混凝土内自然锈蚀钢筋力学性能试验及数值模拟

为了分析受盐侵蚀作用后混凝土内锈蚀钢筋的力学性能退化规律,对预制开裂混凝土构件进行了近4年的"氯盐干湿循环——自然锈蚀"试验,从而得到了一批局部坑蚀明显、且呈现全面锈蚀的钢筋样本.通过锈蚀钢筋的坑蚀深度测定、拉伸试验以及有限元分析等研究,对其锈蚀表面特性、力学性能退化规律以及数值计算模型的有效性进行了探讨.研究结果表明:氯盐干湿环境下,裂缝的存在加剧了钢筋局部锈蚀的程度,使钢筋出现局部坑蚀和大面积均匀锈蚀的全面锈蚀;随着平均截面损失率η_(avg)的增加,锈蚀钢筋的屈服平台逐渐缩短,η_(avg)为5.77%时,钢筋屈服平台消失;经回归拟合,锈蚀钢筋的名义屈服强度、名义极限强度及伸长率等性能随η_(avg)(6%)的增大呈线性下降;建立了锈蚀钢筋力学性能预测的有限元模型,其预测值与试验值吻合良好.相关研究结果可为锈蚀钢筋混凝土结构的性能评价提供一定参考.     

海洋环境下钢筋混凝土构件抗力随时间变化模型研究

考虑混凝土强度变化、钢筋锈蚀过程、混凝土碳化和钢筋锈蚀引起的混凝土与钢筋之间粘结能力的改变等因素,建立了高桩码头钢筋混凝土构件抗力随时间变化的随机过程模型。通过算例研究了混凝土碳化、氯离子侵蚀、混凝土强度、构件所处水位等对高桩码头钢筋混凝土构件抗力的影响。并提出海洋环境条件和使用荷载作用下钢筋混凝土构件的累积损伤、裂缝宽度计算方法、裂缝宽度对氯离子侵蚀速度的影响、以及钢筋混凝土码头健康状态诊断方法等。     

混凝土结构钢筋锈胀数值模拟

通过对混凝土梁在钢筋锈蚀膨胀作用下的开裂全过程进行模拟,得到混凝土梁在钢筋均匀锈蚀膨胀和非均匀锈蚀膨胀情况下的裂缝产生和发展的情况,分析了保护层胀裂时的钢筋膨胀率的影响因素,其中包括混凝土保护层的厚度、钢筋直径、混凝土的强度等级。通过比较试验数据与前人研究成果,结果都体现了相同的钢筋锈胀规律。在此基础上,提出结构耐久性的影响因素并指导结构耐久性设计。     

锈蚀钢筋混凝土大偏心受压柱的数值模拟

基于锈蚀钢筋混凝土偏心受压构件承载力试验研究结果,运用ANSYS有限元分析软件,对锈蚀钢筋混凝土大偏心构件进行分析,通过温度场模拟钢筋锈蚀作用,得到锈蚀构件破坏特征及承载力随锈蚀程度的变化规律。经对比试验结果,该有限元模型数值计算与试验结果能较好吻合,温度场模拟钢筋锈蚀较理想。对不同直径钢筋影响受压柱承载力和裂缝分布规律进一步分析,结果表明:同等条件下,随着钢筋直径增加,钢筋锈胀力减小,裂缝开裂分布区域发生变化。     

现役海港码头钢筋混凝土受弯构件承载力评估方法

在分析钢筋锈蚀造成钢筋混凝土构件力学性能退化的基础上,根据海港码头混凝土构件中钢筋锈蚀规律及混凝土保护层锈胀裂缝宽度与钢筋锈蚀深度的关系,建立了混凝土保护层锈胀开裂前和锈胀开裂后现役海港码头钢筋混凝土受弯构件承载力评估模型,可为现役海港码头钢筋混凝土结构耐久性评估及构件修复决策提供理论依据。     

