Fatigue life estimates for a slender orthotropic steel deck

Fatigue cracks in several types of welded joints and geometrical details have been reported to occur in a large number of slender orthotropic decks of existing steel bridges in many parts of the world. Some of these cracks are initiated very early, a few years after the bridge is brought into service. That is why it is said that fatigue life estimation for the welded joints of orthotropic decks is not an easy designing task. This is so because the random variation of local stresses is sensitive to many factors, in particular to those involved in the dynamic interaction between the vehicle’s tyres, the pavement and the steel structure.This paper presents and discusses the main causes for the observed cracks and the outcome of the ultimate fatigue life estimates for typical welded and geometrical details of a slender orthotropic deck with trapezoidal cross-section longitudinal ribs. This is the deck of an existing long-span steel bridge, which has been strengthened by adding a reinforced concrete layer fixed with shear studs to the steel deck top plate. This was done to avoid continued and extensive repair work and to enhance the fatigue life expectancy of the steel deck structure. The fatigue life estimation is done with the aid of refined numerical modelling and in situ experimental strain measurements and also by taking into account all the built-in structural alterations, changes in volume of traffic and in vehicles loading which have occurred during this bridge’s 32 years of service life.     

正交异性钢桥面板疲劳裂纹的维修加固方法

正交异性钢桥面板的疲劳裂纹是既有钢桥的常见病害,其维修加固难于新桥建设,必须遵守耐久性等基本原则。钢桥面板的维修加固方法分为三类:第一类是改进铺装层结构,减小整个钢桥面板所有部位的应力;第二类是局部补强或者改进纵向加劲肋的构造;第三类是直接对发生疲劳裂纹的局部进行维修。如果疲劳裂纹比较严重,如纵向加劲肋与横肋之间的连接失效、或者纵向加劲肋与面板的连接焊缝处裂纹向上贯穿面板等,则需要同时采用第一类和第三类加固方法。     

正交异性钢桥面板结构体系的疲劳破坏模式和抗力评估

正交异性钢桥面板的疲劳问题属于包含多疲劳破坏模式的结构体系疲劳问题。基于这一本质特性,以典型的正交异性钢桥面板结构体系为研究对象,由结构体系的主导疲劳破坏模式出发,提出正交异性钢桥面板结构体系疲劳抗力评估的新方法。以纵肋与顶板焊接细节和纵肋与横隔板交叉构造细节为主要研究对象,设计8个足尺节段模型,主要包括传统纵肋与顶板焊接细节、新型镦边纵肋与顶板焊接细节和纵肋与横隔板交叉构造细节,通过模型试验研究了两类重要构造细节的主导疲劳破坏模式和实际疲劳抗力,在此基础上结合切口应力评估方法探讨正交异性钢桥面板构造细节切口应力S-N曲线方程、结构体系的主导疲劳破坏模式等关键问题。研究结果表明：传统纵肋与顶板焊接细节和新型镦边纵肋与顶板焊接细节的主导疲劳破坏模式均为疲劳裂纹萌生于焊根并沿顶板厚度方向扩展,二者的实际疲劳抗力基本相同;纵肋与横隔板交叉构造细节的疲劳破坏模式为焊趾开裂沿纵肋腹板方向扩展;对于研究对象而言,萌生于纵肋与顶板焊接细节焊根并沿顶板厚度方向扩展的疲劳破坏模式为控制结构体系疲劳抗力的主导疲劳破坏模式。     

Analytical calculation of internal forces in orthotropic plated bridge decks based on the slope-deflection method

Orthotropic plated bridge decks are highly sensitive to fatigue damage, due to the large amount of welded connections, the high patch loads and the large number of stress cycles they involve. For highway bridges, the stiffener web to deck plate weld is often the determining fatigue detail for the deck design. This paper develops a detailed analytical model for the stresses in this detail, using the slope-deflection method. It models a cross-section of the deck plate, but incorporates into it the influence of the horizontal and vertical stiffness of the entire orthotropic plate as well as the torsional rigidity of the longitudinal stiffeners. This calculation method allows for the determination of all internal forces of the determining cross-section of the bridge deck.     

