共查询到19条相似文献，搜索用时 406 毫秒
1.
Analytical modeling for corrosion-induced cover cracking of corrosive reinforced concrete structures 总被引：1，自引：1，他引：0
An analytical model for predicting the corrosion-induced cracking of concrete cover of reinforced concrete(RC) structures was developed.The effects of influence factors such as practical initial defects,corrosion rate,strength and elastic modulus of concrete on the corrosion-induced cracking of concrete cover were investigated.It was found that the size of practical initial defects was the most effective factor.Therefore,improving the compactness of concrete is an effective way to improve the durability of RC structures.It was also demonstrated that the accelerated corrosion tests may be unfavorable in the study of the relationship between cracking time and crack width. 相似文献
2.
Fatigue crack growth rate test using a frequency sweep method 总被引：1，自引：0，他引：1
Xun ZHOU Xiao-li YU 《浙江大学学报(A卷英文版)》2008,9(3):346-350
Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed. 相似文献
3.
Factors such as errors during the fabrication or construction of structural components and errors of calculation assumption or calculation methods, are very likely to cause serious deviation of many strings＇ actual prestressing forces from the designed values during tension structure construction or service period, and further to threaten the safety and reliability of the structure. Aiming at relatively large errors of the prestressing force of strings in a tension structure construction or service period, this paper proposes a new finite element method （FEM）, the ＂tensile force correction calculation method＂. Based on the measured prestressing forces of the strings, this new method applies the structure from the zero prestressing force status approach to the measured prestressing force status for the first phase, and from the measured prestressing force status approach to the designed prestressing force status for the second phase. The construction tensile force correction value for each string can be obtained by multi-iteration with FEM. Using the results of calculation, the strings＇ tensile force correction by group and in batch will be methodic, simple and accurate. This new calculation method can be applied to the prestressed correction construction simulation analysis for tension structures. 相似文献
4.
Theoretical Calculation and Analysis of Slip and Deformation for Concrete Sandwich Panels 总被引：1，自引：0，他引：1
Slip and deformation of concrete sandwich panels under uniformly distributed loads is concerned. The effect of slip on the deformation of concrete sandwich panels are studied,and the analytical expressions of slip and deformation for concrete sandwich panels is obtained. These formulae can describe the slip distribution and account for its effect on deformation. In order to restrict the bound of formula, the formula of crack moment is obtained. The results of theoretical calculation are compared with those of tests and finite element methods. The comparison shows that the results of theoretical calculation are in accord with those of tests and finite element methods. So the theoretical calculation can be used to calculate slip and deformation of concrete sandwich panels in practical projects. 相似文献
5.
A Method for Reducing Noise Radiated from Structures with Vibration Absorbers by Using an Accelerated Neural Network 总被引：2，自引：0，他引：2
A method for reducing noise radiated from structures by vibration absorbers is presented. Since usual design method for the absorbers is invalid for noise reduction, the peaks of noise power in the frequency domain as cost functions are applied. Hence, the equations for obtaining optimal parameters of the absorbers become nonlinear expressions. To have the parameters, an accelerated neural network procedure has been presented.Numerical calculations have been carried out for a plate-type cantilever beam with a large width, and experimental tests have been also performed for the same beam. It is clarified that the present method is valid for reducing noise radiated from structures. As for the usual design method for the absorbers, model analysis has been given, so the number of absorbers should be the same as that of the considered modes. While the nonlinear problem can be dealt with by the present method, there is no restriction on the number of absorbers or the model number. 相似文献
6.
The design methods of anode and cathode are proposed for precision profile grinding.Based on the electrolytic machining theory, electrolytic equilibrium condition and Faraday‘s law of electrolysis are applied to establishing the mathematical model of profile diamond dressing processes. A finite element method (FEM) program is developed to solve the inverse boundary problem of Laplace‘s equation. Desired anode contour or cathode shape is determined by computing the distribution of electric potential layer by layer. Electrolytic machining experiment is carried out to verify the simulated anode shape. The research result shows that shape deviation between designed cathode and profile wheel increases with the value of angle between feed rate and the normal to anode surface. The shape of simulated anode is consistent with the contour of metal-bonded diamond profile wheel for a given cathode. Based on the anode contour, cathode shape can also be designed accurately. 相似文献
7.
