预裂混凝土氯离子扩散系数计算模型及验证

为探讨水胶比、裂缝宽度、裂缝深度等因素对预裂混凝土内氯离子扩散的综合影响,采用快速氯离子迁移系数法获取多因素影响下的氯离子扩散系数,并考虑水胶比、时间衰减和裂缝等因素,建立了氯离子扩散系数计算模型。结果表明,氯离子扩散系数随水胶比增大而增大,在0.05~0.50mm裂缝宽度范围内与裂缝宽度成正相关,裂缝处氯离子渗透深度与裂缝深度成正比;氯离子扩散系数计算模型拟合结果与试验结果均吻合较好。     

基于随机多边形骨料再生混凝土抗氯离子侵蚀研究

基于氯离子扩散模型和骨料级配理论，采用PYTHON语言和COMSOL软件构建再生混凝土随机多边形骨料细观计算模型，并结合已有试验结果验证模型有效性，开展新老砂浆扩散系数、老砂浆厚度及再生骨料取代率等不同工况下再生混凝土抗氯离子侵蚀计算分析，研究氯离子在再生混凝土内部的扩散规律及各细观组分等关键因素对再生混凝土抗氯离子侵蚀的影响规律。结果表明，模拟结果与试验结果吻合较好，该方法能较好地模拟氯离子在再生混凝土内部的扩散过程；再生混凝土氯离子扩散浓度与深度的关系曲线呈现不连续性特征；随着新老砂浆扩散系数的增加，混凝土内氯离子浓度逐渐增大；再生混凝土抗氯离子侵蚀能力随老砂浆厚度、再生骨料取代率的增加而降低。     

层状组合结构轴拉条件下的裂缝饱和度分析与应用

基于裂缝扩展机理分析了裂缝扩展过程中的饱和现象,建立了层状组合结构的数值模型,分析了轴拉条件下裂缝中心区域的应力分布特征,论证了裂缝饱和度存在的客观性,探讨了荷载边界条件、材料参数与上覆压力对裂缝饱和度的影响,结合钢衬混凝土组合结构工程特性,研究了裂缝饱和度的基本规律。结果表明,轴向拉伸荷载边界条件不影响裂缝饱和度,裂缝层材料的弹性模量和泊松比越大,或相邻层材料的弹性模量和泊松比越小,裂缝饱和间距越大;上覆压力对裂缝饱和间距的影响较小。对于钢衬混凝土组合结构,轴拉条件下的裂缝饱和间距主要取决于外包混凝土厚度;布筋对钢衬混凝土组合结构的裂缝饱和度有显著影响,钢筋的埋入,相当于降低了混凝土裂缝层的有效厚度,可起到控制裂缝最大宽度的效果,建议将钢筋布置在混凝土层中部,以期增加潜在的裂缝条数,而不会出现宽度过大的裂缝。     

压力隧洞钢筋混凝土衬砌开裂数值模拟研究

立足于直接求解压力隧洞设计所关注的衬砌裂缝条数和裂缝宽度,同时考虑混凝土衬砌的开裂、钢筋的作用、钢筋与混凝土间的粘结滑移以及围岩的作用,建立了压力隧洞钢筋混凝土衬砌开裂的数值模型,并编制了相应的计算程序。采用该计算程序对压力隧洞钢筋混凝土衬砌开裂问题进行数值模拟研究,分析了钢筋量、围岩条件对裂缝条数和裂缝宽度的影响,并着重与现行规范进行对比分析。结果表明,所建模型能反映压力隧洞钢筋混凝土衬砌作为地下结构的受力特性;围岩条件对裂缝条数和宽度均有明显影响;压力隧洞钢筋混凝土衬砌限裂的关键在于改善围岩条件,不宜盲目加大钢筋量。该研究结果对压力隧洞工程实践具有一定的指导价值。     

基于二维多向固定裂缝模型的钢筋混凝土梁开裂过程模拟

作为一种准脆性材料,钢筋混凝土开裂是一个复杂的非线性问题。基于二维多向固定裂缝模型,运用DIANA软件对钢筋混凝土三点弯曲梁进行数值模拟。结果表明,在梁内无钢筋、有钢筋、钢筋加密三种条件下的混凝土变形和裂缝扩展过程均可被有效模拟;钢筋的横截面积越大,裂缝的宽度越小,变形结果符合相关理论,且裂缝扩展和分布情况符合实践经验。说明二维多向固定裂缝模型适用于钢筋混凝土结构的开裂模拟。     

韦水倒虹钢筋混凝土管钢筋锈蚀成因分析

混凝土中的钢筋锈蚀主要与其所处环竟有关,经过对韦水倒虹钢筋混凝土管钢筋锈蚀原因分析,认为韦水倒虹钢筋混凝土管钢筋锈蚀主要原因为:钢筋保护层厚度、钢筋混凝土管周围温度及湿度、运用条件、混凝土裂缝宽度等。针对造成钢筋锈蚀的原因,提出了工程处理措施。     