基于CT扫描技术的混凝土结构裂缝宽度与钢筋锈蚀率相关性分析*

为了了解混凝土结构的裂缝宽度与钢筋锈蚀率之间的关系,同时掌握裂缝宽度及钢筋锈蚀率的无损检测技术,特别采用CT扫描技术,对一批加速腐蚀的混凝土构件进行测试,得到了混凝土构件的裂缝宽度及锈蚀率,分析钢筋锈蚀率与裂缝宽度的相关性。从分析的结果来看,钢筋锈蚀率与裂缝宽度的相关曲线与其它学者研究的曲线趋势一致,但变化率有所不同,该曲线可以为揭示混凝土结构裂缝宽度与钢筋锈蚀率变化规律提供参考,同时CT扫描技术可以推广应用在混凝土无损检测中。     

不同环境条件下考虑荷载影响的氯离子扩散模型

钢筋锈蚀是造成钢筋混凝土构件耐久性破坏的重要因素之一,氯离子侵蚀是海洋环境下钢筋锈蚀的首要因素。根据相关文献给出的不同海洋环境、不同荷载水平作用下混凝土中氯离子扩散的实验数据,通过拟合给出氯离子扩散荷载影响系数与构件应力状态之间的关系式及混凝土表面氯离子浓度随时间变化的统计公式,建立了考虑荷载影响的氯离子扩散模型。多组现场实测数据检验表明,建立的考虑荷载影响的氯离子扩散模型是合理的,具有较好的适用性与实用性。     

锈蚀钢筋混凝土小偏心受压构件承载力评估方法

混凝土中钢筋锈蚀造成结构性能退化进而影响到结构的承载力,本文在已有研究成果的基础上,立足现行计算理论,提出锈蚀小偏心受压构件承载力计算模型,并提供验证,为混凝土结构耐久性评估提供科学依据。     

考虑荷载影响的钢筋混凝土构件钢筋锈蚀模型

对现有典型钢筋锈蚀模型进行了比较分析,选择考虑因素较全面合理的Youping Liu指数模型作为钢筋锈蚀基本模型。将考虑荷载影响的氯离子扩散模型引入钢筋锈蚀基本模型中,建立了考虑荷载影响的钢筋混凝土构件钢筋锈蚀模型。通过实例计算,分析了钢筋锈蚀速度随时间的变化规律。     

日照港10万吨煤码头混凝土结构维修

港口工程各种混凝土结构、构件常年处于不利的海洋环境中,受海浪冲击、盐类腐蚀和氯离子对钢筋锈蚀,极易发生腐蚀破坏,影响码头的使用功能和结构的安全性。本文重点介绍了对日照港10万t煤码头腐蚀破损的混凝土结构和构件维修的施工工艺。     

港口工程钢筋混凝土结构性能退化模型研究

根据应力和氯离子共同作用下港口工程混凝土结构的性能退化机理,确定了描述结构性能退化的参数:以承载力描述结构安全性退化,以刚度和纵向裂缝描述结构适用性退化。考虑了应力大小、持续时间和氯离子对结构性能的综合影响,提出了港口工程钢筋混凝土结构钢筋锈蚀率计算模型。以钢筋锈蚀率为表征参数,通过理论分析和室内试验,建立了港工钢筋混凝土结构承裁力衰减模型、纵向裂缝开展模型和刚度退化模型。     

港口工程钢筋混凝土结构性能退化模型研究

根据应力和氯离子共同作用下港口工程混凝土结构的性能退化机理,确定了描述结构性能退化的参数：以承载 力描述结构安全性退化,以刚度和纵向裂缝描述结构适用性退化。考虑了应力大小、持续时间和氯离子对结构性能的综合 影响,提出了港口工程钢筋混凝土结构钢筋锈蚀率计算模型。以钢筋锈蚀率为表征参数,通过理论分析和室内试验,建立 了港工钢筋混凝土结构承载力衰减模型、纵向裂缝开展模型和刚度退化模型。     