The efficacy of error correction and various kinds of correction approaches is one of the key issues in second language writing faced by both teachers and researchers. The current paper reviews the definition of error correction and examines the different views on whether error correction in L2 writing should be corrected. In particular, the paper discusses and analyses the three common correction methods: direct correction, peer feedback and indirect correction. Teachers are encouraged to weigh and analyze the advantages and disadvantages of these methods according to the current literature, employ the most beneficial error correction method in L2 writing, and adapt its suitability to their teaching context. 相似文献
8.
Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks
In this paper, numerical method is used to study the strain rate effect on masonry materials. A typical unit of masonry is selected to serve as a representative volume element (RVE). Numerical model of RVE is established with detailed distinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor (DIF) of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results. 相似文献
9.
Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks
WEI Xueying HAO Hong 《天津大学学报(英文版)》2006,12(B09):147-151
In this paper, numerical method is used als. A typical unit of masonry is selected to serve merical model of RVE is established with detailed to study the strain rate effect on masonry materias a representative volume element （RVE）. Nudistinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor （DIF） of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results. 相似文献
10.
Hydroxyapatite bioceramics is simulated by using finite element method (FEM).The influences of porosity,hole shape,angle of crack and other parameters on the ceramics are analyzed.The results show that with the increase of the angle between crack and horizontal direction,the stress intensity factor KⅠdecreases gradually,but stress intensity factor K II increases at first and then it decreases.The value of K Ⅱ reaches maximum when the angle between crack and horizontal direction is 45°.KⅠ and K Ⅱ rise with the increase of porosity,and they are almost the same for the circular and hexagonal holes.For elliptical holes,KⅠand KⅡreach maximum when the long axis of ellipse is perpendicular to the loading direction and they reach minimum when the same axis is parallel to the loading direction.Moreover,with the increase of the angle between the long axis and loading direction,KⅠ and KⅡ increase gradually. 相似文献
11.
龙靖华 《安徽广播电视大学学报》1999,(4)
依据有关的试验结果,探讨了钢筋砼结构中砼表面裂缝和钢筋处裂缝宽度及钢筋锈蚀三者之间的关系,并分析了钢筋产生锈蚀的原因,认为以砼表面裂缝宽度作为钢筋锈蚀的度量标准不尽合理,控制钢筋处裂缝宽度防止钢筋的局部锈蚀较为有效 相似文献
12.
Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete （SFRSC） as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar’s stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone. 相似文献
13.
采用高延性纤维增强水泥基材料部分代替钢筋混凝土梁受拉区的混凝土得到 ECC/RC 组合梁构件,可以有效提高梁的延性及抗裂性能. 基于平截面假定和材料本构模型,分析组合梁构件在受力过程中各个阶段的截面应力应变状态,得到各阶段承载力的计算方法. 根据混凝土结构设计规范,提出了 ECC/RC 组合梁极限承载力的简化计算方法,并给出了组合梁构件的弯矩-曲率关系,得到组合梁延性的简便计算方法.最后,采用一个组合梁的试验结果对理论公式进行验征. 结果表明: 计算结果和试验结果吻合得较好,证明所提出的组合梁各阶段受弯承载力计算方法是正确的,具有一定的理论意义和参考价值. 相似文献
14.
为研究碳纤维布(CFRP)对加固后钢筋混凝土梁的抗弯疲劳性能的影响,进行了3根CFRP加固梁及1根对比梁的抗弯疲劳试验.研究了碳纤维布加固方式、构件使用荷载等参数对碳纤维布加固损伤钢筋混凝土吊车梁的抗弯疲劳性能影响.试验研究表明:采用碳纤维布加固后,构件裂缝的宽度减小50.2%~66%,发展速度也得到控制,钢筋应力减小24.1%~28.2%,构件的刚度提高14.9%~16.1%.依据试验结果,从现有规范中关于构件刚度计算方法出发,进行了CFRP加固钢筋混凝土吊车梁的疲劳刚度计算分析,该计算方法可用于吊车梁加固工程设计.最后给出了CFRP加固梁的疲劳设计的合理化建议. 相似文献
15.
