浅谈水利工程混凝土裂缝原因与对策

混凝土是21世纪主要的建筑材料,水工混凝土是水工结构的重要建筑材料。裂缝是混凝土结构不可避免存在的损伤,本文从水工混凝土出发,分析了水工混凝土裂缝产生的原因,对水工混凝土的裂缝进行了分类。在此基础上,对水工混凝土出现的裂缝提出了修补方法,为水工混凝土大坝建设和健康维护提供了参考。     

水工建筑物混凝土裂缝成因和预防措施

本文介绍了水工建筑物混凝土裂缝产生的原因,对水工混凝土裂缝修补的技术要求做了阐述,对当前常用的裂缝修补处理的方法和工艺要求做了描述,供大家参考。     

水工建筑物混凝土裂缝成因和修补措施分析

本文介绍了水工建筑物混凝土裂缝的类型和产生原因,对水工混凝土裂缝修补的技术要求做了阐述,对当前常用的裂缝修补处理的方法和工艺要求做了描述,供大家参考.     

水工混凝土裂缝的研究

水工混凝土裂缝产生的原因很多,混凝土开裂后,其性能与原状混凝土性能相差很大,严重影响混凝土结构的安全运行和耐久性能.本文分析了水工混凝土裂缝产生的原因,对预防裂缝产生的综合措施进行了探讨,并提出了一些修补措施.     

混凝土裂缝处理和出新施工技术的探讨

在谏壁抽水站除险增容改造工程中,对抽水站水工建筑物混凝土的裂缝、碳化病害,区别损害的程度、性质采取不同的方案进行修补加固处理,在处理的基础上对建筑物出新,满足使用功能和安全条件。     

生物修复加固材料在土木工程中的应用研究进展

生物修复加固材料生态环保、性能优异。本文综述了近年来生物修复加固材料在石质文物与历史建筑保护、混凝土裂缝修补、提高混凝土耐久性以及岩土工程等领域的应用研究进展,并探讨了材料修复加固机理、存在的问题及应用研究前景。简要梳理一下生物修复加固材料在土木工程中的应用研究思路。     

水工建筑物混凝土裂缝成因和修补措施分析

本文介绍了水工建筑物混凝土裂缝的分类和成因，提出了常用的裂缝修补处理的方法，供大家参考。     

丙乳砂浆在水工混凝土加固工程中应用

丙乳砂浆由于具有优异的粘结、抗裂、防水、防氯离子渗透、耐磨、耐老化等性能,是一种新型混凝土建筑物的水泥基护面修补材料,和树脂基修补材料相比具有成本低、耐老化、易操作、施工工艺简单及质量容易保证等优点。可在水工混凝土建筑物各种老化加固处理中使用和推广。     

某工程二层楼板裂缝原因分析和处理

混凝土裂缝是结构工程的一大病害，随着基础建设的增多，近年来呈增多的趋势。本文结合某工程二层混凝土现浇板裂缝，从材料、施工及工艺方面分析裂缝产生的原因，提出对应的处理措施、修补和加固办法。     

水工涵闸混凝土裂缝控制技术

本文以水工涵闸工程混凝土的墩墙、板裂缝作为典型裂缝,分析了裂缝的形成原因,并从材料选择、施工方法及结构布置三个层面提出了控制水工水工涵闸有害裂缝的技术措施。     

水力冲击内蕴初始裂纹混凝土致裂机理

为研究水力冲击内蕴初始裂纹混凝土破碎机理,采用光滑粒子流体动力学(SPH)方法建立了水力冲击含竖向裂纹混凝土数值模型,并基于图像处理技术,量化表征了混凝土致裂区破碎规律。研究表明:在初始裂纹弱作用区,水锤效应导致液固接触边界出现剪切断裂,贯通后形成近似"碗状"破碎坑;在初始裂纹强作用区,液固接触边界压剪应力和初始裂纹上部应力集中共同作用引发了初始裂纹上尖端裂纹;"水楔+砼楔"效应与初始裂纹下部应力集中导致了初始裂纹下尖端裂纹;水力冲击激发的应力波在自由边界和初始裂纹反射后相互叠加,引发了锥形裂纹;混凝土破碎度沿射流轴向呈非线性阶跃衰减,表明初始裂纹对混凝土破碎演化有明显阻断及强干扰作用。     

