黄浦南汉桥风致抖振疲劳频域分析

提出了在频率域内用Markov过程进行大跨度桥梁风致抖振疲劳分析的计算方法。以黄浦南汉桥为例,用不同的方法对其进行了疲劳分析。其初步计算结果表明,本文提出的方法是可行和有效的。     

基于延性破坏准则的钢管混凝土圆柱低周疲劳寿命研究

将钢筋混凝土结构的等效延性破坏准则应用于钢管混凝土圆柱的低周疲劳寿命分析,提出了钢管混凝土圆柱的低周疲劳寿命计算方法,综合考虑了结构的首超破坏和累积损伤.建立了钢管混凝土圆柱的低周疲劳寿命拟合曲线,拟合公式的相关系数为0.971;通过23根钢管混凝土圆柱的低周疲劳试验结果对提出的计算方法进行了验证.结果表明:建议计算模型能够较好地反映钢管混凝土圆柱在不同位移延性水平下的疲劳寿命.     

关于焊接接头疲劳寿命试验及计算方法研究

焊接接头的疲劳寿命决定着焊接结构件的工作寿命,是进行结构件疲劳计算的基础数据,焊接结构疲劳寿命值及计算方法直接影响了产品可靠性设计.本文以对接接头为例进行试验研究,同时采用有限元疲劳寿命计算方法进行焊接接头疲劳寿命计算,验证有限元疲劳分析计算在结构件寿命计算的可行性,为结构优化寿命设计提供指导.     

高耸结构风振疲劳的随机裂纹扩展分析

采用随机裂纹扩展模型对高耸结构的风振疲劳问题进行分析,同时考虑平均风速的概率分布和时间相关性对裂纹扩展的影响,用ZMNL法模拟相关的平均风速时程样本,根据Monte-Carlo法得出裂纹长度的概率分布.推导出计算裂纹长度和疲劳寿命的二次矩近似法公式,用对数正态模型近似计算其概率分布.通过对一单杆输电塔的计算,证明上述方法的可行性,并对时间相关性对裂纹扩展的影响进行分析.     

大功率风力机基础底法兰焊缝疲劳分析

大功率风力发电机基础底法兰需要整体锻造成型,由于工艺条件限制,造成制造成本较高.现改由四块法兰片拼装,然后与基础环焊接而成,为了评估其疲劳强度,对其进行疲劳分析.采用中国船级社提供的参考疲劳S-N曲线,使用ANSYS建模先进行静力分析计算,再通过疲劳计算模块,计算其疲劳损伤,通过计算,在设计寿命期内,底法兰所发生的疲劳破坏为0.408.     

基于可靠度的机场刚性道面剩余寿命预测方法

介绍了机场刚性道面疲劳破坏模型,编写了道面可靠度计算程序;基于Miner定律和可靠性理论,提出了道面疲劳损坏度的概念和计算方法,基于疲劳损坏度,提出了机场刚性道面剩余寿命预测方法,并将该方法与机场水泥混凝土道面设计规范中的方法进行了比较.     

局部高密度钢纤维混凝土弯曲疲劳性能研究

对局部高密度钢纤维混凝土的弯曲疲劳性能进行了研究.对于高低应力比R不同情况下疲劳寿命的统计问题提出了自己的处理意见.经过统计分析计算,确定PHPFRC的等效疲劳寿命符合两参数威布尔分布,建立了考虑存活率P-lgS-lgN双对数疲劳方程.对PHPFRC在循环荷载作用下的变形过程曲线与普通混凝土及SFRC比较其共性及特点进行了分析,认为由于PHPFRC在开裂后可以继续长时间承受循环荷载,其抗疲劳性能十分优越.     

变截面钢结构疲劳寿命预估方法研究

钢结构的疲劳破坏时有发生,实际构件中难免存在几何突变,导致应力集中、降低构件疲劳强度,因此如何有效预估变截面构件的疲劳寿命尤为重要。基于损伤力学理论建立的疲劳损伤模型被用来预估构件疲劳寿命,且取得很好的效果。基于疲劳损伤模型预估缺口试件的疲劳寿命,利用封闭解的方法给出了缺口构件在拉压载荷下的损伤演化方程,同时计算了不同应力集中系数下缺口试件的疲劳寿命,将利用提出方法计算的结果与利用Manson-Coffin方程计算结果进行对比分析,其结果误差在5%以内。     

腐蚀环境下钢筋混凝土结构疲劳可靠度的分析方法

疲劳分析与验算是承受反复荷载作用结构设计的重要内容之一,相应的可靠度为疲劳可靠度.当结构处于腐蚀环境时,由于腐蚀介质的侵蚀,结构疲劳性能的降低要比静态性能的降低明显.本文研究了腐蚀环境下钢筋混凝土结构的疲劳可靠度问题,提出了相应的计算方法.计算表明,依赖于钢筋的锈蚀程度,钢筋混凝土结构的疲劳可靠度有不同程度的下降.     

