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1.
This paper establishes a 3D numerical model for 15# hydropower house of the Three Gorges Project (TGP) and performs a nonlinear static and dynamic damage analysis. In this numerical model, a coupling model of finite and infinite elements for simulating infinite foundation of hydropower station is adopted. A plastic-damage model based on continuum damage mechanics, which includes the softening and damage behavior under tension is considered for the concrete material. The dynamic equilibrium equations of motion are solved by using the HilberHughes-Taylor (HHT) time integration method. Firstly, the static damage response analysis of the hydropower station is conducted due to high tensile stress resulting from large water head and diameter of an inlet pipe. Then, on the basis of static simulation, the dynamic damage analysis of hydropower house subjected to earthquake motion is simulated. Numerical results show that under large water head and diameter of an inlet pipe of the project, the damages are mainly located near the top of the spiral case from the inlet section to the 0° section; under combined loadings of static loads and earthquake, the damages of the concrete surrounding the spiral case increase insignificantly; however, some damages occur on the side walls of the main powerhouse. 相似文献
2.
水闸是平原地区常见的重要水工建筑物.在施工和运行过程中,裂缝问题较为常见,往往给水闸结构带来危险.分析形成水闸墩墙结构和底板结构的典型裂缝的主要因素,研究了水闸的开裂机理,提出预防裂缝的具体措施. 相似文献
3.
Moving ships and other objects drifting on water often impact a bridge's pile foundation. The mechanical model of the piles-bridge
structure under horizontal forcing was established, and a time-domain approach based on Finite-difference Method was developed
for analyzing the dynamic response of the piles-bridge structure. For a single pile, good agreement between two computed results
validated the present approach. The slenderness ratio of the pile, the pile-soil stiffness ratio and the type of the structure
influence the dynamic response of the piles-bridge structure. The computed results showed that the stiffness of the structure
determines the dynamic response of the piles-bridge structure under horizontal forcing.
Project (No. 001110442) supported by the Science and Technology Bureau of Zhejiang Province, China. 相似文献
4.
Brij Kothari P. G. Vijaya Sherry Chand Rajeev Sharma Amar H. Kalro Parvinder Gupta 《International Journal of Lifelong Education》2013,32(5):407-417
The Shiksha Karmi Project in Rajasthan, one of the most educationally challenged states, is at the frontiers of alternative models of primary education in India. The key ideas underlying this model are: (i) the taking over of ‘sick’ schools in remote regions of the state and turning them around, (ii) creating new schools driven by demand from the ground, (iii) human resource investments to train local village teachers, (iv) strong linkages between the school and the community built upon a spirit of voluntarism, (v) an explicit movement toward gender equity and (vi) a bold attempt at the universalization of primary education through a combination of formal and non-formal institutions. This article provides a grounded feel for the Shiksha Karmi Project in a stellar school, Meena Dant Ka Pura. While the case highlights the shortage of locally based female teachers in the entire Shiksha Karmi Project, it also suggests the very real possibility of employing Shiksha Karmi Project alumni and higher grade students in teaching roles. Overall, primary education in India has much to learn from the Shiksha Karmi Project experience. 相似文献
5.
The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, resulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses costeffective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiffness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to prototypes;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the optimization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press. 相似文献
6.
In this paper, the specific solutions of orthotropic plane problems with body forces are derived. Then, based on the general solution in the case of distinct eigenvalues and the specific solution for density functionally graded orthotropic media, a series of beam problem, including the problems of cantilever beam with body forces depending only on z or on x coordinate and expressed by z or x polynomial is solved by the principle of superposition and the trial-and-error method. 相似文献
7.
To study the mechanical properties of the film/substrate structure, the finite element code ABAQUS v6.9-1 is adopted to simulate the tensile mechanical behavior of the nanoscale thin film bonded to a substrate. The bifurcation phenomenon of the structure under uniaxial tension is found: the single-neck deformation, the multiple-neck deformation and the uniform deformation. The substrate and the film are regarded as power-hardening materials obeying the J 2 deformation theory. Firstly, the influence of material hardening match on tensile bifurcation mode is analyzed under perfectly well-bonded interface condition. Then, the effects of interfacial stiffness and other superficial defects surrounding the imperfection on bifurcation mode are investigated. It is concluded that under the well-bonded interface condition, if the stress of the substrate is larger than the film, the film will uniformly deform with the substrate; if the stress of the substrate is smaller than the film, the film will form a single neck, except the case that a weakly-hardening film is bonded to a steeply-hardening substrate when multiple necks can be formed. With the decrease of interfacial stiffness, the uniform deformation mode can transform into the multiple-neck deformation mode, and further transform into the single-neck deformation mode. And other defects surrounding the imperfection can influence the wavelength of deformation and neck number. 相似文献
8.