采用峰值荷载法确定全级配水工混凝土断裂参数

该文采用峰值荷载法研究了全级配水工混凝土试件的断裂参数。通过有限元方法,得到了适用于全级配水工混凝土的非标准楔入劈拉试件的应力强度因子K、裂缝嘴张开口位移CMOD计算公式以及裂缝张开位移COD与CMOD比值COD/CMOD的相关曲线。基于相关断裂试验,通过该文所提公式得到了全级配水工混凝土的等效断裂韧度与临界裂缝尖端张开口位移CTOD_c等断裂参数。研究结果表明：峰值荷载法可应用于截面尺寸不同而缝高比相同的全级配水工混凝土试件,峰值荷载法只需实测各试件的峰值荷载,就可方便确定全级配水工混凝土的断裂参数。     

On the application of cohesive crack modeling in cementitious materials

Cohesive crack models—in particular the Fictitious Crack Model – are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models—where cohesive stresses are assumed to exist together with a stress singularity at the crack tip—on the other hand, are used typically for multi scale problems such as crack propagation in fiber reinforced composites. Mortar and concrete, however, are multi-scale materials and the question naturally arises, if bridged crack models in fact are more suitable for concrete and mortar as well? In trying to answer this question a model for a centrally cracked sheet is established applying semi-analytical, bridged and fictitious crack modeling. The semi-analytical crack model is compared with a FEM analysis and it is demonstrated, that the standard fictitious crack implementation in FEM packages (in this case DIANA) provides a good approximation. Further, a quantitative condition is established indicating when a bridged crack model can be approximated with a cohesive crack model with smooth crack closure in terms of the ratio between the energy dissipation associated with the crack tip and the process zone.     

Nondestructive Techniques for Studying Fracture Processes in Concrete

Some laboratory nondestructive evaluation techniques have been invaluable in studying fracture processes in concrete. Several nondestructive evaluation methods including acoustic emission (AE), computer vision, digital speckle pattern interferometry (DSPI), and X-ray microtomography (XMT) were used to examine the fracture behavior of concrete in tension and compression. Acoustic emission testing was used in an attempt to characterize the fracture properties of individual microcracks. As the specimens were loaded, AE waveform data was recorded, and analyzed for source location and source characterization. While DSPI analysis is limited to the specimen surface, the resolution is detailed such that microcracks on the order of 0.25 μm can be detected. Computer vision is a very useful method to measure crack openings for multiple crack development. It also can be used in conjunction with a hydraulic testing machine, which often generates vibration problem for some sensitive techniques. Crack patterns in cement-based materials under various material compositions and testing conditions are examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

An embedded cohesive crack model for finite element analysis of mixed mode fracture of concrete*

An embedded cohesive crack model is proposed for the analysis of the mixed mode fracture of concrete in the framework of the Finite Element Method. Different models, based on the strong discontinuity approach, have been proposed in the last decade to simulate the fracture of concrete and other quasi‐brittle materials. This paper presents a simple embedded crack model based on the cohesive crack approach. The predominant local mode I crack growth of the cohesive materials is utilized and the cohesive softening curve (stress vs. crack opening) is implemented by means of a central force traction vector. The model only requires the elastic constants and the mode I softening curve. The need for a tracking algorithm is avoided using a consistent procedure for the selection of the separated nodes. Numerical simulations of well‐known experiments are presented to show the ability of the proposed model to simulate the mixed mode fracture of concrete.     