采用Ansys有限元软件对8根不同锈蚀率的FRP片材加固钢筋混凝土梁的受弯性能进行数值分析,研究纵筋锈蚀率对FRP加固梁的裂纹开展、破坏模式、承载能力以及延性和变形能力的影响.研究结果表明:低钢筋锈蚀率的梁发生受压区混凝土压碎破坏;中等锈蚀率的梁钢筋屈服后,钢筋与混凝土界面发生黏结滑移,最后FRP剥离破坏;高锈蚀率的梁钢筋没有达到屈服强度便发生黏结滑移,最后发生受压区混凝土压碎破坏.钢筋锈蚀越严重,FRP加固钢筋混凝土梁的承载力降低得越多.试件RCB-1(锈蚀率为0)的承载力为115 kN,而试件RCB-7(锈蚀率为20%)的承载力仅为42 kN.与FRP加固未锈蚀的钢筋混凝土梁相比,FRP加固锈蚀钢筋混凝土梁的变形能力较高.试件RCB-1和试件RCB-7的最大跨中挠度分别为20 mm和35 mm,而试件RCB-5(锈蚀率为10%)的最大跨中挠度达到了60 mm. 相似文献
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17.
Time-to-cracking of the concrete cover induced by the steel corrosion is one of the critical problems faced by engineers, operators and asset managers in making strategies for the maintenance and repairs of reinforced concrete (RC)structures affected by corrosion. In this paper, a theoretical model for predicting the time-to-cracking is derived by assuming the bond between the steel bar and the concrete as a linear combination of perfectly smooth and bonded. The model takes into account the characteristics of existing exiguous flaws and initial cracks in the concrete before the load acting on RC structures. The validity of the proposed model is preliminarily verified by comparing the obtained results with the available experimental results. A remarkable advantage of the proposed method is its application to the prediction of the service life of RC structures, made of the deformed steel bars as well as the round bars. By determining an experimental constant α, which is related to the interface bond state between the steel bar and the concrete, the service life of RC structures can be predicted using the proposed scheme. Analysis of major factors affecting the time-to-cracking demonstrates that the length of the initial crack affects the service life of RC structures significantly. Moreover, the larger cover thickness and the smaller diameter of the steel bar within a certain range are beneficial to prolonging the time-to-cracking. 相似文献
18.
为了研究钢筋增强ECC梁受弯性能,进行了钢筋增强ECC梁和普通钢筋混凝土梁受弯的对比研究.结果表明,相比普通钢筋混凝土梁,钢筋增强ECC梁的受弯承载力和延性分别提高了24.8%和187.76%,并且在梁中用ECC代替混凝土可有效延缓裂缝的发展.此外,采用简化的ECC本构模型对钢筋增强ECC及混凝土梁的受弯性能进行了非线性有限元分析,模拟结果与试验结果吻合较好,在服役期间钢筋增强ECC梁的裂缝可以控制在0.4 mm以下.ECC材料的使用可明显提高梁的抗弯承载力、变形能力、延性等受弯性能. 相似文献
19.
利用2种不同的方法加筋沥青罩面:①在沥青混合料中加入短切玻璃纤维改善沥青混凝土的特性,②采用玻璃格珊加筋沥青混凝土.应用断裂力学方法分析沥青路面裂缝扩展机理.采用沥青混合料设计试验、三点弯曲试验和疲劳裂缝扩展试验,确定加筋沥青混凝土的临界应力强度因子KIC,测量每一种沥青罩面抗裂系统的裂缝扩展速率.本研究的主要特点是提出复合型抗裂罩面系统,分析了多层加筋沥青罩面裂缝扩展过程,推荐了若干沥青路面抗裂系统.结果证明,加筋材料可以提高沥青罩面的抗裂特性,复合型抗裂罩面系统能够有效地阻止反射裂缝的扩展. 相似文献