混凝土构件直接粘贴CFRP加固的腐蚀界限研究

为弥补现有规范不足、解决不同腐蚀等级构件碳纤维加固效果参差不齐的问题,在氯化钠溶液中通电模拟海洋腐蚀环境,加速腐蚀出不同腐蚀程度的RC梁,粘贴CFRP加固后进行加载试验,通过分析不同腐蚀程度构件承载力损失和直接粘贴、凿除粘贴两种CFRP处理方式的加固效果,研究腐蚀等级对海工RC梁CFRP抗弯加固的影响,并探讨直接粘贴CFRP加固的腐蚀界限。结果表明,在低腐蚀等级条件下,直接粘贴CFRP加固能有效减小腐蚀梁在荷载作用下的主裂缝宽度,减缓梁开裂的时间,提高抗弯承载力和整体刚度,但随腐蚀等级的增加,这些作用越来越弱,当梁腐蚀裂缝宽度超过1 mm、主筋锈蚀率达15%时,直接粘贴CFRP加固已不再适合。     

CFRP修复的FPSO点蚀船体梁极限强度分析

采用非线性有限元法对中拱和中垂工况条件下碳纤维增强聚合物(Carbon Fiber Reinforced Polymer, CFRP)修复的浮式生产储卸油装置(Floating Production Storage and Offloading, FPSO)点蚀船体梁极限强度进行仿真分析。对比FPSO的完整船体梁、点蚀船体梁和CFRP修复的点蚀船体梁的中拱极限弯矩和中垂极限弯矩，分析CFRP对FPSO点蚀船体梁的修复效果，并分析胶层失效规律。结果表明，CFRP可为船舶的高效修复提供一种新的方式。     

Effect of pitting corrosion on local strength of hold frames of bulk carriers (2nd Report)—Lateral-distortional buckling and local face buckling

Pitting corrosion is typical corrosion observed on coated hold frames of bulk carriers which exclusively carry coal and iron ore. In order to secure the safety of these types of bulk carriers, it is important to understand the effect of pitting corrosion on local strength of hold frames.

In order to investigate this effect, a series of 4- and 3-point bend tests on structural models which consist of web, shell and face plates has been carried out. Artificial pitting was created on the web plate to simulate pitting. In the 4-point bend tests, two equal concentrated loads have been applied vertically at the one-third points of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, lateral-distortional buckling occurred before reaching the ultimate strength and local buckling of the face plate was observed after reaching the ultimate strength. The effect of web plate pitting on the lateral-distortional buckling strength was found to be small but the ultimate strength decreases with increase in the degree of pitting intensity. In the 3-point bend tests, concentrated load has been applied vertically at the center of simply supported models so that compression load due to bending would act on the face plate. In this testing condition, local face buckling occurred just after reaching the ultimate strength. The ultimate strength is found to be decreasing with increase in the degree of pitting intensity.

A series of non-linear FE analyses has been performed to simulate the deformation behavior observed in the tests. It has been revealed that even in the case of randomly distributed pitting corrosion the ultimate strength of the structural models was almost the same as that of the structural models with uniform corrosion corresponding to the average thickness loss.     

Effect of pitting corrosion on the ultimate strength of steel plates subjected to in-plane compression and bending

Corrosion pits with a circular cone shape are typically observed on coated hold frames of aged bulk carriers which carry exclusively coal and iron ore. In order to ensure the safety of these types of bulk carrier, it is necessary to understand the effect of pitting corrosion on the local strength of hold frames. In order to investigate this effect, a series of nonlinear finite-element (FE) analyses has been performed with pitted plates subjected to in-plane compressive loads and bending moments. It has been shown that the ultimate compression load or bending moment of pitted plates is smaller than that of uniformly corroded plates in terms of average thickness loss, and that predictions of the ultimate strength using the average thickness loss at the minimum cross section would be conservative. In order to establish a method of evaluating strength reduction due to pitting corrosion, it is important to identify the failure mode that would be most detrimentally affected by pitting corrosion. It was found that the reduction of the ultimate compressive load or bending moment due to pitting corrosion is smaller than that of the tensile strength in terms of equivalent thickness.     