Fatigue analysis of a pre-fabricated orthotropic steel deck for light-weight vehicles

An orthotropic steel deck designed for carrying light-weight vehicles was investigated to assess its fatigue life. Fracture mechanics analysis was performed with consideration of pre-existing flaws at the fatigue-sensitive region. Three-level models were used to accurately evaluate the stress-intensity factors at the rib-to-diaphragm connection. The crack growth was simulated by numerical integration of the Paris formula. In order to assess the severity of pre-existing flaws at the welded joint of the rib-to-diaphragm connection, the fatigue life of the deck was investigated with different sizes of initial crack. This approach provides a rational quality assessment method for the orthotropic steel deck.     

Fatigue Behavior Investigation and Stress Analysis for Rib-to-Deck Welded Joints in Orthotropic Steel Decks

The fatigue problems in orthotropic steel decks have raised widely concerns in recent years. This study focused on the root crack mechanism at rib-to-deck welded joints, based on the previous test results of sectional specimens and the matching FE analysis, the fatigue behaviors of structure detail were investigated by considering the effect of root gap shapes, weld penetrations, and plate thicknesses on crack initiation. Besides, various root crack depths were simulated in models to clarify the stress variations occurring during the propagation stage under cyclic loading. The results showed that the root gap shape and penetration rate have an impact on the root cracking direction and fatigue life at the initiation stage, but seem not directly related to the crack propagation mechanism; the higher penetration rate is advantageous for the prevention of root crack initiation. However, although the stiffness increased with the increase in plate thickness, the fatigue life of crack initiation might be reduced owing to the low fatigue strength of the thick deck plate, whereas the U-rib thickness has limited effect on the stress response of the root tip. Moreover, the significant difference between the 8 mm-crack model and other crack models is the high stress concentration around the crack tip. The stress conditions of root tip would be changed under loading cycles when a root crack propagated into half of deck plate thickness. Finally, the effect of structural dimensions on fatigue strength were also compared according to test results and FEA.     

Fatigue behavior and statistical evaluation of the stress category for a steel-concrete composite bridge deck

The maintenance cost of bridges is rapidly increasing since many existing bridges are deteriorating or reaching their design life all over the world. Moreover, as many long-span bridges are under construction and planning in Korea, research and development on bridge decks with high load-resistance capacity as well as high fatigue strength has become a growing concern. This research gives experimental results of the fatigue behavior of a new-type of steel-concrete composite bridge deck being developed under such circumstances. The proposed composite bridge deck consists of corrugated steel plate, welded steel ribs, stud shear connectors, and reinforced concrete filler. Fatigue tests were conducted under a four-point bending test with four different stress ranges in constant amplitude. In order to determine the influence of the concrete filling, fatigue tests on partial steel specimens containing only plain corrugated steel plates were performed in advance. The partial steel specimens and the steel-concrete composite deck specimens both showed fatigue failure in the tension part concerning the fillet welding part between the corrugated steel plate and steel rib. Finally, the stress category of the fillet welding part of each specimen is evaluated based on a statistical approach of Albrecht’s probability model. The research concludes that the fatigue behavior of such steel-concrete composite decks under sagging moment can be estimated based on the classical S-N approach, focusing on steel components.     

