要考察联间的碰撞力、LRB滞回耗能、LRB位移量、基底弯矩、剪力以及碰撞力分别对这些因素的影响.     

Performance of composite girders strengthened using carbon fibre reinforced polymer laminates

This paper highlights the structural performance of steel–concrete composite girders strengthened using advanced composite laminates. Nonlinear 3-D finite element models have been developed to investigate the flexural behaviour and load carrying capacity of the girders. The composite laminates comprised carbon fibre reinforced polymer (CFRP) plates and sheets as well as steel reinforced polymer (SRP) sheets. The elastic modulus and ultimate tensile strength of the laminates varied from low to high 60–300 GPa and 700–3100 MPa, respectively. The nonlinear material properties of the strengthened composite girder components comprising concrete, structural steel beam, reinforcement bars, adhesive and composite laminates were incorporated in the finite element model. The interfaces between the composite girder components were also considered allowing the contact and bond behaviour to be modelled and the different components to retain its profile during the deformation of the strengthened composite girder. Furthermore, the load-slip characteristic of headed stud shear connectors was incorporated in the finite element models based on previous experimental and numerical investigations conducted by the author. The finite element models have been validated against published tests on composite girders strengthened using different advanced composite laminates and having different cross-section geometries, lengths, layers of laminates with different elastic moduli and ultimate tensile strengths, concrete strengths and structural steel strengths. The load carrying capacity of strengthened composite girders, load–vertical displacement behaviour and failure modes were predicted from the finite element analyses and compared against test results. Parametric studies were conducted to study the effects on the load carrying capacity and structural behaviour of strengthened composite girders owing to the change in the composite laminate elastic modulus, number of laminate layers, concrete strengths and structural steel strengths. The study has shown that the increase in the load carrying capacity and ductility of strengthened composite girders due to the increase in steel beam strength is significant with high strength concrete slab. Also, it has been shown that the increase in concrete strength offers a considerable increase in the initial stiffness of strengthened composite girders, while the increase in structural steel strength offers a considerable increase in the stiffness of strengthened composite girder in the post-yielding stage.