桥梁缆索断丝检测技术研究

为检测桥梁缆索内部断丝情况,介绍了钢丝磁检测原理,设计了一种由若干单节励磁器连接组成的模块化励磁传感器,实现了对不同直径缆索的周向均匀励磁和断丝检测。搭建了缆索无损检测实验平台,设计了缆索检测的总体方案,实验结果表明检测传感器能提取缆索断丝信号,监测缆索安全状况。     

桥梁缆索特殊断口失效机理分析

为延长桥梁缆索的使用寿命,必须确定其失效机理.通过调研国内外大量的桥检资料,将现场取回的桥梁缆索钢丝做断口电镜扫描( SEM)后,对缆索钢丝断口的两种特殊类型(阶梯状断口和杯口状断口)进行了失效机理分析.结果表明,阶梯状断口主要是由于腐蚀疲劳所致;在钢丝无明显锈蚀,当外界荷载超过钢丝的极限承载力时出现塑性破坏是导致杯口...     

斜拉桥平行钢丝索锈蚀断裂模拟

为模拟拉索各钢丝间的摩擦接触,放弃会带来极大计算量和高度非线性问题的常规接触单元而采用理想弹塑性弹簧单元,并推导了弹簧屈服力的计算公式。建立127丝平行钢丝束有限元模型,拉索钢丝间的摩擦接触采用理想弹塑性弹簧单元模拟,采用单元生死功能模拟钢丝断裂。计算分析结果表明:当拉索出现锈蚀断丝后,断裂钢丝并不会完全退出工作,经过一段发展长度后能恢复到正常应力水平。钢丝断裂后,各钢丝间会出现应力重分布,断裂截面断裂位置周围的钢丝应力增大,远离断丝侧钢丝应力减小,拉索合力作用点偏移拉索截面中心,故荷载恢复完成后拉索截面各钢丝平均应力并不均匀,恢复后拉索截面应力分布规律与断丝截面相反。随着断丝百分比的增加,断裂钢丝荷载恢复长度逐渐增大,相应的索力损失率增大。     

考虑断丝影响的桥梁拉索力学特性研究

拉索安全性关系索支承桥梁的安全运行与服役寿命,由于拉索老化、腐蚀、断丝等原因,拉索断丝成为拉索损伤的主要形式之一。在半平行钢丝拉索非对称断丝损伤模型的基础上,通过数值计算重点讨论了非对称断丝条件下断丝位置、螺旋角、钢丝间摩擦系数等参数对拉索内钢丝拉力分布及轴向刚度的影响。结果表明,非对称断丝引起的截面内钢丝拉力不均匀分布明显,螺旋角和钢丝间摩擦系数对拉索轴向刚度影响较大,应用并联模型设计计算时,误差较大,计算结果偏于不安全。     

桥梁缆索病害与破坏机理分析

结合国内外索承式桥梁事故和换索维修工程,分析了桥梁缆索病害产生的原因,讨论了缆索的腐蚀破坏机理,根据缆索腐蚀形态,对于桥梁缆索钢丝腐蚀病害进行了归类分析,以便于维修工作的开展。     

基于磁弹效应的高强钢丝应力监测实验研究北大核心

高强钢丝作为钢缆索的主要承力部件,它的受力情况直接影响到钢缆索的安全状况,对高强钢丝进行应力监测是评价钢缆索安全状况的有效手段,也是进行钢缆索整体索力监测的研究基础综述了传统的钢结构应力监测方法,讨论了基于磁弹效应的应力监测方法的优势并详细介绍了它的基本原理——磁弹效应。建立了进行高强钢丝应力监测研究的实验装置,开发了一套基于LabVIEW平台的测试系统,并对7mm高强钢丝进行了基于磁弹效应的应力监测实验实验表明,基于磁弹效应的应力监测方法不需要了解受力历史,可直接对高强钢丝的应力进行测量,且具有较高测试精度、较好的稳定性和可重复性。     