基于转角位移法对正交各向异性桥面板内力的分析计算

由于大量的焊接连接件、高度集中荷载作用和它们导致的大量应力循环,正交各向异性桥面板对疲劳破坏非常敏感。在公路桥中,焊接在桥面板的加劲腹板通常易于遭受疲劳破坏。开发了一个分析模型,可以运用转角-位移法计算应力。它构建了一个桥面板的横截面模型,但是其中考虑了整个正交板的水平和竖向刚度以及纵向加劲肋的扭转刚度。这种方法可以计算桥面板横截面上的所有内力。     

轻型组合桥面板球扁钢纵肋-横隔板连接细节局部应力分析

为降低正交异性钢桥面板疲劳开裂的风险,提出带球扁钢纵肋的轻型组合桥面板方案。以洞庭湖二桥轻型组合桥面板为工程背景,建立钢桁梁局部有限元模型和球扁纵肋-横隔板连接细节的子模型,并基于热点应力法,对横隔板上开孔孔型和厚度进行了参数分析。研究表明：球扁纵肋-横隔板连接处3个典型疲劳细节的疲劳性能受横隔板厚度影响显著|综合比较,苹果型开孔的疲劳性能最优。为进一步验证轻型组合桥面板的球扁钢纵肋-横隔板连接处3个细节的疲劳性能,开展了足尺模型疲劳试验,试验模型采用16mm厚带苹果型开孔的横隔板设计。疲劳试验中,控制细节（横隔板切口自由边缘）的应力幅为90.6MPa,历经250万次循环加载后,试验模型中典型疲劳细节均未出现疲劳裂纹。这表明,带球扁钢纵肋的轻型组合桥面板关键细节的疲劳性能良好,能满足洞庭湖二桥的工程要求。     

Analytical and experimental studies on optimal details of orthotropic steel decks for long span bridges

Orthotropic steel decks gradually come into general use in long span bridges due to various advantages such as dead weight reduction, easy quality control, and so on. On the other hand, stress concentration is often observed near the connection details, which may lead to fatigue problems and govern the design of the structure. Therefore, researches to understand the structural behaviors and examine stress distribution of details in orthotropic steel decks are required in order to develop an optimal connection detail. In this paper, optimal parameters regarding height, thickness and shear area of a cross-beam and efficiency and shapes of bulkhead plates are characterized by analytical studies and verified by experiments, so that fatigue cracks could be prevented.     

Experimental study and numerical analysis on mechanical behavior of T-shape stiffened orthotropic steel-concrete composite bridge decks

A new-type of orthotropic steel-concrete composite bridge deck system was developed, by casting the concrete overlay on the top of the orthotropic steel deck ribbed with T-shape steel members. To study its mechanical behavior (in terms of failure mode, load-deflection relationship, concrete crack initiation and propagation, strength, stiffness and so on), two new-type orthotropic steel-concrete composite bridge decks with different section dimensions were experimentally investigated and two reference decks (reinforced concrete deck and orthotropic steel deck) were also involved in the research for comparison. For the two new-type orthotropic steel-concrete composite decks, the average value of ultimate loads per width is 885.7kN, which is 2.35 and 1.61 times of that of the concrete and steel reference decks with almost the same section height. Experimental results proved that the composite deck can effectively control the crack initiation and propagation in the concrete and postpone the yielding of the steel bars and steel plates, due to the composite action between the concrete overlay and the underlying steel plate. Furthermore, the Finite Element (FE) model of the orthotropic steel-concrete composite deck was developed and validated by test results. A parametric study is conducted regarding to the stiffness of shear studs. With the validated FE model, stress distribution in the underlying steel plate and T-shape stiffeners and development of concrete cracking in the concrete overlay were characterized at different load levels.     

钱塘江第四大桥拱肋钢锚箱受力分析

吊杆和拱肋之间的锚固区是把桥面荷栽传给拱肋的关键部位，由于锚固区构造复杂，承受较大的局部荷栽，故建立锚固区的实体模型进行有限元分析，得到了锚固区局部的应力，并对钢锚箱与钢管拱肋的连接部位的焊缝进行了疲劳强度的验算。     