CFRP加固疲劳损伤钢结构的断裂力学分析

金属结构,特别是承受反复荷载作用的在役钢结构,通常存在不同程度的缺陷和疲劳损伤。在钢结构的损伤部位粘贴FRP对其疲劳损伤进行加固具有很多优势。对含中央疲劳损伤裂纹钢板粘贴CFRP加固,改善其剩余疲劳寿命进行了理论分析。基于线弹性断裂力学理论,采用有限元计算模型对裂纹前端的应力强度因子进行了计算。并根据Paris_Erdogan裂纹扩展模型,计算了加固前后疲劳损伤钢板的剩余疲劳寿命,验证了这一加固方法的有效性。     

Statistical analysis of online strain response and its application in fatigue assessment of a long-span steel bridge

This paper covers reliability assessment of the fatigue life of a bridge-deck section based on the statistical analysis of the strain–time histories measured by the structural health monitoring system permanently installed on the long-span steel bridge under study. Through statistical analysis of online strain responses in the frequency domain using multiple linear regression, a representative block of daily cycles of strain history is obtained. It is further assumed that all cycles of online strain response during bridge service are repetitions of the representative block. The rain-flow counting method is then used to determine the stress spectrum of the representative block of daily cycles. The primary assessment of fatigue life at a given value of failure probability is undertaken for the sample component in a bridge-deck section by using the classification of details for welded bridge components and the associated statistical fatigue model provided by the British Standard BS5400. In order to evaluate bridge fatigue at any value of failure probability, a modified probability model is proposed based on BS5400. The fatigue life of the considered component in the bridge-deck section is then evaluated for some other values of probability of failure which are not included in BS5400 by use of the modified probability model. The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.     

钢桥面沥青混合料铺装体系疲劳特性的损伤力学分析

用损伤力学原理及方法,从力学近似法角度分析了单纯的沥青混合料铺装层矩形截面梁疲劳损伤特性,推导出梁的应变场和疲劳寿命预测公式。按抗弯刚度等效简化原则,将疲劳试验复合梁模型中的实际桥面用钢板简化为沥青混合料铺装层叠加到下面的沥青混合料铺装层上,共同组成准单纯的沥青混合料铺装层矩形截面梁,应用该原理及方法推导出梁底缘的应变场,以南京长江第二大桥钢桥面环氧沥青混凝土铺装体系复合梁疲劳试验为例,进一步推导出复合梁的疲劳寿命预测公式。通过实例分析,表明损伤力学原理及方法可用于分析钢桥面沥青混合料铺装体系疲劳特性,其疲劳寿命预测结果是较为精确的,它的实际应用还需给出相应的修正,此外指出了环氧沥青混凝土铺装具有很好的抗疲劳性能。     

公轨两用桥吊杆疲劳分析程序实现方法

针对公轨两用桥吊杆进行疲劳分析的重要性,详细阐述了一种公轨两用拱桥吊杆的疲劳分析程序实现方法,并结合实例证实了该方法的可行性,说明该公轨两用拱桥吊杆在设计基准期内不会发生疲劳破坏。     

焊接钢桥结构细节疲劳裂纹原因及对策分析

从分析现代焊接钢桥疲劳性能的影响因素入手,分析了钢桥的疲劳设计,并探究了焊接钢桥疲劳设计的敏感部位,并依据所得探究结果提出防止疲劳问题的解决对策,为现代钢桥的安全性能提供保障。     

Stochastic analysis of fatigue of concrete bridges

A novel method is proposed in this work for the assessment of the remaining fatigue life and fatigue reliability of concrete bridges subjected to random loads. The fatigue reliability of a bridge is a function of the fatigue damage accumulation; a stochastic fatigue damage model (SFDM) with physical mechanism is introduced for deriving the fatigue damage process. In order to implement the probabilistic analysis, based on the probability density evolution method (PDEM), the generalised density evolution equation (GDEE) for the remaining fatigue life is developed. Finally, a prestressed concrete continuous beam bridge located in China is illustrated. The random fatigue load acting on the bridge is modelled as the compound Poisson process, and the simulation of the random load uses the stochastic harmonic function (SHF) method. To simplify the reliability analysis, an equivalent constant-amplitude (ECA) load process is introduced based on energy equivalence. By employing SFDM, the finite element analysis of the bridge under the fatigue loading is performed. Then, the fatigue damage accumulation process of the bridge under the fatigue loading is obtained. Through solving the probability density evolution equation for the remaining fatigue life, the probability density functions (PDFs) of the remaining fatigue life evolving with time is obtained. The fatigue reliability is then calculated by integrating the PDF of the corresponding remaining life.     