钢丝缺陷磁致伸缩导波检测信号特性实验研究

缆索体系作为现代土木建设广泛应用结构之一,作为主要承载部件对整体结构的安全性和使用寿命至关重要。磁致伸缩导波无损检测技术在缆索损伤和腐蚀检测方面具有检测长度大,覆盖结构区域广等优势,逐渐成为应用广泛的缆索新型无损检测方法。磁致伸缩导波无损检测技术在损伤和腐蚀的定性问题上已经比较稳定,缺陷尺寸和缺陷回波的定量关系与诸多因素有关,本文对缆索的基本单元高强钢丝的缺口检测信号进行了实验研究,得到缺陷回波反射系数与钢丝缺陷截面损失率的关系,发现其与抛物线非常近似;本研究为钢丝及钢丝拉索的损伤和腐蚀磁致伸缩导波无损检测的定量评价提供了基础。     

钢丝裂纹扩展估算模型及其在预腐蚀疲劳寿命计算中的应用

为给桥梁缆索高强度钢丝损伤容限分析提供实用的裂纹扩展计算参数,根据钢材相关试验的结果统计了珠光体钢丝门槛值ΔKth和裂纹扩展计算数据,建立适用于不同屈服强度和应力比的钢丝裂纹扩展经验模型。在此基础上,提出基于一维裂纹扩展假定的预腐蚀钢丝疲劳寿命预测方法,并对锈蚀钢丝恒幅和变幅疲劳寿命进行实例分析。结果表明,珠光体钢材的屈服强度和门槛值之间的相关性随着屈服强度和应力比的提高而增强|提出的钢丝裂纹扩展模型和初始裂纹深度假定可较好地模拟腐蚀钢丝恒幅疲劳试验的离散性和疲劳极限性质|腐蚀钢丝变幅疲劳评估结果对门槛值变化较敏感|按保守门槛值的预测寿命显示,轻微均匀锈蚀钢丝若及时采取养护措施,可在桥梁常规检修期内继续使用。     

远场涡流技术在PCCP断丝检测中的应用

利用远场涡流变压器耦合技术可探测预应力钢筒混凝土管中的钢丝断丝现象。介绍了钢丝断丝检测仪的基本原理,当预应力钢筒混凝土管出现钢丝断丝时会对两次穿透管壁的远场涡流信号产生幅度和相位上的畸变,利用这一现象就可以实现对预应力钢筒混凝土管钢丝断丝根数和断丝位置进行判断;通过试验对该方法进行了验证。     

大直径高强度钢丝主缆索股制造技术

为了增加主缆钢丝强度、减少钢丝用量,以双层悬索桥——杨泗港长江大桥为例,对直径φ6.2 mm、强度1 960 MPa的高强度钢丝主缆索股制造技术进行研究,对主索结构、索股锚具设计、主缆钢丝性能、生产线工艺进行论述分析,提出主缆索股制作工艺流程及主缆索股放索质量和控制方法.     

Probabilistic deterioration model of high-strength steel wires and its application to bridge cables

Bridge inspections reveal that severe corrosion and fatigue are the main failure mechanisms of bridge stay cables. This paper presents an empirical modelling of the long-term deterioration process of steel wires in cables with consideration of the simultaneous occurrence of uniform corrosion, pitting corrosion and fatigue induced by a combined action of environmental aggression and cyclic loading. Accelerated corrosion experiments are conducted to determine the different corrosion levels of high-strength steel wires, and time-dependent statistical models are developed to quantify uniform and pitting corrosion depth. Corrosion-fatigue process of steel wires is subsequently simulated using the corrosion models and cyclic stress obtained through cable force monitoring data. The mechanical properties of corroded steel wires, including yield stress, ultimate stress, ultimate strain and modulus of elasticity, are experimentally characterised, and the statistical models are established through regression analysis. Finally, the deterioration models of high-strength steel wires (including crack depth, ratio of broken wires, and remaining strength, among others) is extended to probabilistically assess the time-variant conditions of bridge cables (sectional area loss and remaining capacity). The presented study on the long-term deterioration of bridge cables would provide guidance to future decision-making regarding the maintenance and replacement of bridge cables.     

光纤光栅智能索及其在深圳万科中心中的应用

斜拉索是深圳万科中心结构的重要构件,监测拉索在施工及运营期间的受力状态非常重要.本文在深圳万科中心工程中采用了一种基于光纤光栅智能筋的索力监测方法,即在拉索制作过程中,将光纤光栅智能筋布设到平行钢丝拉索中,利用智能筋与钢丝协同变形,实现拉索索力的监测.分析了光纤光栅智能索的基本原理及其在深圳万科中心中的应用结果.现场监...     