深圳至中山跨江通道钢桥面板结构疲劳试验研究

正交异性钢桥面板的疲劳开裂问题是制约桥梁工程可持续发展的关键难题,亟需发展具有高疲劳抗力特性的正交异性钢桥面板结构。依托深圳至中山跨江通道项目,在钢桥面板结构中同时引入纵肋与顶板新型双面焊构造细节和纵肋与横隔板新型交叉构造细节两类构造细节,设计9个足尺节段模型,通过模型试验确定了纵肋与顶板传统单面焊构造细节和新型双面焊构造细节、纵肋与横隔板传统交叉构造细节和新型交叉构造细节的疲劳开裂模式和实际疲劳抗力;采用扫描电子显微镜(SEM)确定了不同制造工艺条件下纵肋与顶板焊接细节的初始制造缺陷尺度;采用等效结构应力法确定了两类细节各疲劳开裂模式的疲劳抗力。研究结果表明：纵肋与顶板传统单面焊构造细节的疲劳裂纹起裂于顶板焊根并沿顶板厚度方向扩展,其疲劳抗力为95.1～98.7MPa,新型双面焊构造细节的疲劳裂纹起裂于顶板内侧焊趾并沿顶板厚度方向扩展,其疲劳抗力为108.5～123.2MPa,且在相同加载条件下,双面埋弧焊构造细节的疲劳抗力高于双面焊气体保护焊构造细节的疲劳抗力;传统单面焊构造细节焊根的初始制造缺陷尺度显著大于新型双面焊构造细节焊趾的初始制造缺陷尺度,且双面埋弧焊的初始制造缺陷尺度小于双面气体保护焊的初始制造缺陷尺度,初始制造缺陷尺度的差异是不同制造工艺条件下纵肋与顶板焊接细节疲劳抗力存在差异的主要原因;纵肋与横隔板传统交叉构造细节的疲劳裂纹起裂于纵肋腹板焊缝端部焊趾并沿纵肋腹板扩展,新型交叉构造细节的疲劳裂纹起裂于纵肋底板焊缝端部焊趾并沿纵肋底板扩展,两类构造细节的起裂次数基本一致,但新型构造细节的疲劳裂纹扩展速率远低于传统构造细节的疲劳裂纹扩展速率;纵肋与顶板焊接构造细节和纵肋与横隔板交叉构造细节各疲劳开裂模式的实际疲劳抗力基本位于主S-N曲线±2σ之间。     

Parametric Study on the Interface Layer of Renovation Solutions for Orthotropic Steel Bridge Decks

Abstract: The article presents renovation solutions for orthotropic steel bridge decks consisting of bonding a second steel plate to the existing steel deck in order to reduce the stresses and enlarge the life span of the orthotropic bridge deck. Two solutions for the interface layer between the existing deck plate and the second steel plate are presented: thin epoxy (bonded system) and thick polyurethane (sandwich system). A parametric study based on analytical solutions is carried out on flexural behavior of beams representing the renovation solutions. The influence of geometrical, mechanical and structural parameters on the stiffness and stress reduction factor of the system is studied. Maximum values of stiffness and stress reduction are achieved when maximizing the interface layer thickness and minimizing the second steel plate thickness with in certain practical limits. Based on the weight restrictions one can choose the most efficient interface layer regarding thickness and mechanical properties.     

单向预应力UHPC连续箱梁桥面体系优化设计研究

为方便布置体内预应力束和进一步改善桥面板受力状态,对大跨单向预应力UHPC (Ultra-high Performance Concrete)连续箱梁桥的桥面体系进行优化设计,提出新型正交异性UHPC矮肋板桥面体系方案。以广东省某桥为工程背景,进行了基于正交异性UHPC矮肋板桥面体系方案的UHPC箱梁结构试设计并开展相关的试验研究。结果表明：①与矩形桥面板方案相比,优化的正交异性UHPC箱梁矮肋板桥面体系自重可减少17.0%,并可在矮肋板纵肋处方便地布置体内束;与华夫桥面板方案相比,可在不明显增加桥面体系自重的前提下,大幅减小桥面板的纵向应力,降幅可达46.8%;②基于正交异性UHPC矮肋板桥面体系的UHPC箱梁方案试设计整体计算满足受力要求,桥面体系计算中标准组合作用下桥面板最大纵向拉应力2.66MPa,横隔板最大横向应力6.09MPa;③试验及计算结果表明,矮肋板试件初裂名义应力8.84MPa,抗裂设计名义应力限值10.70MPa,UHPC箱梁横隔板上弦板底面横向应力达到8.43MPa时仍处于线弹性受力阶段,表明试设计方案能满足设计要求。     