富春江水电站220kV开关站混凝土构架的检测及修补技术

富春江水电站运行40多年,电站开关站混凝土构架出现混凝土剥蚀和裂缝。针对实际情况,对混凝土构架进行无损检测,检测内容包括凝土裂缝深度、混凝土强度、混凝土碳化深度、构架内部钢筋保护层厚度和构架内部钢筋锈蚀检测等,并根据检测的情况提出了补强加固方案。该技术对于水电站混凝土构架的检测和加固具有一定指导意义。     

基于非线性接触的风电基础数值模拟

运用通用有限元分析软件ANSYS程序,对风力机基础的简化模型试验进行基于面面接触的非线性有限元模拟与分析,并对其内部钢板表面的应变分布以及钢-混凝土的滑移粘结等性能进行研究,建议基础环的锚固长度为700 mm。根据简化试验模型的非线性接触模型参数,建立足尺风力机基础有限元模型,研究风电基础在极端工况下的混凝土、基础钢环及钢筋的应力应变分布。计算结果表明,该实际风力机基础在极端工况下尽管出现了局部混凝土受拉破坏,但由于钢筋的参与抑制了裂缝的开展,整体结构受力良好,完全能保证上部结构的正常运行。     

水电站蜗壳结构设计参数H与D值影响敏感性分析

在HD值相同的条件下，改变H值和D值，应用三雏有限元程序对蜗壳结构进行线性和非线性分析，以研究H值和D值对蜗壳结构受力特性影响的敏感性。得出参数敏感性的影响规律是，随D值减小（H值增大），钢衬和混凝土的应力呈增大趋势，钢衬承载比逐渐增大，裂缝宽度和范围减小；当D值较大时，腰线处混凝土应力和钢筋应力分布规律与传统相反，即外侧应力大于内侧。故当HD值相同、H值较小、D值较大时，应增加钢筋量，且在腰线处外侧配筋大于内侧。     

钢衬钢筋钢纤维混凝土压力管道非线性有限元分析

针对钢衬钢筋混凝土压力管道在运行期因裂缝过宽导致的结构耐久性问题,在混凝土中掺入体积率分别为0.5%、1.0%、1.5%、2.0%的钢纤维形成钢纤维混凝土,基于模型试验获得的钢纤维混凝土的拉伸软化曲线,采用大型数值分析平台ABAQUS仿真分析了钢衬钢筋钢纤维混凝土压力管道受力开裂的全过程,并与原钢衬钢筋混凝土压力管道的模型试验结果进行了对比分析。结果表明,在相同内水压力荷载下,钢衬钢筋钢纤维混凝土压力管道的承载能力与普通钢衬钢筋混凝土压力管道相比,不仅其初裂荷载有所提高,管道的最大裂缝宽度明显降低,钢材的应力值也随钢纤维体积率的增加而减少。     

Experimental study and numerical simulation on the SSCC in FV520B stainless steel exposed to H2S+Cl− Environment

Constant displacement loading tests using wedge opening loading specimens were carried out in aqueous hydrogen sulfide solution containing sodium chloride to investigate the susceptibility of stress corrosion cracking (SCC) of FV520B precipitation hardening martensitic stainless steel. Results of the SCC tests indicated that the stress corrosion critical stress intensity factor (K_ISCC) dramatically decreased in the corrosion medium investigated and decreased with the increasing of H₂S concentration. Microstructures of fracture surfaces were analyzed using a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscopy (EDS). The fracture surface was typical of sulfide stress corrosion fracture. In addition, large amount of intermittent arc-crack on the side surfaces around the tip of main crack formed even no main crack propagated.A sequentially coupling finite element analysis (FEA) program was utilized to simulate the stress field and calculate the diffused hydrogen concentration distribution of specimen exposed to the corrosion medium investigated. The FEA results indicated that corrosion pit affected the stress and diffusion hydrogen distribution around the corrosion pit where large stress gradients formed. Side surface cracks initiated from those corrosion pits and propagated under the synergy of stress and hydrogen. The effect of the corrosion pit on hydrostatic stress distribution was limited in superficial zone near the side surface, thus side surface cracks propagated along the hoop direction rather than along the direction of specimen thickness. Based on the morphology observation and FEA results, it can be concluded that the SCC mechanism of FV520B steel was hydrogen embrittlement mainly and combination of anodic dissolution. Simultaneously, corrosion pitting was the precondition of side surface crack formation while the stress induced hydrogen diffusion was the dominant factor.     