Carbon fiber reinforced polymer （CFRP） bars were prestressed for the structural strengthening of 8 T-shaped reinforced concrete （RC） beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes of strengthening with CFRP bars including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons-were introduced in detail. In order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed strengthening technology is feasible and effective. 相似文献
9.
INTRODUCTION Failure of reinforced and pre-stressed concrete structures is initiated in many instances by cracking of plain concrete. The post-cracking softening behavior of concrete subjected to tension has been realized for many years (Li et al., 1993). However, the resistance of cracked concrete is generally ignored in conven-tional design practice. Until recently it has become increasingly evident that it is necessary to account for the post-cracking resistance of concrete when per-f… 相似文献
10.
现浇板结构在施工和使用过程中出现裂缝的问题越来越受到社会各方面的关注．结合实际工程案例,对混凝土现浇板裂缝进行了检测,并对裂缝的成因进行了分析,根据目前的施工工艺提出合适的处治措施． 相似文献
11.
The characteristics of acoustic emission(AE)signals given off in the course of the failure of a concrete structure is explored based on the laboratory experiments with concrete specimens.It is observed that the failure of a concrete structure experiences three stages divided by two inflexion points on the AE event curve,which are sequentially no damage,damage initiation and propagation,and major failure stages.In the first stage,existing micro cracks and defects are compacted by loading. but no damage propagated,hence few AE signals are detected,and it appears that there exists a nearly linear relationship between the relative stress and relative strain.In the second stage,the AE event frequency increases implying that micro cracks begin to emerge inside the concrete structure,which is consistent with the damage mechanics.When the load is over 80% of that breaks the structure,i.e.the maximum load,there is a vertical jump on the AE event count curve,which suggests that the failure propagation speeds up.After the second inflexion point,the AE event density increases faster than before,and there is another jump just before breaking,which indicates a quick propagation stage.These findings are valuable for evaluating the damage situations,and for studying and monitoring the dynamic process of the failure behaviors of a concrete structure. 相似文献
12.
ZHU Bin LEUNG A.Y.T. 《浙江大学学报(A卷英文版)》2006,7(8):1351-1357
INTRODUCTION Thin-walled structures have considerable tech-nological importance in many situations of engi-neering practice. The rotary and warping inertia terms should be considered in the analyses of thin-walled structures (Alwis and Wang, 1996), although it is difficult to obtain the analytical solutions of govern-ing differential equations, especially of thin-walled frame and spatial twisted structure. The finite element method (FEM) is widely used for vibration and sta-bility analy… 相似文献
13.
为了研究移动荷载下路面结构内部细观结构的响应,采用离散元方法进行了多尺度路面结构移动荷载响应的分析．建立了柔性基层沥青路面典型结构的离散元模型,并计算了移动荷载作用下沥青层底的应力和应变,通过与已有经典计算程序荷栽响应计算结果的比较,验证了所建立的离散元模型．以该离散元模型为基础,在沥青混凝土结构层的底部,采用尺度较小的离散单元描述粗集料的体积含量、分布特征以及空隙大小等细观结构,以此建立路面结构的多尺度模型．对路面结构宏观响应与细观结构的荷载响应进行了比较分析,并分析了沥青砂浆劲度对细观结构处荷载响应的影响．结果表明：粗集料与沥青砂浆界面位置的拉应力均值和离散系数均大于沥青砂浆内部;荷载引起的应力和应变在沥青砂浆内部和界面内部均存在不均匀分布;沥青砂浆的劲度越大,沥青混凝土内部的荷载响应分布越趋于均匀． 相似文献
14.
A three-dimensional finite element model was established for a large span concrete filled steel tubular (CFST) arch bridge which is currently under construction. The arch rib, the spandrel columns, the prestressed concrete box-beam, the cast-in-situ concrete plate of bridge deck, the steel box-beam and the crossbeams connecting the two pieces of arch ribs, were modeled by three-dimensional Timoshenko beam elements (3DTBE). The suspenders were modeled by three-dimensional cable elements (3DCE). Both geometric nonlinearity and prestress effect could be included in each kind of element. At the same time a second finite element model with the same geometric and material properties excepted for the sectional dimension of arch rib was set up. Static dynamic analyses were performed to determine the corresponding characteristics of the structure. The results showed that the arch rib's axial rigidity could be determined by static analysis. The stability and vibration of this system could be separated into in-plane modes, out-of-plane modes and coupled modes. The in-plane stability and dynamic characteristics are determined by the arch rib's vertical stiffness and that of out-of-plane is determined by the crossbeams' stiffness and arch rib's lateral stiffness mainly. The in-plane stiffness is much greater than that of out-of-plane for this kind of bridge . The effect of geometric nonlinearity and prestress effect on bridge behavior is insignificant. 相似文献
15.