正交异性钢桥面铺装层疲劳寿命的断裂力学分析

计算和分析正交异性钢桥面铺装层表面裂缝应力强度因子,在此基础上应用Paris扩展公式预测铺装层疲劳寿命。将奇异单元布置在铺装层表面裂缝前沿,建立正交异性钢桥面系三维断裂力学有限元模型,计算铺装层表面裂缝的应力强度因子;分析裂缝应力强度因子随轴载作用位置的变化规律,确定了带裂缝铺装层轴载作用的最不利荷位;以最不利荷位作为轴载作用的标准荷位,计算应力强度因子随裂缝扩展深度的变化,并数值拟合得到了应力强度因子与裂缝深度的关系式;将应力强度因子的深度关系式代入Paris公式,积分得到铺装层的疲劳寿命。计算结果表明,基于钢桥面铺装层带裂缝工作的事实,应用断裂力学方法预测钢桥面铺装层疲劳寿命是可行的。     

正交异性钢桥面板结构加工技术工艺

<正>交异性钢桥面板是钢结构桥梁的重要结构件,正交异性钢桥面板由钢板、U肋和横隔板组成。以钢箱梁正交异性钢桥面板为例,介绍正交异性钢桥面板结构特点和组拼、焊接及工地连接工艺特点,探讨在目前焊接和组装工艺条件下,延长正交异性钢桥面板使用寿命的加工技术和工艺。     

正交异性钢桥面板改造的组合粘结系统

<正>交异性钢桥面板改造的问题在于既有钢板与第二个钢板的粘结,以降低应力和增加正交异性钢板的使用寿命。通过试验和分析,对梁的弯曲性能进行参数研究。试验考虑不同厚度、温度和跨度的影响。从试验结果可见,应力降低与温度无关。最小化第二块钢板的厚度及最大化粘结层厚度,可降低重量,增加组合结构的刚度,这是最有效的解决方法。组合梁的弹性性能和屈服荷载取决于钢板的性能,温度的影响不显著。然而,粘结层的受剪最终导致梁的破坏,而粘结层的性能受温度的影响较大。     

正交异性钢桥面板受力特征研究

论述正交异性钢桥面板的结构受力特点,对易出现裂纹的构造受力情况进行分析。通过ANSYS有限元软件,分别对公路正交异性桥面和铁路正交异性桥面建立模型,在移动荷载作用下,对桥面的竖向变形、横隔板部位的面外变形,以及U肋与腹板交叉部位构造的应力变化规律进行分析。研究结果表明:弧形缺口处面外和面内的变形、U肋与面板、U肋与横隔板交叉焊缝的起焊点和弧形缺口部位的最小净截面处的应力是引起正交异性板疲劳的主要因素,其主要受相邻2个横隔板范围内荷载的影响;荷载在桥宽方向只影响与其相邻(左右两侧)的两个U肋的肋角应力。     

轻型车辆的预制正交异性钢板的疲劳分析

对轻型车辆的正交异性钢板进行疲劳分析,考虑疲劳敏感区域处的初始缺陷,获得疲劳寿命。采用3种模型精确模拟肋与隔板连接处的应力集中现象,并用Paris公式模拟裂纹发展状况。为了分析连接处焊接节点初始缺陷的影响,研究了不同初始裂纹下钢板的疲劳寿命。为正交异性钢板疲劳寿命的评估提出了一个合理的方法。