碳钢、低合金钢全浸没海洋环境下最大点蚀深度简化模型

腐蚀是导致老龄船舶结构失效的主要原因之一。结合基本点蚀原理,文章对碳钢、低合金钢海水全浸没点蚀的主要影响因素、具体点蚀进程做了简要解释与评述。基于Melchers点蚀深度模型及其相关实验数据,文中提出一种简化形式的新型点蚀最大深度模型,并采用该模型对三组我国船舶结构常用碳钢、低合金钢的青岛海域全浸没点蚀试验观测数据进行分析。通过对比验证,证明采用Weibull函数表示点蚀最大深度随时间变化关系是合适的。此外,依据青岛、厦门、榆林海域碳钢试验数据,文中还对海水环境因素,如:溶解氧浓度、平均温度、盐度、PH值等,以及钢材成分变化对新型最大点蚀深度模型各参数的影响进行了初步探讨,得出了相应的函数关系式及相关结论。     

Effect of pitting corrosion on local strength of hold frames of bulk carriers (1st report)

Firstly, pitting corrosion observed on hold frames in way of cargo holds of bulk carriers which exclusively carry coal and iron ore has been investigated in detail. It was shown that the shape of the corrosion pits observed on them is a circular cone and the ratio of the diameter to the depth is in the range between 8 to 1 and 10 to 1, which is different from the trend observed for the bottom shell of the oil tanker where the ratio is in the range between 4 to 1 and 6 to1.Secondly, a series of tensile tests has been conducted to investigate the effect of pitting corrosion on tensile strength of members. It was pointed out that the tensile strength decreases gradually and the total elongation decreases drastically with the increase of the thickness loss due to pitting corrosion. The reduction of the tensile strength of the members with pitting corrosion is larger than that of members with uniform thickness loss in terms of average thickness loss.Thirdly, a series of compressive buckling tests has been performed to examine the influence of pitting corrosion on buckling behavior of members. It was found that compressive buckling strength of pitted members is smaller than or equal to that of members with uniform thickness loss in terms of average thickness loss.Finally, an elasto-plastic analysis by FEM has been carried out to simulate the compressive buckling test in order to validate the method of modeling members with pitting corrosion. An attempt has been made to simulate the compressive buckling behavior of pitted members using shell elements of which meshing size is almost the same as the original thickness of the pitted plate.     

点蚀板在纵向压力下的极限强度研究

本文着眼于老龄化船舶结构上的局部点状腐蚀和整体点状腐蚀,利用非线性有限元软件分析了超过100个船体板结构的极限强度。研究了蚀坑形状、蚀坑位置、蚀坑大小、蚀坑深度和板的柔度对含局部点状腐蚀船体板的极限强度的影响,蚀坑分布、板的柔度和腐蚀体积对含点状腐蚀船体板的极限强度的影响。拟合出了单面、双面局部点状腐蚀下的船体板极限强度折减公式,单面、双面点状腐蚀下的船体板极限强度折减公式。并得到同时适用于局部和整体点状腐蚀板极限强度的公式。     

国外混凝土结构耐久性监测传感器在国内工程中的适用性*

采用动电位极化和线性极化技术研究了国内普通钢筋、阳极梯监测传感器所用普通钢筋和ECI-2传感器所用普通钢筋的点蚀临界浓度和点蚀后的腐蚀速率。研究结果表明：ECI-2传感器所用普通钢筋的点蚀临界氯离子浓度与国内普通钢筋相似,点蚀速率略小于国内普通钢筋;阳极梯传感器所用的普通钢筋的点蚀临界氯离子浓度要高于国内普通钢筋,点蚀速率要明显低于国内普通钢筋。因此,在用这两种传感器进行国内工程耐久性监测时应对监测结果进行修正。