王得志 《河北能源职业技术学院学报》2011,11(3):87-88
主体结构砼裂缝、地暖地面砼裂缝问题是一个普遍存在而又难以解决的工程实际问题,是目前较难克服的质量通病之一。该文从砼材料自身及外界作用两个方面探讨了裂缝产生的原因,并有针对性的提出了防治措施,以确保建筑工程质量。 相似文献
16.
李振宇 《辽宁科技学院学报》2010,12(3):11-12,28
隧道工程衬砌结构由于长期处于复杂地层中,衬砌结构混凝土除了受到周围土质对其挤压作用外,还受到非荷载因素的影响,从而导致衬砌内表面出现类型各异的裂缝。文章介绍了隧道衬砌结构在非荷载作用下产生裂缝的原因,以及适用于裂缝修复的技术方法。 相似文献
17.
吴继红胡阳 《福建工程学院学报》2020,(4):324-328
针对一座主梁存在裂缝的混凝土独塔斜拉桥,考虑混凝土裂缝对材料本构关系的影响,对设计荷载作用下桥梁的整体与局部响应进行分析以评估其承载能力。结果表明,在最不利的工况中,开裂后主梁顶板、底板和斜腹板、直腹板上未开裂区域的主拉应力和主压应力都小于规范给出的强度标准值;裂缝法向和切向的压应力均小于规范强度标准值,裂缝切线和法线方向的拉应力在局部很小的范围内略高于规范的抗拉强度标准值。开裂区域局部承载力有所降低,但车辆荷载作用下裂缝不会进一步扩展。 相似文献
18.
A dynamic finite element method combined with finite element mixed formula for contact problem is used to analyze the dynamic characteristics of gear system. Considering the stiffness excitation, error excitation and meshing shock excitation, the dynamic finite element model is established for the entire gear system which includes gears, shafts, bearings and gearbox housing. By the software of I-DEAS, the natural frequency, normal mode, dynamic time-domain response, frequency-domain response and one-third octave velocity grade structure borne noise of gear system are studied by the method of theoretical modal analysis and dynamic response analysis. The maximum values of vibration and structure borne noise are occurred at the mesh frequency of output grade gearing. 相似文献
19.
The weighing system designed for large structure object is mainly composed of three parts. The part of hydraulic system is made up of hydraulic cylinders, high pressure hydraulic hoses and electric pumps; the part of computer controlling system comprises pressure sensors, displacement sensors, data acquisitions, RS 485 network and the computer controlling model; the part of loading system is composed of the fulcrum structure and the concrete girder. The measurement principle and composition of the weighing system are discussed in this paper. Credibility and security of the weighing system are fully considered during the design phase. The hydraulic system is controlled by pilot operated check valves in case of the sudden loss of system pressure. The states of all gauges and RS485 network are monitored by computer controlling system functioning in different modules. When the system is running incorrectly, it will be switched to manual mode and give alarm. The finite element method is employed to analyze fulcrum structure so that the system has enough intensity to be lifted. Hence the reliability of the whole system is enhanced. 相似文献
20.
为了建立实测动响应和桥梁健康状况的实质性联系,提出用双层模型修正方法修正叠合梁斜拉桥理论计算模型.以实测固有频率为第1层修正目标,采用人工调节方法,在可靠范围内变化桥面板质量、网格划分密度、混凝土模量及边跨压重等参数修正模型的动力特性;然后以GPS实测动响应为第2层修正目标,通过逐步减小结构各向刚度EI模拟桥梁整体刚度损伤,采用有限元迭代的方法修正模型的挠度值.以南浦大桥为例,对其进行有限元建模,并利用所提出的方法进行模型修正.分析结果表明,经过第1层模型修正,频率误差的标准偏差小于7%,比初始误差有明显改善;经过第2层模型修正,桥梁跨中挠度误差小于10%,桥梁结构各向刚度EI下降约20%.研究结果表明理论计算结果与实测结果相吻合. 相似文献