石门大桥拉索病害检测与分析

详细介绍了石门大桥拉索病害的检测方法和步骤。通过下锚头渗水检测,指出渗水是由于桥面雨水进入锚箱钢套管所致。分析了护套破损成因及其规律,发现拉索护套破损数量与拉索长度线性相关。提出了一种划分钢丝锈蚀等级的方法。通过对换下旧索进行剖索检测,分析了拉索截面锈蚀分布规律以及沿长锈蚀分布规律。     

石门大桥拉索病害检测与分析

详细介绍了石门大桥拉索病害的检测方法和步骤.通过下锚头渗水检测,指出渗水是由于桥面雨水进入锚箱钢套管所致.分析了护套破损成因及其规律,发现拉索护套破损数量与拉索长度线性相关.提出了一种划分钢丝锈蚀等级的方法.通过对换下旧索进行剖索检测,分析了拉索截面锈蚀分布规律以及沿长锈蚀分布规律.     

桥梁拉吊索用不锈钢钢丝腐蚀性能及斜拉索时变可靠度研究

对零应力普通镀锌钢丝和施加0%,20%,30%,40%强度的应力不锈钢钢丝,分7,20,40 d进行中性盐雾试验,研究零应力普通镀锌钢丝和不同应力水平下不锈钢钢丝的质量损失率、强度、延性和断口形貌的变化。通过算例分析了分别采用普通镀锌钢丝和不锈钢钢丝作斜拉桥拉索时可靠指标随时间的变化。结果表明:零应力下普通镀锌钢丝的质量损失率是不锈钢钢丝的30倍以上;不锈钢钢丝的质量损失率随着应力的增加而增加,高应力下的不锈钢钢丝更容易腐蚀;短期腐蚀对钢丝的极限强度影响不大,不锈钢钢丝随着应力的增加延性变差;随着腐蚀的增加,普通镀锌钢丝和不锈钢钢丝的拉伸端口呈现出脆性增加的趋势,普通钢丝的端口形貌由微裂纹向长宽裂纹发展,而不锈钢钢丝由于腐蚀较轻,只是出现了微裂纹;采用普通镀锌钢丝作斜拉桥拉索时可靠指标随时间的下降速度比采用不锈钢钢丝快。     

Hydrogen embrittlement and corrosion fatigue of corroded bridge wires

Cables of old suspension bridges and stays of cable-stayed bridges often suffer from steel corrosion. Corroded galvanized steel wires on different corrosion levels were produced at laboratories, and their mechanical properties and remaining strength were investigated. Actual tensile strength of corroded wires did not decrease with corrosion levels, whereas elongation decreased sharply after the zinc layer was partly depleted and the steel started to corrode. As the accumulated amounts of diffusive hydrogen of corrosion level-2 wires-with and without added tension-were almost the same and less than 0.2 ppm, the applied tension of steel wires did not affect the amount of diffusive hydrogen which was well below the critical concentration of 0.7 ppm to cause brittleness. This indicates that hydrogen embrittlement is unlikely to occur. Fatigue tests showed that fatigue strength did not change when only the galvanized layer was corroded, but it significantly decreased after corrosion of the steel below the galvanized layer progressed. Fatigue strength further lowered when the steel wire was cyclically stressed under wet environments when compared with the fatigue strength under dry environments. The broken wires of an old suspension bridge were also investigated. The fracture surface was similar to that caused by corrosion fatigue rather than hydrogen embrittlement. It was estimated that the wires were fractured by the mixed effects of corrosion, cyclic stresses and hydrogen.     

Experimental testing of low-energy rockfall catch fence meshes

Flexible catch fences are widely used to protect infrastructure like railways, roads and buildings from rockfall damage. The wire meshes are the most critical components for catch fences as they dissipate most of the impact energy. Understanding their mechanical response is crucial for a catch fence design. This paper presents a new method for testing the wire meshes under rock impact. Wire meshes with different lengths can be used and the supporting cables can be readily installed in the tests. It is found that a smaller boulder causes more deformation localisation in the mesh. Longer mesh length makes the fence more flexible. Under the same impact condition, the longer mesh deforms more along the impact direction and shrinks more laterally. Supporting cables can reduce the lateral shrinkage of the mesh effectively. Most of the impact energy is dissipated by stretching of the wires. Wire breakage has not been observed.