某大型泵站空箱隔墩不均匀沉降敏感度分析

鉴于泵站复杂的进出水流道及泵房结构受力特殊,裂缝普遍存在,直接影响建筑物安全有效服役。以某大型贯流泵站高程9.7m变频器层空箱处混凝土隔墩裂缝工程为例,采用回弹值测法、碳化深度检测、钢筋保护层厚度测定及混凝土钻芯取样测试裂缝区域混凝土病害程度,并采用计算机仿真分析,基于有限单元法,依托泵站运行期垂直位移观测数据,考虑温度变化分析了基础不均匀沉降引发裂缝敏感度。结果表明,在泵站空箱隔墩实际裂缝区域出现应力集中,其结果与实际混凝土开裂区域吻合,说明基础不均匀沉降影响了泵站裂缝发展。因此,泵站设计过程中应考虑基础不均匀沉降问题。     

冻融损伤混凝土梁抗力性能演化的裂缝分形特征

为分析冻融循环作用下钢筋混凝土梁受压区的表面裂缝分布特征,采用自主设计的混凝土梁反力试验架对受压区受冻融循环作用的梁进行抗弯试验,取得各级荷载作用下梁表面的裂缝图像。依据分形理论计算表面裂缝分布的分形维数,并讨论分形维数与梁的荷载、跨中挠度、屈服荷载和冻融循环次数之间的关系。研究表明,受压区冻融损伤的钢筋混凝土梁表面裂缝的分布符合分形特征,其分形维数与荷载、跨中挠度、屈服荷载和冻融循环次数之间均有一定关系,裂缝的分形维数可作为钢筋混凝土构件安全性能预测的指标。研究成果可为冻融损伤混凝土梁安全预测提供参考。     

The shape of a surface crack in a plate based on a given stress intensity factor distribution

A new method is developed for the evaluation of a crack shape based on a given stress intensity factor (SIF) distribution for a surface crack under Mode-I loading conditions. The SIF distribution along the crack front is investigated using a direct simulation technique, in which the effect of crack closure on fatigue crack growth is considered. Then a SIF distribution function is chosen based on the numerical results. Crack shape (and the SIF) is achieved based on the given SIF distribution function using a numerical iterative procedure. Empirical SIF equations for surface cracks in plates subjected to tension and pure bending fatigue load are determined by systematic curve fitting of the numerical results. The depth ratio and the aspect ratio are considered in the ranges of 0.1–0.9 and 0.2–1.2, respectively. The aspect-ratio variation of surface cracks under fatigue loading is predicted. The application of the new method to predict the shape of a surface crack in plates subjected to tension and pure bending and comparisons of the results obtained with the predictions of the empirical equations proposed by Newman and Raju are presented.     

太阳辐射条件下冰温度膨胀力对某水库放水塔工作桥柱裂缝的影响

寒冷地区冬季水工建筑物受冰温度膨胀力破坏严重,为研究不同方位角处太阳辐射量对混凝土柱裂缝开展的影响规律,结合某水库放水塔工作桥裂缝实测结果,采用冰热力耦合理论及扩展有限元方法模拟了混凝土柱12h冰盖升温膨胀对工作桥混凝土柱的挤压破坏过程。结果表明,模拟裂缝开展深度与现场实测结果基本吻合;阳面(方位角为30°)冰盖瞬时吸收的太阳辐射量最大值为阴面(160°)的1.3倍;由于太阳辐射,冰盖上表面逐小时温度变化值增大为未加入前的1.8倍;温度变化较大与阴面冰盖吸收的太阳辐射较少有关,阴面冰盖升温膨胀挤压混凝土柱产生的裂缝深度值为阳面的3倍。研究成果可为寒冷地区抗冰冻设计提供借鉴。     

Creep fracture mechanics parameters for internal axial surface cracks in pressurized cylinders and creep crack growth analysis

In the present study, a low alloy Cr–Mo steel cylinder subjected to internal pressure at high temperature with a semi-elliptical crack located at the inner surface is considered. The creep crack driving force parameter C1-integrals calculated by finite element (FE) method, are compared with results from previous studies, which indicates that empirical equations may be inaccurate under some conditions. A total of 96 cases for wide practical ranges of geometry and material parameters are performed to obtain systematic FE results of C1-integral, which are tabulated and formulated in this paper. It is observed that the maximum C1-integral may occur neither at the deepest point nor at the surface point when the aspect ratio is large enough and the value of C1-integral is significantly sensitive to the crack depth ratio. Furthermore, based on the proposed equations for estimating C1-integrals and a step-by-step analysis procedure, crack profile development, crack depth, crack length and remaining life prediction are obtained for surface cracks with various initial aspect ratios. It is found that when the crack depth ratio is increased, there is no obvious convergence of crack aspect ratio observed. The magnitude of half crack length increment is always minor compared with the crack depth increment. In addition, the remaining life is much more dependent on the surface crack depth than on the surface crack length.