Fatigue evaluation of steel-concrete composite deck in steel truss bridge——A case study

An innovative composite deck system has recently been proposed for improved structural performance. To study the fatigue behavior of a steel-concrete composite bridge deck, we took a newly-constructed rail-cum-road steel truss bridge as a case study. The transverse stress history of the bridge deck near the main truss under the action of a standard fatigue vehicle was calculated using finite element analysis. Due to the fact that fatigue provision remains unavailable in the governing code of highway concrete bridges in China, a preliminary fatigue evaluation was conducted according to the fib Model Code. The results indicate that flexural failure of the bridge deck in the transverse negative bending moment region is the controlling fatigue failure mode. The fatigue life associated with the fatigue fracture of steel reinforcement is 56 years. However, while the top surface of the bridge deck concrete near the truss cracks after just six years, the bridge deck performs with fatigue cracks during most of its design service life. Although fatigue capacity is acceptable under design situations, overloading or understrength may increase its risk of failure. The method presented in this work can be applied to similar bridges for preliminary fatigue assessment.     

Dynamic stress analysis for fatigue damage prognosis of long-span bridges

For fatigue damage prognosis of a long-span steel bridge, the dynamic stress analysis of critical structural components of the bridge under the future dynamic vehicle loading is essential. This paper thus presents a framework of dynamic stress analysis for fatigue damage prognosis of long-span steel bridges under the future dynamic vehicle loading. The multi-scale finite element (FE) model of the bridge is first developed using shell/plate elements to simulate the critical structural components (local models) and using beam/truss elements to simulate the rest part of the bridge (global model). With the appropriate coupling of the global and local models, the multi-scale FE model can accurately capture simultaneously not only the global behavior in terms of displacement and acceleration but also the local behavior in terms of stress and strain. A vehicle traffic load model is then developed for forecasting the future vehicle loading based on the recorded weigh-in-motion (WIM) data and using the agent-based traffic flow microsimulation. The forecasted future vehicle loading is finally applied on the multi-scale model of a real long-span cable-stayed bridge for dynamic stress analysis and fatigue damage prognosis. The obtained results show that the proposed framework is effective and accurate for dynamic stress analysis and fatigue damage prognosis.     

Fatigue evaluation of riveted railway bridges through global and local analysis

This paper presents an overview of recent research efforts by the authors and co-workers on the fatigue assessment of old metallic railway bridges. The investigation focuses on the behaviour of riveted stringer-to-cross-girder connections in a typical, short-span bridge. A generic methodology, which is based on nominal stresses and the S-N method, is presented first, followed by a more detailed analysis using a recently developed fatigue assessment theory, which is based on local stress distributions. The discussion is made within a deterministic as well as a probabilistic context and typical results are presented in terms of fatigue damage and remaining fatigue life.     

Fatigue assessment of a composite railway bridge for high speed trains. Part I: Modeling and fatigue critical details

Steel bridges for high speed trains may sustain excessive fatigue damage due to stronger dynamic effects induced by the increased train speed. Dynamic tests were carried out on a composite railway bridge for high speed trains. A detailed finite element (FE) model of the bridge was established and validated by the dynamic test results. Six types of structural details in the bridge were considered for fatigue evaluation. The stress history of each concerned detail during a single train passage was generated by the validated FE model. The stress spectrum, obtained through Rainflow cycle counting of stress history, was used to calculate the fatigue damage of each detail, based on the detail category specified S–N design curve and the Palmgren–Miner damage rule. Among various structural details, the load carrying fillet weld around the gusset plate of the diagonal bracing at the bridge bearing is predicted to be the most fatigue critical detail. In this paper, a general methodology for determination of fatigue critical details is presented, which can serve as a basis of enhanced fatigue evaluation by using local stress approaches. In “Part II: conditions for which a dynamic analysis is needed” as the continuation of this paper, fatigue assessment will be investigated based on the dynamic stresses predicted by different approaches, i.e. static analysis considering dynamic amplification factor, direct dynamic analysis with a moving load model or a train–bridge interaction model.     

Impact of track irregularities and damping on the fatigue damage of a railway bridge deck slab

The structural response of reinforced concrete slabs in railway bridges is strongly influenced by local dynamic effects and, therefore, detailed calculations of internal forces have to be performed for a realistic fatigue assessment. In this context, this paper discusses the influence of track irregularities and modal damping coefficients in the dynamic response and fatigue behaviour of a railway bridge deck slab. For that purpose, track irregularities were measured (at different instants of time) and damping coefficients were determined based on acceleration records for passing trains in a real bridge. The bridge behaviour was calculated using a train–bridge interaction methodology, considering calibrated numerical models of the viaduct and the train. The fatigue damage was quantified through the linear damage accumulation method. This methodology allowed to understand the way track irregularities and damping coefficients affect the magnitude of applied bending moments and fatigue damage in the slab.