水工混凝土弥散型裂缝数值模型中开裂判据的研究

重大水利工程中,混凝土结构多处于高水压环境,坝体或多或少存在着裂缝,然而大部分开裂的混凝土坝仍能够安全运行,从而引申出是否可以允许混凝土结构出现裂缝,多大的裂缝才不至于引起破坏,以及用怎样一个合理的指标来对混凝土开裂程度进行描述评判的问题。该文以等效塑性应变表征混凝土弥散型裂缝模型数值模拟中的开裂破坏,通过混凝土单轴拉伸数值模拟,并根据试验资料及相关文献,建立了等效塑性应变与主拉应变、裂缝宽度之间的关系,得到对应于“有害裂缝”的等效塑性应变值。将方法和成果运用到混凝土重力坝的开裂研究中,具有较好的实际工程意义。     

Crack formation and fracture energy of normal and high strength concrete

The crack path through composite materials such as concrete depends on the mechanical interaction of inclusions with the cement-based matrix. Fracture energy depends on the deviations of a real crack from an idealized crack plane. FRACTURE energy and strain softening of normal, high strength, and self-compacting concrete have been determined by means of the wedge splitting test. In applying the numerical model called “numerical concrete” crack formation in normal and high strength concrete is simulated. Characteristic differences of the fracture process can be outlined. Finally results obtained are applied to predict shrinkage cracking under different boundary conditions. Crack formation of high strength concrete has to be seriously controlled in order to achieve the necessary durability of concrete structures.     

抽水蓄能电站水泵水轮机的动静干涉与振动分析

针对抽水蓄能电站水泵水轮机运行过程中出现的振动问题,从产生共振的条件出发,分析了转轮叶片和活动导叶形成的叶栅组合的动静干涉机理。根据转轮对水力激振模式的动态响应,研究了不同叶栅组合方式对水力激振力的影响。建立流固耦合数学模型,对转轮、活动导叶、顶盖及底环等过流部件的动态特性进行了有限元分析,以7/20的叶栅组合为例,阐述了流体激发结构共振的可能性。为了避免过流部件发生共振以及由此产生的疲劳裂纹或断裂等事故,提出了最佳叶栅组合的选择原则、降低无叶区压力脉动的方法以及提高结构固有频率和降低局部应力集中系数的具体措施。     

准脆性材料裂纹桥联筋的应力与变形

基于钢筋混凝土的破坏分析,结合混凝土类准脆性材料的断裂特性,本文提出了强化筋桥联基体裂纹力学分析模型,在该虚拟裂纹端部存在粘聚力分布,而强化筋在桥联裂纹处具有与基体脱离的部分段.由变形体的叠加原理和协调性条件,通过断裂力学的应力函数分析方法,推导出了在远场载荷作用下,离裂纹端部较远处桥联筋的轴向受力和变形,与脱粘筋长度之间的函数关系.文中分别就基体和强化筋材料为完全弹性,裂纹端部存在粘聚力,和强化筋为弹塑性材料等不同情况时,对裂纹和强化筋的变形和受力进行了算例分析和讨论.     

Simple lattice model for numerical simulation of fracture of concrete materials and structures

In this paper a numerical model is presented for simulating fracture in heterogeneous materials such as concrete and rock. The typical failure mechanism, crack face bridging, found in concrete and other materials is simulated by use of a lattice model. The model can be used at a small scale, where the particles in the grain structure are generated and aggregate, matrix and bond properties are assigned to the lattice elements. Simulations at this scale are useful for studying the influence of material composition. In addition the model seems a promising tool for simulating fracture in structures. In this case the microstructure of the material is not mimicked in detail but rather the lattice elements are given tensile strengths which are randomly chosen out of a certain distribution. Realistic crack patterns are found compared with experiments on laboratory-scale specimens. The present results indicate that fracture mechanisms are simulated realistically. This is very important because it simplifies the tuning of the model.